TY - JOUR T1 - Duration and ice thickness of a Late Holocene outlet glacier advance near Narsarsuaq, southern Greenland JF - Climate of the Past Y1 - 2023 A1 - Puleo, Peter J. K. A1 - Axford, Yarrow AB - Greenland Ice Sheet (GrIS) outlet glaciers are currently losing mass, leading to sea level rise. Reconstructions of past outlet glacier behavior through the Holocene help us better understand how they respond to climate change. Kiattuut Sermiat, a southern Greenland outlet glacier near Narsarsuaq, is known to have experienced an unusually large Late Holocene advance that culminated at ∼1600 cal yr BP and exceeded the glacier's Little Ice Age extent. We report sedimentary records from two lakes at slightly different elevations in an upland valley adjacent to Kiattuut Sermiat. These reveal when the outlet glacier's surface elevation was higher than during the Little Ice Age and constrain the associated outlet glacier surface elevation. We use bulk sediment geochemistry, magnetic susceptibility, color, texture, and the presence of aquatic plant macrofossils to distinguish between till, glaciolacustrine sediments, and organic lake sediments. Our 14C results above basal till recording regional deglaciation skew slightly old due to a reservoir effect but are generally consistent with regional deglaciation occurring ∼ 11 000 cal yr BP. Neoglacial advance of Kiattuut Sermiat is recorded by deposition of glaciolacustrine sediments in the lower-elevation lake, which we infer was subsumed by an ice-dammed lake that formed along the glacier's margin just after ∼ 3900 cal yr BP. This timing is consistent with several other glacial records in Greenland showing neoglacial cooling driving advance between ∼ 4500–3000 cal yr BP. Given that glaciolacustrine sediments were deposited only in the lower-elevation lake, combined with glacial geomorphological evidence in the valley containing these lakes, we estimate the former ice margin's elevation to have been ∼ 670 m a.s.l., compared with ∼ 420 m a.s.l. today. The ice-dammed lake persisted until the glacier surface fell below this elevation at ∼ 1600 cal yr BP. The retreat timing contrasts with overall evidence for cooling and glacier advance in the region at that time, so we infer that Kiattuut Sermiat's retreat may have resulted from reduced snowfall amounts and/or local glaciological complexity. High sensitivity to precipitation changes could also explain the relatively limited Little Ice Age advance of Kiattuut Sermiat compared with the earlier neoglacial advance. VL - 19 UR - https://cp.copernicus.org/articles/19/1777/2023/ N1 - Publisher: Copernicus GmbH ER - TY - JOUR T1 - The dynamics of warming during the last deglaciation in high-elevation regions of Eastern Equatorial Africa JF - Quaternary Science Reviews Y1 - 2022 A1 - Garelick, Sloane A1 - Russell, James A1 - Richards, Adin A1 - Smith, Jamila A1 - Kelly, Meredith A1 - Anderson, Nathan A1 - Jackson, Margaret S. A1 - Doughty, Alice A1 - Nakileza, Bob A1 - Ivory, Sarah A1 - Dee, Sylvia A1 - Marshall, Charlie AB - Tropical mountain environments, such as the Rwenzori Mountains in equatorial Africa, are thought to be particularly sensitive to climate change. Ongoing warming in the Rwenzori is impacting local environments and communities through glacial retreat, fires, and flooding. Paleoclimate reconstructions from elsewhere in Africa suggest considerable warming accompanied glacier retreat during the last glacial termination, from ∼21 thousand years before present (ka) through the early to mid-Holocene. Quantifying these changes has been difficult but could help to assess future impacts in the Rwenzori. Here, we present a ∼21 thousand-year (kyr) temperature reconstruction based on the relative abundance of branched glycerol dialkyl glycerol tetraethers (brGDGTs) from Lake Mahoma (2,990 m above sea level; m asl) in the Rwenzori Mountains, Uganda. Our record, paired with existing Rwenzori glacial moraine 10Be exposure ages, suggests that deglacial warming and glacial retreat began by ∼20 ka and accelerated at ∼18–18.5 ka. The timing of the onset of rapid warming matches the timing of the post-glacial rise in radiative forcing from atmospheric greenhouse gases (GHGs) from Antarctic ice cores (Brook et al., 1996; Marcott et al., 2014; Monnin et al., 2004; Schilt et al., 2010). Our temperature reconstruction registers ∼4.9 °C warming from the Last Glacial Maximum (LGM) to the late Holocene. This increase is larger than the average ∼2-4 °C warming observed in records from lower elevation sites in tropical East Africa, but similar to that observed at other high-elevation sites in this region. The increased warming at higher elevations thus confirms that the temperature lapse rate steepened during the LGM over this region. Our results also indicate ∼3 °C of warming during the mid-Holocene relative to the late Holocene. This suggests that the freezing-level height rose above Rwenzori summit elevations at that time, likely causing complete deglaciation of the Rwenzori Mountains from ∼5 to 7 ka. The mid-Holocene is thus a potential analog for the glacial and environmental changes that these mountains are likely to experience in the coming decades. Overall, the timing and magnitude of temperature change observed in our record has important implications for climate model projections of future warming in tropical Africa. VL - 281 UR - https://linkinghub.elsevier.com/retrieve/pii/S0277379122000476 ER - TY - JOUR T1 - Deep Equatorial Pacific Ocean Oxygenation and Atmospheric CO2 Over The Last Ice Age JF - Scientific Reports Y1 - 2020 A1 - Marcantonio, Franco A1 - Hostak, Ryan A1 - Hertzberg, Jennifer E. A1 - Schmidt, Matthew W. AB - Ventilation of carbon stored in the deep ocean is thought to play an important role in atmospheric CO2 increases associated with Pleistocene deglaciations. The presence of this respired carbon has been recorded by an array of paleoceanographic proxies from various locations across the global ocean. Here we present a new sediment core from the Eastern Equatorial Pacific (EEP) Ocean spanning the last 180,000 years and reconstruct high-resolution 230Th-derived fluxes of 232Th and excess barium, along with redox-sensitive uranium concentrations to examine past variations in dust delivery, export productivity, and bottom-water oxygenation, respectively. Our bottom-water oxygenation record is compared to other similar high-resolution records from across the Pacific and in the Southern Ocean. We suggest that the deep Pacific is a site of respired carbon storage associated with periods of decreased global atmospheric CO2 concentration during the LGM, confirming the conclusions from a wealth of previous studies. However, our study is the first to show a similar relationship beyond the last glacial, extending to at least 70,000 years VL - 10 UR - http://www.nature.com/articles/s41598-020-63628-x IS - 1 ER - TY - JOUR T1 - Deglacial temperature controls on no-analog community establishment in the Great Lakes Region JF - Quaternary Science Reviews Y1 - 2020 A1 - Fastovich, David A1 - Russell, James M. A1 - Jackson, Stephen T. A1 - Williams, John W. KW - biomarkers KW - brGDGT KW - Climate sensitivity KW - Lagoons & swamps KW - lakes KW - No-analog KW - North America KW - paleoclimatology KW - Pleistocene KW - pollen KW - sedimentology KW - Temperature KW - vegetation AB - Understanding the drivers of vegetation dynamics and no-analog communities in eastern North America is hampered by a scarcity of independent temperature indicators. We present a new branched glycerol dialkyl glycerol tetraether (brGDGT) temperature record from Bonnet Lake, Ohio (18–8 ka) and report uncertainty estimates based on Bayesian linear regression and bootstrapping. We also reanalyze a previously published brGDGT record from Silver Lake, Ohio, using improved chromatographic methods. All pollen- and brGDGT-based temperature reconstructions showed qualitatively similar deglacial trends but varying magnitudes. Separating 5- and 6- methyl brGDGTs resulted in substantially lower estimates of deglacial temperature variations (6.4 °C) than inferred from earlier brGDGT methods and pollen (11.8 °C, 12.0 °C respectively). Similar trends among proxies suggest good fidelity of brGDGTs to temperature, despite calibration uncertainties. At both sites, the rise and decline of no-analog communities closely track brGDGT-inferred temperatures, with a lag of 0–150 years. The timing of temperature and ecological events varies between Bonnet and Silver Lakes, likely due to age model uncertainties. Climate sensitivity analyses indicate a linear sensitivity of vegetation composition to temperature variations, albeit noisy and significant only with a 500-year bin. The formation of no-analog plant communities in the upper Midwest is closely linked to late-glacial warming, but other factors, such as temperature seasonality or end-Pleistocene megafaunal extinctions, remain viable. VL - 234 UR - https://linkinghub.elsevier.com/retrieve/pii/S0277379119303713 ER - TY - JOUR T1 - Delayed maximum and recession of an East Antarctic outlet glacierAbstract JF - Geology Y1 - 2020 A1 - King, Courtney A1 - Hall, Brenda A1 - Hillebrand, Trevor A1 - Stone, John AB - During the last glaciation, East Antarctic outlet glaciers contributed to a grounded ice sheet in the Ross Embayment. The timing of maximum ice extent, as well as of subsequent deglaciation of these outlets, has implications for the behavior of the Antarctic Ice Sheet (AIS) and its impact on global sea level. We present 45 radiocarbon ages of lacustrine cyanobacteria from the Lake Wellman region alongside Hatherton Glacier, which are the first terrestrial data to both record advance of an Antarctic glacier to its maximum position as well as document a high-resolution chronology of subsequent retreat. Seventeen new exposure ages are widely scattered, but the youngest four are in broad agreement with the radiocarbon data. Hatherton Glacier slowly thickened from 13,000 to 9500 yr B.P. and then thinned steadily until at least ca. 2800 yr B.P. Our work affords evidence of both a delayed maximum and recession of an East Antarctic outlet glacier compared to the global Last Glacial Maximum (LGM) and supports growing evidence of a time-transgressive local LGM within the Ross Sea sector of the ice sheet. Both observations are consistent with the idea that the timing of outlet glacier expansion and timing of recession are controlled by the balance between dynamic thinning from ocean forcing and increased accumulation due to atmospheric warming. VL - 48 UR - https://pubs.geoscienceworld.org/gsa/geology/article/48/6/630/583514/Delayed-maximum-and-recession-of-an-East-Antarctic IS - 6 ER - TY - JOUR T1 - Dissolved black carbon is not likely a significant refractory organic carbon pool in rivers and oceansAbstract JF - Nature Communications Y1 - 2020 A1 - Qi, Yuanzhi A1 - Fu, Wenjing A1 - Tian, Jiwei A1 - Luo, Chunle A1 - Shan, Sen A1 - Sun, Shuwen A1 - Ren, Peng A1 - Zhang, Hongmei A1 - Liu, Jiwen A1 - Zhang, Xiaohua A1 - Wang, Xuchen KW - Changjiang KW - cycle KW - flux KW - HUANGHE RIVERS KW - level KW - particulate KW - quantification KW - radiocarbon KW - sea AB - Rivers are the major carriers of dissolved black carbon (DBC) from land to ocean; the sources of DBC during its continuous transformation and cycling in the ocean, however, are not well characterized. Here, we present new carbon isotope data for DBC in four large and two small mountainous rivers, the Yangtze and Yellow river estuaries, the East China Sea and the North Pacific Ocean. We found that the carbon isotope signatures of DBC are relatively homogeneous, and the DBC C-14 ages in rivers are predominantly young and increase during continuous transport and cycling in the ocean. The results of charcoal leaching experiments indicate that DBC is released from charcoal and degraded by bacteria. Our study suggests that riverine DBC is labile and respired during transport and mixing into the ocean and that residual DBC is cycled and aged on the same time scales as bulk DOC in the ocean. Black carbon is a recalcitrant byproduct of biomass burning that ultimately accumulates in oceanic sinks. Here the authors assessed the sources and cycling of dissolved black carbon in rivers and oceans, finding that oceanic pools are cycled and aged on the same time scales as dissolved organic carbon. VL - 11 UR - http://www.nature.com/articles/s41467-020-18808-8http://www.nature.com/articles/s41467-020-18808-8.pdfhttp://www.nature.com/articles/s41467-020-18808-8.pdfhttp://www.nature.com/articles/s41467-020-18808-8 IS - 1 ER - TY - JOUR T1 - Dual carbon isotope (δ13C and Δ14C) characterization of particulate organic carbon in the Geum and Seomjin estuaries, South Korea JF - Marine Pollution Bulletin Y1 - 2020 A1 - Kang, Sujin A1 - Kim, Jung-Hyun A1 - Ryu, Jong-Sik A1 - Shin, Kyung-Hoon KW - carbon isotopes KW - dam KW - Estuary KW - Geum estuary KW - organic carbon KW - particulate KW - Seomjin estuary AB - We investigated the source, composition, and reactivity of particulate organic carbon (POC) in two contrasting Korean estuary systems, a closed estuary (Geum) (i.e., with an estuary dam at the river mouth) and an open (Seomjin) estuary. A dual isotope (δ13CPOC and Δ14CPOC) approach was applied to surface water samples collected along a salinity gradient in August 2016. Our results indicate that phytoplankton-derived POC was the main contributor to the total POC pool in the reservoir of the Geum estuary, while terrestrial-derived POC predominated the upper Seomjin estuary. A simple binary mixing model using Δ14CPOC revealed a higher modern POC contribution (87–90%) in the Geum estuary reservoir than that (77%) of the upper Seomjin estuary. Accordingly, it appears that an estuary dam can alter the source and reactivity of POC in a reservoir, which can be transferred to the adjacent coastal ecosystem. VL - 150 UR - https://linkinghub.elsevier.com/retrieve/pii/S0025326X19308756 ER - TY - JOUR T1 - Discovery of an Extensive Deep-Sea Fossil Serpulid Reef Associated With a Cold Seep, Santa Monica Basin, CaliforniaTable_1.docx JF - Frontiers in Marine Science Y1 - 2019 A1 - Georgieva, Magdalena N. A1 - Paull, Charles K. A1 - Little, Crispin T. S. A1 - McGann, Mary A1 - Sahy, Diana A1 - Condon, Daniel A1 - Lundsten, Lonny A1 - Pewsey, Jack A1 - Caress, David W. A1 - Vrijenhoek, Robert C. AB - 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. VL - 6 UR - https://www.frontiersin.org/article/10.3389/fmars.2019.00115/full ER - TY - JOUR T1 - Dissolved organic carbon in basalt-hosted deep subseafloor fluids of the Juan de Fuca Ridge flank JF - Earth and Planetary Science Letters Y1 - 2019 A1 - Lin, Huei-Ting A1 - Repeta, Daniel J. A1 - Xu, Li A1 - Rappé, Michael S. KW - aromatic organic compound KW - basaltic basement fluid KW - carbon isotopes KW - dissolved organic carbon KW - Juan de Fuca KW - selective removal KW - subseafloor AB - 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. VL - 513 UR - https://linkinghub.elsevier.com/retrieve/pii/S0012821X19300998 ER - TY - JOUR T1 - The distribution and magnitude of subglacial erosion on millennial timescales at Engabreen, NorwayAbstract JF - Annals of Glaciology Y1 - 2019 A1 - Rand, Cari A1 - Goehring, Brent M. KW - Beryllium-10 KW - Carbon-14 KW - cosmogenic nuclides KW - Engabreen KW - glacial erosion AB - 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. VL - 60 UR - https://www.cambridge.org/core/product/identifier/S0260305519000429/type/journal_article IS - 80 ER - TY - JOUR T1 - Data Constraints on Glacial Atlantic Water Mass Geometry and Properties JF - Paleoceanography and Paleoclimatology Y1 - 2018 A1 - Oppo, Delia W. A1 - Gebbie, Geoffrey A1 - Huang, Kuo‐Fang A1 - Curry, William B. A1 - Marchitto, Thomas M. A1 - Pietro, Kathryn R. AB - 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. VL - 33 UR - https://onlinelibrary.wiley.com/doi/abs/10.1029/2018PA003408 IS - 9 ER - TY - JOUR T1 - 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 JF - Marine Chemistry Y1 - 2018 A1 - Xu, Chen A1 - Zhang, Saijin A1 - Beaver, Morgan A1 - Wozniak, Andrew A1 - Obeid, Wassim A1 - Lin, Youmin A1 - Wade, Terry L. A1 - Schwehr, Kathleen A. A1 - Lin, Peng A1 - Sun, Luni A1 - Hatcher, Patrick G. A1 - Chin, Wei-Chun A1 - Chiu, Meng-Hsuen A1 - Knap, Anthony H. A1 - Dean, Kendra A1 - Quigg, Antonietta A1 - Santschi, Peter H. AB - 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. VL - 206 UR - https://linkinghub.elsevier.com/retrieve/pii/S0304420318301415 ER - TY - JOUR T1 - Deglacial floods in the Beaufort Sea preceded Younger Dryas cooling JF - Nature Geoscience Y1 - 2018 A1 - Keigwin, L. D. A1 - Klotsko, S. A1 - Zhao, N. A1 - Reilly, B. A1 - Giosan, L. A1 - Driscoll, N. W. AB - 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. VL - 11 UR - http://www.nature.com/articles/s41561-018-0169-6http://www.nature.com/articles/s41561-018-0169-6.pdfhttp://www.nature.com/articles/s41561-018-0169-6http://www.nature.com/articles/s41561-018-0169-6.pdf IS - 8 ER - TY - JOUR T1 - The demise of the largest and oldest African baobabs JF - Nature Plants Y1 - 2018 A1 - Patrut, Adrian A1 - Woodborne, Stephan A1 - Patrut, Roxana T. A1 - Rakosy, Laszlo A1 - Lowy, Daniel A. A1 - Hall, Grant A1 - von Reden, Karl F. AB - 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. VL - 4 UR - http://www.nature.com/articles/s41477-018-0170-5 IS - 7 ER - TY - JOUR T1 - Dimensions of Radiocarbon Variability within Sedimentary Organic MatterABSTRACT JF - Radiocarbon Y1 - 2018 A1 - Bao, Rui A1 - McNichol, Ann P A1 - McIntyre, Cameron P A1 - Xu, Li A1 - Eglinton, Timothy I KW - arabian sea KW - grain size KW - hydrodynamic processes KW - organicmatter KW - radiocarbon KW - ramped pyrolysis-oxidation AB - 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. VL - 60 UR - https://www.cambridge.org/core/journals/radiocarbon/article/dimensions-of-radiocarbon-variability-within-sedimentary-organic-matter/A81022494F34D8C3B88D39A43112BB08 IS - 03 ER - TY - JOUR T1 - Drought in the northern Bahamas from 3300 to 2500 years ago JF - Quaternary Science Reviews Y1 - 2018 A1 - van Hengstum, Peter J. A1 - Maale, Gerhard A1 - Donnelly, Jeffrey P. A1 - Albury, Nancy A. A1 - Onac, Bogdan P. A1 - Sullivan, Richard M. A1 - Winkler, Tyler S. A1 - Tamalavage, Anne E. A1 - MacDonald, Dana AB - 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. VL - 186 UR - https://linkinghub.elsevier.com/retrieve/pii/S0277379117306273 ER - TY - JOUR T1 - Dual-Isotope Constraints on Seasonally Resolved Source Fingerprinting of Black Carbon Aerosols in Sites of the Four Emission Hot Spot Regions of China JF - Journal of Geophysical Research: Atmospheres Y1 - 2018 A1 - Fang, Wenzheng A1 - Du, Ke A1 - Andersson, August A1 - Xing, Zhenyu A1 - Cho, Chaeyoon A1 - Kim, Sang-Woo A1 - Deng, Junjun A1 - Gustafsson, Örjan KW - aerosol KW - BLACK CARBON KW - carbon isotope KW - china KW - emission sources KW - seasonality AB - 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. VL - 123 UR - http://doi.wiley.com/10.1029/2018JD028607 IS - 20 ER - TY - JOUR T1 - The De Long Trough: a newly discovered glacial trough on the East Siberian continental margin JF - Climate of the Past Y1 - 2017 A1 - O'Regan, Matt A1 - Backman, Jan A1 - Barrientos, Natalia A1 - Cronin, Thomas M. A1 - Gemery, Laura A1 - Kirchner, Nina A1 - Mayer, Larry A. A1 - Nilsson, Johan A1 - Noormets, Riko A1 - Pearce, Christof A1 - Semiletov, Igor A1 - Stranne, Christian A1 - Jakobsson, Martin AB - Ice sheets extending over parts of the East Siberian continental shelf have been proposed for the last glacial period and during the larger Pleistocene glaciations. The sparse data available over this sector of the Arctic Ocean have left the timing, extent and even existence of these ice sheets largely unresolved. Here we present new geophysical mapping and sediment coring data from the East Siberian shelf and slope collected during the 2014 SWERUS-C3 expedition (SWERUS-C3: Swedish – Russian – US Arctic Ocean Investigation of Climate-Cryosphere-Carbon Interactions). The multibeam bathymetry and chirp sub-bottom profiles reveal a set of glacial landforms that include grounding zone formations along the outer continental shelf, seaward of which lies a  >  65 m thick sequence of glacio-genic debris flows. The glacial landforms are interpreted to lie at the seaward end of a glacial trough – the first to be reported on the East Siberian margin, here referred to as the De Long Trough because of its location due north of the De Long Islands. Stratigraphy and dating of sediment cores show that a drape of acoustically laminated sediments covering the glacial deposits is older than ∼ 50 cal kyr BP. This provides direct evidence for extensive glacial activity on the Siberian shelf that predates the Last Glacial Maximum and most likely occurred during the Saalian (Marine Isotope Stage (MIS) 6). VL - 13 UR - https://cp.copernicus.org/articles/13/1269/2017/ IS - 9 ER - TY - JOUR T1 - The deep distributions of helium isotopes, radiocarbon, and noble gases along the U.S. GEOTRACES East Pacific Zonal Transect (GP16) JF - Marine Chemistry Y1 - 2017 A1 - W. J. Jenkins A1 - Dempsey E. Lott III A1 - Christopher R. German A1 - Kevin L. Cahill A1 - Joanne Goudreau A1 - Brett Longworth AB - Abstract We report the deep distributions of noble gases, helium isotopes, and radiocarbon measured during the U.S. \{GEOTRACES\} \{GP16\} East Pacific Zonal Transect between 152 and 77°W at 12–15°S in the South Pacific. The dominant feature is an intense tongue of hydrothermal effluent that extends > 4000 km westward from the East Pacific Rise (EPR) at   2500 m depth. The patterns reveal significant “downstream” variations in water mass structure, advection, and mixing that belie the simple perception of a continuous plume extending westward from the EPR. For example, one feature observed at 120°W, 14°S has tracer signatures that are consistent with a water mass originating from an area as much as 2000 km south of this section, suggesting a quasi-permanent northward flow on the western flank of the EPR. Helium isotope variations in the plume show a uniquely high 3He/4He source in the tongue compared with typical mid-ocean ridge basalts (MORB), consistent with the anomalously high ratios observed in \{MORB\} glasses from the \{EPR\} segment just south of this transect. The water column data also reveal that the background 3He/4He east of the \{EPR\} is significantly lower than values characteristic of MORB, suggesting an additional, more geographically distributed radiogenic 4He flux of order 107 mol/y into the deep Pacific. In the western end of the section, incoming bottom waters have relatively less hydrothermal hydrothermal helium, more radiocarbon, and more oxygen, as well as negative saturation anomalies for the heavy noble gases (Ar, Kr, and Xe). During the basin-scale upwelling of this water, diapycnal mixing serves to erase these negative anomalies. The relative magnitudes of the increases for the heavy noble gases (Ar, Kr, and Xe) are quantitatively consistent with this process. This leads us to estimate the relatively smaller effects on He and Ne saturations, which range from near zero to 0.2% and 0.3% respectively. With this information, we are able to refine our estimates of the magnitude of 3He and 4He excesses and the absolute 3He/4He ratio of non-atmospheric helium introduced into deep Pacific waters. UR - http://www.sciencedirect.com/science/article/pii/S0304420316302353 ER - TY - JOUR T1 - Deglacial sea level history of the East Siberian Sea and Chukchi Sea margins JF - Climate of the Past Y1 - 2017 A1 - Cronin, Thomas M. A1 - O'Regan, Matt A1 - Pearce, Christof A1 - Gemery, Laura A1 - Toomey, Michael A1 - Semiletov, Igor A1 - Jakobsson, Martin AB - Deglacial (12.8–10.7 ka) sea level history on the East Siberian continental shelf and upper continental slope was reconstructed using new geophysical records and sediment cores taken during Leg 2 of the 2014 SWERUS-C3 expedition. The focus of this study is two cores from Herald Canyon, piston core SWERUS-L2-4-PC1 (4-PC1) and multicore SWERUS-L2-4-MC1 (4-MC1), and a gravity core from an East Siberian Sea transect, SWERUS-L2-20-GC1 (20-GC1). Cores 4-PC1 and 20-GC were taken at 120 and 115 m of modern water depth, respectively, only a few meters above the global last glacial maximum (LGM;  ∼  24 kiloannum or ka) minimum sea level of  ∼  125–130 meters below sea level (m b.s.l.). Using calibrated radiocarbon ages mainly on molluscs for chronology and the ecology of benthic foraminifera and ostracode species to estimate paleodepths, the data reveal a dominance of river-proximal species during the early part of the Younger Dryas event (YD, Greenland Stadial GS-1) followed by a rise in river-intermediate species in the late Younger Dryas or the early Holocene (Preboreal) period. A rapid relative sea level rise beginning at roughly 11.4 to 10.8 ka ( ∼  400 cm of core depth) is indicated by a sharp faunal change and unconformity or condensed zone of sedimentation. Regional sea level at this time was about 108 m b.s.l. at the 4-PC1 site and 102 m b.s.l. at 20-GC1. Regional sea level near the end of the YD was up to 42–47 m lower than predicted by geophysical models corrected for glacio-isostatic adjustment. This discrepancy could be explained by delayed isostatic adjustment caused by a greater volume and/or geographical extent of glacial-age land ice and/or ice shelves in the western Arctic Ocean and adjacent Siberian land areas. VL - 13 UR - https://cp.copernicus.org/articles/13/1097/2017/ IS - 9 ER - TY - JOUR T1 - Deglaciation and ice shelf development at the northeast margin of the Laurentide Ice Sheet during the Younger Dryas chronozone JF - Boreas Y1 - 2017 A1 - Furze, Mark F. A. A1 - ńkowski, Anna J. A1 - McNeely, Morgan A. A1 - Bennett, Robbie A1 - Cage, Alix G. AB - Core 2011804-0010 from easternmost Lancaster Sound provides important insights into deglacial timing and style at the marine margin of the NE Laurentide Ice Sheet (LIS). Spanning 13.2–11.0 cal. ka BP and investigated for ice-rafted debris (IRD), foraminifera, biogenic silica and total organic carbon, the stratigraphy comprises a lithofacies progression from proximal grounding line and sub-ice shelf environments to open glaciomarine deposition; a sequence similar to deposits from Antarctic ice shelves. These results are the first marine evidence of a former ice shelf in the eastern Northwest Passage and are consistent with a preceding phase of ice streaming in eastern Lancaster Sound. Initial glacial float-off and retreat occurred >13.2 cal. ka BP, followed by formation of an extensive deglacial ice shelf during the Younger Dryas, which acted to stabilize the retreating margin of the NE LIS until 12.5 cal. ka BP. IRD analyses of sub-ice shelf facies indicate initial high input from source areas on northern Baffin Island delivered to Lancaster Sound by a tributary ice stream in Admiralty Inlet. After ice shelf break-up, Bylot Island became the dominant source area. Foraminifera are dominated by characteristic ice-proximal glaciomarine benthics (Cassidulina reniforme, Elphidium excavatum f. clavata), complemented by advected Atlantic water (Cassidulina neoteretis, Neogloboquadrina pachyderma) and enhanced current indicators (Lobatula lobatula). The biostratigraphy further supports the ice shelf model, with advection of sparse faunas beneath the ice shelf, followed by increased productivity under open water glaciomarine conditions. The absence of Holocene sediments in the core suggests that the uppermost deposits were removed, most likely due to mass transport resulting from the site's proximity to modern tidewater glacier margins. Collectively, this study presents important new constraints on the deglacial behaviour of the NE Laurentide Ice Sheet, with implications for past ice sheet stability, ice-rafted sediment delivery, and ice−ocean interactions in this complex archipelago setting. UR - http://doi.wiley.com/10.1111/bor.12265 ER - TY - JOUR T1 - Determining rates of sediment accumulation on the Mekong shelf: Timescales, steady-state assumptions, and radiochemical tracers JF - Continental Shelf Research Y1 - 2017 A1 - DeMaster, D.J. A1 - Liu, J.P. A1 - Eidam, E. A1 - Nittrouer, C.A. A1 - Nguyen, T.T. KW - 14C geochronology KW - 210Pb geochronology KW - Deltaic sediment accumulation rates KW - Mekong delta KW - Mekong sediment budget AB - Thirty-two kasten cores, collected from the proximal Mekong continental shelf, have been analyzed for their excess 210Pb distributions in an effort to establish rates of sediment accumulation over the past 100 years. The length of the cores varied from 0.5 to 3 m, and stations sampled topset, foreset, and bottomset beds (water depths 7–21 m). Apparent excess 210Pb sediment accumulation rates ranged from > 10 cm/y (no down-core decrease of excess activity over 300 cm core length) near the Song Hau river mouth, to 1–3 cm/y in topset and foreset beds within 20–50 km of the river mouth, to rates as low as 0.4 cm/y in cores from bottomset beds. The 210Pb sediment accumulation rates yield an overall sediment burial rate of 6.1 × 1013 g/y for the proximal deltaic deposits, which corresponds to 43% of the total modern Mekong sediment burial on the southern Vietnam shelf (1.4 × 1014 g/y; based on our 210Pb and seismic data and 210Pb data from the literature). This shelf burial rate is in reasonable agreement with current long-term estimates of Mekong River sediment discharge (1.3–1.6 × 1014 g/y) from the literature. The inventory of excess 210Pb in the proximal Mekong deltaic deposits indicates that the shoreward flow of offshore water (entrained during river/ocean mixing) is approximately twice the flow of the Mekong freshwater discharge. Organic-carbon 14C ages were measured on 10 cores from the proximal Mekong delta and compared to 210Pb sediment accumulation rates in the same core. The 210Pb accumulation rates in all 10 cores were considered to be more robust and accurate than the 14C geochronologies, primarily because of down-core variations in the source of organic carbon deposited on the seafloor (old terrestrial carbon versus younger marine carbon). Variations in the source of organic carbon accumulating in the seabed were resolved by measuring the δ13C value of the seabed organic carbon. VL - 147 UR - https://www.sciencedirect.com/science/article/pii/S0278434316306732 ER - TY - JOUR T1 - The distribution and utility of sea-level indicators in Eurasian sub-Arctic salt marshes (White Sea, Russia) JF - Boreas Y1 - 2017 A1 - Kemp, Andrew C. A1 - Horton, Benjamin P. A1 - Nikitina, Daria A1 - Vane, Christopher H. A1 - Potapova, Marina A1 - Weber-Bruya, Elizabeth A1 - Culver, Stephen J. A1 - Repkina, Tatyana A1 - Hill, David F. AB - In support of efforts to reconstruct relative sea level (RSL), we investigated the utility of foraminifera, diatoms and bulk‐sediment geochemistry (δ13C, C:N and parameters measured by Rock‐Eval pyrolysis) as sea‐level indicators in Eurasian sub‐Arctic salt marshes. At three salt marshes (<15 km apart) in Dvina Bay (White Sea, Russia), we collected surface sediment samples along transects from subtidal to Taiga forest environments. Foraminifera at all sites formed bipartite assemblages, where elevations below mean high higher water (MHHW) were dominated by Miliammina spp. and elevations between MHHW and the highest occurrence of foraminifera were dominated by Jadammina macrescens and Balticammina pseudomacrescens. Five high‐diversity groups of diatoms were identified and they displayed pronounced variability amongst the study sites. Bulk‐sediment geochemistry recognized two groups (clastic‐dominated environments below MHHW and organic‐rich environments above MHHW). As one group included subtidal elevations and the other included supratidal elevations, we conclude that the measured geochemical parameters are not stand‐alone sea‐level indicators. Core JT2012 captured a regressive sediment succession of clastic, tidal‐flat sediment overlain by salt‐marsh organic silt and freshwater peat. The salt‐marsh sediment accumulated at 2804±52 years before present and preserved foraminifera (Jadammina macrescens and Balticammina pseudomacrescens) with good analogy to modern assemblages indicating that RSL was +2.60±0.47 m at this time. Diatoms confirm that marine influence decreased through time, but the lack of analogy between modern and core assemblages limited their utility as sea‐level indicators. Geochemical parameters also indicate a reduction in marine influence through time. We conclude that RSL reconstructions derived from salt‐marsh sediment preserved beneath Eurasian sub‐Arctic peatlands can provide valuable insight into the spatio‐temporal evolution of the Fennoscandian and Eurasian ice sheets. VL - 46 UR - https://onlinelibrary.wiley.com/doi/10.1111/bor.12233 IS - 3 ER - TY - JOUR T1 - Divergent Evolution of Carbonaceous Aerosols during Dispersal of East Asian Haze JF - Scientific Reports Y1 - 2017 A1 - Fang, Wenzheng A1 - Andersson, August A1 - Zheng, Mei A1 - Lee, Meehye A1 - Holmstrand, Henry A1 - Kim, Sang-Woo A1 - Du, Ke A1 - Gustafsson, Örjan AB - Wintertime East Asia is plagued by severe haze episodes, characterized by large contributions of carbonaceous aerosols. However, the sources and atmospheric transformations of these major components are poorly constrained, hindering development of efficient mitigation strategies and detailed modelling of effects. Here we present dual carbon isotope (δ13C and Δ14C) signatures for black carbon (BC), organic carbon (OC) and water-soluble organic carbon (WSOC) aerosols collected in urban (Beijing and BC for Shanghai) and regional receptors (e.g., Korea Climate Observatory at Gosan) during January 2014. Fossil sources (>50%) dominate BC at all sites with most stemming from coal combustion, except for Shanghai, where liquid fossil source is largest. During source-to-receptor transport, the δ13C fingerprint becomes enriched for WSOC but depleted for water-insoluble OC (WIOC). This reveals that the atmospheric processing of these two major pools are fundamentally different. The photochemical aging (e.g., photodissociation, photooxidation) during formation and transport can release CO2/CO or short-chain VOCs with lighter carbon, whereas the remaining WSOC becomes increasingly enriched in δ13C. On the other hand, several processes, e.g., secondary formation, rearrangement reaction in the particle phase, and photooxidation can influence WIOC. Taken together, this study highlights high fossil contributions for all carbonaceous aerosol sub-compartments in East Asia, and suggests different transformation pathways for different classes of carbonaceous aerosols. VL - 7 UR - http://www.nature.com/articles/s41598-017-10766-4 IS - 1 ER - TY - JOUR T1 - Documenting domestication in a lost crop (Polygonum erectum L.): evolutionary bet-hedgers under cultivation JF - Vegetation History and Archaeobotany Y1 - 2017 A1 - Mueller, Natalie G. KW - Domestication KW - Eastern Agricultural Complex KW - Evolutionary bet-hedging KW - Morphometrics KW - Origins of agriculture AB - This study uses morphometrics and digital image analysis to document domestication syndrome in an annual seed crop, Polygonum erectum L. (erect knotweed), which was cultivated by Native Americans for c. 2,500 years in eastern North America. This plant is one of several seed crops referred to as the Eastern Agricultural Complex, a pre-maize agricultural system that supported societies in a core area centred on the central Mississippi valley for millennia. The extinct domesticated subspecies P. erectum ssp. watsoniae N. G. Muell. described here, exhibits some classic markers of domestication, including larger fruits and reduced germination inhibitors in comparison to its wild progenitor. Domesticated P. erectum also exhibits greatly reduced germination heteromorphism. Germination heteromorphism is the classic example of evolutionary bet-hedging in plants: wild P. erectum sacrifices maximum fitness per generation for a reduction in fitness variance over many generations. It does so by producing two different types of fruits: ones that germinate immediately in the spring after they are produced (smooth morphs), and ones that remain in the soil seed bank for one or more growing seasons before germinating (tubercled morphs). Tubercled morphs allow populations to recover after adverse events. Under cultivation, the selective pressures that maintained this strategy were relaxed as humans saved seeds and created predictable microenvironments for seedlings, resulting in homogenous harvests and reliable germination for ancient farmers. VL - 2621544151612277251256252491314471317501927512453130187936325211846611242525023108578256126282112 UR - http://link.springer.com/10.1007/s00334-016-0592-9http://link.springer.com/content/pdf/10.1007/s00334-016-0592-9.pdfhttp://link.springer.com/content/pdf/10.1007/s00334-016-0592-9.pdfhttp://link.springer.com/article/10.1007/s00334-016-0592-9/fulltext.html IS - 3 ER - TY - JOUR T1 - Dynamics of marsh-mangrove ecotone since the mid-Holocene: A palynological study of mangrove encroachment and sea level rise in the Shark River Estuary, Florida JF - PLOS ONE Y1 - 2017 A1 - Yao, Qiang A1 - Liu, Kam-biu ED - Magar, Vanesa AB - Sea level rise and the associated inland shift of the marsh-mangrove ecotone in south Florida have raised many scientific and management concerns in recent years. Holocene paleoecological records can provide an important baseline to shed light on the long-term dynamics of vegetation changes across this ecotone in the past, which is needed to predict the future. In this study, we present palynological, X-ray fluorescence, and loss-on ignition data from four sedimentary cores recovered from a 20-km marine-to-freshwater transect along the Shark River Estuary, southwest Everglades, to document the patterns and processes of coastal vegetation changes in response to sea level rise since the mid-Holocene. Our record indicates that freshwater marsh progressively replaced marl prairies at the Shark River Estuary between 5700 and 4400 cal yr BP. As marine transgression continued, marine influence reached the threshold necessary for mangroves to establish at the current mouth of the Shark River Slough at 3800 cal yr BP. During the next 3000 years, although sea level rise in the Western North Atlantic slowed down to 0.4 mm/yr, a spatial and temporal gradient was evident as the marsh-mangrove ecotone shifted inland by 20 km from 3800 to 800 cal yr BP, accompanied by a gradual landward replacement of freshwater marsh by mangrove forest. If sea level continues to rise at 2.33 mm/yr in the 21st century in south Florida, it is possible that marine influence will reach the threshold for mangroves to establish in the central Everglades, and we could expect a much more aggressive mangrove encroachment toward the northern and interior parts of south Florida in the next few centuries. UR - https://doi.org/10.1371/journal.pone.0173670 ER - TY - JOUR T1 - Detrital cave sediments record Late Quaternary hydrologic and climatic variability in northwestern Florida, USA JF - Sedimentary Geology Y1 - 2016 A1 - Winkler, Tyler S. A1 - van Hengstum, Peter J. A1 - Horgan, Meghan C. A1 - Donnelly, Jeffrey P. A1 - Reibenspies, Joseph H. KW - Apalachicola KW - florida KW - Karst KW - Phreatic KW - Underwater cave AB - Detrital sediment in Florida's (USA) submerged cave systems may preserve records of regional climate and hydrologic variability. However, the basic sedimentology, mineralogy, stratigraphic variability, and emplacement history of the successions in Florida's submerged caves remains poorly understood. Here we present stratigraphic, mineralogical, and elemental data on sediment cores from two phreatic cave systems in northwestern Florida (USA), on the Dougherty Karst Plain: Hole in the Wall Cave (HITW) and Twin Cave. Water flowing through these caves is subsurface flow in the Apalachicola River drainage basin, and the caves are located just downstream from Jackson Blue (1st magnitude spring, > 2.8 m3 s− 1 discharge). Sedimentation in these caves is dominated by three primary sedimentary styles: (i) ferromanganese deposits dominate the basal recovered stratigraphy, which pass upsection into (ii) poorly sorted carbonate sediment, and finally into (iii) fine-grained organic matter (gyttja) deposits. Resolving the emplacement history of the lower stratigraphic units was hampered by a lack of suitable material for radiocarbon dating, but the upper organic-rich deposits have a punctuated depositional history beginning in the earliest Holocene. For example, gyttja primarily accumulated in HITW and Twin Caves from ~ 5500 to 3500 cal yr. BP, which coincides with regional evidence for water-table rise of the Upper Floridian Aquifer associated with relative sea-level rise in the Gulf of Mexico, and evidence for invigorated drainage through the Apalachicola River drainage basin. Gyttja sediments were also deposited in one of the caves during the Bølling/Allerød climate oscillation. Biologically, these results indicate that some Floridian aquatic cave (stygobitic) ecosystems presently receive minimal organic matter supply in comparison to prehistoric intervals. The pre-Holocene poorly sorted carbonate sediment contains abundant invertebrate fossils, and likely documents a period of enhanced limestone dissolution and cave formation (speleogenesis) during lower paleo water levels. Further work is still required to (a) determine whether precipitation of the ferromanganese deposits is inorganically or biologically mediated, (b) temporally constrain the emplacement history of the primary sedimentary styles, and (c) determine the full geographic extent of these sedimentary signals. However, these preliminary observations suggest that sedimentation in the inland underwater caves of northwestern Florida is related to Quaternary-scale hydrographic variability in the Apalachicola River drainage basin in response to broader ocean and atmospheric forcing. VL - 335 UR - http://linkinghub.elsevier.com/retrieve/pii/S0037073816000312http://api.elsevier.com/content/article/PII:S0037073816000312?httpAccept=text/xmlhttp://api.elsevier.com/content/article/PII:S0037073816000312?httpAccept=text/plain ER - TY - JOUR T1 - Differences in coastal subsidence in southern Oregon (USA) during at least six prehistoric megathrust earthquakes JF - Quaternary Science Reviews Y1 - 2016 A1 - Milker, Yvonne A1 - Nelson, Alan R. A1 - Horton, Benjamin P. A1 - Engelhart, Simon E. A1 - Bradley, Lee-Ann A1 - Witter, Robert C. KW - Cascadia subduction zone KW - Coseismic subsidence KW - Megathrust earthquakes KW - Paleoseismology KW - Salt-marsh foraminifera KW - Sea-level change KW - Transfer functions AB - Stratigraphic, sedimentologic (including CT 3D X-ray tomography scans), foraminiferal, and radiocarbon analyses show that at least six of seven abrupt peat-to-mud contacts in cores from a tidal marsh at Talbot Creek (South Slough, Coos Bay), record sudden subsidence (relative sea-level rise) during great megathrust earthquakes at the Cascadia subduction zone. Data for one contact are insufficient to infer whether or not it records a great earthquake—it may also have formed through local, non-seismic, hydrographic processes. To estimate the amount of subsidence marked by each contact, we expanded a previous regional modern foraminiferal dataset to 174 samples from six Oregon estuaries. Using a transfer function derived from the new dataset, estimates of coseismic subsidence across the six earthquake contacts vary from 0.31 m to 0.75 m. Comparison of subsidence estimates for three contacts in adjacent cores shows within-site differences of ≤0.10 m, about half the ±0.22 m error, although some estimates may be minimums due to uncertain ecological preferences for Balticammina pseudomacrescens in brackish environments and almost monospecific assemblages of Miliammina fusca on tidal flats. We also account for the influence of taphonomic processes, such as infiltration of mud with mixed foraminiferal assemblages into peat, on subsidence estimates. Comparisons of our subsidence estimates with values for correlative contacts at other Oregon sites suggest that some of our estimates are minimums and that Cascadia's megathrust earthquake ruptures have been heterogeneous over the past 3500 years. VL - 142 UR - https://doi.org/10.1016/j.quascirev.2016.04.017 ER - TY - JOUR T1 - DISSOLVED INORGANIC RADIOCARBON IN THE NORTHWEST PACIFIC CONTINENTAL MARGIN JF - RADIOCARBON Y1 - 2016 A1 - Ge, Tiantian A1 - Wang, Xuchen A1 - Zhang, Jing A1 - Luo, Chunle A1 - Xue, Yuejun KW - continental margin KW - dissolved inorganic carbon KW - East China Sea KW - radiocarbon KW - stable carbon isotope AB - This article presents a modified method for extraction of dissolved inorganic carbon (DIC) from seawater for radiocarbon measurement by accelerator mass spectrometry (AMS). Standard tests indicate that the extraction efficiencies of DIC are >96%, and the respective precisions of. Delta C-14-DIC and delta C-13-DIC analyses are 6% and 0.1% or better. Using the method, we report. Delta C-14-DIC profiles collected from the shelf and slope in the East China Sea (ECS) of the northwest Pacific Ocean. Both the DIC concentration and. Delta C-14-DIC in the shelf and slope regions seem primarily affected by the Kuroshio Current. It is estimated that 54-65% of the bottom water in the shelf region could be from the intrusion of Kuroshio intermediate water, which carries a high concentration and low. Delta C-14 values of DIC, and which influenced the DIC and its Delta C-14 signature on the shelf. Compared with the. Delta C-14-DIC profiles at other sites in the northwest Pacific reported previously, it appears that the. Delta C-14-DIC distributions are mainly controlled by the major oceanic currents in the region, and large variations in. Delta C-14-DIC occurred mostly in the upper 800m of the water column. The similarity of. Delta C-14-DIC at depth suggests that the deep-water circulation patterns have been relatively stable in the northwest Pacific Ocean in the last 20 yr. VL - 58 ER - TY - JOUR T1 - Distribution, provenance and early diagenesis of major and trace metals in sediment cores from the Mandovi estuary, western India JF - Estuarine, Coastal and Shelf Science Y1 - 2016 A1 - A. Prajith A1 - V. Purnachandra Rao A1 - P. Chakraborty KW - Western India AB - Abstract Major elements and trace metals were analyzed in four sediment cores recovered along a transect in the Mandovi estuary for their distribution, provenance and early diagenesis. The sediments were clayey silts in cores from the upper/lower estuary and sand-dominated in cores from the middle estuary/bay. Organic carbon (OC) content varied from 0.5 to 4%, with higher values in fine-grained sediments. The mean Fe and Mn contents of sediments from the upper/middle estuary were 3–5 times and 8–13 times, respectively higher than the reference sediment (RS) from the same estuary. The mean Fe and Mn contents of sediments from the lower estuary/bay were close to the RS. Strong inter-metal correlation among Ti, V, Cr and Zr in all the cores indicated their contribution from a common source, probably the laterites from hinterland. Trace metals were more enriched in fine-grained sediments than in sand-dominated sediments. Early diagenetic control on the redistribution of metal is evident in core sediments from the middle estuary to Bay. The distribution of Mo, U and Pb followed that of Fe and Mn in the upper estuary and \{OC\} in the lower estuary/bay. Our results indicated strong anthropogenic contribution of metals from ore deposits in the upper/middle estuary. The Mn and Cr contents of sediment in the upper/middle estuary and Fe in the middle estuary were highly enriched suggestive of ‘significant pollution signal’. More trace metals from the middle estuary were moderately enriched. Speciation studies showed Mn and Pb occurred abundantly in non-residual phases. High Mn content and its high percentage in exchangeable and reductive phases indicate that it was susceptible to be mobilized. However, Fe, Cu and Ni occurred abundantly in residual phases and less percentage of them were expected to be bio-available. VL - 170 UR - http://www.sciencedirect.com/science/article/pii/S0272771416300142 ER - TY - JOUR T1 - Distributions and accumulation rates of polycyclic aromatic hydrocarbons in the northern Gulf of Mexico sediments JF - Environmental Pollution Y1 - 2016 A1 - Puspa L. Adhikari A1 - Kanchan Maiti A1 - Edward B. Overton A1 - Brad E. Rosenheim A1 - Brian D. Marx KW - Radiocarbon (Δ14C) AB - Abstract Sediment samples collected from shelf, slope and interior basin of the northern Gulf of Mexico during 2011–2013, 1–3 years after the Deepwater Horizon (DWH) oil spill, were utilized to characterize \{PAH\} pollution history, in this region. Results indicate that the concentrations of surface ΣPAH43 and their accumulation rates vary between 44 and 160 ng g−1 and 6–55 ng cm−2 y−1, respectively. ΣPAH43 concentration profiles, accumulation rates and Δ14C values are significantly altered only for the sediments in the immediate vicinity of the \{DWH\} wellhead. This shows that the impact of \{DWH\} oil input on deep-sea sediments was generally limited to the area close to the spill site. Further, the \{PAHs\} source diagnostic analyses suggest a noticeable change in \{PAHs\} composition from higher to lower molecular weight dominance which reflects a change in source of \{PAHs\} in the past three years, back to the background composition. Results indicate low to moderate levels of \{PAH\} pollution in this region at present, which are unlikely to cause adverse effects on benthic communities. VL - 212 UR - http://www.sciencedirect.com/science/article/pii/S0269749116300641 ER - TY - JOUR T1 - Dual carbon isotope characterization of total organic carbon in wintertime carbonaceous aerosols from northern India JF - Journal of Geophysical Research: Atmospheres Y1 - 2016 A1 - Bikkina, Srinivas A1 - Andersson, August A1 - Sarin, M. M. A1 - Sheesley, R. J. A1 - Kirillova, E. A1 - Rengarajan, R. A1 - Sudheer, A. K. A1 - Ram, K. A1 - Gustafsson, Örjan AB - Large-scale emissions of carbonaceous aerosols (CA) from South Asia impact both regional climate and air quality, yet their sources are not well constrained. Here we use source-diagnostic stable and radiocarbon isotopes (δ13C and Δ14C) to characterize CA sources at a semiurban site (Hisar: 29.2°N, 75.2°E) in the NW Indo-Gangetic Plain (IGP) and a remote high-altitude location in the Himalayan foothills (Manora Peak: 29.4°N, 79.5°E, 1950 m above sea level) in northern India during winter. The Δ14C of total aerosol organic carbon (TOC) varied from −178‰ to −63‰ at Hisar and from −198‰ to −1‰ at Manora Peak. The absence of significant differences in the 14C-based fraction biomass of TOC between Hisar (0.81 ± 0.03) and Manora Peak (0.82 ± 0.07) reveals that biomass burning/biogenic emissions (BBEs) are the dominant sources of CA at both sites. Combining this information with δ13C, other chemical tracers (K+/OC and SO42−/EC) and air mass back trajectory analyses indicate similar source regions in the IGP (e.g., Punjab and Haryana). These results highlight that CA from BBEs in the IGP are not only confined to the atmospheric boundary layer but also extend to higher elevations of the troposphere, where the synoptic-scale circulations could substantially influence their abundances both to the Himalayas and over the downwind oceanic regions such as the Indian Ocean. Given the vast emissions of CA from postharvest crop residue combustion practices in the IGP during early Northeast Monsoon, this information is important for both improved process and model understanding of climate and health effects, as well as in guiding policy decision aiming at reducing emissions. VL - 121 UR - http://doi.wiley.com/10.1002/2016JD024880https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1002%2F2016JD024880 IS - 9 ER - TY - JOUR T1 - Deciphering microbial carbon substrates in PAH contaminated sediments using phospholipid fatty acids, and compound specific δ13C and Δ14C JF - Organic Geochemistry Y1 - 2014 A1 - Morrill, Penny L. A1 - Szponar, Natalie A1 - Johnston, Mathew A1 - Marvin, Chris A1 - Slater, Gregory F. AB - Stable and radiogenic carbon isotopes (δ13C and Δ14C) of organic compounds and phospholipid fatty acids (PLFAs), as well as polycyclic aromatic hydrocarbon (PAH) ratios were used to determine sources and fates of organic contaminants in highly contaminated, and less contaminated sediments of Hamilton Harbour. The highly contaminated sediments had an order of magnitude more total petroleum hydrocarbons (TPHs) compared to the less contaminated sediments. The TPHs extracted from both sites were depleted in 14C (average Δ14C of −775‰ and −973‰, for Sites 1 and 2, respectively) consistent with inputs of fossil derived contaminants. Fossil carbon also contributed to the unextractable residue (Δ14C = −503 ± 55‰) in the sediment at the highly contaminated site relative to the less contaminated site (Δ14C = −132 ± 2‰) indicating inputs of fossil carbon not derived from petroleum or PAHs. Diagnostic PAH ratios (e.g. PAH:NaP between 0.01 and 1), and less negative δ13C (−25.6 ± 0.2‰) of the unextractable residue indicated that a coal derived source was the most likely source of these inputs. Despite the presence of this fossil carbon, there was little evidence of utilization of ancient carbon by the microbial community. The Δ14C of PLFAs from the highly contaminated site were slightly more 14C depleted (Δ14C = −138 ± 20‰) relative to the PLFAs from the less contaminated site (Δ14C = −77 ± 42‰), demonstrating some microbial metabolism of older carbon; however, the majority of the carbon metabolized was modern at both sites, indicating that there was minimal natural attenuation via bioremediation of fossil fuel organic contaminants. VL - 69 UR - http://www.sciencedirect.com/science/article/pii/S0146638014000308 JO - Deciphering microbial carbon substrates in PAH contaminated sediments using phospholipid fatty acids, and compound specific δ13C and Δ14C ER - TY - JOUR T1 - Decreased influence of Antarctic intermediate water in the tropical Atlantic during North Atlantic cold events JF - Earth and Planetary Science Letters Y1 - 2014 A1 - Huang, Kuo-Fang A1 - Oppo, Delia W. A1 - Curry, William B. KW - antarctic intermediate water KW - Atlantic meridional overturning circulation KW - deglacial variability KW - Nd isotopes KW - North Atlantic cold events AB - Antarctic Intermediate Water (AAIW) is a key player in the global ocean circulation, contributing to the upper limb of the Atlantic Meridional Overturning Circulation (AMOC), and influencing interhemispheric heat exchange and the distribution of salinity, nutrients and carbon. However, the deglacial history of AAIW flow into the North Atlantic is controversial. Here we present a multicore-top neodymium isotope calibration, which confirms the ability of unclean foraminifera to faithfully record bottom water neodymium isotopic composition () values in their authigenic coatings. We then present the first foraminifera-based reconstruction of from three sediment cores retrieved from within modern AAIW, in the western tropical North Atlantic. Our records reveal similar glacial and interglacial contributions of AAIW, and a pronounced decrease in the AAIW fraction during North Atlantic deglacial cold episodes, Heinrich Stadial 1 (HS1) and Younger Dryas (YD). Our results suggest two separate phases of reduced fraction of AAIW in the tropical Atlantic during HS1, with a greater reduction during early HS1. If a reduction in AAIW fraction also reflects reduced AMOC strength, this finding may explain why, in many regions, there are two phases of hydrologic change within HS1, and why atmospheric CO2 rose more rapidly during early than late HS1. Our result suggesting less flow of AAIW into the Atlantic during North Atlantic cold events contrasts with evidence from the Pacific, where intermediate-depth records may indicate increased flow of AAIW into the Pacific during the these same events. Antiphased behavior between intermediate depths of the North Atlantic and Pacific implies that the flow of AAIW into Atlantic and Pacific seesawed during the last deglaciation. VL - 389 UR - https://doi.org/10.1016/j.epsl.2013.12.037 ER - TY - JOUR T1 - Deglacial ?18O and hydrologic variability in the tropical Pacific and Indian Oceans JF - Earth and Planetary Science Letters Y1 - 2014 A1 - Gibbons, Fern T. A1 - Oppo, Delia W. A1 - Mohtadi, Mahyar A1 - Rosenthal, Yair A1 - Cheng, Jun A1 - Liu, Zhengyu A1 - Linsley, Braddock K. KW - Deglaciation KW - Eastern Equatorial Pacific KW - heat transport KW - Indo-Pacific KW - δ18O of seawater AB - Evidence from geologic archives suggests that there were large changes in the tropical hydrologic cycle associated with the two prominent northern hemisphere deglacial cooling events, Heinrich Stadial 1 (HS1; ∼19 to 15 kyr BP; kyr BP = 1000 yr before present) and the Younger Dryas (∼12.9 to 11.7 kyr BP). These hydrologic shifts have been alternatively attributed to high and low latitude origin. Here, we present a new record of hydrologic variability based on planktic foraminifera-derived δ18O of seawater (δ18Osw) estimates from a sediment core from the tropical Eastern Indian Ocean, and using 12 additional δ18Osw records, construct a single record of the dominant mode of tropical Eastern Equatorial Pacific and Indo-Pacific Warm Pool (IPWP) hydrologic variability. We show that deglacial hydrologic shifts parallel variations in the reconstructed interhemispheric temperature gradient, suggesting a strong response to variations in the Atlantic Meridional Overturning Circulation and the attendant heat redistribution. A transient model simulation of the last deglaciation suggests that hydrologic changes, including a southward shift in the Intertropical Convergence Zone (ITCZ) which likely occurred during these northern hemisphere cold events, coupled with oceanic advection and mixing, resulted in increased salinity in the Indonesian region of the IPWP and the eastern tropical Pacific, which is recorded by the δ18Osw proxy. Based on our observations and modeling results we suggest the interhemispheric temperature gradient directly controls the tropical hydrologic cycle on these time scales, which in turn mediates poleward atmospheric heat transport. VL - 387 UR - https://doi.org/10.1016/j.epsl.2013.11.032 ER - TY - JOUR T1 - Delta growth and river valleys: the influence of climate and sea level changes on the South Adriatic shelf (Mediterranean Sea) JF - Quaternary Science Reviews Y1 - 2014 A1 - Maselli, V. A1 - Trincardi, F. A1 - Asioli, A. A1 - Ceregato, A. A1 - Rizzetto, F. A1 - Taviani, M. AB - Incised valleys across continental margins represent the response of fluvial systems to changes in their equilibrium dynamics, mainly driven by base level fall forced by glacial–eustatic cycles. The Manfredonia Incised Valley formed during the last glacial sea level lowstand, when most of the southern Adriatic shelf was sub-aerially exposed but the outer shelf remained under water. The pronounced upstream deepening of the valley is ascribed to river incision of the MIS5e highstand coastal prism and related subaqueous clinoform under the influence of MIS5-4 sea level fluctuations, while the downstream shallowing and narrowing mainly reflects the impact of increased rates of sea level fall at the MIS3-2 transition on a flatter mid-outer shelf. Until 15 ka BP, the valley fed an asymmetric delta confined to the mid-outer shelf, testifying that continental and deep marine systems remained disconnected during the lowstand. Sea level rise reached the inner shelf during the Early Holocene, drowning the valley and leading to the formation of a sheltered embayment confined toward the land: at this time part of the incision remained underfilled with a marked bathymetric expression. This mini-basin was rapidly filled by sandy bayhead deltas, prograding from both the northern and southern sides of the valley. In this environment, protected by marine reworking and where sediment dispersal was less effective, the accommodation space was reduced and autogenic processes forced the formation of multiple and coalescing delta lobes. Bayhead delta progradations occurred in few centuries, between 8 and 7.2 ka cal BP, confirming the recent hypothesis that in this area the valley was filled during the formation of sapropel S1. This proximal valley fill, representing the very shallow-water equivalent of the cm-thick sapropel layers accumulated offshore in the deeper southern Adriatic basin, is of key importance in following the signature of the sapropel in a facies-tract ideally from the shoreline to the abyss. VL - 99 UR - http://www.sciencedirect.com/science/article/pii/S0277379114002431 JO - Delta growth and river valleys: the influence of climate and sea level changes on the South Adriatic shelf (Mediterranean Sea) ER - TY - JOUR T1 - A depth refugium from catastrophic coral bleaching prevents regional extinction JF - Ecology Y1 - 2014 A1 - Smith, Tyler B. A1 - Glynn, Peter W. A1 - é, Juan L. A1 - Toth, Lauren T. A1 - Gyory, Joanna KW - Coral bleaching KW - Coral mortality KW - Depth refuge KW - Eastern Tropical Pacific KW - El Nino-Southern Oscillation KW - Extinction KW - Holocene KW - Millepora KW - Refuge AB - Species intolerant of changing climate might avoid extinction within refugia buffered from extreme conditions. Refugia have been observed in the fossil record but are not well documented or understood on ecological time scales. Using a 37-year record from the eastern Pacific across the two most severe El Nin o events on record (1982-1983 and 1997- 1998) we show how an exceptionally thermally sensitive reef-building hydrocoral, Millepora intricata, twice survived catastrophic bleaching in a deeper-water refuge (.11 m depth). During both events, M. intricata was extirpated across its range in shallow water, but showed recovery within several years, while two other hydrocorals without deep-water populations were driven to regional extinction. Evidence from the subfossil record in the same area showed shallow-water persistence of abundant M. intricata populations from 5000 years ago, through severe El Nin o-Southern Oscillation cycles, suggesting a potential depth refugium on a millennial timescale. Our data confirm the deep refuge hypothesis for corals under thermal stress. © 2014 by the Ecological Society of America. VL - 95 UR - http://doi.wiley.com/10.1890/13-0468.1 IS - 6 ER - TY - JOUR T1 - Diverse rupture modes for surface-deforming upper-plate earthquakes in the southern Puget Lowland of Washington State JF - Geosphere Y1 - 2014 A1 - Nelson, Alan R. A1 - Personius, Stephen F. A1 - Sherrod, Brian L. A1 - Kelsey, Harvey M. A1 - Johnson, Samuel Y. A1 - Bradley, Lee-Ann A1 - Wells, Ray E. AB - Earthquake prehistory of the southern Puget Lowland, in the north-south compressive regime of the migrating Cascadia forearc, reflects diverse earthquake rupture modes with variable recurrence. Stratigraphy and Bayesian analyses of previously reported and new 14C ages in trenches and cores along backthrust scarps in the Seattle fault zone restrict a large earthquake to 1040–910 cal yr B.P. (2σ), an interval that includes the time of the M 7–7.5 Restoration Point earthquake. A newly identified surface-rupturing earthquake along the Waterman Point backthrust dates to 940–380 cal yr B.P., bringing the number of earthquakes in the Seattle fault zone in the past 3500 yr to 4 or 5. Whether scarps record earthquakes of moderate (M 5.5–6.0) or large (M 6.5–7.0) magnitude, backthrusts of the Seattle fault zone may slip during moderate to large earthquakes every few hundred years for periods of 1000–2000 yr, and then not slip for periods of at least several thousands of years. Four new fault scarp trenches in the Tacoma fault zone show evidence of late Holocene folding and faulting about the time of a large earthquake or earthquakes inferred from widespread coseismic subsidence ca. 1000 cal yr B.P.; 12 ages from 8 sites in the Tacoma fault zone limit the earthquakes to 1050–980 cal yr B.P. Evidence is too sparse to determine whether a large earthquake was closely predated or postdated by other earthquakes in the Tacoma basin, but the scarp of the Tacoma fault was formed by multiple earthquakes. In the northeast-striking Saddle Mountain deformation zone, along the western limit of the Seattle and Tacoma fault zones, analysis of previous ages limits earthquakes to 1200–310 cal yr B.P. The prehistory clarifies earthquake clustering in the central Puget Lowland, but cannot resolve potential structural links among the three Holocene fault zones. VL - 10 UR - https://pubs.geoscienceworld.org/geosphere/article/10/4/769-796/132175 IS - 4 ER - TY - JOUR T1 - Deciphering hemipelagites from homogenites through anisotropy of magnetic susceptibility. Paleoseismic implications (Sea of Marmara and Gulf of Corinth) JF - Sedimentary Geology Y1 - 2013 A1 - Campos, Corina A1 - Beck, Christian A1 - Crouzet, Christian A1 - Demory, François A1 - Van Welden, Aurélien A1 - Eris, Kadir AB - In closed marine basins and large lakes, gravity re-depositional processes often result in specific turbidites with two abruptly separated layers: a coarse graded lower term and an upper homogenous fine-grained term. An additional mixed term generally occurs in between, indicating to and from particle displacements. The later ones are related to oscillating bottom currents responsible for a high increase of the fine fraction segregation, within the reworked wasted mass. The whole sedimentary event is the association “homogenite + turbidite” (HmTu), which specific a settling condition area here characterized through Anisotropy of Magnetic Susceptibility (AMS). Homogenites's magnetic foliation appears anomalously high with respect to their expected state of compaction, and strikingly higher than hemipelagites's values. We applied this approach to Late Pleistocene/Holocene sediments from the Sea of Marmara and from the Gulf of Corinth. Grain-size and other magnetic parameters related to mineralogy are added to better assess the granular array influence on AMS. As HmTu is considered as often related to earthquake-triggering and tsunami/seiche effects, AMS appears as a useful tool for subaqueous paleoseismic investigations. First, it may evidence the signature of paleo-earthquakes; second, it permits to decipher hemipelagic intervals which are inferred to represent the time elapsed between two successive reworking events. VL - 292 UR - http://www.sciencedirect.com/science/article/pii/S0037073813000614 JO - Deciphering hemipelagites from homogenites through anisotropy of magnetic susceptibility. Paleoseismic implications (Sea of Marmara and Gulf of Corinth) ER - TY - JOUR T1 - The deglaciation and neoglaciation of Upernavik Isstrøm, Greenland JF - Quaternary Research Y1 - 2013 A1 - Briner, Jason P. A1 - åkansson, Lena A1 - Bennike, Ole AB - We constrain the history of the Greenland Ice Sheet margin during the Holocene at Upernavik Isstrøm, a major ice stream in northwestern Greenland. Radiocarbon-dated sediment sequences from proglacial-threshold lakes adjacent to the present ice margin constrain deglaciation of the sites to older than 9.6 ± 0.1 ka. This age of deglaciation is confirmed with 10Be ages of 9.9 ± 0.1 ka from an island adjacent to the historical ice position. The lake sediment sequences also constrain the ice margin to have been less extensive than it is today for the remainder of the Holocene until ~ 1100 to ~ 700 yr ago, when it advanced into two lake catchments. The ice margin retreated back out of these lake catchments in the last decade. The early Holocene deglaciation in Melville Bugt, one of few locations around Greenland where a vast stretch of the current ice margin is marine-based, preceded deglaciation in most other parts of Greenland. Earlier deglaciation in this ice-sheet sector may have been caused by additional ablation mechanisms that apply to marine-based ice margins. Furthermore, despite ice-sheet models depicting this sector of Greenland as relatively stable throughout the Holocene, our data indicate a > 20 km advance-retreat cycle within the last millennium. VL - 80 UR - https://doi.org/10.1016/j.yqres.2013.09.008 IS - 03 ER - TY - JOUR T1 - Diagenetic changes in Lake Superior sediments as seen from FTIR and 2D correlation spectroscopy JF - Organic Geochemistry Y1 - 2013 A1 - Li, Hongyu A1 - Minor, Elizabeth C. A1 - Zigah, Prosper K. AB - Isotopic and elemental analysis, Fourier transform infrared spectroscopy (FTIR), principal components analysis (PCA) and two dimensional (2D) correlation analysis, where core depth was used as perturbation, were used to study the diagenesis of organic matter (OM) in Lake Superior sediments. Changes in OM composition were examined at five lake stations over a depth range of 0–10 cm. PCA results show that depth-related changes among sites are similar, leading to an increased contribution from inorganic (and possibly refractory aromatic organic) components at each site, and a loss of contribution from other organic components. Synchronous spectra reveal that aliphatic esters and carbohydrates are degraded significantly with increasing depth, leading to an increased contribution from clay/biogenic silica/inactive carbohydrates. Asynchronous spectra show that, in general, carboxyl groups, including aliphatic ester and amide in protein, are degraded first, followed by a group of carbohydrates and then aromatic compounds and/or the SiO framework in clay and biogenic silica. Site dependent compositional variation occurs and appears to be influenced by topography and geology, e.g. the delivery of a larger load of terrestrial inorganic silicate minerals to certain sites and re-suspension/re-deposition, leading to less intensive down core variation at mid-lake central and eastern basin sites. The study demonstrates the usefulness of FTIR coupled with PCA and 2D correlation approaches for exploring structural changes in sedimentary material during diagenesis. VL - 58 UR - http://www.sciencedirect.com/science/article/pii/S0146638013000533 N1 - id: 2319 JO - Diagenetic changes in Lake Superior sediments as seen from FTIR and 2D correlation spectroscopy ER - TY - JOUR T1 - Distribution of Radiocarbon Ages in Soil Organic Matter by Thermal Fractionation JF - Radiocarbon Y1 - 2013 A1 - Plante, Alain F. A1 - Beaupré, Steven R. A1 - Roberts, Mark L. A1 - Baisden, Troy VL - 55 IS - 2-3 N1 - id: 2346; PT: J; TC: 0; UT: WOS:000325752100093 JO - Distribution of Radiocarbon Ages in Soil Organic Matter by Thermal Fractionation ER - TY - JOUR T1 - The Duxbury Sunken Forest-Constraints for Local, Late Holocene Environmental Changes Resulting from Marine Transgression, Duxbury Bay, Eastern Massachusetts, USA JF - JOURNAL OF COASTAL RESEARCH Y1 - 2013 A1 - Gontz, Allen M. A1 - Maio, Christopher V. A1 - Rueda, Laura KW - Cape Cod Bay KW - Coastal evolution KW - paleoforest KW - Radiocarbon dating KW - sea level KW - tree stumps AB - The present marine transgression has forced geological and ecological zones vertically higher and landward since the late Pleistocene. A recent investigation in Duxbury Bay, Massachusetts, identified 18 Juniperus virginiana tree stumps emergent on an intertidal flat immediately seaward of a small marsh and pond situated between two eroding drumlins. The position of each stump was mapped with global positioning system (GPS), and its elevation with respect to mean lower low water was surveyed. Samples were selected from four stumps with elevations ranging from 2.03 and 0.75 m above mean lower low water for radiocarbon dating. The samples returned calibrated ages between 2219 +/- 94 and 2867 +/- 79 cal YBP, with the topographically highest sample returning the youngest date. Stump positions suggest a landscape gradient of 1.4 mm/yr between 2000 and 3000 cal YBP. The results are comparable with high-resolution studies of sea level in eastern Massachusetts for the same time period. Comparison of the youngest paleostumps with modern living trees suggests a dramatic change in the landscape gradient, an increase to 1.8 mm/yr. While this is contrary to sea-level studies nearby, it may represent an increase in the energetics of Duxbury Bay and resultant coastal erosion as the bay floods. The site can be used to put the impacts of changing sea-level rates into a landscape evolution framework. VL - 29 ER - TY - JOUR T1 - The deglacial to postglacial marine environments of SEBarrow Strait, Canadian Arctic Archipelago JF - Boreas Y1 - 2012 A1 - Pieńkowski, A. J. A1 - England, John H. A1 - Furze, Mark F. A. A1 - Marret, Fabienne A1 - Eynaud, Frédérique A1 - Vilks, Gustav A1 - MacLean, Brian A1 - Blasco, Steve A1 - Scourse, James D. AB - Core 86027-144 (74°15.56?N, 91°14.21?W) represents a rare, continuous record of Late Pleistocene to Holocene sediments from High Arctic Canada extending from the end of the Last Glaciation. Based on microfossils (dinocysts, non-pollen palynomorphs, benthic and planktonic foraminifera), foraminiferal ?18O and ?13C, and sedimentology, seven palaeoenvironmental zones were identified. Zone I (>10.8?cal.?ka BP) records deglaciation, ice-sheet destabilization, float-off and subsequent break-up. Zone II (c.?10.8?10.4?cal.?ka BP) shows ice-proximal to ice-distal glaciomarine conditions, interrupted by pervasive land-fast sea-ice marked by a hiatus in coarse sediment deposition. Significant biological activity starts in Zone III (10.4?9.9?cal.?ka BP), where planktonic foraminifera (Neogloboquadrina pachyderma) suggest early oceanic throughflow. Surface waters flowed NW?SE; however, the deep-water origin remains unclear (potentially NW Arctic Ocean or Baffin Bay). Postglacial amelioration (open-water season greater than present) in Zone IV (9.9?7.8?cal.?ka BP) perhaps corresponds to the regional ?Holocene Thermal Maximum? previously proposed. A transitional period (Zone V; 7.8?6.7?cal. ka BP) of rapid environmental change fluctuating on a scale not observed today is marked by increasing sea-ice and reduced oceanic influence. This probably signals the exclusion of deeper Atlantic water owing to the glacio-isostatic shallowing of inter-island sills, coupled with generally cooling climate. Conditions analogous to those at present, with increased sea-ice and modern microfossil assemblages, commence at c. 6.7?cal.?ka BP (zones VI?VII). Although climate ultimately forces long-term environmental trends, core 86027-144 data imply that regional dynamics, especially changes in sea-level, exert a significant control on marine conditions throughout the Canadian Arctic Archipelago. VL - 41 UR - http://dx.doi.org/10.1111/j.1502-3885.2011.00227.x IS - 2 N1 - id: 2342 JO - The deglacial to postglacial marine environments of SEBarrow Strait, Canadian Arctic Archipelago ER - TY - JOUR T1 - Direct measurement of riverine particulate organic carbon age structure JF - Geophysical Research Letters Y1 - 2012 A1 - Rosenheim, Brad E. A1 - Galy, Valier AB - Carbon cycling studies focusing on transport and transformation of terrigenous carbon sources toward marine sedimentary sinks necessitate separation of particulate organic carbon (OC) derived from many different sources and integrated by river systems. Much progress has been made on isolating and characterizing young biologically-formed OC that is still chemically intact, however quantification and characterization of old, refractory rock-bound OC has remained troublesome. Quantification of both endmembers of riverine OC is important to constrain exchanges linking biologic and geologic carbon cycles and regulating atmospheric CO2 and O-2. Here, we constrain petrogenic OC proportions in suspended sediment from the headwaters of the Ganges River in Nepal through direct measurement using ramped pyrolysis radiocarbon analysis. The unique results apportion the biospheric and petrogenic fractions of bulk particulate OC and characterize biospheric OC residence time. Compared to the same treatment of POC from the lower Mississippi-Atchafalaya River system, contrast in age spectra of the Ganges tributary samples illustrates the difference between small mountainous river systems and large integrative ones in terms of the global carbon cycle. Citation: Rosenheim, B. E., and V. Galy (2012), Direct measurement of riverine particulate organic carbon age structure, Geophys. Res. Lett., 39, L19703, doi:10.1029/2012GL052883. VL - 39 N1 - id: 2248; PT: J; TC: 0; UT: WOS:000309605800002 JO - Direct measurement of riverine particulate organic carbon age structure ER - TY - JOUR T1 - A decadally-resolved paleohurricane record archived in the late Holocene sediments of a Florida sinkhole JF - Marine Geology Y1 - 2011 A1 - Lane, Philip A1 - Donnelly, Jeffrey P. A1 - Woodruff, Jonathan D. A1 - Hawkes, Andrea D. KW - Apalachee Bay KW - Gulf of Mexico KW - Holocene KW - hurricane KW - paleohurricane KW - Paleotempestology KW - sinkhole KW - SLOSH KW - storm surge KW - tropical cyclone AB - A 4500-year record of hurricane-induced storm surges is developed from sediment cores collected from a coastal sinkhole near Apalachee Bay, Florida. Recent deposition of sand layers in the upper sediments of the pond was found to be contemporaneous with significant, historic storm surges at the site modeled using SLOSH and the Best Track, post-1851 A.D. dataset. Using the historic portion of the record for calibration, paleohurricane deposits were identified by sand content and dated using radiocarbon-based age models. Marine-indicative foraminifera, some originating at least 5 km offshore, were present in several modern and ancient storm deposits. The presence and long-term preservation of offshore foraminifera suggest that this site and others like it may yield promising microfossil-based paleohurricane reconstructions in the future. Due to the sub-decadal (~ 7 years) resolution of the record and the site's high susceptibility to hurricane-generated storm surges, the average, local frequency of recorded events, approximately 3.9 storms per century, is greater than that of previously published paleohurricane records from the region. The high incidence of recorded events permitted a time series of local hurricane frequency during the last five millennia to be constructed. Variability in the frequency of the largest storm layers was found to be greater than what would likely occur by chance alone, with intervals of both anomalously high and low storm frequency identified. However, the rate at which smaller layers were deposited was relatively constant over the last five millennia. This may suggest that significant variability in hurricane frequency has occurred only in the highest magnitude events. The frequency of high magnitude events peaked near 6 storms per century between 2800 and 2300 years ago. High magnitude events were relatively rare with about 0–3 storms per century occurring between 1900 and 1600 years ago and between 400 and 150 years ago. A marked decline in the number of large storm deposits, which began around 600 years ago, has persisted through present with below average frequency over the last 150 years when compared to the preceding five millennia. VL - 287 UR - http://linkinghub.elsevier.com/retrieve/pii/S0025322711001472http://api.elsevier.com/content/article/PII:S0025322711001472?httpAccept=text/xmlhttp://api.elsevier.com/content/article/PII:S0025322711001472?httpAccept=text/plain IS - 1-4 ER - TY - JOUR T1 - The Deglacial Evolution of North Atlantic Deep Convection JF - SCIENCE Y1 - 2011 A1 - Thornalley, David J. R. A1 - Barker, Stephen A1 - Broecker, Wallace S. A1 - Elderfield, Henry A1 - McCave, I. Nick AB - Deepwater formation in the North Atlantic by open-ocean convection is an essential component of the overturning circulation of the Atlantic Ocean, which helps regulate global climate. We use water-column radiocarbon reconstructions to examine changes in northeast Atlantic convection since the Last Glacial Maximum. During cold intervals, we infer a reduction in open-ocean convection and an associated incursion of an extremely radiocarbon (C-14)-depleted water mass, interpreted to be Antarctic Intermediate Water. Comparing the timing of deep convection changes in the northeast and northwest Atlantic, we suggest that, despite a strong control on Greenland temperature by northeast Atlantic convection, reduced open-ocean convection in both the northwest and northeast Atlantic is necessary to account for contemporaneous perturbations in atmospheric circulation. VL - 331 ER - TY - JOUR T1 - A depositional history of particulate organic carbon in a floodplain lake from the lower Ob’ River, Siberia JF - Geochimica et Cosmochimica Acta Y1 - 2011 A1 - Dickens, Angela F. A1 - Baldock, Jeff A1 - Kenna, Timothy C. A1 - Eglinton, Timothy I. AB - Northern, high latitude soils have stored vast amounts of organic carbon (OC) in permafrost and peats for many millennia, however, climate change may mobilize and release this particulate OC (POC) to arctic rivers. Deltaic and floodplain lakes that receive fluvial sediments, primarily during the spring freshet, may provide records of such changes in riverine POC. Here, we examine properties of OC in a sediment core from a lake in the lower floodplain of the Ob’ River, west Siberia, to determine how the properties of OC deposited in this lake varied over many decades and to evaluate use of this sedimentary OC as a recorder of riverine POC load and properties. The core predates the most recent, dramatic changes in arctic climate and hence may serve as a benchmark against which to contrast future variations in fluvial POC discharge. Elemental, stable carbon and radiocarbon isotopic analyses, along with nuclear magnetic resonance (NMR) spectroscopy and molecular-level information (lignin phenol composition), indicate two major sources of OC to most of the sediments in this lake: plant-derived OC and algal-derived OC. However, a mixing model indicates that the nature and 14C content of these two sources change with depth in the sediment, resulting in three distinct layers: surface horizons, a “high-OC” layer and “mixing” horizons found above and below the high-OC layer. The plant-derived component is significantly aged throughout the core (14C ages of 1300–3900 years) and appears to derive from primarily local, tundra sources, whereas the algal component is modern. Our analysis suggests that the usual mode of OC deposition, as exemplified by the “mixing” and surface horizons, involved mixing of varying amounts of new algal production (35–65%) with aged permafrost- or peat-derived OC. This deposition was interrupted by an event, such as the collapse of a riverbank, which laid down the compositionally distinct “high-OC” layer in which plant-derived OC mixes with aged mineral-soil-derived OC without clear input from algae. The relative amounts of the plant and algal components in the lake sediments appear to be controlled primarily by local hydrological conditions rather than by river-wide processes, suggesting that comparison of sediment records from multiple lakes within a floodplain will be important to assess changes in POC export by arctic rivers. However, the flux and nature of the higher plant-derived OC may carry important information on the sources and dynamics of OC stored within the drainage basin. VL - 75 UR - http://www.sciencedirect.com/science/article/pii/S0016703711003085 IS - 17 N1 - id: 2172 JO - A depositional history of particulate organic carbon in a floodplain lake from the lower Ob’ River, Siberia ER - TY - JOUR T1 - Design and reality: Continuous-flow accelerator mass spectrometry (CFAMS) JF - Proceedings of the 10th European Conference on Accelerators in Applied Research and Technology (ECAART10) Y1 - 2011 A1 - von Reden, Karl F. A1 - Roberts, Mark L. A1 - McIntyre, Cameron P. A1 - Burton, Joshua R. AB - In 2007 we published [1] the design of a novel accelerator mass spectrometry (AMS) system capable of analyzing gaseous samples injected continuously into a microwave plasma gas ion source. Obvious advantages of such a system are drastically reduced processing times and avoidance of potentially contaminating chemical preparation steps. Another paper in these proceedings will present the progress with the development of the microwave gas ion source that has since been built and tested at the National Ocean Sciences AMS Facility in Woods Hole [2]. In this paper we will review the original design and present updates, reflecting our recent encouraging experience with the system. A simple summary: large acceptance ion beam optics design is beneficial to accelerator mass spectrometry in general, but essential to AMS with plasma gas ion sources. VL - 269 UR - http://www.sciencedirect.com/science/article/pii/S0168583X11003703 IS - 24 N1 - id: 2157 JO - Design and reality: Continuous-flow accelerator mass spectrometry (CFAMS) ER - TY - JOUR T1 - The detailed palaeoecology of a mid-Wisconsinan interstadial (ca. 32 000 (14)C a BP) vegetation surface from interior Alaska JF - Journal of Quaternary Science Y1 - 2011 A1 - Wooller, Matthew J. A1 - Zazula, Grant D. A1 - Blinnikov, Misha A1 - Gaglioti, Benjamin V. A1 - Bigelow, Nancy H. A1 - Sanborn, Paul A1 - Kuzmina, Svetlana A1 - La Farge, Catherine AB - We present a multi-proxy reconstruction from a well-preserved vegetation surface (ca. 32 000 (14)C a BP) from the Fox Permafrost tunnel near Fairbanks, Alaska. A thick litter layer of plant material on the vegetation surface is consistent with the vegetation lacking evidence of disturbance. Plant macrofossils and graminoid cuticle analysis show the presence of a graminoid assemblage consistent with phytolith data. The pollen data indicate that trees were not local to the site and that Artemisia sp. was present in the region. The insect and bryophyte reconstructions are consistent with the vascular plant reconstruction, indicating the site was at least periodically wet. delta(13)C values from the graminoids present show a large range encompassing both the wet and dry range displayed by modern graminoids in Alaska. Sequential delta(13)C analyses conducted along the length of leaves attached to the vegetation surface indicate a seasonal shift towards relatively higher water use efficiency. The lower water use efficiency earlier in the growing season may have stemmed from the use of winter season meltwater by plants at the site - a scenario consistent with the site's cryostratigraphy. Our multi-proxy reconstruction contributes to the limited palaeoecological data available for graminoid-dominated vegetation present in Eastern Beringia and particularly the interior of Alaska during the mid-Wisconsinan interstadial. Copyright (C) 2011 John Wiley & Sons, Ltd. VL - 26 IS - 7 N1 - id: 2131; PT: J; TC: 1; UT: WOS:000296091300010 JO - The detailed palaeoecology of a mid-Wisconsinan interstadial (ca. 32 000 (14)C a BP) vegetation surface from interior Alaska ER - TY - JOUR T1 - D/H variation in terrestrial lipids from Santa Barbara Basin over the past 1400 years: A preliminary assessment of paleoclimatic relevance RID C-2752-2008 JF - Organic Geochemistry Y1 - 2011 A1 - Li, Chao A1 - Sessions, Alex L. A1 - Valentine, David L. A1 - Thiagarajan, Nivedita AB - We analyzed D/H ratios of common terrestrial leaf wax lipids in a 1400 year sediment core from the Santa Barbara Basin (SBB) to test whether they accurately record terrestrial climate in Southern California. The D/H ratios of long chain n-alkanes vary substantially with depth, but are poorly correlated with other terrestrial climate proxies. Interference from fossil hydrocarbons may be at least partly responsible. Long chain n-alkanoic acids exhibit nearly constant downcore D/H ratio values. This constancy in the face of known climatic shifts presumably reflects a substantial residence time for leaf wax compounds in terrestrial soil and/or on the basin flanks. Alternatively, the isotopic composition of meteoric waters in Southern California may not covary with climate, particularly aridity. However, the delta D values of n-C(22) and n-C(24) fatty acids, commonly attributed to terrestrial aquatic sources, are partially correlated with Southern California winter Palmer Drought Severity Index, a tree ring-based climatic proxy (R(2) 0.25; p VL - 42 IS - 1 N1 - id: 2050; PT: J; UT: WOS:000286995900002 JO - D/H variation in terrestrial lipids from Santa Barbara Basin over the past 1400 years: A preliminary assessment of paleoclimatic relevance RID C-2752-2008 ER - TY - JOUR T1 - Distribution and significance of heavy-mineral concentrations along the southeast Baltic Sea coast JF - Journal of Coastal Research Y1 - 2011 A1 - Pupienis, D. A1 - Buynevich, I. V. A1 - Bitinas, A. AB - Heavy mineral concentrations (HMCs) in coastal sands are important from both scientific and practical standpoints. On one hand, they may serve as local sources of iron and other economically important metals, and on the other they are good indicators of hydro-meteorological and sedimentological conditions along the coast. A variety of HMC types have been documented in beach, foredune, and relict dune environments of Lithuania. The study region is located along the Curonian Spit (Nida) and mainland coast (Būtingė). The ocean beach sites range from 25 to 35 m in width and are backed by 5-10 m-high foredunes. The Great Dune Ridge on the Curonian Spit consists of relict (mid-late Holocene) dunes which are the highest coastal dunes in Northern Europe (more than 60 m above sea level). The prevailing westerly winds attain speeds of 4.2 m/s in the summer and 5.5 m/s in autumn and winter. Along the southeast Baltic Sea coast, quartz and feldspars-rich sands contain variable amounts (1-8%) of heavy minerals, such as garnet, rutile, zircon, magnetite, ilmenite, hornblende, and other accessory minerals. On the beach, HMCs typically range in thickness from 0.1 to more than 3.0 cm and represent increased wave and run-up regime. Based on previous studies of coastal morphodynamics and field observations during 2005, 2006, 2008 and 2010 enriched horizons near the foot of the foredune are the result of storm reworking and subsequent aeolian deflation. Similar process concentrates almandine garnet and magnetite along the Curonian Lagoon shoreline, on the opposite side from the Nida beach site. Based on their occurrence in the Great Dune Ridge, we suggest that buried HMCs likely represent periods of increased wind activity (storminess). Due to their relatively high fraction of heavy minerals, HMCs have substantially higher magnetic susceptibility (MS) values than background quartz-rich sands and, where well developed, they can be used for spatial correlation of subsurface horizons. Therefore, the MS method was used as a tool for cataloguing the properties of HMCs in the field and in the laboratory. For documenting lithological differences between exposed heavy-mineral concentrations and background quartz-rich sands, this study focused on coastal environments with different sedimentary regimes: 1) surface profile and shallow trenches through the upper berm at Bating (wave run-up setting along the mainland shoreline); 2) a 40-m-long shore-normal beach profile at Nida on the Baltic Sea shoreline of the Curonian Spit, (mixed wave/aeolian conditions) and 3) a short surface profile along a lagoon beach at the base of the Paranidis Dune (the landward side of the spit). The 2008 and 2010 data were compared to previous studies of the HMCs in relict dunes (exclusively aeolian setting). The spatial and temporal distribution of HMCs in different sedimentary environments is a function of: 1) the initial heavy-mineral content prior to high-energy events and 2) hydro-meteorological and sedimentary conditions during the events responsible for removal of lighter minerals and HMC formation as a lag deposit. The thickness, degree of concentration, and rhythmicity of HMC horizons offer opportunities for quantifying the periodicity and intensity of hydrodynamic processes along sandy coasts. IS - SI 64 N1 - id: 2126 JO - Distribution and significance of heavy-mineral concentrations along the southeast Baltic Sea coast ER - TY - CONF T1 - Distribution of radiocarbon ages of soil organic matter by thermal fractionation Y1 - 2011 A1 - Plante, A. F. A1 - Beaupre, S. R. A1 - Fernandez, J. M. A1 - Roberts, M. A1 - Baisden, W. T. AB - Radiocarbon analysis has become an important tool in quantifying the dynamics of soil organic matter within the terrestrial carbon cycle (Trumbore 2009). Measuring radiocarbon concentrations in bulk soil samples provides only the mean age or residence time of the associated organic matter, but it is well recognized that representing soil organic matter as a single, homogeneous pool is inadequate. Significant effort has gone into separating soil organic matter into pools with different intrinsic turnover rates (i.e., radiocarbon concentrations), but the success of these separation methods has been mixed. Using thermal analysis techniques to characterize soil organic matter is rooted in the hypothesized link between the thermal and biogeochemical stability of the organic matter (Plante et al. 2011). Two grassland topsoil samples under contrasting land uses (native vegetation and long-term cultivation) were sampled in 2005 and submitted for radiocarbon analysis. Results of bulk (super 14) C showed a significant shift in radiocarbon age (94 to 79 pMC in the soil from Indian Head, Saskatchewan; 104 to 89 pMC in the soil from Akron, Colorado), attributable to the depletion of labile organic matter during long-term cultivation. Thermogravimetry and evolved gas analysis of these soil samples also showed distinct patterns in mass loss and CO (sub 2) release during thermal analysis, suggesting significant changes in organic matter composition. Four to five "fractions" associated with different CO (sub 2) -evolution regions have been identified and will be analyzed for radiocarbon via NOSAMS's established "dirt burner" method (Rosenheim et al. 2008), consisting of the recently developed discrete CO (sub 2) fraction collector interface between NOSAMS's dirt burner and microwave gas ion source (GIS) continuous flow AMS system (CFAMS). The research question is: Do the differing patterns in CO (sub 2) release during thermal analysis reflect organic matter of different ages Our working hypothesis is that thermally labile soil organic matter (combusting at low temperatures) will consist of younger carbon than thermally resistant organic matter. References: Plante, A. F., J. M. Fernandez, M. L. Haddix, and R. T. Conant. 2011. Biological, chemical and thermal indices of soil organic matter stability in four grassland soils. Soil Biol. Biochem. 43: 1051-1058. Rosenheim, B. E., M. B. Day, E. Domack, H. Schrum, A. Benthien, and J. M. Hayes. 2008. Antarctic sediment chronology by programmed-temperature pyrolysis: Methodology and data treatment. Geochemistry Geophysics Geosystems 9: 1-16. Trumbore, S. 2009. Radiocarbon and soil carbon dynamics. Annu Rev Earth Pl Sc 37: 47-66. PB - American Geophysical Union, Washington, DC, United States (USA) CY - United States (USA) VL - 2011 N1 - id: 2207; Source type: scholarlyjournals; Object type: Article; Object type: Conference Paper; Copyright: GeoRef in Process, Copyright 2012, American Geosciences Institute. After editing and indexing, this record will be added to Georef. Reference includes data supplied by, and/or abstract, Copyright, American Geophysical Union, Washington, DC, United States; CSAUnique: 638157-114; AccNum: 638157-114; CODEN: #07548 ER - TY - JOUR T1 - Drilling predation and taphonomy in modern mollusk death assemblages, San Salvador Island, Bahamas JF - Palaeogeography, Palaeoclimatology, Palaeoecology Y1 - 2011 A1 - Pruss, Sara B. A1 - Stevenson, Marquela A1 - Duffey, Siobhan AB - Studies of modern mollusk death assemblages provide an important framework for evaluating the fossil record. An analysis of 1951 shells from two beaches, Sandy Point and Haitian Boat Beach, on the isolated carbonate platform of San Salvador Island, Bahamas, has yielded significantly different frequencies of predation in bivalve-dominated assemblages. At Sandy Point Beach, bivalves and gastropods had a drilling frequency of 0.11 and 0.07, respectively. At Haitian Boat Beach, bivalves and gastropods showed a higher drilling frequency of 0.37 and 0.22, respectively. The prevalence of beveled drill holes suggests that the dominant predator was a naticid gastropod at both sites. Some ecological and environmental differences between the beaches could account for these disparate signals of predation: at Haitian Boat Beach, there is a higher abundance of the naticid Polinices sp. and it is a lower energy setting than Sandy Point Beach. Furthermore, radiocarbon dating of 17 shells at both beaches yielded a maximum age of > 6000 years before present, suggesting that these assemblages record a complex and long taphonomic history. These results imply that future large-scale coupling of predation studies with age dating of assemblages may provide important insights into the temporal structure of predation as well as the role of taphonomic loss of drilled shells. VL - 311 UR - http://www.sciencedirect.com/science/article/pii/S0031018211004287 IS - 1–2 N1 - id: 2166 JO - Drilling predation and taphonomy in modern mollusk death assemblages, San Salvador Island, Bahamas ER - TY - JOUR T1 - Deep-sea faunal provinces and their inferred environments in the Indian Ocean based on distribution of Recent benthic foraminifera JF - Palaeogeography Palaeoclimatology Palaeoecology Y1 - 2010 A1 - De, Soma A1 - Gupta, Anil K. AB - Multivariate analysis was performed on percentages of 46 species of unstained deep-sea benthic foraminifera from 131 core-top to near-core-top samples (322-5013 m) from across the Indian Ocean. Faunal data are combined with GEOSECS geochemical data to investigate any relationship between benthic foraminifera (assemblages and species) and deep-sea properties. In general, benthic foraminifera show a good correlation to surface productivity, organic carbon flux to the sea floor, deep-sea oxygenation and, to a lesser extent, to bottom temperature, without correlation with the water depths. The foraminiferal census data combined with geochemical data has enabled the division of the Indian Ocean into two faunal provinces. Province A occupies the northwestern Indian Ocean (Arabian Sea region) where surface primary production has a major maximum during the summer monsoon season and a secondary maximum during winter monsoon season that leads to high organic flux to the seafloor, making the deep-sea one of the most oxygen-deficient regions in the world ocean, with a pronounced oxygen minimum zone (OMZ). This province is dominated by benthic foraminifera characteristic of low oxygen and high organic food flux including Uvigerina peregrina, Robulus nicobarensis, Bolivinita pseudopunctata, Bolivinita sp., Bulimina aculeata, Bulimina alazanensis, Ehrenbergina carinata and Cassidulina carinata. Province B covers southern, southeastern and eastern parts of the Indian Ocean and is dominated by Nuttallides umbonifera, Epistominella exigua, Globocassidulina subglobosa, Uvigerina proboscidea, Cibicides wuellerstorfi, Cassidulina laevigata, Pullenia bulloides, Pullenia osloensis, Pyrgo murrhina, Oridorsalis umbonatus, Gyroidinoides (=Gyroidina) soldanii and Gyroidinoides cf. gemma suggesting well-oxygenated, cold deep water with low (oligotrophic) and pulsed food supply. (C) 2010 Elsevier B.V. All rights reserved. VL - 291 IS - 3-4 N1 - id: 1967; PT: J; UT: WOS:000278782400021 JO - Deep-sea faunal provinces and their inferred environments in the Indian Ocean based on distribution of Recent benthic foraminifera ER - TY - JOUR T1 - Deepwater Formation in the North Pacific During the Last Glacial Termination JF - Science Y1 - 2010 A1 - Okazaki, Y. A1 - Timmermann, A. A1 - Menviel, L. A1 - Harada, N. A1 - Abe-Ouchi, A. A1 - Chikamoto, M. O. A1 - Mouchet, A. A1 - Asahi, H. AB - Between ~17,500 and 15,000 years ago, the Atlantic meridional overturning circulation weakened substantially in response to meltwater discharges from disintegrating Northern Hemispheric glacial ice sheets. The global effects of this reorganization of poleward heat flow in the North Atlantic extended to Antarctica and the North Pacific. Here we present evidence from North Pacific paleo surface proxy data, a compilation of marine radiocarbon age ventilation records, and global climate model simulations to suggest that during the early stages of the Last Glacial Termination, deep water extending to a depth of ~2500 to 3000 meters was formed in the North Pacific. A switch of deepwater formation between the North Atlantic and the North Pacific played a key role in regulating poleward oceanic heat transport during the Last Glacial Termination. VL - 329 UR - http://www.sciencemag.org/cgi/doi/10.1126/science.1190612 IS - 5988 ER - TY - JOUR T1 - Determination of Microbial Carbon Sources and Cycling during Remediation of Petroleum Hydrocarbon Impacted Soil Using Natural Abundance (14)C Analysis of PLFA JF - Environmental science & technology Y1 - 2010 A1 - Cowie, Benjamin R. A1 - Greenberg, Bruce M. A1 - Slater, Gregory F. AB - In a petroleum impacted land-farm soil in Sarnia, Ontario, compound-specific natural abundance radiocarbon analysis identified biodegradation by the soil microbial community as a major pathway for hydrocarbon removal in a novel remediation system. During remediation of contaminated soils by a plant growth promoting rhizobacteria enhanced phytoremediation system (PEPS), the measured Delta(14)C of phospholipid fatty acid (PLEA) biomarkers ranged from -793 parts per thousand to -897 parts per thousand, directly demonstrating microbial uptake and utilization of petroleum hydrocarbons (Delta(14)C(PHC) = -1000 parts per thousand). Isotopic mass balance indicated that more than 80% of microbial PLEA carbon was derived from petroleum hydrocarbons (PHC) and a maximum of 20% was obtained from metabolism of more modern carbon sources. These PLFA from the contaminated soils were the most (14)C-depleted biomarkers ever measured for an in situ environmental system, and this study demonstrated that the microbial community in this soil was subsisting primarily on petroleum hydrocarbons. In contrast, the microbial community in a nearby uncontaminated control soil maintained a more modern. Delta(14)C signature than total organic carbon (Delta(14)C(PLFA) = +36 parts per thousand to -147 parts per thousand, Delta(14)C(TOC) = -148 parts per thousand), indicating preferential consumption of the most modern plant-derived fraction of soil organic carbon. Measurements of delta(13)C and Delta(14)C of soil CO(2) additionally demonstrated that mineralization of PHC contributed to soil CO(2) at the contaminated site. The CO(2) in the uncontaminated control soil exhibited substantially more modern Delta(14)C values, and lower soil CO(2) concentrations than the contaminated soils, suggesting increased rates of soil respiration in the contaminated soils. In combination, these results demonstrated that biodegradation in the soil microbial community was a primary pathway of petroleum hydrocarbon removal in the PEPS system. This study highlights the power of natural abundance radiocarbon for determining microbial carbon sources and identifying biodegradation pathways in complex remediation systems. VL - 44 IS - 7 N1 - id: 2054; PT: J; UT: WOS:000275993700017 JO - Determination of Microbial Carbon Sources and Cycling during Remediation of Petroleum Hydrocarbon Impacted Soil Using Natural Abundance (14)C Analysis of PLFA ER - TY - JOUR T1 - Determination of rare earth, major and trace elements in authigenic fraction of Andaman Sea (Northeastern Indian Ocean) sediments by Inductively Coupled Plasma-Mass Spectrometry JF - Microchemical Journal Y1 - 2010 A1 - Alagarsamy, R. A1 - You, C. F. A1 - Nath, B. N. A1 - Kumar, A. V. S. AB - Downcore variation of rare earth elements (REEs) in the authigenic Fe-Mn oxides of a sediment core (covering a record of last similar to 40 kyr) from the Andaman Sea, a part of the Indian Ocean shows distinctive positive Ce and Eu anomalies. These positive Ce anomalies (Ce* = 1.1 similar to 1.8) are ascribed to be due to oxidation of deep sea sediments. The large positive Eu anomalies (i.e., Eu* > 1.8 to 3.2) occur within a time span near the glacial/interglacial transition (similar to 7000-14,000yr BP) which could be due to the past hydrothermal activity or to the effects arising from sea level changes. During glacial times, the Andaman Sea was almost completely isolated due to low sea level, leading to a reduction in sediment supply from the Ayeyarwady River. The variations of metal abundances (i.e., Ca, Al, Mn, and Fe) in the authigenic fraction provided independent information to evaluate the water column physicochemical changes during the glacial/interglacial transition period. The studied sediment core records changes in riverine inputs and reflects depositional changes related to sea level fluctuations and climatic events over the past 40 kyr in the Andaman Sea. (C) 2009 Elsevier B.V. All rights reserved. VL - 94 IS - 1 N1 - id: 1838; 539FK Times Cited:1 Cited References Count:32Y JO - Determination of rare earth, major and trace elements in authigenic fraction of Andaman Sea (Northeastern Indian Ocean) sediments by Inductively Coupled Plasma-Mass Spectrometry ER - TY - JOUR T1 - Developing graminoid cuticle analysis for application to Beringian palaeoecology JF - Review of palaeobotany and palynology Y1 - 2010 A1 - Gaglioti, B. V. A1 - Severin, K. A1 - Wooller, M. J. AB - Much of Beringia was composed of graminoid (grass and sedge) dominated habitats during the Late-Pleistocene, yet the account of the actual gramioids that were present is relatively vague. The spatial and temporal variabilities of palaeoclimate, mega-fauna. archaeology, and vegetation interactions could be significantly enhanced with accounts of Beringian graminoids. Fossil graminoid foliage is well preserved in permafrost sediments from Beringia and is available for identification using the micro-morphologies of the leaf epidermis (cuticles), which are often consistent with taxonomic identity. We present a scanning electron microscope (SEM) guide to the leaf cuticles of 38 graminoid species shown to be, or suspected of being present in former Eastern Beringian habitats during marine isotope stages (MIS) 2 and 3 (similar to.56,000-12,000 cal. yrs BP). We examine whether modern specimens have sufficient cuticle variability to identify fossil foliage. We surveyed SEM images from herbarium specimens for 50 quantitative and qualitative features on both sides (adaxial and abaxial) of leaves, and entered these into an interactive key program (Delta Editor). Individual species were unique based on the combined presence of 2-4 cuticle features. Replicate samples (n = 5) of 10 species were integrated into a cluster analysis and visually compared using a dendrogram. Overall, fossils that match modern specimens with a Gower's similarity coefficient of 0.80 or higher can be considered a reliable identification match. Several fossil graminoid specimens were compared and identified with our reference collection. Cuticle identification appears to be a viable method for future macrofossil analysis in Beringia. (C) 2010 Elsevier B.V. All rights reserved. VL - 162 IS - 1 N1 - id: 2132; PT: J; TC: 3; UT: WOS:000281181100009 JO - Developing graminoid cuticle analysis for application to Beringian palaeoecology ER - TY - RPRT T1 - Distribution of Isotopic and Environmental Tracers in Groundwater, Northern Ada County, Southwestern Idaho Y1 - 2010 A1 - Adkins, C. B. A1 - Bartolino, J. R. JF - Scientific Investigations Report PB - U.S. Department of the Interior: U.S. Geological Survey VL - 2010–5144 ER - TY - JOUR T1 - Drowned coastal deposits with associated archaeological remains from a sea-level "slowstand": Northwestern Gulf of Maine, USA JF - Geology Y1 - 2010 A1 - Kelley, Joseph T. A1 - Belknap, Daniel F. A1 - Claesson, Stefan AB - Drowned terrestrial wetland environments, such as lakes, marshes, and beaches, were thought to be rare in formerly glaciated regions like the Gulf of Maine (United States). In the northwestern Gulf of Maine, postglacial relative sea-level changes include a "slowstand" between 11.5 ka and 7.5 ka, when the ocean rose VL - 38 IS - 8 N1 - id: 1996; PT: J; UT: WOS:000279847900006 JO - Drowned coastal deposits with associated archaeological remains from a sea-level "slowstand": Northwestern Gulf of Maine, USA ER - TY - JOUR T1 - Developments in Radiocarbon Technologies: From the Libby Counter to Compound-Specific Ams Analyses JF - Radiocarbon Y1 - 2009 A1 - Povinec, P. P. A1 - Litherland, A. E. A1 - von Reden, K. F. KW - accelerator mass-spectrometry KW - black-sea shelf KW - liquid scintillation techniques KW - low-level c-14 KW - natural-abundance radiocarbon KW - negative-ion source KW - polycyclic aromatic-hydrocarbons KW - proportional counter KW - salt-marsh sediments KW - sedimentary organic-carbon AB - We review developments in radiocarbon measuring techniques from the Libby counter through proportional gas counters and liquid scintillation spectrometers to the more recent developments of accelerator mass spectrometry (AMS), followed by a coupling of gas chromatography with AMS for compound-specific (14)C analyses. While during the first 60 yr of (14)C measurements beta counting, specifically gas counting, was the dominant technique, in the future of (14)C science AMS will be the dominant technology. VL - 51 SN - 0033-8222 IS - 1 N1 - 453wfTimes Cited:15 Cited References Count:273 JO - Radiocarbon ER - TY - JOUR T1 - Distribution of artificial radionuclides in deep sediments of the Mediterranean Sea JF - Science of the Total Environment Y1 - 2009 A1 - Garcia-Orellana, J. A1 - Pates, J. M. A1 - Masque, P. A1 - Bruach, J. M. A1 - Sanchez-Cabeza, J. A. AB - Artificial radionuclides enter the Mediterranean Sea mainly through atmospheric deposition following nuclear weapons tests and the Chernobyl accident, but also through the river discharge of nuclear facility effluents. Previous studies of artificial radionuclides impact of the Mediterranean Sea have focussed on shallow, coastal sediments. However, deep sea sediments have the potential to store and accumulate pollutants, including artificial radionuclides. Deep sea marine sediment cores were collected from Mediterranean Sea abyssal plains (depth >2000 m) and analysed for Pu-239,Pu-240 and Cs-137 to elucidate the concentrations, inventories and sources of these radionuclides in the deepest areas of the Mediterranean. The activity - depth profiles of Pb-210, together with 14 C dating, indicate that sediment mixing redistributes the artificial radionuclides within the first 2.5 cm of the sedimentary column. The excess Pb-210 inventory was used to normalize Pu-239,Pu-240 and Cs-137 inventories for variable sediment fluxes. The Pu-239,Pu-240/Pb-210(xs) ratio was uniform across the entire sea, with a mean value of 1.24 x 10(-3), indicating homogeneous fallout of Pu-239,Pu-240. The Cs-137/Pb-210(xs) ratio showed differences between the eastern (0.049) and western basins (0.030), clearly significant impact of deep sea sediments from the Chernobyl accident. The inventory ratios of Pu-239,Pu-240/Cs-137 were 0.041 and 0.025 in the western and eastern basins respectively, greater than the fallout ratio, 0.021, showing more efficient scavenging of Pu-231,Pu-210 in the water column and major sedimentation of Cs-137 in the eastern basin. Although areas with water depths of >2000 m constitute around 40% of the entire Mediterranean basin, the sediments in these regions only contained 2.7% of the Pu-239,Pu-240 and 0.95% of the Cs-137 deposited across the Sea in 2000. These data show that the accumulation of artificial radionuclides in deep Mediterranean environments is much lower than predicted by other studies from the analysis of continental shelf sediments. (C) 2008 Elsevier B.V, All rights reserved. VL - 407 IS - 2 N1 - id: 871; 389FH Times Cited:2 Cited References Count:63Y JO - Distribution of artificial radionuclides in deep sediments of the Mediterranean Sea ER - TY - JOUR T1 - DNA and lipid molecular stratigraphic records of haptophyte succession in the Black Sea during the Holocene JF - Earth and Planetary Science Letters Y1 - 2009 A1 - Coolen, M. J. L. A1 - Saenz, J. P. A1 - Giosan, L. A1 - Trowbridge, N. Y. A1 - Dimitrov, P. A1 - Dimitrov, D. A1 - Eglinton, T. I. AB - Previous studies suggest that the coccolithophorid haptophyte Emiliania huxleyi entered the Black Sea similar to 3400 yrs ago and since then a coccolith ooze defined as Unit I has developed. Unit I sediments contain long-chain alkenones derived from E huxleyi whereas the alkenone distribution of the deeper coccolith-free sapropel (Unit II) is rather unusual. Alkenone-derived past sea surface temperature (SST) estimates suggest a large difference between Unit II and Unit I, which is likely a result of unusual biological precursors of the alkenones in Unit II. Here, we report a high-resolution stratigraphic analysis of ancient haptophyte DNA to establish the Holocene succession of haptophytes as sources of the alkenones in the Black Sea. Haptophytes related to brackish Isochrysis spp. were the initial sources of alkenones, and appeared immediately after the onset of sapropel deposition (similar to 7550 yrs before present [a BP]). As salinity increased, Isochrysis-related haptophytes were slowly replaced by a complex suite of huxleyi strains as sources of alkenones. Our paleogenetic data showed that E. huxleyi colonized the Black Sea shortly after the onset of sapropel deposition, similar to 4000 yrs earlier than previously recognized based on their preserved coccoliths. E. huxleyi strains were the most likely source of the previously reported abundant and unusual C-36 di-unsaturated "Black Sea alkenone". Strong haptophyte species and strain-specific effects were observed on the level of unsaturation of alkenones which resulted in spurious alkenone-derived SST estimates before 5250 a BP. In contrast, from similar to 5250 a BP onwards a relatively stable haptophyte assemblage dominated by a different suite of E. huxleyi strains yielded robust alkenone-SST values and indicated a gradual cooling from 19 degrees C to similar to 15 degrees C at the top of the record (similar to 450 a BP). Published by Elsevier B.V. VL - 284 IS - 3-4 N1 - id: 1853; 487NY Times Cited:1 Cited References Count:78; YY JO - DNA and lipid molecular stratigraphic records of haptophyte succession in the Black Sea during the Holocene ER - TY - RPRT T1 - Dynamics and Vulnerability of Delta Systems Y1 - 2009 A1 - Overeem, I. A1 - Syvitski, J. P. M. A1 - al, et JF - LOICZ Reports & Studies PB - GKSS Research Center CY - Geesthacht N1 - id: 1898; 35; Y ER - TY - JOUR T1 - Dynamics of particle export on the Northwest Atlantic margin JF - Deep-Sea Research Part I-Oceanographic Research Papers Y1 - 2009 A1 - Hwang, J. A1 - Manganini, S. J. A1 - Montlucon, D. B. A1 - Eglinton, T. I. AB - The Northwest Atlantic margin is characterized by high biological productivity in shelf and slope surface waters. In addition to carbon supply to underlying sediments, the persistent, intermediate depth nepheloid layers emanating from the continental shelves, and bottom nepheloid layers maintained by strong bottom currents associated with the southward flowing Deep Western Boundary Current (DWBC), provide conduits for export of organic carbon over the margin and/or to the interior ocean. As a part of a project to understand dynamics of particulate organic carbon (POC) cycling in this region, we examined the bulk and molecular properties of time-series sediment trap samples obtained at 968 m, 1976 m, and 2938 m depths from a bottom-tethered mooring on the New England slope (water depth, 2988 m). Frequent occurrences of higher fluxes in deep relative to shallower sediment traps and low Delta C-14 values of sinking POC together provide strong evidence for significant lateral transport of aged organic matter over the margin. Comparison of biogeochemical properties such as aluminum concentration and flux, and iron concentration between samples intercepted at different depths shows that particles collected by the deepest trap had more complex sources than the shallower ones. These data also suggest that at least two modes of lateral transport exist over the New England margin. Based on radiocarbon mass balance, about 30% (+/- 10%) of sinking POC in all sediment traps is estimated to be derived from lateral transport of resuspended sediment. A strong correlation between Delta C-14 values and aluminum concentrations suggests that the aged organic matter is associated with lithogenic particles. Our results suggest that lateral transport of organic matter, particularly that resulting from sediment resuspension, should be considered in addition to vertical supply of organic matter derived from primary production, in order to understand carbon cycling and export over continental margins. (C) 2009 Elsevier Ltd. All rights reserved. VL - 56 IS - 10 N1 - id: 1829; 490AT Times Cited:0 Cited References Count:61Y JO - Dynamics of particle export on the Northwest Atlantic margin ER - TY - JOUR T1 - Deepwater circulation on Blake Outer Ridge (western North Atlantic) during the Holocene, Younger Dryas, and Last Glacial Maximum JF - Geochemistry Geophysics Geosystems Y1 - 2008 A1 - Evans, H. K. A1 - Hall, I. R. AB - Three depth transects containing a total of 33 sediment cores were investigated along the Blake Outer Ridge in the western subtropical North Atlantic. Sortable silt mean ((SS) over bar) grain size and stable isotope records were used to assess the position and relative intensity of the Western Boundary Undercurrent (WBUC) during the Holocene, the Last Glacial Maximum (LGM), and the Younger Dryas (YD) intervals. The Holocene reconstruction is consistent with modern physical and chemical hydrographic measurements in the area, suggesting a deep position for the fast flowing core of the WBUC (3000-4000 m, deepening to similar to 4500 m water depth on the ridge flanks) and a water column dominated by North Atlantic Deep Water (NADW). The LGM and YD reconstructions show that a comparable hydrographic regime was present during both these intervals, suggesting a similar mode of circulation that was appreciably different from the Holocene reconstruction. The WBUC's zone of maximum flow speed during these intervals is suggested to have shifted above 2500 m water depth, consistent with nutrient depleted Glacial North Atlantic Intermediate Water formation with an increasing influence of Southern Source Water (SSW) beneath. Below 4000 m water depth, (SS) over bar results hint at increased SSW flow vigor during both the LGM and YD with higher flow speeds than during the Holocene. This study provides a framework for aiding the interpretation of time series records of paleocurrent flow speed changes in the region of the WBUC. VL - 9 N1 - id: 839; 281XG Times Cited:1 Cited References Count:84Y JO - Deepwater circulation on Blake Outer Ridge (western North Atlantic) during the Holocene, Younger Dryas, and Last Glacial Maximum ER - TY - JOUR T1 - Deglacial variability in the surface return flow of the Atlantic meridional overturning circulation JF - Paleoceanography Y1 - 2008 A1 - Came, R. E. A1 - Oppo, D. W. A1 - Curry, W. B. A1 - Lynch-Stieglitz, J. AB - [1] Benthic foraminiferal Cd/Ca from a Florida Current sediment core documents the history of the northward penetration of southern source waters within the surface return flow of the Atlantic meridional overturning circulation (AMOC). Cd seawater estimates (Cd-W) indicate that intermediate-depth southern source waters crossed the equator and contributed to the Florida Current during the Bolling-Allerod warm period of the last deglaciation, consistent with evidence of only a modest AMOC reduction compared to today. The Cd-W estimates also provide the first paleoceanographic evidence of a reduction in the influence of intermediate-depth southern source waters within the Florida Current during the Younger Dryas, a deglacial cold event characterized by a weak North Atlantic AMOC. Our results reveal a close correspondence between the northward penetration of intermediate-depth southern source waters and the influence of North Atlantic Deep Water, suggesting a possible link between intermediate-depth southern source waters and the strength of the Atlantic AMOC. VL - 23 IS - 1 N1 - id: 838; 281YL Times Cited:4 Cited References Count:41; YY JO - Deglacial variability in the surface return flow of the Atlantic meridional overturning circulation ER - TY - JOUR T1 - Determination of biodiesel blending percentages using natural abundance radiocarbon analysis: Testing the accuracy of retail biodiesel blends JF - Environmental Science & Technology Y1 - 2008 A1 - Reddy, C. M. A1 - DeMello, J. A. A1 - Carmichael, C. A. A1 - Peacock, E. E. A1 - Xu, L. A1 - Arey, J. S. AB - Blends of biodiesel and petrodiesel are being used increasingly worldwide. Due to several factors, inaccurate blending of these two mixtures can occur. To test the accuracy of biodiesel blending, we developed and validated a radiocarbon-based method and then analyzed a variety of retail biodiesel blends. Error propagation analysis demonstrated that this method calculates absolute blend content with +/- 1% accuracy, even when real-world variability in the component biodiesel and petrodiesel sources is taken into account. We independently confirmed this accuracy using known endmembers and prepared mixtures. This is the only published method that directly quantifies the carbon of recent biological origin in biodiesel blends. Consequently, it robustly handles realistic chemical variability in biological source materials and provides unequivocal apportionment of renewable versus nonrenewable carbon in a sample fuel blend. Analysis of retail biodiesel blends acquired in 2006 in the United States revealed that inaccurate blending happens frequently. Only one out of ten retail samples passed the specifications that the United States Department of Defense requires for blends that are 20% biodiesel (v/v; referred to as B20). VL - 42 IS - 7 N1 - id: 1864; 281JN Times Cited:3 Cited References Count:39; YY JO - Determination of biodiesel blending percentages using natural abundance radiocarbon analysis: Testing the accuracy of retail biodiesel blends ER - TY - JOUR T1 - Differences in sediment organic matter composition and PAH weathering between non-vegetated and recently vegetated fuel oiled sediments JF - International Journal of Phytoremediation Y1 - 2008 A1 - Gregory, Samuel T., III A1 - Nichols, Elizabeth Guthrie AB - We examined polycyclic aromatic hydrocarbon (PAH) attenuation in contaminated field sediments after only 2 years of plant growth. We collected sediments from vegetated and non-vegetated areas at the Indiana Harbor Canal (IHC), an industrialized area with historic petroleum contamination of soils and sediments. PAH concentrations, PAH weathering indices, and organic matter composition in sediments colonized by Phragmites, cattails, or willow trees were compared to the same indices for non-vegetated sediments. We hypothesized that bulk sediment and humin fractions with measurable increases in plant organic matter content would show measurable changes to PAH attenuation as indicated by more weathered PAH diagnostic ratios or reduced PAH concentrations. Carbon-normalized PAH concentrations were lower in vegetated bulk sediments but higher in vegetated humin fractions relative to non-vegetated sediment fractions. Total organic carbon content was not indicative of more weathered N(3)/P(2) ratios or reduced PAH concentrations in vegetated sediment fractions. More weathered N(3)/P(2) ratios were observed with increased modern carbon (plant carbon) content of vegetated sediment fractions. Phragmites sediments contained more modern carbon (plant carbon) and more weathered PAH ratios [C(3)-naphthalenes and C(2)-phenanthrenes (N(3)/P(2))] than willow, cattail, and non-vegetated sediments. VL - 10 IS - 6 N1 - id: 2025; PT: J; UT: WOS:000258774100001 JO - Differences in sediment organic matter composition and PAH weathering between non-vegetated and recently vegetated fuel oiled sediments ER - TY - JOUR T1 - Dogs, humans and island ecosystems: the distribution, antiquity and ecology of domestic dogs (Canis familiaris) on California's Channel Islands, USA JF - Holocene Y1 - 2008 A1 - Rick, Torben C. A1 - Walker, Phillip L. A1 - Willis, Lauren M. A1 - Noah, Anna C. A1 - Erlandson, Jon M. A1 - Vellanoweth, Rene L. A1 - Braje, Todd J. A1 - Kennett, Douglas J. AB - Archaeologists have made significant contributions to our understanding of ancient island environments, including the timing and implications of the introduction of non-native animals (pigs, chickens, rats, etc.) by humans. Here, we focus on the historical ecology and biogeography of domestic dogs (Canis familiaris) on California's Channel Islands during the Holocene. Dogs are the only animal known unequivocally to have been introduced by Native Americans to the islands, but relatively little is known about their distribution, antiquity or influence on native island fauna and flora. We identified a minimum of 96 dogs from 42 archaeological sites on six of the eight islands. Dogs were present for at least 6000 years and appear to have increased in abundance through time. Our analysis suggests that dogs, along with humans and island foxes (Urocyon littoralis), would have had an impact on native animals and ecosystems, especially breeding birds and marine mammals, togs and island foxes likely competed with one another for food, however, and the impacts of dogs on island ecosystems may have been reduced by the presence of island foxes and the symbiotic relationship between dogs and humans. Dogs have been removed from all but one of the islands today, eliminating one of the few terrestrial carnivores present for most of the Holocene. VL - 18 IS - 7 N1 - id: 2063; PT: J; UT: WOS:000260339000006 JO - Dogs, humans and island ecosystems: the distribution, antiquity and ecology of domestic dogs (Canis familiaris) on California's Channel Islands, USA ER - TY - JOUR T1 - Demise of a submarine canyon? Evidence for highstand infilling on the Waipaoa River continental margin, New Zealand JF - Geophysical Research Letters Y1 - 2007 A1 - Walsh, J. P. A1 - Alexander, C. R. A1 - Gerber, T. A1 - Orpin, A. R. A1 - Sumners, B. W. AB - Submarine canyons are major geomorphologic features on the Earth's surface. Their formation has received considerable debate, but their demise has received less attention. Research of modern canyons with cores and moorings has documented active sediment transport and deposition, but extrapolation of these local observations over larger areas is precluded by complex canyon geomorphology. High-resolution multibeam and chirp data presented here provide convincing evidence of an infilling canyon head on the Waipaoa River margin of New Zealand. Tens of meters of Holocene sediment have accumulated on the outer shelf and in Lachlan canyon as a result of off-shelf sediment transport. Regardless of the ultimate fate of this system over geological time scales, this research demonstrates highstand sedimentation as a possible mechanism for canyon burial and cause of canyon demise, which has important implications for the evolution of canyons globally. VL - 34 IS - 20 N1 - id: 791; 228BW Times Cited:4 Cited References Count:42Y JO - Demise of a submarine canyon? Evidence for highstand infilling on the Waipaoa River continental margin, New Zealand ER - TY - CONF T1 - Deposition and reactivity of aerosol-derived organic carbon in temperate watersheds T2 - ASLO Aquatic Sciences Meeting Y1 - 2007 A1 - Wozniak, A. W. A1 - Bauer, J. E. A1 - Dickhut, R. M. A1 - Keesee, E. J. JF - ASLO Aquatic Sciences Meeting CY - Santa Fe, NM N1 - id: 1029 ER - TY - JOUR T1 - Detection of silica-mediated dissolution of magnetic grains in sediments using FORC diagrams JF - Geophysical Research Letters Y1 - 2007 A1 - Wetter, L. A1 - Verosub, K. A1 - Russell, J. KW - dissolution KW - FORC AB - Recently silica-mediated dissolution has been recognized as a potentially important factor influencing magnetic studies of marine and lacustrine sediments. Although direct evidence for the dissolution of magnetic particles in silica-rich environments is lacking, the process is expected to produce changes in the magnetic grain-size distribution, a hypothesis that is tested in this study on sediments from Lake Tanganyika, East Africa, using First Order Reversal Curves (FORCs). Results from different magnetic intensity zones within the studied samples clearly show changes in the grain-size distribution of magnetic minerals. In particular, zones with high biogenic silica content (BSi) correlated with depletion in fine-grained magnetic material, whereas zones with lower BSi showed no depletion. These results are consistent with the idea that silica-mediated dissolution results in the preferential removal of fine-grained magnetic material, and indicate that FORC diagrams are effective in characterizing silica-mediated dissolution in sediments. VL - 34 IS - 12 N1 - 182vvTimes Cited:3Cited References Count:8 JO - Detection of silica-mediated dissolution of magnetic grains in sediments using FORC diagrams ER - TY - JOUR T1 - Diagenetic and sedimentological controls on the composition of organic matter preserved in California Borderland Basin sediments JF - Limnology and Oceanography Y1 - 2007 A1 - Mollenhauer, G. A1 - Eglinton, T. I. KW - c-14 measurements KW - compound-specific radiocarbon KW - continental-margin KW - fatty-acids KW - marine-sediments KW - monica basin KW - oxic degradation KW - oxygen exposure time KW - santa-barbara basin KW - surface sediments AB - Compound-specific radiocarbon (C-14) contents, stable carbon isotopes, and abundances of phytoplankton and vascular plant derived lipid biomarkers (alkenones and fatty acids) were obtained from Santa Barbara Basin and Santa Monica Basin sediments, along with radiocarbon contents of planktic foraminifera and total organic carbon. We investigated core-top and prebomb sediment intervals at sites from the flanks and depocenters of the basins deposited under contrasting bottom water oxygen concentrations. Bulk organic matter generally has the lowest radiocarbon levels of all sediment constituents measured, whereas planktic foraminifera tend to be the most radiocarbon enriched. Alkenones are systematically depleted in radiocarbon with respect to foraminifera. Short-chain (C-14, C-16, C-18) fatty acids decrease rapidly in absolute abundance and relative to longer-chain (> C-24) homologues from core-top to prebomb samples. The loss of short-chain fatty acids with depth is associated with C-13 depletion of short-chain fatty acids, indicating preferential preservation of terrestrially derived fatty acids. Short-chain fatty acids tend to be more C-14-enriched relative to alkenones in core-top sediments, whereas longer-chain homologues are generally the most radiocarbon depleted of the lipids studied here. Less refractory compounds (e.g., short-chain fatty acids) are thus enriched in radiocarbon with respect to more recalcitrant biomarkers (alkenones, long-chain fatty acids). The lower C-14 content of more refractory compounds reflects a larger proportion of laterally supplied, preaged material. Greater preservation of labile organic compounds observed at the depocenters than in flank sediments results in the presence of "younger" biomarkers, underlining the important influence of selective degradation of labile compounds on their radiocarbon ages. VL - 52 SN - 0024-3590 IS - 2 N1 - 149kgTimes Cited:43 Cited References Count:67 JO - Limnol Oceanogr ER - TY - JOUR T1 - Distribution and sub-bottom features of Holocene oyster deposits in the York River, Virginia and the rate of degradations of oyster shell JF - Geological Society of America Abstracts with Programs Y1 - 2007 A1 - Stackhouse, B. L. A1 - Lockwood, R. VL - 39 N1 - id: 587 ER - TY - JOUR T1 - Distribution and turnover of carbon in natural and constructed wetlands in the Florida Everglades JF - Applied Geochemistry Y1 - 2007 A1 - Stern, J. A1 - Wang, Y. A1 - Gu, B. A1 - Newman, J. AB - Stable and radiocarbon isotopic contents of dissolved organic C (DOC), dissolved inorganic C (DIC), particulate organic C (POC) and plants were used to examine the source and turnover rate of C in natural and constructed wetlands in the Florida Everglades. DOC concentrations decreased, with P concentrations, along a water quality gradient from the agriculturally impacted areas in the northern Everglades to the more pristine Everglades National Park. delta C-13 values of DOC in the area reflect contributions of both wetland vegetation and sugarcane from agriculture. Radiocarbon ages of DOC, POC and DIC in the Everglades ranged from 2.01 ka BP to ">modern". The old C-14 ages of DOC and POC were found in impacted areas near the Everglades Agricultural Area (EAA) in the northern Everglades. In contrast, DOC and POC in pristine marsh areas had near modern or ">modern" C-14 ages. These data indicate that a major source of POC and DOC in impacted areas is the degradation of historic peat deposits in the EAA. In the pristine areas of the marsh, DOC represents a mix of modern and historic C sources, whereas POC comes from modern primary production as indicated by positive A C-14 values, suggesting that DOC is transported farther away from its source than POC. High A C-14 values of DIC indicate that dissolution of limestone bedrock is not a significant source of DIC in the Everglades wetlands. As a restored wetland moves towards its "original" or "natural" state, the C-14 signatures of DOC should approach that of modern atmosphere. In addition, measurements of concentration and C isotopic composition of DOC in two small constructed wetlands (i.e., test cells) indicate that these freshwater wetland systems contain a labile DOC pool with rapid turnover times of 26-39 days and that the test cells are overall net sinks of DOC. (C) 2007 Elsevier Ltd. All rights reserved. VL - 22 IS - 9 N1 - 216vhTimes Cited:23Cited References Count:36 JO - Distribution and turnover of carbon in natural and constructed wetlands in the Florida Everglades ER - TY - JOUR T1 - Deglaciation and Holocene climate change in the western Peruvian Andes JF - Quaternary Research Y1 - 2006 A1 - Weng, C. Y. A1 - Bush, M. B. A1 - Curtis, J. H. A1 - Kolata, A. L. A1 - Dillehay, T. D. A1 - Binford, M. W. AB - Pollen, charcoal, magnetic susceptibility, and bulk density data provide the first paleoecological record spanning the last 33,000 years from the western cordillera of the Peruvian Andes. Sparse super-puna vegetation existed before 30,000 cat yr B.P. around Lake Compuerta (3950 m elevation), prior to a sedimentary hiatus that lasted until c. 16,200 cat yr B.P. When sedimentation resumed, a glacial foreland or super-puna flora is represented in which Polylepis was a significant element. Glacial outwash, marked by high sedimentary magnetic susceptibility, increased from c. 16,200 cat yr B.P. and reached a peak at c. 13,200 cat yr B.P. Between c. 12,500 cat yr B.P. and 10,000 cat yr B.P., magnetic susceptibility was reduced. Vegetation shifts suggest a cool dry time, consistent with regional descriptions of the Younger Dryas event. Deglaciation resumes by 10,000 cat yr B.P. and the last ice is lost from the catchnient at similar to 7500 cat yr B.P. During the early Holocene warm and dry period between 10,000 and 5500 cat yr B.P., Alnus expanded in downslope forests. Alnus declined in abundance at 5500 cat yr B.P. when wetter and cooler conditions returned and human activity intensified. Maize (Zea mays) pollen first occurred in the core at similar to 2600 cat yr B.P., indicating a minimum age for local agriculture. An increase in Alnus pollen abundance at similar to 1000 cat yr B.P. could be due to human activity or perhaps due to a regional climate change associated with cultural turnover elsewhere in the Andes at this time. (c) 2006 University of Washington. All rights reserved. VL - 66 IS - 1 N1 - 058upTimes Cited:27Cited References Count:55 JO - Deglaciation and Holocene climate change in the western Peruvian Andes ER - TY - JOUR T1 - Depth limit for reef building corals in the Au'au Channel, S. E. Hawaii JF - Coral Reefs Y1 - 2006 A1 - Grigg, R. W. VL - 25 N1 - id: 1085 ER - TY - RPRT T1 - Determination of carbon dioxide, hydrographic and chemical parameters during the R/V Nathaniel B. Palmer cruise in the southern Indian Ocean (WOCE section S041) Y1 - 2006 A1 - Takahashi, R. A1 - Millero, F. J. A1 - Key, R. M. A1 - Chipman, D. A1 - Peltola, E. A1 - Rubin, S. A1 - Sweeney, C. A1 - Sutherland, S. N1 - id: 1053 ER - TY - JOUR T1 - Diageneitc and sedimentological controls on the composition of organic matter preserved in California Borderland Basin sediments JF - Limnology & Oceanography Paleoceanography, submitted Y1 - 2006 A1 - Mollenhauer, Gesine A1 - Eglinton, Timothy I. N1 - id: 1705 ER - TY - JOUR T1 - Dissolved and particulate organic matter source-age characterization in the upper and lower Chesapeake Bay: A combined isotope and biochemical approach JF - Limnology and Oceanography Y1 - 2006 A1 - Loh, A. N. A1 - Bauer, J. E. A1 - Canuel, E. A. KW - biomarkers KW - carbon KW - delta-c-13 KW - lipid-composition KW - ocean KW - radiocarbon KW - river KW - san-francisco KW - sediments KW - variability AB - In order to characterize the sources and ages of organic matter contributing to river and estuarine outflow waters, the present study investigated Delta C-14 and delta C-13 signatures of the major operationally defined biochemical classes of ultrafiltered dissolved organic matter (UDOM) in conjunction with lipid biomarker and elemental compositions of UDOM and suspended particulate organic matter (POM) in the Chesapeake Bay. Freshwater (Susquehanna River) UDOM was dominated by a molecularly uncharacterized (MUC) fraction, followed by total carbohydrate (TCHO), total hydrolysable amino acid (THAA) and total lipid (TLE) components. In contrast, UDOM at the bay mouth (salinity similar to 22-24) was comprised mainly of TCHO, followed by MUC, THAA, and TLE. The Delta C-14 and delta C-13 signatures of both UDOM and its major biochemical classes indicate that Susquehanna DOM is derived in part from old allochthonous terrestrial sources, whereas young marine sources dominate at the bay mouth. In contrast to the other biochemical classes, lipophilic DOM at both sites was very old (similar to 5,000-7,000 years B.P.). In addition, factor analysis of lipid biomarker compounds revealed unique signatures for the UDOM and POM pools that imply disparate source and/or recycling properties as well as potential influences due to physical partitioning. Lipid biomarker compounds showed that although autochthonous riverine/estuarine sources dominated both the UDOM and POM pools, terrigenous lipids were elevated in the Susquehanna during high flow conditions. The presence of lipid biomarkers diagnostic of "fresh" algal material in UDOM further suggested its greater reactivity than POM. The observed biochemical and lipid biomarker compositions and isotopic signatures of UDOM and POM are consistent with previous findings suggesting that these two major organic matter pools have dissimilar reactivities and cycling times, and they derive from comparatively unique source-age materials in rivers and estuaries. VL - 51 SN - 0024-3590 IS - 3 N1 - 045nhTimes Cited:24 Cited References Count:37 JO - Limnol Oceanogr ER - TY - CONF T1 - Do inland waters matter in the regional or global C balance: A review and turorial T2 - American Society of Limnology and Oceanography Summer Meeting Y1 - 2006 A1 - Cole, J. J. JF - American Society of Limnology and Oceanography Summer Meeting CY - Victoria, Canada N1 - id: 479 ER - TY - JOUR T1 - A decrease in discharge-normalized DOC export by the Yukon River during summer through autumn JF - Geophysical Research Letters Y1 - 2005 A1 - Striegl, R. G. A1 - Aiken, G. R. A1 - Dornblaser, M. M. A1 - Raymond, P. A. A1 - Wickland, K. P. KW - alaska KW - arctic-ocean KW - climate-change KW - CO2 KW - discontinuous permafrost KW - dissolved organic-carbon KW - flux KW - MATTER KW - tundra AB - Climate warming is having a dramatic effect on the vegetation distribution and carbon cycling of terrestrial subarctic and arctic ecosystems. Here, we present hydrologic evidence that warming is also affecting the export of dissolved organic carbon and bicarbonate (DOC and HCO3-) at the large basin scale. In the 831,400 km(2) Yukon River basin, water discharge (Q) corrected DOC export significantly decreased during the growing season from 1978 - 80 to 2001 - 03, indicating a major shift in terrestrial to aquatic C transfer. We conclude that decreased DOC export, relative to total summer through autumn Q, results from increased flow path, residence time, and microbial mineralization of DOC in the soil active layer and groundwater. Counter to current predictions, we argue that continued warming could result in decreased DOC export to the Bering Sea and Arctic Ocean by major subarctic and arctic rivers, due to increased respiration of organic C on land. VL - 32 SN - 0094-8276 UR - http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=Alerting&SrcApp=Alerting&DestApp=WOS&DestLinkType=FullRecord;UT=WOS:000233354500009 IS - 21 N1 - 985cuTimes Cited:163 Cited References Count:28 JO - Geophys Res Lett ER - TY - JOUR T1 - The deglacial history of surface and intermediate water of the Bering Sea JF - Deep-Sea Research Part Ii-Topical Studies in Oceanography Y1 - 2005 A1 - Cook, M. S. A1 - Keigwin, L. D. A1 - Sancetta, C. A. AB - The lithology of deglacial sediments from the Bering Sea includes intervals of laminated or dysaerobic sediments. These intervals are contemporaneous with the occurrence of laminated sediments from the California margin and Gulf of California, which suggests widespread low-oxygen conditions at intermediate depths in the North Pacific Ocean. The cause could be reduced intermediate water ventilation, increased organic carbon flux, or a combination of the two. We infer abrupt decreases of planktonic foraminifer delta(18)O at 14,400 and 11,650 yr BP, which may be a combination of both freshening and warming. On the Shirshov Ridge, the abundance of sea-ice diatoms of the genus Nitzschia reach local maxima twice during the deglaciation, the latter of which may be an expression of the Younger Dryas. These findings expand the extent of the expression of deglacial millennial-scale climate events to include the northernmost Pacific. (c) 2005 Elsevier Ltd. All rights reserved. VL - 52 IS - 16-18 N1 - 995ksTimes Cited:51Cited References Count:52 JO - The deglacial history of surface and intermediate water of the Bering Sea ER - TY - JOUR T1 - The demise of the alga Botryococcus Braunii from a Norwegian fjord is due to early eutrophication JF - The Holocene Y1 - 2005 A1 - Smittenberg, R. H. A1 - Baas, M. A1 - Schouten, S. A1 - Sinninghe-Damste, J. S. VL - 15 N1 - id: 1148 ER - TY - JOUR T1 - Detailed compositional analysis of gas seepage at the National Carbon Storage Test Site, Teapot Dome, Wyoming, USA JF - Applied Geochemistry Y1 - 2005 A1 - Klusman, Ronald W. VL - 21 N1 - id: 1038 JO - Detailed compositional analysis of gas seepage at the National Carbon Storage Test Site, Teapot Dome, Wyoming, USA ER - TY - JOUR T1 - Determination of microbial carbon sources in petroleum contaminated sediments using molecular 14C analysis JF - Environmental Science and Technology Y1 - 2005 A1 - Slater, G. F. A1 - White, H. K. A1 - Eglinton, T. I. A1 - Reddy, C. M. VL - 39 N1 - id: 595 ER - TY - JOUR T1 - Determination of Microbial Carbon Sources in Petrolleum Contaminated Sediments Using Molecular 14C Analysis JF - Environ. Sci. Technol Y1 - 2005 A1 - Slater, G. F. A1 - White, H. K. A1 - Eglinton, T. I. A1 - Reddy, C. M. VL - 39 N1 - id: 1225 ER - TY - CONF T1 - Dissolved and particulate organic matter source-age characterization in river and estuarine outflow waters: a combined isotope and biochemical approach T2 - ASLO Summer Meeting Y1 - 2005 A1 - Loh, A. N. A1 - Bauer, J. E. A1 - Canuel, E. A. JF - ASLO Summer Meeting CY - Santiago de Compostela, Spain N1 - id: 482 ER - TY - JOUR T1 - Dating the rise of atmospheric oxygen JF - Nature Y1 - 2004 A1 - Bekker, A. A1 - Holland, H. D. A1 - Wang, P. L. A1 - Rumble, D. A1 - Stein, H. J. A1 - Hannah, J. L. A1 - Coetzee, L. L. A1 - Beukes, N. J. AB - Several lines of geological and geochemical evidence indicate that the level of atmospheric oxygen was extremely low before 2.45 billion years (Gyr) ago, and that it had reached considerable levels by 2.22 Gyr ago. Here we present evidence that the rise of atmospheric oxygen had occurred by 2.32 Gyr ago. We found that syngenetic pyrite is present in organic-rich shales of the 2.32-Gyr-old Rooihoogte and Timeball Hill formations, South Africa. The range of the isotopic composition of sulphur in this pyrite is large and shows no evidence of mass-independent fractionation, indicating that atmospheric oxygen was present at significant levels (that is, greater than 10(-5) times that of the present atmospheric level) during the deposition of these units. The presence of rounded pebbles of sideritic iron formation at the base of the Rooihoogte Formation and an extensive and thick ironstone layer consisting of haematitic pisolites and oolites in the upper Timeball Hill Formation indicate that atmospheric oxygen rose significantly, perhaps for the first time, during the deposition of the Rooihoogte and Timeball Hill formations. These units were deposited between what are probably the second and third of the three Palaeoproterozoic glacial events. VL - 427 IS - 6970 N1 - id: 1534; Bekker, A Holland, H D Wang, P-L Rumble, D 3rd Stein, H J Hannah, J L Coetzee, L L Beukes, N J England Nature. 2004 Jan 8;427(6970):117-20. JO - Dating the rise of atmospheric oxygen ER - TY - JOUR T1 - Decline of surface temperature and salinity in the western tropical Pacific Ocean in the Holocene epoch JF - Nature Y1 - 2004 A1 - Stott, L. A1 - Cannariato, K. A1 - Thunell, R. A1 - Haug, G. H. A1 - Koutavas, A. A1 - Lund, S. AB - In the present-day climate, surface water salinities are low in the western tropical Pacific Ocean and increase towards the eastern part of the basin. The salinity of surface waters in the tropical Pacific Ocean is thought to be controlled by a combination of atmospheric convection, precipitation, evaporation and ocean dynamics, and on interannual timescales significant variability is associated with the El Nino/Southern Oscillation cycles. However, little is known about the variability of the coupled ocean-atmosphere system on timescales of centuries to millennia. Here we combine oxygen isotope and Mg/Ca data from foraminifers retrieved from three sediment cores in the western tropical Pacific Ocean to reconstruct Holocene sea surface temperatures and salinities in the region. We find a decrease in sea surface temperatures of approximately 0.5 degrees C over the past 10,000 yr, whereas sea surface salinities decreased by approximately 1.5 practical salinity units. Our data imply either that the Pacific basin as a whole has become progressively less salty or that the present salinity gradient along the Equator has developed relatively recently. VL - 431 IS - 7004 N1 - Stott, LowellCannariato, KevinThunell, RobertHaug, Gerald HKoutavas, AthanasiosLund, SteveengResearch Support, U.S. Gov't, Non-P.H.S.England2004/09/03 05:00Nature. 2004 Sep 2;431(7004):56-9. JO - Decline of surface temperature and salinity in the western tropical Pacific Ocean in the Holocene epoch ER - TY - JOUR T1 - Deep global cycling of carbon constrained by the solidus of anhydrous, carbonated eclogite under upper mantle conditions JF - Earth and Planetary Science Letters Y1 - 2004 A1 - Dasgupta, R. A1 - Hirschmann, M. M. A1 - Withers, A. C. AB - We present partial melting experiments that constrain the near solidus phase relations of carbonated eclogite from 2 to 8.5 GPa. The starting material was prepared by adding 5 wt.% CO2 in the form of a mixture of Fe-Mg-Ca-Na-K carbonates to an eclogite from Salt Lake crater, Oahu, Hawaii and is a reasonable approximation of carbonated oceanic crust from which siliceous hydrous fluids have been extracted during subduction. Melt-present versus melt-absent conditions are distinguished based on textural criteria. Garnet and clinopyroxene appear in all the experiments. Between 2 and 3 GPa, the subsolidus assemblage also includes ilmenite+/-calcio-dolomite(ss)+/-CO2, whereas above the solidus (1050-1075 degreesC at 3 GPa) calcio-dolomitic liquid appears. From 3 to 4.5 GPa, dolomite(ss) is stable at the solidus and the near-solidus melt becomes increasingly dolomitic. The appearance of dolomite above 3 GPa is accompanied by a negative Clapeyron slope of the solidus, with a minimum located between 995 and 1025 degreesC at ca. 4 GPa. Above 4 GPa, the solidus rises with increasing pressure to 1245+35 degreesC at 8.5 GPa and magnesite becomes the subsolidus carbonate. Dolomitic melt coexists with magnesite+garnet+cpx+rutile along the solidus from 5 to 8.5 GPa.Comparison of our results to other recent experimental studies [T. Hammouda, High-pressure melting of carbonated eclogite and experimental constraints on carbon recycling and storage in the mantle, Earth Planet. Sci. Lett. 214 (2003) 357-368; G.M. Yaxley, G.P. Brey, Phase relations of carbonate-beating eclogite assemblages from 2.5 to 5.5 GPa: implications for petropnesis of carbonatites, Contrib. Mineral. Petrol. 146 (2004) 606-6191 shows that carbonate minerals are preserved in anhydrous or slightly hydrous carbonated eclogite to temperatures >1100 and >1200 degreesC at 5 and 9 GPa, respectively. Thus, deep subduction of carbonate is expected along any plausible subduction geotherm. If extrapolated to higher pressures, the carbonated eclogite solidus is likely to intersect the oceanic geotherm at a depth close to 400 km. Carbonated eclogite bodies entering the convecting upper mantle will thus release carbonate melt near the top of the mantle transition zone and may account for anomalously slow seismic velocities at depths of 280-400 km. Upon release, this small volume, highly reactive melt could be an effective agent of deep mantle metasomatism. Comparison of the carbonated eclogite solidus with that of peridotite-CO2 shows a shallower solidus-geotherm intersection for the latter. This implies that carbonated peridotite is a more likely proximal source of magmatic carbon in oceanic provinces. However, carbonated eclogite is a potential source of continental carbonatites, as its solidus crosses the continental shield geotherm at ca. 4 GPa. Transfer of eclogite-derived carbonate melt to peridotite may account for the geochemical characteristics of some oceanic island basalts (OIBs) and their association with high CaO and CO2. (C) 2004 Elsevier B.V. All rights reserved. VL - 227 IS - 1-2 N1 - 864qyTimes Cited:192Cited References Count:49 JO - Deep global cycling of carbon constrained by the solidus of anhydrous, carbonated eclogite under upper mantle conditions ER - TY - JOUR T1 - Deglacial history of the Ecuadorian Andes and implication for climate variations: Preliminary results JF - Eos Trans. AGU Fall Meeting Supplement Y1 - 2004 A1 - Hall, M. A1 - Rinterknecht, V. R. A1 - Schaefer, J. M. A1 - R, Seager A1 - Greene, A. VL - 85 IS - 47 N1 - id: 1003 ER - TY - JOUR T1 - Deglacial sea surface temperatures of the western tropical Pacific: A new look at old coral JF - Paleoceanography Y1 - 2004 A1 - Cohen, A. L. A1 - Hart, S. R. KW - bolling-allerod KW - climate-change KW - coral sr/ca KW - diagenesis KW - ion microprobe KW - last deglaciation KW - paleotemperature proxy KW - radiocarbon KW - record KW - sea surface temperature KW - sr/ca KW - strontium KW - symbiotic coral KW - trace-elements KW - tropical pacific AB - Using Secondary Ion Mass Spectrometry ( SIMS) ion microprobe techniques, we generated annual Sr/Ca cycles with subweekly resolution from chunks of Porites coral retrieved from a Tahiti barrier reef drill core (149degreesW, 17degreesS), representing the period 13,650 to 13,100 years B.P. The centers of pristine skeletal septa were selectively targeted with a 10 mum diameter ion beam spot, avoiding adjacent pore spaces occupied by secondary aragonite needles. Applying a Sr/Ca-sea surface temperature (SST) calibration equation derived from modern Tahiti Porites having the same low growth rate as the fossil specimens, we obtained SSTs similar to0.5degrees-1.5degreesC cooler during the Bolling-Allerod relative to the present day, with no significant change in seasonality. On the contrary, we estimate that analysis of bulk samples would yield excessively cool Sr/Ca-based SST estimates due to the occupation by secondary aragonite crystals of up to 50% of the skeletal pore space in the ancient samples. We find that growth rate effects on coral Sr/Ca further depress the apparent mean annual derived SSTs (by >3degreesC) and amplify the apparent seasonality by selectively enhancing wintertime cooling. Our microscale analysis of pristine skeleton and application of an appropriate growth-dependent calibration yield Sr/Ca-derived SSTs that are in good agreement with those derived from Mg/Ca ratios of calcitic foraminifera which indicate a continuous postglacial warming of the western tropical Pacific, in phase with the warming of the tropical Atlantic. VL - 19 SN - 0883-8305 IS - 4 N1 - 885czTimes Cited:30 Cited References Count:37 JO - Paleoceanography ER - TY - CHAP T1 - Dynamics of tidal salt barren formation and the record of present-day sea level change T2 - The Ecogeomorphology of Tidal Marshes, American Geophysical Union Y1 - 2004 A1 - Hsieh, Y. P. ED - Fagherazzi, S. JF - The Ecogeomorphology of Tidal Marshes, American Geophysical Union N1 - id: 1164 ER - TY - JOUR T1 - Dates, demography, and disease: Cultural contacts and possible evidence for old world epidemics among the island Chumash JF - Pacific Coast Archaeological Society Quarterly Y1 - 2003 A1 - Erlandson, J. M. A1 - Rick, T. C. A1 - Kennett, D. J. A1 - Walker, P. L. VL - 37 IS - 3 N1 - id: 1022 ER - TY - JOUR T1 - Decadal timescale shift in the 14C record of a central equatorial Pacific coral JF - Radiocarbon Y1 - 2003 A1 - Grottoli, A. G. A1 - Gille, S. T. A1 - Druffel, E. R. M. A1 - Dunbar, R. B. VL - 45 IS - 1 N1 - id: 1130 ER - TY - JOUR T1 - Deep sea records from the southeast Labrador Ocean circulation changes and ice-rafting events during hte last 160,000 years JF - Paleoceanography Y1 - 2003 A1 - Rasmussen, T. L. A1 - Oppo, D. W. A1 - Thompson, E. A1 - Lehman, S. J. VL - 18 N1 - id: 989 ER - TY - CHAP T1 - Data report: Australian Bight T2 - Proc. ODP, Sci. Results Y1 - 2002 A1 - Hine, A. C. A1 - Brooks, G. R. A1 - Mallinson, D. A1 - Brunner, C. A. A1 - James, N. P. A1 - Feary, D. A. A1 - Holbourn, A. E. A1 - Drexler, T. M. A1 - Howd, P. ED - Hine, A. C. JF - Proc. ODP, Sci. Results VL - 182 N1 - id: 271 ER - TY - JOUR T1 - Differences in 14C age between stratigraphically associated charcoal and marine shell from the archaic period site of kilometer 4, southern Peru: old wood or old water? JF - Radiocarbon Y1 - 2002 A1 - Kennett, D. J. A1 - Ingram, B. L. A1 - Southon, J. R. A1 - Wise, K. VL - 44 IS - 1 N1 - id: 1023 ER - TY - CONF T1 - The distribution and inventory of bomb produced radiocarbon in the Pacific Ocean T2 - AGU/ASLO Conference Y1 - 2002 A1 - Key, R. M. JF - AGU/ASLO Conference CY - Honolulu, HI N1 - id: 1448 ER - TY - JOUR T1 - Drowned reefs and antecedent karst topography, Au'au Channel, S. E. Hawaiian Island JF - EOS Y1 - 2002 A1 - Grigg, R. W. A1 - Grossman, E. E. A1 - al, et VL - 83 IS - 4 N1 - id: 662 ER - TY - THES T1 - The dynamics of pore water dissolved organic carbon and the fate of organic matter in anoxic marine sediments: As assessment using carbon isotopes and ultrafiltration. PhD thesis Y1 - 2002 A1 - Seagle, Carol A. PB - University of North Carolina at Chapel Hill CY - Chapel Hill, North Carolina VL - PhD ER - TY - CONF T1 - On the d13C:PO4 relationahip in the modern and glacial ocean T2 - Fall AGU Meeting Y1 - 2001 A1 - Toggweiler, J. R. A1 - Key, R. M. A1 - McNeil, B. JF - Fall AGU Meeting CY - San Francisco, CA N1 - id: 1447 ER - TY - JOUR T1 - Dating modern deltas: progress, problems and prognostics JF - Annual Review of Earth and Atmospheric Sciences Y1 - 2001 A1 - Stanley, D. J. AB - Radiocarbon dating is the method most frequently used to date Holocene deltaic sequences, but less than one quarter of 14C dates are within ±500 years of predicted age. Such dates tend to be unreliable, in other words, often too old and commonly inverted upsection, and core sample dates obtained near deltaic plain surfaces may be as old as mid- to late Holocene. Stratigraphic irregularities result primarily from downslope reworking of upland alluvial sediment, with displacement of “old carbon” in the sediment that accumulates in lower valleys and deltaic plains. Use of dates that are too old results in inaccurately calculated rates (most often too low) of relative sea-level rise and/or land subsidence. More reliable timing of deltaic sediment requires a multiple-method dating approach, including, where possible, identification of associated archaeological material. Developing an accurate dating strategy is a critical step for implementing reliable coastal protection measures needed for the rapidly increasing human populations in these low-lying, vulnerable nearshore settings. VL - 28 N1 - id: 1378 JO - Dating modern deltas: progress, problems and prognostics ER - TY - JOUR T1 - Decadal record of climate variability spanning the last 700 years in the southern tropics of East Africa JF - Geology Y1 - 2001 A1 - Johnson, T. C. A1 - Barry, S. L. A1 - Chan, Y. A1 - Wilkinson, P. VL - 29 N1 - id: 1477 ER - TY - CHAP T1 - The deglaciation of eastern Maine: in Deglacial history and relative sea-level changes, northern New England and adjacent Canada T2 - Deglacial history and relative sea-level changes, northern New England and adjacent Canada Y1 - 2001 A1 - Dorion, C. C. A1 - Kaplan, M. R. A1 - Kreutz, K. J. A1 - Balco, G. A1 - Wright, J. A1 - Borns, H. W., Jr. ED - Weddle, T. K. JF - Deglacial history and relative sea-level changes, northern New England and adjacent Canada T3 - Special papers (Geological Society of America) PB - Geological Society of America SN - 0813723515 N1 - id: 1310 ER - TY - CONF T1 - Deposition of Bomb C-14 in Continental Slope Sediments: Use of Radiocarbon in Understanding Benthic Food Web Dynamics T2 - Aquatic Sciences Meeting, ASLO Y1 - 2001 A1 - DeMaster, D. J. A1 - Blair, N. E. A1 - Smith, C. R. A1 - Fornes, W. L. A1 - Thomas, C. J. A1 - Plaia, G. JF - Aquatic Sciences Meeting, ASLO CY - Albuquerque, NM N1 - id: 1368 ER - TY - JOUR T1 - Determination of the the H3 factor in hydrogen isotope ratio monitoring mass spectrometry JF - Anal Chem Y1 - 2001 A1 - Sessions, A. L. A1 - Burgoyne, T. W. A1 - Hayes, J. M. AB - The H3 factor, K, is a parameter required in high-precision, mass spectrometric analyses of hydrogen isotopic abundances. When H2 is used as the sample gas, R* = R - Ki2, where R* is the true HD/H2 ratio, R is the observed (mass 3)/(mass 2) ion-current ratio, and i2 is the ion current at mass 2. Four different methods for the determination of K were defined and tested under conditions characteristic of isotope ratio monitoring systems. Three of these were peak-based. The fourth employed steady flows of H2 from a conventional inlet system. Results obtained using the latter method were more precise (standard deviation of K = 0.1 versus approximately 0.6 ppm mV(-1) for the peak-based methods). However, use of the resulting values of K for correction of isotope ratio monitoring GC/MS results led to systematic errors as large as 9 per thousand, whereas use of the peak-based values led to no systematic errors. Values of K were only weakly dependent on the pressure of He, declining approximately 5% for each 10-fold increase in P(He). Small variations in partial pressures of H2O and CH4, potential contaminants under isotope ratio monitoring conditions, had no significant effect on values of K. VL - 73 SN - 0003-2700 (Print)0003-2700 (Linking) UR - https://www.ncbi.nlm.nih.gov/pubmed/11199966 IS - 2 N1 - Sessions, A LBurgoyne, T W Hayes, J M eng 2001/02/24 12:00 Anal Chem. 2001 Jan 15;73(2):200-7. ER - TY - JOUR T1 - Development of a Carbon Isotope-Based Tracer of Groundwater Fluxes into Estuaries and the Coastal Ocean JF - EOS Y1 - 2001 A1 - McCorkle, D. C. A1 - Gramling, C. M. A1 - Mulligan, A. E. A1 - Woods, T. L. VL - 82 IS - 20 N1 - id: 1409 ER - TY - JOUR T1 - Diastems and time-averaging: The limits of resolution in stratigraphy and paleontology JF - Geological Society of America Abstracts with Programs Y1 - 2001 A1 - Kowalewski, M. A1 - Bambach, R. K. VL - 33 IS - A32 N1 - id: 282 JO - Diastems and time-averaging: The limits of resolution in stratigraphy and paleontology ER - TY - JOUR T1 - Drainage of late Wisconsin glacial lakes and the morphology and late quaternary stratigraphy of the New Jersey-southern New England continental shelf and slope JF - Marine Geology Y1 - 2001 A1 - Uchupi, E. A1 - Driscoll, N. A1 - Ballard, R. D. A1 - Bolmer, S. T. AB - We propose that late Wisconsin deposition and erosion (Hudson Shelf and Block Island valleys) on the shelf and slope from New Jersey to southern New England were a consequence of the catastrophic drainage of glacial lakes behind terminal moraine systems and the huge volume of water stored beneath the Laurentian ice sheet and subsequent erosion of the lake sediments by flash floods. The morphology imparted by glaciation regulated the discharge associated with the ablation of the glaciers. Associated with the deposits west of Hudson Shelf Valley are the remains of mammoth and mastodon which were transported from their living habitats along the lake shores to their present burial sites on the shelf. The floods also triggered gravity flows on the upper continental slope which made possible the transportation of coarse debris over hundreds of km into the deep-sea. That these catastrophic hood morphologies can still be recognized on the middle to outer shelf suggest that much of its surface was little modified during the late Pleistocene/Holocene transgression. Thus the late Pleistocene/Holocene transgression may have been characterized by short periods when sea level rose rapidly allowing for the preservation of relict features. (C) 2001 Elsevier Science B.V. All rights reserved. VL - 172 IS - 1-2 N1 - 400trTimes Cited:50Cited References Count:115 JO - Drainage of late Wisconsin glacial lakes and the morphology and late quaternary stratigraphy of the New Jersey-southern New England continental shelf and slope ER - TY - JOUR T1 - d13C values and radiocarbon dates of microbial biomarkers as tracers fro carbon recycling in peat deposits JF - Geology Y1 - 2000 A1 - Pancost, R. D. A1 - van Geel, B. A1 - Baas, M. A1 - Damste Sinninghe, J. S. VL - 28 N1 - id: 1330 ER - TY - CONF T1 - Deep Sea Sediments off Baja California Reflect Greenland Ice Core climate cycles T2 - Geological Society of America, Annual meeting Y1 - 2000 A1 - Ortiz, J. A1 - O'Connell, S. A1 - van Geen, A. A1 - Party, Melville ' Shipboard Scientific JF - Geological Society of America, Annual meeting PB - Geological Society of America CY - Reno, NV N1 - id: 110 ER - TY - JOUR T1 - Detecting holocene changes in thermohaline circulation JF - Proc Natl Acad Sci U S A Y1 - 2000 A1 - Keigwin, L. D. A1 - Boyle, E. A. KW - *Climate KW - *Plankton KW - Animals KW - Atlantic Ocean KW - carbon isotopes KW - ice KW - oxygen isotopes KW - time AB - Throughout the last glacial cycle, reorganizations of deep ocean water masses were coincident with rapid millennial-scale changes in climate. Climate changes have been less severe during the present interglacial, but evidence for concurrent deep ocean circulation change is ambiguous. VL - 97 SN - 0027-8424 (Print)0027-8424 (Linking) UR - https://www.ncbi.nlm.nih.gov/pubmed/10677463 IS - 4 N1 - Keigwin, L DBoyle, E A eng Research Support, U.S. Gov't, Non-P.H.S. 2000/03/04 09:00 Proc Natl Acad Sci U S A. 2000 Feb 15;97(4):1343-6. ER - TY - JOUR T1 - Differences in great earthquake rupture extent inferred from tsunami-laid sand and foraminiferal assemblages at Alsea Bay, central Oregon coast JF - Geological Society of America Abstracts with Programs Y1 - 2000 A1 - Nelson, A. R. A1 - Jennings, A. E. VL - 33 IS - 7 N1 - id: 257 ER - TY - JOUR T1 - Deep-sea sedimentary record of the late Wisconsin cataclysmic floods from the Columbia River JF - Geology Y1 - 1999 A1 - Brunner, C. A. A1 - Normark, W. R. A1 - Zuffa, G. G. A1 - Serra, F. AB - New results from Ocean Drilling Program Site 1037 and U.S. Geological Survey high-resolution seismic-reflection profiles confirm the great thickness, fast deposition rate, distant source, and convolute path of turbidites that fill the Escanaba Trough, the rift valley of the southernmost segment of the Gorda Ridge. Accelerator mass spectrometry C-14 measurements provide the first direct dating of the Escanaba Trough turbidites, demonstrating an average deposition rate faster than 10 m/k.y. between 32 and 11 ka and as fast as 15 m/k.y. during the oxygen isotope stage 2 lowstand, In the upper 60 m of sediment, the petrology of turbidite sand beds, which are as much as 12 m thick, show that the dominant source for the turbidites is from the Columbia River, which is more than 800 km to the north, rather than from the much closer rivers of northern California. New high-resolution seismic-reflection profiles show that, except for areas of very recent volcanism, the entire Escanaba Trough below 3200 m water depth is floored by the turbidite sequence that was cored in the upper 60 m at Site 1037B, The ages of the upper 120 m of turbidites correspond with the ages of channeled scabland deposits associated with latest Quaternary jokulhlaups from glacial Lake Missoula, The age and source characteristics suggest that these megaturbidite beds in Escanaba Trough are most likely deposits formed by hyperpycnally generated turbidity currents as the largest of the Lake Missoula floods entered the sea. VL - 27 IS - 5 N1 - 193qfTimes Cited:40Cited References Count:19 JO - Deep-sea sedimentary record of the late Wisconsin cataclysmic floods from the Columbia River ER - TY - JOUR T1 - Deglaciation of the northwestern White Mountains, New Hampshire JF - Geographie Physique Et Quaternaire Y1 - 1999 A1 - Thompson, W. B. A1 - Fowler, B. K. A1 - Dorion, C. C. KW - canada KW - chronology KW - climate KW - last termination KW - new-england KW - record KW - tills AB - The mode of deglaciation in the northwestern White Mountains of New Hampshire has been controversial since the mid 1800's. Early workers believed that active ice deposited the Bethlehem Moraine complex in the Ammonoosuc River basin during recession of the last ice sheet. In the 1930's this deglaciation model was replaced by the concept of widespread simultaneous stagnation and downwastage of Late Wisconsinan ice. The present authors reexamined the Bethlehem Moraine complex and support the original interpretation of a series of moraines deposited by active ice. We found other moraine clusters of similar age to the northeast in the Johns River and lsrael River basins. lce-marginal deposits that probably correlate with the Bethlehem Moraine also occur west of Littleton. The Bethlehem Moraine complex and equivalent deposits in adjacent areas were formed by readvance and oscillatory retreat of the Connecticut Valley lobe of the Laurentide Ice Sheet. This event is called the Littleton-Bethlehem Readvance. Throughout the study area, sequences of glaciolacustrine deposits and meltwater drainage channels indicate progressive northward recession of the glacier margin. Radiocarbon dates from nearby New England and Quebec suggest that the ice sheet withdrew from this part of the White Mountains between about 12,500 and 12,000 (14)C yr BP. We attribute the Littleton-Bethlehem Readvance to a brief climatic cooling during Older Dyas time, close to 12,000 BP. VL - 53 SN - 0705-7199 IS - 1 N1 - 218kbTimes Cited:18 Cited References Count:56 JO - Geogr Phys Quatern ER - TY - JOUR T1 - Deltas, radiocarbon dating, and measurements of sediment storage and subsidence JF - Geology Y1 - 1999 A1 - Stanley, D. J. A1 - Hait, A. K. VL - 28 N1 - id: 1376 ER - TY - THES T1 - Diagenetic Zonation and Authigenic Carbonate Formation within Methane- and Gas Hydrate-Bearing Sedimentary Sections, Offshore, Southeastern North America, Thesis Y1 - 1999 A1 - Rodriques, N. M. PB - University of North Carolina CY - Chapel Hill, NC VL - Dissertation/Thesis ER - TY - CONF T1 - The distribution and carbon isotopic composition of dissolved organic matter in Florida Everglades (abstract) T2 - The Sixth Symposium on Biogeochemistry of Wetlands Y1 - 1999 A1 - Wang, Y. A1 - Hsieh, Y. P. A1 - Landing, W. M. A1 - Salters, V. A1 - Cooper, W. A1 - Proctor, L. JF - The Sixth Symposium on Biogeochemistry of Wetlands N1 - id: 165 ER - TY - JOUR T1 - Decadal to millennial variability of fluviomarine sedimentation on the northern California continental shelf JF - EOS Y1 - 1998 A1 - Sommerfield, C. K. VL - Transactions of the American Geophysical Union IS - 79:45 N1 - id: 1328 ER - TY - CONF T1 - Determination of the radiocarbon ages of individual PAH extracted from urban aerosol and marine sediment T2 - 16th International Radiocarbon Conference Y1 - 1997 A1 - Pearson, A. A1 - Eglinton, T. I. A1 - McNichol, A. P. A1 - Currie, L. A. A1 - Schneider, R. J. A1 - von Reden, K. F. A1 - Benner, B. A. A1 - Wise, S. A. JF - 16th International Radiocarbon Conference CY - Groningen VL - Book of Abstracts N1 - id: 951 ER - TY - JOUR T1 - Detritus dynamics in the seagrass Posidonia oceanica: Elements for an ecosystem carbon and nutrient budget JF - Marine Ecology-Progress Series Y1 - 1997 A1 - Mateo, M. A. A1 - Romero, J. AB - Leaf decay, leaf Litter export, burial in belowground sinks, and respiratory consumption of detritus were examined at 2 different depths in a Posidonia oceanica (L.) Delile meadow off the Medes Islands, NW Mediterranean. At 5 m, the amount of exported leaf Litter represented carbon, nitrogen and phosphorus losses of 7, 9 and 6 % of the plant primary production, respectively. About 26 % of the carbon produced by the plant in 1 yr was immobilized by burial in the belowground compartment, i.e. as roots and rhizomes. Annual nitrogen and phosphorus burial in the sediment was 8 and 5 % of total N and P needs, respectively. Respiratory consumption (aerobic) of carbon leaf detritus represented 17% of the annual production. An additional, but very substantial, loss of carbon as very fine particulate organic matter has been estimated at ca 48%. At 13 m the pattern of carbon losses was similar, but the lesser effect of wave action (relative to that at 5 m) reduced exportation, hence increasing the role of respiratory consumption. Data on carbon losses indicated that only a small part of the plant production was actually available to fuel the food web of this ecosystem. Total nutrient losses were in the range of 21 to 47 % of annual needs. From differences found in N and P concentrations between living and dead tissues, it is suggested that important nutrient recycling (50 to 70%) may be due either to reclamation or to leaching immediately after plant death. VL - 151 IS - 1-3 N1 - id: 2004; PT: J; UT: WOS:A1997XE68700005 JO - Detritus dynamics in the seagrass Posidonia oceanica: Elements for an ecosystem carbon and nutrient budget ER - TY - JOUR T1 - Dynamic changes of the Holocene Mississippi River delta plain: The delta cycle JF - Journal of Coastal Research Y1 - 1997 A1 - Roberts, H. H. KW - barrier KW - delta cycle KW - lacustrine deltas KW - progradation KW - shoreline change KW - subsidence AB - Previous geologic research on Holocene Mississippi River deltaic deposits has verified that the present delta plain and associated nearshore barrier islands and submarine shoals are either direct or indirect products of cyclic delta-building events that have operated on a variety of temporal and spatial scales. A major depositional element of the modern delta plain is the delta complex, of which there are six: (1) Maringouin, (2) Teche, (3) St. Bernard, (4) Lafourche, (5) Balize, and (6) Atchafalaya. Major delta-building events have occurred at a frequency of one every 1-2 kyr. Deposits associated with the six major delta complexes are fundamental constructional units of the delta plain, which collectively covers an area of similar to 30,000 km(2). Sedimentary deposits associated with these delta-building events range in thickness from about 10 to 100 m. Their construction is modulated by stream capture, which develops a new delta complex by way of a new river course. Delta complexes may be comprised of one or more delta lobes. As a product of this delta switching, the depositional architecture of the delta plain consists of laterally offset and stacked delta lobes. Within delta lobes are subdeltas and even smaller crevasse-splays. These smaller scale deltas sedimentologically and geomorphically mimic their larger delta lobe counterparts, but they are considerably thinner, cover less area, and have a shorter period of development and abandonment. Subdeltas are usually < 10 m thick and may fill shallow bays that cover over 300 km(2). They build and deteriorate on time-scales of 150-200 years. Crevasse-splays or overbank splays are < 5 m thick, cover only a few square kilometers, and are abandoned after several decades of active growth.Each delta evolves through a rapid regressional phase as water and sediment are captured from an antecedent river course. If highstand conditions persist long enough, deltas may prograde to the outer shelf to form wedges of deltaic sediment much thicker than their inner shelf counterparts. The delta-building process starts with the filling of interior lakes (lacustrine deltas), which is followed by bayhead delta-building at the coast, and finally by progradation across the marine shelf(shelf delta). Delta complexes and delta lobes, as well as their smaller counterparts, experience three phases of growth and abandonment: (1) rapid growth with increasing-to-stable discharge, (2) relative stability during initial stages of waning discharge, when sediment input balances the collective effects of subsidence, and (3) abandonment, followed by rapid subsidence-driven subaerial delta deterioration. In the rapid growth stage, formerly eroding-subsiding coastal environments experience delta plain accretion and coastal progradation from renewed sediment input. On the abandonment side of the cycle, marine processes overwhelm fluvial processes and rework the delta perimeter. Forced by the combined processes of subsidence, the delta surface undergoes progressive submergence. Transgressive sand bodies created by wave reworking of the delta evolve from headland beaches and spits, to barrier islands, and finally to submarine shoals as the abandonment phase is completed. VL - 13 SN - 0749-0208 UR - http://www.jstor.org/stable/4298659 IS - 3 N1 - Xq326Times Cited:167 Cited References Count:74 JO - J Coastal Res ER - TY - CONF T1 - Dating of explosive volcanic events associated with dome growth at Soufriere Hills volcano, Montserrat T2 - Proceedings of the Special Symposium on Volcanism in Montserrat, Second Caribbean Conference on Natural Hazards and Hazard Management Y1 - 1996 A1 - Young, S. R. A1 - Hoblitt, R. P. A1 - Smith, A. L. A1 - Devine, J. D. A1 - Wadge, G. A1 - Shepherd, J. B. JF - Proceedings of the Special Symposium on Volcanism in Montserrat, Second Caribbean Conference on Natural Hazards and Hazard Management T3 - Montserrat Volcano Observatory Open File Report 96/22 CY - Kingston, Jamaica N1 - id: 1306 ER - TY - CONF T1 - Deep water formation and exchange rates in the Arctic Ocean: Implications from the distribution of 14C T2 - 7th International Conference on Accelerator Mass Spectrometry Y1 - 1996 A1 - Schlosser, P. A1 - Kromer, B. A1 - Ekwurzel, B. A1 - Boenisch, G. A1 - McNichol, A. A1 - Schneider, R. A1 - von Reden, K. A1 - Oestlund, G. JF - 7th International Conference on Accelerator Mass Spectrometry PB - Radiocarbon CY - Tucson, AZ VL - 38 N1 - id: 947; 1 ER - TY - RPRT T1 - The development of Ryder Pond in the Cape Cod National Seashore and determination of the causes of recent Ryder Pondwater chemistry changes. Report Y1 - 1996 A1 - Winkler, Marjorie G. PB - University of Wisconsin Center for Climatic Research CY - Madison, WI VL - NPS/NESO-RNR/NRTR/97-01 N1 - id: 92 ER - TY - CONF T1 - Diatom and sediment evidence for late Holocene hydrologic changes, Everglades National Park T2 - ASLO Meeting Y1 - 1996 A1 - Winkler, M. G. A1 - Kaplan, S. JF - ASLO Meeting CY - Milwaukee, WI N1 - id: 1303 ER - TY - JOUR T1 - Direct U-Th dating of marine sediments from the two most recent interglacial periods JF - Nature Y1 - 1996 A1 - Slowey, N. C. A1 - Henderson, G. M. A1 - Curry, W. B. AB - A KNOWLEDGE of the age of marine sediments is necessary to determine the timing of events and rates of processes in the marine realm, and the relationships among marine and other climatically sensitive records. The establishment of an accurate chronology for Pleistocene marine sediments beyond the range of radiocarbon dating (approximately the past 45 kyr) has therefore been a goal of palaeoceanographers for decades. Early attempts(1,2) based on measurements of the radionuclides Th-230 and Pa-231 mere beset with problems, and subsequent studies focused on tying fluctuations in marine sediment oxygen-isotope records to events such as the formation of col al reef terraces and changes in the Earth's magnetic polarity(3,4), and tuning the resultant chronologies to the Earth's orbitally driven insolation variations(5-8). But these chronologies (especially the age and duration of the last interglacial period) have been challenged by several studies(9-12), raising questions about the fundamental cause of Pleistocene climate fluctuations. Here we report the direct U-Th dating of aragonite-rich marine sediments from the Bahamas, and present an accurately dated marine oxygen-isotope record for the last two interglacials. We obtain dates of 120-127 kyr BP for the last interglacial and 189-190 kyr np for the late stage 7 interglacial. These dates are in accord with the general theory of orbitally forced climate fluctuations and demonstrate the potential of our direct-dating approach for developing an absolute chronology for the Pleistocene marine oxygen-isotope record. VL - 383 IS - 6597 N1 - Vh315Times Cited:39Cited References Count:40 JO - Direct U-Th dating of marine sediments from the two most recent interglacial periods ER - TY - JOUR T1 - Distribution of otoliths in surficial sediments of the U. S. Atlantic continental shelf and slope and potential for reconstructing Holocene fish stocks JF - Paleoceanography Y1 - 1996 A1 - Elder, K. L. A1 - Jones, G. A. A1 - Bolz, G. VL - 11 IS - 3 N1 - id: 1755 ER - TY - THES T1 - Development and application of the mollusc Arctica islandicaas a paleoceanographic tool for the North Atlantic Ocean, Thesis Y1 - 1995 A1 - Weidman, C. R. PB - MIT CY - Cambridge, MA and Woods Hole, MA VL - Ph.D. dissertation ER - TY - CONF T1 - Developments at the NOSAMS Facility During 1995 T2 - Symposium of Northeastern Accelerator Personnel Y1 - 1995 A1 - von Reden, K. F. A1 - Cohen, G. J. A1 - Dalton, M. J. A1 - Peden, J. C. A1 - Schneider, R. J. JF - Symposium of Northeastern Accelerator Personnel CY - Durham, NC N1 - id: 1799 ER - TY - JOUR T1 - The Deep-water Radiocarbon Minimum in the Northeastern Pacific Ocean; Early WOCE Results JF - EOS, Transactions, American Geophysical Union; Ocean Sciences Mtg., San Diego, Feb.21-25, 1994 Y1 - 1994 A1 - Key, R. M. A1 - Toggweiller, J. R. VL - 75 IS - 3 N1 - id: 912 JO - The Deep-water Radiocarbon Minimum in the Northeastern Pacific Ocean; Early WOCE Results ER - TY - JOUR T1 - Deglaciation, Lake Levels, and Meltwater Discharge in the Lake-Michigan Basin JF - Quaternary Science Reviews Y1 - 1994 A1 - Colman, S. M. A1 - Clark, J. A. A1 - Clayton, L. A1 - Hansel, A. K. A1 - Larsen, C. E. AB - The deglacial history of the Lake Michigan basin, including discharge and routing of meltwater, is complex because of the interaction among (1) glacial retreats and re-advances in the basin (2) the timing of occupation and the isostatic adjustment of lake outlets and (3) the depositional and erosional processes that left evidence of past lake levels. In the southern part of the basin, a restricted area little affected by differential isostasy, new studies of onshore and offshore areas allow refinement of a lake-level history that has evolved over 100 years. Important new data include the recognition of two periods of influx of meltwater from Lake Agassiz into the basin and details of the highstands gleaned from sedimentological evidence. Major disagreements still persist concerning the exact timing and lake-level changes associated with the Algonquin phase, approximately 11,000 BP. A wide variety of independent data suggests that the Lake Michigan Lobe was thin, unstable, and subject to rapid advances and retreats. Consequently, lake-level changes were commonly abrupt and stable shorelines were short-lived. The long-held beliefs that the southern part of the basin was stable and separated from deformed northern areas by a hinge-line discontinuity are becoming difficult to maintain. Numerical modeling of the ice-earth system and empirical modeling of shoreline deformation are both consistent with observed shoreline tilting in the north and with the amount and pattern of modern deformation shown by lake-level gauges. New studies of subaerial lacustrine features suggest the presence of deformed shorelines higher than those originally ascribed to the supposed horizontal Glenwood level. Finally, the Lake Michigan region as a whole appears to behave in a similar manner to other areas, both local (other Great Lakes) and regional (U.S. east coast), that have experienced major isostatic changes. Detailed sedimentological and dating studies of field sites and additional development of geophysical models offer hope for reconciling the field data with our understanding of earth theology. VL - 13 IS - 9-10 N1 - Qq080Times Cited:30Cited References Count:48 JO - Deglaciation, Lake Levels, and Meltwater Discharge in the Lake-Michigan Basin ER - TY - THES T1 - The deglaciation of southeastern Washington County, Maine. Thesis Y1 - 1994 A1 - Kaplan, M. PB - University of Maine, Orono CY - Orono, Maine VL - Unpublished ER - TY - RPRT T1 - The development of the Gull Pond Chain of Lakes and the Herring River Basin in the Cape Cod National Seashore. Report Y1 - 1994 A1 - Winkler, M. G. N1 - id: 93 ER - TY - CONF T1 - Do AMS measurements approach a Gaussian distribution? T2 - 15th International Radiocarbon Conference Y1 - 1994 A1 - Jirikowic, J. L. A1 - Schneider, R. J. A1 - von Reden, K. F. A1 - Jones, G. A. JF - 15th International Radiocarbon Conference CY - Glasgow, Scotland N1 - id: 940 ER - TY - MGZN T1 - Dating the Climatic Optimum with AMS Y1 - 1993 A1 - Elder, K. L. JF - AMS Pulse, The National Ocean Sciences Accelerator Mass Spectrometry Facility Newsletter VL - Spring 1993 N1 - id: 1645 ER - TY - JOUR T1 - Deep-sea sediments reveal JF - Oceanus Y1 - 1993 A1 - Lehman, Scott J. A1 - Keigwin, L. D. VL - 35 IS - 4 N1 - id: 1248 JO - Deep-sea sediments reveal ER - TY - CONF T1 - Development of the mollusc Artica islandica as a paleoceanographic tool for reconstructing annual and seasonal records of 14C and delta 18O in the mid- to high- latitude North Atlantic Ocean T2 - International Symposium on Applications of Isotope Techniques in the Study of Past and Current Environmental Changes in the Hydrosphere and the Atmosphere Y1 - 1993 A1 - Weidman, C. R. A1 - Jones, G. A. JF - International Symposium on Applications of Isotope Techniques in the Study of Past and Current Environmental Changes in the Hydrosphere and the Atmosphere PB - International Atomic Energy Agency CY - Vienna, Austria VL - SMm-329 N1 - id: 1292 ER -