Annual radiocarbon measurements in a century-old European beech tree (Fagus sylvatica) from coastal northeastern North America - Gaylord, Mary C. Lardie; Longworth, Brett E.; Murphy, Keelan; Cobb, Caroline; McNichol, Ann P. (NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS, 2019)
Radiocarbon (C-14) concentrations of annual tree rings from an European beech tree (Fagus sylvatica) from Woods Hole, MA, USA were analyzed at National Ocean Sciences Accelerator Mass Spectrometry facility (NOSAMS) to construct a C-14 bomb curve record from northeastern North America. The C-14 concentration rises from a pre bomb (1895-1955) average of Fraction Modern ((FC)-C-14) = 0.9764 to a peak of 1.8639 in 1964. After 1964, (FC)-C-14 gradually decreases to 1.0611 in 2014. The annual tree-ring radiocarbon content agrees with the atmospheric radiocarbon content of the Northern Hemisphere and is very similar to the radiocarbon concentration of a red oak (Quercus rubra) tree located in Bear Mountain State Park in New York, USA. Infra-annual tree-ring pairs did not produce evidence of a seasonal effect on the radiocarbon concentration, but there were few samples and more study is warranted.

Antarctic Relic Microbial Mat Community Revealed by Metagenomics and Metatranscriptomics - Zaikova, Elena; Goerlitz, David S.; Tighe, Scott W.; Wagner, Nicole Y.; Bai, Yu; Hall, Brenda L.; Bevilacqua, Julie G.; Weng, Margaret M.; Samuels-Fair, Maya D.; Johnson, Sarah Stewart (Frontiers in Ecology and Evolution, 2019)
Buried upslope from the modern lakes in the McMurdo Dry Valleys of Antarctica are relict lake deposits embedded in valley walls. Within these relict deposits, ancient microbial mats, or paleomats, have been preserved under extremely arid and cold conditions since the receding of larger paleolakes thousands of years ago, and now serve as a sheltered niche for microbes in a highly challenging oligotrophic environment. To explore whether paleomats could be repositories for ancient lake cells or were later colonized by soil microbes, determine what types of metabolic pathways might be present, analyze potential gene expression, and explore whether the cells are in a vegetative or dormant state, we collected paleomat samples from ancient lake facies on the northern slopes of Lake Vanda in Wright Valley in December 2016. Using a gentle lysis technique optimized to preserve longer molecules, combined with a polyenzymatic treatment to maximize yields from different cell types, we isolated high-molecular weight DNA and RNA from ancient paleomat samples. Community composition analysis suggests that the paleomat community may retain a population of indigenous mat cells that may flourish once more favorable conditions are met. In addition to harboring a diverse microbial community, paleomats appear to host heterotrophs in surrounding soils utilizing the deposits as a carbon source. Whole genome long-read PacBio sequencing of native DNA and Illumina metagenomic sequencing of size-sorted DNA (>2,500 nt) indicated possible cell viability, with mat community composed of bacterial taxa. Metagenome assemblies identified genes with predicted roles in nitrogen cycling and complex carbohydrate degradation, and we identified key metabolic pathways such as stress response, DNA repair, and sporulation. Metatranscriptomic data revealed that the most abundant transcripts code for products involved in genetic information processing pathways, particularly translation, DNA replication, and DNA repair. Our results lend new insight into the functional ecology of paleomat deposits, with implications for our understanding of cell biology, Antarctic microbiology and biogeography, and the limits of life in extremely harsh environments.

The application of delta C-13, TOC and C/N geochemistry of mangrove sediments to reconstruct Holocene paleoenvironments and relative sea levels, Puerto Rico - Khan, Nicole S.; Vane, Christopher H.; Engelhart, Simon E.; Kendrick, Chris; Horton, Benjamin P. (MARINE GEOLOGY, 2019)
We assessed the use of delta C-13, TOC and C/N values of bulk sedimentary organic matter (OM) to reconstruct paleoenvironmental and relative sea-level change from mangrove environments in Puerto Rico. The modern distribution of delta C-13, TOC and C/N values was described from 63 vegetation and 59 surface sediment samples collected from three sites containing basin and riverine mangrove stands, and was compared to microfossil (foraminiferal and thecamoebian) assemblages. Four vertically-zoned environments were identified: tidal flat (delta C-13: -18.6 +/- 2.8 parts per thousand; TOC: 10.2 +/- 5.7%; C/N: 12.7 +/- 3.1), mangrove (delta C-13: -26.4 +/- 1.0 parts per thousand; TOC: 33.9 +/- 13.4%; C/N: 24.3 +/- 6.2), brackish transition (delta C-13: -28.8 +/- 0.7 parts per thousand; TOC: 40.8 +/- 11.7%; C/N: 21.7 +/- 3.7), and freshwater swamp (delta C-13: -28.4 +/- 0.4 parts per thousand; TOC: 42.8 +/- 4.8%; C/N: 17.0 +/- 1.1). These environments had distinct delta C-13, TOC and C/N values, with the exception of the brackish transition and freshwater swamp zones that were difficult to distinguish on a geochemical basis alone. The foraminiferal assemblages were complicated by a group that did not show a relationship to elevation due to the presence of calcareous foraminifera occurring above mean higher high water (MHHW), likely resulting from washover or transport by storms. However, the ratio of foraminifera to thecamoebians (F/T) along with delta C-13, TOC and C/N values refines the distinction between brackish and freshwater environments. Using linear discriminant analysis, we applied the delta C-13, TOC, C/N and F/T distributions to a 1.7 m core containing a continuous sequence of Rhizophora mangle peat, which began accumulating at similar to 1650-1930 CE. Together, microfossils, delta C-13, TOC, and C/N values, and the core chronology from Cs-137 and radiocarbon dating revealed that sediments in the core likely accumulated in response to anthropogenic sediment delivery, making it unsuitable for relative sea-level reconstruction. We caution that in the absence of detailed litho-, bio-, chemo-, or chrono-stratigraphic analyses as presented here, care should be taken in interpreting sea-level histories derived from single dates on mangrove peats.

Arsenic variability and groundwater age in three water supply wells in southeast New Hampshire - Levitt, Joseph P.; Degnan, James R.; Flanagan, Sarah M.; Jurgens, Bryant C. (Geoscience Frontiers, 2019)
Three wells in New Hampshire were sampled bimonthly over three years to evaluate the temporal variability of arsenic concentrations and groundwater age. All samples had measurable concentrations of arsenic throughout the entire sampling period and concentrations in individual wells had a mean variation of more than 7 μg/L. The time series data from this sampling effort showed that arsenic concentrations ranged from a median of 4 μg/L in a glacial aquifer well (SGW-65) to medians of 19 μg/L and 37 μg/L in wells (SGW-93 and KFW-87) screened in the bedrock aquifer, respectively. These high arsenic concentrations were associated with the consistently high pH (median ≥ 8) and low dissolved oxygen (median <0.1 mg/L) in the bedrock aquifer wells, which is typical of fractured crystalline bedrock aquifers in New Hampshire. Groundwater from the glacial aquifer often has high dissolved oxygen, but in this case was consistently low. The pH also is generally acidic in the glacial aquifer but in this case was slightly alkaline (median = 7.5). Also, sorption sites may be more abundant in glacial aquifer deposits than in fractured bedrock which may contribute to lower arsenic concentrations. Mean groundwater ages were less than 50 years old in all three wells and correlated with conservative tracer concentrations, such as chloride; however, mean age was not directly correlated with arsenic concentrations. Arsenic concentrations at KFW-87 did correlate with water levels, in addition, there was a seasonal pattern, which suggests that either the timing of or multiple sampling efforts may be important to define the full range of arsenic concentrations in domestic bedrock wells. Since geochemically reduced conditions and alkaline pHs are common to both bedrock and glacial aquifer wells in this study, groundwater age correlates less strongly with arsenic concentrations than geochemical conditions. There also is evidence of direct hydraulic connection between the glacial and bedrock aquifers, which can influence arsenic concentrations. Correlations between arsenic concentrations and the age of the old fraction of water in SGW-65 and the age of the young fraction of water in SGW-93 suggest that water in the two aquifers may be mixing or at least some of the deeper, older water captured by the glacial aquifer well may be from a similar source as the shallow young groundwater from the bedrock aquifer. The contrast in arsenic concentrations in the two aquifers may be because of increased adsorption capacity of glacio-fluvial sediments, which can limit contaminants more than fractured rock. In addition, this study illustrates that long residence times are not necessary to achieve more geochemically evolved conditions such as high pH and reduced conditions as is typically found with older water in other regions.
Keywords: Age tracers; Arsenic variability; Geochemical time series; Groundwater age modeling

Baobabs in Trouble: Accelerator Mass Spectrometry Provides Ages of the Most Ancient Trees - Gledhill, I. (The African Physics Newletter, 2019)

Bigmouth Buffalo Ictiobus cyprinellus sets freshwater teleost record as improved age analysis reveals centenarian longevity - Lackmann, Alec R.; Andrews, Allen H.; Butler, Malcolm G.; Bielak-Lackmann, Ewelina S.; Clark, Mark E. (Communications Biology, 2019)
Understanding the age structure and population dynamics of harvested species is crucial for sustainability, especially in fisheries. The Bigmouth Buffalo (Ictiobus cyprinellus) is a fish endemic to the Mississippi and Hudson Bay drainages. A valued food-fish for centuries, they are now a prized sportfish as night bowfishing has become a million-dollar industry in the past decade. All harvest is virtually unregulated and unstudied, and Bigmouth Buffalo are declining while little is known about their biology. Using thin-sectioned otoliths and bomb-radiocarbon dating, we find Bigmouth Buffalo can reach 112 years of age, more than quadrupling previous longevity estimates, making this the oldest known freshwater teleost (~12,000 species). We document numerous populations that are comprised largely (85-90%) of individuals over 80 years old, suggesting long-term recruitment failure since dam construction in the 1930s. Our findings indicate Bigmouth Buffalo require urgent attention, while other understudied fishes may be threatened by similar ecological neglect.
Keywords: Ageing; Conservation biology; Freshwater ecology; Ichthyology

Bomb Radiocarbon Age Validation of Warsaw Grouper and Snowy Grouper - Sanchez, Phillip J.; Pinsky, Jeffrey P.; Rooker, Jay R. (Fisheries, 2019)
Current stock assessments for both the Warsaw Grouper Hyporthodus nigritus and the Snowy Grouper H. niveatus are based on age‐structured population models determined using traditional otolith‐based aging techniques. However, recent studies using bomb radiocarbon validation have shown that many deepwater fishes live much longer than previously estimated when relying on conventional age determination methods. In this study, we conducted bomb radiocarbon age validations of Warsaw Grouper and Snowy Grouper from the Gulf of Mexico. Radiocarbon age validation supported annual growth increment formation for all Warsaw Grouper size classes and medium‐sized Snowy Grouper. Conversely, ages of larger, older Snowy Grouper were greatly underestimated due to difficulty in discriminating annuli. This bomb radiocarbon analysis validates a minimum 56‐year longevity for both Warsaw Grouper and Snowy Grouper, increasing the currently published longevities of 41 and 54 years, respectively.

CO2-dependent carbon isotope fractionation in Archaea, Part II: The marine water column - Hurley, Sarah J.; Close, Hilary G.; Elling, Felix J.; Jasper, Claire E.; Gospodinova, Kalina; McNichol, Ann P.; Pearson, Ann (GEOCHIMICA ET COSMOCHIMICA ACTA, 2019)
Stable carbon isotope ratios of archaeal glycerol dibiphytanyl glycerol tetraether (GDGT) lipids have been proposed as a proxy to infer past changes in the carbon isotope composition (delta C-13) of dissolved inorganic carbon (DIC). The premise for paleo-delta C-13(DIC) reconstructions from GDGTs is based on observations of relatively constant delta C-13(GDGT) values in recent depositional environments. Marine Thaumarchaeota, thought to be the dominant source of GDGTs to marine sediments, fix inorganic carbon using the 3-hydroxypropionate/4-hydroxybutyrate (3HP/4HB) pathway, which is specific to HCO3- as the substrate. Bicarbonate-dependent autotrophy has been the basis for predicting that the stable carbon isotopic composition of GDGTs (delta C-13(GDGT)) should vary in parallel with water column delta C-13(DIC) values, because HCO3- is by far the dominant fraction of DIC in modern seawater. However, this relationship has never been systematically tested. Here we examine the carbon isotopic composition of GDGTs from four water column profiles in the Southwest and Equatorial Atlantic Ocean. Values of delta C-13(GDGT) increase with depth in the water column, in contrast to the characteristic decrease in delta C-13(DIC) values. These divergent trends imply a decrease in the observed total biosynthetic isotope effect (epsilon(Ar)) with depth, i.e., the offset between delta(13)(DIC) and delta C-13(GDGT) is not constant. Instead, we find that values of epsilon(Ar) specifically correlate with oceanographic variables associated with extent of organic remineralization, decreasing as CO2 concentration increases. This observed relationship is consistent in both magnitude and direction with the results of an isotope flux-balance model for Thaumarchaeota that suggests epsilon(Ar) should be sensitive to growth rate (mu) and CO2 availability under conditions of atmospheric pCO(2) < 4 times the pre-anthropogenic Holocene level. Further tests of the sensitivity of epsilon(Ar) to u and CO2 in the modern marine environment will be essential to exploring the potential for a new, archaeal lipid-derived pCO(2) paleobarometer. (C) 2019 Elsevier Ltd. All rights reserved.

Comparing and improving methods for reconstructing peatland water-table depth from testate amoebae - Nolan, Connor; Tipton, John; Booth, Robert K; Hooten, Mevin B; Jackson, Stephen T (The Holocene, 2019)
Proxies that use changes in the composition of ecological communities to reconstruct temporal changes in an environmental covariate are commonly used in paleoclimatology and paleolimnology. Existing methods, such as weighted averaging and modern analog technique, relate compositional data to the covariate in very simple ways, and different methods are seldom compared systematically. We present a new Bayesian model that better represents the underlying data and the complexity in the relationships between species’ abundances and a paleoenvironmental covariate. Using testate amoeba–based reconstructions of water-table depth as a test case, we systematically compare new and existing models in a cross-validation experiment on a large training dataset from North America. We then apply the different models to a new 7500-year record of testate amoeba assemblages from Caribou Bog in Maine and compare the resulting water-table depth reconstructions. We find that Bayesian models represent an improvement over existing methods in three key ways: more complete use of the underlying compositional data, full and meaningful treatment of uncertainty, and clear paths toward methodological improvements. Furthermore, we highlight how developing and systematically comparing methods lead to an improved understanding of the proxy system. This paper focuses on testate amoebae and water-table depth, but the framework and ideas are widely applicable to other proxies based on compositional data.
Keywords: Bayesian statistics; compositional data; Holocene; hydrology; North America; Northeast United States; Paleoclimate; peatlands; statistical methods; testate amoebae

Coral Skeleton δ15N as a Tracer of Historic Nutrient Loading to a Coral Reef in Maui, Hawaii - Murray, Joseph; Prouty, Nancy G.; Peek, Sara; Paytan, Adina (Scientific Reports, 2019)
Excess nutrient loading to nearshore environments has been linked to declining water quality and ecosystem health. Macro-algal blooms, eutrophication, and reduction in coral cover have been observed in West Maui, Hawaii, and linked to nutrient inputs from coastal submarine groundwater seeps. Here, we present a forty-year record of nitrogen isotopes (δ15N) of intra-crystalline coral skeletal organic matter in three coral cores collected at this site and evaluate the record in terms of changes in nitrogen sources. Our results show a dramatic increase in coral δ15N values after 1995, corresponding with the implementation of biological nutrient removal at the nearby Lahaina Wastewater Reclamation Facility (LWRF). High δ15N values are known to be strongly indicative of denitrification and sewage effluent, corroborating a previously suggested link between local wastewater injection and degradation of the reef environment. This record demonstrates the power of coral skeletal δ15N as a tool for evaluating nutrient dynamics within coral reef environments.

Coupled ocean and atmospheric changes during Greenland stadial 1 in southwestern Europe - Naughton, F.; Costas, S.; Gomes, S.D.; Desprat, S.; Rodrigues, T.; Sanchez Goñi, M.F.; Renssen, H.; Trigo, R.; Bronk-Ramsey, C.; Oliveira, D.; Salgueiro, E.; Voelker, A.H.L.; et al. (Quaternary Science Reviews, 2019)
Paleoclimate reconstructions suggest that the complex variability within the Greenland stadial 1 (GS-1) over western Europe was governed by coupled ocean and atmospheric changes. However, few works from the North Atlantic mid-latitudes document both the GS-1 onset and its termination, which are often considered as single abrupt transition events. Here, we present a direct comparison between marine (alkenone-based sea surface temperatures) and terrestrial (pollen) data, at very high resolution (28 years mean), from the southwestern Iberian shelf record D13882. Our results reveal a rather complex climatic period with internally changing conditions. The GS-1 onset (GS-1a: 12890-12720 yr BP) is marked by a progressive cooling and drying; GS-1b (12720-12390 yr BP) is the coldest and driest phase; GS-1c (12390-12030 yr BP) is marked by a progressive warming and increase in moisture conditions; GS-1 termination (GS-1d: 12030-11770 yr BP) is marked by rapid switches between cool wet, cold dry and cool wet conditions. Although hydroclimate response was very unsteady throughout the GS-1 and in particular during its termination phase, the persistence of an open temperate and Mediterranean forest in southwestern Iberia during the entire episode suggests that at least some moisture was delivered via the Westerlies. We propose coupled ocean and atmospheric mechanisms to reproduce these scenaria. Changes in the strength of the Atlantic Meridional Overturning Circulation (AMOC) as well as variations in the North Atlantic sea-ice growth have favoured the displacement of the polar jet stream's latitudinal position and contributed to a complex spatial pattern and strength of the Westerlies across western Europe.
Keywords: Climate variability; Greenland stadial; Iberian margin; Jet stream; Moisture availability; North Atlantic; Paleoclimate; Westerlies; Younger Dryas Complex

Discovery of an Extensive Deep-Sea Fossil Serpulid Reef Associated With a Cold Seep, Santa Monica Basin, CaliforniaTable_1.docx - Georgieva, Magdalena N.; Paull, Charles K.; Little, Crispin T. S.; McGann, Mary; Sahy, Diana; Condon, Daniel; Lundsten, Lonny; Pewsey, Jack; Caress, David W.; Vrijenhoek, Robert C. (Frontiers in Marine Science, 2019)
Multibeam bathymetric mapping of the Santa Monica Basin in the eastern Pacific has revealed the existence of a number of elevated bathymetric features, or mounds, harboring cold seep communities. During 2013–2014, mounds at ∼600 m water depth were observed for the first time and sampled by Monterey Bay Aquarium Research Institute’s ROV Doc Ricketts. Active cold seeps were found, but surprisingly one of these mounds was characterized by massive deposits composed of fossil serpulid worm tubes (Annelida: Serpulidae) exhibiting various states of mineralization by authigenic carbonate. No living serpulids with equivalent tube morphologies were found at the site; hence the mound was termed “Fossil Hill.” In the present study, the identity of the fossil serpulids and associated fossil community, the ages of fossils and authigenic carbonates, the formation of the fossil serpulid aggregation, and the geological structure of the mound are explored. Results indicate that the tubes were most likely made by a deep-sea serpulid lineage, with radiocarbon dating suggesting that they have a very recent origin during the Late Pleistocene, specifically to the Last Glacial Maximum ∼20,000 years ago. Additional U-Th analyses of authigenic carbonates mostly corroborate the radiocarbon dates, and also indicate that seepage was occurring while the tubes were being formed. We also document similar, older deposits along the approximate trajectory of the San Pedro Basin Fault. We suggest that the serpulid tube facies formed in situ, and that the vast aggregation of these tubes at Fossil Hill is likely due to a combination of optimal physical environmental conditions and chemosynthetic production, which may have been particularly intense as a result of sea-level lowstand during the Last Glacial Maximum.

Dissolved organic carbon in basalt-hosted deep subseafloor fluids of the Juan de Fuca Ridge flank - Lin, Huei-Ting; Repeta, Daniel J.; Xu, Li; Rappé, Michael S. (Earth and Planetary Science Letters, 2019)
Marine dissolved organic carbon (DOC) is highly depleted in radiocarbon and thus inferred to be largely refractory to removal processes that operate on less than millennial timescales. However, a growing number of reports have shown that a large fraction of marine DOC can be effectively removed during circulation through submarine hydrothermal systems. What is not clear, however, is whether the DOC that remains in hydrothermal fluids is remnant non-reactive DOC from recharged seawater, or DOC that has been largely produced in the subsurface. We collected and characterized warm (∼65 °C) hydrothermal fluids from deep (18, 40, 73, 200 m) within the basalt-hosted basement of the Juan de Fuca Ridge flank in the Northeast Pacific Ocean. DOC concentrations in hydrothermal fluids were 9 to 18 μM, much lower than measured in local deep seawater (37.5 μM). DOC C values of −683‰ to −856‰ were much lower than the C-dissolved inorganic carbon (DIC) values of −880‰ to −918‰, while DOC C values of −23.6‰ to −27.0‰ were much heavier than that of the particulate organic carbon (POC) pool (‰), suggesting that biological production in the subsurface is not a primary source of DOC. Rather, our data suggest that isotopically enriched DOC are selectively removed from recharged seawater, leaving DOC that is very isotopically depleted in the basaltic basement fluids. Despite the removal of 50–75% of DOC in the subsurface, nuclear magnetic resonance (NMR) functional group analyses indicate that aromatic compounds were added to basaltic basement fluids during passage through the deep subseafloor and may partly contribute to the depleted 14C DOC in the ridge-flank basement fluids.
Keywords: aromatic organic compound; basaltic basement fluid; carbon isotopes; dissolved organic carbon; Juan de Fuca; selective removal; subseafloor

The distribution and magnitude of subglacial erosion on millennial timescales at Engabreen, NorwayAbstract - Rand, Cari; Goehring, Brent M. (Annals of Glaciology, 2019)
We quantify the magnitude of millennial-scale glacial erosion at Engabreen, a temperate glacier in coastal northern Norway, using the in situ cosmogenic nuclides carbon-14 (14C) and beryllium-10 (10Be) in bedrock exposed recently by glacial retreat. Nuclide concentrations show no dependence on distance down or across the valley. As such, resulting Holocene erosion depths along two transects perpendicular to glacier flow are highly variable with no systematic distribution, ranging from 0.10 to 2.95 m. We observed 14C–10Be ratios elevated above the production ratio in samples of abraded bedrock, which is counter to the expectation for surfaces covered during the Holocene and exposed only recently. Muon reactions produce nuclides at greater depths than do spallation reactions and 14C at production rates at higher than those of 10Be, resulting in 14C–10Be ratios that increase with depth. Therefore, elevated 14C–10Be ratios indicate that sampled sites were deeply plucked during recent cover, the Little Ice Age in this case, and then rapidly abraded prior to retreat. Our results suggest that, while glacial erosion can generate a u-shaped valley profile over long periods of time (e.g., 105–107 years), the discontinuous nature of glacial plucking produces spatially variable patterns of erosion over shorter millennial timescales.
Keywords: Beryllium-10; Carbon-14; cosmogenic nuclides; Engabreen; glacial erosion

Equatorial Pacific seawater pCO2 variability since the last glacial period - Kubota, Kaoru; Yokoyama, Yusuke; Ishikawa, Tsuyoshi; Sagawa, Takuya; Ikehara, Minoru; Yamazaki, Toshitsugu (Scientific Reports, 2019)
The ocean may have played a central role in the atmospheric pCO2 rise during the last deglaciation. However, evidence on where carbon was exchanged between the ocean and the atmosphere in this period is still lacking, hampering our understanding of global carbon cycle on glacial–interglacial timescales. Here we report a new surface seawater pCO2 reconstruction for the western equatorial Pacific Ocean based on boron isotope analysis—a seawater pCO2 proxy—using two species of near-surface dwelling foraminifera from the same marine sediment core. The results indicate that the region remained a modest CO2 sink throughout the last deglaciation.

Evaluating Playas as Point Sources for Recharge of the High Plains Aquifer, Western Kansas - Stotler, Randy L.; Salley, Kaitlin A.; Johnson, William C.; Ryuh, Yon-Gyung (Joint 53rd Annual South-Central/53rd North-Central/71st Rocky Mtn GSA Section Meeting - 2019, 2019)

Evaluating the Radiocarbon Reservoir Effect in Lake Kutubu, Papua New GuineaABSTRACT - Schneider, Larissa; Pain, Colin F; Haberle, Simon; Blong, Russell; Alloway, Brent V; Fallon, Stewart J; Hope, Geoff; Zawadzki, Atun; Heijnis, Henk (Radiocarbon, 2019)
Conceptual models predict a tight coupling between the Intertropical Convergence Zone (ITCZ) and the Southern Westerly Winds (SWW) in response to glacial-interglacial transitions, yet little is known about this relationship under Holocene boundary conditions. Here we present a synthesis of Holocene pollen data from the southwest Pacific mid-latitudes that tracks changes in the SWW. Comparison of our SWW paleoclimate records with data tracking the ITCZ, oceanic circulation, and insolation reveals clearly synchronous and in-phase ITCZ-SWW dynamics between 12 and 5 ka, indicating a tight coupling between the tropics and southern mid-latitudes in response to ocean circulation and insolation. An apparent decoupling of the SWW and ITCZ in the Pacific region after 5 ka is attributable to the overriding influence of the El Niño–Southern Oscillation (ENSO) over the proxy data.

Evaluation of Compartmentalized Aquifers in the Walla Walla Subbasin of Oregon Using Isotopic and Geochemical Tracers - van Stolk, Courtney A. (College of Earth, Ocean, and Atmospheric Sciences, 2019)
The Walla Walla Subbasin (WWSB) in Oregon is underlain by formations of the extensive Columbia River Basalt Group (CRBG) which have been deformed by post-Miocene folding and faulting. Extensive irrigation with groundwater from these basalt groups, as well as sedimentary aquifers and surface water diversions from the Walla Walla River, has enabled the WWSB to become a productive agricultural region despite its semi-arid climate. Over the past 10 years water levels in the basalt aquifer have declined to the point where some senior groundwater right holders cannot access their full water allocation. Effective water management depends on an understanding of the flow and recharge pathways in this complex groundwater system. This research uses spatial analysis of geochemical characteristics of groundwater samples to test the hypothesis that local faults create barriers to flow and isolate compartments of groundwater. For this study 31 wells were sampled for analysis of oxygen isotopes, hydrogen isotopes, pH, temperature, and conductivity. At a subset of 18 of those wells, samples were collected for a more extensive array of tests which also included carbon-14, tritium, and ten major ions. These parameters provide information to evaluate the range and distribution of groundwater age, evidence of modern recharge, and the progression of chemical reactions along hypothesized flow paths. Results of these laboratory analyses were compared with a literature review of fault geology and hydrogeology in the CRBG, results of interference pumping tests of basalt wells in the WWSB, and known physical characteristics of the wells sampled. This information was used to test three conceptual models of groundwater flow through the basalt aquifers. The first conceptual model was based on groundwater movement in unfaulted, sloping CRBG terrain where water infiltrates in upland recharge zones where the basalt is exposed, and moves laterally through the sloping interflow zones of the aquifer to wells. The second conceptual model describes local recharge in the vicinity of a well flowing slowly downward through the aquifer until the depth at which is became hydraulically connected to the well. The third model added faults into the model as lateral barriers to flow and vertical conduits to recharge. Comparisons of the monovalent/divalent cation ratios, stable isotope values, and principal component models with well depth, well surface level elevation, and well locations provide insights that conflict with the first two conceptual models and supported the third model. Further comparisons of these parameters with geologic characteristics of these faults from the literature through the lens of the third conceptual model provide a basis for estimating fault hydrogeologic characteristics in the WWSB.
Keywords: Columbia River Basalt Group; Groundwater tracers; Stable isotope tracers; Walla Walla Valley (Oregon)

Evidence for frequent, large tsunamis spanning locked and creeping parts of the Aleutian megathrust - Witter, Rob; Briggs, Rich; Engelhart, Simon E.; Gelfenbaum, Guy; Koehler, Rich D.; Nelson, Alan; Selle, SeanPaul La; Corbett, Reide; Wallace, Kristi (GSA Bulletin, 2019)
At the eastern end of the 1957 Andreanof Islands, Alaska, USA, moment magnitude 8.6 earthquake rupture, Driftwood Bay (Umnak Island) and Stardust Bay (Sedanka Island) lie along presently locked and creeping parts of the Aleutian megathrust, respectively, based on satellite geodesy onshore. Both bays, located 200 km apart, face the Aleutian trench and harbor coastal evidence for tsunami inundation in 1957. Here we describe the evidence at Driftwood Bay, including eight sheets of landward-fining, normally-graded marine sand that extend up to 375 m inland and 23 m above mean tide level. Drift logs that corroborate historical accounts of 1957 tsunami runup on Umnak Island’s Pacific coast overlie the youngest sand sheet, which 137Cs activity shows was deposited in the decade before 1963. The older sand sheets probably record tsunamis prior to 1957 because an emergent coastal terrace lacks evidence for storm-wave erosion and overwash since ca. 2 ka. Comparisons of the Driftwood Bay and Stardust Bay tsunami histories suggest that at least twice in the past 1700 years inundation occurred at one site but not the other. In contrast, Bayesian age-depth modeling suggests that the two bays may record five tsunamis like the 1957 tsunami, generated by earthquake ruptures that spanned the presently locked and creeping parts of the Aleutian megathrust. However, serial tsunamis occurring within days to centuries cannot be precluded. Our findings imply 164–257-year recurrence intervals for large eastern Aleutian tsunamis and challenge the notion that creeping parts of the megathrust, inferred from geodesy onshore, pose lower earthquake and tsunami hazards than locked areas.

Evidence of Ice Age humans in eastern Beringia suggests early migration to North America - Vachula, Richard S.; Huang, Yongsong; Longo, William M.; Dee, Sylvia G.; Daniels, William C.; Russell, James M. (Quaternary Science Reviews, 2019)
Our understanding of the timing and pathway of human arrival to the Americas remains an important and polarizing topic of debate in archaeology and anthropology. Traditional consensus, supported by archaeological and paleoenvironmental data, favors a 'swift peopling' of the Americas from Asia via the Bering Land Bridge during the last Glacial termination. More recent genetic data and archaeological finds have challenged this view, proposing the 'Beringian standstill hypothesis' (BSH), wherein a population of proto-Americans migrated from Asia during, or even prior to the Last Glacial Maximum (LGM) and lived in Beringia for thousands of years before their eventual spread across the American continents. Using a sediment archive from Lake E5 (68.641667 degrees N, 149.457706 degrees W), located on Alaska's North Slope, we present new data supporting the BSH and shedding new light on the environmental impact of these early American populations. Fecal biomarkers support human presence in the environs of the lake, and our data demonstrate elevated biomass burning in this region during the last Glacial. Elevated burning defies the expectation that natural fires would be less frequent in the Arctic during the last Glacial, thereby suggesting human ignition as the likely culprit. Our data shed new light on the pathway and timing of human migration to the Americas and demonstrate the possibility of the sustainable coexistence of humans and the Ice Age megafauna in Beringia prior to their extinction. (C) 2018 Elsevier Ltd. All rights reserved.
Keywords: Beringia; charcoal; Fecal sterols; Last Glacial; Paleofire; Polycyclic aromatic hydrocarbons (PAHs)

Examining Coastal Dynamics and Archaeological Site Evidence at a Drowned Cirque Basin Influenced by Earthquakes and Little Ice Age Glaciation - Maio, Christopher V.; Crowell, Aron L.; Sullivan, Richard M.; Buzard, Richard M.; Whitley, Matthew A.; Bogardus, Reyce C.; Wit, Cary W. de (Journal of Coastal Research, 2019)
This study contributes baseline information regarding the framework geology, drivers of coastal change, and archaeological record along the fjord-indented coastlines of southcentral Alaska. Field data were collected in July 2015 from James Lagoon, a 30-m-deep drowned cirque valley adjacent to McCarty Fjord in the Nuka Bay region of Kenai Fjords National Park. A 1790 CE terminal moraine deposited by McCarty Glacier extends across the cirque opening and delimits the lagoon. Acoustic surveys of the lagoon reveal bedrock overlain by deltaic, lacustrine, and marine facies containing beds that indicate past submarine landslides. Lagoon and marsh sediment cores contain coarse sand horizons interbedded with silt and peat, evidence of repeated low-frequency, high-intensity events. The largest of the event beds in the marine cores occurs near the surface and is likely associated with the 1964 Great Alaska Earthquake (moment magnitude 9.2). Trees killed during the 1964 earthquake fringe the coastline and indicate ∼2 m of coseismic subsidence. Radiocarbon ages of five exposed subfossil stumps indicate two pre-1964 subsidence events occurring between 1710 and 1789 and 1078 and 1125 median probability calendar year CE (cal CE). A Sugpiaq culture archaeological site dated to 1565 cal CE existed on the western shore of James Lagoon in the interval between these two events, possibly for proximity to an ice floe harbor seal rookery at McCarty Glacier. Archaeological site elevation above mean high water at James Lagoon and around Nuka Bay is inversely related to the extent of cumulative site erosion caused by coastal submergence during the last two great earthquakes. These combined findings lay the groundwork for future research and provide context to ongoing coastal hazards and their effects on cultural resources.

Farming strategies of 1st millennium CE agro-pastoralists on the southern foothills of the Tianshan Mountains: A geoarchaeological and macrobotanical investigation of the Mohuchahangoukou (MGK) site, Xinjiang, China - Li, Yuqi; Storozum, Michael; Tian, Duo; Frachetti, Michael; Su, Kai; Wang, Xin (PLOS ONE, 2019)
Archaeological evidence emerging over the past decade clearly illustrates that agro-pastoralists living along the foothills of major mountain chains in Central Asia (the so-called “Inner Asian Mountain Corridor” or IAMC) facilitated the spread of domesticated grains through their direct involvement in farming. While the environmental conditions across the northwestern slopes of the IAMC provided adequate resources for incipient farming and herding as early as the mid-3rd mill. BCE, the development of local agricultural strategies on the extremely arid and eroded foothills on the southeastern, leeward side of the mountains remain comparatively less studied. Our study tackles this problem by combining geoarchaeological analysis with conventional macrobotanical identification in the investigation of a 1st-mill. CE agro-pastoralist farming site, Mohuchahangoukou (MGK), located on the arid foothills of the Tianshan range. Our results illustrate how ancient agro-pastoralists at MGK innovated irrigation systems both to combat water shortage and, importantly, to trap sediments carried by flood-water for crop cultivation. By synthesizing currently available data, we estimate that they managed to trap about 40 cm of fine-grained sediment within a span of 200 years or even less. These stone-built field systems helped water a diverse stand of crops and create deeper soils in an otherwise deflated landscape with thin desert soils. Since we detected high levels of salt concentration (>2 dSm-1) in the lower portions of all three test trenches we analyzed, we conclude that soil salinization might have affected the long-term sustainability of this form of irrigated field management. We also infer that, besides engineering efforts, the ancient agro-pastoralists at MGK had to resolve the scheduling conflicts between irrigated farming and animal herding through labor specialization.
Keywords: Agricultural irrigation; Agricultural soil science; agriculture; Archaeology; Crops; Geochemistry; Paleopedology; Sediment

First record of the extinct ground sloth, Megalonyx jeffersonii, (Xenarthra, Megalonychidae) from New York and contributions to its paleoecology - McDonald, H. Gregory; Feranec, Robert S.; Miller, Norton (Quaternary International, 2019)
The first record of the Jefferson ground sloth, Megalonyx jeffersonii, in New York is reported. The specimen consists of a partial synsacrum recovered from a peat deposit near Newburgh, Orange County. Compared to other synsacra of Megalonyx, the number of vertebrae is anomalous with one less caudal vertebra than expected. Stable isotope analysis of the bone shows a δ13C value of 20.5‰ and implies a diet of only C3 plants. The specimen has a radiocarbon date of 11,450 ± 55 BP indicating the presence of this taxon in the region immediately prior to the extinction of the North American Pleistocene megafauna.
Keywords: Megalonyx jeffersonii; New York; Stable isotopes; Synsacrum

A fluvially derived flood deposit dating to the Kamikaze typhoons near Nagasaki, Japan - Ladlow, Caroline; Woodruff, Jonathan D.; Cook, Timothy L.; Baranes, Hannah; Kanamaru, Kinuyo (Natural Hazards, 2019)
Previous studies in western Kyushu revealed prominent marine-derived flood deposits that date to the late thirteenth-century and are interpreted to be a result of two legendary typhoons linked to the failed Mongol invasions of Japan in 1274 and 1281. The regional persistence and prominence of sediments dating to these “Kamikaze” typhoon events (meaning divine wind) raise questions about the origins of these late thirteenth-century deposits. This is due in part to uncertainty in distinguishing between tsunami and storm-induced deposition. To provide additional insight into the true cause of prominent late thirteenth-century flood deposits in western Kyushu, we present a detailed assessment of an additional event deposit dating to the late thirteenth-century from Lake Kawahara near Nagasaki, Japan. This particular deposit thickens landward towards the primary river flowing into Lake Kawahara and exhibits anomalously low Sr/Ti ratios that are consistent with a fluvial rather than a marine sediment source. When combined with previous flood reconstructions, results support the occurrence of an extreme, late thirteenth-century event that was associated with both intense marine- and river-derived flooding. Results therefore contribute to a growing line of evidence for the Kamikaze typhoons resulting in widespread flooding in the region, rather than the late thirteenth-century deposit being associated with a significant tsunami impact to western Kyushu.

Four centuries of vegetation change in the mid-elevation Andean forests of Ecuador - Huisman, Seringe N.; Bush, Mark B.; McMichael, Crystal N. H. (Vegetation History and Archaeobotany, 2019)
Mid-elevation Andean ecosystems have immense species richness and endemism. Taxonomic composition is known to change through time on the eastern slopes of the Andes as a result of climatic change and disturbance events, both natural and by human actions. Fossil phytoliths can capture local scale vegetation changes, especially among monocotyledonous plants. Phytolith production is high in grasses and palms, plant groups that are particularly sensitive to climatic changes and disturbance events in Andean ecosystems. Here, we reconstruct four centuries of local-scale vegetation change and the corresponding fire history from lake sediment records retrieved from Lagunas Cormorán and Chimerella, located at ca. 1,700 m a.s.l. in the mid-elevation Andean forests of eastern Ecuador. The charcoal analysis of the lake sediments showed no sign of past fires, and no evidence of cultivation was found at either lake. The phytolith assemblages indicated changes in the relative abundances of palms, grasses and trees over the last few centuries, suggesting that mid-elevation Andean phytolith assemblages are sensitive to local scale vegetation dynamics. The largest change in vegetation occurred at the end of the Little Ice Age, at which point the diversity of palm phytoliths decreases. These phytolith assemblages are probably responding to changes in the cloud base position through time, which strongly influences the distributions of many plants and animals.

Four Major Holocene Earthquakes on the Reelfoot Fault Recorded by Sackungen in the New Madrid Seismic Zone, USA - Gold, Ryan D.; DuRoss, Christopher B.; Delano, Jaime E.; Jibson, Randall W.; Briggs, Richard W.; Mahan, Shannon A.; Williams, Robert A.; Corbett, D. Reide (Journal of Geophysical Research: Solid Earth, 2019)
Three sequences of well‐documented, major ~M7+ earthquakes (1811–1812, ~1450, and ~900 CE) in the New Madrid seismic zone, USA, contribute significantly to seismic hazard in the region. However, it is unknown whether this <550‐year recurrence interval has been constant throughout the Holocene given limited geomorphic evidence of prior earthquakes. We extend the record of paleoearthquakes along the Reelfoot fault via investigation of ridgetop gravitational failure features, interpreted as sackungen. The sackungen occur in bluffs along the eastern margin of the Mississippi River floodplain and are concentrated near (<15 km) the southwest dipping Reelfoot reverse fault. A paleoseismic trench excavated across sackungen at the Paw Paw site exposed four packages of colluvial sediment that postdate 30‐ to 11‐ka Peoria Loess. We interpret the colluvial packages to have been deposited following episodic failure of the sackungen as a result of strong ground motions from the following sequence of earthquakes: event 4, 1640 ± 1730 BCE; event 3, 270 ± 670 CE; event 2, 1430 ± 380 CE; and event 1, 1810 ± 50 CE (2 sigma). Event timing corresponds to previously documented earthquakes and represents the longest archive of paleoearthquakes on the Reelfoot fault. If the trenched sackungen record all major Reelfoot fault earthquakes, our observations in combination with prior investigations indicate a period of quiescence from at least 11 to 4.4 ka, followed by four major seismic events culminating in the 1811–1812 CE sequence. This clustered earthquake recurrence pattern helps place bounds on seismic hazard and geodynamic models in the New Madrid seismic zone.

A fully automated system for the extraction of in situ cosmogenic carbon-14 in the Tulane University cosmogenic nuclide laboratory - Goehring, Brent M.; Wilson, Jim; Nichols, Keir (Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2019)
During 2015 and culminating in early 2016, we acquired a new Carbon Extraction and Graphitization System (CEGS) from Aeon Laboratories, L.L.C. (hereafter, “Aeon”), and adapted it for in situ cosmogenic sample processing. The Tulane University CEGS (TU-CEGS) is fully automated starting from sample insertion into the tube furnace to generation of graphite material ready for accelerator mass spectrometry cathode preparation. The system implements an integrated sequence of sample processing functions: extraction/collection, purification, measurement, and graphite production, which are all integrated into one unified system. The extraction portion is derived from evolving designs of fusions of quartz via lithium metaborate (LiBO2) flux. A critical analysis of system design in concert with analysis of process parameters yield a nearly order of magnitude increase in sample throughput with total samples processed in our laboratory (320 since installation) with consistent process blank levels (0.98 ± 0.32 × 105 atoms 14C, n = 26) and secondary standard values (0.4953 ± 0.0012 Fm, n = 8). In this paper we detail system design, process algorithm, and line performance including system blanks and the results from the CRONUS-A (6.12 ± 0.32 × 105 atoms g−1 14C, n = 13) interlaboratory comparison material.
Keywords: Automation; Cosmogenic nuclide; In situ carbon-14

Glacial geology and cosmogenic-nuclide exposure ages from the Tucker Glacier - Whitehall Glacier confluence, northern Victoria Land, Antarctica - Balco, Greg; Todd, Claire; Goehring, Brent M.; Moening-Swanson, Isaac; Nichols, Keir (American Journal of Science, 2019)
We describe glacial-geological observations and cosmogenic-nuclide exposure ages from the vicinity of the present grounding line of Tucker Glacier, a large alpine glacier flowing from the mountains of northern Victoria Land, East Antarctica, into the outer Ross Sea. These data are relevant for constraining the extent of ice sheet expansion and retreat in the Ross Sea, and associated eustatic sea level impact, between the Last Glacial Maximum (LGM) and the present. In addition, a terrestrial geological record of ice thickness change from this region could provide evidence for or against the hypothesis that rapid eustatic sea-level rise during meltwater pulse 1A (“MWP-1A”) at 14.6 ka was in part the result of rapid, large-scale thinning or breakup of a marine-based portion of the LGM ice sheet in the outer Ross Sea. Glacial-geological observations, exposure ages on glacial deposits, and a novel application of in-situ-produced cosmogenic 14C in quartz-bearing bedrock to identify the limits of LGM ice cover in the absence of direct geomorphic evidence, show that Tucker Glacier near its present grounding line was 300 to 350 m thicker than present during the LGM and thinned steadily between 17 to 5 ka. The largest possible rapid thickness change in the time period 14 to 15 ka that could be accommodated by the exposure-age data is ∼50 m, which is a small fraction of that predicted for the western Ross Sea by model simulations of the Antarctic contribution to MWP-1A. There do exist possible scenarios in which hypothesized marine ice sheet collapse in the outer Ross Sea during MWP-1A might not be recorded by ice thickness changes at Tucker Glacier. However, our record of ice thickness changes spanning this time period is the closest such record to the outer Ross Sea that is likely to exist, and it agrees with all exposure-age deglaciation chronologies from other regions of the Ross embayment in providing no evidence for such an event.
Keywords: Antarctica; cosmogenic-nuclide geochemistry; exposure-dating; glacial geology; Last glacial maximum; Ross Sea; Tucker Glacier; Victoria Land

Glacial–interglacial Nd isotope variability of North Atlantic Deep Water modulated by North American ice sheet - Zhao, Ning; Oppo, Delia W.; Huang, Kuo-Fang; Howe, Jacob N. W.; Blusztajn, Jerzy; Keigwin, Lloyd D. (Nature Communications, 2019)
The Nd isotope composition of seawater has been used to reconstruct past changes in the contribution of different water masses to the deep ocean. In the absence of contrary information, the Nd isotope compositions of endmember water masses are usually assumed constant during the Quaternary. Here we show that the Nd isotope composition of North Atlantic Deep Water (NADW), a major component of the global overturning ocean circulation, was significantly more radiogenic than modern during the Last Glacial Maximum (LGM), and shifted towards modern values during the deglaciation. We propose that weathering contributions of unradiogenic Nd modulated by the North American Ice Sheet dominated the evolution of the NADW Nd isotope endmember. If water mass mixing dominated the distribution of deep glacial Atlantic Nd isotopes, our results would imply a larger fraction of NADW in the deep Atlantic during the LGM and deglaciation than reconstructed with a constant northern endmember.

Growth and longevity of Hawaiian grouper (Hyporthodus quernus) — input for management and conservation of a large, slow-growing grouper - Andrews, Allen H.; DeMartini, Edward E.; Brodziak, Jon; Nichols, Ryan S.; Humphreys, Robert L. (Canadian Journal of Fisheries and Aquatic Sciences, 2019)
Hawaiian grouper (Hyporthodus quernus) is endemic to the Hawaiian Islands and is regionally important, yet little is known about its life history. This large species is managed within the Deep 7 bottom fish complex, which includes six snapper species that are assumed to have similar life history traits. Previous age estimates were not validated and suggested a maximum age of 34 years. To evaluate the preliminary study and provide a valid basis for life history parameters, we aged otoliths using bomb radiocarbon (14C) dating. Measured 14C values provided ages for smallest to largest fish that differed from the original study. The fundamental information provided here when evaluating Hawaiian grouper conservation status is longevity (valid to 50 years and estimated to 76 years) — no male sampled was <80 cm total length (TL) and younger than 34 years — and age-at-sexual maturity and age-at-sex change, which were indirectly estimated and compared with prior published estimates for this and other groupers. Updated life history parameters (k = 0.078, L∞ = 95.8 cm TL) should be used to improve future management and conservation assessments.

History and Mystery of Age and Growth Studies in Elasmobranchs: Common Methods and Room for Improvement - Andrews, Allen; Natanson, Lisa; Wintner, Sabine; Passerotti, Michelle (2019)
Age determination is a fundamental field of study that is of critical importance to management and conservation of a species. Determining population demographics can only be accomplished with the input of age data; yet, despite years of age determination efforts, it continues to be one of the most challenging and nuanced aspects of life history investigation in elasmobranchs. A variety of methods have been used to determine ages in elasmobranchs, some successful and some not. New techniques to obtain accurate and precise ages are being developed, and it is important to recognize the value of both old and new methodologies.

Holocene and Last Interglacial climate of the Faroe Islands from sedimentary plant wax hydrogen and carbon isotopes - Curtin, Lorelei; D'Andrea, William J.; Balascio, Nicholas; Pugsley, Genevieve; de Wet, Gregory; Bradley, Raymond (Quaternary Science Reviews, 2019)
The Last Interglacial period (LIG) is Earth's most recent globally warm period and is analogous in some ways to projected future global warming. However, questions remain regarding the state of the climate during the LIG in the North Atlantic, a region that is extremely sensitive to changes in oceanic and atmospheric circulation. Here, we present hydrogen and carbon isotope (δD and δ13C) records from a suite of plant wax biomarkers preserved in Holocene and LIG lacustrine sediments from the North Atlantic Faroe Islands and interpret them as qualitative proxies for temperature and hydroclimate variability. These data are used to directly compare LIG and Holocene climate using the same proxy approaches from the same terrestrial location. Measuring multiple isotopes on multiple types of waxes elucidates the sources of homologous plant waxes. We deduce that the δD values of long-chain n-alkanes (C27–C33) and mid-chain n-alkanes (C23–C25) in these sedimentary archives reflect leaf water and lake water δD values, respectively, while the δD values for both long-chain (C28–C30) and mid-chain n-alkanoic acids (C24–C26) primarily represent lake water δD values. Plant wax-inferred δD values of precipitation during the early Holocene (10,100 to 8,200  cal  yr BP) are ∼35‰ more positive than late Holocene values, and decline over the Holocene. δD-inferred hydrologic change and δ13C -inferred plant water use efficiency both indicate that the Faroe Islands became drier throughout the Holocene. Comparison with measurements from LIG plant waxes indicates that late LIG in the Faroe Islands was hydrologically similar to the early-to mid-Holocene (8,200 to 4,000  cal  yr BP), with enriched precipitation isotopes and reduced evapotranspiration indicating a warmer, wetter environment.
Keywords: Holocene; interglacial; North Atlantic; Organic geochemistry; paleoclimatology; Stable isotopes

Holocene glacier fluctuations on the northern flank of Cordillera Darwin, southernmost South America - Hall, B.L.; Lowell, T.V.; Bromley, G.R.M.; Denton, G.H.; Putnam, A.E. (Quaternary Science Reviews, 2019)

Holocene paleodepositional changes reflected in the sedimentary microbiome of the Black Sea - More, Kuldeep D.; Giosan, Liviu; Grice, Kliti; Coolen, Marco J. L. (Geobiology, 2019)
Subsurface microbial communities are generally thought to be structured through in situ environmental conditions such as the availability of electron acceptors and donors and porosity, but recent studies suggest that the vertical distribution of a subset of subseafloor microbial taxa, which were present at the time of deposition, were selected by the paleodepositional environment. However, additional highly resolved temporal records of subsurface microbiomes and paired paleoenvironmental reconstructions are needed to justify this claim. Here, we performed a highly resolved shotgun metagenomics survey to study the taxonomic and functional diversity of the subsurface microbiome in Holocene sediments underlying the permanently stratified and anoxic Black Sea. Obligate aerobic bacteria made the largest contribution to the observed shifts in microbial communities associated with known Holocene climate stages and transitions. This suggests that the aerobic fraction of the subseafloor microbiome was seeded from the water column and did not undergo post-depositional selection. In contrast, obligate and facultative anaerobic bacteria showed the most significant response to the establishment of modern-day environmental conditions 5.2 ka ago that led to a major shift in planktonic communities and in the type of sequestered organic matter available for microbial degradation. No significant shift in the subseafloor microbiome was observed as a result of environmental changes that occurred shortly after the marine reconnection, 9 ka ago. This supports the general view that the marine reconnection was a gradual process. We conclude that a high-resolution analysis of downcore changes in the subseafloor microbiome can provide detailed insights into paleoenvironmental conditions and biogeochemical processes that occurred at the time of deposition.
Keywords: geomicrobiology; palaeo-environment; paleoecology; sedimentary metagenomes; subsurface microbiome; sulfur cycle.

Holocene sea-level variability from Chesapeake Bay Tidal Marshes, USA - Cronin, Thomas M; Clevenger, Megan K; Tibert, Neil E; Prescott, Tammy; Toomey, Michael; Hubeny, J Bradford; Abbott, Mark B; Seidenstein, Julia; Whitworth, Hannah; Fisher, Sam; Wondolowski, Nick; Ruefer, Anna (The Holocene, 2019)
We reconstructed the last 10,000 years of Holocene relative sea-level rise (RSLR) from sediment core records near Chesapeake Bay, eastern United States, including new marsh records from the Potomac and Rappahannock Rivers, Virginia. Results show mean RSLR rates of 2.6 mm yr−1 from 10 to 8 kilo-annum (ka) due to combined final ice-sheet melting during deglaciation and glacio-isostatic adjustment (GIA subsidence). Mean RSLR rates from ~6 ka to present were 1.4 mm yr−1 due mainly to GIA, consistent with other East Coast marsh records and geophysical models. However, a progressively slower mean rate (<1.0 mm yr−1) characterized the last 1000 years when a multi-century-long period of tidal marsh development occurred during the ‘Medieval Climate Anomaly’ (MCA) and ‘Little Ice Age’ (LIA) in the Chesapeake Bay region and other East Coast marshes. This decrease was most likely due to climatic and glaciological processes and, correcting for GIA, represents a fall in global mean sea level (GMSL) near the end of Holocene Neoglacial cooling. These pre-historical climate- and GIA-driven Chesapeake Bay sea-level changes contrast sharply with those based on Chesapeake Bay tide-gauge rates (3.1–4.5 mm yr−1) (back to 1903). After subtracting the GIA subsidence component, these rates can be attributed to long-term (millennial) global factors of accelerated ocean thermal expansion (~1.0 mm yr−1) and mass loss from alpine glaciers and Greenland and Antarctic Ice Sheets (1.5–2.0 mm yr−1).
Keywords: chesapeake bay; Foraminifera; Holocene; sea level; tidal marsh; US East Coast

Holocene temperature history of northwest Greenland - With new ice cap constraints and chironomid assemblages from Deltaso - Axford, Y.; Lasher, G. E.; Kelly, M. A.; Osterberg, E. C.; Landis, J.; Schellinger, G. C.; Pfeiffer, A.; Thompson, E.; Francis, D. R. (QUATERNARY SCIENCE REVIEWS, 2019)
Arctic temperature shifts drive changes in carbon cycling, sea ice extent and Greenland Ice Sheet mass balance, all of which have global ramifications. Paleoclimate data from past warm periods provide a unique means for assessing the sensitivity of these systems to warming climate, but the magnitude and timing of past temperature changes in many parts of the Arctic are poorly known. Here we assess orbital scale Holocene temperature change in northwest Greenland near the margin of the ice sheet using subfossil insect assemblages from lake Deltaso. Based upon sedimentation history in this currently proglacial lake, we also place constraints on Holocene extents of the adjacent North Ice Cap, a large independent ice cap. Reconstructed summer temperatures were warmer than present at the onset of lacustrine sedimentation following regional deglaciation by the Greenland Ice Sheet, sometime between 10.8 and 10.1 ka BP. Deltaso experienced the warmest summer temperatures of the Holocene between similar to 10 and 6.2 ka BP, followed by progressive cooling that continued through the late Holocene as summer insolation declined, culminating in the lowest temperatures during the pre-industrial last millennium. Deltaso chironomids indicate peak early Holocene summer temperatures at least 2.5-3 degrees C warmer than modern and at least 3.5-4 degrees C warmer than the pre-industrial last millennium. We infer based upon lake sediment organic and biogenic content that in response to declining temperatures, North Ice Cap reached its present-day size similar to 1850 AD, having been smaller than present through most of the preceding Holocene. Our synthesis of paleoclimate evidence from northwest Greenland, Ellesmere Island and northern Baffin Bay supports the timing of temperature trends inferred at Deltaso, and suggests that quantitative temperature reconstructions from Deltas(?) may represent a minimum bound on regional early Holocene warming. Collectively, records from the region indicate >4 degrees C summer cooling through the Holocene. Intense early Holocene warmth around northwest Greenland argues against delayed onset of warmer than -present conditions due to the influence of the nearby waning Laurentide Ice Sheet, and has implications for understanding the Greenland Ice Sheet's sensitivity to climate change. (C) 2019 Elsevier Ltd. All rights reserved.

Holocene Vegetation, Climate, and Carbon History on Western Kodiak Island, Alaska - Peteet, Dorothy M.; Nichols, Jonathan E.; Mann, Daniel H. (Frontiers in Earth Science, 2019)
At Phalarope Pond, western Kodiak Island, a multidisciplinary study using pollen and spores, macrofossils, stable isotopes, and carbon accumulation provides the Holocene vegetation and climate history following the deglaciation that began over 16,000 cal years ago (yr BP). Following a cold and dry Younger Dryas, a warm and wet early Holocene was characterized by abundant ferns in a sedge tundra environment with maximum carbon accumulation, similar to high latitude peatlands globally. About 8,700 cal yr BP sedge and ferns declined and climate remained warm as drier conditions prevailed, limiting carbon sequestration. The abrupt shift in D/H isotopes of about 60% indicates a shift to cooler conditions or a more distal moisture source. Neoglaciation beginning about 3,700 cal yr BP is evident from increases in Artemisia, Empetrum and Betula, signifying cooler conditions, while Alnus declines, paralleling regional trends.

A human role in Andean megafaunal extinction? - Raczka, M.F.; Mosblech, N.A.; Giosan, L.; Valencia, B.G.; Folcik, A.M.; Kingston, M.; Baskin, S.; Bush, M.B. (Quaternary Science Reviews, 2019)
A new fossil pollen, Sporormiella, and sediment chemistry record from Lake Llaviucu, Ecuador, spanning the period from 16,280–9000 years Before Present, provides a high-resolution record of paleoecological change in the high Andes. The deglacial transition from super-páramo through páramo grasslands, to Andean forest is traced, with near-modern systems being established by c. 11,900 years ago. It is suggested that forest elements probably existed in microrefugial populations close to the ice front. Sporormiella is used as a proxy for megafaunal abundance, and its decline to background levels is inferred to indicate a local extinction event at c. 12,800 years ago. About 1800 years prior to the extinction, charcoal becomes a regular sedimentary component in this very wet valley. An early date for human activity in the valley is suggested, with the direct implication of humans in the extinction of the megafauna.
Keywords: Andes; Deglaciation; Ecuador Extinction; Fossil pollen; Human arrival; Pleistocene megafauna; Sporormiella

Illuminating microbial species‐specific effects on organic matter remineralization in marine sediments - Mahmoudi, Nagissa; Enke, Tim N.; Beaupré, Steven R.; Teske, Andreas P.; Cordero, Otto X.; Pearson, Ann (Environmental Microbiology, 2019)

Implications of radiocarbon ages of organic and inorganic carbon in coastal lakes in Florida for establishing a reliable chronology for sediment-based paleoclimate reconstructionAbstract - Wang, Yang; Das, Oindrila; Xu, Xiaomei; Liu, Jin; Jahan, Shakura; Means, Guy H.; Donoghue, Joseph; Jiang, Shijun (Quaternary Research, 2019)
Coastal lake sediments are valuable paleoclimate archives provided that they can be accurately dated. Here, we report radiocarbon ages of bulk sediment organic matter (OM), plants, shells, particulate OM, and dissolved OM from coastal lakes in Florida. Bulk sediment OM yielded ages that are consistently older than contemporaneous plants and shells, indicating significant radiocarbon deficiencies in sedimentary OM in these lakes. The data show that the OM radiocarbon deficiency varies over time and with location, making it impossible to determine a proper correction factor for radiocarbon ages of bulk sediments from these lakes. As a result, we consider ages obtained from bulk sediment OM from these lakes unreliable. The age reversals in bulk sediment OM observed in the sediment cores are likely caused by rapid increases in erosion and sedimentation resulting from large storm events. The data also show that sedimentation rate can vary considerably within a given lake, implying that an age-depth model established for one core cannot be directly applied to other cores despite their close proximity. Analyses of shells from one of the lakes suggest that fresh/brackish-water shells may serve as a good substrate for radiocarbon dating owing to a small reservoir effect on inorganic carbon.

Improved C− efficiency and ion beam currents by modifying SNICS cathode material - Hlavenka, Joshua D.; Abrams, Henry; Roberts, Mark L.; Longworth, Brett E.; Fallon, Stewart (Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2019)
We investigated the possibility of increasing the C-14 AMS efficiency and maximizing C- beam currents by modifying sample cathode geometry and material. Previously, we reported results which showed an increase in C- beam current and improved ionization efficiency when reducing the cathode sample well diameter from 1 mm to 0.75 mm and using zinc inserts, pressed into the aluminum cathode holder [4]. In this study we expand that effort by using cathodes with inserts made of Fe, Mo, Ni, Ti, Cu, and Zn. We pressed cathodes with 100 mu g of Oxalic Acid I (OX-I) and ran them to exhaustion. C-12 beam currents, C-14 counts, and graphite weight were used to determine ion source efficiency.
Keywords: Cathode; Efficiency; Ion source; SNICS

In situ cosmogenic 3He and 36Cl and radiocarbon dating of volcanic deposits refine the Pleistocene and Holocene eruption chronology of SW Peru - Bromley, Gordon R. M.; Thouret, Jean-Claude; Schimmelpfennig, Irene; Mariño, Jersy; Valdivia, David; Rademaker, Kurt; del Pilar Vivanco Lopez, Socorro; Team, ASTER; Aumaître, Georges; Bourlès, Didier; Keddadouche, Karim (Bulletin of Volcanology, 2019)
Constraining the age of young lavas, which generally fall outside the effective range of traditional geochronology methods, remains a key challenge in volcanology, limiting the development of high-resolution eruption chronologies. We present an in situ cosmogenic 3He and 36Cl surface-exposure chronology, alongside new minimum-limiting 14C ages, documenting young eruptions at five sites in the Western Cordillera, southern Peru. Four 3He-dated lavas on the Nevado Coropuna volcanic complex (hitherto thought to be dormant) indicate that the central dome cluster is young and potentially active; two Holocene lavas on the easternmost dome are the youngest directly dated lavas in Peru to date. East of Coropuna, lava domes and block-lava flows represent the most extensive output to date of Nevado Sabancaya, one of Peru’s most active volcanoes. Two 3He measurements confirm the Holocene age of these deposits and expand the chronology for one of the youngest major lava fields in Peru. 36Cl surface-exposure ages from the Purupurini dome cluster and Nevado Casiri document middle-late-Holocene episodes of effusive activity, while basal 14C ages from a lava-dammed wetland constrain an effusive eruption at Mina Arcata, north of Coropuna, to the late-glacial period. These new data advance the recent Western Cordillera volcanic record whilst demonstrating both the considerable potential and fundamental limitations of cosmogenic surface-exposure methods for such applications.

INFLUENCE OF DIFFERENT ACID TREATMENTS ON THE RADIOCARBON CONTENT SPECTRUM OF SEDIMENTARY ORGANIC MATTER DETERMINED BY RPO/ACCELERATOR MASS SPECTROMETRY - Bao, Rui; McNichol, Ann P.; Hemingway, Jordon D.; Gaylord, Mary C. Lardie; Eglinton, I, Timothy (RADIOCARBON, 2019)
In practice, obtaining radiocarbon (C-14) composition of organic matter (OM) in sediments requires first removing inorganic carbon (IC) by acid-treatment. Two common treatments are acid rinsing and fumigation. Resulting C-14 content obtained by different methods can differ, but underlying causes of these differences remain elusive. To assess the influence of different acid-treatments on C-14 content of sedimentary OM, we examine the variability in C-14 content for a range of marine and river sediments. By comparing results for unacidified and acidified sediments [HCl rinsing (Rinse(HCl)) and HCl fumigation (Fume(HCl))], we demonstrate that the two acid-treatments can affect C-14 content differentially. Our findings suggest that, for low-carbonate samples, Rinse(HCl) affects the Fm values due to loss of young labile organic carbon (OC). Fume(HCl) makes the Fm values for labile OC decrease, leaving the residual OC older. High-carbonate samples can lose relatively old organic components during Rinse(HCl), causing the Fm values of remaining OC to increase. Fume(HCl) can remove thermally labile, usually young, OC and reduce the Fm values. We suggest three factors should be taken into account when using acid to remove carbonate from sediments: IC abundance, proportions of labile and refractory OC, and environmental matrix.

Influence of Different Acid Treatments on the Radiocarbon Content Spectrum of Sedimentary Organic Matter Determined by RPO/Accelerator Mass SpectrometryABSTRACT - Bao, Rui; McNichol, Ann P; Hemingway, Jordon D; Lardie Gaylord, Mary C; Eglinton, Timothy I (Radiocarbon, 2019)
In practice, obtaining radiocarbon (C-14) composition of organic matter (OM) in sediments requires first removing inorganic carbon (IC) by acid-treatment. Two common treatments are acid rinsing and fumigation. Resulting C-14 content obtained by different methods can differ, but underlying causes of these differences remain elusive. To assess the influence of different acid-treatments on C-14 content of sedimentary OM, we examine the variability in C-14 content for a range of marine and river sediments. By comparing results for unacidified and acidified sediments [HCl rinsing (Rinse(HCl)) and HCl fumigation (Fume(HCl))], we demonstrate that the two acid-treatments can affect C-14 content differentially. Our findings suggest that, for low-carbonate samples, Rinse(HCl) affects the Fm values due to loss of young labile organic carbon (OC). Fume(HCl) makes the Fm values for labile OC decrease, leaving the residual OC older. High-carbonate samples can lose relatively old organic components during Rinse(HCl), causing the Fm values of remaining OC to increase. Fume(HCl) can remove thermally labile, usually young, OC and reduce the Fm values. We suggest three factors should be taken into account when using acid to remove carbonate from sediments: IC abundance, proportions of labile and refractory OC, and environmental matrix.

Intense Hurricane Activity Over the Past 1500 Years at South Andros Island, The Bahamas - Wallace, E. J.; Donnelly, J. P.; Hengstum, P. J.; Wiman, C.; Sullivan, R. M.; Winkler, T. S.; d'Entremont, N. E.; Toomey, M.; Albury, N. (Paleoceanography and Paleoclimatology, 2019)
Hurricanes cause substantial loss of life and resources in coastal areas. Unfortunately, historical hurricane records are too short and incomplete to capture hurricane‐climate interactions on multi‐decadal and longer timescales. Coarse‐grained, hurricane‐induced deposits preserved in blue holes in the Caribbean can provide records of past hurricane activity extending back thousands of years. Here we present a high resolution record of intense hurricane events over the past 1500 years from a blue hole on South Andros Island on the Great Bahama Bank. This record is corroborated by shorter reconstructions from cores collected at two nearby blue holes. The record contains coarse‐grained event deposits attributable to known historical hurricane strikes within age uncertainties. Over the past 1500 years, South Andros shows evidence of four active periods of hurricane activity. None of these active intervals occurred in the past 163 years. We suggest that Intertropical Convergence Zone position modulates hurricane activity on the island based on a correlation with Cariaco Basin titanium concentrations. An anomalous gap in activity on South Andros Island in the early 13th century corresponds to a period of increased volcanism. The patterns of hurricane activity reconstructed from South Andros Island closely match those from the northeastern Gulf of Mexico but are anti‐phased with records from New England. We suggest that either changes in local environmental conditions (e.g., SSTs) or a northeastward shift in storm tracks can account for the increased activity in the western North Atlantic when the Gulf of Mexico and southeastern Caribbean are less active.

Investigating environmental changes as the driving force of agricultural intensification in the lower reaches of the Yellow River: A case study at the Sanyangzhuang site - Qin, Zhen; Storozum, Michael; Liu, Haiwang; Zhang, Xiaohu; Kidder, Tristram R. (Quaternary International, 2019)
In many different societies around the world, people transitioned from slash-and-burn agriculture to an intensive mode of agricultural production. However, why agriculture was increasingly intensified by early farmers remains less understood. This study investigates the driving forces of agricultural intensification from an environmental perspective. Based on our fieldwork at the Sanyangzhuang site and previous paleoclimatic studies, we reconstruct the depositional processes and climatic changes at Sanyangzhuang and its surrounding area between 5000 yr BP and 2000 yr BP. Data suggest that farmers in the lower reaches of the Yellow River were confronted with increasingly severe Yellow River flooding and drier and colder climate during this time period. The environmental changes increase risks of crop failure and famine, disrupt the equilibrium of the social system and induce a process that brings about initial agricultural intensification. This environmental pressure is aggravated by social/political factors and results in the further development of agricultural intensification.
Keywords: Agricultural intensification; Environmental changes; Sanyangzhuang; The Yellow River

Isolation of quartz for cosmogenic in situ 14C analysis - Nichols, Keir A.; Goehring, Brent M. (Geochronology, 2019)
Froth flotation is a commonly used procedure for separating feldspars and micas from quartz for the preparation of quartz mineral separates to carry out cosmogenic nuclide analysis. Whilst extracting carbon from quartz we observed in situ carbon-14 (14C) concentrations which were anomalously high and in excess of theoretical geological maximum concentrations. Further etching of sample material reduced carbon yields and 14C concentrations, yet the latter remained unrealistically high. When quartz from the original whole rock sample was isolated in our laboratory, we observed even lower carbon yields and geologically plausible in situ 14C concentrations. After ruling out unlikely geological scenarios and systematic measurement issues, we decided to investigate the quartz isolation procedure as a potential source of 14C contamination. We hypothesised that laurylamine (dodecylamine), an organic compound used as part of the froth flotation procedure, elevates 14C concentrations if residual laurylamine is present. We demonstrate that laurylamine has a 14C modern carbon source and thus has the potential to influence in situ 14C measurements if present in minute but measurable quantities. Furthermore, we show that insufficient sample etching results in contaminant 14C persisting through the step heating of quartz that is subsequently collected with the in situ component released at 1100 ∘C. We demonstrate that froth flotation contaminates in situ 14C measurements. We provide guidelines for the preparation of quartz based on methods developed in our laboratory and demonstrate that all froth-flotation-derived carbon and 14C is removed when applied. We recommend that the procedures presented be used at a minimum when using froth flotation to isolate quartz for in situ 14C measurements.

Lake-level variability in Salar de Coipasa, Bolivia during the past ∼40,000 yrAbstract - Nunnery, J. Andrew; Fritz, Sherilyn C.; Baker, Paul A.; Salenbien, Wout (Quaternary Research, 2019)
Various paleoclimatic records have been used to reconstruct the hydrologic history of the Altiplano, relating this history to past variability of the South American summer monsoon. Prior studies of the southern Altiplano, the location of the world’s largest salt flat, the Salar de Uyuni, and its neighbor, the Salar de Coipasa, generally agree in their reconstructions of the climate history of the past ∼24 ka. Some studies, however, have highly divergent climatic records and interpretations of earlier periods. In this study, lake-level variation was reconstructed from a ∼14-m-long sediment core from the Salar de Coipasa. These sediments span the last ∼40 ka. Lacustrine sediment accumulation was apparently continuous in the basin from ∼40 to 6 ka, with dry or very shallow conditions afterward. The fossil diatom stratigraphy and geochemical data (δ13C, δ15N, %Ca, C/N) indicate fluctuations in lake level from shallow to moderately deep, with the deepest conditions correlative with the Heinrich-1 and Younger Dryas events. The stratigraphy shows a continuous lake of variable depth and salinity during the last glacial maximum and latter stages of Marine Oxygen Isotope Stage 3 and is consistent with environmental inferences and the original chronology of a drill core from Salar de Uyuni.
Keywords: Altiplano; Andes; Paleoclimate; paleohydrology; Paleolake; South America

Laser ablation–accelerator mass spectrometry reveals complete bomb 14C signal in an otolith with confirmation of 60-year longevity for red snapper (Lutjanus campechanus) - Andrews, Allen H.; Yeman, Christiane; Welte, Caroline; Hattendorf, Bodo; Wacker, Lukas; Christl, Marcus (Marine and Freshwater Research, 2019)
Bomb-produced14C has been used to make valid estimates of age for various marine organisms for 25 years, but fish ages that lead to birth years earlier than the period of increase in14C lose their time specificity. As a result, bomb14Cdating is limited to a minimum age from the last year of prebomb levels because the temporal variation in14C in the marine surface layer is negligible for decades before c. 1958. The longevity of red snapper (Lutjanus campechanus) in the Gulf of Mexico remains unresolved despite various forms of support for ages near 50–60 years. Although the age and growth of red snapper have been verified or validated to a limited extent, some scepticism remains about longevity estimates that exceed30 years. In this study, red snapper otoliths were analysed for14C using a novel laser ablation–accelerator mass spectrometry technique to provide a continuousrecordof14C uptake. This approach provided a basis for age validation that extends beyond the normal limits of bomb14C dating with confirmation of a 60-year longevity for red snapper in the Gulf of Mexico.
Keywords: Age validation; Carbon-14; Gulf of Mexico; Lutjanidae; radiocarbon.

Late Holocene long arid phase in the Indian subcontinent as seen in shallow sediments of the eastern Arabian Sea - Saravanan, Ponnusamy; Gupta, Anil K.; Zheng, Hongbo; Panigrahi, Mruganka K.; Prakasam, Muthusamy (Journal of Asian Earth Sciences, 2019)
Multi-proxy record of benthic and planktic foraminifera, total organic carbon and carbon and oxygen isotope ratios from Core SK291/GC15, off the coast of Goa, eastern Arabian Sea reveals significant paleoceanographic and paleoclimatic turnovers during ~6000 to 1700 calibrated years before the Present (cal yr BP). Benthic foraminiferal census data was analyzed with multivariate techniques including factor and cluster analyses of highest ranked species from the studied core that enabled to identify seven biofacies. The record suggests centennial to millennial-scale changes in the surface conditions driven by monsoon-linked upwelling in the eastern Arabian Sea during the studied interval. Various benthic biofacies combined with isotope and planktic foraminiferal data suggest that depletion of dissolved oxygen and increase in organic productivity in the study area was caused by intense monsoonal upwelling since the middle Holocene. The results suggest that during 5400–4700 and 3000–2500 cal yr BP the southwest (SW) monsoon was strong leading to intense upwelling in the study area as reflected by increased Globigerina bulloides percentages. These were generally warmer intervals in the northern hemisphere. The SW monsoon significantly weakened (abrupt decrease in G. bulloides population) during 4700–3400 cal yr BP roughly coinciding with a long arid phase in the Indian subcontinent and a cold interval in Europe. Our record suggests an abrupt increase in SW monsoon intensity during ~3000 to 2500 cal yr BP, when a pronounced change in benthic biofacies is also noted that suggests a major shift in the sub-surface conditions. Our data document a prolong weak SW monsoon phase beginning at ~4600 cal yr BP, little earlier than 4.2 ka event, in the eastern Arabian Sea.

Legacy sediment storage in New England river valleys: Anthropogenic processes in a postglacial landscape - Johnson, Kaitlin M.; Snyder, Noah P.; Castle, Stephanie; Hopkins, Austin J.; Waltner, Mason; Merritts, Dorothy J.; Walter, Robert C. (Geomorphology, 2019)
Legacy sediment associated with erosion from land clearing is a common feature in river valleys of the unglaciated Mid-Atlantic Piedmont region. Here, we quantify the volume of legacy sediment storage in three watersheds in New England, a formerly glaciated region with similar history and intensity of forest clearing and milldam construction during the seventeenth to nineteenth centuries. We combine field observations of bank stratigraphy, radiocarbon dating, and mapping of terraces and floodplains using lidar digital elevation models and other GIS datasets. The 68 km2 South River watershed in western Massachusetts exhibits the most extensive evidence for legacy sediment storage. We visited 18 historic dam sites in the watershed and found field evidence for up to 2.2 m of fine sand and silt legacy sediment storage at 14 of the sites. In the 555 km2 Sheepscot River watershed in coastal Maine, we visited 13 historic dam sites and found likely legacy sediment up to 2.3 m thick at six of the dams. In the 171 km2 upper Charles River watershed in eastern Massachusetts, we investigated 14 dam sites, and found legacy sediment up to 1.8 m thick at two of them. Stratigraphically, we identified the base of fine-grained legacy sediment from a change to much coarser grain size (gravel at most sites) or to glacial lacustrine or marine deposits. Along the Sheepscot River, we observed cut timbers underlying historic sediment at several locations, likely associated with sawmill activities. Only at the Charles River were we able to radiocarbon date the underlying gravel layer (1281–1391 calibrated CE). At no site did we find a buried organic-rich Holocene soil, in contrast to the field relations commonly observed in the Mid-Atlantic region. We use lidar elevation data to map planar terrace extents in each watershed, estimate thickness of remaining legacy sediment found stored behind breached or removed milldams, and estimate volumes of remaining legacy sediment storage in valley bottoms for entire watersheds. The maximum volume of stored legacy sediment estimated for the South, Sheepscot, and upper Charles watersheds is 2.5 × 106 m3, 3.7 × 106 m3, and 2.6 × 104 m3, respectively. These volumes of legacy sediment can be translated to an equivalent thickness of soil eroded from each watershed: 37 mm, 7 mm, and 0.2 mm, respectively. We attribute the variation in presence and thickness of legacy sediment at the New England sites to the existence or absence of upstream sediment supply in the form of thick glacial deposits and to sinks such as lakes and wetlands along valley bottoms. Of the three study watersheds, the South River has the most extensive glacial sediments, fewest sinks, and the most legacy sediment in storage along the river corridor.
Keywords: Anthropogenic sediment; Legacy sedimen; Milldams

Mapping Isotopic and Dissolved Organic Matter Baselines in Waters and Sediments of the Gulf of Mexico - Chanton, Jeffrey P.; Jaggi, Aprami; Radović, Jagoš R.; Rosenheim, Brad E.; Walker, Brett D.; Larter, Stephen R.; Rogers, Kelsey; Bosman, Samantha; Oldenburg, Thomas B. P. (Springer International Publishing, 2019)
The Deepwater Horizon oil spill released petroleum hydrocarbons that were depleted in δ13C and Δ14C at depth into the Gulf of Mexico. Stable-carbon and radiocarbon isotopic values and high-resolution mass spectrometry were used to follow the distributions of this petroleum and to track its transformation into petrocarbon, a term used to describe crude oil or transformed crude oil following biodegradation, weathering, oxygenation, or loss of lighter components. The term petrocarbon includes oil- or methane-derived carbon assimilated or incorporated into microbial biomass or into the food web as well as degraded and undegraded petroleum constituents. Here we report (1) the increase in the relative abundance of oxygen-containing carbon compounds making up the dissolved organic matter (DOM) with increasing depth through the water column, indicating the biodegradation of DOM as it was transported to depth in the water column, (2) the finding of 14C depletion in DOM indicating petrocarbon inputs, and (3) the decrease and subsequent increase of 14C in the isotopic composition of sinking particles indicating the capture of petrocarbon in sediment traps. In addition, we discuss the 14C depletion of this material once it is sedimented to the seafloor and the implications for oil spill budgets of seafloor petrocarbon deposition.
Keywords: Dissolved organic matter; FTICR-MS; Gulf baselines; High-resolution mass spectrometry; organic carbon; radiocarbon; Ramped pyrolysis; Sediment organic matter

Medieval warmth confirmed at the Norse Eastern Settlement in Greenland - Lasher, G. Everett; Axford, Yarrow (Geology, 2019)
Recent work has documented glacier advances in West Greenland coincident with the Medieval Climate Anomaly (MCA) and warmth across much of northern Europe. The North Atlantic Oscillation (NAO) has been invoked to explain antiphasing of temperatures between these North Atlantic regions. Historical and model observations suggest negative correlation between the mode of NAO and both temperature and δ18O values of precipitation over much of Greenland. We test for a hypothesized positive NAO mode and associated cool conditions during the MCA in South Greenland within the Norse Eastern Settlement by reconstructing δ18O values of precipitation at subcentennial resolution over the past 3000 yr using aquatic insect subfossils preserved in lake sediments. More positive δ18O values are found between 900 and 1400 CE, indicating a period of warmth in South Greenland superimposed on late Holocene insolation-forced Neoglacial cooling, and thus not supporting a positive NAO anomaly during the MCA. Highly variable δ18O values record an unstable climate at the end of the MCA, preceding Norse abandonment of Greenland. The spatial pattern of paleoclimate in this region supports proposals that North Atlantic subpolar ocean currents modulated South Greenland’s climate over the past 3000 yr, particularly during the MCA. Terrestrial climate in the Labrador Sea and Baffin Bay regions may be spatially heterogeneous on centennial time scales due in part to the influence of the subpolar gyre.

Mid-late Holocene rainfall variation in Taiwan: A high-resolution multi-proxy record unravels the dual influence of the Asian monsoon and ENSO - Chen, Jinxia; Li, Tiegang; Nan, Qingyun; Shi, Xuefa; Liu, Yanguang; Jiang, Bo; Zou, Jianjun; Selvaraj, Kandasamy; Li, Dongling; Li, ChuanShun (Palaeogeography, Palaeoclimatology, Palaeoecology, 2019)
Taiwan is particularly sensitive to changes in monsoonal precipitation and to typhoon-induced heavy precipitation events, however, rainfall variability in Taiwan on centennial and millennial time scales during the Holocene has not been well understood. This study describes mid-Holocene rainfall features of Taiwan based on pollen, total organic carbon (TOC), total nitrogen (TN), and C/N ratio records of core MD05-2908. The step-wise increase in sedimentation rate, fern spore percentage and concentration, TOC content, and C/N ratio suggests an increasing terrestrial material supply due to the intensified rainfall in Taiwan since 6800 cal. yr BP. This rainfall pattern shows an inverse pattern to the decreasing East Asian summer monsoon (EASM) strength represented by the multi-proxy records from North China. Variation of the East Asian summer circulation and associated moisture transport may account for the long-term rainfall changes in Taiwan. Superimposed on this trend, we interpreted three prominent rainfall changes, which focus on the periods of 6800–6600, 1090–880 and 490–190 cal. yr BP. These centennial time scale rainfall variations in our records are linked to the intensity of El-Niño Southern Oscillations.
Keywords: C/N ratio; Fern spore; La Niña; Okinawa Trough; tropical cyclone

The Mighty Susquehanna—Extreme Floods in Eastern North America During the Past Two Millennia - Toomey, Michael; Cantwell, Meagan; Colman, Steven; Cronin, Thomas; Donnelly, Jeffrey; Giosan, Liviu; Heil, Clifford; Korty, Robert; Marot, Marci; Willard, Debra (Geophysical Research Letters, 2019)
The hazards posed by infrequent major floods to communities along the Susquehanna River and the ecological health of Chesapeake Bay remain largely unconstrained due to the short length of streamgage records. Here we develop a history of high‐flow events on the Susquehanna River during the late Holocene from flood deposits contained in MD99‐2209, a sediment core recovered in 26 m of water from Chesapeake Bay near Annapolis, Maryland, United States. We identify coarse‐grained deposits left by Hurricane Agnes (1972) and the Great Flood of 1936, as well as during three intervals that predate instrumental flood records (~1800–1500, 1300–1100, and 400–0 CE). Comparison to sedimentary proxy data (pollen and ostracode Mg/Ca ratios) from the same core site indicates that prehistoric flooding on the Susquehanna often accompanied cooler‐than‐usual winter/spring temperatures near Chesapeake Bay—typical of negative phases of the North Atlantic Oscillation and conditions thought to foster hurricane landfalls along the East Coast.

Millennial-scale carbon accumulation and molecular transformation in a permafrost core from Interior Alaska - Hutchings, J.A.; Bianchi, T.S.; Kaufman, D.S.; Kholodov, A.L.; Vaughn, D.R.; Schuur, E.A.G. (Geochimica et Cosmochimica Acta, 2019)
Organic carbon stored in high-latitude permafrost represents a potential positive feedback to climate warming as well as a valuable store of paleoenvironmental information. The below-freezing conditions have effectively removed permafrost organic material from the modern carbon cycle and preserved its pre-freezing bulk and molecular states. The conditions that lead to efficient burial of organic carbon (OC) within permafrost were investigated by measuring OC stocks, past accumulation rates, and biogeochemical composition of a permafrost core taken from Interior Alaska dating back to 40 ka. The post-glacial Marine Isotope Stage 1 is represented by the top 1.2 m of the core and contains 64.7 kg OC/m2 with an accumulation rate of 4.3 g OC/m2/yr. The sediments that accumulated around the Last Glacial Maximum contain 9.9 kg OC/m2 with an accumulation rate of 0.5 g OC/m2/yr. Carbon storage (144.7 kg OC/m2) and accumulation (26.1 g OC/m2/yr) are both observed to be greatest between 35 and 40 ka, late during the Marine Isotope Stage 3 global interstadial. The extent of OC degradation was assessed using lignin and amino acid biomarkers with both approaches indicating well-preserved contemporary active layer and interstadial OC, whereas stadial OC was highly degraded. Lignin compositional indices throughout the core appear altered by sorptive processes that confounded some expected trends in the overall organic matter composition, while amino acids provided a more integrated pattern of change. Significant correlations between carbon-normalized hydroxyproline and total lignin concentrations further support the usefulness of hydroxyproline as an indicator for the abundance of plant organic matter. A novel amino acid plant-microbial index of the ratio of microbial-specific muramic acid and diaminopimelic acid biomarkers to the plant-specific hydroxyproline biomarker, indicate a transition from plant-dominated organic matter in fresh organic soils (index values of 0.01–0.20) to more microbial-dominated organic matter in degraded mineral soils (index values of 0.50–2.50). The branched glycerol dialkyl glycerol tetraether composition is complex and is not immediately compatible with existing temperature transfer functions. Residence time within the active layer is interpreted to integrate key factors such as primary productivity, inorganic sediment delivery, and other climate factors that control soil organic matter degradation. The Marine Isotope Stage 3, mid-Wisconsin interstadial period at this locality was forest-dominated and suggests the currently prevailing tundra ecotone is sensitive to environmental change. The majority of buried permafrost OC is high in degradability and if thawed, would be expected to be highly vulnerable to microbial decomposition.
Keywords: amino acids; biomarkers; branched GDGTs; lignin phenols; organic carbon; permafrost

Millennial-scale fluctuations in water volume transported by the Tsushima Warm Current in the Japan Sea during the Holocene - Horikawa, Keiji; Kodaira, Tomohiro; Ikehara, Ken; Murayama, Masafumi; Zhang, Jing (Global and Planetary Change, 2019)
Cyclic changes in volume transport of the Tsushima Warm Current (TWC) have been argued from diatom records in the southern Japan Sea off the Japanese islands during the Holocene. Although this phenomenon has not yet been confirmed by various proxy data, determining whether or not these oceanographic changes occurred is crucial for clarifying the nature of oceanographic changes in the southern Japan Sea. Here, we conducted a coupled analysis of Mg/Ca ratios and oxygen isotopes (δ18O) in shallow-dwelling Neogloboquadrina incompta from 13 core-top sediments in southern Japan, and developed a new equation for Mg/Ca temperature calibration (Mg/Ca = 0.311 × exp (0.07 × T)) as a proxy for spring sea surface temperature (SST). Using the newly developed, species-specific Mg/Ca-paleothermometry, we reconstructed SST variability for the past 6800 years from core YK10-7-PC09 in the southern Japan Sea. The Mg/Ca-derived SST record clearly represented five warmer periods at 6200–6000, 4900–4500, 4200–3800, 2600–2100, and 900–400 cal. year BP, almost consistent with previously published diatom records. These warmer events also corresponded to the periods in which warm molluscan assemblages increased at the northern end of the TWC, suggesting that periods of higher SST can be seen as reflecting the increased volume transport of the TWC. We interpreted the results of a model study showing that higher solar irradiance provoked positive Arctic Oscillation (AO)-like spatial patterns and the negative phase of the Pacific Decadal Oscillation (PDO) to mean that increased (reduced) TWC volume transport on the multi-centennial to millennial time scales was caused by high (low) solar insolation via a potential link between AO and PDO. Given that larger and more frequent volcanic eruptions occurred in the mid Holocene than in the late Holocene, volcanic forcing on the TWC volume transport changes would have been more significant during the former, as seen in the highly variable SST from this period and distinct decreases in SST around ~5900 cal. year BP and ~6400 cal. year BP. The millennial-scale fluctuations seen in SSTs in the southern Japan Sea would have had a large impact on the evolution of vegetation and human adaptation in the northern Japanese islands, adjacent to the Japan Sea, over the last 6800 years.
Keywords: Holocene; Mg/Ca-derived; Neogloboquadrina incompta; sea-surface temperature; Solar forcing; The Japan Sea; Tsushima; Warm Current

Mineral protection regulates long-term global preservation of natural organic carbon - Hemingway, Jordon D.; Rothman, Daniel H.; Grant, Katherine E.; Rosengard, Sarah Z.; Eglinton, Timothy I.; Derry, Louis A.; Galy, Valier V. (Nature, 2019)
The balance between photosynthetic organic carbon production and respiration controls atmospheric composition and climate1,2. The majority of organic carbon is respired back to carbon dioxide in the biosphere, but a small fraction escapes remineralization and is preserved over geological timescales3. By removing reduced carbon from Earth’s surface, this sequestration process promotes atmospheric oxygen accumulation2 and carbon dioxide removal1. Two major mechanisms have been proposed to explain organic carbon preservation: selective preservation of biochemically unreactive compounds4,5 and protection resulting from interactions with a mineral matrix6,7. Although both mechanisms can operate across a range of environments and timescales, their global relative importance on 1,000-year to 100,000-year timescales remains uncertain4. Here we present a global dataset of the distributions of organic carbon activation energy and corresponding radiocarbon ages in soils, sediments and dissolved organic carbon. We find that activation energy distributions broaden over time in all mineral-containing samples. This result requires increasing bond-strength diversity, consistent with the formation of organo-mineral bonds8 but inconsistent with selective preservation. Radiocarbon ages further reveal that high-energy, mineral-bound organic carbon persists for millennia relative to low-energy, unbound organic carbon. Our results provide globally coherent evidence for the proposed7 importance of mineral protection in promoting organic carbon preservation. We suggest that similar studies of bond-strength diversity in ancient sediments may reveal how and why organic carbon preservation—and thus atmospheric composition and climate—has varied over geological time.

Multiple independent records of local glacier variability on Nuussuaq, West Greenland, during the Holocene - Schweinsberg, Avriel D.; Briner, Jason P.; Licciardi, Joseph M.; Bennike, Ole; Lifton, Nathaniel A.; Graham, Brandon L.; Young, Nicolás E.; Schaefer, Joerg M.; Zimmerman, Susan H. (Quaternary Science Reviews, 2019)
The sensitivity of mountain glaciers to small-scale climate fluctuations makes records of their past extent among the best proxies for identifying spatio-temporal climate variability. Here we build on the few existing Holocene records of local glacier change in Greenland by using three independent geochronological methods—proglacial lake sediment analysis, cosmogenic 10Be surface-exposure dating, and in situ 14C burial modeling—to reconstruct continuous records of Holocene glacier variability on Nuussuaq, West Greenland. 10Be ages of perched boulders indicate eastern Nuussuaq was deglaciated between ∼11.0 and 10.5 ka. Radiocarbon-dated sediments from two lakes on Nuussuaq contain mineral-rich layers between ∼9.6 and 9.0 and ∼8.7–8.0 cal ka BP that may be correlative with nearby ice sheet moraines deposited in the early Holocene. Multiple proxies for glacier size indicate frequent, high-amplitude glacier fluctuations superimposed on net glacier growth during the late Holocene, with significant ice expansion phases at ∼3.7 ka, 2.8 ka, and throughout the past ∼2 ka. Mean 10Be ages from five nested moraine crests confirm that local glacier extents on Nuussuaq culminated during both the Little Ice Age [∼1470 C.E. (n = 3) and 1750 C.E. (n = 3)] and the preceding centuries (∼520–1320 C.E.; n = 11). Results reveal that local glaciers on Nuussuaq episodically advanced and retreated at centennial timescales throughout the Holocene, most likely in response to regional climate changes in West Greenland superimposed on the progressive insolation-driven cooling trend in the Northern Hemisphere. Our new 10Be moraine chronologies coupled with other glacier-size proxies corroborate an emerging pattern of significant summer cooling and glacier expansion in the centuries prior to the Little Ice Age in the Arctic.
Keywords: Cosmogenic 10Be; Cosmogenic in situ 14C; Greenland; Holocene; lake sediment; Mountain glaciers; Neoglaciation

MULTI-SUBSTRATE RADIOCARBON DATA CONSTRAIN DETRITAL AND RESERVOIR EFFECTS IN HOLOCENE SEDIMENTS OF THE GREAT SALT LAKE, UTAH - Bowen, Gabriel J.; Nielson, Kristine E.; Eglinton, Timothy I. (RADIOCARBON, 2019)
The radiocarbon (C-14) content of simultaneously deposited substrates in lacustrine archives may differ due to reservoir and detrital effects, complicating the development of age models and interpretation of proxy records. Multi-substrate C-14 studies quantifying these effects remain rare, however, particularly for large, terminal lake systems, which are excellent recorders of regional hydroclimate change. We report C-14 ages of carbonates, brine shrimp cysts, algal mat biomass, total organic carbon (TOC), terrestrial macrofossils, and n-alkane biomarkers from Holocene sediments of the Great Salt Lake (GSL), Utah. C-14 ages for co-deposited aquatic organic substrates are generally consistent, with small offsets that may reflect variable terrestrial organic matter inputs to the system. Carbonates and long-chain n-alkanes derived from vascular plants, however, are similar to 1000-4000 C-14 years older than other substrates, reflecting deposition of pre-aged detrital materials. All lacustrine substrates are C-14-depleted compared to terrestrial macrofossils, suggesting that the reservoir age of the GSL was > 1200 years throughout most of the Holocene, far greater than the modern reservoir age of the lake (similar to 300 years). These results suggest good potential for multi-substrate paleoenvironmental reconstruction from Holocene GSL sediments but point to limitations including reservoir-induced uncertainty in( 14)C chronologies and attenuation and time-shifting of some proxy signals due to detrital effects.

New AMS Dates for Verteba Cave and Stable Isotope Evidence of Human Diet in The Holocene Forest-Steppe, UkraineABSTRACT - Ledogar, Sarah H; Karsten, Jordan K; Madden, Gwyn D; Schmidt, Ryan; Sokohatskyi, Mykhailo P; Feranec, Robert S (Radiocarbon, 2019)
Excavations at several locations in Verteba Cave have uncovered a large amount of human skeletal remains in association with faunal bones and Tripolye material culture. We aim to establish radiocarbon (14C) dates for eight sites and to evaluate whether these deposits are singular events, or slow accumulations over time. 14C measurements, along with stable carbon and nitrogen isotope data from human and faunal remains, were collected from 18 specimens. Stable isotope values were used to evaluate human and animal diet, and whether freshwater reservoir effects offset measured dates. We found diets of the sampled species had limited to no influence from freshwater resources. Human diet appears to be dominated by terrestrial plants and herbivores. Four new sites were identified as Eneolithic. Comparisons of dates from top and bottom strata for two sites (7 and 20) reveal coeval dates, and we suggest that these deposits represent discrete events rather than slow continuous use. Lastly, we identified dates from the Mesolithic (8490±45 BP, 8765±30 BP), Iron Age (2505±20 BP), Slavic state era (1315±25 BP), and Medieval Period (585±15 BP), demonstrating periodic use of the cave by humans prior to and after the Eneolithic.
Keywords: archaeometry; cave burials; Eastern Europe; funerary ritual; Tripolye culture

New Last Glacial Maximum ice thickness constraints for the Weddell Sea Embayment, Antarctica - Nichols, Keir A.; Goehring, Brent M.; Balco, Greg; Johnson, Joanne S.; Hein, Andrew S.; Todd, Claire (The Cryosphere, 2019)
We describe new Last Glacial Maximum (LGM) ice thickness constraints for three locations spanning the Weddell Sea Embayment (WSE) of Antarctica. Samples collected from the Shackleton Range, Pensacola Mountains, and the Lassiter Coast constrain the LGM thickness of the Slessor Glacier, Foundation Ice Stream, and grounded ice proximal to the modern Ronne Ice Shelf edge on the Antarctic Peninsula, respectively. Previous attempts to reconstruct LGM-to-present ice thickness changes around the WSE used measurements of long-lived cosmogenic nuclides, primarily Be-10. An absence of post-LGM apparent exposure ages at many sites led to LGM thickness reconstructions that were spatially highly variable and inconsistent with flow line modelling. Estimates for the contribution of the ice sheet occupying the WSE at the LGM to global sea level since deglaciation vary by an order of magnitude, from 1.4 to 14.1m of sea level equivalent. Here we use a short-lived cosmogenic nuclide, in situ-produced C-14, which is less susceptible to inheritance problems than Be-10 and other long-lived nuclides. We use in situ C-14 to evaluate the possibility that sites with no post-LGM exposure ages are biased by cosmogenic nuclide inheritance due to surface preservation by cold-based ice and non-deposition of LGM-aged drift. Our measurements show that the Slessor Glacier was between 310 and up to 655m thicker than present at the LGM. The Foundation Ice Stream was at least 800m thicker, and ice on the Lassiter Coast was at least 385m thicker than present at the LGM. With evidence for LGM thickening at all of our study sites, our in situ C-14 measurements indicate that the long-lived nuclide measurements of previous studies were influenced by cosmogenic nuclide inheritance. Our inferred LGM configuration, which is primarily based on minimum ice thickness constraints and thus does not constrain an upper limit, indicates a relatively modest contribution to sea level rise since the LGM of < 4.6 m, and possibly as little as < 1.5 m.

On the Origin of Aged Sedimentary Organic Matter Along a River‐Shelf‐Deep Ocean Transect - Bao, Rui; Zhao, Meixun; McNichol, Ann; Wu, Ying; Guo, Xinyu; Haghipour, Negar; Eglinton, Timothy I. (Journal of Geophysical Research: Biogeosciences, 2019)
To assess the influences of carbon sources and transport processes on the C-14 age of organic matter (OM) in continental margin sediments, we examined a suite of samples collected along a river-shelf-deep ocean transect in the East China Sea (ECS). Ramped pyrolysis-oxidiation was conducted on suspended particulate matter in the Yangtze River and on surface sediments from the ECS shelf and northern Okinawa Trough. C-14 ages were determined on OM decomposition products within different temperature windows. These measurements suggest that extensive amounts of pre-old (i.e., millennial age) organic carbon (OC) are subject to degradation within and beyond the Yangtze River Delta, and this process is accompanied by an exchange of terrestrial and marine OM. These results, combined with fatty acid concentration data, suggest that both the nature and extent of OM preservation/degradation as well as the modes of transport influence the C-14 ages of sedimentary OM. Additionally, we find that the age of (thermally) refractory OC increases during across-shelf transport and that the age offset between the lowest and highest temperature OC decomposition fractions also increases along the shelf-to-trough transect. Amplified interfraction spread or C-14 heterogeneity is the greatest in the Okinawa Trough. Aged sedimentary OM across the transect may be a consequence of several reasons including fossil OC input, selective degradation of younger OC, hydrodynamic sorting processes, and aging during lateral transport. Consequently, each of them should be considered in assessing the C-14 results of sedimentary OM and its implications for the carbon cycle and interpretation of sedimentary records.
Keywords: Carbon cycle; hydrodynamic processes; organic carbon; radiocarbon; sediments

Pacific climate influences on ocean conditions and extreme shell growth events in the Northwestern Atlantic (Gulf of Maine) - Wanamaker, Alan D.; Griffin, Shelly M.; Ummenhofer, Caroline C.; Whitney, Nina M.; Black, Bryan; Parfitt, Rhys; Lower-Spies, Erin E.; Introne, Douglas; Kreutz, Karl J. (Climate Dynamics, 2019)
The Gulf of Maine is undergoing rapid environmental and ecological changes, yet our spatial and temporal understanding of the climatic and hydrographic variability in this region, including extreme events, is limited and biased to recent decades. In this study, we utilize a highly replicated, multi-century master shell growth chronology derived from the annual increments formed in the shells of the long-lived bivalve Arctica islandica collected in 38 m from the central coastal region in the Gulf of Maine. Our results indicate that shell growth is highly synchronous and inversely related to local seawater temperatures. Using composite analyses of extreme shell growth events from CE 1900 to 2013, we extend our understanding of the factors driving oceanic variability and shell growth in the Northwestern Atlantic back to CE 1761. We suggest that extreme shell growth events are primarily controlled by Gulf of Maine sea surface temperature (SST) and stratification conditions, which in turn appear to be largely influenced by SST patterns in the Pacific Ocean through their influence on mid-latitude atmospheric circulation patterns and the location of the eddy-driven jet. The large-scale jet dynamics during these extreme years manifest as precipitation and moisture transport anomalies and regional SST conditions in the Gulf of Maine that either enhance or inhibit shell growth. Pacific climate variability is thus an important, yet understudied, influence on Gulf of Maine ocean conditions.

Paleoseismic Investigation of the Levan and Fayette Segments of the Wasatch Fault Zone, Juab and Sanpete Counties, Utah - McDonald, Greg N.; Hiscock, Adam I.; Hylland, Micheal D. (Utah Geological Survey, 2019)

Petrocarbon evolution: Ramped pyrolysis/oxidation and isotopic studies of contaminated oil sediments from the Deepwater Horizon oil spill in the Gulf of Mexico - Rogers, Kelsey L.; Bosman, Samantha H.; Lardie-Gaylord, Mary; McNichol, Ann; Rosenheim, Brad E.; Montoya, Joseph P.; Chanton, Jeffrey P. (PLOS ONE, 2019)
Hydrocarbons released during the Deepwater Horizon (DWH) oil spill weathered due to exposure to oxygen, light, and microbes. During weathering, the hydrocarbons' reactivity and lability was altered, but it remained identifiable as "petrocarbon" due to its retention of the distinctive isotope signatures (C-14 and C-13) of petroleum. Relative to the initial estimates of the quantity of oil-residue deposited in Gulf sediments based on 2010-2011 data, the overall coverage and quantity of the fossil carbon on the seafloor has been attenuated. To analyze recovery of oil contaminated deep-sea sediments in the northern Gulf of Mexico we tracked the carbon isotopic composition (C-13 and C-14, radiocarbon) of bulk sedimentary organic carbon through time at 4 sites. Using ramped pyrolysis/oxidation, we determined the thermochemical stability of sediment organic matter at 5 sites, two of these in time series. There were clear differences between crude oil (which decomposed at a lower temperature during ramped oxidation), natural hydrocarbon seep sediment (decomposing at a higher temperature; Delta C-14 = -189 parts per thousand) and our control site (decomposing at a moderate temperature; Delta C-14 = -189 parts per thousand), in both the stability (ability to withstand ramped temperatures in oxic conditions) and carbon isotope signatures. We observed recovery toward our control site bulk Delta C-14 composition at sites further from the wellhead in similar to 4 years, whereas sites in closer proximity had longer recovery times. The thermographs also indicated temporal changes in the composition of contaminated sediment, with shifts towards higher temperature CO2 evolution over time at a site near the wellhead, and loss of higher temperature CO2 peaks at a more distant site.
Keywords: C-14 ANALYSES; MARINE SNOW; degradation; fractionation; organic-matter; POLYCYCLIC AROMATIC-HYDROCARBONS; MICROBIAL COMMUNITY RESPONSE; radiocarbon; STABLE CARBON; surface sediments

Radiocarbon age of different photoreactive fractions of freshwater dissolved organic matter - Ishikawa, Naoto F.; Butman, David; Raymond, Peter A. (Organic Geochemistry, 2019)
Dissolved organic carbon (DOC) plays a major role in aquatic carbon cycling. In order to determine if DOC photolability was related to DOC age, we tested the effect of oxidation time using UV irradiation on natural radiocarbon concentrations (Δ14C) of DOC in six US rivers. The most photo-labile DOC was 14C youngest. After a 100 min UV irradiation, most DOC (>93%) was oxidized in two out of the six rivers studied. On the other hand, the other four rivers still had a considerable amount (>20%) of DOC resistant to UV oxidation, which showed lower Δ14C values than those of bulk DOC. We also found that the concentration and Δ14C value of bulk DOC are controlled by the photochemically intermediate fraction. The results suggest that 14C age of organic matter is not homogeneous within DOC, the degree of which may depend on the characteristics unique to rivers.
Keywords: dissolved organic carbon; Mixing model; Oxidation time; UV irradiation; Δ14C

Reconstructing reef fish communities using fish otoliths in coral reef sediments - Lin, Chien-Hsiang; De Gracia, Brigida; Pierotti, Michele E. R.; Andrews, Allen H.; Griswold, Katie; O’Dea, Aaron (PLOS ONE, 2019)
Little is known about long-term changes in coral reef fish communities. Here we present a new technique that leverages fish otoliths in reef sediments to reconstruct coral reef fish communities. We found over 5,400 otoliths in 169 modern and mid-Holocene bulk samples from Caribbean Panama and Dominican Republic mid-Holocene and modern reefs, demonstrating otoliths are abundant in reef sediments. With a specially-built reference collection, we were able to assign over 4,400 otoliths to one of 56 taxa (35 families) though mostly at genus and family level. Many otoliths were from juvenile fishes for which identification is challenging. Richness (by rarefaction) of otolith assemblages was slightly higher in modern than mid-Holocene reefs, but further analyses are required to elucidate the underlying causes. We compared the living fish communities, sampled using icthyocide, with the sediment otolith assemblages on four reefs finding the otolith assemblages faithfully capture the general composition of the living fish communities. Radiocarbon dating performed directly on the otoliths suggests that relatively little mixing of sediment layers particularly on actively accreting branching coral reefs. All otolith assemblages were strongly dominated by small, fast-turnover fish taxa and juvenile individuals, and our exploration on taxonomy, functional ecology and taphonomy lead us to the conclusion that intense predation is likely the most important process for otolith accumulation in reef sediments. We conclude that otolith assemblages in modern and fossil reef sediments can provide a powerful tool to explore ecological changes in reef fish communities over time and space.

Salt marsh ecosystem restructuring enhances elevation resilience and carbon storage during accelerating relative sea-level rise - Gonneea, Meagan Eagle; Maio, Christopher V.; Kroeger, Kevin D.; Hawkes, Andrea D.; Mora, Jordan; Sullivan, Richard; Madsen, Stephanie; Buzard, Richard M.; Cahill, Niamh; Donnelly, Jeffrey P. (Estuarine, Coastal and Shelf Science, 2019)
Salt marshes respond to sea-level rise through a series of complex and dynamic bio-physical feedbacks. In this study, we found that sea-level rise triggered salt marsh habitat restructuring, with the associated vegetation changes enhancing salt marsh elevation resilience. A continuous record of marsh elevation relative to sea level that includes reconstruction of high-resolution, sub-decadal, marsh elevation over the past century, coupled with a lower-resolution 1500-year record, revealed that relative sea-level rose 1.5 ± 0.4 m, following local glacial isostatic adjustment (1.2 mm/yr). As sea-level rise has rapidly accelerated, the high marsh zone dropped 11 cm within the tidal frame since 1932, leading to greater inundation and a shift to flood- and salt-tolerant low marsh species. Once the marsh platform fell to the elevation favored by low-marsh Spartina alterniflora, the elevation stabilized relative to sea level. Currently low marsh accretion keeps pace with sea-level rise, while present day high marsh zones that have not transitioned to low marsh have a vertical accretion deficit. Greater biomass productivity, and an expanding subsurface accommodation space favorable for salt marsh organic matter preservation, provide a positive feed-back between sea-level rise and marsh platform elevation. Carbon storage was 46 ± 28 g C/m2/yr from 550 to 1800 CE, increasing to 129 ± 50 g C/m2/yr in the last decade. Enhanced carbon storage is controlled by vertical accretion rates, rather than soil carbon density, and is a direct response to anthropogenic eustatic sea-level rise, ultimately providing a negative feedback on climate warming.
Keywords: 14-Carbon; accretion; Carbon storage; Elevation; Salt marsh; Sea level index point; sea-level rise

Sea Level Rise Explains Changing Carbon Accumulation Rates in a Salt Marsh Over the Past Two Millennia - McTigue, Nathan; Davis, Jenny; Rodriguez, Antonio B.; McKee, Brent; Atencio, Anna; Currin, Carolyn (Journal of Geophysical Research: Biogeosciences, 2019)
High rates of carbon burial observed in wetland sediments have garnered attention as a potential “natural fix” to reduce the concentration of carbon dioxide (CO2) in Earth's atmosphere. A carbon accumulation rate (CAR) can be determined through various methods that integrate a carbon stock over different time periods, ranging from decades to millennia. Our goal was to assess how CAR changed over the lifespan of a salt marsh. We applied a geochronology to a series of salt marsh cores using both 14C and 210Pb markers to calculate CARs that were integrated between 35 and 2,460 years before present. CAR was 39 g C·m−2·year−1 when integrated over millennia but was upward of 148 g C·m−2·year−1 for the past century. We present additional evidence to account for this variability by linking it to changes in relative sea level rise (RSLR), where higher rates of RSLR were associated with higher CARs. Thus, the CAR calculated for a wetland should integrate timescales that capture the influence of contemporary RSLR. Therefore, caution should be exercised not to utilize a CAR calculated over inappropriately short or long timescales as a current assessment or forecasting tool for the climate change mitigation potential of a wetland.
Keywords: Carbon storage; Geochronology; Salt marsh; sea‐level rise

Sea-level, monsoonal, and anthropogenic impacts on the millennial-scale variability of siliciclastic sediment input into the western Philippine sea since 27 ka - Xu, Zhaokai; Li, Tiegang; Clift, Peter D.; Wan, Shiming; Lim, Dhongil; Chang, Fengming; Sun, Rongtao (Journal of Asian Earth Sciences, 2019)
Multiproxy records from Core MD06-3054 in the western Philippine Sea and published results from the nearby Core MD06-3052, which are both located at the northern margin of the Western Pacific Warm Pool (WPWP), provide precise reconstructions and evidence for the potential controls on continental erosion and weathering intensities in Luzon. These data also constrain sediment source-to-sink processes in the sea since 27 ka at the millennial scale. We demonstrate that the siliciclastic fraction is derived from Luzon volcanic rocks and eolian dust from mainland Asia. Stronger physical erosion and chemical weathering generally occurred during the last glaciation, Heinrich Event 1, the Younger Dryas, and the period from 10.3 to 11.3 ka. In contrast, the Bølling-Allerød was characterized by weaker physical erosion and chemical weathering. During the last glaciation, Heinrich Event 1, and the Younger Dryas, the lower sea level led to enhanced erosion and weathering of the exposed shelf sediments. In contrast, the weaker physical erosion and chemical weathering that occurred during the Bølling-Allerød and the Holocene, except after 2.1 ka, are closely correlated with the higher sea level. The stronger physical erosion and chemical weathering at 10.3–11.3 ka may be derived from the reworking of older sediments during the time of a strengthening summer monsoon. Furthermore, enhanced human activity since 2.1 ka has become the dominant control on erosion in Luzon. Rapid weathering changes in the WPWP during the last deglaciation highlight the high variability in local controls at low latitudes during these periods and the potential influence of controls at high latitudes.

Sediment accumulation and sedimentation rates in playas on the High Plains of western Kansas, USA - Bowen, Mark W.; Johnson, William C. (Geomorphology, 2019)
Grassland ecosystems are some of the most modified ecosystems in the world, largely due to conversion to cropland, and the High Plains of the central United States is no exception. Playa wetlands are ubiquitous features of the High Plains and have experienced increased sediment accumulation, which is the primary cause of reduced playa ecosystem function. Seven playas on the High Plains of western Kansas, five with cropland-dominated watersheds and two with grassland-dominated watersheds, were examined to quantify the amount of recent (past ~100–175 yr) sediment accumulated within playas and to establish chronologies of playa filling. Thicknesses of recent sediment were determined in the field, and soil cores were extracted from study playas. Four playa cores were analyzed for 210Pb to establish the chronology of recent sediment accumulation and sedimentation rates. Chronologies of pre-agricultural sediments and sedimentation rates were calculated by 14C dating of buried soils preserved within playa cores. Radiocarbon ages indicate playa stratigraphic records span the Holocene and that these playas have persisted on the landscape since at least the Late Pleistocene. Long-term, natural sedimentation rates were highest during the Pleistocene-Holocene transition and early Holocene, at ~2–4 cm/century. During the middle and late Holocene, sedimentation rates averaged ~1 cm/century. Cropland playas accumulated ~10–15 cm of recent sediment at average rates of ~6.5–10 cm/century, while grassland playas accumulated only ~2 cm of recent sediment. Conversion of watersheds to cropland has greatly accelerated sediment accumulation within playas, which is generally resulting in a decline in critical playa ecosystem functions.
Keywords: 210Pb; Agricultural; chronology; Holocene; Radiocarbon dating; sedimentation

Sedimentary Data from Grand Bay, Alabama/Mississippi, 2014–2016 - Marot, Marci; Smith, Christopher G.; McCloskey, Terrence A.; Locker, Stanley D. (U.S. Geological Survey, 2019)
This data release is an archive of sedimentary field and laboratory analytical data collected in Grand Bay, Alabama/Mississippi from 2014-2016 by scientists from the U.S. Geological Survey St. Petersburg Coastal and Marine Science Center (USGS SPCMSC). This work, a component of the SPCMSC’s Sea-level and Storm Impacts on Estuarine Environments and Shorelines (SSIEES) project, provides the necessary data to quantify sedimentation rates and sediment sources for the marsh and estuary. The SSIEES project objective is to evaluate the exchange of sediment material between the marsh and estuary due to extreme storms and sea-level rise. Micropaleontological data from select cores and surface samples are available in Haller and others (2018, https://doi.org/10.5066/F7MC8X5F, https://doi.org/10.5066/F7445KSG). Single-beam bathymetry of Grand Bay proper and multi-beam bathymetry of several marsh-edge eroding shorelines are reported in Dewitt and others (2017, https://doi.org/10.3133/ds1070) and Stalk and others (2018, https://doi.org/10.5066/F7MC8Z9N), respectively. Subbottom and sidescan sonar data for Grand Bay proper are reported in Locker and others (2018, https://doi.org/10.5066/P9374DKQ). This publication includes data for the sediment cores and surface sediments taken in Grand Bay marsh and estuary during five sampling periods of this study, which were designated as USGS Field Activity Numbers (FAN) 2014-323-FA (project ID 14CCT01), 2015-315-FA (project ID 15CCT02), 2016-331-FA (project ID 16CCT03), 2016-348-FA (project ID 16CCT04), and 2016-358-FA (project ID 16CCT07). Data products include: GPS-derived site locations and elevations; core photographs, logs, and x-radiographs; lithologic, radiochemical, elemental composition, stable isotopic composition, and radiocarbon data; and Federal Geographic Data Committee (FGDC) metadata. Note: This data release was versioned on April 28, 2020. Please see the Suggested Citation section for details.

Selective Preservation of Coccolith Calcite in Ontong‐Java Plateau Sediments - Subhas, Adam V.; McCorkle, Daniel C.; Quizon, Alex; McNichol, Ann P.; Long, Matthew H. (Paleoceanography and Paleoclimatology, 2019)
Keywords: BIOMINERALIZATION; caco3 dissolution; CEARA RISE; dissolution kinetics; IN-SITU MEASUREMENTS; DEEP-SEA CARBONATES; PLANKTONIC-FORAMINIFERA; EQUATORIAL PACIFIC; surface sediments; WATER INTERFACE

Shellfish, Geophytes, and Sedentism on Early Holocene Santa Rosa Island, Alta California, USA - Erlandson, Jon M.; Rick, Torben C.; Ainis, Amira F.; Gill, Kristina M.; Jew, Nicholas P.; Reeder-Myers, Leslie A. (The Journal of Island and Coastal Archaeology, 2019)
Archaeobotanical remains recovered from a large ∼8000-year-old-shell midden (CA-SRI-666) on Santa Rosa Island provide the first ancient plant data from this large island, shedding light on ancient patterns of plant use, subsistence, and sedentism. Faunal data from shell midden samples retrieved from three site loci contain evidence for harvesting of rocky intertidal shellfish and estuarine clams and oysters from a paleo-estuary in the vicinity. CA-SRI-666 appears to have been an Early Holocene village site occupied year round. A key to the development of early sedentary societies on the island may have been geophytes, especially Brodiaea-type corms, which provided an abundant source of carbohydrates and calories that complemented marine resources rich in fat and whole animal proteins. Our data demonstrate the value of integrating paleobotanical and zooarchaeological data from island and coastal archaeological sites to help elucidate human social, cultural, and environmental dynamics, including sedentism.

Significance of Perylene for Source Allocation of Terrigenous Organic Matter in Aquatic SedimentsSignificance of Perylene for Source Allocation of Terrigenous Organic Matter in Aquatic Sediments - Hanke, Ulrich M.; Lima-Braun, Ana L.; Eglinton, Timothy I.; Donnelly, Jeffrey P.; Galy, Valier; Poussart, Pascale; Hughen, Konrad; McNichol, Ann P.; Xu, Li; Reddy, Christopher M. (Environmental Science & Technology, 2019)
Perylene is a frequently abundant, and sometimes the only polycyclic aromatic hydrocarbon (PAH) in aquatic sediments, but its origin has been subject of a longstanding debate in geochemical research and pollutant forensics because its historical record differs markedly from typical anthropogenic PAHs. Here we investigate whether perylene serves as a source-specific molecular marker of fungal activity in forest soils. We use a well-characterized sedimentary record (1735-1999) from the anoxic-bottom waters of the Pettaquamscutt River basin, RI to examine mass accumulation rates and isotope records of perylene, and compare them with total organic carbon and the anthropogenic PAH fluoranthene. We support our arguments with radiocarbon (14C) data of higher plant leaf-wax n-alkanoic acids. Isotope-mass balance-calculations of perylene and n-alkanoic acids indicate that ∼40% of sedimentary organic matter is of terrestrial origin. Further, both terrestrial markers are pre-aged on millennial time-scales prior to burial in sediments and are insensitive to elevated 14C concentrations following nuclear weapons testing in the mid-20th Century. Instead, changes coincide with enhanced erosional flux during urban sprawl. These findings suggest that perylene is definitely a product of soil-derived fungi, and a powerful chemical tracer to study the spatial and temporal connectivity between terrestrial and aquatic environments.

Single step Production of graphite from organic Samples for Radiocarbon Measurements - Elder, K L; Roberts, M L; Walther, T; Xu, L (Radiocarbon, 2019)
We present a new low-cost, high-throughput method for converting many types of organic carbon samples into graphite for radiocarbon (14C) measurements by accelerator mass spectrometry (AMS). The method combines sample combustion and reduction to graphite into a single procedure. In the Single Step method, solid samples are placed directly into Pyrex containing zinc, titanium hydride and iron catalyst. The tube is evacuated, flame sealed, and placed in a muffle furnace for 7 hr. A variety of organic samples have been tested including oxalic acid, sucrose, wood, peat, collagen, humic acid, and contamination swipe samples. The method significantly reduces the time required to produce a graphite sample for 14C measurement, with analytical precision and accuracy approaching that of traditional two-step combustion and hydrogen reduction methods. The details and applicability of the method are presented.
Keywords: graphite; radiocarbon; sealed tube graphite; single step graphite

Sinking particle flux and composition at three sites of different annual sea ice cover in the Amundsen Sea, Antarctica - Kim, Minkyoung; Yang, Eun J.; Kim, Dongseon; Jeong, Jin-Hyun; Kim, Hyung J.; Park, Jisoo; Jung, Jinyoung; Ducklow, Hugh W.; Lee, SangHoon; Hwang, Jeomshik (Journal of Marine Systems, 2019)
This study examines the sinking particle flux and composition of samples collected at three sites in the western Amundsen Sea, Antarctica: a perennial sea-ice-covered area, the central region of the Amundsen Sea polynya, and close to the Dotson Ice Shelf within the polynya. Time series sediment traps were deployed for one year at depths of 400-500 m from February and March 2012. Observations from the three sites confirm previously reported findings that the majority of annual POC (particulate organic carbon) flux in the Amundsen Sea occurs during the austral summer, with much smaller POC fluxes during other seasons. In the perennial ice-covered area, sea ice diatoms were the dominant source of sinking particles. In this region, the summertime POC flux is similar to that in the central polynya. However, the POC flux exhibited large interannual variability, with the reduction in sea ice cover and sufficient insolation being critical to enhanced sinking POC flux. Within the Amundsen Sea polynya, the sinking POC flux was higher in the central region than near the Dotson Ice Shelf, consistent with spatial variability in primary production. The site near the Dotson Ice Shelf had the lowest contribution of diatoms to sinking particles and the smallest POC flux among the three sites.
Keywords: Amundsen sea; Biological pump; particulate organic carbon; Perennial ice-covered area; Polynya

Sortable silt records of intermediate-depth circulation and sedimentation in the Southwest Labrador Sea since the Last Glacial Maximum - Hoffmann, Sharon S.; Dalsing, Risa E.; Murphy, Sarah C. (Quaternary Science Reviews, 2019)
The Labrador Sea is a vital region for the Atlantic Meridional Overturning Circulation (AMOC), where overflow waters from the Nordic Seas mix with locally produced Labrador Sea Water (LSW), before exiting to the interior of the Atlantic Ocean. The dynamical sedimentary proxy of mean sortable silt size () can give information on past changes in deep water circulation speed and the strength of AMOC. We have produced records from two core sites at depths between 1500 and 2000 m on the continental slope east of Newfoundland, to reconstruct changes in intermediate depth water circulation speed, including Glacial North Atlantic Intermediate Water and Labrador Sea Water over the past 22,000 years. Increases in appear to coincide with much of the deglaciation as well as the mid-late Holocene. End-member modeling suggests that ice-rafted debris (IRD) is an important factor in interpreting during the deglaciation. We find that a robust increase in is likely unrelated to IRD during the past 5 ka, and probably reflects increased flow at intermediate depths due to local production of LSW strengthening as Nordic Seas overflows weakened at this depth. Our results highlight both the complications of producing records in IRD-rich, slope environments and the promise that this proxy nevertheless has for reconstructing dynamical changes in deep ocean currents.
Keywords: Holocene; labrador sea; paleoceanography; Sedimentology-marine cores

Sources and sink of black carbon in Arctic Ocean sediments - Ren, Peng; Liu, Yanguang; Shi, Xuefa; Sun, Shuwen; Fan, Di; Wang, Xuchen (SCIENCE OF THE TOTAL ENVIRONMENT, 2019)
The concentrations and carbon isotopic (C-13, C-14) compositions of total organic carbon (TOC) and black carbon (BC) were measured for four sediment cores collected from the shelf to slope in the Arctic Ocean. Contents of TOC and BC ranged from 0.46% to 1.94% and 0.04% to 0.13% by dry weight, and BC accounted for 3.5% to 15.2% of the TOC preserved in the shelf and slope sediments. Sediment of the Chukchi shelf contained relatively high BC contents compared with the sediments of the Arctic slope, suggesting strong influence from the river and terrestrial inputs to the shelf region. Radiocarbon measurements revealed that the ages of BC are in the range of 7330 to 29,700 years (before present) and they are 4093 to 7723 years older than the C-14 ages of TOC preserved in the same sediment depths. Based on an isotopic mass balance model, we calculated that fossil fuel combustion contributed 62-96%, and biomass burning contributed 4-38% of the BC pool in the sediments of the study area. This ``slow-cycling'' old BC is an important fraction of the inert organic carbon pool preserved in the sediments, and represents a significant sink of atmospheric CO2 and global carbon cycle. With the thawing permafrost caused by continuous global warming, the size of this BC pool mobilized and exported by rivers to the Arctic Ocean could increase in the future. (C) 2019 Elsevier B.V. All rights reserved.

Sources of carbon to suspended particulate organic matter in the northern Gulf of Mexico - Rogers, Kelsey L.; Bosman, Samantha H.; Weber, Sarah; Magen, Cedric; Montoya, Joseph P.; Chanton, Jeffrey P. (Elem Sci Anth, 2019)
Suspended particulate organic carbon (POCsusp) in the Gulf of Mexico is unique compared to other seas and oceans. In addition to surface primary production, isotopic analysis indicates that microbial cycling of oil and riverine inputs are primary sources of carbon to POCsusp in the Gulf. To characterize POCsusp from seep sites and non-seep north central Gulf (NCG) sites potentially affected by the Deepwater Horizon (DWH) spill, we analyzed 277 and 123 samples for δ13C and Δ1C signatures, respectively. Depth, partitioned into euphotic (300 m), was the main driver of spatial δ13C differences, with deep depths exhibiting 13C depletion. Both deep depths and proximity to sources of natural seepage resulted in 14C depletion. A two-endmember mixing model based on Δ14C indicated that sources to POCsusp were 14–29% fossil carbon at NCG sites and 19–57% at seep sites, with the balance being modern surface production. A six-component Bayesian mixing model MixSIAR, using both 13C and 14C, suggested that riverine inputs were an important carbon source to POCsusp contributing 34–46%. The influence of seeps was localized. Below the euphotic zone at seep sites, 46 ± 5% (n = 9) of the carbon in POCsusp was derived from environmentally degraded, transformed oil; away from seeps, transformed oil contributed 15 ± 4% (n = 39). We hypothesized that, at NCG sites removed from hydrocarbon seep sources, isotopic signatures would be depleted following the spill and then shift towards background-like enriched values over time. At deep depths we observed decreasing Δ14C signatures in POCsusp from 2010 to 2012, followed by isotopic enrichment from 2012 to 2014 and a subsequent recovery rate of 159‰ per year, consistent with this hypothesis and with biodegraded material from DWH hydrocarbons contributing to POCsusp.

Springwater provenance and flowpath evaluation in Blue Lake, Bonneville basin, Utah - Lerback, Jory Chapin; Hynek, Scott A.; Bowen, Brenda B.; Bradbury, Christopher D.; Solomon, D. Kip; Fernandez, Diego P. (Chemical Geology, 2019)
Water in Utah and Nevada is important for agriculture, municipal use, solute transport, and ecosystem preservation. Large spring wetland systems occur on the playa margin of the Bonneville basin, including Blue Lake, 15 km south of the Bonneville Salt Flats on the Utah-Nevada state border. Large spring systems have historically been studied as water budgets don't apparently balance from direct mountain front recharge (Nelson and Mayo, 2014; Gardner and Heilweil, 2014; and others). Blue Lake is no exception; prior studies here have suggested discharge rates 0.04 - 0.05 km3/yr (Louderback and Rhode, 2009), greater than expected for modelled recharge in the surrounding mountain range (0.03 km3/yr). Three hypothesized recharge mechanisms for Blue Lake are tested: mountain-front recharge, interbasinal groundwater flow, and infiltration from historic Lake Bonneville. Remote sensing suggests that a conservative estimate of Blue Lake discharge constitutes 50-64% of modelled mountain-front recharge (Flint et al., 2011). Major ions, δ18O, δ2H, dissolved gases (14C, 3He, 4He, Ne, Ar, Kr, Xe) and trace elements (Sr and 87Sr/86Sr isotopes) comprehensively constrain recharge conditions, water-rock interactions, flowpaths, and groundwater provenance of this large spring system. 14C signatures suggest that Blue Lake discharge has a transit time between 5,600 and 12,200 years, older than that of Fish Springs. Noble gas concentrations in Blue Lake water suggest an elevated recharge temperature greater than 19°C and low salinity, indicating a deep water table and high geothermal gradient in the recharge area. 87Sr/86Sr ratios of playa-margin springs are elevated from that of mid-playa groundwaters, springwaters from the adjacent mountain range, and alluvial fill groundwater from the valley directly south of Blue Lake. Playa-margin spring Sr isotope values (0.713-0.714) are most similar to direct runoff from the Deep Creek Range granodiorite outcrop (>0.713). Interbasinal groundwater flow in combination with mountain-front recharge is best supported by chemical data rather than mountain-front recharge alone or the slow discharge of regional aquifers recharged by lacustrine infiltration from Lake Bonneville.
Keywords: Bonneville basin; Geochemistry; groundwater; Isotope chemistry

Stable isotope analyses of ancient and modern Adélie Penguin (Pygoscelis adeliae) mummies from the Ross Sea Region, Antarctica - Kristan, Allyson K.; Emslie, Steven D.; Patterson, William P. (Polar Biology, 2019)
We performed stable carbon (δ13C) and nitrogen (δ15N) isotope analyses of 12 ancient Adélie penguin (Pygoscelis adeliae) chick mummies recovered from abandoned colonies in the Ross Sea region, Antarctica, to investigate isotopic variation and fractionation over time. We also examined latitudinal variation in penguin diet to address if the modern dietary pattern (an increase in krill as dominant prey to the north) in this region has existed in the past or if this is a recent phenomenon. The ancient mummies range in age from > 48,000 14C years before present (BP) to ~ 500 calendar years BP. Feather, skin, bone, and toenail samples were analyzed from each individual where available. Identical analyses were performed on five modern mummified Adélie penguin chick carcasses and breast feathers of ten recently dead chicks from each of two active colonies, Cape Hallett and Adélie Cove. We found significantly lower δ15N values in Cape Hallett modern chicks as compared to those from Adélie Cove, indicating an entire trophic-level difference in modern diet that agrees with other studies in this region. The ancient mummies exhibited consistent isotopic fractionation of δ13C among the four different tissues through time. Variation in δ15N and δ13C values was greater in bone and skin than in feather or toenail, but δ15N in all four tissues indicated similar dietary trends with latitude as occurs in this region today. These results provide insight into the dietary variability of Adélie penguins across the Ross Sea region and a framework for similar analyses with other avian species.

Sunlight Converts Polystyrene to Carbon Dioxide and Dissolved Organic Carbon - Ward, Collin P.; Armstrong, Cassia J.; Walsh, Anna N.; Jackson, Julia H.; Reddy, Christopher M. (Environmental Science & Technology Letters, 2019)
Numerous international governmental agencies that steer policy assume that polystyrene persists in the environment for millennia. Here, we show that polystyrene is completely photochemically oxidized to carbon dioxide and partially photochemically oxidized to dissolved organic carbon. Lifetimes of complete and partial photochemical oxidation are estimated to occur on centennial and decadal time scales, respectively. These lifetimes are orders of magnitude faster than biological respiration of polystyrene and thus challenge the prevailing assumption that polystyrene persists in the environment for millennia. Additives disproportionately altered the relative susceptibility to complete and partial photochemical oxidation of polystyrene and accelerated breakdown by shifting light absorbance and reactivity to longer wavelengths. Polystyrene photochemical oxidation increased approximately 25% with a 10 °C increase in temperature, indicating that temperature is unlikely to be a primary driver of photochemical oxidation rates. Collectively, sunlight exposure appears to be a governing control of the environmental persistence of polystyrene, and thus, photochemical loss terms need to be included in mass balance studies on the environmental fate of polystyrene. The experimental framework presented herein should be applied to a diverse array of polymers and formulations to establish how general these results are for other plastics in the environment.

Temperature-controlled tundra fire severity and frequency during the last millennium in the Yukon-Kuskokwim Delta, Alaska - Sae-Lim, Jarunetr; Russell, James M; Vachula, Richard S; Holmes, Robert M; Mann, Paul J; Schade, John D; Natali, Susan M (The Holocene, 2019)
Wildfire is an important disturbance to Arctic tundra ecosystems. In the coming decades, tundra fire frequency, intensity, and extent are projected to increase because of anthropogenic climate change. To more accurately predict the effects of climate change on tundra fire regimes, it is critical to have detailed knowledge of the natural frequency and extent of past wildfires and how they responded to past climate variability. We present analyses of fire frequency and temperature from a lake sediment core from the Yukon-Kuskokwim (YK) Delta. Our ca. 1000 macroscopic charcoal record shows more frequent but possibly less severe tundra fires during the first half of the last millennium, whereas less frequent, possibly more severe fires characterize the latter half. Our temperature reconstruction, based on distributional changes of branched glycerol dialkyl glycerol tetraethers (brGDGTs), shows slightly warmer conditions from ca. AD 1000 to 1500, and cooler conditions thereafter (ca. AD 1500 to 2000), suggesting that fire frequency increases when climate is relatively warmer in this region. When wildfires occur more frequently, fire severity may decrease because of limited biomass (fuel source) accumulating between fires. The data suggest that tundra ecosystems are highly sensitive to climate change, and that a warmer climate, which is predicted to develop in the near future, will result in more frequent tundra wildfires.
Keywords: alaska; Arctic; charcoal; glycerol dialkyl glycerol tetraethers (GDGTs); late-holocene; Paleoclimate; Paleofire

Temporal constraints on lateral organic matter transport along a coastal mud belt - Bao, Rui; Zhao, Meixun; McNichol, Ann; Galy, Valier; McIntyre, Cameron; Haghipour, Negar; Eglinton, Timothy I. (Organic Geochemistry, 2019)
Constraints on timescales of lateral transport of sedimentary organic carbon (OC) over continental shelves and associated influences on the distribution and abundance of OC remain sparse. Preferential degradation of labile, young OC during lateral transport results in apparent “diagenetic aging” of OC. Additionally, sediment translocation can also result in “transport time-associated aging” of associated organic matter (OM) as a function of the lateral transport time (LTT). Here, we use a coupled thermal decomposition and radiocarbon (14C) approach to constrain timescales of lateral transport and concomitant loss of OC associated with different grain size fractions of sediments collected from two locations ∼275 km apart along a dispersal pathway on the inner shelf of the East China Sea. The 14C age contrasts between corresponding thermal fractions are used to distinguish these two components of sedimentary OM “aging”. To minimize interferences from hydrodynamic sorting and diagenetic aging of OC accompanying lateral transport, we assess 14C age differences of decomposition products from the most thermally-refractory OC components associated with specific grain size fractions between locations. We show that LTTs vary among different grain size fractions, and examine relationships between LTTs and sedimentary OC loss in order to assess the decomposition of OC as a consequence of lateral transport. We suggest that the decomposition of OC associated with protracted lateral transport exerts a strong influence on OC burial efficiency, with broad implications for carbon cycling over continental shelves.
Keywords: 14C aging; Continental shelf seas; East China Sea; Mud belt; organic matter; Sediment resuspension

Temporal deconvolution of vascular plant-derived fatty acids exported from terrestrial watersheds - Vonk, Jorien E.; Drenzek, Nicholas J.; Hughen, Konrad A.; Stanley, Rachel H.R.; McIntyre, Cameron; çon, Daniel B.; Giosan, Liviu; Southon, John R.; Santos, Guaciara M.; Druffel, Ellen R.M.; Andersson, August A.; öld, Martin; et al. (Geochimica et Cosmochimica Acta, 2019)
Relatively little is known about the amount of time that lapses between the photosynthetic fixation of carbon by vascular land plants and its incorporation into the marine sedimentary record, yet the dynamics of terrestrial carbon sequestration have important implications for the carbon cycle. Vascular plant carbon may encounter multiple potential intermediate storage pools and transport trajectories, and the age of vascular plant carbon accumulating in marine sediments will reflect these different pre-depositional histories. Here, we examine down-core C-14 profiles of higher plant leaf wax-derived fatty acids isolated from high fidelity sedimentary sequences spanning the so-called "bomb-spike", and encompassing a ca. 60-degree latitudinal gradient from tropical (Cariaco Basin), temperate (Saanich Inlet), and polar (Mackenzie Delta) watersheds to constrain integrated vascular plant carbon storage/transport times ("residence times"). Using a modeling framework, we find that, in addition to a "young" (conditionally defined as < 50 y) carbon pool, an old pool of compounds comprises 49 to 78 % of the fractional contribution of organic carbon (OC) and exhibits variable ages reflective of the environmental setting. For the Mackenzie Delta sediments, we find a mean age of the old pool of 28 ky (+/- 9.4, standard deviation), indicating extensive pre-aging in permafrost soils, whereas the old pools in Saanich Inlet and Cariaco Basin sediments are younger, 7.9 (+/- 5.0) and 2.4 (+/- 0.50) to 3.2 (+/- 0.54) ky, respectively, indicating less protracted storage in terrestrial reservoirs. The "young" pool showed clear annual contributions for Saanich Inlet and Mackenzie Delta sediments (comprising 24% and 16% of this pool, respectively), likely reflecting episodic transport of OC from steep hillside slopes surrounding Saanich Inlet and annual spring flood deposition in the Mackenzie Delta, respectively. Contributions of 5-10 year old OC to the Cariaco Basin show a short delay of OC inflow, potentially related to transport time to the offshore basin. Modeling results also indicate that the Mackenzie Delta has an influx of young but decadal material (20-30 years of age), pointing to the presence of an intermediate reservoir. Overall, these results show that a significant fraction of vascular plant C undergoes pre-aging in terrestrial reservoirs prior to accumulation in deltaic and marine sediments. The age distribution, reflecting both storage and transport times, likely depends on landscape-specific factors such as local topography, hydrographic characteristics, and mean annual temperature of the catchment, all of which affect the degree of soil buildup and preservation. We show that catchment-specific carbon residence times across landscapes can vary by an order of magnitude, with important implications both for carbon cycle studies and for the interpretation of molecular terrestrial paleoclimate records preserved in sedimentary sequences.
Keywords: british-columbia; CARIACO BASIN; compound-specific radiocarbon; MACKENZIE DELTA; marine-sediments; odp leg 169s; saanich inlet; SANTA-MONICA BASIN; SOIL ORGANIC-MATTER; TROPICAL VEGETATION

Testing the Utility of Geochemical Proxies to Reconstruct Holocene Coastal Environments and Relative Sea Level: A Case Study from Hungry Bay, Bermuda - Kemp, Andrew C.; Vane, Christopher H.; Khan, Nicole S.; Ellison, Joanna C.; Engelhart, Simon E.; Horton, Benjamin P.; Nikitina, Daria; Smith, Struan R.; Rodrigues, Lisa J.; Moyer, Ryan P. (Open Quaternary, 2019)
On low-lying, tropical and sub-tropical coastlines freshwater marshes may be replaced by salt‑tolerant mangroves in response to relative sea-level rise. Pollen analysis of radiocarbon‑dated sediment cores showed that such a change occurred in Hungry Bay, Bermuda during the late Holocene. This well-established paleoenvironmental trajectory provides an opportunity to explore if geochemical proxies (bulk-sediment δ13C and Rock-Eval pyrolysis) can reconstruct known environmental changes and relative sea level. We characterized surface sediment from depositional environments in Bermuda (freshwater wetlands, saline mangroves, and wrack composed of Sargassum natans macroalgae) using geochemical measurements and demonstrate that a multi-proxy approach can objectively distinguish among these environments. However, application of these techniques to the transgressive sediment succession beneath Hungry Bay suggests that freshwater peat and mangrove peat cannot be reliably distinguished in the sedimentary record, possibly because of post‑depositional convergence of geochemical characteristics on decadal to multi‑century timescales and/or the relatively small number of modern samples analyzed. Sediment that includes substantial contributions from Sargassum is readily identified by geochemistry, but has a limited spatial extent. Radiocarbon dating indicates that beginning at –700 CE, episodic marine incursions into Hungry Bay (e.g., during storms) carried Sargassum that accumulated as wrack and thickened through repeated depositional events until ~300 CE. It took a further ~550 years for a peat‑forming mangrove community to colonize Hungry Bay, which then accumulated sediment rapidly, but likely out of equilibrium with regional relative sea-level rise.
Keywords: mangrove; radiocarbon; Rock-Eval pyrolysis; Sargassum; δ13C

Thermal oxidation of carbon in organic matter rich volcanic soils: insights into SOC age differentiation and mineral stabilization - Grant, Katherine E.; Galy, Valier V.; Chadwick, Oliver A.; Derry, Louis A. (Biogeochemistry, 2019)
Radiocarbon ages and thermal stability measurements can be used to estimate the stability of soil organic carbon (OC). Soil OC is a complex reservoir that contains a range of compounds with different sources, reactivities, and residence times. This heterogeneity can shift bulk radiocarbon values and impact assessment of OC stability and turnover in soils. Four soil horizons (Oa, Bhs, Bs, Bg) were sampled from highly weathered 350 ka Pololu basaltic volcanics on the Island of Hawaii and analyzed by Ramped PyrOX (RPO) in both the pyrolysis (PY) and oxidation (OX) modes to separate a complex mixture of OC into thermally defined fractions. Fractions were characterized for carbon stable isotope and radiocarbon composition. PY and OX modes yielded similar results. Bulk radiocarbon measurements were modern in the Oa horizon (Fm = 1.013) and got progressively older with depth: the Bg horizon had an Fm value of 0.73. Activation energy distributions (p(E)) calculated using the ‘rampedpyrox’ model yielded consistent mean E values of 140 kJ mol−1 below the Oa horizon. The ‘rampedpyrox’ model outputs showed a mostly bimodal distribution in the p(E) below the Oa, with a primary peak at 135 kJ mol−1 and a secondary peak at 148 kJ mol−1, while the Oa was dominated by a single, higher E peak at 157 kJ mol−1. We suggest that mineral-carbon interaction, either through mineral surface-OC or metal-OC interactions, is the stabilization mechanism contributing to the observed mean E of 140 kJ mol−1 below the Oa horizon. In the Oa horizon, within individual RPO analyses, radiocarbon ages in the individual thermal fractions were indistinguishable (p > 0.1). The flat age distributions indicate there is no relationship between age and thermal stability (E) in the upper horizon (> 25 cm). Deeper in the soil profile higher µEf values were associated with older radiocarbon ages, with slopes progressively steepening with depth. In the deepest (Bg) horizon, there was the largest, yet modest change in Fm of 0.06 (626 radiocarbon years), indicating that older OC is slightly more thermally stable.

Timescales of water-quality change in a karst aquifer, south-central Texas - Musgrove, M.; Solder, J. E.; Opsahl, S. P.; Wilson, J. T. (Journal of Hydrology X, 2019)
Understanding the drivers and timescales over which groundwater quality changes informs groundwater management, use, and protection. To better understand timescales of water-quality change over short (daily to monthly) and long (seasonal to decadal) timescales, the U.S. Geological Survey’s National Water-Quality Assessment (NAWQA) Enhanced Trends Network (ETN) program instrumented and sampled three wells in the Edwards aquifer in south-central Texas. The wells were instrumented to provide high-frequency continuous (subhourly) water-quality data (temperature, pH, specific conductance, and dissolved oxygen), which were augmented by the collection of discrete samples (about 6 per year) for a range of geochemical constituents (including selected isotopes and age tracers). ETN data (2013–2017) are considered with data from additional sites for the same time period, and also historical records (over more than 80 years) of climatic and hydrologic conditions. During the four-year study, hydrologic conditions transitioned from very dry to very wet. Sites in the updip/unconfined part of the aquifer showed notable changes in water level and geochemistry (1) in response to rainfall/recharge events, and (2) over the multiyear dry/wet cycle. Sites in the downdip/confined part of the aquifer showed changes in water level/spring discharge over similar timescales, although the response is more muted. Geochemistry at the downdip/confined sites, however, varied slowly and minimally, indicating that the geochemical response of the deeper aquifer is decoupled from recent hydrologic responses. Changes at the updip/unconfined sites reflect mixing with recent recharge, whereas the downdip/confined sites were dominated by mineral-solution reactions resulting from longer (decadal) residence times. Mean groundwater ages interpreted from measured age tracers and lumped parameter models range from 7 to >700 years (where mixed with premodern downdip water) but were mostly modern. The aquifer is characterized by updip-to-downdip trends in geochemistry with respect to water-rock interaction and groundwater age. Fourier spectral analysis of historical records indicate hydrologic variability has occurred at dominant periods of 30 and 15 years; in conjunction with age tracers, these results provide insight into timescales at which the aquifer’s public supply is vulnerable to changes in the water quality of recharge.
Keywords: Edwards aquifer; Groundwater age; Karst; Trends; Water quality

Upwelling in the Ocean Basins North of the ACC: 1. On the Upwelling Exposed by the Surface Distribution of C-14 - Toggweiler, J. R.; Druffel, Ellen R. M.; Key, Robert M.; Galbraith, Eric D. (Journal of Geophysical Research: Oceans, 2019)
he upwelling associated with the ocean's overturning circulation is hard to observe directly. Here, a large data set of surface C-14 measurements is compiled in order to show where deep water is brought back up to the surface in the ocean basins north of the Antarctic Circumpolar Current (ACC). Maps constructed from the data set show that low-C-14 deep water from the ACC is drawn up to the surface in or near the upwelling zones off Northwest Africa and Namibia in the Atlantic, off Costa Rica and Peru in the Pacific, and in the northern Arabian Sea in the Indian Ocean. Deep water also seems to be reaching the surface in the subarctic Pacific gyre near the Kamchatka Peninsula. The low-C-14 water drawn up to the surface in the upwelling zones is also shown to spread across the ocean basins. It is easily seen, for example, in the western Atlantic off Florida and in the western Pacific off New Guinea and Palau. The spreading allows one to estimate the volumes of upwelling, which, it turns out, are similar to the volumes of large-scale upwelling derived from inverse box models. This means that very large volumes of cool subsurface water are reaching the surface in and near the upwelling zonesmuch larger volumes than would be expected from the local winds. Plain Language Summary The deep layers of the ocean are filled with cold dense water that sinks from the surface near Antarctica and in the northern North Atlantic. This process is understood reasonably well. The countervailing processthe way that the dense water is brought back up to the surfaceis not as well understood. Oceanographers now agree that the ocean's deep water is drawn back up to the surface (upwelled) mainly around Antarctica as part of the wind-driven overturning in the Antarctic Circumpolar Current (ACC). But cool water is also known to reach the surface in upwelling zones around the ocean's margins. Here we map the upwelling north of the ACC with the radioactive isotope carbon-14 and show that the deep water upwelled to the surface around Antarctica seems to be drawn up to the surface a second time in the upwelling zones. The water drawn up to the surface in the upwelling zones then flows back to the North Atlantic and sinks again to complete the cycle.
Keywords: Ocean circulation; overturning circulation; radiocarbon; Upwelling

Upwelling in the Ocean Basins North of the ACC: 2. How Cool Subantarctic Water Reaches the Surface in the Tropics - Toggweiler, J. R.; Druffel, Ellen R. M.; Key, Robert M.; Galbraith, Eric D. (Journal of Geophysical Research: Oceans, 2019)
Large volumes of cool water are drawn up to the surface in the tropical oceans. A companion paper shows that the cool water reaches the surface in or near the upwelling zones off northern and southern Africa and Peru. The cool water has a subantarctic origin and spreads extensively across the Atlantic and Pacific basins after it reaches the surface. Here, we look at the spreading in two low-resolution ocean general circulation models and find that the spreading in the models is much less extensive than observed. The problem seems to be the way the upwelling and the spreading are connected (or not connected) to the ocean's large-scale overturning. As proposed here, the cool upwelling develops when warm buoyant water in the western tropics is drawn away to become deep water in the North Atlantic. The drawing away shoals the tropical thermocline in a way that allows cool subantarctic water to be drawn up to the surface along the eastern margins. The amounts of upwelling produced this way exceed the amounts generated by the winds in the upwelling zones by as much as 4 times. Flow restrictions make it difficult for the warm buoyant water in our models to be drawn away. Plain Language Summary A companion paper uses the radioactive isotope carbon-14 to map the upwelling in the ocean basins north of the Antarctic Circumpolar Current (ACC). It shows that deep water drawn up to the surface to the south of the ACC is drawn up to the surface a second time in a number of upwelling areas in the tropics. In this paper, we attempt to simulate the tropical upwelling in an ocean circulation model and find that it is largely missing. Other circulation features are missing as well. The other features operate on the opposite sides of the ocean basins from the upwelling areas and help carry warm water out of the tropics (outflows). The combination of missing elements leads to a hypothesis about the upwelling mechanism. Our hypothesis is that the tropical upwelling is driven by the outflows and the fact that the warm water being carried away ultimately becomes deep water again in the North Atlantic.
Keywords: numerical modeling; Ocean circulation; overturning circulation; Upwelling

Using Stable Carbon Isotopes to Quantify Radiocarbon Reservoir Age Offsets in the Coastal Black SeaAbstract - Soulet, Guillaume; Giosan, Liviu; Flaux, Clément; Galy, Valier (Radiocarbon, 2019)
Constraining radiocarbon (C-14) reservoir age offsets is critical to deriving accurate calendar-age chronologies from C-14 dating of materials which did not draw carbon directly from the atmosphere. The application of C-14 dating to such materials is severely limited in hydrologically sensitive environments like the Black Sea because of the difficulty to quantify reservoir age offsets, which can vary quickly and significantly through time, due to the dynamics of the biogeochemical cycling of carbon. Here we reconstruct C-14 reservoir age offsets (Rshell-atm) of Holocene bivalve shells from the coastal Black Sea relatively to their contemporaneous atmosphere. We show that the C-14 reservoir age offset and the stable carbon isotope composition of bivalve shells are linearly correlated in this region. From a biogeochemical standpoint, this suggests that inorganic stable carbon isotope and C-14 compositions of Black Sea coastal waters are controlled by the balance between autochthonous primary productivity and heterotrophic respiration of allochthonous pre-aged terrestrial organic matter supplied by rivers. This provided an important implication for Black Sea geochronology as the reservoir age offset of C-14-dated bivalve shell can be inferred from its stable carbon isotope composition. Our results provide a fundamental and inexpensive geochemical tool which will considerably improve the accuracy of Holocene calendar age chronologies in the Black Sea.
Keywords: Black Sea; Carbon cycle; freshwater reservoir effect; Geochronology; Reservoir age

The Utility of Stable and Radioisotopes in Fish Tissues as Biogeochemical Tracers of Marine Oil Spill Food Web Effects - Patterson III, William F.; Chanton, Jeffery P.; Hollander, David J.; Goddard, Ethan A.; Barnett, Beverly K.; Tarnecki, Joseph H. (Springer International Publishing, 2019)
Direct exposure to petroleum compounds was widely reported for a variety of taxa following the DWH. Evidence of exposure ranged from oiling of skin, shells, or feathers, depending on the taxa, to observation of ingested oil in small translucent, invertebrates, to biomarkers of petroleum compounds within an organism’s tissues, such as PAHs in the hepatopancreas of invertebrates or the liver of fishes, or metabolic products of PAH catabolism in the bile of various vertebrate taxa. Development of natural biogeochemical tracers to examine indirect effects, especially over long (months to years) time scales, can be much more problematic. In this chapter, we describe the utility of employing stable isotopes and radioisotopes to 1) examine whether food web effects can be inferred from shifts in stable isotope values measured in vertebrate taxa; 2) examine the assimilation and trophic transfer of petrocarbon in marine food webs; and, 3) serve as long-term biogeochemical tracers either of petrocarbon assimilation or trophic shifts that are indicative of food web effects of marine oil spills. Data and analyses are largely drawn from DWH-related studies but with broader implications to marine oil spills in general.
Keywords: Petrocarbon; radiocarbon; Reef fish; Stable isotopes

1500 years of lake sedimentation due to fire, earthquakes, floods and land clearance in the Oregon Coast Range: geomorphic sensitivity to floods during timber harvest period - Richardson, K.N.D.; Hatten, J.A.; Wheatcroft, R.A. (Earth Surface Processes and Landforms, 2018)
Sediment cores retrieved from landslide-dammed Loon Lake recorded events back to the 5th century AD in a forested, mountainous catchment, thereby providing an opportunity to compare the impacts of known recent perturbations, including floods and timber harvesting with those of an early period in the cores, floods, fires, and earthquakes. High-resolution multi-parameter (grain size, %TC, %TN, and magnetic susceptibility) data allowed the core stratigraphy to be classified as background sedimentation and events. Cs-137 and radiocarbon dating, as well as a varved record in the last 75years provided age control. Mean mass accumulation rate from 1939 to 1978AD, the time of peak timber harvest and a cool wet phase of the Pacific Decadal Oscillation, was 0.79 (0.74-0.92, 95% C.L.) g cm(-2) y(-1), significantly higher than mean rates of both the more recent contemporary period (coincident with the passing of the legislation that regulated harvesting practices in the region), 1979-2012AD, at 0.58 (0.48-0.70) and the entire early period, 0.44 (0.41-0.46). Several event deposits are coeval with independently estimated ages of eight Cascadia subduction zone earthquakes in the early period, including the 1700AD Mw 9.0 event. These deposits are predominantly formed by hyperpycnal flows, as are the known event deposits in the contemporary period. The high mass accumulation rate and greater frequency of thick event deposits during the early contemporary period point to the extraordinary role of timber harvesting in priming the landscape for subsequent sedimentary delivery during floods. Copyright (c) 2017 John Wiley & Sons, Ltd.
Keywords: erosion; GREAT EARTHQUAKES; history; NEW-ZEALAND; radiocarbon age; record; TEMPORAL PATTERNS; USA; WASHINGTON; WESTERN OREGON

Active Ooid Growth Driven By Sediment Transport in a High-Energy Shoal, Little Ambergris Cay, Turks and Caicos Islands - Trower, Elizabeth J.; Cantine, Marjorie D.; Gomes, Maya L.; Grotzinger, John P.; Knoll, Andrew H.; Lamb, Michael P.; Lingappa, Usha; O'Reilly, Shane S.; Present, Theodore M.; Stein, Nathan; Strauss, Justin V.; Fischer, Woodward W. (Journal of Sedimentary Research, 2018)
Ooids are a common component of carbonate successions of all ages and present significant potential as paleoenvironmental proxies, if the mechanisms that control their formation and growth can be understood quantitatively. There are a number of hypotheses about the controls on ooid growth, each offering different ideas on where and how ooids accrete and what role, if any, sediment transport and abrasion might play. These hypotheses have not been well tested in the field, largely due to the inherent challenges of tracking individual grains over long timescales. This study presents a detailed field test of ooid-growth hypotheses on Little Ambergris Cay in the Turks and Caicos Islands, British Overseas Territories. This field site is characterized by westward net sediment transport from waves driven by persistent easterly trade winds. This configuration makes it possible to track changes in ooid properties along their transport path as a proxy for changes in time. Ooid size, shape, and radiocarbon age were compared along this path to determine in which environments ooids are growing or abrading. Ooid surface textures, petrographic fabrics, stable-isotope compositions (δ13C, δ18O, and δ34S), lipid geochemistry, and genetic data were compared to characterize mechanisms of precipitation and degradation and to determine the relative contributions of abiotic (e.g., abiotic precipitation, physical abrasion) and biologically influenced processes (e.g., biologically mediated precipitation, fabric destruction through microbial microboring and micritization) to grain size and character. A convergence of evidence shows that active ooid growth occurs along the transport path in a high-energy shoal environment characterized by frequent suspended-load transport: median ooid size increases by more than 100 μm and bulk radiocarbon ages decrease by 360 yr westward along the ∼ 20 km length of the shoal crest. Lipid and 16S rRNA data highlight a spatial disconnect between the environments with the most extensive biofilm colonization and environments with active ooid growth. Stable-isotope compositions are indistinguishable among samples, and are consistent with abiotic precipitation of aragonite from seawater. Westward increases in ooid sphericity and the abundance of well-polished ooids illustrate that ooids experience subequal amounts of growth and abrasion—in favor of net growth—as they are transported along the shoal crest. Overall, these results demonstrate that, in the Ambergris system, the mechanism of ooid growth is dominantly abiotic and the loci of ooid growth is determined by both carbonate saturation and sediment transport mode. Microbes play a largely destructive, rather than constructive, role in ooid size and fabric.

On the Age and Origin of Lake Ejagham, Cameroon, and Its Endemic FishesAbstract - Curt Stager, Jay; Alton, Kenneth; Martin, Christopher H.; King, David T.; Petruny, Lucille W.; Wiltse, Brendan; Livingstone, Daniel A. (Quaternary Research, 2018)
Lake Ejagham is a small, shallow lake in Cameroon, West Africa, which supports five endemic species of cichlid fishes in two distinct lineages. Genetic evidence suggests a relatively young age for the species flocks, but supporting geologic evidence has thus far been unavailable. Here we present diatom, geochemical, mineralogical, and radiocarbon data from two sediment cores that provide new insights into the age and origin of Lake Ejagham and its endemic fishes. Radiocarbon ages at the base of the longer core indicate that the lake formed approximately 9 ka ago, and the diatom record of the shorter core suggests that hydroclimate variability during the last 3 millennia was similar to that of other lakes in Cameroon and Ghana. These findings establish a maximum age of ca. 9 cal ka BP for the lake and its endemic species and suggest that repeated cichlid speciation in two distinct lineages occurred rapidly within the lake. Local geology and West African paleoclimate records argue against a volcanic, chemical, or climatic origin for Lake Ejagham. Although not conclusive, the morphometry of the lake and possible signs of impact-induced effects on quartz grains are instead more suggestive of a bolide impact.
Keywords: Africa; cameroon; Cichlid; Diatom; evolution; Lake Ejagham; Speciation; West African monsoon

Aging and Molecular Changes of Dissolved Organic Matter Between Two Deep Oceanic End-Members - Bercovici, S. K.; Koch, B. P.; Lechtenfeld, O. J.; McCallister, S. L.; Schmitt-Kopplin, P.; Hansell, D. A. (Global Biogeochemical Cycles, 2018)
The global ocean contains a massive reservoir of dissolved organic carbon (DOC), rivaling the atmosphere's pool of CO2. The most recalcitrant fractions have mean radiocarbon ages of ~4,000 years in the Atlantic to ~6,000 years in the Pacific. Knowing the radiocarbon signatures of DOC and the molecular composition of dissolved organic matter (DOM) is crucial to develop understanding of the persistence and lifetime of the DOC pool. In this research, we collected samples from the deep North Pacific in August 2013 (aboard the RV Melville) to couple the Δ14C content of solid‐phase‐extracted DOM (Δ14C‐SPE‐DOM) with its molecular composition in the ocean's oldest deep waters. We find that deep waters in this region held a mean Δ14C‐SPE‐DOM value of −554 ± 9‰ (~6,400 14C years), substantially more depleted than that in the deep Atlantic, which held a mean Δ14C‐SPE‐DOM value of −445 ± 5‰. While we find a more degraded molecular composition of DOM in the deep Pacific than the deep Atlantic, the molecular formulae within the Island of Stability (Lechtenfeld et al., 2014, https://doi.org/10.1016/j.gca.2013.11.009), are largely retained. These results imply that a fraction of deep DOM is resistant to removal and present in both the deep Atlantic and Pacific Oceans.

Along-slope variations in sediment lithofacies and depositional processes since the Last Glacial Maximum on the northeast Baffin margin, Canada - Jenner, K.A.; Campbell, D.C.; Piper, D.J.W. (Marine Geology, 2018)
Twelve piston cores were used to characterize late Quaternary lithofacies, depositional processes and deglacial history along the Baffin Bay slope between Lancaster Sound and Home Bay. Core investigations show four distinct laterally correlatable lithofacies along the slope – basal and upper diamicton, laminated red brown mud, tan carbonate gravelly, sandy mud and bioturbated brown mud. Basal diamicton largely represents glacigenic debris flow deposits during a glacial advance from Baffin Island at ~25 cal ka. The distribution and character of laminated red brown mud suggests a lateral supply to Baffin Bay slope from ice-proximal meltwater plumes and turbidity currents sourced in glacial ice from both Baffin Bay shelf and Home Bay between 41.5 cal ka to ~14.2 cal ka. An upper diamicton records a lesser, localized glacial advance that ended at about 14.2 cal ka. Tan carbonate mud events represent ice-rafted, enhanced detrital carbonate delivery to the slope between ~25 cal ka and ~11 cal ka. A gradual thinning of these events, from northern to southern Baffin Bay, corroborates a northern Baffin Bay, Lancaster Sound or Nares Strait iceberg source. Proglacial facies seaward of Home Bay contain beds with slightly elevated detrital carbonate that may represent the distal edge of carbonate ice-rafted from Lancaster Sound. Baffin Bay is a type example of a polar glacial basin in which direct glacial supply predominates over the effects of glacial meltwater. As a result, axial supply from the large ice streams north of Baffin Bay (particularly Lancaster Sound) is dominant in the Baffin Bay basin and lateral supply from smaller ice streams on Baffin Island predominates on the NE Baffin Slope.
Keywords: Baffin Bay; Glacigenic debris flow; Late Quaternary; lithofacies; stratigraphy; Tan carbonate events

Ancient water wells reveal a prolonged drought in the lower Yellow River area about 2800 years ago - Yu, Shiyong; Chen, Xuexiang; Liu, Xiuling; Fang, Zhen; Guo, Junfeng; Zhan, Senyang; Fang, Hui; Chen, Fahu (Science Bulletin, 2018)
Given that the Holocene is the most recent interglacial period that has spurred the development of modern societies, scrutinizing climate changes during this period may provide a knowledge base for better understanding the rise and fall of ancient civilizations. However, our knowledge about the mechanism of millennial-scale climate variability particularly in the absence of major continental ice sheets during the second half of the Holocene remains highly uncertain. Although cold spells manifested as the Bond events have been widely reported in the North Atlantic sector during the mid-to-late Holocene, it is not clear whether or not there is a global expression of these events. Therefore, well-tuned far-field proxy records are indispensable to pinpoint the geographical extent of these climate events. Here we show evidence from ancient water wells in North China for a prolonged drought corresponding to a period of pervasive cooling in the North Atlantic region lasting from about 800 to 550 before the Common Era (BCE). Inferred climatic conditions using a conceptual hydrological model, in line with other proxy records, support the hypothesis of the Sun-climate link probably through the complex ocean-atmospheric interactions in the tropical oceans. Our finding suggests that water well construction represented a major technical invention in human history, which greatly improved the resilience against the depletion of surface water at times when arid climate prevailed. The linked climatic and societal changes demonstrated here can serve as a historical analogue for the socio-economic response to potentially large climate changes in the future.

Asynchronous behavior of the Antarctic Ice Sheet and local glaciers during and since Termination 1, Salmon Valley, Antarctica - Jackson, Margaret S.; Hall, Brenda L.; Denton, George H. (Earth and Planetary Science Letters, 2018)
The stability of the Antarctic Ice Sheet under future warming remains an open question with broad implications for sea-level prediction and adaptation. In particular, knowledge of whether the ice sheet has the capacity for rapid drawdown or collapse, or whether it can remain stable during periods of warming, is essential for predicting its future behavior. Here we use 55 radiocarbon dates, coupled with geomorphologic mapping, to reconstruct the timing of changes in ice extent and elevation during the last ice-age termination in Salmon Valley, adjacent to McMurdo Sound in the western Ross Sea Embayment. Results indicate that a grounded ice sheet in the Ross Sea Embayment achieved its maximum elevation and extent along the headlands of Salmon Valley at ∼18,000 yr BP, during a period of increasing temperatures and accumulation over the Antarctic continent. This ice remained at or near its maximum on the headlands near the valley mouth until after ∼14,000 yr BP. Removal of grounded Ross Sea ice from Salmon Valley was complete shortly after ∼7900 yr BP, indicating that the grounding line had retreated through southern McMurdo Sound by that time. We suggest the primary driver of Ross Sea ice removal from McMurdo Sound was marine-based, either through basal melting or calving due to sea-level rise. When combined with regional data, the Salmon Valley record suggests that this sector of the Antarctic Ice Sheet did not contribute in a significant way to deglacial meltwater pulses, such as meltwater pulse 1a. In contrast to the Ross Sea ice, our work also shows that local, independent alpine glaciers in Salmon Valley have advanced through the Holocene. Land-terminating glaciers such as these elsewhere in the region show a similar pattern, and may reflect the continued influence of increased accumulation following the termination of the last ice age.
Keywords: Antarctic Ice Sheet; glacial geomorphology; ice sheet stability; Termination I

An atmospheric chronology for the glacial-deglacial Eastern Equatorial Pacific - Zhao, Ning; Keigwin, Lloyd D. (Nature Communications, 2018)
Paleoclimate reconstructions are only as good as their chronology. In particular, different chronological assumptions for marine sediment cores can lead to different reconstructions of ocean ventilation age and atmosphere-ocean carbon exchange history. Here we build the first high-resolution chronology that is free of the dating uncertainties common in marine sediment records, based on radiocarbon dating twigs found with computed tomography scans in two cores from the Eastern Equatorial Pacific (EEP). With this accurate chronology, we show that the ventilation ages of the EEP thermocline and intermediate waters were similar to today during the Last Glacial Maximum and deglaciation, in contradiction with previous studies. Our results suggest that the glacial respired carbon pool in the EEP was not significantly older than today, and that the deglacial strengthening of the equatorial Pacific carbon source was probably driven by low-latitude processes rather than an increased subsurface supply of upwelled carbon from high-latitude oceans.

A base-level stratigraphic approach to determining Holocene subsidence of the Ganges-Meghna-Brahmaputra Delta plain - Grall, C; Steckler, MS; Pickering, JL; Goodbred, S (EARTH AND PLANETARY SCIENCE LETTERS, 2018)
Relative sea level history, which is the result of the combined effects of land subsidence, sediment supply and absolute sea level history may be reconstructed from preserved sediment thicknesses. However, variations in the preserved sediment thicknesses between different sedimentary environments strongly limit the accuracy of this type of geological approach, particularly in fluvial channelized systems, such as delta plains. To address this, we apply three different and independent stratigraphic approaches to the case of the Ganges-Brahmaputra-Meghna Delta (GBMD). Our approach has been made possible by a broad dataset of geological archives we have collected, which includes more than 400 hand-drilled stratigraphic wells, 198 radiocarbon ages, and river seismic reflection data (255 km of high-resolution multichannel seismic images). The seaward gradient of accommodation and the limit of the subsiding delta plain are estimated, assuming that the delta is near or at the base-level, which is considered to be the relative sea-level. First, a statistical analysis of the variability of preserved sediment thicknesses is used to derive the average pattern of accommodation from the Holocene isopach. Secondly, the preserved sediment thicknesses are analyzed by geomorphotectonic domains to estimate an average pattern of accommodation. Thirdly, the burial history of the seismically imaged last glacial incision of the Brahmaputra River is reconstructed. Results suggest that the variability of preserved sediment thicknesses can be up to 35% in a delta plain between river channel and flood plain deposits for the same relative sea-level history. Taking this variability into consideration, the Holocene relative sea-level history of the GBMD and the most likely pattern of subsidence are determined. Results provide evidence of moderate Holocene subsidence over the delta, gently increasing seaward from <0.2 mm/yr landward of the Hinge Zone, which can be considered as the northern limit of the subsiding delta plain, to 2 ± 0.7 mm/yr in the middle fluvial delta to 4 ± 1.4 mm/yr in the lower tidal delta. This enables us to construct the first millennial-scale map of subsidence pattern on the GBMD in which uncertainties on subsidence rates are provided. This map may aid in evaluating the negative impact that human modification may have on subsidence and relative sea level in the GBMD, and thereby help to determine better sustainable coastal management practices for the GBMD and other large delta plains.
Keywords: base level stratigraphic method; delta plain; Ganges–Brahmaputra–Meghna Delta; indicative meaning of sea level index; relative sea level; subsidence

A base-level stratigraphic approach to determining Holocene subsidence of the Ganges–Meghna–Brahmaputra Delta plain - Grall, C.; Steckler, M.S.; Pickering, J.L.; Goodbred, S.; Sincavage, R.; Paola, C.; Akhter, S.H.; Spiess, V. (Earth and Planetary Science Letters, 2018)
Relative sea level history, which is the result of the combined effects of land subsidence, sediment supply and absolute sea level history may be reconstructed from preserved sediment thicknesses. However, variations in the preserved sediment thicknesses between different sedimentary environments strongly limit the accuracy of this type of geological approach, particularly in fluvial channelized systems, such as delta plains. To address this, we apply three different and independent stratigraphic approaches to the case of the Ganges-Brahmaputra-Meghna Delta (GBMD). Our approach has been made possible by a broad dataset of geological archives we have collected, which includes more than 400 hand-drilled stratigraphic wells, 198 radiocarbon ages, and river seismic reflection data (255 km of high-resolution multichannel seismic images). The seaward gradient of accommodation and the limit of the subsiding delta plain are estimated, assuming that the delta is near or at the base-level, which is considered to be the relative sea-level. First, a statistical analysis of the variability of preserved sediment thicknesses is used to derive the average pattern of accommodation from the Holocene isopach. Secondly, the preserved sediment thicknesses are analyzed by geomorphotectonic domains to estimate an average pattern of accommodation. Thirdly, the burial history of the seismically imaged last glacial incision of the Brahmaputra River is reconstructed. Results suggest that the variability of preserved sediment thicknesses can be up to 35% in a delta plain between river channel and flood plain deposits for the same relative sea-level history. Taking this variability into consideration, the Holocene relative sea-level history of the GBMD and the most likely pattern of subsidence are determined. Results provide evidence of moderate Holocene subsidence over the delta, gently increasing seaward from <0.2 mm/yr landward of the Hinge Zone, which can be considered as the northern limit of the subsiding delta plain, to 2 +/- 0.7 mm/yr in the middle fluvial delta to 4 +/- 1.4 mm/yr in the lower tidal delta. This enables us to construct the first millennial-scale map of subsidence pattern on the GBMD in which uncertainties on subsidence rates are provided. This map may aid in evaluating the negative impact that human modification may have on subsidence and relative sea level in the GBMD, and thereby help to determine better sustainable coastal management practices for the GBMD and other large delta plains. (C) 2018 The Authors. Published by Elsevier B.V.
Keywords: base level stratigraphic method; delta plain; Ganges-Brahmaputra-Meghna Delta; indicative meaning of sea level index; relative sea level; subsidence

Bathyal records of enhanced silicate erosion and weathering on the exposed Luzon shelf during glacial lowstands and their significance for atmospheric CO2 sink - Xu, Zhaokai; Li, Tiegang; Clift, Peter D.; Wan, Shiming; Qiu, Xiaohua; Lim, Dhongil (Chemical Geology, 2018)
We present a new high-resolution multiproxy data set of mass accumulation rates, Sr-Nd isotopes, as well as major and trace elements for the siliciclastic sediment fraction from International Marine Global Change Study Core MD06-3052, located on the continental slope of the western Philippine Sea. We integrate our new data with published grain sizes and sea surface temperatures from the same core, as well as with Equatorial Pacific sea level, and East Asian summer monsoon precipitation, in order to constrain at high-resolution changes in physical erosion and chemical weathering intensities on Luzon, and sediment source-to-sink processes. We assess the potential significance of chemical weathering of arc silicates in regulating global atmospheric CO2 since 156 kyr BP. Sr-Nd isotopes show that the siliciclastic sediments were dominantly sourced from volcanic rocks exposed on Luzon (~ 68–100%), with a lesser contribution from Asian dust (~ 0–32%). Different indices indicate that stronger physical erosion and chemical weathering occurred during Marine Isotope Stage (MIS) 6 (130–156 kyr BP), as well as in the latter stage of MIS 3 and MIS 2 (14–40 kyr BP). The large sea-level lowstands and associated significant exposure of continental shelf in the western Philippine Sea during these two cold periods should favor physical erosion and chemical weathering of unconsolidated sediments on the exposed shelf. Furthermore, we notice the relatively good coherence between chemical weathering intensities on Luzon and global atmospheric CO2 concentrations over these cold intervals. We suggest that strengthening of chemical weathering of silicates on Luzon and other tropical arcs (within 20° of the Equator) during the Quaternary glacial sea-level lowstands may significantly contribute to the lowering of atmospheric CO2 concentrations during ice ages. We estimate that a significant fraction, up to ~ 16% (i.e., ~ 8 ppmv), of all atmospheric CO2 ultimately sequestered by silicate weathering may be processed through an area corresponding to only ~ 1% of the exorheic drainage area worldwide.
Keywords: Atmospheric CO2 concentration; Chemical weathering; East Asian summer monsoon; sea level; Western Philippine Sea

Blue marlin ( Makaira nigricans ) longevity estimates confirmed with bomb radiocarbon dating - Andrews, Allen H.; Humphreys, Robert L.; Sampaga, Jeffery D. (Canadian Journal of Fisheries and Aquatic Sciences, 2018)
The longevity of blue marlin (Makaira nigricans) remains unresolved. The use of fin spines and sagittal otoliths for age reading has led to unconfirmed longevity estimates near 20-30 years. Age validation has been elusive because large individuals are uncommonly caught, and a technique that can be applied to structures that provide estimates of age was absent. The use of otolith chemical signatures has been limited by sagittal otoliths that are very small-whole otolith mass of adult blue marlin rarely exceeds 10 mg for the largest fish. Recent advances in the detection limits of radiocarbon (14C) with accelerator mass spectrometry-coupled with recently acquired knowledge of marine bomb 14C signals spanning the tropical Pacific Ocean-have led to an opportunity to age blue marlin from small amounts of otolith material. In this study, otoliths from a recently collected 1245 lb (565 kg) female blue marlin at a measured 146-inch (371 cm) lower jaw fork length were analyzed for 14C. Estimated longevity was either 12-21 or 32-44 years on the basis of bomb 14C dating. Using multiple lines of evidence, it was determined that the young age scenario was most likely, with evidence for an age close to 20 years using a series of deductions in the bomb 14C dating method.
Keywords: Accelerator mass spectrometry; Biology; Blue marlin; Ecology; Fish measurement; FisheryLongevity; Otolith; Radiocarbon dating

Breaching of Mustang Island in response to the 8.2 ka sea-level event and impact on Corpus Christi Bay, Gulf of Mexico: Implications for future coastal change - Ferguson, Shannon; Warny, Sophie; Anderson, John B; Simms, Alexander R; White, Crawford (The Holocene, 2018)
The results from an investigation of the coupled Mustang Island–Corpus Christi Bay complex, Gulf of Mexico, shows that the island was eliminated as an effective salinity barrier between 8.86 and 8.17 ka. This event is recorded by a 5-fold increase in dinoflagellate cysts within Corpus Christi Bay. During this time, the bay-head delta shifted 15 km landward and oyster reefs within the bay died off. Our age model indicates that this event most likely resulted from the most rapid period of eustatic rise of the Holocene, which peaked at 8.18–8.31 ka. This event is attributed to late-stage ice sheet disintegration, particularly in North America, by the rapid draining of Lake Agassiz–Ojibway. Local glacial-isostatic factors resulted in a sea-level rise of only 0.2–0.56 m in the western Gulf of Mexico, which was less than needed to submerge the barrier. Rather, it was the marked nature of this sea-level rise that led to the virtual destruction of Mustang Island as an effective salinity barrier. These results provide an analog for predicting coastal morphodynamic response to accelerated sea-level rise and emphasize the need for better understanding of barrier response to sea-level rise and developing improved numerical models for predicting future changes to coastal barrier shorelines.
Keywords: barrier island; dinoflagellates; Gulf of Mexico; Holocene; North America; Sea-level changes

A centuries-long delay between a paleo-ice-shelf collapse and grounding-line retreat in the Whales Deep Basin, eastern Ross Sea, Antarctica - Bart, Philip J.; DeCesare, Matthew; Rosenheim, Brad E.; Majewski, Wojceich; McGlannan, Austin (Scientific Reports, 2018)
Recent thinning and loss of Antarctic ice shelves has been followed by near synchronous acceleration of ice flow that may eventually lead to sustained deflation and significant contraction in the extent of grounded and floating ice. Here, we present radiocarbon dates from foraminifera that constrain the time elapsed between a previously described paleo-ice-shelf collapse and the subsequent major grounding-line retreat in the Whales Deep Basin (WDB) of eastern Ross Sea. The dates indicate that West Antarctic Ice Sheet (WAIS) grounding-line retreat from the continental shelf edge was underway prior to 14.7 ± 0.4 cal kyr BP. A paleo-ice-shelf collapse occurred at 12.3 ± 0.2 cal kyr BP. The grounding position was maintained on the outer-continental shelf until at least 11.5 ± 0.3 cal kyr BP before experiencing a 200-km retreat. Given the age uncertainties, the major grounding-line retreat lagged ice-shelf collapse by at least two centuries and by as much as fourteen centuries. In the WDB, the centuries-long delay in the retreat of grounded ice was partly due to rapid aggradational stacking of an unusually large volume of grounding-zone-wedge sediment as ice-stream discharge accelerated following ice-shelf collapse. This new deglacial reconstruction shows that ongoing changes to ice shelves may trigger complex dynamics whose consequences are realized only after a significant lag.

Climate variability and cultural eutrophication at Walden Pond (Massachusetts, USA) during the last 1800 years - Stager, J. Curt; Wiltse, Brendan; Hubeny, J. Bradford; Yankowsky, Eric; Nardelli, David; Primack, Richard (PLOS ONE, 2018)
Recent shifts in the ecological condition of Walden Pond, MA, are of potentially wide interest due to the lake's importance as a cultural, historical, and recreational resource in addition to its scientific value as an indicator of local and global environmental change. Algal microfossils in six sediment cores document changes in hydroclimate and trophic status of the lake during the last 1800 years and extend two previous sediment core records of shorter length. Low percentages of planktonic diatoms in the longest cores (WAL-3, WAL-15) indicate shallowing and/or greater water clarity associated with a relatively arid interval during the Medieval Climate Anomaly, ca. A.D. 1150-1300, Cultural eutrophication of the lake since the A.D. 1920s caused diatoms in the genera Asterionella and Synedra to increase in relative abundance at the expense of Cyclotella, Discostella, and the chrysophyte alga Mallomonas allorgel. Percentages of Asterionella and Synedra have remained fairly stable since A.D. 2000 when a previous sediment core study was conducted, but scaled chrysophytes have become more numerous. These findings suggest that, although mitigation efforts have curtailed anthropogenic nutrient inputs to Walden Pond, the lake has not returned to the pre-impact condition described by Henry David Thoreau and may become increasingly vulnerable to further changes in water quality in a warmer and possibly wetter future.
Keywords: BOREAL LAKES; canada; CRAWFORD LAKE; DEPTH MODELS; ENVIRONMENTAL-CHANGE; ice-age; new-england; NORTH-AMERICA; NORTHEASTERN UNITED-STATES; organic-matter

Climatic control of Mississippi River flood hazard amplified by river engineering - Munoz, Samuel E.; Giosan, Liviu; Therrell, Matthew D.; Remo, Jonathan W. F.; Shen, Zhixiong; Sullivan, Richard M.; Wiman, Charlotte; O’Donnell, Michelle; Donnelly, Jeffrey P. (Nature, 2018)
Over the past century, many of the world’s major rivers have been modified for the purposes of flood mitigation, power generation and commercial navigation1. Engineering modifications to the Mississippi River system have altered the river’s sediment levels and channel morphology2, but the influence of these modifications on flood hazard is debated3,4,5. Detecting and attributing changes in river discharge is challenging because instrumental streamflow records are often too short to evaluate the range of natural hydrological variability before the establishment of flood mitigation infrastructure. Here we show that multi-decadal trends of flood hazard on the lower Mississippi River are strongly modulated by dynamical modes of climate variability, particularly the El Niño–Southern Oscillation and the Atlantic Multidecadal Oscillation, but that the artificial channelization (confinement to a straightened channel) has greatly amplified flood magnitudes over the past century. Our results, based on a multi-proxy reconstruction of flood frequency and magnitude spanning the past 500 years, reveal that the magnitude of the 100-year flood (a flood with a 1 per cent chance of being exceeded in any year) has increased by 20 per cent over those five centuries, with about 75 per cent of this increase attributed to river engineering. We conclude that the interaction of human alterations to the Mississippi River system with dynamical modes of climate variability has elevated the current flood hazard to levels that are unprecedented within the past five centuries.

The collapse of the North Song dynasty and the AD 1048–1128 Yellow River floods: Geoarchaeological evidence from northern Henan Province, China - Storozum, Michael J; Zhen, Qin; Xiaolin, Ren; Haiming, Li; Yifu, Cui; Kui, Fu; Haiwang, Liu (The Holocene, 2018)
From AD 1048 to 1128, Yellow River flooding killed over a million people, left many more homeless and destitute, and turned parts of the once fertile North China Plain into a silted-up agricultural wasteland. Brought on in part by climate change and the Northern Song dynasty’s (AD 960–1127) mismanagement of the environment, the Yellow River floods likely hastened the collapse of the Northern Song dynasty. Despite the magnitude of this flood event, no sedimentary deposits have yet been linked to these historically recorded floods. In this research paper, we provide archaeological, sedimentary, and radiocarbon evidence of the AD 1048–1128 Yellow River floods at the Dazhanglongcun, Xidacheng, and Daguxiancun sites in Neihuang County, Henan Province. Based on our data, we argue that the AD 1048–1128 Yellow River floods deposited over 5 m of alluvium on villages in the North China Plain, radically changing both the physical and political landscape of Northern Song dynasty China.
Keywords: floods; Geoarchaeology; land use; North China Plain; Song dynasty; Yellow River

Combining Conflicting Bayesian Models to Develop Paleoseismic Records: An Example from the Wasatch Fault Zone, Utah - DuRoss, Christopher B.; Bennett, Scott E. K.; Briggs, Richard W.; Personius, Stephen F.; Gold, Ryan D.; Reitman, Nadine G.; Hiscock, Adam I.; Mahan, Shannon A. (Bulletin of the Seismological Society of America, 2018)
Bayesian statistical analyses of paleoseismic data result in the probabilistic determination of earthquake times using geochronological data evaluated in the context of a stratigraphic model. However, a fundamental problem in paleoseismology is how to use the Bayesian approach to model sparse and/or conflicting geochronological datasets, such as those derived from sites exhibiting episodic sedimentary and pedogenic processes in moderate‐ to high‐energy environments (e.g., a normal‐faulted alluvial fan). Using paleoseismic data for the Corner Canyon site on the Salt Lake City segment of the Wasatch fault zone (Utah), we develop an approach by which multiple Bayesian models are combined to generate an earthquake history at a site. This approach accommodates mutually exclusive interpretations of the geochronological data and thereby limits the influence of sparse data, stratigraphically inconsistent ages, or a single, subjective model interpretation. For the Corner Canyon site, we integrate four OxCal Bayesian models to generate a chronology of six events between ∼4.8 and ∼0.5  ka. Late Holocene (post‐5 ka) mean recurrence and vertical slip‐rate estimates are ∼0.9  ky (0.7–1.0 ky; 95% confidence) and 1.1  mm/yr (0.8–1.7  mm/yr range), respectively. Although our method increases the uncertainty in the timing of individual earthquakes, it more objectively accounts for potential geochronological errors and different interpretations of stratigraphic age control. By relaxing the need to select a single age model, our approach yields more accurate earthquake‐timing results that will better facilitate evaluations of along‐fault event correlation and earthquake rupture length.

Data Constraints on Glacial Atlantic Water Mass Geometry and Properties - Oppo, Delia W.; Gebbie, Geoffrey; Huang, Kuo‐Fang; Curry, William B.; Marchitto, Thomas M.; Pietro, Kathryn R. (Paleoceanography and Paleoclimatology, 2018)
The chemical composition of benthic foraminifera from marine sediment cores provides information on how glacial subsurface water properties differed from modern, but separating the influence of changes in the origin and end‐member properties of subsurface water from changes in flows and mixing is challenging. Spatial gaps in coverage of glacial data add to the uncertainty. Here we present new data from cores collected from the Demerara Rise in the western tropical North Atlantic, including cores from the modern tropical phosphate maximum at Antarctic Intermediate Water (AAIW) depths. The results suggest lower phosphate concentration and higher carbonate saturation state within the phosphate maximum than modern despite similar carbon isotope values, consistent with less accumulation of respired nutrients and carbon, and reduced air‐sea gas exchange in source waters to the region. An inversion of new and published glacial data confirms these inferences and further suggests that lower preformed nutrients in AAIW, and partial replacement of this still relatively high‐nutrient AAIW with nutrient‐depleted, carbonate‐rich waters sourced from the region of the modern‐day northern subtropics, also contributed to the observed changes. The results suggest that glacial preformed and remineralized phosphate were lower throughout the upper Atlantic, but deep phosphate concentration was higher. The inversion, which relies on the fidelity of the paleoceanographic data, suggests that the partial replacement of North Atlantic sourced deep water by Southern Ocean Water was largely responsible for the apparent deep North Atlantic phosphate increase, rather than greater remineralization.

Decreased sedimentation efficiency of petro- and non-petro-carbon caused by a dispersant for Macondo surrogate oil in a mesocosm simulating a coastal microbial community - Xu, Chen; Zhang, Saijin; Beaver, Morgan; Wozniak, Andrew; Obeid, Wassim; Lin, Youmin; Wade, Terry L.; Schwehr, Kathleen A.; Lin, Peng; Sun, Luni; Hatcher, Patrick G.; Chin, Wei-Chun; et al. (Marine Chemistry, 2018)
Large amounts of mucous-rich oil-containing marine snow formed in surface waters adjacent to the Deepwater Horizon spill. This marine oil snow (MOS) was implicated in oil delivery to the seafloor. Whether the use of chemical dispersants increased or decreased MOS sedimentation remains controversial. We conducted mesocosm experiments testing the effects of oil and oil plus a dispersant on MOS formation and sedimentation, in coastal seawater. The four treatments used were a surrogate Macondo oil water accommodated fraction (“WAF”), two concentrations of chemically-enhanced WAF (“CEWAF” and diluted CEWAF, “DCEWAF”) containing a dispersant and oil, and Controls (no additions). Based on radiocarbon and 13C NMR results, the presence of dispersants enhanced the amounts of petro-carbon being incorporated into the sinking oil-carrying aggregates (aka MOS). However, most of the chemically-dispersed oil preferentially partitioned into the colloidal and suspended particulate fractions rather than into the rapidly forming MOS. Thus the oil and non-petro-carbon sedimentation efficiency in treatments with a dispersant was much lower, compared to those in the Control and WAF treatments, during the four-day mesocosm experiment. Formation of MOS and its subsequent sinking sequestered the oil in two stages: first via terrestrial-derived detritus containing humic compounds, and subsequently via freshly produced material, such as exopolymeric substances produced by phytoplankton and bacteria.

Deglacial floods in the Beaufort Sea preceded Younger Dryas cooling - Keigwin, L. D.; Klotsko, S.; Zhao, N.; Reilly, B.; Giosan, L.; Driscoll, N. W. (Nature Geoscience, 2018)
A period of cooling about 13,000 years ago interrupted about 2,000 years of deglacial warming. Known as the Younger Dryas (YD), the event is thought to have resulted from a slowdown of the Atlantic meridional overturning circulation in response to a sudden flood of Laurentide Ice Sheet meltwater that reached the Nordic Seas. Oxygen isotope evidence for a local source of meltwater to the open western North Atlantic from the Gulf of St Lawrence has been lacking. Here we report that the eastern Beaufort Sea contains the long-sought signal of O-18-depleted water. Beginning at similar to 12.94 ± 0.15 thousand years ago, oxygen isotopes in the planktonic foraminifera from two sediment cores as well as sediment and seismic data indicate a flood of meltwater, ice and sediment to the Arctic via the Mackenzie River that lasted about 700 years. The minimum in the oxygen isotope ratios lasted similar to 130 years. We suggest that the floodwater travelled north along the Canadian Archipelago and then through the Fram Strait to the Nordic Seas, where freshening and freezing near sites of deep-water formation would have suppressed convection and caused the YD cooling by reducing the meridional overturning.

The demise of the largest and oldest African baobabs - Patrut, Adrian; Woodborne, Stephan; Patrut, Roxana T.; Rakosy, Laszlo; Lowy, Daniel A.; Hall, Grant; von Reden, Karl F. (Nature Plants, 2018)
The African baobab is the biggest and longest-living angiosperm tree. By using radiocarbon dating we identified the stable architectures that enable baobabs to reach large sizes and great ages. We report that 9 of the 13 oldest and 5 of the 6 largest individuals have died, or at least their oldest parts/stems have collapsed and died, over the past 12 years; the cause of the mortalities is still unclear.

Dimensions of Radiocarbon Variability within Sedimentary Organic MatterABSTRACT - Bao, Rui; McNichol, Ann P; McIntyre, Cameron P; Xu, Li; Eglinton, Timothy I (Radiocarbon, 2018)
Organic carbon (OC) radiocarbon (14C) signatures in marine surface sediments are highly variable and the causes of this heterogeneity remain ambiguous. Here, we present results from a detailed 14C-based investigation of an Arabian Sea sediment, including measurements on organic matter (OM) in bulk sediment, specific grain size fractions, and OC decomposition products from ramped-pyrolysis-oxidation (RPO). Our results show that 14C ages of OM increase with increasing grain size, suggesting that grain size is an important factor controlling the 14C heterogeneity in marine sediments. Analysis of RPO decomposition products from different grain size fractions reveals an overall increase in age of corresponding thermal fractions from finer to coarser fractions. We suggest that hydrodynamic properties of sediment grains exert the important control on the 14C age distribution of OM among grain size fractions. We propose a conceptual model to account for this dimensionality in 14C variability that invokes two predominant modes of OM preservation within different grain size fractions of Arabian Sea sediment: finer (<63 μm) fractions are influenced by OM-mineral grain aggregation processes, giving rise to relatively uniform 14C ages, whereas OM preserved in coarser (>63 μm) fractions includes materials encapsulated within microfossils and/or entrained fossil (14C-depleted) OC hosted in detrital mineral grains. Our findings highlight the value of RPO for assessment of 14C age variability in sedimentary OC, and for assessing mechanisms of OM preservation in aquatic sediments.
Keywords: arabian sea; grain size; hydrodynamic processes; organicmatter; radiocarbon; ramped pyrolysis-oxidation

Drought in the northern Bahamas from 3300 to 2500 years ago - van Hengstum, Peter J.; Maale, Gerhard; Donnelly, Jeffrey P.; Albury, Nancy A.; Onac, Bogdan P.; Sullivan, Richard M.; Winkler, Tyler S.; Tamalavage, Anne E.; MacDonald, Dana (Quaternary Science Reviews, 2018)
Intensification and western displacement of the North Atlantic Subtropical High (NASH) is projected for this century, which can decrease Caribbean and southeastern American rainfall on seasonal and annual timescales. However, additional hydroclimate records are needed from the northern Caribbean to understand the long-term behavior of the NASH, and better forecast its future behavior. Here we present a multi-proxy sinkhole lake reconstruction from a carbonate island that is proximal to the NASH (Abaco Island, The Bahamas). The reconstruction indicates the northern Bahamas experienced a drought from ∼3300 to ∼2500 Cal yrs BP, which coincides with evidence from other hydroclimate and oceanographic records (e.g., Africa, Caribbean, and South America) for a synchronous southern displacement of the Intertropical Convergence Zone and North Atlantic Hadley Cell. The specific cause of the hydroclimate change in the northeastern Caribbean region from ∼3300 to 2500 Cal yrs BP was probably coeval southern or western displacement of the NASH, which would have increased northeastern Caribbean exposure to subsiding air from higher altitudes.

Dual-Isotope Constraints on Seasonally Resolved Source Fingerprinting of Black Carbon Aerosols in Sites of the Four Emission Hot Spot Regions of China - Fang, Wenzheng; Du, Ke; Andersson, August; Xing, Zhenyu; Cho, Chaeyoon; Kim, Sang-Woo; Deng, Junjun; Gustafsson, Örjan (Journal of Geophysical Research: Atmospheres, 2018)
Despite much recent efforts, the emission sources of black carbon (BC) aerosols―central input to understanding and predicting environmental and climate impact―remain highly uncertain. Here we present observational δ13C/Δ14C‐based constraints on the sources of BC aerosols over the four seasons in each of the four key hot spot emission regions of China: Beijing‐Tianjin‐Hebei (BTH‐Wuqing; where Wuqing is the sampling location), Yangtze River Delta (YRD‐Haining), Pearl River Delta (PRD‐Zhongshan), and Sichuan Basin (SC‐Deyang). Overall, BC loadings were highest in winter, yet elevated loadings were also observed in other seasons, for example, spring at SC‐Deyang and fall at PRD‐Zhongshan. Annually, the dominant BC sources were coal (50 ± 20%) for BTH‐Wuqing, liquid fossil for YRD‐Haining (46 ± 8%) and PRD‐Zhongshan (48 ± 18%), whereas liquid fossil (42 ± 17%) and biomass burning (41 ± 14%) equally affected SC‐Deyang. There is also different but distinct seasonalities in BC sources for the different sites. As an example, for BTH‐Wuqing coal burning increased from summer to winter, while summer and spring BTH‐Wuqing were more influenced by liquid fossil. In contrast, for YRD‐Haining, the relative importance of emission sources was more constant over the year. These quantitative observational constraints on source‐seasonality of BC aerosols in receptor sites located in China's four key economic zones highlight that regulatory control on BC aerosol emissions from different fuels should consider both seasonal and regional variations. Our results also suggest that models on estimates of BC‐induced climate and air quality should consider variations over both regional and seasonal scales.
Keywords: aerosol; BLACK CARBON; carbon isotope; china; emission sources; seasonality

Early Holocene sea level in the Canadian Beaufort Sea constrained by radiocarbon dates from a deep borehole in the Mackenzie Trough, Arctic Canada - O'Regan, Matt; Coxall, Helen; Hill, Philip; Hilton, Robert; Muschitiello, Francesco; Swärd, Henrik (Boreas, 2018)
Deglacial and Holocene relative sea level (RSL) in the Canadian Beaufort Sea was influenced by the timing and extent of glacial ice in the Mackenzie River corridor and adjacent coastal plains. Considerable evidence indicates extensive ice cover in this region of northwestern Canada during the Late Wisconsinan. However, no absolute ages exist to constrain maximum RSL lowering before the late Holocene (4.2–0 ka). In 1984, the Geological Survey of Canada drilled an 81.5‐m‐deep borehole in the western Mackenzie Trough at 45 m water depth (MTW01). The lower 52.5 m of the borehole was interpreted as a deltaic progradational sequence deposited during a period of rising sea level. The upper 29 m was described as foraminifer‐bearing marine sediments deposited after transgression of the site, when RSL rose above ~−74 m. Here, we present radiocarbon measurements from MTW01, acquired from benthic foraminifera, mollusc fragments and particulate organic carbon in the >63 μm fraction (POC>63 μm) in an attempt to constrain the chronology of sediments within this borehole and date the timing of transgression. The deepest carbonate macrofossil was acquired from 8 m above the transgressive surface (equivalent to 21 m b.s.l.), where mollusc fragments returned a date of 9400 +180–260 cal. a BP (2σ). This provides the oldest constraint on Holocene sea‐level lowering in the region, and implies that transgression at this site occurred prior to the early Holocene. Ages obtained from the lower 52.5 m of the borehole are limited to POC>63 μm samples. These indicate that progradational sediments were deposited rapidly after 24 820 +390–380 cal. a BP (2σ). Due to the incorporation of older reworked organic matter, the actual age of progradation is likely to be younger, occurring after Late Wisconsinan glacial ice retreated from the coast.

Ecological history of a long-lived conifer in a disjunct population - Herring, Erin M.; Gavin, Daniel G.; Dobrowski, Solomon Z.; Fernandez, Matias; Hu, Feng Sheng (Journal of Ecology, 2018)
In northern Idaho (USA), more than 100 vascular plant species are disjunct >160 km from their main distribution along the Pacific Northwest coast. It remains unclear whether most species within this interior forest disjunction, including Tsuga mertensiana, survived the last glacial period in a north‐Idaho refugium or whether these species colonized the region via long‐distance dispersal during the Holocene. Sediment cores were extracted from three mid‐ to high‐elevation lakes within T. mertensiana‐dominated forests in the Northern Rocky Mountains of Idaho. Pollen and macrofossils were used to reconstruct forest composition, determine the timing of T. mertensiana establishment, examine the hypothesis that the region was a glacial refugium, and contrast how climate, competition and/or dispersal limitation have influenced its modern distribution. The modern distribution of T. mertensiana was analysed by constructing a range map and modelling the potential species distribution. The presence of outlier populations surrounding the Idaho disjunction along with broad areas of unoccupied suitable habitat indicates that the range of T. mertensiana is currently expanding. To assess the accuracy of T. mertensiana pollen at detecting its range limit, a network of pollen surface samples was used to analyse the probability of detecting T. mertensiana pollen as a function of distance from its geographical range limit. Consistent T. mertensiana pollen occurrence at ≥1% abundance is likely only within 42 km of its range limit. Tsuga mertensiana first appears in the pollen and macrofossil record at the highest‐elevation site at c. 4,100 cal year bp, then at the next highest‐elevation site at c. 1,600 cal year bp, and last at the mid‐elevation site at 800 cal year bp. Tsuga mertensiana pollen occurs continuously at ≥1% at all three sites by c. 300 cal year bp suggesting regional presence. The timing of arrival suggests that T. mertensiana is a recent component of the forests of Idaho, having arrived during the Holocene via long‐distance dispersal from coastal populations over 160 km away. Synthesis. Comparison with palaeoclimate reconstructions from the broader region suggests that climate was a greater limiting factor than dispersal in the Holocene establishment in the interior, indicating little difficulty overcoming a large dispersal barrier. However, T. mertensiana remained at low abundances for millennia until Little Ice Age climates promoted its recent increase in abundance. Unoccupied areas of suitable habitat suggest that competition, rather than climate or dispersal, is a limiting range infilling in the interior mesic forests today.
Keywords: climate; disjunction; dispersal; Holocene; Idaho; mertensiana; Palaeoecology; pollen; refugia; Tsuga

The effect of sample drying temperature on marine particulate organic carbon composition - Rosengard, Sarah Z.; Lam, Phoebe J.; McNichol, Ann P.; Johnson, Carl G.; Galy, Valier V. (Limnology and Oceanography: Methods, 2018)
Compositional changes in marine particulate organic carbon (POC) throughout the water column trace important processes that underlie the biological pump's efficiency. While labor‐intensive, particle sampling efforts offer potential to expand the empirical POC archive at different stages in the water column, provided that organic composition is sufficiently preserved between sampling and analysis. The standard procedure for preserving organic matter composition in marine samples is to immediately store particles at −80°C to −20°C until they can be freeze‐dried for analysis. This report investigates the effect of warmer drying and storage temperatures on POC composition, which applies to the majority of POC samples collected in the field without intention for organic analysis. Particle samples collected off Woods Hole, Massachusetts were immediately dried at 56°C, at room temperature, or stored in a freezer until freeze‐drying. Results show that oven‐ and air‐drying did not shift the bulk composition (i.e., carbon and nitrogen content and stable isotope composition) of POC in the samples relative to freeze‐drying. Similarly, warmer drying temperatures did not affect POC thermal stability, as inferred by ramped pyrolysis/oxidation, a growing technique that uses a continuous temperature ramp to differentiate components of organic carbon by their decomposition temperature. Oven‐ and air‐drying did depress lipid abundances relative to freeze‐drying, the extent of which depended on compound size and structure. The data suggest that field samples dried at room temperatures and 56°C are appropriate for assessing bulk POC composition and thermal stability, but physical mechanisms such as molecular volatilization bias their lipid composition.

Effects of the Younger Dryas climate event recorded in sediment near the western Irish seaboard - Wood, Bill L.; Williams, D. Michael; Murray, John (Geological Journal, 2018)
Results of analyses of a shallow marine sediment vibrocore from the Atlantic seafloor just west of the Aran Islands, western Ireland, are presented. The sediments range from ~16,000 to younger than 9,000 cal BP in age, based on 14C dating of foraminifers and molluscs. One sample within the core is dated at 12804 ± 125 cal BP and lies a very short distance stratigraphically below a conspicuous horizon containing isolated pebbles and sand‐size clasts, in what is an otherwise fine‐grained sequence of sediment. These outsized clasts are interpreted to be ice‐rafted debris. Approximately coeval with this horizon, the diversity and abundance of foraminifers decrease significantly and the foraminifer Nonionellina labradorica makes its first appearance in the core sediment. Stable isotope analysis shows a significant increase in values of δ18O approaching the horizon containing ice‐rafted debris. These results show the effects of a relatively sudden cooling of this part of the Atlantic Ocean at middle latitudes coincident with, or just after, the onset of the Younger Dryas event and demonstrate the extent of floating icebergs and probable later pack ice as a result of this temperature decrease.
Keywords: Atlantic Ocean; Foraminifers; Holocene; ice rafted debris; Ireland; sediment core; Younger Dryas

The Effects of Tropical Cyclone-Generated Deposition on the Sustainability of the Pearl River Marsh, Louisiana: The Importance of the Geologic FrameworkPresentation_1.PPTX - McCloskey, Terrence A.; Smith, Christopher G.; Liu, Kam-biu; Nelson, Paul R. (Frontiers in Ecology and Evolution, 2018)
Shoreline retreat is a tremendously important issue along the coast of the northern Gulf of Mexico, especially in Louisiana. Although this marine transgression results from a variety of causes, the crucial factor is the difference between marsh surface elevation and rising sea levels. In most cases, the primary cause of a marsh's inability to keep up with sea level is the lack of input of inorganic material. Although tropical cyclones provide an important source of such sediment, little effort has been made to determine the point of origin of the deposited material. In this study we use sedimentary, geochemical and biogeochemical data to identify the bed of the Pearl River and/or Lake Borgne as the source of a ~5 cm thick clastic layer deposited on the surface of the Pearl River marsh on the Louisiana/Mississippi border. Radiochemical chronologies and sedimentary evidence indicate that this layer was associated with the passage of Hurricane Katrina in 2005. As this material would otherwise have been lost to the system, this deposition indicates a net gain to marsh surface elevation. Accretion rates, determined from 137Cs and 14C profiles and the use of the Katrina layer as a stratigraphic marker, indicate that short-term (~50 years) rates are as much as an order of magnitude higher than the long- term (1000s of years) rates. We suggest that the marsh's geologic setting in an incised river valley with steep vertical constraints and a large fluvial discharge, promotes rapid accretion rates, with rates accelerating as the sea moves inland, due to extended hydroperiods and the input of clastic material from both the marine and terrestrial sides. These rates are especially large when compared to accretion occurring in the more common open marshes fringing the Gulf that lack fluvial input. The difference is particularly large when related to marsh recovery/regrowth following the deposition of thick hurricane-generated clastic layers. Given the number of similar incised river valleys along the Gulf Coast, we believe that understanding the processes controlling marsh accretion in such environments is essential in evaluating marsh sustainability on a regional basis.

The Ephemeral Signature of Permafrost Carbon in an Arctic Fluvial Network - Drake, Travis W.; Guillemette, François; Hemingway, Jordon D.; Chanton, Jeffery P.; Podgorski, David C.; Zimov, Nikita S.; Spencer, Robert G. M. (Journal of Geophysical Research: Biogeosciences, 2018)
Arctic fluvial networks process, outgas, and transport significant quantities of terrestrial organic carbon (C), particularly dissolved organic carbon (DOC). The proportion of permafrost C in these fluxes, however, is poorly constrained. A primary obstacle to the quantification of permafrost‐derived DOC is that it is rapidly respired without leaving a unique tracer of its presence. In this study, we investigated the production of bacterial respiratory carbon dioxide (CO2; measured as dissolved inorganic carbon; DIC) during maximum late‐summer thaw in sites spanning a fluvial network (Kolyma Basin, Siberia) to assess whether the biodegradation of permafrost DOC could be detected by the presence of a persistent aged (14C‐depleted) signature on the DIC pool. Using Keeling plot interpretation of DIC produced in bioincubations of river water, we show that bacteria respire varying sources of DOC moving downstream through the fluvial network. Respiration of permafrost (production of aged CO2) was only detected in heavily permafrost thaw influenced sites. In nonpermafrost thaw impacted sites, ambient DIC was modern (14C‐enriched), but rather than precluding the respiration of permafrost OC upstream, we suggest that 14C‐depleted DIC is overwhelmed by modern DIC. Investigation of dissolved organic matter composition via Fourier transform ion cyclotron resonance mass spectrometry highlighted that elevated levels of aliphatic and nitrogen‐containing compounds were associated with the production of aged DIC, providing molecular‐level insight as to why permafrost‐derived dissolved organic matter is rapidly respired. Overall, results from this study demonstrate the difficulty of tracing inputs of a highly reactive substrate to systems with diverse organic matter sources.

Evidence for Stable Holocene Basin‐Scale Overturning Circulation Despite Variable Currents Along the Deep Western Boundary of the North Atlantic Ocean - Hoffmann, Sharon S.; McManus, Jerry F.; Swank, Emerson (Geophysical Research Letters, 2018)
While substantial changes in thermohaline circulation related to deglacial climate variability are well established, the role of this circulation in Holocene climate variability remains uncertain. Here we use two dynamical proxies, 231Pa/230Th ratios and mean sortable silt size ( urn:x-wiley:00948276:media:grl58406:grl58406-math-0001), to reconstruct Holocene bottom water circulation at the intermediate‐depth Carolina Slope. We find no substantial change in deep current speed or 231Pa export at this site during the Holocene, suggesting consistent 231Pa export via the Deep Western Boundary Current. urn:x-wiley:00948276:media:grl58406:grl58406-math-0002 shows increasing millennial‐scale variability in the middle‐late Holocene, which may reflect Labrador Sea Water contribution to current speed. We conclude that deepwater export from the North Atlantic has remained remarkably stable during the Holocene, decoupled from changing rates of specific water masses, while production of these water masses varied at millennial to centennial time scales. The persistence of the large‐scale overturning may reflect the ocean's stabilizing influence on Holocene climate.
Keywords: chemical tracers; interglacial; Radioactivity and radioisotopes; sedimentation (1861); thermohaline

Faunal and stable isotopic analyses of benthic foraminifera from the Southeast Seep on Kimki Ridge offshore southern California, USA - McGann, Mary; Conrad, James E. (Deep Sea Research Part II: Topical Studies in Oceanography, 2018)
We investigated the benthic foraminiferal faunal and stable carbon and oxygen isotopic composition of a 15-cm push core (NA075-092b) obtained on a Telepresence-Enabled cruise to the Southeast Seep on Kimki Ridge offshore southern California. The seep core was taken at a depth of 973 m in the vicinity of a Beggiatoa bacterial mat and vesicomyid clams (Calyptogena) and compared to previously published data of living assemblages from ~ 714 m, four reference cores obtained at ~ 1030 m, and another one at 739 m. All of the reference sites are also from the Inner Continental Borderland but with no evidence of methane seepage. No endemic species were found at the seep site and most of the taxa recovered there have been reported previously from other seep or low oxygen environments. Q- and R-mode cluster analyses clearly illustrated differences in the faunal assemblages of the seep and non-seep sites. The living assemblage at Southeast Seep was characterized by abundant Takayanagia delicata, Cassidulina translucens, and Spiroplectammina biformis, whereas the non-seep San Pedro Basin reference assemblage was comprised primarily of Chilostomella oolina and Globobulimina pacifica. Density and species richness were lower at the seep site compared to the non-seep site, reflecting the harsher living conditions there. The dead assemblage at the seep site was dominated by Gyroidina turgida compared to Cassidulina translucens at the ~ 1030 m non-seep site and Cassidulina translucens, Pseudoparrella pacifica, and Takayanagia delicata at the 739 m non-seep site. Density was three times lower at Southeast Seep than at the non-seep sites of comparable water depth but species richness was ~ 30% higher. Stable carbon isotopic values were considerably depleted in the seep samples compared to the non-seep samples, with a progression from lightest to heaviest average δ13C values evident at the seep site reflecting microhabitat preference and vital effect: the deep infaunal species of Globobulimina, the shallow infaunal species Uvigerina peregrina, the epifaunal species Cibicidoides wuellerstorfi, and the shallow infaunal but aragonite-shelled species Hoeglundina elegans. The δ13C values downcore among each benthic species indicates ongoing fluid seepage through at least the last 3800 cal yr B.P. at Southeast Seep. Besides the continual local seepage, evidence from δ13C values of planktic foraminifera in the seep core suggest two pulses of methane (at 3000 and 3700 cal yr B.P.) were released that were large enough to influence much of the water column. Paired benthic and planktic foraminiferal stable oxygen isotope records provide evidence that there were no paleoenvironmental changes such as increased bottom-water temperature or changes in oxygen isotopic composition of bottom and pore waters during this 3800-year record to induce the methane releases. Instead, Southeast Seep appears to be the result of local faulting providing pathways for fluid to flow to the seafloor at a fault stepover or transpressional bend in the regional strike-slip system.
Keywords: Beggiatoa; benthic foraminifera; Calyptogena; Kimki Ridge; Santa Catalina Basin; Southeast Seep; Southern California; stable carbon isotopes

Fifty-five-year longevity for the largest member of the family Sparidae: the endemic red steenbras Petrus rupestris from South Africa - Andrews, AH; Smale, MJ; Cowley, PD; Chang, N (African Journal of Marine Science, 2018)
A previous study that explored the age and growth of red steenbras Petrus rupestris (Valenciennes, 1830), a large sparid (family Sparidae, seabreams or porgies) endemic to South Africa and reported to approach 2 m in length, provided estimates as a moderately slow-growing species with a maximum age near 30 years. The stock is considered collapsed and a fishing moratorium was imposed in 2012, resulting in this species being assessed as Endangered by the IUCN. One consideration in addressing population status is validation of life-history traits. In this study, estimates of age for red steenbras from thin-sectioned otoliths were reassessed visually in terms of both the original ages and revised estimates using a different age-reading pattern. The revised ages exceeded the original ages by up to 30 years, with a maximum estimated age of 55 years from a well-defined otolith section that provided a basis for the revised age-reading procedure. Bomb radiocarbon (14C) dating revealed there was an offset in the timing of the 14C rise on the Agulhas Bank that, when coupled with considerations for regional oceanography, provided support for the revised age-reading pattern and an estimated longevity that exceeds 50 years. These findings were further supported by the fortuitous recapture of a tagged red steenbras that was at liberty for 22 years.
Keywords: Age validation; bomb radiocarbon dating; Carbon-14; copper steenbras; endangered species; fishery closure; otoliths

Five Younger Dryas black mats in Mexico and their stratigraphic and paleoenvironmental context - Israde-Alcántara, Isabel; Domínguez-Vázquez, G.; Gonzalez, S.; Bischoff, J.; West, A.; Huddart, D. (Journal of Paleolimnology, 2018)
The Younger Dryas interval (YD) was a period of widespread, abrupt climate change that occurred between 12,900 and 11,700 cal yr BP (10,900–10,000 14C BP). Many sites in the Northern Hemisphere preserve a sedimentary record across the onset of the YD interval, including sites investigated in sedimentary basins located in central Mexico (Chapala, Cuitzeo, Acambay), the Basin of Mexico (Tocuila), and northern Mexico (El Cedral). Deposits consist of lacustrine or marginal lake sediments that were deposited during the Pleistocene and the Holocene. At the Tocuila and Acambay sites, Pleistocene fossil vertebrate assemblages, mainly mammoths (Mammuthus columbi), are found in association with a distinctive organic layer, sometimes called the black mat that formed during the YD. At the Chapala, Cuitzeo, Acambay, and Tocuila sites the black mats contain a suite of distinctive microscopic and mineralogical signatures and are accompanied by a sharp change in the depositional environments as supported by diatom and pollen studies reported here. The signatures include magnetic, Fe-rich microspherules, silica melted droplets with aerodynamic shapes (tektites), large amounts of charcoal, and sometimes nanodiamonds (Cuitzeo), all of which were deposited at the onset of the YD. The geochemistry of the microspherules indicates that they are not anthropogenic, authigenic or of cosmic or volcanic origin, and instead, were produced by melting and quenching of terrestrial sediments. Here, we present the stratigraphy at five field sites, the analyses of magnetic microspherules, including major element composition and scanning electron microscopy images. All of these materials are associated with charcoal and soot, which are distinctive stratigraphic markers for the YD layer at several sites in Mexico.

Fossil Fuel Combustion Emission From South Asia Influences Precipitation Dissolved Organic Carbon Reaching the Remote Tibetan Plateau: Isotopic and Molecular Evidence - Li, Chaoliu; Chen, Pengfei; Kang, Shichang; Yan, Fangping; Tripathee, Lekhendra; Wu, Guangjian; Qu, Bin; Sillanpää, Mika; Yang, Di; Dittmar, Thorsten; Stubbins, Aron; Raymond, Peter A. (Journal of Geophysical Research: Atmospheres, 2018)
The dissolved organic carbon in precipitation (water‐soluble organic carbon, WSOC) can provide a carbon subsidy to receiving ecosystems. The concentrations, isotopic signatures (δ13C/Δ14C), and molecular signatures (transform ion cyclotron mass spectrometry) of WSOC being delivered to Nam Co—a remote site on the inland Tibetan Plateau (TP)—were compared to those of WSOC in the snowpack, and in wet deposition from urban cities fringing the TP. The average WSOC concentration at Nam Co (1.0 ± 0.9 mg C L−1) was lower than for the large cities (1.6 to 2.3 mg C L−1) but higher than in the snowpack samples (0.26 ± 0.09 mg C L−1). Based upon radiocarbon data, it is estimated that 15 ± 6% of Nam Co WSOC was fossil derived, increasing to 20 ± 8% for snowpack WSOC, 29 ± 4% for Lhasa WSOC, and 34 ± 8% for the three cities. Transform ion cyclotron mass spectrometry results revealed that the abundance of dissolved black carbon and sulfur‐containing molecules of WSOC increased in the order Nam Co < snow pack < urban. The enrichment in 14C and depletion in dissolved black carbon and sulfurous organic molecules of Nam Co WSOC was suggestive of low, but still detectable inputs of fossil‐derived organics to WSOC on the remote TP. Backward air mass trajectories for the precipitation events at Nam Co suggested that the fossil fuel contributions to WSOC in Nam Co region originated mainly from South Asia. This study provides novel radiocarbon age, chemistry, and source evidence that anthropogenic WSOC is delivered to the remote TP, one of the most remote regions on Earth.

Fossil Fuel-Derived Polycyclic Aromatic Hydrocarbons in the Taiwan Strait, China, and Fluxes across the Air–Water InterfaceFossil Fuel-Derived Polycyclic Aromatic Hydrocarbons in the Taiwan Strait, China, and Fluxes across the AirWater Interface - Ya, Miaolei; Xu, Li; Wu, Yuling; Li, Yongyu; Zhao, Songhe; Wang, Xinhong (Environmental Science & Technology, 2018)
On the basis of the application of compound-specific radiocarbon analysis (CSRA) and air–water exchange models, the contributions of fossil fuel and biomass burning derived polycyclic aromatic hydrocarbons (PAHs) as well as their air–water transport were elucidated. The results showed that fossil fuel-derived PAHs (an average contribution of 89%) presented the net volatilization process at the air–water interface of the Taiwan Strait in summer. Net volatile fluxes of the dominant fluorene and phenanthrene (>58% of the total PAHs) were 27 ± 2.8 μg m–2 day–1, significantly higher than the dry deposition fluxes (average 0.43 μg m–2 day–1). The Δ14C contents of selected PAHs (fluorene, phenanthrene plus anthracene, fluoranthene, and pyrene) determined by CSRA in the dissolved seawater ranged from −997 ± 4‰ to −873 ± 6‰, indicating that 89–100% (95 ± 4%) of PAHs were supplied by fossil fuels. The South China Sea warm current originating from the southwest China in summer (98%) and the Min-Zhe coastal current originating from the north China in winter (97%) input more fossil fuel PAHs than the Jiulong River estuary (90%) and Xiamen harbor water (93%). The more radioactive decayed 14C of fluoranthene (a 4-ring PAH) than that of phenanthrene and anthracene (3-ring PAHs) represented a greater fossil fuel contribution to the former in dissolved seawater.

On the Holocene evolution of the Ayeyawady megadelta - Giosan, Liviu; Naing, Thet; Min Tun, Myo; Clift, Peter D.; Filip, Florin; Constantinescu, Stefan; Khonde, Nitesh; Blusztajn, Jerzy; Buylaert, Jan-Pieter; Stevens, Thomas; Thwin, Swe (Earth Surface Dynamics, 2018)
The Ayeyawady delta is the last Asian megadelta whose evolution has remained essentially unexplored so far. Unlike most other deltas across the world, the Ayeyawady has not yet been affected by dam construction, providing a unique view on largely natural deltaic processes benefiting from abundant sediment loads affected by tectonics and monsoon hydroclimate. To alleviate the information gap and provide a baseline for future work, here we provide a first model for the Holocene development of this megadelta based on drill core sediments collected in 2016 and 2017, dated with radiocarbon and optically stimulated luminescence, together with a reevaluation of published maps, charts and scientific literature. Altogether, these data indicate that Ayeyawady is a mud-dominated delta with tidal and wave influences. The sediment-rich Ayeyawady River built meander belt alluvial ridges with avulsive characters. A more advanced coast in the western half of the delta (i.e., the Pathein lobe) was probably favored by the more western location of the early course of the river. Radiogenic isotopic fingerprinting of the sediment suggests that the Pathein lobe coast does not receive significant sediment from neighboring rivers. However, the eastern region of the delta (i.e., Yangon lobe) is offset inland and extends east into the mudflats of the Sittaung estuary. Wave-built beach ridge construction during the late Holocene, similar to several other deltas across the Indian monsoon domain, suggests a common climatic control on monsoonal delta morphodynamics through variability in discharge, changes in wave climate or both. Correlation of the delta morphological and stratigraphic architecture information on land with the shelf bathymetry, as well as its tectonic, sedimentary and hydrodynamic characteristics, provides insight on the peculiar growth style of the Ayeyawady delta. The offset between the western Pathein lobe and the eastern deltaic coast appears to be driven by tectonic–hydrodynamic feedbacks as the extensionally lowered shelf block of the Gulf of Mottama amplifies tidal currents relative to the western part of the shelf. This situation probably activates a perennial shear front between the two regions that acts as a leaky energy fence. Just as importantly, the strong currents in the Gulf of Mottama act as an offshore-directed tidal pump that helps build the deep mid-shelf Mottama clinoform with mixed sediments from the Ayeyawady, Sittaung and Thanlwin rivers. The highly energetic tidal, wind and wave regime of the northern Andaman Sea thus exports most sediment offshore despite the large load of the Ayeyawady River.

Holocene history of the Greenland Ice-Sheet margin in Northern Nunatarssuaq, Northwest Greenland - Farnsworth, Lauren B.; Kelly, Meredith A.; Bromley, Gordon R. M.; Axford, Yarrow; Osterberg, Erich C.; Howley, Jennifer A.; Jackson, Margaret S.; Zimmerman, Susan R. (arktos, 2018)
Records of past Greenland Ice-Sheet (GrIS) extents are important for understanding the response of the ice sheet to climate conditions, providing a longer term perspective on present ice-margin fluctuations, and evaluating ice-sheet models. We present a record of Holocene GrIS extents in Nunatarssuaq, Northwest Greenland, based on geomorphic mapping combined with 10Be surface exposure dating of rock surfaces and 14C dating of subfossil plants. 10Be ages of boulders and bedrock exposed during deglaciation from the Last Glacial Maximum range from ~ 81 to 15 ka. The apparently old ages of some samples and scatter in the dataset indicate the presence of 10Be inherited from prior periods of exposure and suggest that overriding ice was minimally erosive. Subfossil plants exposed on a debris band in the GrIS margin date to ~ 4.7 cal ka BP and register a time when the Northwest GrIS was smaller than at present. Geomorphic evidence, including a drift sheet, grounding-line moraines, and higher levels of Nordsø, document an advance of the Nuna and Tunge Rampen (GrIS outlet glaciers). 14C ages of in situ subfossil plants and 10Be ages of boulders bracket this advance to ~ 3.2–2.1 ka, a period of regional cooling. Unweathered, lichen-free drift occurs < 50 m beyond the present GrIS margin in most locations. 10Be ages of this drift are 2.2–0.5 ka and likely contain inherited nuclides. 14C ages of in situ subfossil plants atop this drift are between cal AD ~ 1640 and 2001, suggesting recent ice-margin fluctuations.

Holocene mountain glacier history in the Sukkertoppen Iskappe area, southwest Greenland - Schweinsberg, Avriel D.; Briner, Jason P.; Miller, Gifford H.; Lifton, Nathaniel A.; Bennike, Ole; Graham, Brandon L. (Quaternary Science Reviews, 2018)
Mountain glaciers and ice caps (GIC) independent of the Greenland Ice Sheet respond rapidly to climate variations and records of their past extent provide information on the natural envelope of climate variability. Here, we use a multi-proxy approach that combines proglacial lake sediment analysis, cosmogenic nuclide surface-exposure dating (in situ 10Be and 14C), and radiocarbon dating of recently ice-entombed moss to generate a centennial-scale record of Holocene GIC fluctuations in southwestern Greenland. Following local deglaciation ∼10-9 ka, sediments from proglacial Crash Lake record a glacier advance at ∼9 ka that is indistinguishable from nearby ice sheet moraines, implying a synchronous response of GIC and the Greenland Ice Sheet to a centennial-scale climate event. Following this local glacier advance, GIC experienced net recession until ∼4.6 ka. Radiocarbon ages of in situ moss (n = 29) and Crash Lake sediments reveal intervals of glacier expansion at ∼1.8, 1.2 and 0.7 ka that are superimposed on an overall trend of net glacier expansion throughout the late Holocene. In situ 14C concentrations from bedrock adjacent to radiocarbon-dated moss samples further constrain the duration of ice cover through the Holocene in this region. We find that our glacier-size proxy records during the past ∼4 ka are broadly consistent with relatively lower temperatures recorded in GISP2 and occur during, or following, intervals of volcanic perturbations. Thus, we speculate that volcanic activity, although less frequent and intense than in the early Holocene and during the Little Ice Age, may have led to centennial-scale variability imprinted on net glacier expansion due to decreasing summer insolation through the late Holocene.
Keywords: Cosmogenic in situ 14C; Glacier fluctuations; Greenland; Holocene; lake sediment; Neoglaciation

How Could a Freshwater Swamp Produce a Chemical Signature Characteristic of a Saltmarsh?How Could a Freshwater Swamp Produce a Chemical Signature Characteristic of a Saltmarsh? - McCloskey, Terrence A.; Smith, Christopher G.; Liu, Kam-biu; Marot, Marci; Haller, Christian (ACS Earth and Space Chemistry, 2018)
Reduction–oxidation (redox) reaction conditions, which are of great importance for the soil chemistry of coastal marshes, can be temporally dynamic. We present a transect of cores from northwest Florida wherein radical postdepositional changes in the redox regime has created atypical geochemical profiles at the bottom of the sedimentary column. The stratigraphy is consistent along the transect, consisting of, from the bottom upward, carbonate bedrock, a gray clay, an organic mud section, a dense clay layer, and an upper organic mud unit representing the current saltwater marsh. However, the geochemical signature of the lower organic mud unit suggests pervasive redox reactions, although the interval has been identified as representing a freshwater marsh, an unlikely environment for such conditions. Analyses indicate that this discrepancy results from postdepositional diagenesis driven by millennial-scale environmental parameters. Rising sea level that led to the deposition of the capping clay layer, created anaerobic conditions in the freshwater swamp interval, and isolated it hydrologically from the rest of the sediment column. The subsequent infiltration of marine water into this organic material led to sulfate reduction, the buildup of H2S and FeS, and anoxic conditions. Continued sulfidation eventually resulted in euxinic conditions, as evidenced by elevated levels of Fe, S, and especially Mo, the diagnostic marker of euxinia. Because this chemical transformation occurred long after the original deposition the geochemical signature does not reflect soil chemistry at the time of deposition and cannot be used to infer syn-depositional environmental conditions, emphasizing the importance of recognizing diagenetic processes in paleoenvironmental studies.
Keywords: anoxic; diagenesis; euxinic; florida; Molybdenum; reactions; redox; XRF

Human use of small forage fish: Improved ancient DNA species identification techniques reveal long term record of sustainable mass harvesting of smelt fishery in the northeast Pacific Rim - Palmer, Erica; Tushingham, Shannon; Kemp, Brian M. (Journal of Archaeological Science, 2018)
The bulk storage and mass capture of small forage fish has played a primary role in the cultural traditions and subsistence practices of many ancient and modern indigenous communities throughout the world. Archaeologists are improving their recognition of human interaction with these fisheries through the application of fine-mesh screening techniques and ichthyofaunal analysis of fish bone. Because of the differing life histories of many of these fish, determining their species from archaeological contexts can improve our resolution of past harvesting and consumption patterns. This has remained a challenge for many categories of fish, such as salmon and smelt. Here, we present an improved genetic species identification process that utilizes ancient DNA amplification techniques involving a reagent-rich PCR protocol (i.e., “Rescue PCR”) and a PCR Enhancer Cocktail P (i.e., PEC-P) to identify smelt and other forage fish bone from five archaeological sites located along the northern California (United States) Pacific coast dating to the Late Period (after 1300 cal BP). Through the application of these novel techniques, our species identification success rate increased to 71.2% overall, with some sites having a remarkable 100% success rate. We identified the species of 104 of 146 fish vertebrae, and determined that inhabitants at these sites harvested primarily surf smelt with potentially less emphasis on night smelt. Observations of herring, perch, sculpin and rainbow trout/steelhead were also made. Along with these small surf fish, we found evidence of larger fish such as shark and Pacific hake (common predatory fish in the area). The study demonstrates a significant breakthrough in ancient DNA identification techniques that resulted in information that speak to the long term continuity of use of mass harvested forage fish by indigenous peoples. The results of this project help establish a better understanding of subsistence and cultural traditions of northern California indigenous communities, with the potential to provide a more global understanding of fishing technologies, sustainability, and mass harvesting of small fishes.
Keywords: aDNA; Ichythyarchaeology; Northern California; Smelt; Species identification

The Impact of Aquifer Flushing on Groundwater Arsenic Across a 35‐km Transect Perpendicular to the Upper Brahmaputra River in Assam, India - Choudhury, R.; Nath, B.; Khan, M. R.; Mahanta, C.; Ellis, T.; Geen, A. (Water Resources Research, 2018)
Well testing in the floodplain of the Brahmaputra River in Golaghat and Jorhat districts of Assam, India, shows that groundwater arsenic (As) concentrations increase with distance from the river. To establish the origin of this pattern, an additional 900 wells <60‐m deep were tested for As and nine sites were drilled along a 35‐km transect perpendicular to the river. The field data show no relation between groundwater As concentrations ranging from <1 to 660 μg/L along the transect and (a) As concentrations of <1–5 mg/kg in cuttings of aquifer sand recovered while drilling or (b) the degree of reduction of iron oxides in these cuttings. The drilling indicates, however, a marked increase in the thickness of a clay layer capping the aquifer starting from <1–5 m near the river to over 60 m at the most distant site toward the base of the Naga foothills. Organic radiocarbon ages of 18–46 kyr obtained from all but one of 13 clay samples indicate pre‐Holocene deposition of the underlying sands across the entire transect. Radiocarbon ages of dissolved inorganic carbon of 0.2, 4.7, and 17.8 kyr were measured in groundwater from three monitoring wells installed to 30–60‐m depth at distances of 10, 20, and 40 km from the river, respectively. A conceptual groundwater flow model consistent with monitored heads and groundwater ages suggests that thick clay layers capping the aquifer further from the river inhibited flushing of the aquifer and, as a result, preserved higher As levels in groundwater.
Keywords: aquifer flushing; Arsenic; groundwater; South Asia

Interstadial Rise and Younger Dryas Demise of Scotland's Last Ice Fields - Bromley, G.; Putnam, A.; Borns, H.; Lowell, T.; Sandford, T.; Barrell, D. (Paleoceanography and Paleoclimatology, 2018)
Establishing the atmospheric expression of abrupt climate change during the last glacial termination is key to understanding driving mechanisms. In this paper, we present a new 14C chronology of glacier behavior during late‐glacial time from the Scottish Highlands, located close to the overturning region of the North Atlantic Ocean. Our results indicate that the last pulse of glaciation culminated between ~12.8 and ~12.6 ka, during the earliest part of the Younger Dryas stadial and as much as a millennium earlier than several recent estimates. Comparison of our results with existing minimum‐limiting 14C data also suggests that the subsequent deglaciation of Scotland was rapid and occurred during full stadial conditions in the North Atlantic. We attribute this pattern of ice recession to enhanced summertime melting, despite severely cool winters, and propose that relatively warm summers are a fundamental characteristic of North Atlantic stadials.
Keywords: late glacial; Loch Lomond Readvance; marine reservoir effect; moraine chronology; radiocarbon; seasonality

An Investigation of Gas Exchange and Water Circulation in the Amundsen Sea Based On Dissolved Inorganic Radiocarbon - Kim, Bumsoo; Lee, SangHoon; Kim, Minkyoung; Hahm, Doshik; Rhee, Tae Siek; Hwang, Jeomshik (Geophysical Research Letters, 2018)
We used radiocarbon isotope ratios in dissolved inorganic carbon to assess gas exchange and water circulation in the western Amundsen Sea. Radiocarbon isotope ratios indicate that Circumpolar Deep Water enters the basin along the seafloor and that the upper layer is formed through modification of this water mass. In the Amundsen Sea Polynya, radiocarbon isotope ratios of surface water are higher than those of underlying Winter Water, implying rapid absorption of atmospheric CO2. A CO2 absorption rate of 45mmol m(-2) d(-1) calculated for a site in the central polynya is higher than that near the Dotson Ice Shelf (28mmolm(-2) d(-1)). The turnover time of water in the Dotson Trough region of the western Amundsen Sea is estimated to be 10-30years, based on results from a box model and radiocarbon mass balance. Plain Language Summary The western Amundsen Sea is experiencing raid physical changes including rapid glacial melting and declining sea ice cover. The suggested heat source is the intrusion of warm Circumpolar Deep Water (CDW) along the seafloor of the Amundsen Shelf. Therefore, understanding the behavior of the intruded CDW, especially how long it stays on the shelf, is important. Physical oceanographic studies have examined the flux of CDW onto and out of the Amundsen Shelf. However, the turnover time of water in the Amundsen Sea is still poorly understood. In this paper, we use radiocarbon isotope signature from dissolved inorganic carbon to examine how rapidly atmospheric CO2 is absorbed into the Amundsen Sea Polynya and how long the water should stay in the western Amundsen Shelf to have the observed radiocarbon isotope signature. Based on our results and the current understanding of the water circulation in the western Amundsen Sea, we found that the water sits on the Amundsen Shelf for a few decades before it moves off shelf.
Keywords: Amundsen sea; dissolved inorganic carbon; gas exchange; radiocarbon; water circulation

Isotopic composition of sinking particles: Oil effects, recovery andbaselines in the Gulf of Mexico, 2010–2015 - Chanton, Jeffrey P.; Giering, Sarah L. C.; Bosman, Samantha H.; Rogers, Kelsey L.; Sweet, Julia; Asper, Vernon L.; Diercks, Arne R.; Passow, Uta (Elem Sci Anth, 2018)
The extensive release of oil during the 2010 Deepwater Horizon spill in the northern Gulf of Mexico perturbed the pelagic ecosystem and associated sinking material. To gauge the recovery and post-spill baseline sources, we measured Δ14C, δ13C and δ34S of sinking particles near the spill site and at a reference site and natural seep site. Particulates were collected August 2010–April 2016 in sediment traps moored at sites with depths of 1160–1660 m. Near the spill site, changes in Δ14C indicated a 3-year recovery period, while δ34S indicated 1–2 years, which agreed with estimates of 1–2 years based on hydrocarbon composition. Under post-spill baseline conditions, carbon inputs to sinking particulates in the northern Gulf were dominated by surface marine production (80–85%) and riverine inputs (15–20%). Near the spill site, Δ14C values were depleted in October 2010 (–140 to –80‰), increasing systematically by 0.07 ± 0.02‰ day–1 until July 2013 when values reached –3.2 ± 31.0‰. This Δ14C baseline was similar to particulates at the reference site (3.8 ± 31.1‰). At both sites, δ13C values stayed constant throughout the study period (–21.9 ± 0.5‰ and –21.9 ± 0.9‰, respectively). δ34S near the spill site was depleted (7.4 ± 3.1‰) during October 2010–September 2011, but enriched (16.9 ± 2.0‰) and similar to the reference site (16.2 ± 3.1‰) during November 2012–April 2015. At the seep site, Δ14C values were –21.7 ± 45.7‰ except during August 2012–January 2013 when a significant Δ14C depletion of –109.0 ± 29.1‰ was observed. We interpret this depletion period, also observed in δ13C data, as caused by the incorporation of naturally seeped oil into sinking particles. Determination of post-spill baselines for these isotopic signatures allows for evaluation of anthropogenic inputs in future.
Keywords: Deep Water Horizon Oil Spill; Gulf of Mexico; isotopes; radiocarbon; sediment trap; sinking particulates

Labile organic carbon dynamics in continental shelf sediments after the recent collapse of the Larsen ice shelves off the eastern Antarctic Peninsula: A radiochemical approach - Isla, E.; DeMaster, D.J. (Geochimica et Cosmochimica Acta, 2018)
Labile organic carbon (LOC) dynamics (i.e., of recently produced, planktonic material) and sediment dynamics were studied in the seabed using naturally occurring C-14(org), and Pb-210 measurements in the region where the Larsen Ice Shelves A and B were floating almost two decades ago. A non-steady-state diagenetic model was used to estimate sediment mixing coefficients as well as LOC fluxes to the seabed and LOC turnover times (i.e., mean residence times) in a suite of 14 sediment cores from the continental shelf, including a glacial trough. At four of the stations, cores were collected during 2007 and 2011 cruises, enabling a time-series approach for understanding the evolution of sedimentary processes and LOC dynamics in the deposits below a collapsed ice shelf. Sediment mixing coefficients, based on non-steady-state Pb-210 profiles, varied between 0.01 cm(2) y(-1) and 1.6 cm(2) y(-1) in these post-ice shelf sediments. These values were similar to those found in polar deep-sea environments, where sedimentary conditions are less dynamic than in shallower provinces. LOC, whose abundance decreased uniformly with depth, was detected to depths ranging from 2 to 16 cm, with LOC seabed inventories varying from 1.5 to 22 mg LOC cm(-2). Excess Pb-210 and LOC fluxes were relatively uniform across the study area suggesting that similar particle fluxes have taken place within theLarsen system since the disintegration of the various ice shelves. The LOC mean residence time at the different stations varied from 3 y to >60 y. The C-14(org), approach, calculating LOC content based on a two-end member model with planktonic 14C(org) as the labile carbon end member, most closely correlated with the lipid content of the sediment, which has been considered one of the best descriptors of reactive organic matter readily available to benthic consumers. We suggest that the irregular combination of sea ice coverage, organic matter production and supply to the sea floor introduce scatter in the determination of sediment and LOC dynamics such that short-term temporal (<5 years) and spatial trends could not be readily resolved.

Large Variability of Dissolved Inorganic Radiocarbon in the Kuroshio Extension of the Northwest North PacificABSTRACT - Ding, Ling; Ge, Tiantian; Gao, Huiwang; Luo, Chunle; Xue, Yuejun; Druffel, Ellen R M; Wang, Xuchen (Radiocarbon, 2018)
Radiocarbon (C-14) in dissolved inorganic carbon (DIC) was measured for water samples collected from six deep stations in the Kuroshio Extension (KE) region in the northwestern North Pacific in April-May 2015. Vertical profiles of Delta C-14-DIC indicate that bomb-produced Delta C-14 was present from the surface to similar to 1500 m water depth. Large variations in Delta C-14-DIC values (300 parts per thousand) were observed at 500 m water depth among the stations and the differences were likely controlled by transport and mixing dynamics of different water masses in the region. The major Pacific western boundary currents, such as Kuroshio and Oyashio and regional mesoscale eddies, could play important roles affecting the observed Delta C-14-DIC variability. The depth profiles of both Delta C-14-DIC and DIC concentrations can be predicted by the solution mixing model and can be used as conservative tracers of water mass movement and water parcel homogenization in the ocean.
Keywords: bomb radiocarbon; carbon; intermediate water; MIXED WATER REGION; ocean; WESTERN BOUNDARY CURRENTS

Large‐Scale Intrusion of Circumpolar Deep Water on Antarctic Margin Recorded by Stylasterid Corals - King, Theresa M.; Rosenheim, Brad E.; Post, Alexandra L.; Gabris, Theresa; Burt, Taylor; Domack, Eugene W. (Paleoceanography and Paleoclimatology, 2018)
We present centennial‐scale radiocarbon (14C) records archived by deep sea stylasterid corals from the outer shelf and upper slope of the Antarctic margin. These novel stylasterids (Errina spp.) were collected from the western Ross Sea shelf (500 m) and slope (1,700 m), as well as the eastern Wilkes Land shelf (670 m). We provide two corals from each region and document an abrupt reversal of 14C ages in the upper (younger) part of each coral. We test the statistical robustness of each record and demonstrate the significance of the age reversals, as well as the ability of these corals to record environmental change. We discuss a variety of possible drivers for this 14C reversal and conclude that it is most likely an encroachment of 14C‐depeleted Circumpolar Deep Water (CDW). This water mass has regionally intruded onto the Antarctic margin in recent decades, facilitating loss of grounded Antarctic ice; which has implications for global sea level, deep‐water formation, and carbon sequestration in the Southern Ocean. Thus, understanding the past variability of CDW on the margin is vital to better constrain climate change trajectories in the near future. We estimate large‐scale encroachment of CDW onto the shelf likely commencing after 1830 CE (±120 year). We present possible drivers for the intrusion, but highlight the need for additional chronologic constraint. This study not only demonstrates the utility of a novel coral taxon but also presents the paleoceanographic community with a testable hypothesis concerning a recent, widespread CDW intrusion.

Last Glacial Maximum surface water properties and circulation over Laurentian Fan, western North Atlantic - Gil, Isabelle M.; Keigwin, Lloyd D. (Earth and Planetary Science Letters, 2018)
Millennial scale events marked by the contribution of detrital sand are recorded in North Atlantic sediments during the Last Glacial Maximum (LGM), between Heinrich events (HE) 1 and 2, and left their imprint on Laurentian Fan (LF – 43°N) sediments off eastern Canada. The LF counterpart of the well-known detrital events consist of glacial red-brick sediments resulting from subglacial flows separated by olive-grey sediments appears at ∼21.4–19.9 and ∼19.5–18.65 cal kyr BP. High-resolution analyses of diatom assemblages and lithic grains coupled with planktonic oxygen isotopic records reveal that while the red sediment is almost barren of diatoms, foraminifera and lithics (>150 μm), they are abundant in the olive-grey sediment. Diatom assemblages reveal three phases during these events: (1) initial relatively warm/temperate conditions followed by (2) very cold surface water and drifting ice, and (3) a final phase characterized by relatively warmer waters and the appearance of detrital carbonate. Although these events possibly reflect the variability specific to the slope water region, they are likely the response to Atlantic Meridional Overturning Circulation perturbations and ice-sheet instability. Through a chain of mechanisms, meltwater inputs into the North Atlantic led ultimately to an increased volume of tropical waters and part of the heat stored in the subsurface was flushed by a brief convective episode that was not sustained, accounting for the return of cold conditions after the events. The sequence of mechanisms deduced from the paleo data here and elsewhere is consistent with previous modeling results. These data suggest that the detrital events between Heinrich event 1 and 2 may be synchronous across the North Atlantic, and that the LGM was probably not a time of prolonged steady state in the climate system.
Keywords: detrital events; diatoms; ice rafted debris; Last glacial maximum; Laurentide ice sheet; subglacial flows

Late Holocene paleoceanography in the Chukchi and Beaufort Seas, Arctic Ocean, based on benthic foraminifera and ostracodes - Seidenstein, Julia L.; Cronin, Thomas M.; Gemery, Laura; Keigwin, Lloyd D.; Pearce, Christof; Jakobsson, Martin; Coxall, Helen K.; Wei, Emily A.; Driscoll, Neal W. (arktos, 2018)
Calcareous microfossil assemblages in late Holocene sediments from the western Arctic continental shelf provide an important baseline for evaluating the impacts of today’s changing Arctic oceanography. This study compares 14C-dated late Holocene microfaunal assemblages of sediment cores SWERUS-L2-2-PC1, 2-MC4 and 2-KL1 (57 mwd), which record the last 4200 years in the Herald Canyon (Chukchi Sea shelf), and HLY1302-JPC-32, GGC-30, MC-29 (60 mwd), which record the last 3000 years in the Beaufort Sea shelf off the coast of Canada. Foraminiferal and ostracode assemblages are typical of Arctic continental shelf environments with annual sea-ice cover and show relatively small changes in terms of variability of dominant species. Important microfaunal changes in the Beaufort site include a spike in Spiroplectammina biformis coinciding with a decrease in Cassidulina reniforme in the last few centuries suggesting an increase of Pacific Water influence and decreased sea-ice. There is low-amplitude centennial-scale variability in proportions of benthic foraminiferal species, such as C. reniforme. In addition to these species, Cassidulina teretis s.l., Elphidium excavatum clavatum and Stainforthia feylingi are also common at this site. At the Herald Canyon site in the last few centuries, C. reniforme peaks around 150 years BP and then decreases while Spiroplectammina earlandi spikes and Acanthocythereis dunelmensis decreases also suggesting an increase in Pacific Water influence and decreased sea-ice at this site. This site also includes Buccella spp. and Elphidium excavatum clavatum. Differences in benthic foraminifera and ostracode species dominance between the two sites may be due to a greater influence of Pacific Water in the Chukchi shelf, compared to the more distal Beaufort shelf, which is also affected by the Beaufort Gyre and the Mackenzie River.

Late Pleistocene to Holocene productivity changes in the western equatorial Pacific (Sulu Sea, Philippines) from calcareous nannofossils - Tangunan, Deborah N.; Peleo-Alampay, Alyssa M. (Marine Micropaleontology, 2018)
We present a new calcareous nannofossil paleoproductivity reconstruction of the southeastern margin of the Sulu Sea to understand how marine productivity varied through time in one of the major fishing grounds of the Philippine archipelago. The study is based on two sediment cores obtained from two different hydrographic locations in the western equatorial Pacific region: an upwelling region off Zamboanga Peninsula (U-GC12) and a non-upwelling area off Panay Island (NU-GC14), covering the past 18,000 years before present (B.P.). Calcareous nannofossil assemblages in the investigated areas were of low diversity and largely dominated by Gephyrocapsa oceanica and Florisphaera profwida, followed by small placolith-bearing taxa, Emiliania hwcleyi, small Gephyrocapsa, and Reticulofenestra minuta. Upwelling episodes off the Zamboanga Peninsula were recorded several times in the past as shown by an increase in the abundance of high productivity indicator species (G. oceanica, small Gephyrocapsa, E. hwcleyi) and of bulk sediment CaCO3 (%), and a concomitant decline in the total organic carbon (TOC; %). The high abundance of low surface water productivity species F. profunda and Umbellosphaera irregularis indicates a stratified water column with a deeper nutricline, probably caused by the reduced upwelling intensity. This condition was corroborated by the decrease in CaCO3 (%) and an increase in TOC (%). We propose that the modern day high productivity conditions off Zamboanga Peninsula started at 2500 years B.P., whereas the low productivity off Panay Island was recorded from 4000 years B.P., and persists to the present day. Evidence of the Younger Dryas (YD) event was recorded from 11,100 to 10,400 years B.P. in UGC12, synchronous to the YD event reported from other areas in the Northern Hemisphere, and in accordance with the timing in the Sulu Sea as reported from previous studies in this region. This event in the Sulu Sea is characterized by a decrease in total nannofossil abundance and estimated primary productivity, together with an increase in CaCO3 (%) and a decrease in TOC (%). We interpreted that dilution caused by the increase in precipitation experienced in the Southeast Asian region during the YD event could have led to the decline of the total calcareous nannofossils whereas the recorded increase in CaCO3 (%) is attributed to the high abundance of planktonic foraminifera during this interval.
Keywords: arabian sea; EAST-ASIAN MONSOON; GLOBAL YOUNGER-DRYAS; indian-ocean; last deglaciation; OCEANIC PRIMARY PRODUCTION; south china sea; surface sediments; UPWELLING SYSTEM; YR BP

Linear decline in red snapper (Lutjanus campechanus) otolith Δ14C extends the utility of the bomb radiocarbon chronometer for fish age validation in the Northern Gulf of Mexico - Barnett, Beverly K; Thornton, Laura; Allman, Robert; Chanton, Jeffrey P; Patterson, William F (ICES Journal of Marine Science, 2018)
Radiocarbon (D14C) was analyzed in northern Gulf of Mexico (nGOM) red snapper (Lutjanus campechanus) otolith cores (n¼23), otolith edge samples (n¼12), and whole age-0 otoliths (n¼9), with edge samples and whole age-0 otoliths constituting known-age samples. There was no significant difference in the linear relationship of D14C versus year of formation between regional corals and known-age otolith samples, and a linear regression fit to the combined data from 1980 to 2015 extends the utility of the bomb radiocarbon chronometer for age validation. The entire regional coral and known-age otolith data set (1940 to 2015) was then utilized as a reference series to validate otolith-derived red snapper age estimates for cored otolith samples. A loess regression was fit to the reference data and then the sum of squared residuals (SSR) was computed from predicted versus observed birth years for cored adult otolith samples. This process was then repeated for ages biased 61–4 years. Ages with no bias applied had the lowest SSR, thus validating red snapper age estimates and demonstrating the utility of the combined regional coral and known-age red snapper otolith D14C time series for age validation of nGOM marine fishes.
Keywords: Age validation; otoliths; radiocarbon; red snapper

Longitudinal discontinuities in riverine greenhouse gas dynamics generated by dams and urban wastewater - Jin, Hyojin; Yoon, Tae Kyung; Begum, Most Shirina; Lee, Eun-Ju; Oh, Neung-Hwan; Kang, Namgoo; Park, Ji-Hyung (Biogeosciences, 2018)
Surface water concentrations of CO2, CH4, and N2O have rarely been measured simultaneously in river systems modified by human activities, contributing to large uncertainties in estimating global riverine emissions of greenhouse gases (GHGs). Basin-wide surveys of the three GHGs were combined with a small number of measurements of C isotope ratios in dissolved organic matter (DOM), CO2, and CH4 in the Han River basin, South Korea, to examine how longitudinal patterns of the three gases and DOM are affected by four cascade dams along a middle section of the North Han River (hereafter termed “middle reach”) and treated wastewater discharged to the lower Han River (“lower reach”) traversing the Seoul metropolitan area. Monthly monitoring and two-season comparison were conducted at 6 and 15 sites, respectively, to measure surface water gas concentrations and ancillary water quality parameters including concentrations of dissolved organic carbon (DOC) and optical properties of DOM. The basin-wide surveys were complemented with a sampling cruise along the lower reach and synoptic samplings along an urban tributary delivering effluents from a large wastewater treatment plant (WWTP) to the lower reach. The levels of pCO2 were relatively low in the middle reach (51–2465 µatm), particularly at the four dam sites (51–761 µatm), compared with those found in the largely forested upper basin with scattered patches of croplands (163–2539 µatm), the lower reach (78–11298 µatm), and three urban tributaries (2120–11970 µatm). The upper and middle reaches displayed generally low concentration ranges of CH4 and N2O, with some local peaks influenced by agricultural runoff and impoundments. By comparison, the lower reach exhibited exceptionally high concentrations of CH4 (1.2–15766 nmol L−1) and N2O (7.5–1396 nmol L−1), which were significantly correlated with different sets of variables such as DO and PO3−4 for CH4 and NH+4 and NO−3 for N2O. Downriver increases in the levels of DOC and optical properties such as fluorescence index (FI) and protein-like fluorescence indicated an increasing DOM fraction of anthropogenic and microbial origin. The concentrations of the three GHGs and DOC were similar in magnitude and temporal variation at a WWTP discharge and the receiving tributary, indicating a disproportionate contribution of the WWTP effluents to the tributary gas and DOC exports to the lower reach. The values of δ13C in surface water CO2 and CH4 measured during the sampling cruise along the lower reach, combined with δ13C and Δ14C in DOM sampled across the basin, implied a strong influence of the wastewater-derived gases and aged DOM delivered by the urban tributaries. The downstream enrichment of 13C in CO2 and CH4 suggested that the spatial distribution of these gases across the eutrophic lower reach may also be constrained by multiple concomitant processes including outgassing, photosynthesis, and CH4 oxidation. The overall results suggest that dams and urban wastewater may create longitudinal discontinuities in riverine metabolic processes leading to large spatial variations in the three GHGs correlating with different combinations of DOM properties and nutrients. Further research is required to evaluate the relative contributions of anthropogenic and in-stream sources of the three gases and DOM in eutrophic urbanized river systems and constrain key factors for the contrasting impoundment effects such as autotrophy-driven decreases in pCO2 and in-lake production of CH4 and N2O.

A long-term decrease in the persistence of soil carbon caused by ancient Maya land use - Douglas, Peter M. J.; Pagani, Mark; Eglinton, Timothy I.; Brenner, Mark; Curtis, Jason H.; Breckenridge, Andy; Johnston, Kevin (Nature Geoscience, 2018)
The long-term effects of deforestation on tropical forest soil carbon reservoirs are important for estimating the consequences of land use on the global carbon cycle, but are poorly understood. The Maya Lowlands of Mexico and Guatemala provide a unique opportunity to assess this question, given the widespread deforestation by the ancient Maya that began ~4,000 years ago. Here, we compare radiocarbon ages of plant waxes and macrofossils in sediment cores from three lakes in the Maya Lowlands to record past changes in the mean soil transit time of plant waxes (MTTwax). MTTwax indicates the average age of plant waxes that are transported from soils to lake sediments, and comparison of radiocarbon data from soils and lake sediments within the same catchment indicates that MTTwax reflects the age of carbon in deep soils. All three sediment cores showed a decrease in MTTwax, ranging from 2,300 to 800 years, over the past 3,500 years. This decrease in MTTwax, indicating shorter storage times for carbon in lake catchment soils, is associated with evidence for ancient Maya deforestation. MTTwax never recovered to pre-deforestation values, despite subsequent reforestation, implying that current tropical deforestation will have long-lasting effects on soil carbon sinks.

Maar sediment in central Vietnam Highland near Pleiku: An archive of regional monsoon intensity? - Schimmelmann, A., H.; Nguyễn-Văn, D.; Nguyễn-Thùy, J.P.; Schimmelmann, A.E.K.; Ojala, N.; Nguyễn-Ánh, Q.; Trọng Đỗ, D.; Thùy Nguyễn, P.; Hòa Tạ, V.; Huỳnh-Kim, N.; Quỳnh Phạm-Nữ, B.; Zolitschka, I. (2018)
Keywords: flood layer; land use; monsoon

Mangrove sediment carbon stocks along an elevation gradient: Influence of the late Holocene marine regression (New Caledonia) - Jacotot, Adrien; Marchand, Cyril; Rosenheim, Brad E.; Domack, Eugene W.; Allenbach, Michel (Marine Geology, 2018)
Among blue carbon ecosystems, mangroves are very efficient in storing carbon in their sediments over decadal to millennial time scales. However, this ability varies with numerous parameters, including climate and sea-level variations. In New Caledonia, mangrove ecosystems develop in semi-arid conditions with a typical zonation: Rhizophora spp. colonize the seaward side of the intertidal area, while Avicennia marina develops at higher elevations, just below the salt-flat. Within this context, we determined both the quantity (organic carbon content and carbon stocks) and the characteristics (carbon over nitrogen ratios (C/N), stable carbon and nitrogen isotopes, radiocarbon age) of the organic matter stored beneath each mangrove stands. Carbon stocks were determined down to different limits with depth: approximate extension of the root systems, one-meter depth, and the hard substrate. Within the extension of the root systems, the sediment carbon stock was lower than 100 MgC ha−1 regardless of the mangrove species. This low value resulted directly from the dry climate that limits mangrove productivity. At depth beneath every zone, a buried layer enriched in mangrove-derived organic matter, with C/N values around 40 and δ13C values around −26‰ was observed. This layer likely resulted from a sea-level high stand during the late Holocene that allowed a long period of stability of the mangrove, slowly accumulating organic matter within the sediment. In this buried layer, the carbon stock was higher than in the upper sediment and reached up to 665, 255 and 300 MgC ha−1 in the salt-flat zone, the A. marina stand and the R. spp. stand, respectively. The highest stock, determined beneath the salt-flat, was suggested to be related to a period of sea-level stability that lasted ~3000 years, whereas beneath the other zones, which are at lower elevations, mangrove colonization was more recent and the sea-level was continuously decreasing till recently. Sea-level variations, and, specifically current sea-level rise, may strongly influence mangrove development due to their migration along the tidal elevation gradient to maintain the biotic conditions needed for their development.
Keywords: Blue carbon; carbon isotopes; carbon sequestration; Coastal wetlands; Sea-level change; Semi-arid mangrove forest

Menardiiform planktonic foraminifera stratigraphy from Middle Pleistocene to Holocene in the Western South Atlantic - Costa, Karen Badaraco; Camillo Jr, Edmundo; Santarosa, Ana Cláudia Aoki; Iwai, Fabiane Sayuri; Quadros, Juliana Pereira de; Leipnitz, Itamar Ivo; Toledo, Felipe Antonio de Lima (REVISTA BRASILEIRA DE PALEONTOLOGIA, 2018)
We studied the Middle Pleistocene to Holocene menardiiform planktonic foraminifera (MPF) stratigraphy in six continuous deep-sea sediment cores recovered from the Brazilian continental slope to evaluate its use in climatic characterization and as a reliable biostratigraphic tool in the western South Atlantic. For this purpose, an important issue was to construct a robust local biochronological framework for the past 772 ky in the western South Atlantic (Santos Basin). The oxygen isotope chronostratigraphic control allowed us to recalibrate the MPF events in the Santos Basin and identify diachronous bioevents. The bio-horizons found in the Santos Basin, such as the V/W and T/U (bio)zone boundaries, were found in a different chronostratigraphic position compared to previous studies. Results indicate that typical cyclic disappearances and reappearances of the MPF are not synchronous throughout the Atlantic Ocean and should not be employed for ‘climatic zonation’. This asynchronous evidence also provides information on the timing of the mechanisms responsible for the proliferation of these species throughout the Atlantic Ocean. Therefore, we strongly recommend that a local biochronological framework should be used for inter-basin comparisons and also accumulation rate estimates, both for paleoclimatic studies and continental slope geohazard assessment. © 2018, Sociedade Brasileira de Paleontologia. All rights reserved.

Microbial decomposition of marine dissolved organic matter in cool oceanic crust - Shah Walter, Sunita R.; Jaekel, Ulrike; Osterholz, Helena; Fisher, Andrew T.; Huber, Julie A.; Pearson, Ann; Dittmar, Thorsten; Girguis, Peter R. (Nature Geoscience, 2018)
Marine dissolved organic carbon (DOC) is one of the largest active reservoirs of reduced carbon on Earth. In the deep ocean, DOC has been described as biologically recalcitrant and has a radiocarbon age of 4,000 to 6,000 years, which far exceeds the timescale of ocean overturning. However, abiotic removal mechanisms cannot account for the full magnitude of deep-ocean DOC loss. Deep-ocean water circulates at low temperatures through volcanic crust on ridge flanks, but little is known about the associated biogeochemical processes and carbon cycling. Here we present analyses of DOC in fluids from two borehole observatories installed in crustal rocks west of the Mid-Atlantic Ridge, and show that deep-ocean DOC is removed from these cool circulating fluids. The removal mechanism is isotopically selective and causes a shift in specific features of molecular composition, consistent with microbe-mediated oxidation. We suggest organic molecules with an average radiocarbon age of 3,200 years are bioavailable to crustal microbes, and that this removal mechanism may account for at least 5% of the global loss of DOC in the deep ocean. Cool crustal circulation probably contributes to maintaining the deep ocean as a reservoir of 'aged' and refractory DOC by discharging the surviving organic carbon constituents that are molecularly degraded and depleted in C-14 and C-13 into the deep ocean.
Keywords: carbon; community; deep-ocean; DISTINCT; extraction; fluid-flow; HEAT; MID-ATLANTIC RIDGE; SEAWATER; WESTERN FLANK

Microbial oxidation of lithospheric organic carbon in rapidly eroding tropical mountain soils - Hemingway, Jordon D.; Hilton, Robert G.; Hovius, Niels; Eglinton, Timothy I.; Haghipour, Negar; Wacker, Lukas; Chen, Meng-Chiang; Galy, Valier V. (Science, 2018)
Lithospheric organic carbon (“petrogenic”; OCpetro) is oxidized during exhumation and subsequent erosion of mountain ranges. This process is a considerable source of carbon dioxide (CO2) to the atmosphere over geologic time scales, but the mechanisms that govern oxidation rates in mountain landscapes are poorly constrained. We demonstrate that, on average, 67 ± 11% of the OCpetro initially present in bedrock exhumed from the tropical, rapidly eroding Central Range of Taiwan is oxidized in soils, leading to CO2 emissions of 6.1 to 18.6 metric tons of carbon per square kilometer per year. The molecular and isotopic evolution of bulk OC and lipid biomarkers during soil formation reveals that OCpetro remineralization is microbially mediated. Rapid oxidation in mountain soils drives CO2 emission fluxes that increase with erosion rate, thereby counteracting CO2 drawdown by silicate weathering and biospheric OC burial.

Millennial-scale variations in dustiness recorded in Mid-Atlantic sediments from 0 to 70 ka - Middleton, Jennifer L.; Mukhopadhyay, Sujoy; Langmuir, Charles H.; McManus, Jerry F.; Huybers, Peter J. (Earth and Planetary Science Letters, 2018)
Sedimentary records of dust deposition in the subtropical Atlantic provide important constraints on millennial- and orbital-scale variability in atmospheric circulation and North African aridity. Constant flux proxies, such as extraterrestrial helium-3, yield dust flux records that are independent of the biases caused by lateral sediment transport and limited resolution that may be associated with age-model-derived mass accumulation rates. However, Atlantic dust records constrained using constant flux proxies are sparsely distributed and generally limited to the past 20 ka. Here we extend the Atlantic record of North African dust deposition to 70 ka using extraterrestrial helium-3 and measurements of titanium, thorium, and terrigenous helium-4 in two sediment cores collected at 26°N and 29°N on the Mid-Atlantic Ridge and compare results to model estimates for dust deposition in the subtropical North Atlantic. Dust proxy fluxes between 26°N and 29°N are well correlated, despite variability in lateral sediment transport, and underscore the utility of extraterrestrial helium-3 for constraining millennial-scale variability in dust deposition. Similarities between Mid-Atlantic dust flux trends and those observed along the Northwest African margin corroborate previous interpretations of dust flux variability over the past 20 ka and suggest that long distance transport and depositional processes do not overly obscure the signal of North African dust emissions. The 70 ka Mid-Atlantic record reveals a slight increase in North African dustiness from Marine Isotope Stage 4 through the Last Glacial Maximum and a dramatic decrease in dustiness associated with the African Humid Period. On the millennial-scale, the new records exhibit brief dust maxima coincident with North Atlantic cold periods such as the Younger Dryas, and multiple Heinrich Stadials. The correlation between Mid-Atlantic dust fluxes and previous constraints on North African aridity is high. However, precipitation exerts less control on dust flux variability prior to the African Humid Period, when wind variability governs dust emissions from consistently dry dust source regions. Thus, the Mid-Atlantic dust record supports the hypothesis that both aridity and wind strength drive dust flux variability across changing climatic conditions.
Keywords: helium-3; mass accumulation rate; mineral dust; North Africa; Subtropical North Atlantic; thorium-232

Organic Carbon Aging During Across‐Shelf Transport - Bao, Rui; Uchida, Masao; Zhao, Meixun; Haghipour, Negar; Montlucon, Daniel; McNichol, Ann; Wacker, Lukas; Hayes, John M.; Eglinton, Timothy I. (Geophysical Research Letters, 2018)
Compound-specific radiocarbon analysis (CSRA) was performed on different grain-size fractions of surficial sediments to examine and compare lateral transport times (LTTs) of organic carbon. 14C aging of long-chain leaf wax fatty acids along two dispersal pathways of fluvially-derived material on adjacent continental margins implies LTTs over distances of ~30 to 500 km that range from hundreds to thousands of years. The magnitude of aging differs among grain size fractions. Our finding suggests that LTTs vary both temporally and spatially as a function of the specific properties of different continental shelf settings. Observations suggest that 14C aging is widespread during lateral transport over continental shelves, with hydrodynamic particle sorting inducing age variations among organic components residing in different grain sizes. Consideration of these phenomena is of importance for understanding carbon cycle processes and interpretation on sedimentary records on continental margins.

Organic matter sources and lateral sedimentation in a Bahamian karst basin (sinkhole) over the late Holocene: Influence of local vegetation and climate - Tamalavage, Anne E.; van Hengstum, Peter J.; Louchouarn, Patrick; Molodtsov, Sergey; Kaiser, Karl; Donnelly, Jeffrey P.; Albury, Nancy A.; Fall, Patricia L. (Palaeogeography, Palaeoclimatology, Palaeoecology, 2018)
Karst basins (e.g., blueholes, sinkholes) accumulate well-preserved sedimentary successions that provide transformative paleoclimatic and paleoenvironmental information. However, the sedimentary processes within these basins are not yet fully understood. Here we present stable carbon isotopic values (δ13Corg) and C:N ratios of bulk organic matter in well-dated sediment cores from Blackwood Sinkhole (Abaco, The Bahamas) to investigate the changing flux of organic matter into the sinkhole during the late Holocene. The provenance of preserved organic matter changed through the late Holocene between three primary sources, as determined by three-endmember mixing modeling: wetland organic matter from the adjacent epikarst surface, authigenic primary productivity in the oligohaline meteoric lens, and terrestrial organic matter from the surrounding landscape. Expansion of wetlands on the adjacent epikarst surface played a critical role by increasing the flux of wetland organic matter to the sinkhole, especially during the last 1000 years. Hurricanes and regional rainfall may have mediated organic matter delivery to the benthos, either through hampering wetland development (prior to 1000 cal yr BP) or by changing dissolved nutrient concentrations available in the basin for primary producers. These results demonstrate that organic matter provenance in karst basins is not constant through time, and is significantly dependent upon both landscape vegetation on the epikarst surface and changing hydrographic conditions that impacts nutrient availability to primary producers.
Keywords: Caribbean; Karst; Mixing model; Stable isotopes; Subtropical landscape

Paleoceanography of northeastern Fram Strait since the last glacial maximum: Palynological evidence of large amplitude changes - Falardeau, Jade; de Vernal, Anne; Spielhagen, Robert F. (Quaternary Science Reviews, 2018)
Sea-surface conditions in northeastern Fram Strait since the last glacial maximum (LGM) were reconstructed from cores MSM5/5-712-2 and PS2863/1-2 based on palynological assemblages, ecological preferences of dinocysts and application of the modern analog technique. Dinocyst in LGM sediments are sparse, but their assemblages reflect mild summer conditions. Given the regional context and evidence from other tracers, the dinocyst assemblages of the LGM could relate to regional fluxes of dinocysts during exceptional mild summers. From 19 to 14.7 ka, dinocyst data suggest very cold conditions with extensive sea-ice cover, while abundant reworked palynomorphs indicate intense glacial erosion. An abrupt transition at 14.7-14.5 ka was marked by a peak in summer temperatures coinciding with a rapidly deposited sediment layer related to a regional meltwater plume event in western Svalbard. From 14.7 to 12.6 ka, large seasonal temperature contrasts with mild summers and cold winters together with low salinity indicate continuous melting of the Svalbard Barents Sea ice sheet fostered by warm climate. At 12.6 ka, the regional onset of the Younger Dryas was marked by cooling and increased salinity. On a regional scale, the 12.6-12 ka interval corresponds to an important transition involving enhanced circulation of Arctic waters around Svalbard and establishment of coastal fronts along its northern and western margins. Modern-like oceanic conditions with relatively high salinity and low seasonal temperature contrast developed at about 7.6 ka. Since then, a slight cooling is observed, especially in winter. This study offers a comprehensive picture of the deglacial phases in eastern Fram Strait with unique data on the sea surface salinity, which controls surface water stratification and plays an important role in ocean circulation. (C) 2018 Elsevier Ltd. All rights reserved.

Paleomagnetism and rock magnetism from sediments along a continental shelf-to-slope transect in the NW Barents Sea: Implications for geomagnetic and depositional changes during the past 15 thousand years - Caricchi, C.; Lucchi, R.G.; Sagnotti, L.; MacrÌ, P.; Morigi, C.; Melis, R.; Caffau, M.; Rebesco, M.; Hanebuth, T.J.J. (Global and Planetary Change, 2018)
Paleomagnetic and rock magnetic data were measured on glaciomarine silty-clay successions along an E-W sediment-core transect across the continental shelf and slope of the Kveithola paleo-ice stream system (south of Svalbard, north-western Barents Sea), representing a stratigraphic interval spanning the last deglaciation and the Holocene. The records indicate that magnetite is the main magnetic mineral and that magnetic minerals are distinctly less abundant on the shelf than at the continental slope. The paleomagnetic properties allow for the reconstruction of a well-defined characteristic remanent magnetization (ChRM) throughout the sedimentary successions. The stratigraphic trends of rock magnetic and paleomagnetic parameters are used for a shelf-slope core correlation and sediment facies analysis is applied for depositional processes reconstruction. The new paleomagnetic records compare to the PSV and RPI variation predicted for the core sites by a simulation using the global geomagnetic field variation models SHA.DIF.14k and CALS7K.2 and closest PSV and RPI regional stack curves. The elaborated dataset, corroborated by available 14C ages, provides a fundamental chronological framework to constrain the coupling of shelf-slope sedimentary processes and environmental changes in the NW Barents Sea region during and after deglaciation.
Keywords: Barents Sea; Kveithola glacial trough; Paleomagnetism; Rock magnetism

Paleoseismic Results from the Alpine Site, Wasatch Fault Zone: Timing and Displacement Data for Six Holocene Earthquakes at the Salt Lake City–Provo Segment Boundary - Bennett, S. E. K.; DuRoss, C. B.; Gold, R. D.; Briggs, R. W.; Personius, S. F.; Reitman, N. G.; Devore, J. R.; Hiscock, A. I.; Mahan, S. A.; Gray, H. J.; Gunnarson, S.; Stephenson, W. J.; et al. (Bulletin of the Seismological Society of America, 2018)
To improve the characterization of Holocene earthquakes on the Wasatch fault zone (WFZ), we conducted light detection and ranging (lidar)‐based neotectonic mapping and excavated a paleoseismic trench across an 8‐m‐high fault scarp near Alpine, Utah, located <1  km south of the boundary between the Salt Lake City and Provo segments (SLCS and PS). We document evidence for six paleoearthquakes (AL6–AL1) from scarp‐derived colluvial wedges and crosscutting relations. A ground‐penetrating radar survey across the scarp resolved fault‐zone width, but not paleoearthquake stratigraphy. Bayesian (OxCal) modeling of 13 radiocarbon and 13 optically stimulated luminescence ages indicates that six earthquakes occurred ∼6.2–0.4  ka. Interseismic recurrence ranges from 0.2 to 1.8 ky (mean 1.2 ky). We estimate 6.5±0.7  m of cumulative vertical tectonic displacement across the ≥14‐m‐wide fault zone used near‐field observations of scarp‐derived colluvial‐wedge thicknesses, antithetic faulting, and graben backtilting. This is similar to our independent estimate of 6.5±0.5  m using far‐field observations of the offset ground surface and correlation of alluvial‐fan stratigraphy across the WFZ. These results suggest that colluvial‐wedge thickness at the Alpine site approximates one‐half the original west‐facing fault scarp height. Per‐event vertical displacements range from 0.8 to 1.2 m (mean 1.1 m), which we use to estimate surface rupture lengths that may exceed 50 km from earthquakes as large as moment magnitude (Mw) ∼7.0. The late Holocene average vertical slip rate is 0.9  mm/yr (0.7–1.2  mm/yr range). Earthquake frequency has increased in the past ∼1  ky, whereas displacement per event has been similar for the past ∼6  ky, suggesting that strain accumulation is not the sole factor that controls the frequency and size of earthquakes at the SLCS–PS segment boundary. These findings can be used for a more nuanced characterization of earthquakes at the SLCS–PS boundary and improve earthquake hazard assessments along the Wasatch Front.

The Potential Impact of Hydrocarbons on Mussels in Port au Port Bay, Newfoundland - Cook, Melissa C.; May, Adam; Kohl, Lucas; Van Biesen, Geert; Parrish, Christopher C.; Morrill, Penny L. (Elsevier, 2018)
Since 2012, the scallop fishery in Port au Port Bay, Newfoundland, Canada has experienced a drastic decline, while no decline was observed in adjacent St. George's Bay. Local fishermen have raised concerns about an abandoned oil exploration well in the Port au Port Bay. This study investigated the potential impact of petroleum hydrocarbons on sediments and blue mussels [Mytilus edulis] (a proxy organism for scallops) in the area. Sediments from both bays were characterized for their hydrocarbons and compared to potential petroleum hydrocarbon sources. Mussels were analysed for health indices and their 14C content. The results showed that the concentration of hydrocarbons found in the sediments of the fishing ground was within the range of unpolluted marine sediments and that the hydrocarbons present were likely from a mixture of sources. The health indices of the mussels in Port au Port Bay were similar to the health indices of mussels in St. George's Bay and the 14C content of the mussels from both bays was modern. These data suggest that the Port au Port fishing ground was not solely contaminated from crude oil leaking from an oil exploration well, that the mussels were not contaminated with petroleum hydrocarbons, and that Port au Port mussels were just as healthy as the mussels of St. George's Bay. Therefore, whatever caused the scallop decline was most likely scallop- and bay-specific. During this study a fast and efficient method for extracting petroleum hydrocarbons from sediment using accelerated solvent extraction with integrated silica gel was developed.
Keywords: Health indices; Hydrocarbon contamination; Mussels; Petroleum; Scallops

Pronounced summer warming in northwest Greenland during the Holocene and Last Interglacial - McFarlin, Jamie M.; Axford, Yarrow; Osburn, Magdalena R.; Kelly, Meredith A.; Osterberg, Erich C.; Farnsworth, Lauren B. (Proceedings of the National Academy of Sciences, 2018)
Projections of future rates of mass loss from the Greenland Ice Sheet are highly uncertain because its sensitivity to warming is unclear. Geologic reconstructions of Quaternary interglacials can illustrate how the ice sheet responded during past warm periods, providing insights into ice sheet behavior and important tests for data-model comparisons. However, paleoclimate records from Greenland are limited: Early Holocene peak warmth has been quantified at only a few sites, and terrestrial sedimentary records of prior interglacials are exceptionally rare due to glacial erosion during the last glacial period. Here, we discuss findings from a lacustrine archive that records both the Holocene and the Last Interglacial (LIG) from Greenland, allowing for direct comparison between two interglacials. Sedimentary chironomid assemblages indicate peak July temperatures 4.0 to 7.0 °C warmer than modern during the Early Holocene maximum in summer insolation. Chaoborus and chironomids in LIG sediments indicate July temperatures at least 5.5 to 8.5 °C warmer than modern. These estimates indicate pronounced warming in northwest Greenland during both interglacials. This helps explain dramatic ice sheet thinning at Camp Century in northwest Greenland during the Early Holocene and, for the LIG, aligns with controversial estimates of Eemian warming from ice core data retrieved in northern Greenland. Converging geologic evidence for strong LIG warming is challenging to reconcile with inferred Greenland Ice Sheet extent during the LIG, and the two appear incompatible in many models of ice sheet evolution. An increase in LIG snowfall could help resolve this problem, pointing to the need for hydroclimate reconstructions from the region.

Quaternary Glaciation of the Great Lakes Region: Process, Landforms, Sediments, and ChronologyMinimum age of the Mapleton, Tully, and Labrador Hollow moraines indicates correlation with the Port Huron Phase in central New York State - Kehew, Alan E.; Curry, B. Brandon; Kozlowski, Andrew L.; Bird, Brian C.; Lowell, Thomas V.; Smith, Colby A.; Feranec, Robert S.; Graham, Brandon Lars (Geological Society of America, 2018)
The glaciated terrain along the northern edge of the Appalachian Plateau in the eastern Finger Lakes of central New York has long been recognized as an important location for meltwater routing and for proglacial lake development in the Great Lakes region. Despite recognition of multiple ice margins formed by the Ontario Lobe of the Laurentide ice sheet during the late Wisconsinan, numerical age control of several margins has been elusive, particularly in regard to regional readvances of the Port Bruce (ca. 16,980–18,000 cal [calibrated] yr B.P.) and Port Huron (ca. 14,300– 16,000 cal yr B.P.) Phases. Utilizing light detection and ranging (LiDAR) terrain models in the eastern Finger Lakes area, we identified and described the Mapleton, Tully, and Labrador Hollow moraines. Associated ice-marginal landforms include push moraines, fans, and hummocky topography. In places, these features intrude into the northern heads of through valleys. Coring of three basins directly associated with these landforms yielded more than 20 samples of boreal tree needles and twigs, and Dryas leaves. Accelerated mass spectrometry (AMS) radiocarbon assay results indicate that poststadial lacustrine sedimentation began at ca. 15,000 cal yr B.P., consistent with ages of the Port Huron Phase.

Radiocarbon and Stable Isotope Evidence for Changes in Sediment Mixing in the North Pacific over the Past 30 kyrAbstract - Costa, Kassandra M; McManus, Jerry F; Anderson, Robert F (Radiocarbon, 2018)
Deep-sea sediment mixing by bioturbation is ubiquitous on the seafloor, and it can be an important influence on the fidelity of paleoceanographic records. Bioturbation can be difficult to quantify, especially in the past, but diffusive models based on radioactive tracer profiles have provided a relatively successful approach. However, a singular, constant mixing regime is unlikely to prevail in a region where dynamic oceanographic changes in the bottom water environment are a consequence of paleoclimatic variability. In this study, foraminiferal stable isotopes, radiocarbon (14C) dating, and 230Th fluxes are utilized to understand the sediment mixing history in the easternmost region of the North Pacific. In the uppermost sediment, a 12,000-yr offset between planktonic foraminifera species N. incompta and G. bulloides is observed that coincides with age plateaus at 2000–2500 yr for N. incompta and 15,000–16,000 yr for G. bulloides despite coincident glacial-interglacial shifts in δ18O of benthic species. These age plateaus, particularly for G. bulloides, are a result of changing foraminiferal abundance related to assemblage shifts and carbonate preservation changes since the last glacial period, providing a window into the extent of mixing in the past. The 14C and stable isotope results can be simulated using an iterative model that couples these changes in foraminiferal abundance with variability in mixing depth over time. The best-fit model output suggests that the deepest, or most intense, mixing of the past 30,000 yr (30 kyr) may have occurred during the Holocene. Even though changes in mixing affect the 14C and δ18O of planktonic species that have dramatically varying abundance, substantial age control is nevertheless provided by δ18O measurements on the more consistently abundant benthic foraminifera Uvigerina, thus allowing the construction of a reliable chronology for these cores.
Keywords: bioturbation; north pacific; radiocarbon; Stable isotopes

Radiocarbon, Cesium-137, Grain Size, and X-ray Fluorescence Data for Tsunami Geology Investigation, Driftwood Bay, Umnak Island, Alaska (2018) - Witter, Rob; Gelfenbaum, Guy; Corbett, Reide; Tam, Angela; La Selle, SeanPaul (Alaska Science Center, U.S. Geological Survey, 2018)
These files provide the complete data release for the paper entitled, "Frequent large tsunamis spanned locked/creeping parts of the Aleutian megathrust." The data set consists of nine tables that include radiocarbon dates, cesium-137 activity, grain size measurements, and scanning X-ray fluorescence element intensity counts.

Radiocarbon Content of Dissolved Organic Carbon in the South Indian Ocean - Bercovici, S. K.; McNichol, A. P.; Xu, L.; Hansell, D. A. (Geophysical Research Letters, 2018)
We report four profiles of the radiocarbon content of dissolved organic carbon (DOC) spanning the South Indian Ocean (SIO), ranging from the Polar Front (56°S) to the subtropics (29°S). Surface waters held mean DOC Δ14C values of −426 ± 6‰ (~4,400 14C years) at the Polar Front and DOC Δ14C values of −252 ± 22‰ (~2,000 14C years) in the subtropics. At depth, Circumpolar Deep Waters held DOC Δ14C values of −491 ± 13‰ (~5,400 years), while values in Indian Deep Water were more depleted, holding DOC Δ14C values of −503 ± 8‰ (~5,600 14C years). High‐salinity North Atlantic Deep Water intruding into the deep SIO had a distinctly less depleted DOC Δ14C value of −481 ± 8‰ (~5,100 14C years). We use multiple linear regression to assess the dynamics of DOC Δ14C values in the deep Indian Ocean, finding that their distribution is characteristic of water masses in that region.
Keywords: dissolved organic carbon; indian ocean; radiocarbon

Radiocarbon dating of the old ash of Aiton, Romania - Patrut, Adrian; Patrut, Roxana T.; Rakosy, Laszlo; Ratiu, Ileana-Andreea; Lowy, Daniel A.; Bodis, Jenő; von Reden, Karl F. (Studia Universitatis Babeș-Bolyai Chemia, 2018)
The article reports the AMS (accelerator mass spectrometry) radiocarbon investigation results of the old common ash of Aiton. Five wood samples were collected from the trunk of the tree. The deepest ends of the samples were analysed by AMS radiocarbon. We found radiocarbon dates between 165 ± 20 BP and 240 ± 18 BP, which correspond to calibrated ages of 230 – 360 years. These results, combined with a ring counting estimate, indicate an age of 330 ± 30 years for the ash of Aiton. By this value, the ash of Aiton becomes the oldest known common ash with accurate dating results. © 2018, Universitatea Babes-Bolyai, Catedra de Filosofie Sistematica. All rights reserved.

Rapid precipitation changes in the tropical West Pacific linked to North Atlantic climate forcing during the last deglaciation - Xiong, Zhifang; Li, Tiegang; Chang, Fengming; Algeo, Thomas J.; Clift, Peter D.; Bretschneider, Lisa; Lu, Zhengyao; Zhu, Xiao; Frank, Martin; Sauer, Peter E.; Jiang, FuQing; Wan, Shiming; et al. (Quaternary Science Reviews, 2018)
The cause of rapid hydrological changes in the tropical West Pacific during the last deglaciation remains controversial. In order to test whether these changes were triggered by abrupt climate change events in the North Atlantic Ocean, variations in precipitation during the last deglaciation (18-10 ka) were extracted from proxy records of chemical weathering and terrigenous input in the western Philippine Sea (WPS). The evolution of chemical weathering and terrigenous input since 27 ka was reconstructed using the chemical index of alteration (CIA), elemental ratios (K/Al, TOC/TN and Ti/Ca), δ13Corg, terrigenous fraction abundance and flux data from International Marine Global Change Study Program (IMAGES) core MD06-3054 collected on the upper continental slope of eastern Luzon (northern Philippines). Sediment deposited during the Last Glacial Maximum (LGM) shows weathering equal to or slightly greater than Holocene sediment in the WPS. This unusual state of chemical weathering, which is inconsistent with lower air temperatures and decreased precipitation in Luzon during the LGM, may be due to reworking of poorly consolidated sediments on the eastern Luzon continental shelf during the LGM sea-level lowstand. Rapid changes in chemical weathering, characterized by higher intensity during the Heinrich event 1 (H1) and Younger Dryas (YD) and lower intensity during the Bølling-Allerød (B/A), were linked to rapid variations in precipitation in the WPS during the last deglaciation. The higher terrigenous inputs during the LGM relative to those of the Holocene were controlled by sea-level changes rather than precipitation. The terrigenous inputs show a long-term decline during the last deglaciation, punctuated by brief spikes during the H1 and YD related to sea-level rises and rapid precipitation changes in the WPS, respectively. The proxy records of chemical weathering and terrigenous input from eastern Luzon suggest high rainfall during the H1 and YD events, consistent with inferred rainfall patterns based on Fe/Ca records from offshore Mindanao. Rapid precipitation changes in the WPS did not coincide with migrations of the Intertropical Convergence Zone (ITCZ) but, rather, were related to state shifts of the El Niño-Southern Oscillation (ENSO) during the last deglaciation. Based on proxy records and modeling results, we argue that the Atlantic meridional overturning circulation (AMOC) controlled rapid precipitation changes in the tropical West Pacific through zonal shifts of ENSO or meridional migration of the ITCZ during the last deglaciation. Our findings highlight the dominant role of the North Atlantic Ocean in the tropical hydrologic cycle during the last deglaciation.
Keywords: AMOC; Chemical weathering; enso; ITCZ; Terrigenous input; Western Philippine Sea

Recent occupation by Adélie Penguins (Pygoscelis adeliae) at Hope Bay and Seymour Island and the ‘northern enigma’ in the Antarctic Peninsula - Emslie, Steven D.; McKenzie, Ashley; Marti, Lucas J.; Santos, Mercedes (Polar Biology, 2018)
We excavated active and abandoned Adélie Penguin (Pygoscelis adeliae) colonies at Seymour Island and Hope Bay, Antarctic Peninsula, to determine an occupation history for this species at these sites. Previous research at Hope Bay has indicated an occupation there since the middle Holocene, based on a sediment record from Lake Boeckella. Excavations revealed only shallow and relatively fresh ornithogenic soils in the active colonies at the two localities. At least 53 abandoned pebble mounds were located at Hope Bay of which nine were excavated and four were sampled by probing to recover organic remains to determine their age. Radiocarbon dating of egg membrane, feather, and bone from both sites revealed a young occupation dating to less than ~600 years after correcting for the marine carbon reservoir effect. The mismatch in the geologic record of Adélie Penguin occupation in the northern Antarctic Peninsula, including Lake Boeckella sediments and geologic deposits and lake sediments on King George Island, with more direct evidence of breeding colonies from ornithogenic soils from active and abandoned colonies is hereby referred to as the ‘northern enigma’ as it does not occur in other regions of Antarctica including the southern Antarctic Peninsula, East Antarctica, or the Ross Sea, where the penguin record extends to the early to middle Holocene and matches well with the geologic record of deglaciation and penguin occupation. As yet, there is no convincing explanation for the ‘northern enigma’.

Relative sea-level change in Newfoundland, Canada during the past ∼3000 years - Kemp, Andrew C.; Wright, Alexander J.; Edwards, Robin J.; Barnett, Robert L.; Brain, Matthew J.; Kopp, Robert E.; Cahill, Niamh; Horton, Benjamin P.; Charman, Dan J.; Hawkes, Andrea D.; Hill, Troy D.; van de Plassche, Orson (Quaternary Science Reviews, 2018)
Several processes contributing to coastal relative sea-level (RSL) change in the North Atlantic Ocean are observed and/or predicted to have distinctive spatial expressions that vary by latitude. To expand the latitudinal range of RSL records spanning the past ∼3000 years and the likelihood of recognizing the characteristic fingerprints of these processes, we reconstructed RSL at two sites (Big River and Placentia) in Newfoundland from salt-marsh sediment. Bayesian transfer functions established the height of former sea level from preserved assemblages of foraminifera and testate amoebae. Age-depth models constrained by radiocarbon dates and chronohorizons estimated the timing of sediment deposition. During the past ∼3000 years, RSL rose by ∼3.0 m at Big River and by ∼1.5 m at Placentia. A locally calibrated geotechnical model showed that post-depositional lowering through sediment compaction was minimal. To isolate and quantify contributions to RSL from global, regional linear, regional non-linear, and local-scale processes, we decomposed the new reconstructions (and those in an expanded, global database) using a spatio-temporal statistical model. The global component confirms that 20th century sea-level rise occurred at the fastest, century-scale rate in over 3000 years (P > 0.999). Distinguishing the contributions from local and regional non-linear processes is made challenging by a sparse network of reconstructions. However, only a small contribution from local-scale processes is necessary to reconcile RSL reconstructions and modeled RSL trends. We identified three latitudinally-organized groups of sites that share coherent regional non-linear trends and indicate that dynamic redistribution of ocean mass by currents and/or winds was likely an important driver of sea-level change in the North Atlantic Ocean during the past ∼3000 years.

Remobilization of old permafrost carbon to Chukchi Sea sediments during the end of the last deglaciation - Martens, Jannik; Wild, Birgit; Pearce, Christof; Tesi, Tommaso; Andersson, August; Broder, Lisa; O’Regan, Matt; Jakobsson, Martin; Sköld, Martin; Gemery, Laura; Cronin, Thomas M.; Semiletov, Igor; et al. (Global Biogeochemical Cycles, 2018)
Climate warming is expected to destabilize permafrost carbon (PF‐C) by thaw‐erosion and deepening of the seasonally thawed active layer and thereby promote PF‐C mineralization to CO2 and CH4. A similar PF‐C remobilization might have contributed to the increase in atmospheric CO2 during deglacial warming after the last glacial maximum. Using carbon isotopes and terrestrial biomarkers (Δ14C, δ13C, and lignin phenols), this study quantifies deposition of terrestrial carbon originating from permafrost in sediments from the Chukchi Sea (core SWERUS‐L2‐4‐PC1). The sediment core reconstructs remobilization of permafrost carbon during the late Allerød warm period starting at 13,000 cal years before present (BP), the Younger Dryas, and the early Holocene warming until 11,000 cal years BP and compares this period with the late Holocene, from 3,650 years BP until present. Dual‐carbon‐isotope‐based source apportionment demonstrates that Ice Complex Deposit—ice‐ and carbon‐rich permafrost from the late Pleistocene (also referred to as Yedoma)—was the dominant source of organic carbon (66 ± 8%; mean ± standard deviation) to sediments during the end of the deglaciation, with fluxes more than twice as high (8.0 ± 4.6 g·m−2·year−1) as in the late Holocene (3.1 ± 1.0 g·m−2·year−1). These results are consistent with late deglacial PF‐C remobilization observed in a Laptev Sea record, yet in contrast with PF‐C sources, which at that location were dominated by active layer material from the Lena River watershed. Release of dormant PF‐C from erosion of coastal permafrost during the end of the last deglaciation indicates vulnerability of Ice Complex Deposit in response to future warming and sea level changes.
Keywords: carbon isotope; climate change feedback; coastal erosion; Deglaciation; past carbon cycling; permafrost

Residential Coal Combustion as a Source of Levoglucosan in ChinaResidential Coal Combustion as a Source of Levoglucosan in China - Yan, Caiqing; Zheng, Mei; Sullivan, Amy P.; Shen, Guofeng; Chen, Yingjun; Wang, Shuxiao; Zhao, Bin; Cai, Siyi; Desyaterik, Yury; Li, Xiaoying; Zhou, Tian; Gustafsson, Örjan; et al. (Environmental Science & Technology, 2018)
Levoglucosan (LG) has been widely identified as a specific marker for biomass burning (BB) sources and frequently utilized in estimating the BB contribution to atmospheric fine particles all over the world. However, this study provides direct evidence to show that coal combustion (CC) is also a source of LG, especially in the wintertime in Northern China, based on both source testing and ambient measurement. Our results show that low-temperature residential CC could emit LG with emission factors (EF) ranging from 0.3 to 15.9 mg kg–1. Ratios of LG to its isomers, mannosan and galactosan, differ between CC and BB emissions, and the wintertime ratios in Beijing ambient PM2.5 and source-specific tracers including carbon isotopic signatures all indicated a significant contribution from CC to ambient levoglucosan in winter in Beijing. The results suggest that LG cannot be used as a distinct source marker for biomass burning in special cases such as some cities in the northern China, where coal is still widely used in the residential and industrial sectors. Biomass burning sources could be overestimated, although such an over-estimation could vary spatially and temporally.

The rise and fall of an ancient Adélie penguin ‘supercolony’ at Cape Adare, Antarctica - Emslie, Steven D.; McKenzie, Ashley; Patterson, William P. (Royal Society Open Science, 2018)
We report new discoveries and radiocarbon dates on active and abandoned Adélie penguin (Pygoscelis adeliae) colonies at Cape Adare, Antarctica. This colony, first established at approximately 2000 BP (calendar years before present, i.e. 1950), is currently the largest for this species with approximately 338 000 breeding pairs, most located on low-lying Ridley Beach. We hypothesize that this colony first formed after fast ice began blocking open-water access by breeding penguins to the Scott Coast in the southern Ross Sea during a cooling period also at approximately 2000 BP. Our results suggest that the new colony at Cape Adare continued to grow, expanding to a large upper terrace above Ridley Beach, until it exceeded approximately 500 000 breeding pairs (a ‘supercolony’) by approximately 1200 BP. The high marine productivity associated with the Ross Sea polynya and continental shelf break supported this growth, but the colony collapsed to its present size for unknown reasons after approximately 1200 BP. Ridley Beach will probably be abandoned in the near future due to rising sea level in this region. We predict that penguins will retreat to higher elevations at Cape Adare and that the Scott Coast will be reoccupied by breeding penguins as fast ice continues to dissipate earlier each summer, restoring open-water access to beaches there.
Keywords: population movement; Pygoscelis adeliae; Ross Sea; sea level rise; Stable isotopes

Riverine Export of Aged Carbon Driven by Flow Path Depth and Residence Time - Barnes, Rebecca T.; Butman, David E.; Wilson, Henry F.; Raymond, Peter A. (Environmental Science & Technology, 2018)
The flux of terrestrial C to rivers has increased relative to preindustrial levels, a fraction of which is aged dissolved organic C (DOC). In rivers, C is stored in sediments, exported to the ocean, or (bio)chemically processed and released as CO2. Disturbance changes land cover and hydrology, shifting potential sources and processing of DOC. To investigate the likely sources of aged DOC, we analyzed radiocarbon ages, chemical, and spectral properties of DOC and major ions from 19 rivers draining the coterminous U.S. and Arctic. DOC optics indicated that the majority is exported as aromatic, high molecular weight, modern molecules while aged DOC tended to consist of smaller, microbial degradation products. Aged DOC exports, observed regularly in arid basins and during base flow in arctic rivers, are associated with higher proportion of mineral weathering products, suggesting deeper flows paths. These patterns also indicate potential for production of microbial byproducts as DOC ages in soil and water with longer periods of time between production and transport. Thus, changes in hydrology associated with landscape alteration (e.g., tilling or shifting climates) that can result in deeper flow paths or longer residence times will likely lead to a greater proportion of aged carbon in riverine exports.

The role of sediment compaction and groundwater withdrawal in local sea-level rise, Sandy Hook, New Jersey, USA - Johnson, Christopher S.; Miller, Kenneth G.; Browning, James V.; Kopp, Robert E.; Khan, Nicole S.; Fan, Ying; Stanford, Scott D.; Horton, Benjamin P. (Quaternary Science Reviews, 2018)
The rate of relative sea-level (RSL) rise at Sandy Hook, NJ (4.0 ± 0.5 mm/yr) was higher than The Battery, NY (3.0 ± 0.3 mm/yr) from 1900 to 2012 despite being separated by just 26 km. The difference cannot be explained by differential glacial isostatic adjustment (GIA; 1.4 ± 0.4 and 1.3 ± 0.4 mm/yr RSL rise, respectively) alone. We estimate the contribution of sediment compaction to subsidence at Sandy Hook using high-resolution grain size, percent organic matter, and porosity data from three upper Quaternary (≤13,350 cal yr) cores. The organic matter content (<2%) is too low to contribute to local subsidence. However, numerical modeling of the grain size-depth-age-porosity relationship indicates that compaction of deglacial silts likely reduced the column thickness by 10–20% over the past 13,350 cal yrs. While compaction rates were high immediately after the main silt deposition (13,350–13,150 cal yrs BP), rates decreased exponentially after deposition to an average 20th century rate of 0.16 mm/yr (90% Confidence Interval (C.I.), 0.06–0.32 mm/yr). The remaining ∼0.7 mm/yr (90% C.I. 0.3–1.2 mm/yr) difference in subsidence between Sandy Hook and The Battery is likely due to anthropogenic groundwater withdrawal. Historical data from Fort Hancock wells (2 km to the southeast of the Sandy Hook tide gauge) and previous regional work show that local and regional water extraction lowered the water levels in the aquifers underlying Sandy Hook. We suggest that the modern order of contribution to subsidence (highest to lowest) appears to be GIA, local/regional groundwater extraction, and compaction of thick Quaternary silts.
Keywords: Marginal marine; North America; numerical modeling; Quaternary; Sea-level change; sedimentology

Seafloor fluid seeps on Kimki Ridge, offshore southern California: Links to active strike-slip faulting - Conrad, James E.; Prouty, Nancy G.; Walton, Maureen A.L.; Kluesner, Jared W.; Maier, Katherine L.; McGann, Mary; Brothers, Daniel S.; Roland, Emily C.; Dartnell, Peter (Deep Sea Research Part II: Topical Studies in Oceanography, 2018)
The Kimki Ridge fluid seeps are located in western Catalina Basin about 60 km southwest of the southern California mainland and at a water depth of approximately 1100 m. Multichannel seismic reflection profiles collected by the U.S. Geological Survey (USGS) in 2014 show acoustic transparency within the Kimki Ridge, suggesting the possibility of fluid seeps and possible sub-seafloor fluid pathways. Subsequent multibeam bathymetric and backscatter intensity data collected during a cooperative University of Washington/USGS cruise in early 2016 show subtle seafloor buildups with high acoustic backscatter (reflectivity) in three places along Kimki Ridge, supporting the existence of fluid seepage. A Remotely Operated Vehicle (ROV) dive, conducted as part of the Nautilus Exploration Program, took place in August 2016 to confirm the presence of these previously unknown seeps and document their characteristics as well as those of any associated biological communities. Two of the three seeps were explored by ROV, and showed abundant evidence of fluid seepage, including characteristic algal mats, chemosynthetic clams, and authigenic carbonate formation. The seeps are comprised of carbonate buildups 1–3 m thick and 300–500 m across. Within these areas, we interpret broad crater-like depressions 30–50 m across and 1–2 m deep to be individual seep vents. The seep areas appear to be broad zones of diffuse seepage that support chemosynthetic biologic communities; however, active venting was not observed. Geochemical analyses of rock samples collected from the seeps indicate microbially driven anaerobic oxidation of methane at or near the sediment water interface. Seismic-reflection profiles show chimney-like fluid pathways along the limbs and in the axis of the fold forming Kimki Ridge, and evidence of methane in shallow sediments can be traced into the adjacent Catalina Basin. A system of closely spaced faults located at the axis of the Kimki Ridge anticline may serve as pathways to allow fluid flow to the seafloor. Our data are consistent with other studies that suggest that transpression is an important component in the formation and localization of fluid seeps in a strike-slip setting, implying that seep formation may be a common occurrence at fault stepovers or transpressional bends in strike-slip systems.
Keywords: California Inner Continental Borderland; E/V Nautilus; Faulting; methane; Seepages

Slope failures within and upstream of Lake Quinault, Washington, as uneven responses to Holocene earthquakes along the Cascadia subduction zoneAbstract - Leithold, Elana L.; Wegmann, Karl W.; Bohnenstiehl, Delwayne R.; Smith, Stephen G.; Noren, Anders; O’Grady, Ryan (Quaternary Research, 2018)
Investigation of Lake Quinault in western Washington, including a reflection seismic survey, analysis of piston cores, and preliminary mapping in the steep, landslide-prone Quinault River catchment upstream of the lake, reveals evidence for three episodes of earthquake disturbance in the past 3000 yr. These earthquakes triggered failures on the lake’s underwater slopes and delta front, as well as subaerial landsliding, partial channel blockage, and forced fluvial sediment aggradation. The ages of the three Lake Quinault disturbance events overlap with those of coseismically subsided, coastal marsh soils nearby in southwest Washington that are interpreted to record ruptures of the Cascadia megathrust. Absent from Lake Quinault, however, are signals of obvious disturbance from five additional subduction earthquakes inferred to have occurred during the period of record. The lack of evidence for these events may reflect the limitations of the data set derived from the detrital, river-dominated lake stratigraphy but may also have bearing on debates about segmentation and the distribution of slip along the Cascadia subduction zone during prior earthquakes.
Keywords: Cascadia; Earthquake; lakes; Paleoseismic; Sediment

Sources and radiocarbon ages of aerosol organic carbon along the east coast of China and implications for atmospheric fossil carbon contributions to China marginal seas - Yu, Meng; Guo, Zhigang; Wang, Xuchen; Eglinton, Timothy Ian; Yuan, Zineng; Xing, Lei; Zhang, Hailong; Zhao, Meixun (Science of The Total Environment, 2018)
Aerosol deposition is an important mechanism for the delivery of terrestrial organic carbon (OC) to marginal seas, but OC age characteristics of aerosols are not well constrained and their contributions to sediment OC burial have not been quantified. Total suspended particle samples were collected along the east coast of China at Changdao (CD), Qingdao (QD) and Huaniao Island (HNI), and were analyzed for total organic carbon (TOC) isotopes (13C and 14C) in order to bridge this information gap. TOC δ13C and Δ14C values ranged from − 23.6 to − 30.5‰, and − 153 to − 687‰, respectively, with the latter corresponding to 14C ages ranging from 1280 to 9260 yr. Estimated contributions of fossil carbon to TOC based on 14C mass balance approach ranged from 26 to 73%, with strong seasonal variations in fossil carbon observed at CD. Fossil carbon at CD showed the highest proportion (73%) in winter, reflecting anthropogenic emissions and the lowest proportion (26%) in summer, caused by biomass contribution (annual ave., 52% ± 17%). In contrast, the fossil carbon at both QD (57–64%) and HNI (57–67%) dominated throughout the year, reflecting local anthropogenic influences and long-range transport. Mass balance estimates indicate that atmospheric deposition and riverine export accounted for 31% and 69% of fossil carbon inputs to the China marginal seas (CMS) respectively, with fossil carbon burial efficiencies approaching 100% in the CMS. On a global scale, an atmospheric fossil carbon deposition flux of 17.2 Tg C yr− 1 was estimated, equivalent to 40% of the estimated fluvial flux to the ocean, and potentially accounting for 24–41% of fossil OC burial in marine sediments. Therefore, the atmospheric deposition constitutes an important source of fossil carbon to marine sediments, and could play a key role in regional and global scale OC budgets and biogeochemical cycles.
Keywords: AEROSOLS; China marginal seas; Fossil carbon; Radiocarbon (14C) tracer; Total organic carbon

Spatiotemporal Variation of the Quality, Origin, and Age of Particulate Organic Matter Transported by the Yangtze River (Changjiang) - Wu, Ying; Eglinton, Timothy I.; Zhang, Jing; Montluçon, Daniel B. (Journal of Geophysical Research: Biogeosciences, 2018)
Information on the age dynamics of particulate organic matter (POM) in large river systems is currently sparse and represents an important knowledge gap in our understanding of the global carbon cycle. Here we examine variations in organic geochemical characteristics of suspended sediments from the Changjiang (Yangtze River) system collected between 1997 and 2010. Higher particulate organic carbon content (POC%) values were observed in the middle reach, especially after 2003, and are attributed to the increase of in situ (aquatic) primary production associated with decreased total suspended matter concentrations. Corresponding C-14 values from depth profiles taken in 2009 and 2010 indicate spatial and temporal variations in POC sources within the basin. Two isotopic mass balance approaches were explored to quantitatively apportion different sources of Changjiang POM. Results indicate that contributions of biomass and pre-aged soil organic matter are dominant, regardless of hydrological conditions, with soil-derived organic carbon comprising 17-56% of POC based on a Monte Carlo three-end-member mixing model. In contrast, binary mixing model calculations suggest that up to 80% of POC (2009 samples only) derived from biospheric sources. The emplacement of the Three Gorges Dam and resulting trapping of sediment from the upper reach of the watershed resulted in a modification of POM C-14 ages in the reservoir. With the resulting decline in sediment load and increase in the proportion of modern POC in the lower reach, these changes in POM flux and composition of the Changjiang have significant implications for downstream carbon cycle processes.
Keywords: Changjiang; organic carbon; radiocarbon; suspended particulate matter; Three Gorges Dam

Tectonically-triggered sediment and carbon export to the Hadal zone - Bao, Rui; Strasser, Michael; McNichol, Ann P.; Haghipour, Negar; McIntyre, Cameron; Wefer, Gerold; Eglinton, Timothy I. (Nature Communications, 2018)
Sediments in deep ocean trenches may contain crucial information on past earthquake history and constitute important sites of carbon burial. Here we present 14C data on bulk organic carbon (OC) and its thermal decomposition fractions produced by ramped pyrolysis/oxidation for a core retrieved from the >7.5 km-deep Japan Trench. High-resolution 14C measurements, coupled with distinctive thermogram characteristics of OC, reveal hemipelagic sedimentation interrupted by episodic deposition of pre-aged OC in the trench. Low δ13C values and diverse 14C ages of thermal fractions imply that the latter material originates from the adjacent margin, and the co-occurrence of pre-aged OC with intervals corresponding to known earthquake events implies tectonically triggered, gravity-flow-driven supply. We show that 14C ages of thermal fractions can yield valuable chronological constraints on sedimentary sequences. Our findings shed new light on links between tectonically driven sedimentological processes and marine carbon cycling, with implications for carbon dynamics in hadal environments.

Temperature variations in the southern Great Lakes during the last deglaciation: Comparison between pollen and GDGT proxies - Watson, Benjamin I.; Williams, John W.; Russell, James M.; Jackson, Stephen T.; Shane, Linda; Lowell, Thomas V. (Quaternary Science Reviews, 2018)
Our understanding of deglacial climate history in the southern Great Lakes region of the United States is primarily based upon fossil pollen data, with few independent and multi-proxy climate reconstructions. Here we introduce a new, well-dated fossil pollen record from Stotzel-Leis, OH, and a new deglacial temperature record based on branched glycerol dialkyl glycerol tetraethers (brGDGTs) at Silver Lake, OH. We compare these new data to previously published records and to a regional stack of pollen-based temperature reconstructions from Stotzel-Leis, Silver Lake, and three other well-dated sites. The new and previously published pollen records at Stotzel-Leis are similar, but our new age model brings vegetation events into closer alignment with known climatic events such as the Younger Dryas (YD). brGDGT-inferred temperatures correlate strongly with pollen-based regional temperature reconstructions, with the strongest correlation obtained for a global soil-based brGDGT calibration (r2 = 0.88), lending confidence to the deglacial reconstructions and the use of brGDGT and regional pollen stacks as paleotemperature proxies in eastern North America. However, individual pollen records show large differences in timing, rates, and amplitudes of inferred temperature change, indicating caution with paleoclimatic inferences based on single-site pollen records. From 16.0 to 10.0ka, both proxies indicate that regional temperatures rose by ∼10 °C, roughly double the ∼5 °C estimates for the Northern Hemisphere reported in prior syntheses. Change-point analysis of the pollen stack shows accelerated warming at 14.0 ± 1.2ka, cooling at 12.6 ± 0.4ka, and warming from 11.6 ± 0.5ka into the Holocene. The timing of Bølling-Allerød (B-A) warming and YD onset in our records lag by ∼300–500 years those reported in syntheses of temperature records from the northern mid-latitudes. This discrepancy is too large to be attributed to uncertainties in radiocarbon dating, and correlation between pollen and brGDGT temperature reconstructions rules out vegetation lags as a cause. However, the YD termination appears synchronous among the brGDGT record, regional pollen stack, and Northern Hemisphere stack. The cause of the larger and lagged temperature changes in the southern Great Lakes relative to Northern Hemisphere averages remains unclear, but may be due to the effects of continentality and ice sheet extent on regional climate evolution.
Keywords: Continental biomarkers; GDGT; Lagoons and Swamps; lakes; North America; paleoclimatology; Pleistocene; pollen; sedimentology

Tracing biogeochemical subsidies from glacier runoff into Alaska's coastal marine food webs - Arimitsu, Mayumi L.; Hobson, Keith A.; Webber, D'Arcy N.; Piatt, John F.; Hood, Eran W.; Fellman, Jason B. (Global Change Biology, 2018)
Nearly half of the freshwater discharge into the Gulf of Alaska originates from landscapes draining glacier runoff, but the influence of the influx of riverine organic matter on the trophodynamics of coastal marine food webs is not well understood. We quantified the ecological impact of riverine organic matter subsidies to glacier‐marine habitats by developing a multi‐trophic level Bayesian three‐isotope mixing model. We utilized large gradients in stable (δ13C, δ15N, δ2H) and radiogenic (Δ14C) isotopes that trace riverine and marine organic matter sources as they are passed from lower to higher trophic levels in glacial‐marine habitats. We also compared isotope ratios between glacial‐marine and more oceanic habitats. Based on isotopic measurements of potential baseline sources, ambient water and tissues of marine consumers, estimates of the riverine organic matter source contribution to upper trophic‐level species including fish and seabirds ranged from 12% to 44%. Variability in resource use among similar taxa corresponded to variation in species distribution and life histories. For example, riverine organic matter assimilation by the glacier‐nesting seabirds Kittlitz's murrelet (Brachyramphus brevirostris) was greater than that of the forest‐nesting marbled murrelet (B. marmoratus). The particulate and dissolved organic carbon in glacial runoff and near surface coastal waters was aged (12100–1500 years BP 14C‐age) but dissolved inorganic carbon and biota in coastal waters were young (530 years BP 14C‐age to modern). Thus terrestrial‐derived subsidies in marine food webs were primarily composed of young organic matter sources released from glacier ecosystems and their surrounding watersheds. Stable isotope compositions also revealed a divergence in food web structure between glacial‐marine and oceanic sites. This work demonstrates linkages between terrestrial and marine ecosystems, and facilitates a greater understanding of how climate‐driven changes in freshwater runoff have the potential to alter food web dynamics within coastal marine ecosystems in Alaska.
Keywords: Bayesian isotope mixing model; glacier runoff; marine ecosystem; marine food web; δ13C; Δ14C; δ15N; δ2H

Tropical peatland carbon storage linked to global latitudinal trends in peat recalcitrance - Hodgkins, Suzanne B.; Richardson, Curtis J.; Dommain, René; Wang, Hongjun; Glaser, Paul H.; Verbeke, Brittany; Winkler, B. Rose; Cobb, Alexander R.; Rich, Virginia I.; Missilmani, Malak; Flanagan, Neal; Ho, Mengchi; et al. (Nature Communications, 2018)
Peatlands represent large terrestrial carbon banks. Given that most peat accumulates in boreal regions, where low temperatures and water saturation preserve organic matter, the existence of peat in (sub)tropical regions remains enigmatic. Here we examined peat and plant chemistry across a latitudinal transect from the Arctic to the tropics. Near-surface low-latitude peat has lower carbohydrate and greater aromatic content than near-surface high-latitude peat, creating a reduced oxidation state and resulting recalcitrance. This recalcitrance allows peat to persist in the (sub)tropics despite warm temperatures. Because we observed similar declines in carbohydrate content with depth in high-latitude peat, our data explain recent field-scale deep peat warming experiments in which catotelm (deeper) peat remained stable despite temperature increases up to 9 °C. We suggest that high-latitude deep peat reservoirs may be stabilized in the face of climate change by their ultimately lower carbohydrate and higher aromatic composition, similar to tropical peats.

Unifying Concepts Linking Dissolved Organic Matter Composition to Persistence in Aquatic EcosystemsUnifying Concepts Linking Dissolved Organic Matter Composition to Persistence in Aquatic Ecosystems - Kellerman, Anne M.; Guillemette, François; Podgorski, David C.; Aiken, George R.; Butler, Kenna D.; Spencer, Robert G. M. (Environmental Science & Technology, 2018)
The link between composition and reactivity of dissolved organic matter (DOM) is central to understanding the role aquatic systems play in the global carbon cycle; yet, unifying concepts driving molecular composition have yet to be established. We characterized 37 DOM isolates from diverse aquatic ecosystems, including their stable and radiocarbon isotopes (δ13C-dissolved organic carbon (DOC) and Δ14C-DOC), optical properties (absorbance and fluorescence), and molecular composition (ultrahigh resolution mass spectrometry). Isolates encompassed end-members of allochthonous and autochthonous DOM from sites across the United States, the Pacific Ocean, and Antarctic lakes. Modern Δ14C-DOC and optical properties reflecting increased aromaticity, such as carbon specific UV absorbance at 254 nm (SUVA254), were directly related to polyphenolic and polycyclic aromatic compounds, whereas enriched δ13C-DOC and optical properties reflecting autochthonous end-members were positively correlated to more aliphatic compounds. Furthermore, the two sets of autochthonous end-members (Pacific Ocean and Antarctic lakes) exhibited distinct molecular composition due to differences in extent of degradation. Across all sites and end-members studied, we find a consistent shift in composition with aging, highlighting the persistence of certain biomolecules concurrent with degradation time.

Using Stable and Radiocarbon Analyses as a Forensic Tool to Find Evidence of Oil in the Particulates of the Water Column and on the Seafloor Following the 2010 Gulf of Mexico Oil Spill - Bosman, Samantha H.; Chanton, Jeffrey P.; Rogers, Kelsey L. (Elsevier, 2018)
Over 600 million liters of oil and copious amounts of methane were released into the Gulf of Mexico between April 20, 2010 and July 15, 2010. We used stable and radiocarbon analyses as a forensic tool to trace these hydrocarbons from the Deepwater Horizon (DwH) well into suspended particulate organic carbon (POCsusp), sinking particulate organic carbon (POCsink), and sedimentary organic carbon on the seafloor. POCsusp samples were considerably depleted both in δ13C and Δ14C relative to surface production, with δ13C and Δ14C values as low as −37.2‰ and −618‰, respectively. POCsink time series data revealed a modern Δ14C value due to a large diatom bloom in early September 2010, but values became depleted as oil contaminated particles continued to descend in the water column until the end of the year. Sediment cores collected in the vicinity of the DwH wellhead revealed evidence of oil contamination in the surface layer (0–1 cm), as indicated by a depletion in Δ14C values compared to the layers below the surface. In addition to providing evidence of oil contamination using stable and radiocarbon analyses, our study was consistent with the existence of a pathway by which spilled oil was deposited onto the seafloor.
Keywords: Deepwater Horizon; isotopes; methane; Petrocarbon; POCsin; POCsusp; Sediment

Variability in carbon uptake and (re)cycling in Antarctic cryptoendolithic microbial ecosystems demonstrated through radiocarbon analysis of organic biomarkers - Brady, A. L.; Goordial, J.; Sun, H. J.; Whyte, L. G.; Slater, G. F. (Geobiology, 2018)
Cryptoendolithic lichens and cyanobacteria living in porous sandstone in the high‐elevation McMurdo Dry Valleys are purported to be among the slowest growing organisms on Earth with cycles of death and regrowth on the order of 103–104 years. Here, organic biomarker and radiocarbon analysis were used to better constrain ages and carbon sources of cryptoendoliths in University Valley (UV; 1,800 m.a.s.l) and neighboring Farnell Valley (FV; 1,700 m.a.s.l). Δ14C was measured for membrane component phospholipid fatty acids (PLFA) and glycolipid fatty acids, as well as for total organic carbon (TOC). PLFA concentrations indicated viable cells comprised a minor (<0.5%) component of TOC. TOC Δ14C values ranged from −272‰ to −185‰ equivalent to calibrated ages of 1,100–2,550 years old. These ages may be the result of fractional preservation of biogenic carbon and/or sudden large‐scale community death and extended period(s) of inactivity prior to slow recolonization and incorporation of 14C‐depleted fossil material. PLFA Δ14C values were generally more modern than the corresponding TOC and varied widely between sites; the FV PLFA Δ14C value (+40‰) was consistent with modern atmospheric CO2, while UV values ranged from −199‰ to −79‰ (calibrated ages of 1,665–610 years). The observed variability in PLFA Δ14C depletions is hypothesized to reflect variations in the extent of fixation of modern atmospheric CO2 and the preservation and recycling of older organic carbon by the community in various stages of sandstone recolonization. PLFA profiles and microbial community compositions as determined by molecular genetic characterizations and microscopy differed between the two valleys (e.g., predominance of biomarker 18:2 [>50%] in FV compared to UV), representing microbial communities that may reflect distinct stages of sandstone recolonization and/or environmental conditions. It is thus proposed that Dry Valley cryptoendolithic microbial communities are faster growing than previously estimated.

Variance and Rate-of-Change as Early Warning Signals for a Critical Transition in an Aquatic Ecosystem State: A Test Case From Tasmania, Australia - Beck, Kristen K.; Fletcher, Michael-Shawn; Gadd, Patricia S.; Heijnis, Henk; Saunders, Krystyna M.; Simpson, Gavin L.; Zawadzki, Atun (Journal of Geophysical Research: Biogeosciences, 2018)
Critical transitions in ecosystem states are often sudden and unpredictable. Consequently, there is a concerted effort to identify measurable early warning signals (EWS) for these important events. Aquatic ecosystems provide an opportunity to observe critical transitions due to their high sensitivity and rapid response times. Using palaeoecological techniques, we can measure properties of time series data to determine if critical transitions are preceded by any measurable ecosystem metrics, that is, identify EWS. Using a suite of palaeoenvironmental data spanning the last 2,400 years (diatoms, pollen, geochemistry, and charcoal influx), we assess whether a critical transition in diatom community structure was preceded by measurable EWS. Lake Vera, in the temperate rain forest of western Tasmania, Australia, has a diatom community dominated by Discostella stelligera and undergoes an abrupt compositional shift at ca. 820 cal yr BP that is concomitant with increased fire disturbance of the local vegetation. This shift is manifest as a transition from less oligotrophic acidic diatom flora (Achnanthidium minutissimum, Brachysira styriaca, and Fragilaria capucina) to more oligotrophic acidic taxa (Frustulia elongatissima, Eunotia diodon, and Gomphonema multiforme). We observe a marked increase in compositional variance and rate‐of‐change prior to this critical transition, revealing these metrics are useful EWS in this system. Interestingly, vegetation remains complacent to fire disturbance until after the shift in the diatom community. Disturbance taxa invade and the vegetation system experiences an increase in both compositional variance and rate‐of‐change. These trends imply an approaching critical transition in the vegetation and the probable collapse of the local rain forest system.
Keywords: carbon and nitrogen stable isotopes; critical transitions; diatoms; early warning signals; polleen; Tasmania

Vegetation responses to late Holocene climate changes in an Andean forest - Schiferl, Jacob D.; Bush, Mark B.; Silman, Miles R.; Urrego, Dunia H. (Quaternary Research, 2018)
A paleoecological record from Lake Palotoa (1370 m elevation) in the Andean foothills of Peru spans the last 3800 years. Lake Palotoa lies near the modern cloud base in a location sensitive to changes in atmospheric moisture. In many areas, these forests have been destroyed, but Lake Palotoa shows no sign of human occupation today or in the past. The modern forest surrounding the lake is dominated by the Andean palm, Dictyocaryum lamarckianum, which is also the most abundant taxon in the fossil pollen record. Fossil pollen data show the vegetation assemblages have not experienced strong compositional changes in the late Holocene. Global-scale climatic events such as the Medieval Climate Anomaly (MCA) and the Little Ice Age (LIA) are identified within the record, though the vegetation responses are subtle. Hedyosmum and Sloanea pollen percentages increase near the onset of the MCA and may reflect decreased seasonality. The LIA coincides with increased Hedyosmum pollen percentages, and increases in Clethra and Begonia, two elements that tend to occupy forests now found at higher elevations. Our findings demonstrate the stability of montane forest systems to natural Holocene climate change.
Keywords: Cloud forest; Dictyocaryum; Fossil pollen; Little ice age; Medieval Climate Anomaly; seasonality; Tropical ecology

3000 Years of Human Subsistence and Estuarine Resource Exploitation on the Rhode River Estuary, Chesapeake Bay, Maryland - Rick, Torben C.; Reeder-Myers, Leslie A.; Carr, Michael J.; Hines, Anson H. (Journal of the North Atlantic, 2017)
Chesapeake Bay is home to highly productive marine ecosystems that were a key part of Native American subsistence for millennia. Despite a number of archaeological projects focused on Chesapeake Bay prehistory, key questions remain about the nature of human use of the estuary through time and across space. Recent work at 7 shell middens on the Rhode River Estuary, MD, provides insight into human subsistence and estuarine res ource exploitation from ∼3200 years ago through the mid-19th century. This is an important diachronic sequence of coastal land use and subsistence for the Chesapeake and helps fill a gap in our understanding of coastal adaptations along North America's Atlantic Coast. Despite climate change, fluctuating sea levels, and the likely appearance of maize agriculture in the area ∼1000 years ago, Native American exploitation of oysters and estuarine resources remained fairly consistent across the Early to Late Woodland. These data stand in contrast to the mid-1800s assemblage, which was likely deposited by 19th-century Euro-Americans and contains overall larger oysters perhaps obtained from deeper waters that may not have been a focus of Native American harvest. When placed in the context of other regional data, our analysis illustrates the value of shell middens for helping understand human subsistence strategies and the historical ecol ogy of the North American Atlantic Coast.

The 3.6 ka Aniakchak tephra in the Arctic Ocean: a constraint on the Holocene radiocarbon reservoir age in the Chukchi Sea - Pearce, Christof; Varhelyi, Aron; Wastegård, Stefan; Muschitiello, Francesco; Barrientos, Natalia; O'Regan, Matt; Cronin, Thomas M.; Gemery, Laura; Semiletov, Igor; Backman, Jan; Jakobsson, Martin (Climate of the Past, 2017)
The caldera-forming eruption of the Aniakchak volcano in the Aleutian Range on the Alaskan Peninsula at 3.6 cal kyr BP was one of the largest Holocene eruptions worldwide. The resulting ash is found as a visible sediment layer in several Alaskan sites and as a cryptotephra on Newfoundland and Greenland. This large geographic distribution, combined with the fact that the eruption is relatively well constrained in time using radiocarbon dating of lake sediments and annual layer counts in ice cores, makes it an excellent stratigraphic marker for dating and correlating mid–late Holocene sediment and paleoclimate records. This study presents the outcome of a targeted search for the Aniakchak tephra in a marine sediment core from the Arctic Ocean, namely Core SWERUS-L2-2-PC1 (2PC), raised from 57 m water depth in Herald Canyon, western Chukchi Sea. High concentrations of tephra shards, with a geochemical signature matching that of Aniakchak ash, were observed across a more than 1.5 m long sediment sequence. Since the primary input of volcanic ash is through atmospheric transport, and assuming that bioturbation can account for mixing up to ca. 10 cm of the marine sediment deposited at the coring site, the broad signal is interpreted as sustained reworking at the sediment source input. The isochron is therefore placed at the base of the sudden increase in tephra concentrations rather than at the maximum concentration. This interpretation of major reworking is strengthened by analysis of grain size distribution which points to ice rafting as an important secondary transport mechanism of volcanic ash. Combined with radiocarbon dates on mollusks in the same sediment core, the volcanic marker is used to calculate a marine radiocarbon reservoir age offset ΔR = 477 ± 60 years. This relatively high value may be explained by the major influence of typically "carbon-old" Pacific waters, and it agrees well with recent estimates of ΔR along the northwest Alaskan coast, possibly indicating stable oceanographic conditions during the second half of the Holocene. Our use of a volcanic absolute age marker to obtain the marine reservoir age offset is the first of its kind in the Arctic Ocean and provides an important framework for improving chronologies and correlating marine sediment archives in this region. Core 2PC has a high sediment accumulation rate averaging 200 cm kyr throughout the last 4000 years, and the chronology presented here provides a solid base for high-resolution reconstructions of late Holocene climate and ocean variability in the Chukchi Sea.

A ~6000 yr diatom record of mid- to late Holocene fluctuations in the level of Lago Wiñaymarca, Lake Titicaca (Peru/Bolivia)Abstract - Weide, D. Marie; Fritz, Sherilyn C.; Hastorf, Christine A.; Bruno, Maria C.; Baker, Paul A.; Guedron, Stephane; Salenbien, Wout (Quaternary Research, 2017)
A multidecadal-scale lake-level reconstruction for Lago Wiñaymarca, the southern basin of Lake Titicaca, has been generated from diatom species abundance data. These data suggest that ~6500 cal yr BP Lago Wiñaymarca was dry, as indicated by a sediment unconformity. At ~4400 cal yr BP, the basin began to fill, as indicated by the dominance of shallow epiphytic species. It remained somewhat saline with extensive wetlands and abundant aquatic plants until ~3800 cal yr BP, when epiphytic species were replaced by planktic saline-indifferent species, suggesting a saline shallow lake. Wiñaymarca remained a relatively shallow lake that fluctuated on a multidecadal scale until ~1250 cal yr BP, when freshwater planktic species increased, suggesting a rise in lake level with a concomitant decrease in salinity. The lake became gradually fresher, dominated by deep, freshwater species from ~850 cal yr BP. By ~80 cal yr BP, saline-tolerant species were rare, and the lake was dominated by freshwater planktic diatoms, resembling the fresh and deep lake of today. These results reveal a more dynamic and chronologically specific record of lake-level fluctuations and associated ecological conditions that provide important new data for paleoclimatologists and archaeologists, to better understand human-environmental dynamics during the mid- to late Holocene.
Keywords: diatoms; Lago Huiñaimarca; Lago Wiñaymarca; Lake level; lake titicaca; Mid-Holocene; Tropical Andes

A 7000-year history of coastal environmental changes from Mexico’s Pacific coast: A multi-proxy record from Laguna Mitla, Guerrero - Bianchette, Thomas A; McCloskey, Terrence A; Liu, Kam-biu (The Holocene, 2017)
The lack of multi-millennial multi-proxy paleoenvironmental reconstructions from Mexico’s Pacific coast has limited our understanding of the regional response to climate change and sea-level rise. A 479-cm core covering the last 6900 years was extracted from Laguna Mitla in the state of Guerrero on Mexico’s Pacific coast. Beginning as a Rhizophora-dominated salt pan ~6900 yr BP, at ~6500 yr BP, the site transitioned to a mangrove swamp dominated by Laguncularia, which lasted about 300 years. The beach barrier formed from ~6200 to 5200 yr BP, during which time, the site existed as an intermittently sheltered bay, the result of large, rapid changes in wave energy associated with the shifting barrier location and changes in stability. After the beach barrier was stabilized at ~5200 yr BP, water level at the coring site became a function of precipitation rather than sea level. Since that time, deposition has alternated between peat, laid down in a mangrove swamp, and clay intervals characterized by high concentrations of titanium and a predominantly regional pollen signal, representing open-water lagoon phases. Seven periods of increased water level, varying in duration, occurred during the backbarrier period, with El Niño-Southern Oscillation (ENSO) likely the main climatic mechanism causing these periodic shifts in the paleo-precipitation levels. We suggest that the deepest water levels detected over the last ~3200 years correlate with periods of increased ENSO activity. The spatial distribution of tropical cyclone rainfall, which represents a significant percentage of total annual precipitation along Mexico’s Pacific coast, may explain the inconsistencies between our record and paleoclimatic records from Mexico’s interior, but more work is needed to test this hypothesis.
Keywords: El Nino-Southern Oscillation; Laguna Mitla; mangroves; Pacific coast of Mexico; Paleoclimate; paleoenvironmental reconstruction; pollen; Sediment; tropical cyclones; x-ray fluorescence

African Baobabs with a Very Large Number of Stems and False Stems: Radiocarbon Investigation of the Baobab of Warang - Patrut, Adrian; Garnaud, ébastien; Ka, Oumar; Patrut, Roxana T.; Diagne, Tomas; Lowy, Daniel A.; Forizs, Edit; Bodis, ő; von Reden, Karl F. (Studia Universitatis Babeș-Bolyai Chemia, 2017)
The article presents the AMS (accelerator mass spectrometry) radiocarbon dating results of the baobab of Warang, Senegal. The investigation of the baobab revealed that it consists of 18 partially fused stems, which represents the largest number of stems reported for an African baobab. Three stems build the ring that closes a false cavity, while 15 stems grow outside the ring. Seven wood samples were collected from the false cavity and from the outer part of other stems. The dating results evinced that the stems belong to four different generations, out of which the first generation is around 500 years old. We also documented the presence of false stems, which emerge from a large adjacent stem, are triangular in horizontal section and act as an anchor. The baobab of Warang possesses 12 ordinary stems and 6 false stems.
Keywords: Adansonia digitata; Age determination; AMS radiocarbon dating; inner cavity; multiple stems; tropical trees

Age Constraints on Gulf of Mexico Deep Water Ventilation as Determined by 14C MeasurementsAbstract - Chapman, Piers; DiMarco, Steven F; Key, Robert M; Previti, Connie; Yvon-Lewis, Shari (Radiocarbon, 2017)
While the exchange of water through Yucatan Strait is reasonably well known, the age of the deep water in both the Caribbean Sea and Gulf of Mexico is not. We recently measured the radiocarbon (14C) concentrations in deep water in the Gulf of Mexico from a line of stations along 90°30′W. The mean apparent age of water below 900 m, the depth of the Florida Strait sill, was found to be about 740 yr relative to the 1950 14C standard. Depending on how the corrections for biological activity in the upper water are applied, this converts to a “true” age of between 231 ± 28 and 293 ± 74 yr. These ages agree with a previous estimate of the age of the deep water in the Gulf of Mexico based on heat flows, put upper limits on the age of the deep water in the Caribbean Sea, and provide constraints on modelers for the return of deep water from the Gulf of Mexico to the Caribbean. This might be important in the event of a future deep water oil or other chemical spill in the region.
Keywords: Gulf of Mexico; radiocarbon AMS dating; water

Aged dissolved organic carbon exported from rivers of the Tibetan Plateau - Qu, Bin; Sillanpää, Mika; Li, Chaoliu; Kang, Shichang; Stubbins, Aron; Yan, Fangping; Aho, Kelly Sue; Zhou, Feng; Raymond, Peter A. (PLOS ONE, 2017)
The role played by river networks in regional and global carbon cycle is receiving increasing attention. Despite the potential of radiocarbon measurements (14C) to elucidate sources and cycling of different riverine carbon pools, there remain large regions such as the climate-sensitive Tibetan Plateau for which no data are available. Here we provide new 14C data on dissolved organic carbon (DOC) from three large Asian rivers (the Yellow, Yangtze and Yarlung Tsangpo Rivers) running on the Tibetan Plateau and present the carbon transportation pattern in rivers of the plateau versus other river system in the world. Despite higher discharge rates during the high flow season, the DOC yield of Tibetan Plateau rivers (0.41 gC m-2 yr-1) was lower than most other rivers due to lower concentrations. Radiocarbon ages of the DOC were older/more depleted (511±294 years before present, yr BP) in the Tibetan rivers than those in Arctic and tropical rivers. A positive correlation between radiocarbon age and permafrost watershed coverage was observed, indicating that 14C-deplted/old carbon is exported from permafrost regions of the Tibetan Plateau during periods of high flow. This is in sharp contrast to permafrost regions of the Arctic which export 14C-enriched carbon during high discharge periods.
Keywords: Carbon cycle; Carbon dioxide; Climate change; Rain; Rivers; Surface water; Tibetan people; TIBETAN PLATEAU

Allochthonous sources and dynamic cycling of ocean dissolved organic carbon revealed by carbon isotopes - Zigah, Prosper K.; McNichol, Ann P.; Xu, Li; Johnson, Carl; Santinelli, Chiara; Karl, David M.; Repeta, Daniel J. (GEOPHYSICAL RESEARCH LETTERS, 2017)
We present concentration and isotopic profiles of total, size, and polarity fractionated dissolved organic carbon (DOC) from Station ALOHA (A Long-term Oligotrophic Habitat Assessment), an oligotrophic site in the North Pacific Ocean. The data show that, between the surface and 3500 m, low molecular weight (LMW) hydrophilic DOC, LMW hydrophobic DOC, and high molecular weight (HMW) DOC constitute 22-33%, 45-52%, and 23-35% of DOC, respectively. LMW hydrophilic DOC is more isotopically depleted (delta C-13 of -23.9 parts per thousand to -31.5 parts per thousand and Delta C-14 of -304 parts per thousand to -795 parts per thousand; mean age of 2850 to 15000 years) than the LMW hydrophobic DOC (delta C-13 of -22 parts per thousand to -23 parts per thousand and Delta C-14 of -270 parts per thousand to -568 parts per thousand; 2470 to 6680 years) and HMW DOC (delta C-13 of similar to-21 parts per thousand and Delta C-14 of -24 parts per thousand to -294 parts per thousand; 135-2700 years). Our analyses suggest that a large fraction of DOC may be derived from allochthonous sources such as terrestrial and hydrothermal DOC and cycle on much longer time scales of > 10000 years or enter the ocean as preaged carbon.
Keywords: ATLANTIC BIGHT; BLACK CARBON; C-14; HUMIC SUBSTANCES; MATTER; NORTH PACIFIC-OCEAN; RADIOCARBON ANALYSIS; SARGASSO SEA; SEAWATER; SPECTROMETRY

Analysis of piston cores and high-resolution sub-bottom profiler data, Baffin Bay slope, Nunavut - Campbell, D C; Jenner, K A; Higgins, J; Piper, D J W (2017)
Preface This Open File report summarizes a set of 20 piston cores, up to 822 cm long, taken from the continental slope of Baffin Bay, Canada, in water depths between 833 and 1715 m. It provides down-core lithostratigraphy, physical properties measurements, core photography and core X-radiography, in addition to high-resolution seismic data over most core sites, selected grain size data and portable X-ray fluorescence data. Preliminary along-slope correlation between cores and AMS radiocarbon ages are also provided. Further information on these cores is available through the Expedition Database at http://ed.gdr.nrcan.gc.ca/index_e.php Acknowledgments We thank Dan Meagher, Jesse Sherwin and Meaghan MacQuarrie for assistance with core processing and core logging and Jessica Parkinson and Simon Poirier for core data compilation. Owen Brown completed grain size analyses and Linda Fan assisted with these analyses and plotted the grain size data.We also thank Kate Jarrett for assistance with core subsampling.

Anthropogenic CO2 accumulation and uptake rates in the Pacific Ocean based on changes in the C-13/C-12 of dissolved inorganic carbon - Quay, P.; Sonnerup, R.; Munro, D.; Sweeney, C. (GLOBAL BIOGEOCHEMICAL CYCLES, 2017)
The anthropogenic CO2 accumulation rate for the Pacific Ocean was estimated from the decrease in C-13 of the dissolved inorganic carbon measured on six World Ocean Circulation Experiment cruises during the 1990s and repeated during Climate Variability and Predictability in the 2000s. A mean depth-integrated anthropogenic C-13 change of -8320mdecade(-1) was estimated for the basin by using the multiple linear regression approach. The largest anthropogenic C-13 decreases occurred between 40 degrees S and 60 degrees S, whereas the smallest decreases occurred in the Southern Ocean and subpolar North Pacific. A mean anthropogenic CO2 accumulation rate of 0.410.13molCm(-2)yr(-1) (0.820.26PgCyr(-1)) was determined based on observed C-13 changes and is in agreement with previous observation- and model-based estimates. The mean dissolved inorganic carbon DIC13 inventory change of -178 +/- 43 parts per thousand molm(-2)decade(-1) was primarily the result of air-sea CO2 exchange acting on the measured air-sea C-13 disequilibrium of similar to-1.2 +/- 0.1 parts per thousand. Regional differences between the DIC13 inventory change and air-sea (CO2)-C-13 flux yielded net anthropogenic CO2 uptake rates (independent of pCO(2)) that ranged from similar to 0 to 1molm(-2)yr(-1) and basin-wide mean of 1.2 +/- 1.5PgCyr(-1). High rates of surface ocean DIC increase and C-13 decrease observed in the Drake Passage (53 degrees S-60 degrees S) support above average anthropogenic CO2 accumulation since 2005. Observed C-13 changes in the Pacific Ocean indicate that ocean transport significantly impacted the anthropogenic CO2 distribution and illustrate the utility of C-13 as a tracer to unravel the processes controlling the present and future accumulation of anth ropogenic CO2 in the ocean.
Keywords: anthropogenic change; C-12; C-13; CO2; Pacific Ocean

Assessing the Blank Carbon Contribution, Isotope Mass Balance, and Kinetic Isotope Fractionation of the Ramped Pyrolysis/Oxidation Instrument at NOSAMS - Hemingway, Jordon D; Galy, Valier V; Gagnon, Alan R; Grant, Katherine E; Rosengard, Sarah Z; Soulet, Guillaume; Zigah, Prosper K; McNichol, Ann P (Radiocarbon, 2017)
We estimate the blank carbon mass over the course of a typical Ramped PyrOx (RPO) analysis (150-1000 degrees C; 5 degrees C x min(-1)) to be (3.7 +/- 0.6) mu g C with an Fm value of 0.555 +/- 0.042 and a delta C-13 value of (-29.0 +/- 0.1)parts per thousand VPDB. Additionally, we provide equations for RPO Fm and delta C-13 blank corrections, including associated error propagation. By comparing RPO mass-weighted mean and independently measured bulk delta C-13 values for a compilation of environmental samples and standard reference materials (SRMs), we observe a small yet consistent delta C-13 depletion within the RPO instrument (mean-bulk: mu = -0.8 parts per thousand; +/- 1 sigma = 0.9 parts per thousand; n = 66). In contrast, because they are fractionation-corrected by definition, mass-weighted mean Fm values accurately match bulk measurements (mean-bulk: mu = 0.005; +/- 1 sigma = 0.014; n = 36). Lastly, we show there exists no significant intra-sample delta C-13 variability across carbonate SRM peaks, indicating minimal mass-dependent kinetic isotope fractionation during RPO analysis. These data are best explained by a difference in activation energy between C-13- and C-12-containing compounds ((13-12)Delta E) of 0.3-1.8 J x mol(-1), indicating that blank and mass-balance corrected RPO delta C-13 values accurately retain carbon source isotope signals to within 1-2 parts per thousand.
Keywords: Ramped PyrOx; blank assessment; kinetic fractionation

ASSESSING THE EFFECTS OF ANTHROPOGENIC EUTROPHICATION ON MARINE BIVALVE LIFE HISTORY IN THE NORTHERN GULF OF MEXICO - HARNIK, PAUL G.; TORSTENSON, MORGAN L.; WILLIAMS, MARIO A. (PALAIOS, 2017)
Natural and anthropogenic eutrophication can increase food supply to basal consumers in aquatic food webs. All else being equal, increased food supply is expected to relax life history trade-offs between egg size and number, resulting in a reduction in egg size over time as individuals that produce more numerous, small eggs exhibit greater fitness. We tested this hypothesis by comparing the sizes of larval shells (PI) of the marine bivalve Nuculana acuta in living and death assemblages collected from surficial seafloor sediments on the Alabama continental shelf; PI size is positively correlated with egg size and can be measured from adult shells. We found that the mean PI size of living N. acuta was approximately three microns smaller than that of the associated death assemblage and that this difference was robust to potential taphonomic biases. This life history shift occurred relatively recently as no trend exists in PI size over the past 3100 years. The live-dead disagreement that we observed is consistent with the history of anthropogenic eutrophication in the Mississippi Bight. These data provide a baseline for comparison with other regions in the Gulf of Mexico that have more sustained histories of anthropogenic eutrophication. More broadly, live-dead comparisons of molluscan life history coupled with age dating of molluscan shells can complement community-level metrics when assessing the impacts of anthropogenic eutrophication on coastal ecosystems, and offer a unique study system for investigating life history adaptation in a field context.