Insights of Pb isotopic signature into the historical evolution and sources of Pb contamination in a sediment core of the southwestern Iberian Atlantic shelf - Mário Mil-Homens; Carlos Vale; Pedro Brito; Filipa Naughton; Teresa Drago; Joana Raimundo; Bárbara Anes; Sabine Schmidt; Miguel Caetano (Science of The Total Environment, 2017)
Abstract Stable Pb isotopic ratios and concentrations of Al, Cu and Pb were measured in a 5 m long sediment core (VC2B) retrieved at 96 m water depth in the southwestern Iberian Atlantic shelf. Five phases during the last 9.5 kyrs were identified, two of them (Roman Period and modern mining) marked by a decrease of 206Pb/207Pb ratios reflecting additional inputs of Pb derived from mining activities. The Roman Period was also characterized by high 208Pb/206Pb ratios suggesting the exploitation of the outcropping portion of the orebody intensely weathered when compared with the other formations later mined. The shift of 208Pb/206Pb ratios towards linearity took approximately 1.0 kyrs, which may mirror the time of environmental recovery from the impact of Roman mining activities. The application of a mixing model allowed the quantification of the contribution associated with anthropogenic mining activities to the shelf sediments. The maximum values of Pb contamination occurred in the 20th century. This study gives direct evidence of Pb and Cu exploitation over the last 2000 years. The stable Pb isotopic signatures point to legacy of mining activities that are still the prevailing metal source recorded in the southwestern Iberian Atlantic shelf sediments.
Keywords: Environment recovery

Insights of Pb isotopic signature into the historical evolution and sources of Pb contamination in a sediment core of the southwestern Iberian Atlantic shelf - Mil-Homens, ário; Vale, Carlos; Brito, Pedro; Naughton, Filipa; Drago, Teresa; Raimundo, Joana; Anes, árbara; Schmidt, Sabine; Caetano, Miguel (Science of The Total Environment, 2017)
Stable Pb isotopic ratios and concentrations of Al, Cu and Pb were measured in a 5 m long sediment core (VC2B) retrieved at 96 m water depth in the southwestern Iberian Atlantic shelf. Five phases during the last 9.5 kyrs were identified, two of them (Roman Period and modern mining) marked by a decrease of Pb-206/Pb-207 ratios reflecting additional inputs of Pb derived from mining activities. The Roman Period was also characterized by high Pb-208/Pb-206 ratios suggesting the exploitation of the outcropping portion of the orebody intensely weathered when compared with the other formations later mined. The shift of Pb-208/Pb-206 ratios towards linearity took approximately 1.0 kyrs, which may mirror the time of environmental recovery from the impact of Roman mining activities. The application of a mixing model allowed the quantification of the contribution associated with anthropogenic mining activities to the shelf sediments. The maximum values of Pb contamination occurred in the 20th century. This study gives direct evidence of Pb and Cu exploitation over the last 2000 years. The stable Pb isotopic signatures point to legacy of mining activities that are still the prevailing metal source recorded in the southwestern Iberian Atlantic shelf sediments.
Keywords: Environment recovery; Marine sediments; Pb isotopes; Roman and modem mining activities; Southwestern Iberian shelf; Temporal evolution

Land-use change and managed aquifer recharge effects on the hydrogeochemistry of two contrasting atoll island aquifers, Roi-Namur Island, Republic of the Marshall Islands - Mehrdad Hejazian; Jason J. Gurdak; Peter Swarzenski; Kingsley O. Odigie; Curt D. Storlazzi (Applied Geochemistry, 2017)
Abstract Freshwater resources on low-lying atoll islands are highly vulnerable to climate change and sea-level rise. In addition to rainwater catchment, groundwater in the freshwater lens is a critically important water resource on many atoll islands, especially during drought. Although many atolls have high annual rainfall rates, dense natural vegetation and high evapotranspiration rates can limit recharge to the freshwater lens. Here we evaluate the effects of land-use/land-cover change and managed aquifer recharge on the hydrogeochemistry and supply of groundwater on Roi-Namur Island, Republic of the Marshall Islands. Roi-Namur is an artificially conjoined island that has similar hydrogeology on the Roi and Namur lobes, but has contrasting land-use/land-cover and managed aquifer recharge only on Roi. Vegetation removal and managed aquifer recharge operations have resulted in an estimated 8.6 × 105 m3 of potable groundwater in the freshwater lens on Roi, compared to only 1.6 × 104 m3 on Namur. We use groundwater samples from a suite of 33 vertically nested monitoring wells, statistical testing, and geochemical modeling using \{PHREEQC\} to show that the differences in land-use/land-cover and managed aquifer recharge on Roi and Namur have a statistically significant effect on several groundwater-quality parameters and the controlling geochemical processes. Results also indicate a six-fold reduction in the dissolution of carbonate rock in the freshwater lens and overlying vadose zone of Roi compared to Namur. Mixing of seawater and the freshwater lens is a more dominant hydrogeochemical process on Roi because of the greater recharge and flushing of the aquifer with freshwater as compared to Namur. In contrast, equilibrium processes and dissolution-precipitation non-equilibrium reactions are more dominant on Namur because of the longer residence times relative to the rate of geochemical reactions. Findings from Roi-Namur Island support selective land-use/land-cover change and managed aquifer recharge as a promising management approach for communities on other low-lying atoll islands to increase the resilience of their groundwater supplies and help them adapt to future climate change related stresses.

Local glaciation in West Greenland linked to North Atlantic Ocean circulation during the Holocene - Schweinsberg, Avriel D.; Briner, Jason P.; Miller, Gifford H.; Bennike, Ole; Thomas, Elizabeth K. (Geology, 2017)
Recent observations indicate that ice-ocean interaction drives much of the recent increase in mass loss from the Greenland Ice Sheet; however, the role of ocean forcing in driving past glacier change is poorly understood. To extend the observational record and our understanding of the ocean-cryosphere link, we used a multi-proxy approach that combines new data from proglacial lake sediments, C-14-dated in situ moss that recently emerged from beneath cold-based ice caps, and Be-10 ages to reconstruct centennial-scale records of mountain glacier activity for the past similar to 10 k. y. in West Greenland. Proglacial lake sediment records and C-14 dating of moss indicate the onset of Neoglaciation in West Greenland at ca. 5 ka with substantial snowline lowering and glacier expansion at ca. 3.7 ka followed by additional ice expansion phases at ca. 2.9, ca. 1.7, and ca. 1.4 ka and during the Little Ice Age. We find that widespread glacier growth at ca. 3.7 ka in West Greenland coincides with marked cooling and reduced strength of the West Greenland Current in Disko Bugt. The transition to cooler ocean conditions at ca. 3.7 ka identified in Disko Bugt is registered by marine proxy data farther afield in East Greenland and on the northwestern Icelandic shelf, implying large-scale paleoceanographic changes across the North Atlantic during this interval. The similarity between glacier change on West Greenland and multiple marine and terrestrial records across the North Atlantic suggests that glaciers are strongly influenced by changes in ocean circulation and consequently implies that the ocean-cryosphere teleconnection is a persistent feature of the Arctic system.

Millennial mode of variability of sea ice conditions in the Okhotsk Sea during the last glaciation (MIS 4–MIS 2) - Vasilenko, Yuriy P.; Gorbarenko, Sergey A.; Bosin, Aleksandr A.; Shi, Xue-fa; Chen, Min-Te; Zou, Jian-jun; Liu, Yan-guang; Artemova, Antonina V.; Yanchenko, Elena A.; Savenko, Mikhail P. (Quaternary International, 2017)
Coarse fraction (CF) content, grain-size distribution, roundness of CF, gravels and pebbles, and examination of surface of pebbles were studied in core LV28-44-4, recovered from the eastern Okhotsk Sea (OS). The age model of the studied core was based on the AMS 14C data, tephrochronology, δ18O benthic foraminifera record, and correlation of peaks of productivity proxies with long-lasted Dansgaard-Oeschger (DO) interstadials. The results show that sea ice was the main transport agent for CF (ice-rafted debris, IRD) in the eastern OS. Published mineralogical studies of clastic material of the OS indicated that the coast of western Kamchatka was the main source of IRD in the eastern OS. We found 19 peaks of IRD, which mostly coincided with DO stadials. The distribution of CF indicates a different pattern of IRD supply during MIS 4, 3, and 2. Comparison of IRD records in the eastern and central parts of the OS allow us to reconstruct millennial changes in ice and wind modes for MIS 4–MIS 2. Significant strengthening of northeastern and eastern winds during DOSs of MIS 3 and of northern and north-western winds during MIS 2 were observed.
Keywords: Ice mode; Ice-rafted debris; Millennial-scale variation; Okhotsk Sea; Wind mode

Millennial-scale iron fertilization of the eastern equatorial Pacific over the past 100,000 years - Loveley, Matthew R.; Marcantonio, Franco; Wisler, Marilyn M.; Hertzberg, Jennifer E.; Schmidt, Matthew W.; Lyle, Mitchell (Nature Geoscience, 2017)
The eastern equatorial Pacific Ocean plays a crucial role in global climate, as it is a substantial source of CO2 to the atmosphere and accounts for a significant portion of global new export productivity. Here we present a 100,000-year sediment core from the eastern equatorial Pacific, and reconstruct dust flux, export productivity and bottom-water oxygenation using excess-230Th-derived fluxes of 232Th and barium, and authigenic uranium concentrations, respectively. We find that during the last glacial period (71,000 to 41,000 years ago), increased delivery of dust to the eastern equatorial Pacific was coeval with North Atlantic Heinrich stadial events. Millennial-scale pulses of increased dust flux coincided with episodes of heightened biological productivity, suggesting that dissolution of dust released iron that promoted ocean fertilization. We also find that periods of low atmospheric CO2 concentrations were associated with suboxic conditions and increased storage of respired carbon in the deep eastern equatorial Pacific. Increases in CO2 concentrations during the deglaciation are coincident with increases in deep Pacific and Southern Ocean water oxygenation levels. We suggest that deep-ocean ventilation was a primary control on CO2 outgassing in this region, with superimposed pulses of high productivity providing a negative feedback.

More reducing bottom-water redox conditions during the Last Glacial Maximum in the southern Challenger Deep (Mariana Trench, western Pacific) driven by enhanced productivity - Min Luo; Thomas J. Algeo; Hongpeng Tong; Joris Gieskes; Linying Chen; Xuefa Shi; Duofu Chen (Deep Sea Research Part II: Topical Studies in Oceanography, 2017)
Abstract The modern southern Mariana Trench is characterized by oligotrophic surface waters, resulting in low primary productivity and well-oxygenated bottom waters. This study investigates changes in the redox conditions of bottom waters in the southern Mariana Trench during the Last Glacial Maximum (LGM) and their potential causes. We measured major, trace, and rare earth elements (REE) in three gravity cores (GC03, GC04, and GC05) and one box core (BC11) retrieved from the southern Challenger Deep at water depths from 5289 to 7118 m. The upper sediment layers of both \{GC05\} and \{BC11\} are dominated by valve fragments of the giant diatom Ethmodiscus rex, forming laminated diatom mats (LDMs). 14C-AMS dates of bulk organic matter show that the \{LDMs\} accumulated between 18.4 and 21.8 kyr B.P., corresponding to the LGM. Modest enrichments of U and Mo along with weak or absent Ce anomalies in the \{LDM\} point to suboxic conditions during the LGM. In contrast, non-LDM samples exhibit little to no enrichment of redox-sensitive elements as well as negative Ce anomalies, indicating deposition under oxic bottom-water conditions. The Ce anomalies are considered valid proxies for bottom-water redox conditions because \{REE\} signatures were acquired in the early diagenetic environment, as indicated by strong P-REE correlations and middle-REE enrichment associated with early diagenetic cycling of Fe-Mn oxyhydroxides in the sediment column followed by capture of the \{REE\} signal by biogenic and/or authigenic apatite. We postulate that the more reducing bottom-water conditions during the \{LGM\} were linked to increased primary productivity induced by enhanced Asian dust input. As shown in earlier studies, the increased primary productivity associated with Ethmodiscus rex blooms in the eastern Philippine Sea played a significant role in capturing atmospheric \{CO2\} during the LGM. Consequently, the magnitude of atmospheric \{CO2\} sequestration by giant diatom blooms during the \{LGM\} may have been greater than previously envisaged.
Keywords: Laminated diatom mats

Open-File ReportOpen-File ReportDeepwater Program: Lophelia II, continuing ecological research on deep-sea corals and deep-reef habitats in the Gulf of Mexico - Demopoulos, Amanda W.J.; Ross, Steve W.; Kellogg, Christina A.; Morrison, Cheryl L.; Nizinski, Martha S.; Prouty, Nancy G.; Bourque, Jill R.; Galkiewicz, Julie P.; Gray, Michael A.; Springmann, Marcus J.; Coykendall, D. Katharine; Miller, Andrew; et al. (2017)
The deep sea is a rich environment composed of diverse habitat types. While deep-sea coral habitats have been discovered within each ocean basin, knowledge about the ecology of these habitats and associated inhabitants continues to grow. This report presents information and results from the Lophelia II project that examined deep-sea coral habitats in the Gulf of Mexico. The Lophelia II project focused on Lophelia pertusa habitats along the continental slope, at depths ranging from 300 to 1,000 meters. The chapters are authored by several scientists from the U.S. Geological Survey, National Oceanic and Atmospheric Administration, University of North Carolina Wilmington, and Florida State University who examined the community ecology (from microbes to fishes), deep-sea coral age, growth, and reproduction, and population connectivity of deep-sea corals and inhabitants. Data from these studies are presented in the chapters and appendixes of the report as well as in journal publications. This study was conducted by the Ecosystems Mission Area of the U.S. Geological Survey to meet information needs identified by the Bureau of Ocean Energy Management.

The perfect storm: climate change and ancient Maya response in the Puuc Hills region of YucatánAbstract - Smyth, Michael P.; Dunning, Nicholas P.; Weaver, Eric M.; van Beynen, Philip; Zapata, David Ortegón (Antiquity, 2017)
Climatic fluctuation is often cited as a major factor in the collapse of Maya civilisation during the Terminal Classic Period (e.g. Luzzadder-Beach et al. 2016). Evidence of how people dealt or failed to deal with it has only recently become a more widespread focus for archaeologists. Investigations at Xcoch in the Puuc Hills show the various ways in which resident populations sought to manage water stores when faced with a climate prone to drought and other meteorological extremes. The study also presents results from the analysis of nearby speleothem laminae, which indicate that severe episodes of flooding and droughts may have contributed to a collapse in the population around AD 850.
Keywords: drought; flooding; Maya; México; speleothem; Xcoch; Yucatán

Permafrost Organic Carbon Mobilization From the Watershed to the Colville River Delta: Evidence From 14C Ramped Pyrolysis and Lignin Biomarkers - Zhang, Xiaowen; Bianchi, Thomas S.; Cui, Xingqian; Rosenheim, Brad E.; Ping, Chien‐Lu; Hanna, Andrea J. M.; Kanevskiy, Mikhail; Schreiner, Kathryn M.; Allison, Mead A. (Geophysical Research Letters, 2017)
The deposition of terrestrial‐derived permafrost particulate organic carbon (POC) has been recorded in major Arctic river deltas. However, associated transport pathways of permafrost POC from the watershed to the coast have not been well constrained. Here we utilized a combination of ramped pyrolysis‐oxidation radiocarbon analysis (RPO 14C) along with lignin biomarkers, to track the linkages between soils and river and delta sediments. Surface and deep soils showed distinct RPO thermographs which may be related to degradation and organo‐mineral interaction. Soil material in the bed load of the river channel was mostly derived from deep old permafrost. Both surface and deep soils were transported and deposited to the coast. Hydrodynamic sorting and barrier island protection played important roles in terrestrial‐derived permafrost POC deposition near the coast. On a large scale, ice processes (e.g., ice gauging and strudel scour) and ocean currents controlled the transport and distribution of permafrost POC on the Beaufort Shelf.
Keywords: Arctic; carbon cycling; Colville River; Lignin; permafrost; pyrolysis

Pleistocene iceberg dynamics on the west Svalbard margin: Evidence from bathymetric and sub-bottom profiler data - Fang Zhao; Timothy A. Minshull; Anya J. Crocker; Julian A. Dowdeswell; Shiguo Wu; Simon M. Soryal (Quaternary Science Reviews, 2017)
Abstract Large icebergs leave evidence of their drift via ploughing of the seabed, thereby providing a geological record of episodes of calving from thick ice sheets. We interpret large-scale curvilinear depressions on the western Svalbard margin as ploughmarks produced by the keels of icebergs that grounded on the seafloor as they drifted through this area. Iceberg ploughmarks were identified at modern water depths between 300 m and 1000 m and in two distinct stratigraphic units. Combining data from sediment cores with seismic stratigraphy from sub-bottom profiler data suggests that the ploughmarks developed in two phases: (1) during Marine Isotope Stage (MIS) 6; and (2) during \{MIS\} 2, indicating the presence of large drifting icebergs on the western Svalbard margin during both the Late Saalian and Late Weichselian glaciations. Sediment-core data along the western Svalbard margin indicate a sharp increase in mass-transported sediments dated at 23.7 ± 0.2 ka, consistent with the \{MIS\} 2 age of the younger iceberg-ploughed surface. The ploughmarks are oriented in two main directions: SW-NE and S-N. S-N oriented ploughmarks, which shallow to the north, indicate iceberg drift from the south with a SW–NE component marking the zone of splitting of the West Spitsbergen Current (WSC) into the Yermak Slope Current (YSC) and North Spitsbergen Current (NSC). Large \{MIS\} 6 and \{MIS\} 2 icebergs most likely had an Arctic Ocean source. We suggest that these icebergs probably left the Arctic Ocean southward through Fram Strait and circulated within the Norwegian-Greenland Sea before being transported northwards along the Svalbard margin by the WSC. An additional likely source of icebergs to the western Svalbard margin during \{MIS\} 2 was the ice-sheet terminating in the western Barents Sea, from which icebergs drifted northward.
Keywords: Pleistocene

Proceedings of the International Ocean Discovery ProgramExpedition 357 methods - Früh-Green, G.L.; Orcutt, B.N.; Green, S.L.; Cotterill, C.; Morgan, S.; Akizawa, N.; Bayrakci, G.; Behrmann, J.-H.; Boschi, C.; Brazleton, W.J.; Cannat, M.; Dunkel, K.G.; et al. (International Ocean Discovery Program, 2017)

Reconstructing Common Era relative sea-level change on the Gulf Coast of Florida - Gerlach, Matthew J.; Engelhart, Simon E.; Kemp, Andrew C.; Moyer, Ryan P.; Smoak, Joseph M.; Bernhardt, Christopher E.; Cahill, Niamh (Marine Geology, 2017)
To address a paucity of Common Era data in the Gulf of Mexico, we reconstructed ~ 1.1 m of relative sea-level (RSL) rise over the past ~ 2000 years at Little Manatee River (Gulf Coast of Florida, USA). We applied a regional-scale foraminiferal transfer function to fossil assemblages preserved in a core of salt-marsh peat and organic silt that was dated using radiocarbon and recognition of pollution, 137Cs and pollen chronohorizons. Our proxy reconstruction was combined with tide-gauge data from four nearby sites spanning 1913–2014 CE. Application of an Errors-in-Variables Integrated Gaussian Process (EIV-IGP) model to the combined proxy and instrumental dataset demonstrates that RSL fell from ~ 350 to 100 BCE, before rising continuously to present. This initial RSL fall was likely the result of local-scale processes (e.g., silting up of a tidal flat or shallow sub-tidal shoal) as salt-marsh development at the site began. Since ~ 0 CE, we consider the reconstruction to be representative of regional-scale RSL trends. We removed a linear rate of 0.3 mm/yr from the RSL record using the EIV-IGP model to estimate climate-driven sea-level trends and to facilitate comparison among sites. This analysis demonstrates that since ~ 0 CE sea level did not deviate significantly from zero until accelerating continuously from ~ 1500 CE to present. Sea level was rising at 1.33 mm/yr in 1900 CE and accelerated until 2014 CE when a rate of 2.02 mm/yr was attained, which is the fastest, century-scale trend in the ~ 2000-year record. Comparison to existing reconstructions from the Gulf coast of Louisiana and the Atlantic coast of northern Florida reveal similar sea-level histories at all three sites. We explored the influence of compaction and fluvial processes on our reconstruction and concluded that compaction was likely insignificant. Fluvial processes were also likely insignificant, but further proxy evidence is needed to fully test this hypothesis. Our results indicate that no significant Common Era sea-level changes took place on the Gulf and southeastern Atlantic U.S. coasts until the onset of modern sea-level rise in the late 19th century.

Relative sea-level trends in New York City during the past 1500 years - Kemp, Andrew C; Hill, Troy D; Vane, Christopher H; Cahill, Niamh; Orton, Philip M; Talke, Stefan A; Parnell, Andrew C; Sanborn, Kelsey; Hartig, Ellen K (The Holocene, 2017)
New York City (NYC) is threatened by 21st-century relative sea-level (RSL) rise because it will experience a trend that exceeds the global mean and has high concentrations of low-lying infrastructure and socioeconomic activity. To provide a long-term context for anticipated trends, we reconstructed RSL change during the past ~1500 years using a core of salt-marsh sediment from Pelham Bay in The Bronx. Foraminifera and bulk-sediment δ13C values were used as sea-level indicators. The history of sediment accumulation was established by radiocarbon dating and recognition of pollution and land-use trends of known age in down-core elemental, isotopic, and pollen profiles. The reconstruction was generated within a Bayesian hierarchical model to accommodate multiple proxies and to provide a unified statistical framework for quantifying uncertainty. We show that RSL in NYC rose by ~1.70 m since ~575 CE (including ~0.38 m since 1850 CE). The rate of RSL rise increased markedly at 1812–1913 CE from ~1.0 to ~2.5 mm/yr, which coincides with other reconstructions along the US Atlantic coast. We investigated the possible influence of tidal-range change in Long Island Sound on our reconstruction using a regional tidal model, and we demonstrate that this effect was likely small. However, future tidal-range change could exacerbate the impacts of RSL rise in communities bordering Long Island Sound. The current rate of RSL rise is the fastest that NYC has experienced for >1500 years, and its ongoing acceleration suggests that projections of 21st-century local RSL rise will be realized.
Keywords: Bayesian transfer function; carbon isotope; Foraminifera; Salt marsh; sedimentation; The Bronx

Reversible adsorption and flushing of arsenic in a shallow, Holocene aquifer of Bangladesh - Kathleen A. Radloff; Yan Zheng; Martin Stute; Beth Weinman; Benjamin Bostick; Ivan Mihajlov; Margaret Bounds; M.Moshiur Rahman; M.Rezaul Huq; Kazi M. Ahmed; Peter Schlosser; Alexander van Geen (Applied Geochemistry, 2017)
Abstract The spatial heterogeneity of dissolved arsenic (As) concentrations in shallow groundwater of the Bengal Basin has been attributed to transport of As (and reactive carbon) from external sources or to the release of As from within grey sand formations. We explore the latter scenario in this detailed hydrological and geochemical study along a 300 m transect of a shallow aquifer extending from a groundwater recharge area within a sandy channel bar to its discharge into a nearby stream. Within the 10–20 m depth range, groundwater ages along the transect determined by the 3H–3He method increase from <10 yr in the recharge area to a maximum of 40 yr towards the stream. Concentrations of groundwater As within the same grey sands increase from 10 to 100 to ∼500 μg/L along this transect. Evidence of reversible adsorption of As between the groundwater and sediment was obtained from a series of push–pull experiments, traditional batch adsorption experiments, and the accidental flooding of a shallow monitoring well. Assuming reversible adsorption and a distribution coefficient, Kd, of 0.15–1.5 L/kg inferred from these observations, a simple flushing model shows that the increase in As concentrations with depth and groundwater age at this site, and at other sites in the Bengal and Red River Basins, can be attributed to the evolution of the aquifer over 100–1000 years as aquifer sands are gradually flushed of their initial As content. A wide range of As concentrations can thus be maintained in groundwater with increases with depth governed by the history of flushing and local recharge rates, without external inputs of reactive carbon or As from other sources.
Environmental and Health Roles of Geogenic Arsenic
Keywords: Push–pull tests

Sedimentary record from the Canada Basin, Arctic Ocean: implications for late to middle Pleistocene glacial history - Dong, Linsen; Liu, Yanguang; Shi, Xuefa; Polyak, Leonid; Huang, Yuanhui; Fang, Xisheng; Liu, Jianxing; Zou, Jianjun; Wang, Kunshan; Sun, Fuqiang; Wang, Xuchen (Climate of the Past, 2017)
ediment core ARC4-BN05 collected from the Canada Basin, Arctic Ocean, covers the late to middle Quaternary (Marine Isotope Stage – MIS – 1–15, ca. 0.5–0.6 Ma) as estimated by correlation to earlier proposed Arctic Ocean stratigraphies and AMS14C dating of the youngest sediments. Detailed examination of clay and bulk mineralogy along with grain size, content of Ca and Mn, and planktic foraminiferal numbers in core ARC4–BN05 provides important new information about sedimentary environments and provenance. We use increased contents of coarse debris as an indicator of glacier collapse events at the margins of the western Arctic Ocean, and identify the provenance of these events from mineralogical composition. Notably, peaks of dolomite debris, including large dropstones, track the Laurentide Ice Sheet (LIS) discharge events to the Arctic Ocean. Major LIS inputs occurred during the stratigraphic intervals estimated as MIS 3, intra-MIS 5 and 7 events, MIS 8, and MIS 10. Inputs from the East Siberian Ice Sheet (ESIS) are inferred from peaks of smectite, kaolinite, and chlorite associated with coarse sediment. Major ESIS sedimentary events occurred in the intervals estimated as MIS 4, MIS 6 and MIS 12. Differences in LIS vs. ESIS inputs can be explained by ice-sheet configurations at different sea levels, sediment delivery mechanisms (iceberg rafting, suspension plumes, and debris flows), and surface circulation. A long-term change in the pattern of sediment inputs, with an apparent step change near the estimated MIS 7–8 boundary (ca. 0.25 Ma), presumably indicates an overall glacial expansion at the western Arctic margins, especially in North America.

Sequential bioavailability of sedimentary organic matter to heterotrophic bacteria - Mahmoudi, Nagissa; é, Steven R.; Steen, Andrew D.; Pearson, Ann (Environmental Microbiology, 2017)
Aquatic sediments harbour diverse microbial communities that mediate organic matter degradation and influence biogeochemical cycles. The pool of bioavailable carbon continuously changes as a result of abiotic processes and microbial activity. It remains unclear how microbial communities respond to heterogeneous organic matrices and how this ultimately affects heterotrophic respiration. To explore the relationships between the degradation of mixed carbon substrates and microbial activity, we incubated batches of organic-rich sediments in a novel bioreactor (IsoCaRB) that permitted continuous observations of CO2 production rates, as well as sequential sampling of isotopic signatures (δ13C, Δ14C), microbial community structure and diversity, and extracellular enzyme activity. Our results indicated that lower molecular weight (MW), labile, phytoplankton-derived compounds were degraded first, followed by petroleum-derived exogenous pollutants, and finally by higher MW polymeric plant material. This shift in utilization coincided with a community succession and increased extracellular enzyme activities. Thus, sequential utilization of different carbon pools induced changes at both the community and cellular level, shifting community composition, enzyme activity, respiration rates, and residual organic matter reactivity. Our results provide novel insight into the accessibility of sedimentary organic matter and demonstrate how bioavailability of natural organic substrates may affect the function and composition of heterotrophic bacterial populations.

Siberian Arctic black carbon sources constrained by model and observation - Winiger, Patrik; Andersson, August; Eckhardt, Sabine; Stohl, Andreas; Semiletov, Igor P.; Dudarev, Oleg V.; Charkin, Alexander; Shakhova, Natalia; Klimont, Zbigniew; Heyes, Chris; Gustafsson, Örjan (Proceedings of the National Academy of Sciences, 2017)
Black carbon (BC) in haze and deposited on snow and ice can have strong effects on the radiative balance of the Arctic. There is a geographic bias in Arctic BC studies toward the Atlantic sector, with lack of observational constraints for the extensive Russian Siberian Arctic, spanning nearly half of the circum-Arctic. Here, 2 y of observations at Tiksi (East Siberian Arctic) establish a strong seasonality in both BC concentrations (8 ng⋅m−3 to 302 ng⋅m−3) and dual-isotope–constrained sources (19 to 73% contribution from biomass burning). Comparisons between observations and a dispersion model, coupled to an anthropogenic emissions inventory and a fire emissions inventory, give mixed results. In the European Arctic, this model has proven to simulate BC concentrations and source contributions well. However, the model is less successful in reproducing BC concentrations and sources for the Russian Arctic. Using a Bayesian approach, we show that, in contrast to earlier studies, contributions from gas flaring (6%), power plants (9%), and open fires (12%) are relatively small, with the major sources instead being domestic (35%) and transport (38%). The observation-based evaluation of reported emissions identifies errors in spatial allocation of BC sources in the inventory and highlights the importance of improving emission distribution and source attribution, to develop reliable mitigation strategies for efficient reduction of BC impact on the Russian Arctic, one of the fastest-warming regions on Earth.
Keywords: Arctic haze; atmospheric transport modeling; carbon isotopes; Climate change; emission inventory

Sub-ice shelf sediment geochronology utilizing novel radiocarbon methodology for highly detrital sediments - Subt, C.; Yoon, H. I.; Yoo, K. C.; Lee, J. I.; Leventer, A.; Domack, E. W.; Rosenheim, B. E. (Geochemistry, Geophysics, Geosystems, 2017)
Sub‐ice shelf sediments near Larsen C ice shelf (LIS‐C) show fine‐scale rhythmic laminations that could provide a near‐continuous seasonal‐resolution record of regional ice mass changes. Despite the great potential of these sediments, a dependable Late Quaternary chronology is difficult to generate, rendering the record incomplete. As with many marginal Antarctic sediments, in the absence of preserved carbonate microfossils, the reliability of radiocarbon chronologies depends on presence of high proportions of autochthonous organic carbon with minimized detrital organic carbon. Consequently, acid insoluble organic (AIO) 14C dating works best where high productivity drives high sediment accumulation rates, but can be problematic in condensed sequences with high proportions of detrital organic carbon. Ramped PyrOx 14C dating has progressively been shown to improve upon AIO 14C dates, to the point of matching foraminiferal carbonate 14C dates, through differential thermochemical degradation of organic components within samples. But in highly detrital sediments, proportions of contemporaneously deposited material are too low to fully separate autochthonous organic carbon from detrital carbon in samples large enough to 14C date. We introduce two modifications of the Ramped PyrOx 14C approach applied to highly detrital sediments near LIS‐C to maximize accuracy by utilizing ultra‐small fractions of the highly detrital AIO material. With minimization of the uncertainty cost, these techniques allow us to generate chronologies for cores that would otherwise go undated, pushing the limits of radiocarbon dating to regions and facies with high proportions of pre‐aged detritus. Wider use of these techniques will enable more coordinated a priori coring efforts to constrain regional glacial responses to rapid warming where sediments had previously been thought too difficult to date.

A Terminal Pleistocene/Early Holocene Environmental Record and Fluted Point from Twain Harte, California - Moratto, Michael J.; Davis, Owen K.; Davis-King, Shelly; Meyer, Jack; Rosenthal, Jeffrey; Sylwester, Laurie (PaleoAmerica, 2017)
Although more than 500 Clovis points have been found at no fewer than 60 locations in California, the age of these points remains problematic. Here we report stratified deposits more than 3 meters deep at a site in the central Sierra Nevada from which a Clovis point was recovered in 1969. Five radiocarbon (14C) dates provide temporal control for terminal Pleistocene and early Holocene strata at the site, including the sediments in which the point reposed. We also report the analysis of pollen samples from these strata. Our research indicates that the Clovis point most likely dates to ∼11,900–11,400 cal yr BP. We interpret this, in the context of other fluted-point discoveries, to mean that Clovis lithic technology evidently persisted longer in the Far West than it did elsewhere in the U.S.
Keywords: California prehistory; Clovis chronology; Geomorphology; palynology; terminal Pleistocene/early Holocene

Trends in catchment processes and lake evolution during the late-glacial and early- to mid-Holocene inferred from high-resolution XRF data in the Yellowstone region - Lu, Yanbin; Fritz, Sherilyn C.; Stone, Jeffery R.; Krause, Teresa R.; Whitlock, Cathy; Brown, Erik T.; Benes, James V. (Journal of Paleolimnology, 2017)
High-resolution records of geochemical data from four lakes in the Greater Yellowstone region were used to investigate watershed and lake history during the late-glacial and early-Holocene periods. Clastic input to regional lakes was high and variable during the early stages of lake development, when the surrounding landscape was geomorphically unstable and sparsely vegetated, and it decreased as vegetation gradually developed in each catchment. The decrease of clastic input was not regionally synchronous but occurred in a time-transgressive pattern from south to north. Long-term organic matter concentration and diatom production were inversely related to catchment erosion during the early stages of lake development and increased as temperatures warmed and in-lake nutrient concentrations increased. Similarly, calcite production usually was low following lake formation and increased over time, driven by climate change and its associated influences on lake-level, algal production, and lake thermal structure. Overall differences in the timing and pattern of geochemical change indicate that once the landscape had stabilized following deglaciation, changes in the geochemical character of the sediments were strongly influenced by local factors.

The tropical lapse rate steepened during the Last Glacial Maximum - Loomis, Shannon E.; Russell, James M.; Verschuren, Dirk; Morrill, Carrie; De Cort, Gijs; Sinninghe Damsté, Jaap S.; Olago, Daniel; Eggermont, Hilde; Street-Perrott, F. Alayne; Kelly, Meredith A. (Science Advances, 2017)
The gradient of air temperature with elevation (the temperature lapse rate) in the tropics is predicted to become less steep during the coming century as surface temperature rises, enhancing the threat of warming in high-mountain environments. However, the sensitivity of the lapse rate to climate change is uncertain because of poor constraints on high-elevation temperature during past climate states. We present a 25,000-year temperature reconstruction from Mount Kenya, East Africa, which demonstrates that cooling during the Last Glacial Maximum was amplified with elevation and hence that the lapse rate was significantly steeper than today. Comparison of our data with paleoclimate simulations indicates that state-of-the-art models underestimate this lapse-rate change. Consequently, future high-elevation tropical warming may be even greater than predicted.

Utility of salt-marsh foraminifera, testate amoebae and bulk-sediment δ13C values as sea-level indicators in Newfoundland, Canada - Kemp, Andrew C.; Wright, Alexander J.; Barnett, Robert L.; Hawkes, Andrea D.; Charman, Dan J.; Sameshima, Colby; King, Alexandra N.; Mooney, Hailey C.; Edwards, Robin J.; Horton, Benjamin P.; van de Plassche, Orson (Marine Micropaleontology, 2017)
We investigated the utility of foraminifera, testate amoebae and bulk-sediment δ13C measurements for reconstructing Holocene relative sea level from sequences of salt-marsh sediment in Newfoundland, Canada. Modern, surface sediment was collected along transects from low to supra-tidal elevations in eastern (at Placentia) and western (at Hynes Brook and Big River) Newfoundland. Consistent with previous work, low-diversity assemblages of foraminifera display an almost binary division into a higher salt-marsh assemblage dominated by Jadammina macrescens and Balticammina pseudomacrescens and a lower salt-marsh assemblage comprised of Miliammina fusca. This pattern and composition resembles those identified at other high latitude sites with cool climates and confirms that foraminifera are sea-level indicators. The lowest occurrence of testate amoebae was at approximately mean higher high water. The composition of high salt-marsh testate amoebae assemblages (Centropyxis cassis type, Trinema spp., Tracheleuglypha dentata type, and Euglypha spp.) in Newfoundland was similar to elsewhere in the North Atlantic, but preservation bias favors removal of species with idiosomic tests over those with xenosomic tests. The mixed high salt-marsh plant community in Newfoundland results in bulk surface-sediment δ13C values that are typical of C3 plants, making them indistinguishable from freshwater sediment. Therefore we propose that the utility of this proxy for reconstructing RSL in eastern North America is restricted to the coastline between Chesapeake Bay and southern Nova Scotia. Using a simple, multi-proxy approach to establish that samples in three radiocarbon-dated sediment cores formed between the lowest occurrence of testate amoebae and the highest occurrence of foraminifera, we generated three example late Holocene sea-level index points at Hynes Brook.

Vulnerability of Coral Reefs to Bioerosion From Land‐Based Sources of Pollution - Prouty, Nancy G.; Cohen, Anne; Yates, Kimberly K.; Storlazzi, Curt D.; Swarzenski, Peter W.; White, Darla (Journal of Geophysical Research: Oceans, 2017)
Ocean acidification (OA), the gradual decline in ocean pH and [ urn:x-wiley:21699275:media:jgrc22505:jgrc22505-math-0001] caused by rising levels of atmospheric CO2, poses a significant threat to coral reef ecosystems, depressing rates of calcium carbonate (CaCO3) production, and enhancing rates of bioerosion and dissolution. As ocean pH and [ urn:x-wiley:21699275:media:jgrc22505:jgrc22505-math-0002] decline globally, there is increasing emphasis on managing local stressors that can exacerbate the vulnerability of coral reefs to the effects of OA. We show that sustained, nutrient rich, lower pH submarine groundwater discharging onto nearshore coral reefs off west Maui lowers the pH of seawater and exposes corals to nitrate concentrations 50 times higher than ambient. Rates of coral calcification are substantially decreased, and rates of bioerosion are orders of magnitude higher than those observed in coral cores collected in the Pacific under equivalent low pH conditions but living in oligotrophic waters. Heavier coral nitrogen isotope (δ15N) values pinpoint not only site‐specific eutrophication, but also a sewage nitrogen source enriched in 15N. Our results show that eutrophication of reef seawater by land‐based sources of pollution can magnify the effects of OA through nutrient driven‐bioerosion. These conditions could contribute to the collapse of coastal coral reef ecosystems sooner than current projections predict based only on ocean acidification.
Keywords: aragonite saturation; bioerosion; coral reefs; nutrients; submarine groundwater; Wastewater

What on Earth Have We Been Burning? Deciphering Sedimentary Records of Pyrogenic CarbonWhat on Earth Have We Been Burning? Deciphering Sedimentary Records of Pyrogenic Carbon - Hanke, Ulrich M.; Reddy, Christopher M.; Braun, Ana L. L.; Coppola, Alysha I.; Haghipour, Negar; McIntyre, Cameron P.; Wacker, Lukas; Xu, Li; McNichol, Ann P.; Abiven, Samuel; Schmidt, Michael W. I.; Eglinton, Timothy I. (Environmental Science & Technology, 2017)
Humans have interacted with fire for thousands of years, yet the utilization of fossil fuels marked the beginning of a new era. Ubiquitous in the environment, pyrogenic carbon (PyC) arises from incomplete combustion of biomass and fossil fuels, forming a continuum of condensed aromatic structures. Here, we develop and evaluate 14C records for two complementary PyC molecular markers, benzene polycarboxylic acids (BPCAs) and polycyclic aromatic hydrocarbons (PAHs), preserved in aquatic sediments from a suburban and a remote catchment in the United States (U.S.) from the mid-1700s to 1998. Results show that the majority of PyC stems from local sources and is transferred to aquatic sedimentary archives on subdecadal to millennial time scales. Whereas a small portion stems from near-contemporaneous production and sedimentation, the majority of PyC (∼90%) experiences delayed transmission due to “preaging” on millennial time scales in catchment soils prior to its ultimate deposition. BPCAs (soot) and PAHs (precursors of soot) trace fossil fuel-derived PyC. Both markers parallel historical records of the consumption of fossil fuels in the U.S., yet never account for more than 19% total PyC. This study demonstrates that isotopic characterization of multiple tracers is necessary to constrain histories and inventories of PyC and that sequestration of PyC can markedly lag its production.

Age of the Mt. Ortles ice cores, the Tyrolean Iceman and glaciation of the highest summit of South Tyrol since the Northern Hemisphere Climatic Optimum - Gabrielli, Paolo; Barbante, Carlo; Bertagna, Giuliano; ó, Michele; Binder, Daniel; Carton, Alberto; Carturan, Luca; Cazorzi, Federico; Cozzi, Giulio; Dalla Fontana, Giancarlo; Davis, Mary; De Blasi, Fabrizio; et al. (The Cryosphere, 2016)
In 2011 four ice cores were extracted from the summit of Alto dell’Ortles (3859 m), the highest glacier of South Tyrol in the Italian Alps. This drilling site is located only 37 km southwest from where the Tyrolean Iceman, ∼5.3 kyrs old, was discovered emerging from the ablating ice field of Tisenjoch (3210 m, near the Italian–Austrian border) in 1991. The excellent preservation of this mummy suggested that the Tyrolean Iceman was continuously embedded in prehistoric ice and that additional ancient ice was likely preserved elsewhere in South Tyrol. Dating of the ice cores from Alto dell’Ortles based on 210Pb, tritium, beta activity and 14C determinations, combined with an empirical model (COPRA), provides evidence for a chronologically ordered ice stratigraphy from the modern glacier surface down to the bottom ice layers with an age of ∼7 kyrs, which confirms the hypothesis. Our results indicate that the drilling site has continuously been glaciated on frozen bedrock since ∼7 kyrs BP. Absence of older ice on the highest glacier of South Tyrol is consistent with the removal of basal ice from bedrock during the Northern Hemisphere Climatic Optimum (6–9 kyrs BP), the warmest interval in the European Alps during the Holocene. Borehole inclinometric measurements of the current glacier flow combined with surface ground penetration radar (GPR) measurements indicate that, due to the sustained atmospheric warming since the 1980s, an acceleration of the glacier Alto dell’Ortles flow has just recently begun. Given the stratigraphic chronological continuity of the Mt. Ortles cores over millennia, it can be argued that this behaviour has been unprecedented at this location since the Northern Hemisphere Climatic Optimum.

Biospheric and petrogenic organic carbon flux along southeast Alaska - Xingqian Cui; Thomas S. Bianchi; John M. Jaeger; Richard W. Smith (Earth and Planetary Science Letters, 2016)
Abstract Holocene fjords store ca. 11–12% of the total organic carbon (OC) buried in marine sediments with fjords along southeast (SE) Alaska possibly storing half of this \{OC\} (Smith et al., 2015). However, the respective burial of biospheric (OCbio) and petrogenic \{OC\} (OCpetro) remains poorly constrained, particularly across glaciated versus non-glaciated systems. Here, we use surface sediment samples to quantify the sources and burial of sedimentary \{OC\} along \{SE\} Alaska fjord-coastal systems, and conduct a latitudinal comparison across a suite of fjords and river-coastal systems with distinctive \{OC\} sources. Our results for \{SE\} Alaska show that surface sediments in northern fjords (north of Icy Strait) with headwater glaciers are dominated by OCpetro, in contrast to marine and terrestrially-derived fresh \{OC\} in non-glaciated southern fjords. Along the continental shelf of the Gulf of Alaska, terrestrial \{OC\} is exported from rivers. Using end-member mixing models, we determine that glaciated fjords have significantly higher burial rates of \{OCpetro\} ( ∼ 1.1 × 10 3   g \{OC\}   m − 2 yr − 1 ) than non-glaciated fjords and other coastal systems, making \{SE\} Alaska potentially the largest sink of \{OCpetro\} in North America. In contrast, non-glaciated fjords in \{SE\} Alaska are effective in burying marine \{OC\} (OCbio-mari) (13–82 g  \{OC\}   m − 2 yr − 1 ). Globally, \{OC\} in fjord sediments are comprised of a mixture of \{OCpetro\} and fresh OCbio, in contrast to the pre-aged \{OC\} from floodplain river-coastal systems. We find that there may be a general latitudinal trend in the role of fjords in processing OC, where high-latitude temperate glacial fjords (e.g., Yakutat Bay, \{SE\} Alaska) rebury \{OCpetro\} and non-glacial mid-latitude fjords (e.g., Doubtful Sound, Fiordland) sequester \{CO2\} from phytoplankton and/or temperate forests. Overall, we propose that fjords are effective in sequestering \{OCbio\} and re-burying OCpetro. Based on our study, we hypothesize that climate change will have a semi-predictable impact on fjords' \{OC\} cycling in the near future.
Keywords: glaciers

Bomb Radiocarbon and the Hawaiian Archipelago: Coral, Otoliths, and SeawaterAbstract - Andrews, Allen H; Siciliano, Daria; Potts, Donald C; DeMartini, Edward E; Covarrubias, Stephannie (Radiocarbon, 2016)
Corals of the Hawaiian Archipelago are well situated in the North Pacific Gyre (NPG) to record how bomb-produced radiocarbon has been sequestered and transported by the sea. While this signal can be traced accurately through time in reef-building corals and used to infer oceanographic processes and determine the ages of marine organisms, a comprehensive and validated record has been lacking for the Hawaiian Archipelago. In this study, a coral core from Kure Atoll in the northwestern Hawaiian Islands was used to create a high-resolution bomb 14C record for the years 1939–2002, and was then used with other 14C measurements in fish otoliths and seawater to explore differences and similarities in the bomb 14C signal throughout the Hawaiian Archipelago. The Kure Atoll sample series produced a well-defined bomb 14C curve that, with some exceptions, was similar to other coral 14C records from the Hawaiian Archipelago. Subtle differences in the coral 14C records across the region may be explained by the large-scale ocean circulation patterns and decadal cycles of the NPG. The most rapid increase of 14C, in the 1950s and 1960s, showed similar timing across the Hawaiian Archipelago and provides a robust basis for use of bomb 14C dating to obtain high-precision age determinations of marine organisms. Reference otoliths of juvenile fish demonstrated the use of the post-peak 14C decline period as a viable reference in the age validation of younger and more recently collected fishes, and effectively extended the utility of bomb 14C dating to the latest 30 yr.

Clumped isotope composition of cold-water corals: A role for vital effects? - Peter T. Spooner; Weifu Guo; Laura F. Robinson; Nivedita Thiagarajan; Katharine R. Hendry; Brad E. Rosenheim; Melanie J. Leng (Geochimica et Cosmochimica Acta, 2016)
Abstract The carbonate clumped isotope thermometer is a promising tool for determining past ocean temperatures. It is based on the temperature dependence of rare isotopes ‘clumping’ into the same carbonate ion group in the carbonate mineral lattice. The extent of this clumping effect is independent of the isotope composition of the water from which carbonate precipitates, providing unique advantages over many other paleotemperature proxies. Existing calibrations of this thermometer in cold-water and warm-water corals suggest clumped isotope ‘vital effects’ are negligible in cold-water corals but may be significant in warm-water corals. Here, we test the calibration of the carbonate clumped isotope thermometer in cold-water corals with a recently collected and well characterised sample set spanning a range of coral genera (Balanophyllia, Caryophyllia, Dasmosmilia, Desmophyllum, Enallopsammia and Javania). The clumped isotope compositions (Δ47) of these corals exhibit systematic dependences on their growth temperatures, confirming the basis of the carbonate clumped isotope thermometer. However, some cold-water coral genera show Δ47 values that are higher than the expected equilibrium values by up to 0.05‰ (equivalent to underestimating temperature by ∼9 °C) similar to previous findings for some warm-water corals. This finding suggests that the vital effects affecting corals Δ47 are common to both warm- and cold-water corals. By comparison with models of the coral calcification process we suggest that the clumped isotope offsets in these genera are related to the kinetic isotope effects associated with \{CO2\} hydration/hydroxylation reactions in the corals’ calcifying fluid. Our findings complicate the use of the carbonate clumped isotope thermometer in corals, but suggest that species- or genus-specific calibrations could be useful for the future application of this paleotemperature proxy.

Comparison of eastern tropical Pacific TEX 86 and Globigerinoides ruber Mg/Ca derived sea surface temperatures: Insights from the Holocene and Last Glacial Maximum - Hertzberg, Jennifer E.; Schmidt, Matthew W.; Bianchi, Thomas S.; Smith, Richard W.; Shields, Michael R.; Marcantonio, Franco (Earth and Planetary Science Letters, 2016)
The use of the TEX86TEX86 temperature proxy has thus far come to differing results as to whether TEX86TEX86 temperatures are representative of surface or subsurface conditions. In addition, although TEX86TEX86 temperatures might reflect sea surface temperatures based on core-top (Holocene) values, this relationship might not hold further back in time. Here, we investigate the TEX86TEX86 temperature proxy by comparing TEX86TEX86 temperatures to Mg/Ca temperatures of multiple species of planktonic foraminifera for two sites in the eastern tropical Pacific (on the Cocos and Carnegie Ridges) across the Holocene and Last Glacial Maximum. Core-top and Holocene View the MathML sourceTEX86H temperatures at both study regions agree well, within error, with the Mg/Ca temperatures of Globigerinoides ruber , a surface dwelling planktonic foraminifera. However, during the Last Glacial Maximum, View the MathML sourceTEX86H temperatures are more representative of upper thermocline temperatures, and are offset from G. ruber Mg/Ca temperatures by 5.8 °C and 2.9 °C on the Cocos Ridge and Carnegie Ridge, respectively. This offset between proxies cannot be reconciled by using different TEX86TEX86 temperature calibrations, and instead, we suggest that the offset is due to a deeper export depth of GDGTs at the LGM. We also compare the degree of glacial cooling at both sites based on both temperature proxies, and find that View the MathML sourceTEX86H temperatures greatly overestimate glacial cooling, especially on the Cocos Ridge. This study has important implications for applying the TEX86TEX86 paleothermometer in the eastern tropical Pacific.
Keywords: Foraminifera; Holocene; LGM; Pacific Ocean; Mg/Ca; TEX86TEX86

Complex coastal change in response to autogenic basin infilling: An example from a sub-tropical Holocene strandplain - Hein, Christopher J.; FitzGerald, Duncan M.; de Souza, Luis H. P.; Georgiou, Ioannis Y.; Buynevich, Ilya V.; Klein, Antonio H. da F.; de Menezes, ão Thadeu; Cleary, William J.; Scolaro, Thelma L. (Sedimentology, 2016)
Thick bay-fill sequences that often culminate in strandplain development serve as important sedimentary archives of land–ocean interaction, although distinguishing between internal and external forcings is an ongoing challenge. This study employs sediment cores, ground-penetrating radar surveys, radiocarbon dates, palaeogeographic reconstructions and hydrodynamic modelling to explore the role of autogenic processes – notably a reduction in wave energy in response to coastal embayment infilling – in coastal evolution and shoreline morphodynamics. Following a regional 2 to 4 m highstand at ca 5·8 ka, the 75 km2 Tijucas Strandplain in southern Brazil built from fluvial sediments deposited into a semi-enclosed bay. Holocene regressive deposits are underlain by fluvial sands and a Pleistocene transgressive–regressive sequence, and backed by a highstand barrier-island. The strandplain is immediately underlain by 5 to 16 m of seaward-thickening, fluvially derived, Holocene-age, basin-fill mud. Several trends are observed from the landward (oldest) to the seaward (youngest) sections of the strandplain: (i) the upper shoreface and foreshore become finer and thinner and shift from sand-dominated to mud-dominated; (ii) beachface slopes decrease from >11° to ca 7°; and (iii) progradation rates increase from 0·4 to 1·8 m yr−1. Hydrodynamic modelling demonstrates a correlation between progressive shoaling of Tijucas Bay driven by sea-level fall and sediment infilling and a decrease in onshore wave-energy transport from 18 to 4 kW m−1. The combination of allogenic (sediment supply, falling relative sea-level and geology) and autogenic (decrease in wave energy due to bay shoaling) processes drove the development of a regressive system with characteristics that are rare, if not unique, in the Holocene and rock records. These findings demonstrate the complexities in architecture styles of highstand and regressive systems tracts. Furthermore, this article highlights the diverse internal and external processes and feedbacks responsible for the development of these intricate marginal marine sedimentary systems.

Conduits, timing and processes of sediment delivery across a high-relief continental margin: Continental shelf to basin in Late Quaternary, Gulf of Papua - Erlangga Septama; Samuel J. Bentley; André W. Droxler (Marine and Petroleum Geology, 2016)
Abstract The Gulf of Papua (GoP), between Australia and Papua New Guinea, is the receiving basin for multiple substantial rivers draining southern Papua New Guinea with collective sediment discharge >> 220 million metric tons (Mt) per year, comparable to a continental-scale river, but draining a combined catchment area of only ∼160,000 km2. This study of the deepest marginal basins in the Gulf of Papua was undertaken to build a regional late Quaternary lithofacies and stratigraphic framework to better understand processes, timing, and conduits of sediment delivery from terrestrial and shelf settings to deep marginal basins, using the GoP as a natural laboratory. Methods include observations of sediment-core stratigraphy and physical properties, accelerometer mass spectrometry (AMS) C-14 dates, core x-radiographs and thin sections. Six lithofacies across the deep water Gulf of Papua (GoP) are identified based on core visual and textural observation. Chronological constraints permit an assessment of changes in sediment supply and depositional environments across time and space, from marine isotope stage (MIS) -3 to -1, or in the last 40 cal ka. The sediment delivery to the deep water GoP is dominated by two mechanisms, gravity-driven flows down slopes and into deep sea basin primarily during lowstands in the western portions of the study area, and hemipelagic sediment accumulation during transgression and highstand. Although the sediment flux appears to be overall dominated by sediment-gravity flows, hemipelagic sediment delivery is widespread during periods of sea level highstand. In the eastern portions of the study area, off-shelf sediment delivery continued into the Holocene in sufficient local volumes to produce turbidity currents. This late, localized sediment delivery appears to have been facilitated by oceanographic processes that allowed seaward sediment transport after flooding of the shelf. A simple sediment budget comparing basinal sediment accumulation to modern estimated river-sediment discharge indicates that peak sediment accumulation in proximal basins occurred during MIS-2; and declined thereafter, generally shifting to upper slope locations, except for the eastern margin of Moresby Trough. There, turbidite deposition continued until 7.4 cal ka, well after drowning of the shelf edge. This continued Holocene deep-sea sediment delivery is likely explained by the local narrow shelf width, and the presence of oceanographic processes capable of transporting sediments from shore to shelf edge.
Keywords: Deep-sea

Dual carbon isotope characterization of total organic carbon in wintertime carbonaceous aerosols from northern India - Bikkina, Srinivas; Andersson, August; Sarin, M. M.; Sheesley, R. J.; Kirillova, E.; Rengarajan, R.; Sudheer, A. K.; Ram, K.; Gustafsson, Örjan (Journal of Geophysical Research: Atmospheres, 2016)
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.

Fate of terrigenous organic matter across the Laptev Sea from the mouth of the Lena River to the deep sea of the Arctic interior - Broder, Lisa; Tesi, Tommaso; Salvad?, Joan A.; Semiletov, Igor P.; Dudarev, Oleg V.; Gustafsson, ?rjan (Biogeosciences, 2016)
Ongoing global warming in high latitudes may cause an increasing supply of permafrost-derived organic carbon through both river discharge and coastal erosion to the Arctic shelves. Mobilized permafrost carbon can be either buried in sediments, transported to the deep sea or degraded to CO2 and outgassed, potentially constituting a positive feedback to climate change. This study aims to assess the fate of terrigenous organic carbon (TerrOC) in the Arctic marine environment by exploring how it changes in concentration, composition and degradation status across the wide Laptev Sea shelf. We analyzed a suite of terrestrial biomarkers as well as source-diagnostic bulk carbon isotopes (δ13C, Δ14C) in surface sediments from a Laptev Sea transect spanning more than 800 km from the Lena River mouth (< 10 m water depth) across the shelf to the slope and rise (2000–3000 m water depth). These data provide a broad view on different TerrOC pools and their behavior during cross-shelf transport. The concentrations of lignin phenols, cutin acids and high-molecular-weight (HMW) wax lipids (tracers of vascular plants) decrease by 89–99 % along the transect. Molecular-based degradation proxies for TerrOC (e.g., the carbon preference index of HMW lipids, the HMW acids ∕ alkanes ratio and the acid ∕ aldehyde ratio of lignin phenols) display a trend to more degraded TerrOC with increasing distance from the coast. We infer that the degree of degradation of permafrost-derived TerrOC is a function of the time spent under oxic conditions during protracted cross-shelf transport. Future work should therefore seek to constrain cross-shelf transport times in order to compute a TerrOC degradation rate and thereby help to quantify potential carbon–climate feedbacks.

Footprint of roman and modern mining activities in a sediment core from the southwestern Iberian Atlantic shelf - Mário Mil-Homens; Carlos Vale; Filipa Naughton; Pedro Brito; Teresa Drago; Bárbara Anes; Joana Raimundo; Sabine Schmidt; Miguel Caetano (Science of The Total Environment, 2016)
Abstract A 5-m long sediment core (VC2B), retrieved in the Southwestern Iberian Atlantic shelf, at 96 m water depth, was used to assess major changes in climate and human activities during the last 9.7 kyrs. Analytical measurements included sedimentological (mean grain size, and the contents of sand, silt and clay), geochemical (major, minor, trace and rare earth elements; REEs) and chronological (210Pb and 14C) parameters. Two episodes of increment of fine-grained particles, occurring at 3050 \{BCE\} and 1350 CE, suggest the retreat of the coast line to the present level and the beginning of a wetter phase associated with the “Little Ice Age”. The North American Shale Composite (NASC)-normalized REE-pattern detected in the shelf is similar to that found in the Guadiana estuarine sediments. The possibility of this estuary as a contributor to the sediment load deposited in the adjacent coastal zone was indicated. Trace elements were significantly correlated with Al until 1850 CE, pointing that grain-size rules its distribution in sediments. The depth variation of As, Cu and Pb enrichment factors relative to background values shows two periods of intense human activity that can be mainly linked to mining: (i) across the Roman Period, marked by low enrichments; and (ii) starting on the second half of the 19th century until nowadays with significantly increased enrichments, especially of Pb and Cu. In addition to As, Cu and Pb, this period is also marked by high enrichments of Hg and Zn. Despite the decrease/closure of sulphide massive deposits mining exploitation (e.g., São Domingos, Las Herrerias) during the second half of the 20th century, results showed ongoing input of Pb, Cu, As, Hg and Zn to coastal sediments. Thus, the legacy of contamination by these elements, mainly from leaching of slags and tailings, and remobilization/reworking of contaminated estuarine sediments, is still recorded in marine sediments.
Keywords: mining activities; Rare earth elements

Historical records of organic matter supply and degradation status in the East Siberian Sea - Broder, Lisa; Tesi, Tommaso; Andersson, August; Eglinton, Timothy I.; Semiletov, Igor P.; Dudarev, Oleg V.; Roos, Per; Gustafsson, ?rjan (Organic Geochemistry, 2016)
Destabilization and degradation of permafrost carbon in the Arctic regions could constitute a positive feedback to climate change. A better understanding of its fate upon discharge to the Arctic shelf is therefore needed. In this study, bulk carbon isotopes as well as terrigenous and marine biomarkers were used to construct two centennial records in the East Siberian Sea. Differences in topsoil and Pleistocene Ice Complex Deposit permafrost concentrations, modeled using δ13C and Δ14C, were larger between inner and outer shelf than the changes over time. Similarly, lignin-derived phenol and cutin acid concentrations differed by a factor of ten between the two stations, but did not change significantly over time, consistent with the dual-carbon isotope model. High molecular weight (HMW) n-alkane and n-alkanoic acid concentrations displayed a smaller difference between the two stations (factor of 3–6). By contrast, the fraction for marine OC drastically decreased during burial with a half-life of 19–27 years. Vegetation and degradation proxies suggested supply of highly degraded gymnosperm wood tissues. Lipid Carbon Preference Index (CPI) values indicated more extensively degraded HMW n-alkanes on the outer shelf with no change over time, whereas n-alkanoic acids appeared to be less degraded toward the core top with no large differences between the stations. Taken together, our results show larger across-shelf changes than down-core trends. Further investigation is required to establish whether the observed spatial differences are due to different sources for the two depositional settings or, alternatively, a consequence of hydrodynamic sorting combined with selective degradation during cross-shelf transport.
Keywords: 210Pb; Arctic; East Siberian Arctic Shelf; HMW wax lipids; Lignin; Monte Carlo; δ13C; Δ14C

Indus Basin sediment provenance constrained using garnet geochemistry - Anwar Alizai; Peter D. Clift; John Still (Journal of Asian Earth Sciences, 2016)
Abstract The chemical and mineralogical diversity of western Himalayan rivers is the result of each of them draining different tectonic and lithologic units, whose character is partly transferred to the sediments carried by those rivers. Garnet geochemistry was employed to discriminate provenance in the Indus River system. We characterized the geochemistry of garnet sediment grains from the modern Indus and all its major tributaries, as well as the related but ephemeral Ghaggar-Hakra River and dune sand from the Thar Desert. Garnet geochemistry displays a unique signature for the Himalayan rivers on the east of the Indus drainage compared to those in the western drainage. The trunk Indus remains distinct because of the dominant arc-type pyrope-garnet derived from Kohistan and the Karakoram. The Jhellum, which lies just east of the modern Indus has modest concentrations of arc-type pyrope garnets, which are more depleted in the other eastern tributaries. Their presence in the Jhellum reflects recycling of trunk Indus garnets through the Miocene Siwalik Group foreland sedimentary rocks. The Thar Desert dune sample contains significant numbers of grains similar to those in the trunk Indus, likely reworked by monsoon winds from the SW. Our data further indicate the presence of a Himalayan river channel east of the present Indus, close to the delta, in the Nara River valley during the middle Holocene. Sands from this channel cannot be distinguished from the Indus on the basis of their garnet geochemistry alone but we favour their sedimentation from an Indus channel rather than reworking of desert sands by another stream. The garnet geochemistry shows some potential as a provenance tool, but cannot be used alone to uniquely discriminate Indus Basin provenance.
Keywords: Provenance

Late Quaternary evolution of Lago Castor (Chile, 45.6°S): Timing of the deglaciation in northern Patagonia and evolution of the southern westerlies during the last 17 kyr - Maarten Van Daele; Sébastien Bertrand; Inka Meyer; Jasper Moernaut; Willem Vandoorne; Giuseppe Siani; Niels Tanghe; Zakaria Ghazoui; Mario Pino; Roberto Urrutia; Marc De Batist (Quaternary Science Reviews, 2016)
Abstract Even though Patagonia is ideally located to study climate of the southern mid-latitudes, many questions on the late Quaternary climate evolution remain unresolved. The timing of maximum glacier extent is still uncertain in vast areas, and the postglacial evolution of the Southern Westerly Wind Belt (SWWB) remains highly debated. Here, we study the sedimentary infill of a glacigenic lake (Lago Castor; 45.6°S, 71.8°W) located at the leeside of the Andes in Chilean Patagonia to i) reconstruct the deglacial evolution of the eastern flank of the Patagonian Ice Sheet (PIS), and ii) discuss postglacial changes in wind strength at a critical location where westerly wind records are critically lacking. A dense grid of high-resolution reflection-seismic data was used to reconstruct the large-scale infill history of the lake, and a radiocarbon dated sediment core penetrating all lacustrine seismic units, was retrieved. Results indicate that the deglaciation of the lake basin and its catchment occurred no later than ∼28 cal kyr \{BP\} (i.e. an early LGM), but possibly even already after \{MIS\} 4. Afterwards, the Lago Castor area was covered by a large proglacial lake that drained – possibly through an outburst flood – when the \{PIS\} outlet glaciers retreated to a critical location. Subsequently, very dry conditions caused the lake to desiccate, as evidenced by an unconformity visible on the seismic profiles and in the sediment core. This dry period likely resulted from the increased orographic effect of the PIS-covered Andes, accompanied by weaker westerlies. From ∼20 kyr \{BP\} onwards, the combination of a shrinking \{PIS\} and a southward shift of the \{SWWB\} resulted in increased precipitation, which caused the lake level to rise. After ∼17 cal kyr BP, lake sedimentation was more directly influenced by the southern westerlies, with the formation of sediment drifts resulting from strong bottom current during periods of intense westerly winds. Our results suggest a progressive increase in wind strength at 46°S from 11.2 to 4.5 cal kyr BP, which supports the hypothesis that the \{SWWB\} broadened during the early and middle Holocene.
Keywords: Sediment drift

Late Quaternary fingerprints of precession and sea level variation over the past 35 kyr as revealed by sea surface temperature and upwelling records from the Indian Ocean near southernmost Sumatra - Ziye Li; Xuefa Shi; Min-Te Chen; Houjie Wang; Shengfa Liu; Jian Xu; Haiyan Long; Rainer Arief Troa; Rina Zuraida; Eko Triarso (Quaternary International, 2016)
Abstract We report high-resolution paleoclimatic reconstructions using isotope, alkenone sea surface temperature (SST), productivity, and terrigenous proxy variations over the past 35 kyr from core SO184-10043 (07°18.57′S, 105°03.53′E) in the eastern tropical Indian Ocean offshore of southernmost (S) Sumatra. The core was retrieved at 2171 m water depth, from the monsoon driven seasonal upwelling area off southernmost Sumatra. Our paleoclimatic reconstructions show that an enhanced marine productivity was closely linked to strengthening of coastal upwelling during the increases of boreal summer insolation and associated southeastern (SE) monsoon strength, with pronounced semi-precession cycles (∼11 kyr). In contrast, our record of alkenone \{SSTs\} shows glacial to interglacial, a sea-level variation, but this fluctuates at dominant precession cycles (∼21 kyr). We also observed four \{SST\} “plateaus” with relatively warmer hydrographic stability in our records over the past 35 kyr: 32-27 ka, 24-20 ka, 17-12 ka, and 9-4 ka. The time scale of each plateau is ∼4-6 kyr. Our study indicates that since the last glacial maximum (LGM), the sea level rise has been responsible for the Sunda shelf flooding and the Indonesian Throughflow (ITF) from the South China Sea (SCS) to the eastern Indian Ocean, leaving a dominant fingerprint of a glacial to interglacial increase in \{SSTs\} since ∼9.5 ka We further argue that the a most recent centennial to millennial scale cooling at ∼3.5 ka observed in our \{SST\} record is a widespread event in the tropical Pacific, which has implications for advancing our understanding of the climate dynamics of the tropical oceans at these time scales.
Keywords: Quaternary

Micropaleontologic record of Pliocene and Quaternary paleoenvironments in the southern Albemarle Embayment, North Carolina, U.S.A - Stephen J. Culver; Kathleen M. Farrell; David J. Mallinson; Debra A. Willard; Benjamin P. Horton; Stanley R. Riggs; E. Robert Thieler; John F. Wehmiller; Peter R. Parham; Jessica Pierson Moore; Scott W. Snyder; Caroline Hillier (Palaeogeography, Palaeoclimatology, Palaeoecology, 2016)
Abstract The Albemarle Embayment, a Cenozoic depositional basin on the Atlantic coast of the USA, is an ideal setting to understand the temporal and spatial variation of eustatic sea-level fluctuations, glacio-hydro-isostasy, tectonics, subsidence, environments and sedimentation patterns of a passive margin Quaternary section. A NE–SW transect of cores and seismic data in the southern Albemarle Embayment were analyzed using micropaleontologic (foraminifera, diatoms, pollen), sedimentologic, stratigraphic, and geochronologic data to reconstruct the paleoenvironmental evolution and paleoclimates in the nearly 90 m thick Quaternary section. The study area is a very low gradient Quaternary landscape that is cross-cut by several Pleistocene incised valleys; a Holocene barrier island complex forms its eastern margin. In the subsurface, the Albemarle Embayment is bordered to the north by the Norfolk Arch and to the south by the depositionally-constructed Cape Lookout High, which is positioned on the northern flank of the structural Carolina Platform. The Quaternary section overlies mid-Pliocene carbonates in three cores; the contact rises in elevation towards the Cape Lookout High. Fossils and sediment characteristics suggest a subtropical, shallow, high energy marine environment during the Pliocene. Overlying units include incomplete Pleistocene, clastic, transgressive-regressive (T-R) deposits. These have similar ages and stratigraphic signatures as the T-R cycles in the central and north-central Albemarle Embayment, although mid-Pleistocene deposits may be older in the southern region. The bulk of the early and mid-Pleistocene record consists of inner to mid-shelf sand and muddy sand. In contrast, late Pleistocene sands are of inner shelf origin, reflecting the infilling of the basin. Lowstand paleovalleys, with fluvial, wetland and estuarine fill, dissect the early, mid- and late Pleistocene marine units; their locations reflect antecedent topography. Holocene sediments were deposited in shoreface and barrier island environments. Quaternary foraminiferal assemblages in the southern Albemarle Embayment exhibit greater species richness than those in the central and north-central embayment reflecting the presence of a major biogeographic boundary at the same location as the modern biogeographic boundary at Cape Hatteras.
Keywords: Holocene

No iron fertilization in the equatorial Pacific Ocean during the last ice age - Costa, K. M.; McManus, J. F.; Anderson, R. F.; Ren, H.; Sigman, D. M.; Winckler, G.; Fleisher, M. Q.; Marcantonio, F.; Ravelo, A. C. (Nature, 2016)
The equatorial Pacific Ocean is one of the major high-nutrient, low-chlorophyll regions in the global ocean. In such regions, the consumption of the available macro-nutrients such as nitrate and phosphate is thought to be limited in part by the low abundance of the critical micro-nutrient iron1. Greater atmospheric dust deposition2 could have fertilized the equatorial Pacific with iron during the last ice age—the Last Glacial Period (LGP)—but the effect of increased ice-age dust fluxes on primary productivity in the equatorial Pacific remains uncertain3, 4, 5, 6. Here we present meridional transects of dust (derived from the 232Th proxy), phytoplankton productivity (using opal, 231Pa/230Th and excess Ba), and the degree of nitrate consumption (using foraminifera-bound δ15N) from six cores in the central equatorial Pacific for the Holocene (0–10,000 years ago) and the LGP (17,000–27,000 years ago). We find that, although dust deposition in the central equatorial Pacific was two to three times greater in the LGP than in the Holocene, productivity was the same or lower, and the degree of nitrate consumption was the same. These biogeochemical findings suggest that the relatively greater ice-age dust fluxes were not large enough to provide substantial iron fertilization to the central equatorial Pacific. This may have been because the absolute rate of dust deposition in the LGP (although greater than the Holocene rate) was very low. The lower productivity coupled with unchanged nitrate consumption suggests that the subsurface major nutrient concentrations were lower in the central equatorial Pacific during the LGP. As these nutrients are today dominantly sourced from the Subantarctic Zone of the Southern Ocean, we propose that the central equatorial Pacific data are consistent with more nutrient consumption in the Subantarctic Zone, possibly owing to iron fertilization as a result of higher absolute dust fluxes in this region7, 8. Thus, ice-age iron fertilization in the Subantarctic Zone would have ultimately worked to lower, not raise, equatorial Pacific productivity.
Keywords: Biogeochemistry; Palaeoceanography

A Note on Reporting of Reservoir C-14 Disequilibria and Age Offsets - Soulet, Guillaume; Skinner, Luke C.; Beaupré, Steven R.; Galy, Valier (RADIOCARBON, 2016)
Reservoir age offsets are widely used to correct marine and speleothem radiocarbon age measurements for various calibration purposes. They also serve as a powerful tracer for carbon cycle dynamics. However, a clear terminology regarding reservoir age offsets is lacking, sometimes leading to miscalculations. This note seeks to provide consistent conventions for reporting reservoir C-14 disequilibria useful to a broad range of environmental sciences. This contribution introduces the (FR)-R-14 and R-14 metrics to express the relative C-14 disequilibrium between two contemporaneous reservoirs and the R metric as the associated reservoir age offset.
Keywords: freshwater effect; hardwater effect; radiocarbon; Reservoir age; Reservoir effect; ventilation age

Plankton biochronology for the last 772,000 years from the western South Atlantic Ocean - Felipe A.L. Toledo; Juliana P. Quadros; Edmundo Camillo Jr.; Ana Cláudia A. Santarosa; José-Abel Flores; Karen B. Costa (Marine Micropaleontology, 2016)
Abstract Calcareous microfossils have potential in the biostratigraphy of Pleistocene sediments and a clear relationship with paleoceanographic studies. Conversely, there are few quantitative biostratigraphic studies of chronologically-tuned events or sections in the western South Atlantic. In order to improve the stratigraphical framework for South Atlantic paleoceanographic studies, the present work attempts to review the last 772,000 years by carrying out a quantitative analysis of the calcareous nannofossil and planktonic foraminiferal assemblages by comparing them with a high resolution marine isotopic record (δ18O). This work is based on the analysis of two piston cores obtained from the continental slope of the Santos Basin in the Santos Drift, southeastern Brazilian Continental Margin. Twelve Pleistocene calcareous nannofossil events and twenty planktonic foraminifera events calibrated with oxygen isotopes and correlated with literature stratigraphies are discussed. This is the first calcareous plankton biochronology study for the last 772 kyr in the western South Atlantic Ocean. More studies in this region will help to establish a more precise biochronology for these calcareous microfossils. This study also presents six new biostratigraphic events of isotopically-caibrated planktonic foraminifera which can be used as markers in the western South Atlantic.
Keywords: Biochronology

Sediment chronology in Antarctic deglacial sediments: Reconciling organic carbon 14 C ages to carbonate 14 C ages using Ramped PyrOx - Subt, Cristina; Fangman, Kimberly A; Wellner, Julia S; Rosenheim, Brad E (The Holocene, 2016)
We present the first study which directly compares carbonate radiocarbon (14C) dates with the Ramped PyrOx (RP) radiocarbon dating technique within a single sediment core, and we confirm the utility for the latter constructing chronologies of high latitude, Holocene marine margin sediment successions. Historically, the heavily detrital nature of Antarctic margin sedimentary organic material and lack of carbonate preservation have made these sediments difficult to date accurately. Here, we use archived cores with existing foraminiferal ages to compare with RP dates at equal or similar depth intervals. The lowest temperature RP splits were integrated over narrower intervals than in previous studies to reduce the amount of mixing with older, more thermochemically stable end-members during pyrolytic decomposition. Ages of the low-temperature RP splits coincide with their corresponding carbonate counterparts, suggesting that the RP 14C dating method is a reliable alternative to carbonate dates in sediments where carbonates are absent or not sufficiently preserved for 14C dating. The rarity of calcareous material in most Antarctic sediments often obligates the use of the bulk acid insoluble organic (AIO) fraction of the sediment, which can be problematic because of contamination by older carbon. The bulk AIO 14C ages, which are calculated using the weighted arithmetic mean of all RP splits of individual samples, show that age reversals and biases can occur using bulk AIO dates for age models because of variable proportions of pre-aged organic matter down-core. The application of the RP dating method can reduce these effects to produce a more reliable chronology that is statistically identical to the foraminiferal dating chronology.

Sediment dynamics and hydrographic conditions during storm passage, Waquoit Bay, Massachusetts - Christopher V. Maio; Jeffrey P. Donnelly; Richard Sullivan; Stephanie M. Madsen; Christopher R. Weidman; Allen M. Gontz; Vitalii A. Sheremet (Marine Geology, 2016)
Abstract The impact of storm events on the sediment dynamics of the shallow groundwater fed estuaries of Cape Cod, Massachusetts, \{USA\} is little understood. To address this, the objectives of this study are to assess sediment dynamics during storm passage and determine whether shallow back-barrier lagoons like Waquoit Bay have the preservation potential for a sedimentary archive of hurricanes. When setting out in this study, it was unclear whether paleotempestological methods could be applied successfully to cores collected from the landward reaches of shallow estuaries of southern New England. Water level and bottom current data using Arm-and-Float tide gauges and SeaHorse Tilt Current Meters was collected during Tropical Storm Irene (2011) and coupled with storm surge modeling projections to better elucidate storm-induced sediment transport mechanisms. Three sediment cores were collected at the head of Waquoit Bay, located 2.8 km from the barrier beach. Grain size analysis of sediment cores was conducted with a laser particle size analyzer at 1 cm increments in order to identify coarse grain anomalies, which can act as a storm event proxy. Bayesian statistics were applied to develop age models of two of the cores based on three Pb pollution chronomarkers and 21 continuous flow 14C \{AMS\} ages. The results yield variable sediment accumulation rates between 2 mm/yr to 10 mm/yr, with significantly higher rates occurring in the upper 1 m of sediments. Grain size results are highly variable, and contain numerous large amplitude, short duration fluctuations suggesting that during storm passage coarse sand is deposited in the coring site. The sensitivity of the site to both tropical and extratropical storm events, uncertainties in the age model, and the multiple sediment sources and transport pathways limits the utility of using the Waquoit sediments to determine long-term hurricane frequencies. Results nonetheless provide insights into how extreme storm events impact coastal lagoons.
Keywords: Sediment transport

The sources of atmospheric black carbon at a European gateway to the Arctic - Winiger, P; Andersson, A; Eckhardt, S; Stohl, A; Gustafsson, O. (Nature Communications, 2016)
Black carbon (BC) aerosols from incomplete combustion of biomass and fossil fuel contribute to Arctic climate warming. Models—seeking to advise mitigation policy—are challenged in reproducing observations of seasonally varying BC concentrations in the Arctic air. Here we compare year-round observations of BC and its δ13C/Δ14C-diagnosed sources in Arctic Scandinavia, with tailored simulations from an atmospheric transport model. The model predictions for this European gateway to the Arctic are greatly improved when the emission inventory of anthropogenic sources is amended by satellite-derived estimates of BC emissions from fires. Both BC concentrations (R2=0.89, P<0.05) and source contributions (R2=0.77, P<0.05) are accurately mimicked and linked to predominantly European emissions. This improved model skill allows for more accurate assessment of sources and effects of BC in the Arctic, and a more credible scientific underpinning of policy efforts aimed at efficiently reducing BC emissions reaching the European Arctic.

Stability of peatland carbon to rising temperatures - Wilson, R. M.; Hopple, A. M.; Tfaily, M. M.; Sebestyen, S. D.; Schadt, C. W.; Pfeifer-Meister, L.; Medvedeff, C.; McFarlane, K. J.; Kostka, J. E.; Kolton, M.; Kolka, R.K.; Kluber, L. A.; et al. (Nature Communications, 2016)
Peatlands contain one-third of soil carbon (C), mostly buried in deep, saturated anoxic zones (catotelm). The response of catotelm C to climate forcing is uncertain, because prior experiments have focused on surface warming. We show that deep peat heating of a 2 m-thick peat column results in an exponential increase in CH4 emissions. However, this response is due solely to surface processes and not degradation of catotelm peat. Incubations show that only the top 20–30 cm of peat from experimental plots have higher CH4 production rates at elevated temperatures. Radiocarbon analyses demonstrate that CH4 and CO2 are produced primarily from decomposition of surface-derived modern photosynthate, not catotelm C. There are no differences in microbial abundances, dissolved organic matter concentrations or degradative enzyme activities among treatments. These results suggest that although surface peat will respond to increasing temperature, the large reservoir of catotelm C is stable under current anoxic conditions.

Stratigraphy, morphology, and geochemistry of late Quaternary buried soils on the High Plains of southwestern Kansas, USA - Anthony L. Layzell; Rolfe D. Mandel; Tammy M. Rittenour; Jon J. Smith; R. Hunter Harlow; Greg A. Ludvigson (CATENA, 2016)
Abstract This study investigated two stratigraphic sequences that record the complex interplay of sedimentation and pedogenesis over the past ca. 84 ka on the High Plains of southwestern Kansas. Up to eight eolian sand and loess units with associated soils were identified in two cores collected from an upland setting. Soil morphological and geochemical data were used to quantitatively assess and compare soil development between multiple buried soils. Chronostratigraphic relationships indicate that 1) loess and eolian sands were episodically deposited during late Marine Isotope Stage (MIS) 5 (ca. 84–70 ka), 2) the Sangamon soil at this site formed between \{MIS\} 3/4 (ca. 70–52 ka), which is consistent with age estimates for renewed Sangamon pedogenesis in the Mississippi River valley, and 3) soil development in the Gilman Canyon Formation began at ca. 44 ka and continued until at least 29.2 ka. Multiple lines of evidence, including grain-size distributions, structure, clay content, and chemical weathering index data, indicate that the morphology and chemistry of the Ak horizon developed in the Gilman Canyon Formation is a product of cumulization by slow loess additions. Similar evidence suggests that cumulization processes are also responsible for the morphology and chemistry of other buried soils in the stratigraphic sequence. Overall, loess inputs during pedogenesis complicate the quantification of weathering processes in these soils.
Keywords: Sangamon soil

Subsurface Evidence of Storm-Driven Breaching along a Transgressing Barrier System, Cape Cod, U.S.A. - Maio, Christopher V.; Gontz, Allen M.; Sullivan, Richard M.; Madsen, Stephanie M.; Weidman, Christopher R.; Donnelly, Jeffrey P. (Journal of Coastal Research, 2016)
Relict and historic tidal channels buried within coastal barriers provide a geologic signature of environmental change, thus enhancing our understanding of how barrier systems respond to extreme storm events. Earliest maps from 1846 depict three inlets along the Waquoit Bay barrier system located on Cape Cod, Massachusetts. These channels were not depicted on maps after 1846, and we lack any information pertaining to them before 1846. The principle objective of this study was to identify the location and map the internal geometry and channel-fill configuration of the buried inlet structures using geophysical and sedimentological data acquisition methods. This was done by collecting 6.2 km of shore-parallel ground-penetrating radar data and five sediment cores ranging in depth from 4 to 5 m. The sediment cores allowed for the ground truthing of the ground-penetrating radar data and provided six samples for radiocarbon dating. The 13 paleochannels identified ranged in depths from 1.3 to 3.7 m below the present beach surface. These appeared in the radar imagery as broad U-shaped cut-and-fill features incised into adjacent barrier facies. The 13 paleochannels composed 24% of the barrier lithosome totaling 704 m in length. Individual channels were primarily less than 65 m in length and between 2.5 and 1.3 m in depth, although an additional 275-m-wide, 3.7-m-deep channel sequence was imaged and likely represents a major and long-lived paleochannel. The results will contribute toward deciphering the evolution of the Waquoit system and identify areas vulnerable to storm-driven coastal change.
Keywords: coastal change; Coastal evolution; ground-penetrating radar; marine transgression; overwash; paleochannel; paleogeography; South Cape Beach

Tracing the intrusion of fossil carbon into coastal Louisiana macrofauna using natural 14C and 13C abundances - Wilson, Rachel M.; Cherrier, Jennifer; Sarkodee-Adoo, Judith; Bosman, Samantha; Mickle, Alejandra; Chanton, Jeffrey P. (Deep Sea Research Part II: Topical Studies in Oceanography, 2016)
The Deepwater Horizon oil spill released a large volume of 13C and radiocarbon depleted organic matter to the northern Gulf of Mexico. Evidence of petroleum-derived carbon entering the offshore planktonic foodweb, as well as widespread oiling of coastal areas documented in previous studies suggests that hydrocarbons could have entered the near shore foodweb. To test this hypothesis, we measured radiocarbon (Δ14C%) and stable carbon isotopes (δ13C) in an assortment of fish tissue, invertebrate tissue and shell samples collected within a year of the spill at seven sites from Louisiana to Florida USA across the northern Gulf of Mexico. We observed a west–east gradient with the most depleted radiocarbon values found in Terrebonne Bay, Louisana and increasingly enriched radiocarbon values in organisms collected at sites to the east. Depleted radiocarbon values as low as −10% in invertebrate soft tissue from Terrebonne suggest assimilation of fossil carbon (2.8±1.2%), consistent with the hypothesis that organic matter from petrochemical reservoirs released during the Deepwater Horizon spill entered the coastal food web to a limited extent. Further there was a significant correlation between radiocarbon and δ13C values in invertebrate tissue consistent with this hypothesis. Both oyster tissue and hard head catfish tissue collected in impacted areas of coastal Louisiana were significantly depleted in 14C and 13C relative to organisms collected in the unaffected Apalachicola Bay, Florida (p<0.014). Alternative explanations for these results include the influence of chronic hydrocarbon pollution along the western gulf coast or that the organisms ingest carbon derived from 14C depleted organic matter mobilized during the erosion of coastal marshes in southern Louisiana.

Variations in microbial carbon sources and cycling in the deep continental subsurface - Danielle N. Simkus; Greg F. Slater; Barbara Sherwood Lollar; Kenna Wilkie; Thomas L. Kieft; Cara Magnabosco; Maggie C.Y. Lau; Michael J. Pullin; Sarah B. Hendrickson; K. Eric Wommack; Eric G. Sakowski; Esta van Heerden; et al. (Geochimica et Cosmochimica Acta, 2016)
Abstract Deep continental subsurface fracture water systems, ranging from 1.1 to 3.3 km below land surface (kmbls), were investigated to characterize the indigenous microorganisms and elucidate microbial carbon sources and their cycling. Analysis of phospholipid fatty acid (PLFA) abundances and direct cell counts detected varying biomass that was not correlated with depth. Compound-specific carbon isotope analyses (δ13C and Δ14C) of the phospholipid fatty acids (PLFAs) and carbon substrates combined with genomic analyses did identify, however, distinct carbon sources and cycles between the two depth ranges studied. In the shallower boreholes at circa 1 kmbls, isotopic evidence indicated microbial incorporation of biogenic \{CH4\} by the in situ microbial community. At the shallowest site, 1.05 kmbls in Driefontein mine, this process clearly dominated the isotopic signal. At slightly deeper depths, 1.34 kmbls in Beatrix mine, the isotopic data indicated the incorporation of both biogenic \{CH4\} and dissolved inorganic carbon (DIC) derived from \{CH4\} oxidation. In both of these cases, molecular genetic analysis indicated that methanogenic and methanotrophic organisms together comprised a small component (<5%) of the microbial community. Thus, it appears that a relatively minor component of the prokaryotic community is supporting a much larger overall bacterial community in these samples. In the samples collected from >3 kmbls in Tau Tona mine (TT107, \{TT109\} Bh2), the \{CH4\} had an isotopic signature suggesting a predominantly abiogenic origin with minor inputs from microbial methanogenesis. In these samples, the isotopic enrichments (δ13C and Δ14C) of the \{PLFAs\} relative to \{CH4\} were consistent with little incorporation of \{CH4\} into the biomass. The most 13C-enriched \{PLFAs\} were observed in \{TT107\} where the dominant CO2-fixation pathway was the acetyl-CoA pathway by non-acetogenic bacteria. The differences in the δ13C of the \{PLFAs\} and the \{DIC\} and \{DOC\} for \{TT109\} Bh2 were ∼−24‰ and 0‰, respectively. The dominant CO2-fixation pathways were 3-HP/4-HB cycle > acetyl-CoA pathway > reductive pentose phosphate cycle.

Viable Species of Flamella (Amoebozoa: Variosea) Isolated from Ancient Arctic Permafrost Sediments - Lyubov Shmakova; Natalya Bondarenko; Alexey Smirnov (Protist, 2016)
Six viable strains of amoebae belonging to the genus Flamella (Amoebozoa, Variosea) were isolated from permafrost sediments sampled in the Russian Arctic region. Two of them are from late Pleistocene permafrost in North-East Siberia, and four - from Holocene and late Pleistocene in North-West Siberia. Light- and electron-microscopic study and molecular phylogeny show that these isolates represent two new species belonging to the genus Flamella. Both species are cyst-forming. This is a remarkable case of high resistance of protozoan cysts, allowing them to survive and recover an amoebae population after a very long, geologically significant period of rest; a “snapshot” of evolution in time. This study directly shows for the first time that amoeba cysts can be conserved not only for years and decades but for many thousand years and then recover, contributing to the formation of an active microbial community. We propose to name the new species as Flamella pleistocenica n.sp. and Flamella beringiania n.sp. Phylogenetic analysis shows that the genus Flamella is a robust and potentially species-rich group of Variosea.
Keywords: cryptobiosis.

Accretion history of mid-Holocene coral reefs from the southeast Florida continental reef tract, USA - Stathakopoulos, A.; Riegl, B. M. (Coral Reefs, 2015)
Sixteen new coral reef cores were collected to better understand the accretion history and composition of submerged relict reefs offshore of continental southeast (SE) Florida. Coral radiometric ages from three sites on the shallow inner reef indicate accretion initiated by 8,050 Cal BP and terminated by 5,640 Cal BP. The reef accreted up to 3.75 m of vertical framework with accretion rates that averaged 2.53 m kyr-1. The reef was composed of a nearly even mixture of Acropora palmata and massive corals. In many cases, cores show an upward transition from massives to A. palmata and may indicate local dominance by this species prior to reef demise. Quantitative macroscopic analyses of reef clasts for various taphonomic and diagenetic features did not correlate well with depth/environmental-related trends established in other studies. The mixed coral framestone reef lacks a classical Caribbean reef zonation and is best described as an immature reef and/or a series of fused patch reefs; a pattern that is evident in both cores and reef morphology. This is in stark contrast to the older and deeper outer reef of the SE Florida continental reef tract. Accretion of the outer reef lasted from 10,695–8,000 Cal BP and resulted in a larger and better developed structure that achieved a distinct reef zonation. The discrepancies in overall reef morphology and size as well as the causes of reef terminations remain elusive without further study, yet they likely point to different climatic/environmental conditions during their respective accretion histories.
Keywords: Backstepping; Holocene; Reef accretion; Relict reef; SE Florida continental reef tract

Ancient population genomics and the study of evolution - Parks, M.; Subramanian, S.; Baroni, C.; Salvatore, M. C.; Zhang, G.; Millar, C. D.; Lambert, D. M. (Philosophical Transactions of the Royal Society B: Biological Sciences, 2015)
Recently, the study of ancient DNA (aDNA) has been greatly enhanced by the development of second-generation DNA sequencing technologies and targeted enrichment strategies. These developments have allowed the recovery of several complete ancient genomes, a result that would have been considered virtually impossible only a decade ago. Prior to these developments, aDNA research was largely focused on the recovery of short DNA sequences and their use in the study of phylogenetic relationships, molecular rates, species identification and population structure. However, it is now possible to sequence a large number of modern and ancient complete genomes from a single species and thereby study the genomic patterns of evolutionary change over time. Such a study would herald the beginnings of ancient population genomics and its use in the study of evolution. Species that are amenable to such large-scale studies warrant increased research effort. We report here progress on a population genomic study of the Adélie penguin (Pygoscelis adeliae). This species is ideally suited to ancient population genomic research because both modern and ancient samples are abundant in the permafrost conditions of Antarctica. This species will enable us to directly address many of the fundamental questions in ecology and evolution.

Applications and limitations of U–Th disequilibria systematics for determining ages of carbonate alteration minerals in peridotite - Mervine, Evelyn M.; Sims, Kenneth W.W.; Humphris, Susan E.; Kelemen, Peter B. (Chemical Geology, 2015)
238U–234U–230Th dating was conducted on carbonate alteration minerals in the peridotite layer of the Samail Ophiolite, Sultanate of Oman, in order to assess the applicability of U-series dating techniques to these types of Quaternary terrestrial carbonates and also to further constrain natural rates of carbonation of the peridotite. Due to their low U concentrations and relatively high Th/U ratios, Samail carbonates are challenging to date with the 230Th technique because of the sensitivity of ages to corrections for initial 230Th. Uncorrected 230Th ages for Ca-rich travertines are consistently older than previously obtained 14C ages. However, geologically reasonable initial 230Th corrections bring the two sets of ages into concordance. This age concordance suggests that the travertines are generally closed systems, adding a level of credence to the reliability of previously obtained 14C ages. In contrast, uncorrected 230Th ages for Mg-rich carbonate veins are generally younger than previously obtained 14C ages. These young ages are interpreted in terms of remobilization of hexavalent U, which is subsequently deposited as tetravalent U by reduced serpentinization fluids. Two Mg-rich carbonate veins sampled at a roadcut have near-equilibrium (230Th/238U) and (234U/238U) values, which indicate that these veins are > 375,000 years in age, consistent with their “14C dead” (> 50,000 years BP) ages. The variable young and old ages for these Mg-rich carbonate veins indicate that carbonation of the peridotite layer of the Samail Ophiolite is an ongoing process and that there have been multiple generations of subsurface carbonate vein formation. Overall, this study provides insights into some of the challenges associated with applying U-series dating methods to Quaternary terrestrial carbonates, in particular carbonate alteration minerals in peridotites, and highlights some areas where there is room for improvement, such as obtaining better constraints on the isotopic composition of admixed detritus, and also some advantages, such as the ability to identify open system behavior not apparent from 14C dating and stable C and O isotopic analysis alone.

Climate forcing of unprecedented intense-hurricane activity in the last 2000 years - Donnelly, Jeffrey P.; Hawkes, Andrea D.; Lane, Philip; MacDonald, Dana; Shuman, Bryan N.; Toomey, Michael R.; van Hengstum, Peter J.; Woodruff, Jonathan D. (EARTHS FUTURE, 2015)
How climate controls hurricane variability has critical implications for society is not well understood. In part, our understanding is hampered by the short and incomplete observational hurricane record. Here we present a synthesis of intense-hurricane activity from the western North Atlantic over the past two millennia, which is supported by a new, exceptionally well-resolved record from Salt Pond, Massachusetts (USA). At Salt Pond, three coarse grained event beds deposited in the historical interval are consistent with severe hurricanes in 1991 (Bob), 1675, and 1635 C.E., and provide modern analogs for 32 other prehistoric event beds. Two intervals of heightened frequency of event bed deposition between 1400 and 1675 C.E. (10 events) and 150 and 1150 C.E. (23 events), represent the local expression of coherent regional patterns in intense-hurricane-induced event beds. Our synthesis indicates that much of the western North Atlantic appears to have been active between 250 and 1150 C.E., with high levels of activity persisting in the Caribbean and Gulf of Mexico until 1400 C.E. This interval was one with relatively warm sea surface temperatures (SSTs) in the main development region (MDR). A shift in activity to the North American east coast occurred ca. 1400 C.E., with more frequent severe hurricane strikes recorded from The Bahamas to New England between 1400 and 1675 C.E. A warm SST anomaly along the western North Atlantic, rather than within the MDR, likely contributed to the later active interval being restricted to the east coast.
Keywords: Climate change; common era; Holocene; sea surface temperature; tropical cyclones

Climatic and biotic thresholds of coral-reef shutdown - Toth, Lauren T.; Aronson, Richard B.; Cobb, Kim M.; Cheng, Hai; Edwards, R. Lawrence; Grothe, Pamela R.; Sayani, Hussein R. (Nature Climate Change, 2015)
Climate change is now the leading cause of coral-reef degradation and is altering the adaptive landscape of coral populations1, 2. Increasing sea temperatures and declining carbonate saturation states are inhibiting short-term rates of coral calcification, carbonate precipitation and submarine cementation3, 4, 5. A critical challenge to coral-reef conservation is understanding the mechanisms by which environmental perturbations scale up to influence long-term rates of reef-framework construction and ecosystem function6, 7. Here we reconstruct climatic and oceanographic variability using corals sampled from a 6,750-year core from Pacific Panamá. Simultaneous reconstructions of coral palaeophysiology and reef accretion allowed us to identify the climatic and biotic thresholds associated with a 2,500-year hiatus in vertical accretion beginning ~4,100 years ago8. Stronger upwelling, cooler sea temperatures and greater precipitation—indicators of La Niña-like conditions—were closely associated with abrupt reef shutdown. The physiological condition of the corals deteriorated at the onset of the hiatus, corroborating theoretical predictions that the tipping points of radical ecosystem transitions should be manifested sublethally in the biotic constituents9. Future climate change could cause similar threshold behaviours, leading to another shutdown in reef development in the tropical eastern Pacific.
Keywords: Climate-change ecology; Palaeoceanography; Palaeoclimate; Palaeoecology

Comparing dust flux records from the Subarctic North Pacific and Greenland: Implications for atmospheric transport to Greenland and for the application of dust as a chronostratigraphic tool - Serno, Sascha; Winckler, Gisela; Anderson, Robert F.; Maier, Edith; Ren, Haojia; Gersonde, Rainer; Haug, Gerald H. (PALEOCEANOGRAPHY, 2015)
We present a new record of eolian dust flux to the western Subarctic North Pacific (SNP) covering the past 27,000years based on a core from the Detroit Seamount. Comparing the SNP dust record to the North Greenland Ice Core Project (NGRIP) ice core record shows significant differences in the amplitude of dust changes to the two regions during the last deglaciation, while the timing of abrupt changes is synchronous. If dust deposition in the SNP faithfully records its mobilization in East Asian source regions, then the difference in the relative amplitude must reflect climate-related changes in atmospheric dust transport to Greenland. Based on the synchronicity in the timing of dust changes in the SNP and Greenland, we tie abrupt deglacial transitions in the Th-230-normalized He-4 flux record to corresponding transitions in the well-dated NGRIP dust flux record to provide a new chronostratigraphic technique for marine sediments from the SNP. Results from this technique are complemented by radiocarbon dating, which allows us to independently constrain radiocarbon paleoreservoir ages. We find paleoreservoir ages of 745140years at 11,653year B.P., 680228years at 14,630year B.P., and 790498years at 23,290year B.P. Our reconstructed paleoreservoir ages are consistent with modern surface water reservoir ages in the western SNP. Good temporal synchronicity between eolian dust records from the Subantarctic Atlantic and equatorial Pacific and the ice core record from Antarctica supports the reliability of the proposed dust tuning method to be used more widely in other global ocean regions.
Keywords: atmospheric circulation; chronostratigrapy; eolian dust; helium-4; paleoreservoir age; Subarctic North Pacific

Field techniques for sea-level reconstruction - Coastal sediment - Shennan, I.; Long, A.J.; Horton, B.E. (Handbook of Sea-Level Research, 2015)
Measuring sea-level change – be that rise or fall – is one of the most pressing scientific goals of our time and requires robust scientific approaches and techniques. This Handbook aims to provide a practical guide to readers interested in this challenge, from the initial design of research approaches through to the practical issues of data collection and interpretation from a diverse range of coastal environments. Building on thirty years of international research, the Handbook comprises 38 chapters that are authored by leading experts from around the world. The Handbook will be an important resource to scientists interested and involved in understanding sea-level changes across a broad range of disciplines, policy makers wanting to appreciate our current state of knowledge of sea-level change over different timescales, and many teachers at the university level, as well as advanced-level undergraduates and postgraduate research students, wanting to learn more about sea-level change.

Forces driving late Pleistocene (ca. 77–12 ka) landscape evolution in the Cimarron River valley, southwestern Kansas - Layzell, Anthony L.; Mandel, Rolfe D.; Ludvigson, Greg A.; Rittenour, Tammy M.; Smith, Jon J. (Quaternary Research, 2015)
This study presents stratigraphic, geomorphic, and paleoenvironmental (δ13C) data that provide insight into the late Pleistocene landscape evolution of the Cimarron River valley in the High Plains of southwestern Kansas. Two distinct valley fills (T-1 and T-2) were investigated. Three soils occur in the T-2 fill and five in the T-1 fill, all indicating periods of landscape stability or slow sedimentation. Of particular interest are two cumulic soils dating to ca. 48–28 and 13–12.5 ka. δ13C values are consistent with regional paleoenvironmental proxy data that indicate the prevalence of warm, dry conditions at these times. The Cimarron River is interpreted to have responded to these climatic changes and to local base level control. Specifically, aggradation occurred during cool, wet periods and slow sedimentation with cumulic soil formation occurred under warmer, drier climates. Significant valley incision (~ 25 m) by ca. 28 ka likely resulted from a lowering of local base level caused by deep-seated dissolution of Permian evaporite deposits.

Freshening of the Marmara Sea prior to its post-glacial reconnection to the Mediterranean Sea - Aloisi, G.; Soulet, G.; Henry, P.; Wallmann, K.; Sauvestre, R.; Vallet-Coulomb, C.; Lecuyer, C.; Bard, E. (EARTH AND PLANETARY SCIENCE LETTERS, 2015)
During the last glaciation the Marmara Sea was isolated from the Mediterranean Sea because global sea level was below the depth of the Dardanelles sill. Prior to the postglacial reconnection to the Mediterranean Sea (similar to 14.7 cal kyr BP), the surface waters of the Marmara Sea were brackish (Marmara Lake). Freshening of a previously saline Marmara Sea could have happened via spill-out of brackish to fresh water from the surface water of the Black Sea through the Bosphorus Strait. This hypothesis has not been tested against alternative possibilities (salt flushing by river run-off and precipitation). Here we use the dissolved Cl- and stable isotope composition (delta O-18 and delta D) of Marmara Sea sediment pore water to estimate the salinity and stable isotope composition of Marmara Lake bottom water and to evaluate possible freshening scenarios. We use a transport model to simulate pore water Cl-, delta O-18 and delta D in Marmara Sea sediments in the past 130 kyr, which includes the last interglacial (130-75 cal kyr BP), the last glacial (75-14 cal kyr BP) and the current postglacial period. Our results show that the bottom waters of the Marmara Lake were brackish (similar to 4 parts per thousand salinity) and isotopically depleted (delta O-18 similar to -10.2 parts per thousand and delta D similar to -70 parts per thousand, respectively) compared to modern seawater. Their salinity and stable isotope ratios show that they are a mixture of Mediterranean waters and Danube-like waters implying that the freshening took place via spill-out of freshwater through the Bosphorus. Our modelling approach indicates that the transit of fresh water from glacial Eurasia to the Mediterranean via the Marmara Sea started at least 50 cal kyr BP, was continuous throughout most of the last glaciation and persisted up to the post glacial reconnection to the Mediterranean through the Dardanelles sill (14.7 cal kyr BP). These results are consistent with previously published micropaleontological and geochemical investigations of sediment cores that indicate lacustrine conditions in the Marmara Sea from about 75 to 14.7 cal kyr BP. (C) 2015 Elsevier B.V. All rights reserved.
Keywords: Black Sea outflow; Last glacial maximum; Marmara Lake; pore water isotope composition

Glacial-interglacial changes in central tropical Pacific surface seawater property gradients - Lynch-Stieglitz, Jean; Polissar, Pratigya J.; Jacobel, Allison W.; Hovan, Steven A.; Pockalny, Robert A.; Lyle, Mitchell; Murray, Richard W.; Ravelo, A. Christina; Bova, Samantha C.; Dunlea, Ann G.; Ford, Heather L.; Hertzberg, Jennifer E.; et al. (Paleoceanography, 2015)
Much uncertainty exists about the state of the oceanic and atmospheric circulation in the tropical Pacific over the last glacial cycle. Studies have been hampered by the fact that sediment cores suitable for study were concentrated in the western and eastern parts of the tropical Pacific, with little information from the central tropical Pacific. Here we present information from a suite of sediment cores collected from the Line Islands Ridge in the central tropical Pacific, which show sedimentation rates and stratigraphies suitable for paleoceanographic investigations. Based on the radiocarbon and oxygen isotope measurements on the planktonic foraminifera Globigerinoides ruber, we construct preliminary age models for selected cores and show that the gradient in the oxygen isotope ratio of G. ruber between the equator and 8°N is enhanced during glacial stages relative to interglacial stages. This stronger gradient could reflect enhanced equatorial cooling (perhaps reflecting a stronger Walker circulation) or an enhanced salinity gradient (perhaps reflecting increased rainfall in the central tropical Pacific).

Handbook of Sea-Level ResearchPre-fieldwork surveys - Witter, Robert C. (John Wiley & Sons, Ltd, 2015)
Using maps, imagery, tidal measurements, and other historical data to assess the geomorphology of a study area prior to fieldwork helps select optimal sites, identify the most effective field methods to test research hypotheses, highlight the primary geomorphic processes, and may provide preliminary estimates of sea-level change. Here, I review the common types of data useful for pre-fieldwork surveys in sea-level research and discuss the many benefits of assessing the geomorphology of a site in advance of fieldwork. I also review briefly some case studies where historical data led to new directions in research and a scientific breakthrough.
Keywords: aerial photography; barrier island; bathymetric data; beach ridge; coastal geomorphology; geomorphological map; LiDAR; nautical chart; remote sensing; satellite imagery

High-frequency surface water changes in the Tagus prodelta off Lisbon, eastern North Atlantic, during the last two millennia - Bartels-Jónsdóttir, Helga B.; Voelker, Antje H. L.; Abrantes, Fatima G.; Salgueiro, Emilia; Rodrigues, Teresa; Knudsen, Karen Luise (Marine Micropaleontology, 2015)
A high-resolution sedimentary sequence recovered from the Tagus prodelta has been studied with the objective to reconstruct multi-decadal to centennial-scale climate variability on the western Iberian Margin and to discuss the observations in a wider oceanographic and climatic context. Between ca. 100 BC and AD 400 the foraminiferal fauna and high abundance of Globorotalia inflata indicate advection of subtropical waters via the Azores Current and the winter-time warm Portugal Coastal Current. Between ca. AD 400 and 1350, encompassing the Medieval Climate Anomaly (MCA), enhanced upwelling is indicated by the planktonic foraminiferal fauna, in particular by the high abundance of upwelling indicator species Globigerina bulloides. Relatively light δ18O values and high sea surface temperature (SST) (reconstructed from foraminiferal assemblages) point to upwelling of subtropical Eastern North Atlantic Central Water. Between ca. AD 1350 and 1750, i.e. most of the Little Ice Age, relatively heavy δ18O values and low reconstructed SST, as well as high abundances of Neogloboquadrina incompta, indicate the advection of cold subpolar waters to the area and a southward deflection of the subpolar front in the North Atlantic, as well as changes in the mode of the North Atlantic Oscillation. In addition, the assemblage composition together with the other proxy data reveals less upwelling and stronger river input than during the MCA. Stronger Azores Current influence on the Iberian Margin and strong anthropogenic effect on the climate after AD 1750 is indicated by the foraminiferal fauna. The foraminiferal assemblage shows a significant change in surface water conditions at ca. AD 1900, including enhanced river runoff, a rapid increase in temperature and increased influence of the Azores Current. The Tagus record displays a high degree of similarity to other North Atlantic records, indicating that the site is influenced by atmospheric–oceanic processes operating throughout the North Atlantic, as well as by local changes.

How Unique was Hurricane Sandy? Sedimentary Reconstructions of Extreme Flooding from New York Harbor - Brandon, Christine M.; Woodruff, Jonathan D.; Donnelly, Jeffrey P.; Sullivan, Richard M. (Scientific Reports, 2015)
The magnitude of flooding in New York City by Hurricane Sandy is commonly believed to be extremely rare, with estimated return periods near or greater than 1000 years. However, the brevity of tide gauge records result in significant uncertainties when estimating the uniqueness of such an event. Here we compare resultant deposition by Hurricane Sandy to earlier storm-induced flood layers in order to extend records of flooding to the city beyond the instrumental dataset. Inversely modeled storm conditions from grain size trends show that a more compact yet more intense hurricane in 1821 CE probably resulted in a similar storm tide and a significantly larger storm surge. Our results indicate the occurrence of additional flood events like Hurricane Sandy in recent centuries, and highlight the inadequacies of the instrumental record in estimating current flood risk by such extreme events.
Keywords: Environmental sciences; Geomorphology; Palaeoclimate; sedimentology

Late Holocene precipitation variability recorded in the sediments of Reloncaví Fjord (41°S, 72°W), Chile - Rebolledo, Lorena; Lange, Carina B.; Bertrand, Sébastien; Muñoz, Praxedes; Salamanca, Marco; Lazo, Pablo; Iriarte, José L.; Vargas, Gabriel; Pantoja, Silvio; Dezileau, Laurent (Quaternary Research, 2015)
We present reconstructions of late Holocene changes in the source of organic matter and siliceous export production in the Relocanví Fjord (41°S, 72°W), Northern Chilean Patagonia, based on organic carbon content, δ13Corg, N/C ratio, diatom assemblages and biogenic silica contents from three sediment cores. The age models are based on a combination of 210Pb profiles, AMS 14C dating, and on the first occurrence of the diatom Rhizosolenia setigera f. pungens, as a stratigraphic marker in the fjords. The cores span the last 300 to 700 yr. Diatoms dominate the siliceous assemblages in the three cores (98% on average). Our results suggest that precipitation seasonality in the region of Reloncaví was high in CE 1300–1400 and CE 1700–1850, with a clear decreasing trend since CE 1850. The latter trend is in agreement with instrumental records and tree-ring reconstructions. These fluctuations seem to be associated with the Southern Annular Mode (SAM).
Co0ceTimes Cited:1Cited References Count:93

Low-frequency storminess signal at Bermuda linked to cooling events in the North Atlantic region - van Hengstum, Peter J.; Donnelly, Jeffrey P.; Kingston, Andrew W.; Williams, Bruce E.; Scott, David B.; Reinhardt, Eduard G.; Little, Shawna N.; Patterson, William P. (Paleoceanography, 2015)
North Atlantic climate archives provide evidence for increased storm activity during the Little Ice Age (150 to 600 calibrated years (cal years) B.P.) and centered at 1700 and 3000 cal years B.P., typically in centennial-scale sedimentary records. Meteorological (tropical versus extratropical storms) and climate forcings of this signal remain poorly understood, although variability in the North Atlantic Oscillation (NAO) or Atlantic Meridional Overturning Circulation (AMOC) are frequently hypothesized to be involved. Here we present records of late Holocene storminess and coastal temperature change from a Bermudian submarine cave that is hydrographically circulated with the coastal ocean. Thermal variability in the cave is documented by stable oxygen isotope values of cave benthic foraminifera, which document a close linkage between regional temperature change and NAO phasing during the late Holocene. However, erosion of terrestrial sediment into the submarine cave provides a “storminess signal” that correlates with higher-latitude storminess archives and broader North Atlantic cooling events. Understanding the driver of this storminess signal will require higher-resolution storm records to disentangle the contribution of tropical versus extratropical cyclones and a better understanding of cyclone activity during hemispheric cooling periods. Most importantly, however, the signal in Bermuda appears more closely correlated with proxy-based evidence for subtle AMOC reductions than NAO phasing.

Methods and codes for reservoir-atmosphere C-14 age offset calculations - Soulet, Guillaume (QUATERNARY GEOCHRONOLOGY, 2015)
Reservoir C-14 age offsets are invaluable tracers for past changes in carbon cycle and oceanic circulation. Reconstruction of reservoir age offsets with time is also required for calibration purposes (reconstruction of atmospheric calibration curve, calibration of non-atmospheric radiocarbon ages). Thus, properly propagating the various uncertainties linked to reservoir age offset is important for proper interpretation. However, approaches for reservoir age offset calculation especially when considering pairs of reservoir-derived C-14 and calenidar ages are usually not detailed and inadequate for proper propagation of uncertainties. Here, the various ways to properly calculate reservoir age offsets are described with a focus on a new approach when considering pairs of C-14 and calendar ages. This approach maps the calendar age distribution onto the C-14 time scale prior to reservoir age offset calculation the ``uncalibration-convolution process{''}. R codes computing reservoir age offsets based on available data are presented. Finally, a case study focusing on the reconstruction of the speleothem-atmosphere C-14 age offsets of speleothem C-14 data used in the latest release of the atmospheric calibration curve is discussed. (C) 2015 Elsevier B.V. All rights reserved.
Keywords: Calibration curve; Dead carbon fraction; Radiocarbon modeling; Reservoir age; Reservoir effect; Uncalibration process

Millennial-scale fluctuations of the European Ice Sheet at the end of the last glacial, and their potential impact on global climate - Toucanne, Samuel; Soulet, Guillaume; Freslon, Nicolas; Jacinto, Ricardo Silva; Dennielou, Bernard; Zaragosi, Sebastien; Eynaud, Frédérique; Bourillet, Jean-Francois; Bayon, Germain (QUATERNARY SCIENCE REVIEWS, 2015)
Reconstructing Northern Hemisphere ice-sheet oscillations and meltwater routing to the ocean is important to better understand the mechanisms behind abrupt climate changes. To date, research efforts have mainly focused on the North American (Laurentide) ice-sheets (LIS), leaving the potential role of the European Ice Sheet (EIS), and of the Scandinavian ice-sheet (SIS) in particular, largely unexplored. Using neodymium isotopes in detrital sediments deposited off the Channel River, we provide a continuous and well-dated record for the evolution of the EIS southern margin through the end of the last glacial period and during the deglaciation. Our results reveal that the evolution of EIS margins was accompanied with substantial ice recession (especially of the SIS) and simultaneous release of meltwater to the North Atlantic. These events occurred both in the course of the EIS to its LGM position (i.e., during Heinrich Stadial -HS- 3 and HS2; similar to 31-29 ka and similar to 26-23 ka, respectively) and during the deglaciation (i.e., at similar to 22 ka, similar to 20-19 ka and from 18.2 +/- 0.2 to 16.7 +/- 0.2 ka that corresponds to the first part of HS1). The deglaciation was discontinuous in character, and similar in timing to that of the southern LIS margin, with moderate ice-sheet retreat (from 22.5 +/- 0.2 ka in the Baltic lowlands) as soon as the northern summer insolation increase (from similar to 23 ka) and an acceleration of the margin retreat thereafter (from similar to 20 ka). Importantly, our results show that EIS retreat events and release of meltwater to the North Atlantic during the deglaciation coincide with AMOC destabilisation and interhemispheric climate changes. They thus suggest that the EIS, together with the LIS, could have played a critical role in the climatic reorganization that accompanied the last deglaciation. Finally, our data suggest that meltwater discharges to the North Atlantic produced by large-scale recession of continental parts of Northern Hemisphere ice sheets during HS, could have been a possible source for the oceanic perturbations (i.e., AMOC shutdown) responsible for the marine-based ice stream purge cycle, or so-called HE's, that punctuate the last glacial period. (C) 2015 Elsevier Ltd. All rights reserved.
Keywords: Channel River; Deglaciation; European ice-sheet; Meltwater; Neodymium; Termination

Multimolecular tracers of terrestrial carbon transfer across the pan-Arctic: C-14 characteristics of sedimentary carbon components and their environmental controls - Feng, Xiaojuan; Gustafsson, Örjan; Holmes, R. Max; Vonk, Jorien E.; van Dongen, Bart E.; Semiletov, Igor P.; Dudarev, Oleg V.; Yunker, Mark B.; Macdonald, Robie W.; Wacker, Lukas; Montluçon, Daniel B.; Eglinton, Timothy I. (GLOBAL BIOGEOCHEMICAL CYCLES, 2015)
Distinguishing the sources, ages, and fate of various terrestrial organic carbon (OC) pools mobilized from heterogeneous Arctic landscapes is key to assessing climatic impacts on the fluvial release of carbon from permafrost. Through molecular C-14 measurements, including novel analyses of suberin- and/or cutin-derived diacids (DAs) and hydroxy fatty acids (FAs), we compared the radiocarbon characteristics of a comprehensive suite of terrestrial markers (including plant wax lipids, cutin, suberin, lignin, and hydroxy phenols) in the sedimentary particles from nine major arctic and subarctic rivers in order to establish a benchmark assessment of the mobilization patterns of terrestrial OC pools across the pan-Arctic. Terrestrial lipids, including suberin-derived longer-chain DAs (C-24,C-26,C-28), plant wax FAs (C(24,26,2)8), and n-alkanes (C-27,C-29,C-31), incorporated significant inputs of aged carbon, presumably from deeper soil horizons. Mobilization and translocation of these ``old{''} terrestrial carbon components was dependent on nonlinear processes associated with permafrost distributions. By contrast, shorter-chain (C-16,C-18) DAs and lignin phenols (as well as hydroxy phenols in rivers outside eastern Eurasian Arctic) were much more enriched in C-14, suggesting incorporation of relatively young carbon supplied by runoff processes from recent vegetation debris and surface layers. Furthermore, the radiocarbon content of terrestrial markers is heavily influenced by specific OC sources and degradation status. Overall, multitracer molecular C-14 analysis sheds new light on the mobilization of terrestrial OC from arctic watersheds. Our findings of distinct ages for various terrestrial carbon components may aid in elucidating fate of different terrestrial OC pools in the face of increasing arctic permafrost thaw.

Multiproxy record of monsoon variability from the Ganga Plain during 400–1200 A.D - Singh, Dhruv Sen; Gupta, Anil K.; Sangode, S. J.; Clemens, Steven C.; Prakasam, M.; Srivastava, Priyeshu; Prajapati, Shailendra K. (Updated Quaternary Climatic Research in parts of the Third Pole Selected papers from the HOPE-2013 conference, Nainital, India, 2015)
Understanding on the Indian Summer Monsoon (ISM) variability is chiefly based upon the marine proxies and a few continental records. The Ganga Plain, one of the most densely populated regions of the world marked by intensive cultivation of monsoon dependent crops and a rich cultural history, is not yet well understood in the context of monsoon variability. We present here a 400–1200 A.D. AMS radiocarbon dated record of Ropan Chhapra tal in the Central Ganga Plain using sedimentology, environmental magnetism, and stable isotope of oxygen for ISM variability. The environmental magnetic parameters (χlf, χARM, SIRM/χlf, S-Ratio, B(0)CR and HIRM) inferred antiferromagnetic mineralogy (hematite and/or goethite) independent of grain size variation during 400–900 A.D., depicting climate variability within warm humid to warm arid conditions favouring stronger ISM seasonality. Prevalence of ferrimagnetic mineralogy under less oxygenated conditions intermittently demonstrates an altered catchment regime or possibly in response to stronger winter monsoon. The higher δ18O values around 500, 580 and 740 A.D. indicate warm and arid conditions under weak ISM. The lower δ18O values around 480, 540 and 700 A.D. and from 900 to 1200 A.D. occur during warm and humid conditions indicating maximum intensity of the ISM. Increased silt content from 800 A.D. onwards is due to increased surface runoff in response to enhanced precipitation, and the higher clay percentage around 500, 580 and 740 indicates low-energy (ponding) conditions under weak ISM. The well sorted nature of sediment indicates consistency of the lacustrine environments under fairly uniform energy and constant bottom water conditions, under varied monsoonal intensity. Combinations of sediment textures and stable isotope indicate intense ISM at ∼480 and ∼540 A.D. with flooding around ∼700 A.D. and a weak monsoon at 580 and 740 A.D., with drought at 500 A.D. During ∼900–1200 A.D. the multiproxy record suggests strong summer monsoon synchronous with Medieval Warm Period (MWP), whereas after 1200 A.D. the weak monsoon phase coincides with the onset of the Little Ice Age (LIA).

Rapid, high-resolution C-14 chronology of ooids - Beaupré, Steven R.; Roberts, Mark L.; Burton, Joshua R.; Summons, Roger E. (GEOCHIMICA ET COSMOCHIMICA ACTA, 2015)
Ooids are small, spherical to ellipsoidal grains composed of concentric layers of CaCO3 that could potentially serve as biogeochemical records of the environments in which they grew. Such records, however, must be placed in the proper temporal context. Therefore, we developed a novel acidification system and employed an accelerator mass spectrometer (AMS) with a gas accepting ion source to obtain radiocarbon (C-14) chronologies extending radially through ooids within one 8-h workday. The method was applied to ooids from Highborne Cay, Bahamas and Shark Bay, Australia, yielding reproducible C-14 chronologies, as well as constraints on the rates and durations of ooid growth and independent estimates of local C-14 reservoir ages. (C) 2015 Elsevier Ltd. All rights reserved.

Sedimentation Pulse in the NE Gulf of Mexico following the 2010 DWH Blowout - Brooks, Gregg R.; Larson, Rebekka A.; Schwing, Patrick T.; Romero, Isabel; Moore, Christopher; Reichart, Gert-Jan; Jilbert, Tom; Chanton, Jeff P.; Hastings, David W.; Overholt, Will A.; Marks, Kala P.; Kostka, Joel E.; et al. (PLOS ONE, 2015)
The objective of this study was to investigate the impacts of the Deepwater Horizon (DWH) oil discharge at the seafloor as recorded in bottom sediments of the DeSoto Canyon region in the northeastern Gulf of Mexico. Through a close coupling of sedimentological, geochemical, and biological approaches, multiple independent lines of evidence from 11 sites sampled in November/December 2010 revealed that the upper ~1 cm depth interval is distinct from underlying sediments and results indicate that particles originated at the sea surface. Consistent dissimilarities in grain size over the surficial ~1 cm of sediments correspond to excess 234Th depths, which indicates a lack of vertical mixing (bioturbation), suggesting the entire layer was deposited within a 4–5 month period. Further, a time series from four deep-sea sites sampled up to three additional times over the following two years revealed that excess 234Th depths, accumulation rates, and 234Th inventories decreased rapidly, within a few to several months after initial coring. The interpretation of a rapid sedimentation pulse is corroborated by stratification in solid phase Mn, which is linked to diagenesis and redox change, and the dramatic decrease in benthic formanifera density that was recorded in surficial sediments. Results are consistent with a brief depositional pulse that was also reported in previous studies of sediments, and marine snow formation in surface waters closer to the wellhead during the summer and fall of 2010. Although sediment input from the Mississippi River and advective transport may influence sedimentation on the seafloor in the DeSoto Canyon region, we conclude based on multidisciplinary evidence that the sedimentation pulse in late 2010 is the product of marine snow formation and is likely linked to the DWH discharge.

Single cell genomics indicates horizontal gene transfer and viral infections in a deep subsurface Firmicutes population - Labonte, Jessica M.; Field, Erin K.; Lau, Maggie; Chivian, Dylan; Van Heerden, Esta; Wommack, K. Eric; Kieft, Thomas L.; Onstott, Tullis C.; Stepanauskas, Ramunas (Frontiers in Microbiology, 2015)
A major fraction of Earth's prokaryotic biomass dwells in the deep subsurface, where cellular abundances per volume of sample are lower, metabolism is slower, and generation times are longer than those in surface terrestrial and marine environments. How these conditions impact biotic interactions and evolutionary processes is largely unknown. Here we employed single cell genomics to analyze cell-to-cell genome content variability and signatures of horizontal gene transfer (HGT) and viral infections in five cells of Candidatus Desulforudis audaxviator, which were collected from a three km-deep fracture water in the 2.9 Ga-old Witwatersrand Basin of South Africa. Between 0 and 32 % of genes recovered from single cells were not present in the original, metagenomic assembly of Desulforudis, which was obtained from a neighboring subsurface fracture. We found a transposable prophage, a retron, multiple clustered regularly interspaced short palindromic repeats (CRISPRs) and restriction-modification systems, and an unusually high frequency of transposases in the analyzed single cell genomes. This indicates that recombination, HGT and viral infections are prevalent evolutionary events in the studied population of microorganisms inhabiting a highly stable deep subsurface environment.
PT: J; TC: 0; UT: WOS:000352551600004

South Asian monsoon history over the past 60 kyr recorded by radiogenic isotopes and clay mineral assemblages in the Andaman Sea - Ali, Sajid; Hathorne, Ed C.; Frank, Martin; Gebregiorgis, Daniel; Stattegger, Karl; Stumpf, Roland; Kutterolf, Steffen; Johnson, Joel E.; Giosan, Liviu (Geochemistry, Geophysics, Geosystems, 2015)
The Late Quaternary variability of the South Asian (or Indian) monsoon has been linked with glacial-interglacial and millennial scale climatic changes but past rainfall intensity in the river catchments draining into the Andaman Sea remains poorly constrained. Here we use radiogenic Sr, Nd, and Pb isotope compositions of the detrital clay-size fraction and clay mineral assemblages obtained from sediment core NGHP Site 17 in the Andaman Sea to reconstruct the variability of the South Asian monsoon during the past 60 kyr. Over this time interval εNd values changed little, generally oscillating between −7.3 and −5.3 and the Pb isotope signatures are essentially invariable, which is in contrast to a record located further northeast in the Andaman Sea. This indicates that the source of the detrital clays did not change significantly during the last glacial and deglaciation suggesting the monsoon was spatially stable. The most likely source region is the Irrawaddy river catchment including the Indo-Burman Ranges with a possible minor contribution from the Andaman Islands. High smectite/(illite + chlorite) ratios (up to 14), as well as low 87Sr/86Sr ratios (0.711) for the Holocene period indicate enhanced chemical weathering and a stronger South Asian monsoon compared to marine oxygen isotope stages 2 and 3. Short, smectite-poor intervals exhibit markedly radiogenic Sr isotope compositions and document weakening of the South Asian monsoon, which may have been linked to short-term northern Atlantic climate variability on millennial time scales.

Spatial Variation in the Origin of Dissolved Organic Carbon in Snow on the Juneau Icefield, Southeast Alaska - Fellman, Jason B.; Hood, Eran; Raymond, Peter A.; Stubbins, Aron; Spencer, Robert G.M. (Environmental Science & Technology, 2015)
Dissolved organic carbon (DOC) plays a fundamental role in the biogeochemistry of glacier ecosystems. However, the specific sources of glacier DOC remain unresolved. To assess the origin and nature of glacier DOC, we collected snow from 10 locations along a transect across the Juneau Icefield, Alaska extending from the coast toward the interior. The Δ14C-DOC of snow varied from −743 to −420‰ showing progressive depletion across the Icefield as δ18O of water became more depleted (R2 = 0.56). Older DOC corresponded to lower DOC concentrations in snow (R2 = 0.31) and a decrease in percent humic-like fluorescence (R2 = 0.36), indicating an overall decrease in modern DOC across the Icefield. Carbon isotopic signatures (13C and 14C) combined with a three-source mixing model showed that DOC deposited in snow across the Icefield reflects fossil fuel combustion products (43–73%) and to a lesser extent marine (21–41%) and terrestrial sources (1–26%). Our finding that combustion aerosols are a large source of DOC to the glacier ecosystem during the early spring (April–May) together with the pronounced rates of glacier melting in the region suggests that the delivery of relic DOC to the ocean may be increasing and consequently impacting the biogeochemistry of glacial and proglacial ecosystems in unanticipated ways.

A warm and poorly ventilated deep Arctic Mediterranean during the last glacial period - Thornalley, D. J. R.; Bauch, H. A.; Gebbie, G.; Guo, W.; Ziegler, M.; Bernasconi, S. M.; Barker, S.; Skinner, L. C.; Yu, J. (Science, 2015)
Changes in the formation of dense water in the Arctic Ocean and Nordic Seas [the “Arctic Mediterranean” (AM)] probably contributed to the altered climate of the last glacial period. We examined past changes in AM circulation by reconstructing radiocarbon ventilation ages of the deep Nordic Seas over the past 30,000 years. Our results show that the glacial deep AM was extremely poorly ventilated (ventilation ages of up to 10,000 years). Subsequent episodic overflow of aged water into the mid-depth North Atlantic occurred during deglaciation. Proxy data also suggest that the deep glacial AM was ~2° to 3°C warmer than modern temperatures; deglacial mixing of the deep AM with the upper ocean thus potentially contributed to the melting of sea ice, icebergs, and terminal ice-sheet margins.

Adélie penguin dietary remains reveal Holocene environmental changes in the western Ross Sea (Antarctica) - Lorenzini, Sandra; Baroni, Carlo; Baneschi, Ilaria; Salvatore, Maria Cristina; Fallick, Anthony E.; Hall, Brenda L. (Palaeogeography, Palaeoclimatology, Palaeoecology, 2014)
Carbon and nitrogen stable isotope analyses were performed on modern and Holocene Adélie penguin guano samples collected from ornithogenic soils along the Scott Coast (Southern Victoria Land, Antarctica), from Cape Irizar to Dunlop Island, and at Cape Bird (Ross Island). Guano samples also were sieved and sorted under stereomicroscope in order to select penguin dietary remains, such as fish bones and otoliths. Carbon and nitrogen stable isotope composition, coupled with the taxonomic identification of fish otoliths from Scott Coast Holocene samples, indicated a mainly fish-based diet for this area, with Pleuragramma antarcticum as the most eaten prey throughout the investigated period (from 390 cal BP to ca 7300 cal BP). The isotopic values of Ross Island samples (from modern to 3850 cal BP) showed a krill consumption increase in the samples younger than 2000 cal BP, with the maximum in modern samples. Scott Coast and Ross Island Holocene samples showed δ13C and δ15N trends similar to those previously published from Terra Nova Bay (northern Victoria Land), whereas modern samples from Ross Island have similar δ15N composition but different δ13C values. This δ13C divergence started at ca 2000 BP and follows the abandonment of the Scott Coast colonies. The δ13C trend observed in Ross Island and Terra Nova Bay samples and the abandonment of the Scott Coast colonies could suggest the stability and the persistence of the previous oceanographic conditions (i.e. polynya) for the Terra Nova Bay area and the establishment of new conditions for water circulation in the Southern Ross Sea since ~ 2000 BP when persistent sea-ice sealed the Scott Coast.
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Carbonation rates of peridotite in the Samail Ophiolite, Sultanate of Oman, constrained through 14C dating and stable isotopes - Mervine, Evelyn M.; Humphris, Susan E.; Sims, Kenneth W. W.; Kelemen, Peter B.; W. J. Jenkins (Geochimica et Cosmochimica Acta, 2014)
Detailed 14C dating as well as stable C and O isotope analyses were conducted on carbonates formed during alteration of the peridotite layer of the Samail Ophiolite, Sultanate of Oman. 14C results obtained in this and previous studies indicate that surface travertines range in age from modern to >45,000 yr BP, indicating long-term deposition and preservation. Travertine deposition rates in two localities were ∼0.1 to 0.3 mm/yr between ∼30,000 and 45,000 yr BP. Using an estimate of total travertine area, this would result in a maximum of ∼1000 to 3000 m3/yr of travertine being deposited throughout the ophiolite during this time period. This travertine deposition would have sequestered a maximum of ∼1 to 3 × 106 kg CO2/yr. Ca-rich carbonate veins that are associated with the surface travertine deposits have ages ranging from ∼4000 to 36,000 yr BP (average: 15,000 yr BP). Mg-rich carbonate veins exposed in outcrops have ages ranging from ∼8000 to 45,000 yr BP (average: 35,000 yr BP). Detailed sampling from numerous locations (3 locations in this study and 10 locations in the previous studies) indicates that no carbonate veins from the natural peridotite weathering surface are older than the ∼50,000 yr BP dating limit of 14C. However, 14C dating of Mg-rich carbonate veins from three roadcut exposures (Qafeefah, Fanja, and Al-Wuqbah) indicates that a significant number of roadcut veins are 14C dead (>50,000 yr BP). A location weighted average indicates that ∼40% of veins sampled at the three roadcuts are 14C dead. An average including veins sampled at both roadcuts and outcrops indicates that overall ∼8% of Mg-rich carbonate veins are 14C dead. Mg-rich carbonate veins are estimated to sequester on the order of 107 kg CO2/yr throughout the ophiolite.

Centennial-to-millennial hydrologic trends and variability along the North Atlantic Coast, USA, during the Holocene - Newby, Paige E.; Shuman, Bryan N.; Donnelly, Jeffrey P.; Karnauskas, Kristopher B.; Marsicek, Jeremiah (Geophysical Research Letters, 2014)
Geophysical and sedimentary records from five lakes in Massachusetts reveal regionally coherent hydrologic variability during the Holocene. All of the lakes have risen since ~9.0 ka, but multicentury droughts after 5.6 ka repeatedly lowered their water levels. Quantified water level histories from the three best-studied lakes share >70% of their reconstructed variance. Four prominent low-water phases at 4.9–4.6, 4.2–3.9, 2.9–2.1, and 1.3–1.2 ka were synchronous across coastal lakes, even after accounting for age uncertainties. The droughts also affected sites up to ~200 km inland, but water level changes at 5.6–4.9 ka appear out of phase between inland and coastal lakes. During the enhanced multicentury variability after ~5.6 ka, droughts coincided with cooling in Greenland and may indicate circulation changes across the North Atlantic region. Overall, the records demonstrate that current water levels are exceptionally high and confirm the sensitivity of water resources in the northeast U.S. to climate change.

Composition and origin of authigenic carbonates in the Krishna-Godavari and Mahanadi Basins, eastern continental margin of India - Teichert, B. M. A.; Johnson, J. E.; Solomon, E. A.; Giosan, L.; Rose, K.; Kocherla, M.; Connolly, E. C.; Torres, M. E. (Marine and Petroleum Geology, 2014)
The mineralogical and stable isotopic composition of authigenic carbonates from the Krishna-Godavari (KG) and Mahanadi Basin provide a deeper insight into the processes inducing carbonate formation in the sediments of the eastern continental margin of India in the Bay of Bengal. Authigenic carbonate cements, (micro) nodules, bioturbation casts and tubes from 12 core locations drilled during the Indian National Gas Hydrate Program (NGHP) Expedition 01 were investigated for this study. Three main processes responsible for authigenic carbonate precipitation are identified: organoclastic sulfate reduction, anaerobic oxidation of methane and methanogenesis. Evidence of vigorous methane seepage is indicated in carbonates recovered at Sites 7, 10, 12 (KG Basin) and 19 (Mahanadi Basin). These methane-derived carbonates display typical paragenetic carbonate mineralogies (aragonite, high-Mg calcite with >15 Mol% MgCO3, Ca-rich dolomite). Two separate horizons of methane derived-carbonates are correlated between 4 drill holes (up to ∼16 km apart). The upper horizon has been dated with 14C (40,100 – 51,600 a B.P. 1950) clearly indicating that methane seepage has been much more vigorous in the past possibly due to a glacial sea level lowstand.
AAy4wyTimes Cited:5Cited References Count:63

A continuous multi-millennial record of surficial bivalve mollusk shells from the São Paulo Bight, Brazilian shelf - Dexter, Troy A.; Kaufman, Darrell S.; Krause Jr, Richard A.; Barbour Wood, Susan L.; Simões, Marcello G.; Huntley, John Warren; Yanes, Yurena; Romanek, Christopher S.; Kowalewski, Michał (Quaternary Research, 2014)
To evaluate the potential of using surficial shell accumulations for paleoenvironmental studies, an extensive time series of individually dated specimens of the marine infaunal bivalve mollusk Semele casali was assembled using amino acid racemization (AAR) ratios (n = 270) calibrated against radiocarbon ages (n = 32). The shells were collected from surface sediments at multiple sites across a sediment-starved shelf in the shallow sub-tropical São Paulo Bight (São Paulo State, Brazil). The resulting 14C-calibrated AAR time series, one of the largest AAR datasets compiled to date, ranges from modern to 10,307 cal yr BP, is right skewed, and represents a remarkably complete time series: the completeness of the Holocene record is 66% at 250-yr binning resolution and 81% at 500-yr binning resolution. Extensive time-averaging is observed for all sites across the sampled bathymetric range indicating long water depth-invariant survival of carbonate shells at the sediment surface with low net sedimentation rates. Benthic organisms collected from active depositional surfaces can provide multi-millennial time series of biomineral records and serve as a source of geochemical proxy data for reconstructing environmental and climatic trends throughout the Holocene at centennial resolution. Surface sediments can contain time-rich shell accumulations that record the entire Holocene, not just the present.

Cryostratigraphy and Permafrost Evolution in the Lacustrine Lowlands of West-Central Alaska - Kanevskiy, Mikhail; Jorgenson, Torre; Shur, Yuri; O'Donnell, Jonathan A.; Harden, Jennifer W.; Zhuang, Qianlai; Fortier, Daniel (Permafrost and Periglacial Processes, 2014)
The influence of permafrost growth and thaw on the evolution of ice-rich lowland terrain in the Koyukuk-Innoko region of interior Alaska is fundamental but poorly understood. To elucidate this influence, the cryostratigraphy and properties of perennially frozen sediments from three areas in this region are described and interpreted in terms of permafrost history. The upper part of the late Quaternary sediments at the Koyukuk and Innoko Flats comprise frozen organic soils up to 4.5 m thick underlain by ice-rich silt characterised by layered and reticulate cryostructures. The volume of visible segregated ice in silt locally reaches 50 per cent, with ice lenses up to 10 cm thick. A conceptual model of terrain evolution from the Late Pleistocene to the present day identifies four stages of yedoma degradation and five stages of subsequent permafrost aggradation-degradation: (1) partial thawing of the upper ice wedges and the formation of small shallow ponds in the troughs above the wedges; (2) formation of shallow thermokarst lakes above the polygons; (3) deepening of thermokarst lakes and yedoma degradation beneath the lakes; (4) complete thawing of yedoma beneath the lakes; (5) lake drainage; (6) peat accumulation; (7) permafrost aggradation in drained lake basins; (8) formation of permafrost plateaus; and (9) formation and expansion of a new generation of thermokarst features. These stages can occur in differing places and times, creating a highly complex mosaic of terrain conditions, complicating predictions of landscape response to future climatic changes or human impact. Copyright © 2014 John Wiley & Sons, Ltd.

Deciphering microbial carbon substrates in PAH contaminated sediments using phospholipid fatty acids, and compound specific δ13C and Δ14C - Morrill, Penny L.; Szponar, Natalie; Johnston, Mathew; Marvin, Chris; Slater, Gregory F. (Organic Geochemistry, 2014)
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.

A depth refugium from catastrophic coral bleaching prevents regional extinction - Smith, Tyler B.; Glynn, Peter W.; é, Juan L.; Toth, Lauren T.; Gyory, Joanna (Ecology, 2014)
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.
Keywords: Coral bleaching; Coral mortality; Depth refuge; Eastern Tropical Pacific; El Nino-Southern Oscillation; Extinction; Holocene; Millepora; Refuge

Diverse rupture modes for surface-deforming upper-plate earthquakes in the southern Puget Lowland of Washington State - Nelson, Alan R.; Personius, Stephen F.; Sherrod, Brian L.; Kelsey, Harvey M.; Johnson, Samuel Y.; Bradley, Lee-Ann; Wells, Ray E. (Geosphere, 2014)
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.

Glacial to deglacial ventilation and productivity changes in the southern Okhotsk Sea - Okazaki, Yusuke; Kimoto, Katsunori; Asahi, Hirofumi; Sato, Miyako; Nakamura, Yuriko; Harada, Naomi (Palaeogeography, Palaeoclimatology, Palaeoecology, 2014)
As a source region of North Pacific Intermediate Water, the Okhotsk Sea plays an important role in the ventilation of the North Pacific. To understand the detailed oceanographic changes in this marginal sea since the last glaciation, we studied decadal to centennial scale proxy records from new sediment cores from the southwestern Okhotsk Sea. Glacial to Holocene Δ14C records of benthic foraminiferal shells suggested enhanced ventilation in the Okhotsk Sea during the early deglacial period between 18 and 15 ka, corresponding to Heinrich Event 1. Although the Δ14C reconstruction has considerable uncertainties, the Okhotsk Sea may have acted as a source for vigorous ventilation of the subarctic Pacific during this period. CaCO3 preservation events appear to be better explained by the ventilation history of the Okhotsk Sea than by coccolithophores and foraminifera production. CaCO3 preservation started to improve during 18 to 15 ka, and pronounced peaks in the CaCO3 content corresponded to the Bølling–Allerød (15 to 13 ka) and Preboreal (11.5 to 10 ka) warm periods. Diatom and coccolithophore productivity remained low in the Okhotsk Sea throughout the glacial to deglacial periods, different from the situation in the open subarctic Pacific, where high productivity was observed during the Bølling–Allerød period. After the Preboreal period, biogenic opal gradually increased and δ15N decreased in the southern Okhotsk Sea, suggesting that productivity was enhanced by a relaxation of the nitrate limitation.
Keywords: Glacial–deglacial change; Okhotsk Sea; productivity; ventilation

Hidden cycle of dissolved organic carbon in the deep ocean - Follett, Christopher L.; Repeta, Daniel J.; Rothman, Daniel H.; Xu, Li; Santinelli, Chiara (Proceedings of the National Academy of Sciences, 2014)
Marine dissolved organic carbon (DOC) is a large (660 Pg C) reactive carbon reservoir that mediates the oceanic microbial food web and interacts with climate on both short and long timescales. Carbon isotopic content provides information on the DOC source via [Formula: see text]C and age via [Formula: see text]C. Bulk isotope measurements suggest a microbially sourced DOC reservoir with two distinct components of differing radiocarbon age. However, such measurements cannot determine internal dynamics and fluxes. Here we analyze serial oxidation experiments to quantify the isotopic diversity of DOC at an oligotrophic site in the central Pacific Ocean. Our results show diversity in both stable and radio isotopes at all depths, confirming DOC cycling hidden within bulk analyses. We confirm the presence of isotopically enriched, modern DOC cocycling with an isotopically depleted older fraction in the upper ocean. However, our results show that up to 30% of the deep DOC reservoir is modern and supported by a 1 Pg/y carbon flux, which is 10 times higher than inferred from bulk isotope measurements. Isotopically depleted material turns over at an apparent time scale of 30,000 y, which is far slower than indicated by bulk isotope measurements. These results are consistent with global DOC measurements and explain both the fluctuations in deep DOC concentration and the anomalous radiocarbon values of DOC in the Southern Ocean. Collectively these results provide an unprecedented view of the ways in which DOC moves through the marine carbon cycle.
Keywords: Carbon cycle; carbon isotopes; dissolved organic carbon; Oceanography; radiocarbon

The high-supply, current-dominated continental margin of southeastern South America during the late Quaternary - Lantzsch, Hendrik; Hanebuth, Till J. J.; Chiessi, Cristiano M.; Schwenk, Tilmann; Violante, Roberto A. (Quaternary Research, 2014)
The continental margin off the La Plata Estuary (SE South America) is characterized by high fluvial sediment supply and strong ocean currents. High-resolution sediment-acoustic data combined with sedimentary facies analysis, AMS-14C ages, and neodymium isotopic data allowed us to reconstruct late Quaternary sedimentary dynamics in relation to the two major sediment sources, the La Plata Estuary and the Argentine margin. Sediments from these two provinces show completely different dispersal patterns. We show that the northward-trending La Plata paleo-valley was the sole transit path for the huge volumes of fluvial material during lower sea levels. In contrast, material from the Argentine margin sector was transported northwards by the strong current system. Despite the large sediment volumes supplied by both sources, wide parts of the shelf were characterized by either persistent non-deposition or local short-term depocenter formation. The location and formation history of these depocenters were primarily controlled by the interplay of sea level with current strength and local morphology. The high sediment supply was of secondary importance to the stratigraphic construction, though locally resulting in high sedimentation rates. Thus, the shelf system off the La Plata Estuary can be considered as a hydrodynamic-controlled end-member.

Holocene earthquakes and right-lateral slip on the left-lateral Darrington-Devils Mountain fault zone, northern Puget Sound, Washington - Personius, S. F.; Briggs, R. W.; Nelson, A. R.; Schermer, E. R.; Maharrey, J. Z.; Sherrod, B. L.; Spaulding, S. A.; Bradley, L.-A. (Geosphere, 2014)
Sources of seismic hazard in the Puget Sound region of northwestern Washington include deep earthquakes associated with the Cascadia subduction zone, and shallow earthquakes associated with some of the numerous crustal (upper-plate) faults that crisscross the region. Our paleoseismic investigations on one of the more prominent crustal faults, the Darrington–Devils Mountain fault zone, included trenching of fault scarps developed on latest Pleistocene glacial sediments and analysis of cores from an adjacent wetland near Lake Creek, 14 km southeast of Mount Vernon, Washington. Trench excavations revealed evidence of a single earthquake, radiocarbon dated to ca. 2 ka, but extensive burrowing and root mixing of sediments within 50–100 cm of the ground surface may have destroyed evidence of other earthquakes. Cores in a small wetland adjacent to our trench site provided stratigraphic evidence (formation of a laterally extensive, prograding wedge of hillslope colluvium) of an earthquake ca. 2 ka, which we interpret to be the same earthquake documented in the trenches. A similar colluvial wedge lower in the wetland section provides possible evidence for a second earthquake dated to ca. 8 ka. Three-dimensional trenching techniques revealed evidence for 2.2 ± 1.1 m of right-lateral offset of a glacial outwash channel margin, and 45–70 cm of north-side-up vertical separation across the fault zone. These offsets indicate a net slip vector of 2.3 ± 1.1 m, plunging 14° west on a 286°-striking, 90°-dipping fault plane. The dominant right-lateral sense of slip is supported by the presence of numerous Riedel R shears preserved in two of our trenches, and probable right-lateral offset of a distinctive bedrock fault zone in a third trench. Holocene north-side-up, right-lateral oblique slip is opposite the south-side-up, left-lateral oblique sense of slip inferred from geologic mapping of Eocene and older rocks along the fault zone. The cause of this slip reversal is unknown but may be related to clockwise rotation of the Darrington–Devils Mountain fault zone into a position more favorable to right-lateral slip in the modern N-S compressional stress field.

Holocene glacier history of the Lago Argentino basin, Southern Patagonian Icefield - Strelin, Jorge A.; Kaplan, Michael R.; Vandergoes, Marcus J.; Denton, George H.; Schaefer, Joerg M. (Quaternary Science Reviews, 2014)
We present new geomorphic, stratigraphic, and chronologic data for Holocene glacier fluctuations in the Lago Argentino basin on the eastern side of the southern Patagonian Andes. Chronologic control is based on 14C and surface-exposure 10Be dating. After the Lateglacial maximum at 13,000 cal yrs BP, the large ice lobes that filled the eastern reaches of Lago Argentino retreated and separated into individual outlet glaciers; this recession was interrupted only by a stillstand or minor readvance at 12,200 cal yrs BP. The eight largest of these individual outlet glaciers are, from north to south: Upsala, Agassiz, Onelli, Spegazzini, Mayo, Ameghino, Perito Moreno, and Grande (formerly Frías). Holocene recession of Upsala Glacier exposed Brazo Cristina more than 10,115 ± 100 cal yrs BP, and reached inboard of the Holocene moraines in Agassiz Este Valley by 9205 ± 85 cal yrs BP; ice remained in an inboard position until 7730 ± 50 cal yrs BP. Several subsequent glacier readvances are well documented for the Upsala and Frías glaciers. The Upsala Glacier readvanced at least seven times, the first being a relatively minor expansion – documented only in stratigraphic sections – between 7730 ± 50 and 7210 ± 45 cal yrs BP. The most extensive Holocene advances of Upsala Glacier resulted in the deposition of the Pearson 1 moraines and related landforms, which are divided into three systems. The Pearson 1a advance occurred about 6000–5000 cal yrs BP and was followed by the slightly less-extensive Pearson 1b and 1c advances dated to 2500–2000 and 1500–1100 cal yrs BP, respectively. Subsequent advances of Upsala Glacier resulted in deposition of the Pearson 2 moraines and corresponding landforms, also separated into three systems, Pearson 2a, 2b, and 2c, constructed respectively at ∼700, >400, and <300 cal yrs BP to the early 20th century. Similar advances are also recorded by moraine systems in front of Grande Glacier and herein separated into the Frías 1 and Frías 2a, 2b, and 2c. The Onelli and Ameghino glacier valleys also preserve older Holocene moraines. In the Agassiz, Spegazzini, and Mayo valleys, ice of the late-Holocene advances appears to have overridden landforms equivalent in age to Pearson 1. Perito Moreno Glacier is an extreme case in which ice of historical (Pearson 2c) advances overrode all older Holocene moraines. Based on the distribution and number of moraines preserved, we infer that the response to climate differed among the Lago Argentino outlet glaciers during the Holocene. This led us to examine the effects of climatic and non-climatic factors on individual glaciers. As a consequence, we detected an important effect of the valley geometry (hypsometry) on the timing and magnitude of glacier response to climate change. These results indicate that caution is needed in correlating moraines among glacier forefields without firm morpho-stratigraphic and age control. Finally, we note important similarities and differences between the overall moraine chronology in the Lago Argentino basin and that in other areas of southern South America and elsewhere in the Southern Hemisphere.

Holocene sea-surface temperature variability in the Chilean fjord region - Caniupán, Magaly; Lamy, Frank; Lange, Carina B.; Kaiser, Jérôme; Kilian, Rolf; Arz, Helge W.; León, Tania; Mollenhauer, Gesine; Sandoval, Susana; De Pol-Holz, Ricardo; Pantoja, Silvio; Wellner, Julia; et al. (Quaternary Research, 2014)
Here we provide three new Holocene (11–0 cal ka BP) alkenone-derived sea surface temperature (SST) records from the southernmost Chilean fjord region (50–53°S). SST estimates may be biased towards summer temperature in this region, as revealed by a large set of surface sediments. The Holocene records show consistently warmer than present-day SSTs except for the past ~ 0.6 cal ka BP. However, they do not exhibit an early Holocene temperature optimum as registered further north off Chile and in Antarctica. This may have resulted from a combination of factors including decreased inflow of warmer open marine waters due to lower sea-level stands, enhanced advection of colder and fresher inner fjord waters, and stronger westerly winds. During the mid-Holocene, pronounced short-term variations of up to 2.5°C and a cooling centered at ~ 5 cal ka BP, which coincides with the first Neoglacial glacier advance in the Southern Andes, are recorded. The latest Holocene is characterized by two pronounced cold events centered at ~ 0.6 and 0.25 cal ka BP, i.e., during the Little Ice Age. These cold events have lower amplitudes in the offshore records, suggesting an amplification of the SST signal in the inner fjords.

Mid- to Late-Holocene Australian–Indonesian summer monsoon variability - Steinke, Stephan; Mohtadi, Mahyar; Prange, Matthias; Varma, Vidya; Pittauerova, Daniela; Fischer, Helmut W. (Quaternary Science Reviews, 2014)
The Australian–Indonesian monsoon has a governing influence on the agricultural practices and livelihood in the highly populated islands of Indonesia. However, little is known about the factors that have influenced past monsoon activity in southern Indonesia. Here, we present a ∼6000 years high-resolution record of Australian-Indonesian summer monsoon (AISM) rainfall variations based on bulk sediment element analysis in a sediment archive retrieved offshore northwest Sumba Island (Indonesia). The record suggests lower riverine detrital supply and hence weaker AISM rainfall between 6000 yr BP and ∼3000 yr BP compared to the Late Holocene. We find a distinct shift in terrigenous sediment supply at around 2800 yr BP indicating a reorganization of the AISM from a drier Mid Holocene to a wetter Late Holocene in southern Indonesia. The abrupt increase in rainfall at around 2800 yr BP coincides with a grand solar minimum. An increase in southern Indonesian rainfall in response to a solar minimum is consistent with climate model simulations that provide a possible explanation of the underlying mechanism responsible for the monsoonal shift. We conclude that variations in solar activity play a significant role in monsoonal rainfall variability at multi-decadal and longer timescales. The combined effect of orbital and solar forcing explains important details in the temporal evolution of AISM rainfall during the last 6000 years. By contrast, we find neither evidence for volcanic forcing of AISM variability nor for a control by long-term variations in the El Niño-Southern Oscillation (ENSO).

North Atlantic forcing of tropical Indian Ocean climate - Mohtadi, Mahyar; Prange, Matthias; Oppo, Delia W.; De Pol-Holz, Ricardo; Merkel, Ute; Zhang, Xiao; Steinke, Stephan; ückge, Andreas (Nature, 2014)
The response of the tropical climate in the Indian Ocean realm to abrupt climate change events in the North Atlantic Ocean is contentious. Repositioning of the intertropical convergence zone is thought to have been responsible for changes in tropical hydroclimate during North Atlantic cold spells1, 2, 3, 4, 5, but the dearth of high-resolution records outside the monsoon realm in the Indian Ocean precludes a full understanding of this remote relationship and its underlying mechanisms. Here we show that slowdowns of the Atlantic meridional overturning circulation during Heinrich stadials and the Younger Dryas stadial affected the tropical Indian Ocean hydroclimate through changes to the Hadley circulation including a southward shift in the rising branch (the intertropical convergence zone) and an overall weakening over the southern Indian Ocean. Our results are based on new, high-resolution sea surface temperature and seawater oxygen isotope records of well-dated sedimentary archives from the tropical eastern Indian Ocean for the past 45,000 years, combined with climate model simulations of Atlantic circulation slowdown under Marine Isotope Stages 2 and 3 boundary conditions. Similar conditions in the east and west of the basin rule out a zonal dipole structure as the dominant forcing of the tropical Indian Ocean hydroclimate of millennial-scale events. Results from our simulations and proxy data suggest dry conditions in the northern Indian Ocean realm and wet and warm conditions in the southern realm during North Atlantic cold spells.
Keywords: Palaeoceanography; Palaeoclimate

Organic matter transformation in the peat column at Marcell Experimental Forest: Humification and vertical stratification - Tfaily, Malak M.; Cooper, William T.; Kostka, Joel E.; Chanton, Patrick R.; Schadt, Christopher W.; Hanson, Paul J.; Iversen, Colleen M.; Chanton, Jeffrey P. (JOURNAL OF GEOPHYSICAL RESEARCH-BIOGEOSCIENCES, 2014)
We characterized peat decomposition at the Marcell Experimental Forest (MEF), Minnesota, USA, to a depth of 2m to ascertain the underlying chemical changes using Fourier transform infrared (FT IR) and C-13 nuclear magnetic resonance (NMR) spectroscopy) and related these changes to decomposition proxies C:N ratio, C-13 and N-15, bulk density, and water content. FT IR determined that peat humification increased rapidly between 30 and 75cm, indicating a highly reactive intermediate-depth zone consistent with changes in C:N ratio, C-13 and N-15, bulk density, and water content. Peat decomposition at the MEF, especially in the intermediate-depth zone, is mainly characterized by preferential utilization of O-alkyl-C, carboxyl-C, and other oxygenated functionalities with a concomitant increase in the abundance of alkyl- and nitrogen-containing compounds. Below 75cm, less change was observed but aromatic functionalities and lignin accumulated with depth. Significant correlations with humification indices, identified by FT IR spectroscopy, were found for C:N ratios. Incubation studies at 22 degrees C revealed the highest methane production rates, greatest CH4:CO2 production ratios, and significant O-alkyl-C utilization within this 30 and 75cm zone. Oxygen-containing functionalities, especially O-alkyl-C, appear to serve as excellent proxies for soil decomposition rate and should be a sensitive indicator of the response of the solid phase peat to increased temperatures caused by climate change and the field study manipulations that are planned to occur at this site. Radiocarbon signatures of microbial respiration products in deeper pore waters at the MEF resembled the signatures of more modern dissolved organic carbon rather than solid phase peat, indicating that recently photosynthesized organic matter fueled the bulk of subsurface microbial respiration. These results indicate that carbon cycling at depth at the MEF is not isolated from surface processes.
Keywords: FT-IR spectroscopy; humification; NMR spectroscopy; organic matter; peatlands; vertical stratification

Phylogeny and phylogeography of functional genes shared among seven terrestrial subsurface metagenomes reveal N-cycling and microbial evolutionary relationships - Lau, Maggie C. Y.; Cameron, Connor; Magnabosco, Cara; Brown, C. Titus; Schilkey, Faye; Grim, Sharon; Hendrickson, Sarah; Pullin, Michael; Lollar, Barbara Sherwood; Van Heerden, Esta; Kieft, Thomas L.; Onstott, Tullis C. (FRONTIERS IN MICROBIOLOGY, 2014)
Comparative studies on community phylogenetics and phylogeography of microorganisms living in extreme environments are rare. Terrestrial subsurface habitats are valuable for studying microbial biogeographical patterns due to their isolation and the restricted dispersal mechanisms. Since the taxonomic identity of a microorganism does not always correspond well with its functional role in a particular community, the use of taxonomic assignments or patterns may give limited inference on how microbial functions are affected by historical, geographical and environmental factors. With seven metagenomic libraries generated from fracture water samples collected from five South African mines, this study was carried out to (1) screen for ubiquitous functions or pathways of biogeochemical cycling of CH4, S, and N; (2) to characterize the biodiversity represented by the common functional genes; (3) to investigate the subsurface biogeography as revealed by this subset of genes; and (4) to explore the possibility of using metagenomic data for evolutionary study. The ubiquitous functional genes are NarV, NPD, PAPS reductase, NifH, NifD, NifK, NifE, and NifN genes. Although these eight common functional genes were taxonomically and phylogenetically diverse and distinct from each other, the dissimilarity between samples did not correlate strongly with geographical or environmental parameters or residence time of the water. Por genes homologous to those of Thermodesulfovibrio yellowstonii detected in all metagenomes were deep lineages of Nitrospirae, suggesting that subsurface habitats have preserved ancestral genetic signatures that inform the study of the origin and evolution of prokaryotes.
Keywords: evolution; functional genes; N-cycle; phylogenetics; phylogeny; phylogeography; terrestrial subsurface

Preferential burial of permafrost-derived organic carbon in Siberian-Arctic shelf waters - Vonk, Jorien E.; Semiletov, Igor P.; Dudarev, Oleg V.; Eglinton, Timothy I.; Andersson, August; Shakhova, Natalia; Charkin, Alexander; Heim, Birgit; Gustafsson, Örjan (JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS, 2014)
The rapidly changing East Siberian Arctic Shelf (ESAS) receives large amounts of terrestrial organic carbon (OC) from coastal erosion and Russian-Arctic rivers. Climate warming increases thawing of coastal Ice Complex Deposits (ICD) and can change both the amount of released OC, as well as its propensity to be converted to greenhouse gases (fueling further global warming) or to be buried in coastal sediments. This study aimed to unravel the susceptibility to degradation, and transport and dispersal patterns of OC delivered to the ESAS. Bulk and molecular radiocarbon analyses on surface particulate matter (PM), sinking PM and underlying surface sediments illustrate the active release of old OC from coastal permafrost. Molecular tracers for recalcitrant soil OC showed ages of 3.4-13 C-14-ky in surface PM and 5.5-18 C-14-ky in surface sediments. The age difference of these markers between surface PM and surface sediments is larger (i) in regions with low OC accumulation rates, suggesting a weaker exchange between water column and sediments, and (ii) with increasing distance from the Lena River, suggesting preferential settling of fluvially derived old OC nearshore. A dual-carbon end-member mixing model showed that (i) contemporary terrestrial OC is dispersed mainly by horizontal transport while being subject to active degradation, (ii) marine OC is most affected by vertical transport and also actively degraded in the water column, and (iii) OC from ICD settles rapidly and dominates surface sediments. Preferential burial of ICD-OC released into ESAS coastal waters might therefore lower the suggested carbon cycle climate feedback from thawing ICD permafrost.
Keywords: biomarkers; carbon; permafrost; radiocarbon

Recent unprecedented warming and oligotrophy of the eastern Mediterranean Sea within the last millennium - Sisma-Ventura, Guy; Yam, Ruth; Shemesh, Aldo (Geophysical Research Letters, 2014)
The Mediterranean region is a climatic transitional zone between the subtropical/monsoon regime and the temperate westerlies and is subject to forces acting upon the global climate system. Much knowledge about its climate over the last millennium is derived from terrestrial records, whereas changes in sea surface temperatures (SSTs) and in the dissolved inorganic carbon pool (DIC) are poorly known. We present continuous high-resolution reconstructions of SST and δ13CDIC in the eastern Mediterranean (EM) Sea, as inferred from oxygen and carbon isotope records from the skeletons of the reef builder gastropod Dendropoma sp. Spanning the past millennium, the SST reconstruction reveals a 250 year persistent warming trend during which the twentieth century was the warmest on record. Coupled with a distinct trend of 13CDIC depletion and superimposed upon decreased primary production, this climate reconstruction reflects a new state of the EM over the Anthropocene era that exceeds the natural variability of the last millennium.

Seafloor fault ruptures along the North Anatolia Fault in the Marmara Sea, Turkey: Link with the adjacent basin turbidite record - McHugh, Cecilia M. G.; Braudy, Nicole; Çağatay, M. Namik; Sorlien, Christopher; Cormier, Marie-Helene; Seeber, Leonardo; Henry, Pierre (Marine Geology, 2014)
The relation between seafloor fault ruptures and the generation of turbidity currents was investigated to better understand the structural growth of tectonic basins with direct implications for earthquake hazard assessment. This study focuses on the Holocene earthquake record of transtensional basins in the Marmara Sea, Turkey, that are associated with the North Anatolian Fault system. The physical and chemical composition of three 10 m-long cores recovered from the Central Basin was studied at high-resolution and turbidite–homogenite units were identified. Turbidite–homogenite units (T–H units) are complex deposits that consist of a sharp basal contact and multiple fining upward beds of sand to coarse silt, above. All are capped by a 25 cm to 75 cm thick layer of medium to fine silt. A chronology developed from radiocarbon and short-lived radioisotopes allowed the correlation of these T–H units to the historical record of earthquakes that in Turkey goes back 2000 years. We found that the best location to recover the most complete sedimentation record is in the deepest part of a basin or “depocenter” where T–H units constitute ~ 80% of the sediments. A very good correlation was established between T–H units in Central Basin and proximal inferred historic epicentres along the central Marmara segment of the North Anatolia Fault that occurred in 1343, 860, 740, and 557 AD, and two more distal earthquakes that occurred in 268 and 1963 (or possibly1964). These sedimentation events can then be referred to as “seismo-turbidites”. The results when compared to findings from other transform basins in Marmara Sea reveal a very good correlation between T–H units and historic ruptures. Most importantly, there is a strong correlation between the inferred locations of historical earthquakes and the preservation of turbidite–homogenite units in the basin adjacent to the inferred rupture. The 740 AD earthquake correlates with T–H units in Izmit Gulf and Central Basin and could represent a multi-segment rupture of the NAF. Generally, T–H units appear to be clustered through the Holocene sections, suggesting temporal earthquake clustering in the Marmara Sea region. Such clustering may account for the lack of T–H units and hence large ruptures through the Central Basin since 1343.

Seasonal variability of organic matter composition in an Alaskan glacier outflow: insights into glacier carbon sources - Spencer, Robert G M; Vermilyea, Andrew; Fellman, Jason; Raymond, Peter; Stubbins, Aron; Scott, Durelle; Hood, Eran (Environmental Research Letters, 2014)
Glacier ecosystems are a significant source of bioavailable, yet ancient dissolved organic carbon (DOC). Characterizing DOC in Mendenhall Glacier out flow (southeast Alaska) we document a seasonal persistence to the radiocarbon-depleted signature of DOC, highlighting ancient DOC as a ubiquitous feature of glacier out flow. We observed no systematic depletion in Δ14C-DOC with increasing discharge during the melt season that would suggest mobilization of an aged subglacial carbon store. However, DOC concentration, δ13C-DOC,Δ14C-DOC and fluorescence signatures appear to have been in fluenced by runoff from vegetated hillslopes above the glacier during onset and senescence of melt. In the peak glacier melt period, the Δ 14 C-DOC of stream samples at the out flow (−181.7 to−355.3‰) was comparable to the Δ 14 C-DOC for snow samples from the accumulation zone (−207.2 to−390.9‰), suggesting that ancient DOC from the glacier surface is exported in glacier runoff. The pre-aged DOC in glacier snow and runoff is consistent with contributions from fossil fuel combustion sources similar to those documented previously in ice cores and thus provides evidence for anthropogenic perturbation of the carbon cycle. Overall, our results emphasize the need to further characterize DOC inputs to glacier ecosystems, particularly in light of predicted changes in glacier mass and runoff in the coming century.
Keywords: alaska; dissolved organic carbon; glacier; organic matter; radiocarbon

Source and biolability of ancient dissolved organic matter in glacier and lake ecosystems on the Tibetan Plateau - Spencer, Robert G.M.; Guo, Weidong; Raymond, Peter A.; Dittmar, Thorsten; Hood, Eran; Fellman, Jason; Stubbins, Aron (Geochimica et Cosmochimica Acta, 2014)
The Tibetan Plateau is the world’s largest and highest plateau and holds the largest mass of ice on Earth outside the ice-sheets of Greenland and Antarctica, as well as abundant lakes. This study examined the molecular and isotopic signatures of dissolved organic matter (DOM) along with its biolability in glacier ice, glacier-fed streams, and alpine lakes on the Tibetan Plateau. The aim was to assess the sources of DOM and the potential of DOM to provide a carbon subsidy to downstream ecosystems. Tibetan glaciers and glacier streams exhibited low dissolved organic carbon (DOC) concentrations (17.7–27.9 μM) and ancient DOC radiocarbon ages (749–2350 ybp). The optical properties, stable carbon isotope ratios (δ13C-DOC) and the molecular composition (Fourier transform ion cyclotron resonance mass spectrometry) of Tibetan glacier DOM are consistent with data from other glacier systems around the world. The geochemical signatures and the ancient apparent ages of Tibetan glacier DOM suggest a significant fraction is derived from the atmospheric deposition of pre-aged, possibly fossil fuel derived organics. Within the Tibetan alpine lakes, DOC was also ancient (525–675 ybp), due to either inputs of pre-aged organics from glacier runoff, direct deposition, or due to the aging of organics in situ (i.e. a radiocarbon reservoir effect). The glacier ice and glacier stream sites exhibited high biolability of DOC and so provide a carbon subsidy to downstream environments that will change as glaciers on the Tibetan Plateau recede.

Submarine Paleoseismology Along Populated Transform Boundaries: The Enriquillo-Plantain-Garden Fault, Canal du Sud, Haiti, and the North Anatolian Fault, Marmara Sea, Turkey - McHugh, Cecilia M. G.; Seeber, Leonardo; Cormier, Marie-Helene; Hornbach, Matthew (OCEANOGRAPHY, 2014)
Continental transform boundaries cross heavily populated regions and are associated with destructive earthquakes worldwide. The devastating 1999 Turkey earthquakes and the offshore 2010 Haiti earthquake emphasized the urgent need to study the submerged segments of continental transforms. In response, the rapidly evolving field of submarine paleoseismology is focusing its attention on understanding the relationships between sedimentation, seafloor ruptures, and earthquake recurrence intervals along submarine faults. In Canal du Sud, Haiti, the 2010 earthquake-triggered sedimentation events were documented from nearshore to the deep basin by measuring the excess Th-234 in sediment cores. This radioisotope, with a half-life of 24 days, tracked mass wasting, turbidites, turbidite-homogenite units, and a sediment plume that remained in the water column for at least two months after the earthquake. However, the turbidite units in Canal du Sud, Haiti, provide an incomplete record of the region's earthquake history, likely because sedimentation rates are too low for sedimentation events to be triggered by all earthquakes. In contrast, in the Marmara Sea basins, there is very good correlation between turbidites and the historical record of earthquakes dating back 2,000 years. The difference between these correlations is likely related to both sedimentation rates and particulars of the ruptures. Future research along the Enriquillo-Plantain-Garden fault in Haiti and along similar low sedimentation plate boundaries should focus on multiple fault segments in order to obtain complete earthquake recurrence histories.

Subsurface Evidence of Storm-Driven Breaching along a Transgressing Barrier System, Cape Cod, USA - Maio, Christopher V.; Gontz, Allen M.; Sullivan, Richard M.; Madsen, Stephanie M.; Weidman, Christopher R.; Donnelly, Jeffrey P. (JOURNAL OF COASTAL RESEARCH, 2014)
Relict and historic tidal channels buried within coastal barriers provide a geologic signature of environmental change, thus enhancing our understanding of how barrier systems respond to extreme storm events. Earliest maps from 1846 depict three inlets along the Waquoit Bay barrier system located on Cape Cod, Massachusetts. These channels were not depicted on maps after 1846, and we lack any information pertaining to them before 1846. The principle objective of this study was to identify the location and map the internal geometry and channel-fill configuration of the buried inlet structures using geophysical and sedimentological data acquisition methods. This was done by collecting 6.2 km of shoreparallel ground-penetrating radar data and five sediment cores ranging in depth from 4 to 5 m. The sediment cores allowed for the ground truthing of the ground-penetrating radar data and provided six samples for radiocarbon dating. The 13 paleochannels identified ranged in depths from 1.3 to 3.7 m below the present beach surface. These appeared in the radar imagery as broad U-shaped cut-and-fill features incised into adjacent barrier facies. The 13 paleochannels composed 24% of the barrier lithosome totaling 704 m in length. Individual channels were primarily less than 65 m in length and between 2.5 and 1.3 m in depth, although an additional 275-m-wide, 3.7-m-deep channel sequence was imaged and likely represents a major and long-lived paleochannel. The results will contribute toward deciphering the evolution of the Waquoit system and identify areas vulnerable to storm-driven coastal change.
Keywords: coastal change; Coastal evolution; ground-penetrating radar; marine transgression; overwash; paleochannel; paleogeography; South Cape Beach

Temporal and spatial distributions of cold-water corals in the Drake Passage: Insights from the last 35,000 years - Margolin, Andrew R.; Robinson, Laura F.; Burke, Andrea; Waller, Rhian G.; Scanlon, Kathryn M.; Roberts, Mark L.; Auro, Maureen E.; van de Flierdt, Tina (Deep Sea Research Part II: Topical Studies in Oceanography, 2014)
Scleractinian corals have a global distribution ranging from shallow tropical seas to the depths of the Southern Ocean. Although this distribution is indicative of the corals having a tolerance to a wide spectrum of environmental conditions, individual species seem to be restricted to a much narrower range of ecosystem variables. One way to ascertain the tolerances of corals, with particular focus on the potential impacts of changing climate, is to reconstruct their growth history across a range of environmental regimes. This study examines the spatial and temporal distribution of the solitary scleractinian corals Desmophyllum dianthus, Gardineria antarctica, Balanophyllia malouinensis, Caryophyllia spp. and Flabellum spp. from five sites in the Drake Passage which cross the major frontal zones. A rapid reconnaissance radiocarbon method, cooupled with U-Th dating, extends the age range back more than 100 thousand. Within this age range there are distinct changes in the temporal and spatial distributions of these corals, both with depth and latitude, and on millennial timescales. Two major patterns that emerge are: 1) D. dianthus populations show clear variability in their occurrence through time depending on the latitudinal position within the Drake Passage. North of the Subantarctic Front, D. dianthus first appears in the late deglaciation (~17,000 years ago) and persists to today. South of the Polar Front, in contrast, populations existed during the glacial and early deglacial periods, with only few modern occurrences. A seamount site between the two fronts exhibits characteristics similar to both the north and south sites. This shift across the frontal zones within one species cannot yet be fully explained, but it is likely to be linked to changes in surface productivity, subsurface oxygen concentrations, and carbonate saturation state. 2) at locations where multiple genera were dated, clear differences in age and depth distribution of the populations provide clear evidence that each genus has unique environmental requirements to sustain its population.
id: 2278

Timing and preservation mechanism of deglacial pteropod spike from the Andaman Sea, northeastern Indian Ocean - Sijinkumar, Adukkam V.; Nath, Bejugam N.; Guptha, Medimi V. S.; Ahmad, Syed M.; Rao, Bandaru R. (BOREAS, 2014)
The aragonite compensation depth (ACD) fluctuated considerably during the last glacial until the Holocene with a dominant pteropod preservation spike during the deglacial period, which is prominently seen in three well-dated cores covering the Andaman Sea, northeastern Indian Ocean. The precise time period of the preservation spike of pteropods is not known but this knowledge is crucial for stratigraphical correlation and also for understanding the driving mechanism. Isotopic and foraminiferal proxies were used to decipher the possible mechanism for pteropods preservation in the Andaman Sea. The poor preservation/absence of pteropods during the Holocene in the Andaman Sea may have implications for ocean acidification, driven by enhanced atmospheric CO2 concentration. Strengthening of the summer monsoon and the resultant high biological productivity may also have played a role in the poor preservation of pteropods. The deglacial pteropod spike is characterized by high abundance/preservation of the pteropods between approximate to 19 and 15cal. ka BP, associated with very low atmospheric CO2 concentration. Isotope data suggest the prevalence of a glacial environment with reduced sea surface temperature, upwelling and enhanced salinity during the pteropod preservation spike. Total planktic foraminifera and Globigerina bulloides abundances are low during this period, implying a weakened summer monsoon and reduced foraminiferal productivity. Based on the preservation record of pteropods, it is inferred that the ACD was probably deepest (>2900m) at 16.5cal. ka BP. The synchronous regional occurrence of the pteropod preservation spike in the Andaman Sea and in the northwestern Indian Ocean could potentially be employed as a stratigraphic marker.

Vertebral Bomb Radiocarbon Suggests Extreme Longevity in White Sharks - Hamady, Li Ling; Natanson, Lisa J.; Skomal, Gregory B.; Thorrold, Simon R. (Plos One, 2014)
Conservation and management efforts for white sharks (Carcharodon carcharias) remain hampered by a lack of basic demographic information including age and growth rates. Sharks are typically aged by counting growth bands sequentially deposited in their vertebrae, but the assumption of annual deposition of these band pairs requires testing. We compared radiocarbon (Delta C-14) values in vertebrae from four female and four male white sharks from the northwestern Atlantic Ocean (NWA) with reference chronologies documenting the marine uptake of C-14 produced by atmospheric testing of thermonuclear devices to generate the first radiocarbon age estimates for adult white sharks. Age estimates were up to 40 years old for the largest female (fork length [FL]: 526 cm) and 73 years old for the largest male (FL: 493 cm). Our results dramatically extend the maximum age and longevity of white sharks compared to earlier studies, hint at possible sexual dimorphism in growth rates, and raise concerns that white shark populations are considerably more sensitive to human-induced mortality than previously thought.
PT: J; TC: 0; UT: WOS:000329862500089

Anatomy of the La Jolla Submarine Canyon system; offshore southern California - Paull, C. K.; Caress, D. W.; Lundsten, E.; Gwiazda, R.; Anderson, K.; McGann, M.; Conrad, J.; Edwards, B.; Sumner, E. J. (Marine Geology, 2013)
An autonomous underwater vehicle (AUV) carrying a multibeam sonar and a chirp profiler was used to map sections of the seafloor within the La Jolla Canyon, offshore southern California, at sub-meter scales. Close-up observations and sampling were conducted during remotely operated vehicle (ROV) dives. Minisparker seismic-reflection profiles from a surface ship help to define the overall geometry of the La Jolla Canyon especially with respect to the pre-canyon host sediments. The floor of the axial channel is covered with unconsolidated sand similar to the sand on the shelf near the canyon head, lacks outcrops of the pre-canyon host strata, has an almost constant slope of 1.0° and is covered with trains of crescent shaped bedforms. The presence of modern plant material entombed within these sands confirms that the axial channel is presently active. The sand on the canyon floor liquefied during vibracore collection and flowed downslope, illustrating that the sediment filling the channel can easily fail even on this gentle slope. Data from the canyon walls help constrain the age of the canyon and extent of incision. Horizontal beds of moderately cohesive fine-grained sediments exposed on the steep canyon walls are consistently less than 1.232 million years old. The lateral continuity of seismic reflectors in minisparker profiles indicate that pre-canyon host strata extend uninterrupted from outside the canyon underneath some terraces within the canyon. Evidence of abandoned channels and point bar-like deposits are noticeably absent on the inside bend of channel meanders and in the subsurface of the terraces. While vibracores from the surface of terraces contain thin (
id: 2302

Assessing microbial carbon sources and potential PAH degradation using natural abundance 14C analysis - Mahmoudi, Nagissa; Fulthorpe, Roberta R.; Burns, Leanne; Mancini, Silvia; Slater, Greg F. (Environmental Pollution, 2013)
Natural abundance 14C analysis was applied to PLFAs collected from an industrial site in southern Ontario in order to assess microbial carbon sources and potential PAH biodegradation in soils. Δ14C of microbial phospholipid fatty acids (PLFA) at the site ranged from +54‰ to −697‰. Comparison of these values to surrounding carbon sources found that microbial carbon sources were derived primarily from vegetation and/or natural organic matter present in the soils rather than PAHs. This study highlights that microbes are able to utilize almost all available pools of organic matter including older pools which are thought to contain recalcitrant compounds. Furthermore, it shows that even with the presence of an active microbial community, there may be little biodegradation of PAHs. This study illustrates challenges in assessing microbial activity in the environment and the advantage of using natural abundance 14C analysis as a tool to elucidate microbial carbon sources.
id: 2268

Carbon isotopic characterization of hydrophobic dissolved organic carbon in rainwater - Avery Jr, G. Brooks; Biswas, K. Farhana; Mead, Ralph; Southwell, Melissa; Willey, Joan D.; Kieber, Robert J.; Mullaugh, Katherine M. (Atmospheric Environment, 2013)
The 14C and 13C content of the hydrophobic fraction (C18 extractable) of dissolved organic carbon (DOC) in Wilmington North Carolina USA rainwater was determined for six rain events to elucidate potential sources. A two end member mass-balance calculation indicated that 42–61% of the hydrophobic DOC was of fossil fuel origin compared to previously published values (4–24%) for bulk rain DOC indicating a strong anthropogenic contribution to the hydrophobic component. All fossil fuel derived organic carbon in the bulk DOC (∼15% fossil fuel derived) could be accounted for in the hydrophobic fraction (∼52% fossil fuel derived) which represents approximately 1/3 of the bulk DOC. The δ13C values of the hydrophobic DOC were consistent (−28.8 ± 0.9‰) similar to that for terrestrial and fossil fuel derived organic carbon. This is in contrast to previously published bulk rain DOC δ13C values that displayed a strong influence of air-mass back-trajectory with δ13C values ranging from −20.8‰ (typical of marine organic carbon) for marine air-mass back-trajectory rain to −28.2‰ (typical of terrestrial or fossil fuel derived organic carbon) for terrestrial air-mass back-trajectory rain. The combination of 14C and 13C isotopic data strongly suggests that a large fraction of hydrophobic organic material in rain comes from incompletely combusted fossil fuels. Changes in energy usage patterns and efforts to reduce fossil fuel emissions will alter the abundance of this hydrophobic material in the atmosphere which may impact the spectral distribution of sunlight reaching the earth's surface as well as the degree of oceanic primary productivity.
id: 2288

Carbon isotopic evidence for microbial control of carbon supply to Orca Basin at the seawater-brine interface - Shah, S. R.; Joye, S. B.; Brandes, J. A.; McNichol, A. P. (BIOGEOSCIENCES, 2013)
Orca Basin, an intraslope basin on the Texas-Louisiana continental slope, hosts a hypersaline, anoxic brine in its lowermost 200m in which limited microbial activity has been reported. This brine contains a large reservoir of reduced and aged carbon, and appears to be stable at decadal time scales: concentrations and isotopic composition of dissolved inorganic (DIC) and organic carbon (DOC) are similar to measurements made in the 1970s. Both DIC and DOC are more ``aged{''} within the brine pool than in overlying water, and the isotopic contrast between brine carbon and seawater carbon is much greater for DIC than DOC. While the stable carbon isotopic composition of brine DIC points towards a combination of methane and organic carbon remineralization as its source, radiocarbon and box model results point to the brine interface as the major source region for DIC, allowing for only limited oxidation of methane diffusing upwards from sediments. This conclusion is consistent with previous studies that identify the seawater-brine interface as the focus of microbial activity associated with Orca Basin brine. Isotopic similarities between DIC and DOC suggest a different relationship between these two carbon reservoirs than is typically observed in deep ocean basins. Radiocarbon values implicate the seawater-brine interface region as the likely source region for DOC to the brine as well as DIC.

Environmental isotopes and noble gases in the deep aquifer system of Kazan Trona Ore Field, Ankara, central Turkey and links to paleoclimate - Arslan, Sebnem; Yazicigil, Hasan; Stute, Martin; Schlosser, Peter (Quaternary Research, 2013)
Environmental isotopes and noble gases in groundwater samples from the Kazan Trona Ore Field are studied to establish the temperature change between the Holocene and the late Pleistocene. Noble gas temperatures (NGTs) presented in this study add an important facet to the global paleotemperature map in the region between Europe and North Africa. The groundwater system under investigation consists of three different aquifers named shallow, middle and deep in which δ18O and δ2H vary from − 8.10‰ to − 12.80‰ and from − 60.89‰ to − 92.60‰ VSMOW, respectively. The average isotopic depletion between unconfined and confined parts of the system is − 2.5‰ in δ18O and − 20‰ in δ2H. It is not possible to explain this depletion solely with the elevation effect. Recharge temperatures derived from dissolved atmospheric noble gases reflect the current average yearly ground temperatures (13°C) for samples collected near the recharge area but are 3 to 8°C lower than today's temperatures in the deep aquifer system. Low 14C activities and high He excesses in the confined parts of the aquifer system suggest that the water in the deep aquifer was recharged during the last Pleistocene under considerably cooler climatic conditions.
id: 2269

Export of submicron particulate organic matter to mesopelagic depth in an oligotrophic gyre - Close, H. G.; Shah, S. R.; Ingalls, A. E.; Diefendorf, A. F.; Brodie, E. L.; Hansman, R. L.; Freeman, K. H.; Aluwihare, L. I.; Pearson, A. (Proceedings of the National Academy of Sciences, 2013)
Sixty percent of the world ocean by area is contained in oligotrophic gyres [Longhurst A (1995) Prog Oceanog 36:77-16], the biomass of which is dominated by picophytoplankton, including cyanobacteria and picoeukaryotic algae, as well as picoheterotrophs. Despite their recognized importance in carbon cycling in the surface ocean, the role of small cells and their detrital remains in the transfer of particulate organic matter (POM) to the deep ocean remains disputed. Because oligotrophic marine conditions are projected to expand under current climate trends, a better understanding of the role of small particles in the global carbon cycle is a timely goal. Here we use the lipid profiles, radiocarbon, and stable carbon isotopic signatures of lipids from the North Pacific Subtropical Gyre to show that in the surface ocean, lipids from submicron POM (here called extra-small POM) are distinct from larger classes of suspended POM. Remarkably, this distinct extra-small POM signature dominates the total lipids collected at mesopelagic depth, suggesting that the lipid component of mesopelagic POM primarily contains the exported remains of small particles. Transfer of submicron material to mesopelagic depths in this location is consistent with model results that claim the biological origin of exported carbon should be proportional to the distribution of cell types in the surface community, irrespective of cell size [Richardson TL, Jackson GA (2007) Science 315:838-840]. Our data suggest that the submicron component of exported POM is an important contributor to the global biological pump, especially in oligotrophic waters.
Keywords: Biogeochemistry; biomarkers; carbon isotopes; Oceanography

The Holocene onset in the southwestern South Atlantic - Pivel, M. A. G.; Santarosa, A. C. A.; Toledo, F. A. L.; Costa, K. B. (Palaeogeography, Palaeoclimatology, Palaeoecology, 2013)
In this paper we present a paleoceanographic reconstruction of the southwestern South Atlantic for the past 13 kyr based on faunal and isotopic analysis of planktonic foraminifera from a high-resolution core retrieved at the South Brazil Bight continental slope. Our record indicates that oceanographic changes in the southwestern South Atlantic during the onset of the Holocene were comparable in strength to those that occurred during the Younger Dryas. Full interglacial conditions started abruptly after 8.2 kyr BP with a sharp change in faunal composition and surface hydrography (SST and SSS). Part of the observed events may be explained in terms of changes in thermohaline circulation while the other part suggests a dominant role of winds. Our data indicate that during the Early Holocene upwelling was significantly strengthened in the South Brazil Bight promoting high productivity and preventing the establishment of the typically interglacial menardiiform species. In general terms, oceanographic changes recorded by core KF02 occurred in synchrony with Antarctica's climate.
id: 2323

Holocene variability in hydrology, vegetation, fire, and eolian activity in the Nebraska Sand Hills, USA - Schmieder, Jens; Fritz, Sherilyn C; Grimm, Eric C; Jacobs, Kimberly C; Brown, Kendrick J; Swinehart, James B; Porter, Stephen C (The Holocene, 2013)
This study combined multiple aquatic and terrestrial proxies, including diatoms, pollen, grain size, and bulk-sediment chemistry to reconstruct the history of three lake sites located in the central Sand Hills of Nebraska, USA. Long-term changes in effective moisture are evident at all sites, with significant changes occurring at ~6000, ~4000, and ~ 2000 cal. yr BP. Both aquatic and terrestrial indicators suggest that effective moisture was low between 10,000 and ~6000 cal. yr BP, and that this time interval was the driest period of the Holocene. The dominance of benthic and tychoplanktic diatom taxa indicates relatively shallow lake-level, high sand influx indicates moderately high eolian activity, and the pollen assemblage suggests xeric grasslands with abundant mud flats. About 6000 cal. yr BP, all three sites experienced an increase in effective moisture. Lake-level rise is indicated by increases in planktic and tychoplanktic diatoms relative to benthic taxa, while greater abundance of grass pollen and charcoal, and decreased eolian flux indicate stabilized dunes with dense vegetation sufficient to fuel local fires. A significant hydrologic shift recorded at all sites occurred at ~4000 cal. yr BP. This event was characterized by substantial lake-level rise, yet decreased grass cover and fire frequency, and increased eolian activity. Water-table rise may have been caused by a combination of factors including: (1) formation of dune-dams that blocked old drainage channels, (2) reduced grass cover and hence reduced evapotranspiration, and (3) changes in the frequency and duration of drought. The most likely cause(s) of the differential response of the terrestrial and aquatic systems at this time is not clear, none-the-less the late Holocene was not nearly as dry as the interval prior to 6000 cal. yr BP. The last ~2000 yr were characterized by several short-term fluctuations in lake level, including an interval of drought between 950 and 750 cal. yr BP, coincident with increased eolian activity during the latter part of the Medieval Climatic Anomaly.
Keywords: diatoms; drought; Holocene climate change; lakes; Nebraska Sand Hills; pollen

Improving a gas ion source for 14C AMS - Fahrni, S. M.; Wacker, L.; Synal, H. A.; Szidat, S. (Proceedings of the Twelfth International Conference on Accelerator Mass Spectrometry, Wellington, New Zealand, 20-25 March 2011, 2013)
For more than 4 years, gaseous samples of 1–50 μg carbon have been routinely measured with the gas ion source of the small AMS (Accelerator Mass Spectrometer) facility MICADAS (MIni CArbon DAting System) at ETH Zurich. The applied measurement technique offers a simple and fast way of 14C measurements without the need of sample graphitization. A major drawback of gaseous 14C measurements, however, is the relatively low negative ion current, which results in longer measurement times and lower precision compared to graphitized samples. In December 2009, a new, improved Cs sputter ion source was installed at MICADAS and we began to optimize conditions for the measurement of gaseous samples. 12C− currents from the new ion source were improved from initially 3 to 12–15 μA for routine measurements and the negative ion yield was increased by a factor of 2, reaching 8% on average during routine operation. Moreover, the new measurement settings enable a doubled CO2 flow, thus substantially reducing measurement times. The achieved performance allows closing the sample size gap between gaseous and solid samples and makes the gas ion source a promising tool for dating with a measurement precision of 5‰ on samples as small as 50 μg carbon.
id: 2304

Late Holocene expansion of Istorvet ice cap, Liverpool Land, east Greenland - Lowell, Thomas V.; Hall, Brenda L.; Kelly, Meredith A.; Bennike, Ole; Lusas, Amanda R.; Honsaker, William; Smith, Colby A.; Levy, Laura B.; Travis, Scott; Denton, George H. (Quaternary Science Reviews, 2013)
The Greenland Ice Sheet is undergoing dynamic changes that will have global implications if they continue into the future. In this regard, an understanding of how the ice sheet responded to past climate changes affords a baseline for anticipating future behavior. Small, independent ice caps adjacent to the Greenland Ice Sheet (hereinafter called “local ice caps”) are sensitive indicators of the response of Greenland ice-marginal zones to climate change. Therefore, we reconstructed late Holocene ice-marginal fluctuations of the local Istorvet ice cap in east Greenland, using radiocarbon dates of subfossil plants, 10Be dates of surface boulders, and analyses of sediment cores from both threshold and control lakes. During the last termination, the Istorvet ice cap had retreated close to its maximum Holocene position by ∼11,730 cal yr BP. Radiocarbon dates of subfossil plants exposed by recent recession of the ice margin indicate that the Istorvet cap was smaller than at present from AD 200 to AD 1025. Sediments from a threshold lake show no glacial input until the ice cap advanced to within 365 m of its Holocene maximum position by ∼AD 1150. Thereafter the ice cap remained at or close to this position until at least AD 1660. The timing of this, the most extensive of the Holocene, expansion is similar to that recorded at some glaciers in the Alps and in southern Alaska. However, in contrast to these other regions, the expansion in east Greenland at AD 1150 appears to have been very close to, if not at, a maximum Holocene value. Comparison of the Istorvet ice-cap fluctuations with Holocene glacier extents in Southern Hemisphere middle-to-high latitude locations on the Antarctic Peninsula and in the Andes and the Southern Alps suggests an out-of-phase relationship. If correct, this pattern supports the hypothesis that a bipolar see-saw of oceanic and/or atmospheric circulation during the Holocene produced asynchronous glacier response at some localities in the two polar hemispheres.
id: 2290

Mid-Late Holocene coastal environmental changes in southeastern Sri Lanka: New evidence for sea level variations in southern Bay of Bengal - Ranasinghe, R. N.; Ortiz, J. D.; Moore, A. L.; McAdoo, B.; Wells, N.; Siriwardana, C. H. E. R.; Wijesundara, D. T. D. S. (QUATERNARY INTERNATIONAL, 2013)
The 2004 Indian Ocean tsunami highlighted the need to better understand the dynamics of the South Asian coastlines. Very little knowledge on paleo-coastal variability hinders the development of a paleo-tsunami chronology of the western Bay of Bengal. Also, limited sea level records for the southern Bay of Bengal are remarkably different from rest of the Indian Ocean due to alternating highstands and lowstands during mid-late Holocene. This study was undertaken to recognize how the coastal environment in tectonically stable eastern and southeastern coasts of Sri Lanka changed during mid-late Holocene and to derive evidence of sea level variability. Sediment cores were collected from Kirinda and Panama estuaries, Okanda lagoon and Vakarai beach ridge plain, situated on the eastern and southeastern coasts of Sri Lanka. Physical and chemical variations in sediments, caused by the coastal environmental changes occurred due to fluctuating eustatic sea level, were determined using X-ray fluorescence, visible reflectance, magnetic susceptibility and grain size. Chronology of events were developed using AMS C-14 dates on bulk organic matter, wood, inorganic carbonate and mollusk shells. Results suggest that key periods of transition in the coastal environment in the studied area occurred between about 7300 and 3000 BP. Submergence of coastal environments by mid-Holocene transgression began around 7300 BP. Barrier development initiated at the end of the submergence phase around 4900 BP. Onset of beach ridge development in areas with high sediment supply took place around 4000 BP and continued later than 2400 BP. Marine influence ended around 3000 BP. These coastal environmental changes suggest that Holocene transgression, which started flooding southeastern coastal lowlands, either slowed or the sea level stabilized around 4900 BP. Sea level fell down to its present level at around 3000 BP by the subsequent slow regression. Some cores carry evidence for a possible pause in the transgression or a short lowstand that ended around 5200 BR (c) 2013 Elsevier Ltd and INQUA. All rights reserved.

Moisture and temperature changes associated with the mid-Holocene Tsuga decline in the northeastern United States - Marsicek, Jeremiah P.; Shuman, Bryan; Brewer, Simon; Foster, David R.; Oswald, W. Wyatt (Quaternary Science Reviews, 2013)
A decline of hemlock (Tsuga) populations at ca 5.5 ka (thousands of calibrated radiocarbon years before 1950 AD) stands out as the most abrupt vegetation change of the Holocene in North America, but remains poorly understood after decades of study. Recent analyses of fossil pollen have revealed a concurrent, abrupt oak (Quercus) decline and increases in the abundance of beech (Fagus) and pine (Pinus) on Cape Cod in eastern Massachusetts, but the replacement of drought-tolerant oaks by moisture-sensitive beeches appears inconsistent with low lake levels in the region at the same time. The oak and beech changes are also limited to coastal areas, and the coastal-inland differences require an explanation. Here, we develop a new lake-level reconstruction from Deep Pond, Cape Cod by using a transect of sediment cores and ground-penetrating radar (GPR) profiles to constrain the past elevations of the sandy, littoral zone of the pond. The reconstruction shows that a series of multi-century episodes of low water coincide with the abrupt hemlock and oak declines, and interrupt subsequent phases of hemlock recovery. The lake-level variations equal precipitation deficits of ∼100 mm superimposed on a Holocene long moisture increase of >400 mm. However, because moisture deficits do not easily explain the oak and beech changes, we also evaluate how the climate preferences of the regional vegetation changed over time by matching the fossil pollen assemblages from Deep Pond with their modern equivalents. Reconstructions of the precipitation requirements of the vegetation correlate well even in detail with the lake-level record (r = 0.88 at Deep Pond), and indicate close tracking of effective moisture (precipitation minus evapotranspiration) by the vegetation despite the abrupt species declines, which could have decoupled climate and vegetation trends. Reconstructions of the temperature preferences of the vegetation indicate that coastal sites may have cooled by 0.5–2.5 °C after ca 5.5 ka, while inland sites warmed by 0.5–1 °C. The change in coastal temperature preferences agrees with sea surface cooling in the western Atlantic Ocean of >1 °C. Consequently, the persistence of low hemlock abundance after 5.5 ka in the northeast U.S. may have resulted from oceanic changes that produced multi-century droughts and thus delayed the post-decline recovery of hemlock populations.

Onshore-offshore surficial geologic map of the Newburyport East and northern half of the Ipswich Quadrangles, Massachusetts - Hein, C.J.; FitzGerald, D.M.; Barnhardt, W.A.; Stone, B.D. (Geologic Map, 2013)
This geologic map shows the distribution of surficial subaerial and subaqueous materials in the Newburyport East and northern half of the Ipswich 7.5' quadrangles (northeast Massachusetts) and the area of the Gulf of Maine immediately offshore, to an approximate depth of 80 m below modern mean sea level (MSL). This map was compiled from the onshore surficial geologic map of Stone et al. (2006) and the offshore surficial mapping of Barnhardt et al. (2009), and includes newly mapped shallow offshore geologic features. Onshore and offshore units are continuous across the shallow- water zone (0-20 m below MSL). The definition of map units is based on lithologic characteristics (grain size, mineralogy and structure), stratigraphic relationships and relative ages, and sedimentologic processes. The map describes the evolution of the surficial geology in terms of the sediment sources, transportation mechanisms, and depositional, post-depositional and modern processes that have acted on the late Quaternary sediments that compose these units. Cross sections are derived from subsurface data compiled from the literature and collected as part of this study. This maps supersedes MGS OFR 2011-01

Paleoclimate changes of the last 1000 yr on the eastern Qinghai–Tibetan Plateau recorded by elemental, isotopic, and molecular organic matter proxies in sediment from glacial Lake Ximencuo - Pu, Yang; Nace, Trevor; Meyers, Philip A.; Zhang, Hucai; Wang, Yongli; Zhang, Chuanlun L.; Shao, Xiaohua (Palaeogeography, Palaeoclimatology, Palaeoecology, 2013)
Total organic carbon (Corg) and nitrogen (Ntot) concentrations and isotope compositions and n-alkane and n-alkan-ol molecular biomarker compositions were measured in two parallel sediment cores from Lake Ximencuo, a typical glacial lake on the eastern Qinghai–Tibetan Plateau (QTP), to reconstruct local climatic variations during the past 1000 yr. Concentrations of Corg and Ntot vary similarly with changes in precipitation recorded by tree rings in Dulan, northeastern QTP, indicating their close relation to precipitation. Carbon Preference Index (CPI) values of C22–C33 n-alkanes and C22–C28 n-alkan-1-ols and Average Chain Length (ACL) values of C27–C33 n-alkanes generally negatively correlate with δ13Corg and δ15Ntot and also vary comparably with the oxygen isotope temperature record from the Dunde ice core, northeastern QTP. These patterns indicate that high CPI values and negative shifts of the δ13Corg and δ15Ntot correspond to warmer conditions that favor the growth of vascular land plants and that lower values and positive shifts correspond to cooler conditions in the Lake Ximencuo locality. This observation contradicts previous interpretations from peat and modern soil studies that conclude that the CPI indices were controlled by microbial degradation under different climate conditions. Here we propose that the changes of organic matter sources under different climate regimes, combined with physiological adjustments of vascular plants to different air temperatures, might yield different CPI responses to climate changes in glacial plateau lakes. Air temperature and precipitation increases and decreases reconstructed in this 1000-yr study were generally independent of each other, but they both occurred at centennial or multi-centennial scales. The interaction between subtropical (Asian Monsoon) and mid-latitude (Westerly) atmospheric circulation systems probably dominated the local precipitation variations in the Lake Ximencuo catchment, whereas solar insolation, volcanism and greenhouse gas variations were likely responsible for the air temperature changes that are recorded in the lake sediments and that are consistent with regional temperature variations in the eastern QTP.
id: 2310

Pleistocene sequence stratigraphy of the shallow continental shelf, offshore New Jersey: Constraints of Integrated Ocean Drilling Program Leg 313 core holes - Miller, Kenneth G.; Sugarman, Peter J.; Browning, James V.; Sheridan, Robert E.; Kulhanek, Denise K.; Monteverde, Donald H.; Wehmiller, John F.; Lombardi, Christopher; Feigenson, Mark D. (GEOSPHERE, 2013)
We used cores and logs from Integrated Ocean Drilling Program (IODP) Expedition 313 to generate biostratigraphic, lithofacies, biofacies, and geochemical data that constrain the ages and paleoenvironments of Pleistocene sequences. We integrate sequence stratigraphy on cores with new seismic stratigraphic data to interpret the Pleistocene history of the Hudson shelf valley and paleoenvironmental and sea-level changes on the inner to middle continental shelf. Improved age control compared to previous studies is provided by integrated calcareous nannofossil biostratigraphy, Sr isotopic stratigraphy, and amino acid racemization. We recognize four upper Pleistocene-Holocene sequences: sequence uP1 is correlated with Marine Isotope Chrons (MIC; ``chron{''} is the correct stratigraphic term for a time unit, not ``stage{''}) 7 or 5e, sequence uP2 with MIC 5c, sequence uP3 with MIC 5a, and sequence uP4 with the latest Pleistocene to Holocene (MIC 1-2). However, within our age resolution it is possible that sequences uP2 and uP3 correlate with MIC 4-3c and 3a, respectively, as suggested by previous studies. Lower Pleistocene sequences lP1 and lP2 likely correlate with peak interglacials (e. g., MIC 31 and MIC 45 or 47, respectively). Thus, we suggest that preservation of sequences occurs only during peak eustatic events (e. g., MIC 45 or 47, MIC 31, and MIC 5), unless they are preserved in eroded valleys. The architecture of the Pleistocene deposits at Sites M27 and M29 is one of thin remnants of highstand and transgressive systems tracts, with lowstand deposits only preserved in the thalwegs of incised valleys. Incised valleys at the bases of sequences uP3 (IODP Site M27) and uP2 (IODP Site M29) document more southward courses of the paleo-Hudson valley, compared to the more southeastward course of the MIC 1-2 paleo-Hudson valley. The patchy distribution of Pleistocene sequences beneath the New Jersey inner-middle continental shelf is due to low accommodation during an interval of large eustatic changes; this predicts that sequences in such settings will be discontinuous, patchy, and difficult to correlate, consistent with previous studies in Virginia and North Carolina.

Prominent bacterial heterotrophy and sources of C-13-depleted fatty acids to the interior Canada Basin - Shah, S. R.; Griffith, D. R.; Galy, V.; McNichol, A. P.; Eglinton, T. I. (BIOGEOSCIENCES, 2013)
In recent decades, the Canada Basin of the Arctic Ocean has experienced rapidly decreasing summer sea ice coverage and freshening of surface waters. It is unclear how these changes translate to deeper waters, particularly as our baseline understanding of organic carbon cycling in the deep basin is quite limited. In this study, we describe full-depth profiles of the abundance, distribution and carbon isotopic composition of fatty acids from suspended particulate matter at a seasonally ice-free station and a semi-permanently ice-covered station. Fatty acids, along with suspended particulate organic carbon (POC), are more concentrated and C-13-enriched under ice cover than in ice-free waters. But this influence, apparent at 50 m depth, does not propagate downward below 150m depth, likely due to the weak biological pump in the central Canada Basin. Branched fatty acids have delta C-13 values that are similar to suspended POC at all depths and are more C-13-enriched than even-numbered saturated fatty acids at depths above 3000 m. These are likely to be produced in situ by heterotrophic bacteria incorporating organic carbon that is isotopically similar to total suspended POC. Below surface waters, there is also the suggestion of a source of saturated even-numbered fatty acids which could represent contributions from laterally advected organic carbon and/or from chemoautotrophic bacteria. At 3000 m depth and below, a greater relative abundance of long-chain (C20-24), branched and unsaturated fatty acids is consistent with a stronger influence of re-suspended sedimentary organic carbon. At these deep depths, two individual fatty acids (C-12 and iso-C-17) are significantly depleted in C-13, allowing for the possibility that methane oxidizing bacteria contribute fatty acids, either directly to suspended particulate matter or to shallow sediments that are subsequently mobilized and incorporated into suspended particulate matter within the deep basin.

Resolving varve and radiocarbon chronology differences during the last 2000 years in the Santa Barbara Basin sedimentary record, California - Hendy, Ingrid L.; Dunn, L.; Schimmelmann, A.; Pak, D. K. (Quaternary International, 2013)
Santa Barbara Basin (SBB) is well known for producing high quality paleoclimate reconstructions, but the validity of correlations between the basin and other regions rests upon age model accuracy. Yet, the two independent and well-established chronologies based on varve counting and radiocarbon dating do not consistently agree during the last two millennia. Here the validity of age model assumptions is tested including whether 1) the regional reservoir age of surface waters was invariably 641 ± 119 years through time, and/or 2) SBB laminae couplets are consistently annual varves and counted with sufficient precision. This high-resolution 14C study of SBB sediments compares 49 mixed planktonic foraminiferal carbonate and 20 terrestrial organic carbon 14C dates to the varve chronology, to extend the high-resolution paleoclimate chronology of the basin back ∼2000 years. Evidence indicates that regional reservoir ages do not remain constant through time with ΔR, (i.e. regional reservoir age minus variations in the global mixed-layer ocean reservoir age) fluctuating between 80 and 350 years. Second, there is a consistent (R2 = 0.96) undercounting of the varves between 150 and ∼1700 AD based on a new varying ΔR 14C chronology, indicating that some laminae couplets may not be annual. Loss of varves may occur when low riverine input and infrequent winter storm activity during drought intervals fail to supply a siliciclastic layer.
id: 2289

Seasonal climate change across the Roman Warm Period/Vandal Minimum transition using isotope sclerochronology in archaeological shells and otoliths, southwest Florida, USA - Wang, Ting; Surge, Donna; Walker, Karen Jo (Quaternary International, 2013)
Archaeological evidence suggests that southwest Florida experienced variably warmer and wetter climate during the Roman Warm Period (RWP; 300 BC–550 AD) relative to the Vandal Minimum (VM; 550–800 AD). This hypothesis was tested by reconstructing seasonal-scale climate conditions for the latter part of the RWP (1–550 AD) by using high-resolution oxygen isotope ratios (δ18O) of archaeological shells (Mercenaria campechiensis) and otoliths (Ariopsis felis). Eight shells radiocarbon-dated to 150–550 AD recorded that the RWP summers at 150–250 AD were insignificantly different from today and the RWP summers at 250–350 AD and 450–550 AD were drier relative to today. Eight otoliths indicate that the winters were variable during the RWP, colder than today at 150–200 AD and 250–300 AD, similar to today at 200–250 AD, 300–350 AD and 450–500 AD, and warmer than today at 500–550 AD. The climate reconstructions agree with archaeological observations and are partially coherent with the history of sea-level change, with a drying and cooling trend at the 95% confidence level across the RWP/VM transition. The climate transition is not only consistent with falling sea level, but also coherent with reduced solar radiation. Reduced solar radiation may have triggered a change in atmospheric circulation patterns that precipitated the observed climate transition.
id: 2298

Sedimentological and Geophysical Signatures of A Relict Tidal Inlet Complex Along A Wave-Dominated Barrier: Assateague Island, Maryland, U.S.A - Seminack, C. T.; Buynevich, I. V. (Journal of Sedimentary Research, 2013)
Assateague Island is a classic example of a wave-dominated, retrograding barrier island, with its recent geological history punctuated by episodes of overwash and breaching (comparable to the Outer Banks, North Carolina; northern New Jersey coast; Long Island, New York, etc.). This study aims to provide high-resolution data of a paleo-inlet which may lead to a more precise evolutionary model of other wave-dominated barrier islands. The study focuses on a historically stable segment fronting the Green Run Bay. The site lies north of the historical Green Run Inlet (active until 1880); however, there is no morphological or historical evidence of this inlet occupying the more northerly position, thus suggesting that the study site may represent a relict part of the barrier. High-resolution ground-penetrating radar (GPR) images, complemented with sediment cores and multi-dating techniques, were used to reconstruct the geological legacy of the Green Run Bay segment. The findings indicate that a shallow backbarrier channel, still visible within the Green Run Bay, can be traced to a large (> 380 m wide, 3.0–3.5 m thick) channel cut-and-fill structure beneath the barrier. The channel fill consists of tangential- to sigmoidal-oblique, southward-dipping reflections downlapping onto channel lag facies, which overlie subhorizontal bay-fill strata. Mollusks from the bay fill yield calibrated ages of 4419–2018 yr BP. The paleo-channel facies overlying the bay deposits exhibit a fining-upward sequence, with a mean grain size decreasing from 0.44 to 2.43 φ (0.74 to 0.19 mm). Optically stimulated luminescence dating places the middle part of the inlet fill at 730–590 yr BP. The paleo-channel fill does not extend to the south and therefore is a separate relict feature that predates the historical Green Run Inlet. The paleo-tidal prism of the relict channel was at least 17 × 106 m3, which is comparable to many wave-dominated historical and active inlets along the Atlantic Seaboard. Findings in this study provide the geological background for coastal hazard assessments and offer a mesoscale example of inlet-facies architecture in wave-dominated barrier sequences identified in the rock record.

Stratigraphy and wiggle-matching-based age-depth model of late Holocene marine sediments in Beppu Bay, southwest Japan - Kuwae, Michinobu; Yamamoto, Masanobu; Ikehara, Ken; Irino, Tomohisa; Takemura, Keiji; Sagawa, Takuya; Sakamoto, Tatsuhiko; Ikehara, Minoru; Takeoka, Hidetaka (New Global Perspectives on Paleontology, Stratigraphy, Paleoceanography, Paleoclimatology, and Tectonics in the East Asia and Western Pacific, 2013)
We analyzed the lithology, magnetic susceptibility, bulk density, and X-ray radiographs of 14 sediment cores (1–9 m long) from Beppu Bay in the western Seto Inland Sea, Japan, to establish the late Holocene stratigraphy in the deepest part of the bay and to develop an age–depth model for the sediments there. The cores contained 18 thick (major event) high-density layers (16 turbidites and two volcanic ash; >1 cm thick), and both lithological observations and density variations in the hemipelagic mud that is dominant in the cores revealed a further 55 thin (minor event) high-density layers (
id: 2295

Three approaches to radiocarbon calibration of amino acid racemization in Mulinia lateralis from the Holocene of the Chesapeake Bay, USA - Simonson, Amy E.; Lockwood, Rowan; Wehmiller, John F. (Amino Acid Racemization, 2013)
A radiocarbon-calibrated aminochronology, based on the bivalve Mulinia lateralis, is presented for Chesapeake Bay core MD03-2661, a 25 m piston core drilled near Kent Island (38°53.21′N; 76°23.89′W) during the 2003 USGS Marion-Dufresne cruise. Three separate approaches were used to calibrate amino acid racemization (AAR) data for aspartic acid with radiocarbon data. For the first approach, a direct or paired analysis calibration incorporated eight articulated specimens, thereby allowing for the application of AAR and radiocarbon analysis of the same specimen and effectively eliminating both intrashell variability and time averaging as factors in the calibration. A second direct approach relied on valves that were bilaterally split to facilitate both AAR and radiocarbon dating, thus effectively eliminating time averaging effects from this calibration. For the third indirect approach, nine independent radiocarbon dates were combined with 129 Asx D/L ratios from the same core depths to produce an indirect calibration model, from which intershell variability and time averaging could be estimated. Variability in AAR ratios was recognized from a myriad of sources, including analytical error, intrashell variability, inherent variability, time averaging, and contamination. The majority of this variability was controlled for through experimental design or by the application of these three independent calibration approaches. The direct calibration of articulated shells and the indirect calibration yielded virtually identical age models, well within their respective 95% confidence intervals. This study establishes an aminostratigraphic reference section for the Holocene record of the Chesapeake Bay and demonstrates the usefulness of multiple calibration approaches and the potential utility of AAR for future studies of sedimentary processes and chronologies in the bay.
id: 2292

An ~11,200 cal yr BP paleolimnological perspective for the archeological findings at Quartz Lake, Alaska - Wooller, M. J.; Kurek, J.; Gaglioti, B. V.; Cwynar, L. C.; Bigelow, N.; Reuther, J. D.; Gelvin-Reymiller, C.; Smol, J. P. (Journal of Paleolimnology, 2012)
Wetlands and lakes in the Tanana Valley, Alaska, have provided important resources for prehistoric humans who inhabited this region. We examine an ~11,200 cal yr BP record of environmental and paleolimnological changes from Quartz Lake in the middle Tanana Valley. Our data are also presented in the context of recent archaeological findings in the lake’s general vicinity that have 18 associated AMS 14C dates. We analyzed the stable-carbon and nitrogen isotope composition of total organic matter from the core, coupled with oxygen and carbon isotope analyses of Pisidiidae shells (fingernail clams), in addition to chironomid assemblage changes. Lacustrine sediments began to accumulate at ~11,200 cal yr BP. Initially, autochthonous production was low and allochthonous organic input was negligible between 11,000 and 10,500 cal yr BP, and were associated with relatively cool conditions at Quartz Lake at ~10,700 cal yr BP. After 10,500 cal yr BP, autochthonous production was higher coincident with a shift to chironomid assemblages dominated by taxa associated with warmer summer climates. A decrease in δ13C values of total organic carbon (TOC) and organic content of the sediment between 9,000 and 4,000 cal yr BP may indicate declining autochthonous primary production. This period ended with an abrupt (~7 ‰) decrease in the δ18O values from Pisidiidae shells at ~3,000 cal yr BP, which we hypothesize represented an episodic connection (flood) of the lake with flow from the nearby (~6 km) Tanana River. Our findings coincide with evidence for major flooding at other locations connected to the Tanana River and further afield in Alaska. From ~3,000 cal yr BP Quartz Lake subsequently appeared to become a relatively closed system, as indicated by the δ18OPisidiidae and δ13CPisidiidae data that are positively correlated and generally higher, which also correlates with a shift to moderately higher abundances of littoral chironomids. The cause of the transition to closed-basin conditions may have been geomorphic rather than climatic. This evidence of a progressively stronger evaporative influence on the lake’s closed hydrology after ~3,000 cal yr BP is consistent with our modern δ18O and δD water data from Quartz Lake that plot along a regional evaporative line we base on isotopic measurements from other local lakes and rivers.
id: 2134

Anomalous biogeochemical behavior of cadmium in subantarctic surface waters: Mechanistic constraints from cadmium isotopes - Gault-Ringold, Melanie; Adu, Toyin; Stirling, Claudine H.; Frew, Russell D.; Hunter, Keith A. (Earth and Planetary Science Letters, 2012)
Cadmium, a highly toxic metal, exhibits a nutrient-type profile in the oceans that is closely correlated to that of the major nutrients phosphate and nitrate. Despite its complexity, the relationship between cadmium and phosphate has been used to infer historic phosphate utilization and biological controls on oceanic CO2 concentrations. Cadmium isotopes offer the potential to constrain the mechanisms controlling cadmium cycling in the oceans, reducing uncertainty associated with the cadmium paleonutrient proxy. Using techniques in double spiking and MC-ICPMS, we report seasonal Cd isotopic and concentration data along with major nutrients and other essential trace metal (Fe, Zn, and Co) concentrations from subantarctic surface waters. We show, for the first time, a 50-fold seasonal decrease in dissolved cadmium concentrations in subantarctic waters that is due to biological uptake. However, this drawdown in Cd is decoupled from phosphate and shows no coincident shift in cadmium isotopic composition. These data, along with the preferential removal of Cd from surface waters relative to Zn, imply that cadmium is supply-limited to phytoplankton and may have a more significant biological role in these low Zn subantarctic surface waters than in regions with higher Zn concentrations.
id: 2339

Anthropogenic aerosols as a source of ancient dissolved organic matter in glaciers - Stubbins, Aron; Hood, Eran; Raymond, Peter A.; Aiken, George R.; Sleighter, Rachel L.; Hernes, Peter J.; Butman, David; Hatcher, Patrick G.; Striegl, Robert G.; Schuster, Paul; Abdulla, Hussain A. N.; Vermilyea, Andrew W.; et al. (Nature Geoscience, 2012)
Glacier-derived dissolved organic matter represents a quantitatively significant source of ancient, yet highly bioavailable carbon to downstream ecosystems1. This finding runs counter to logical perceptions of age–reactivity relationships, in which the least reactive material withstands degradation the longest and is therefore the oldest2. The remnants of ancient peatlands and forests overrun by glaciers have been invoked as the source of this organic matter1, 3, 4. Here, we examine the radiocarbon age and chemical composition of dissolved organic matter in snow, glacier surface water, ice and glacier outflow samples from Alaska to determine the origin of the organic matter. Low levels of compounds derived from vascular plants indicate that the organic matter does not originate from forests or peatlands. Instead, we show that the organic matter on the surface of the glaciers is radiocarbon depleted, consistent with an anthropogenic aerosol source. Fluorescence spectrophotometry measurements reveal the presence of protein-like compounds of microbial or aerosol origin. In addition, ultrahigh-resolution mass spectrometry measurements document the presence of combustion products found in anthropogenic aerosols. Based on the presence of these compounds, we suggest that aerosols derived from fossil fuel burning are a source of pre-aged organic matter to glacier surfaces. Furthermore, we show that the molecular signature of the organic matter is conserved in snow, glacier water and outflow, suggesting that the anthropogenic carbon is exported relatively unchanged in glacier outflows.
Keywords: Atmospheric chemistry; Biogeochemistry; Cryospheric science

Apparent oxygen utilization rates calculated from tritium and helium-3 profiles at the Bermuda Atlantic Time-series Study site - Stanley, R. H. R.; Doney, S. C.; W. J. Jenkins; Lott, D. E., III (Biogeosciences, 2012)
We present three years of Apparent Oxygen Utilization Rates (AOUR) estimated from oxygen and tracer data collected over the ocean thermocline at monthly resolution between 2003 and 2006 at the Bermuda Atlantic Timeseries Study (BATS) site. We estimate water ages by calculating a transit time distribution from tritium and helium-3 data. The vertically integrated AOUR over the upper 500 m, which is a regional estimate of export, during the three years is 3.1 +/- 0.5 mol O-2 m(-2) yr(-1). This is comparable to previous AOUR-based estimates of export production at the BATS site but is several times larger than export estimates derived from sediment traps or Th-234 fluxes. We compare AOUR determined in this study to AOUR measured in the 1980s and show AOUR is significantly greater today than decades earlier because of changes in AOU, rather than changes in ventilation rates. The changes in AOU are likely a methodological artefact associated with problems with early oxygen measurements.
id: 2253; PT: J; TC: 0; UT: WOS:000305830000003

Characterization of soils beneath a Posidonia oceanica meadow - Serrano, O.; Mateo, M. A.; Renom, P.; Julià, R. (Geoderma, 2012)
The study of a 475 cm core (spanning 4316 y BP) sampled in a Posidonia oceanica meadow (Portlligat Bay, NW Mediterranean) allowed us to make the first detailed description of the soil below this endemic seagrass. The sediments under P. oceanica (often referred to as mat or matte) are low density (average bulk density of 0.69 g DW cm− 3) marine soils mainly composed of siliciclastic (46%) and biogenic carbonated (46%) fine-grained sediments (particles 1 mm) and finer organic matter (3% of SOM;
id: 2300

Chemical and bacteriological analysis of soil from the Middle and Late Weichselian from Western Spitsbergen, Arctic - Singh, Shiv Mohan; Sharma, Jagdev; Gawas-Sakhalkar, Puja; Upadhyay, Ajay K.; Naik, Simantini; Bande, Dnyanesh; Ravindra, Rasik (The environment and chronology of the earliest occupation of north-west Europe: current knowledge, problems and new research directions, 2012)
This paper discusses temporal variability in the biogeochemical properties of the deeper permafrost soils of Western Spitsbergen, Arctic, that dates back up to the Middle Weichselian period (44.8 ka BP). Results indicate that during the mid of the last interstadial (∼37 ka BP) the chemical and biological properties of the soils were different from the stadial period that followed. Trace element concentration during the period remained low. Electrical conductivity along with K, Mg, Na, SO4−2, Cl− and HCO3− content of the soils during this period was high. Mineralizable nitrogen, organic carbon, biomass nitrogen and total bacterial counts were also high. These observations concurrently lead to a conclusion that the soils of Western Spitsbergen during the interstadial period were under marine influence. The culturability of bacterial cells was low which increased later with the onset of the stadial.
id: 2316

Climatic and megaherbivory controls on late-glacial vegetation dynamics: a new, high-resolution, multi-proxy record from Silver Lake, Ohio - Gill, Jacquelyn L.; Williams, John W.; Jackson, Stephen T.; Donnelly, Jeffrey P.; Schellinger, Grace C. (Quaternary Science Reviews, 2012)
Novel plant assemblages are a long-recognized feature of late-glacial North America, but identifying their causes has been hampered by inaccurate radiocarbon chronologies and the multiplicity of ecological and climatic events during the late Pleistocene. Recently we reported that the formation of no-analog vegetation may have been linked to declines in Pleistocene megafaunal communities, based on pollen and spores from the coprophilous fungus Sporormiella at sites in Indiana and New York. We present a new, multi-proxy analysis from Silver Lake, OH, which 1) updates the radiocarbon chronology of a classic pollen record with a well-established zone of no-analog vegetation, 2) combines a new sub-centennial pollen record with charcoal, Sporormiella, and x-ray fluorescence (XRF) spectroscopy analyses for an integrated record of landscape change before, during, and after the period of no-analog vegetation, and 3) replicates both the absolute and relative temporal patterns of landscape change at Appleman Lake, IN. At Silver Lake, the decline in Sporormiella at 13.9 ka BP was immediately followed by the formation of novel plant assemblages, as well as the highest-magnitude charcoal peak in the record. Increased Ca and Sr concentrations during the no-analog interval indicate either increased moisture, increased input of nutrients from deciduous litter, or both. The duration of the no-analog assemblages (13.9–11.8 ka BP) roughly corresponds to the period of peak insolation dissimilarity, but is more temporally constrained than previously reported in subcontinental-scale syntheses (17–11 ka BP). We propose a hierarchy of controls on late-glacial plant communities, where biotic interactions such as megaherbivory mediate climate-driven vegetation change.
id: 2141

Composition and fate of gas and oil released to the water column during the Deepwater Horizon oil spill - Reddy, Christopher M.; Arey, J. Samuel; Seewald, Jeffrey S.; Sylva, Sean P.; Lemkau, Karin L.; Nelson, Robert K.; Carmichael, Catherine A.; McIntyre, Cameron P.; Fenwick, Judith; Ventura, G. Todd; Van Mooy, Benjamin A. S.; Camilli, Richard (Proceedings of the National Academy of Sciences of the United States of America, 2012)
Quantitative information regarding the endmember composition of the gas and oil that flowed from the Macondo well during the Deepwater Horizon oil spill is essential for determining the oil flow rate, total oil volume released, and trajectories and fates of hydrocarbon components in the marine environment. Using isobaric gas-tight samplers, we collected discrete samples directly above the Macondo well on June 21, 2010, and analyzed the gas and oil. We found that the fluids flowing from the Macondo well had a gas-to-oil ratio of 1,600 standard cubic feet per petroleum barrel. Based on the measured endmember gas-to-oil ratio and the Federally estimated net liquid oil release of 4.1 million barrels, the total amount of C-1-C-5 hydrocarbons released to the water column was 1.7 x 10(11) g. The endmember gas and oil compositions then enabled us to study the fractionation of petroleum hydrocarbons in discrete water samples collected in June 2010 within a southwest trending hydrocarbon-enriched plume of neutrally buoyant water at a water depth of 1,100 m. The most abundant petroleum hydrocarbons larger than C-1-C-5 were benzene, toluene, ethylbenzene, and total xylenes at concentrations up to 78 mu gL(-1). Comparison of the endmember gas and oil composition with the composition of water column samples showed that the plume was preferentially enriched with water-soluble components, indicating that aqueous dissolution played a major role in plume formation, whereas the fates of relatively insoluble petroleum components were initially controlled by other processes.
id: 2247; PT: J; TC: 10; UT: WOS:000312605600028

Constraining Holocene 10Be production rates in Greenland - Briner, Jason P.; Young, ás E.; Goehring, Brent M.; Schaefer, Joerg M. (Journal of Quaternary Science, 2012)
The absence of a production rate calibration experiment on Greenland has limited the ability to link 10Be exposure dating chronologies of ice-margin change to independent records of rapid climate change. We use radiocarbon age control on Holocene glacial features near Jakobshavn Isbræ, western Greenland, to investigate 10Be production rates. The radiocarbon chronology is inconsistent with the 10Be age calculations based on the current globally averaged 10Be production rate calibration data set, but is consistent with the 10Be production rate calibration data set from north-eastern North America, which includes a calibration site nearby on north-eastern Baffin Island. Based on the best-dated feature available from the Jakobshavn Isbræ forefield, we derive a 10Be production rate value of 3.98 ± 0.24 atoms g a−1, using the ‘St’ scaling scheme, which overlaps with recently published reference 10Be production rates. We suggest that these 10Be production rate data, or the very similar data from north-eastern North America, are used on Greenland. Copyright © 2011 John Wiley & Sons, Ltd.

The deglacial to postglacial marine environments of SEBarrow Strait, Canadian Arctic Archipelago - Pieńkowski, A. J.; England, John H.; Furze, Mark F. A.; Marret, Fabienne; Eynaud, Frédérique; Vilks, Gustav; MacLean, Brian; Blasco, Steve; Scourse, James D. (Boreas, 2012)
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.
id: 2342

Evaluation of sediment trace metal records as paleoproductivity and paleoxygenation proxies in the upwelling center off Concepción, Chile (36°S) - Muñoz, Praxedes; Dezileau, Laurent; Lange, Carina; Cardenas, Lissette; Sellanes, Javier; Salamanca, Marco A.; Maldonado, Antonio (Variability of the coastal upwelling and coastal transition zones off central-southern Chile, 2012)
This study analyzes the records of several trace metals sensitive to redox conditions in continental shelf sediments off Concepción, Chile (36°S). The continental margin off Concepción (36°S; 73°W) lies beneath an important upwelling center characterized by high primary production rates and, consequently, high fluxes of organic matter. In spring and summer, this material settles to the seafloor where it decays, producing periods of very low oxygen content in bottom waters (1 mL L−1). The goals of this study were to determine the input of trace metals to the sediment and to decipher how this information can be used to reveal variations in primary productivity or bottom oxygenation. Gravity cores collected at two stations – VG06-2 over the mid-shelf station (88 m water depth, upper boundary of the oxygen minimum zone) and VG06-3 over the outer shelf (120 m water depth, within the oxygen minimum zone) – were sampled for high resolution profiles (1 cm) of trace metals, biogenic opal, stable isotopes, and total organic carbon. The results suggest that the variability in the trace metal distribution on the continental shelf off Concepción is determined by redox conditions and the organic carbon flux to the bottom. Some sections of the sediment cores from the outer shelf showed appreciable authigenic enrichment of U, Cd, and Mo (EF: 5–10, 2–5, and 10–16 respectively) along with heavier values of δ15N, suggesting periods of suboxic conditions. During these periods, fluxes of organic material to the bottom were higher, as indicated by elevated TOC and opal contents. Alternating periods of higher and lower trace metal contents were not observed mid-shelf as they were on the outer shelf. Rather, the mid-shelf samples showed authigenic enrichment of U, Cd, and Mo (EF: 1–6, 4–5, and 10–20, respectively) throughout the core except in a 10-cm-thick gray layer. In general, authigenic enrichment of U, Mo, and Cd occurred at both sites, coincident with olive green layers in the cores. These layers were associated with periods of elevated primary productivity and suboxic conditions. Such periods did not seem to last as long as the oxygenated periods, which had higher inputs of refractive detrital material, coincident with the occurrence of distinct gray sediment layers.
id: 2154

Fine scale sediment structure and geochemical signature between eastern and western North Atlantic during Heinrich events 1 and 2 - Rashid, H.; Saint-Ange, F.; Barber, D. C.; Smith, M. E.; Devalia, N. (Quaternary Science Reviews, 2012)
Heinrich iceberg-rafting events 1 and 2 (H1 and H2) in the Labrador Sea are identified by their typical nepheloid-flow deposit sedimentary structure, high bulk carbonate, increase in iceberg-rafted detritus (IRD), and depletion of δ18O in the surface-dwelling foraminifer, Neogloboquadrina pachyderma (s). H-layers in this region have sedimentological characteristics different than those in the North Atlantic, and consist of IRD interspersed in pelagic sediments. High resolution 14C-AMS dates allowed us to delineate the leads and lags in instability between different ice-streams of the former Laurentide ice-sheet (LIS). Our data suggest that the discharge from the Hudson Strait ice-stream was followed by Cumberland Sound ice-sheet during H1 and H2. New radiogenic isotopes from the ice-proximal and surficial sediments of the greater Hudson Strait region and Labrador Sea H0, H1 and H2 layers suggest that carbonate-rich layers were only derived from Hudson Strait, not Baffin Bay. Fine scale structure of H1 and H2 intervals in Labrador Sea slope cores is characterized by two lithic peaks dominated by detrital carbonate grains and a single peak in cores from the central Labrador Sea. A similar pattern in the structure of H1 and H2 is observed along the western European margin. These findings contrast with North Atlantic H1 and H2 intervals, which are characterized by a peak of carbonate-rich grains, followed by a peak of quartz and volcanic grains. This comparison with North Atlantic and western European margin cores leads us to suggest that the coupling or lack thereof, between the LIS and European ice-sheet, is related to the depositional processes occurring along the margins, as well as the distance from the sources and the ability of the oceanic currents to disperse icebergs. Any significant change in ice-sheet dynamics would be recorded close to the ice-sheet margin, while distal locations would only record extreme events. We hypothesize that the discordance between the findings reported in the literature is most likely similar to the difference between the upper slope/deep Labrador sites and the Flemish Pass site described in this contribution but requires vigorous testing.
id: 2308

Geological interpretation of a low-backscatter anomaly found on the New Jersey continental margin - Sweeney, Edward M.; Gardner, James V.; Johnson, Joel E.; Mayer, Larry A. (Marine Geology, 2012)
An enigmatic low-backscatter, acoustic anomaly occurs on the New Jersey continental margin between Hudson and Wilmington Canyon channels. The presence of the low-backscatter anomaly, as seen with 6.5- and 12-kHz data, indicates a change in the physical properties of the seafloor or near sub-surface. Analyses of seafloor and sub-surface acoustic data with previously collected sediment cores suggest the low-backscatter feature corresponds to an outcrop of older strata uncovered by erosion and non-deposition by the Western Boundary Undercurrent (WBUC). The decrease in backscatter strength is enhanced by the presence of gas in the sub-surface sediments found in the buried Chesapeake Drift.
id: 2328

Insights into the Holocene environmental setting of Terra Nova Bay region (Ross Sea, Antarctica) from oxygen isotope geochemistry of Adélie penguin eggshells - Lorenzini, Sandra; Baneschi, Ilaria; Fallick, Anthony E.; Salvatore, Maria Cristina; Zanchetta, Giovanni; Dallai, Luigi; Baroni, Carlo (The Holocene, 2012)
An oxygen isotope record of Adélie penguin (Pygoscelis adeliae) eggshells from Terra Nova Bay (Victoria Land, Antarctica) has been reconstructed in order to provide insights into the palaeoenviroment of this region during the last ~8000 years. The d18O values measured in eggshell carbonate show a great variability over the course of the studied period, with maximum values consistently around +27.5‰. Adopting a metabolic enrichment relative to water source of ~+28.5‰, eggshell d18O values can be interpreted in terms of marine water uptake by the penguins. The spread in d18O of eggshell carbonate at any given time toward more negative values reflects the existence of a low d18O water end member, most plausibly snow or snowmelt. Samples younger than 2000 years are characterized by a general lack of very negative d18O values. As also attested by other proxies, this shift toward more positive isotopic values is likely to be related both to a decreasing contribution of snow or meltwater in the seawaters and consequently to an absence or paucity on the boundary of the nesting sites of snow or snowfall and freshwater that could be directly eaten or drunk by penguins.
id: 2348

Marine climatic seasonality during medieval times (10th to 12th centuries) based on isotopic records in Viking Age shells from Orkney, Scotland - Surge, Donna; Barrett, James H. (Palaeogeography, Palaeoclimatology, Palaeoecology, 2012)
Seasonal sea-surface temperature (SST) variability during the Medieval Climate Anomaly (MCA), which corresponds to the height of Viking exploration (800–1200 AD), was estimated using oxygen isotope ratios (δ18O) obtained from high-resolution samples micromilled from archaeological shells of the European limpet, Patella vulgata. Our findings illustrate the advantage of targeting SST archives from fast-growing, short-lived molluscs that capture summer and winter seasons simultaneously. Shells from the 10th to 12th centuries (early MCA) were collected from well-stratified horizons, which accumulated in Viking shell and fish middens at Quoygrew on Westray in the archipelago of Orkney, Scotland. Their ages were constrained based on artifacts and radiocarbon dating of bone, charred cereal grain, and the shells used in this study. We used measured δ18OWATER values taken from nearby Rack Wick Bay (average 0.31 ± 0.17‰ VSMOW, n = 11) to estimate SST from δ18OSHELL values. The standard deviation of δ18OWATER values resulted in an error in SST estimates of ± 0.7 °C. The coldest winter months recorded in the shells averaged 6.0 ± 0.6 °C and the warmest summer months averaged 14.1 ± 0.7 °C. Winter and summer SST during the late 20th century (1961–1990) was 7.77 ± 0.40 °C and 12.42 ± 0.41 °C, respectively. Thus, during the 10th to 12th centuries winters were colder and summers were warmer by ~ 2 °C and seasonality was higher relative to the late 20th century. Without the benefit of seasonal resolution, SST averaged from shell time series would be weighted toward the fast-growing summer season, resulting in the conclusion that the early MCA was warmer than the late 20th century by ~ 1 °C. This conclusion is broadly true for the summer season, but not true for the winter season. Higher seasonality and cooler winters during early medieval times may result from a weakened North Atlantic Oscillation index.
id: 2320

The Medieval Climate Anomaly in the Iberian Peninsula reconstructed from marine and lake records - Moreno, Ana; Pérez, Ana; Frigola, Jaime; Nieto-Moreno, Vanesa; Rodrigo-Gámiz, Marta; Martrat, Belén; González-Sampériz, Penélope; Morellón, Mario; Martín-Puertas, Celia; Corella, Juan Pablo; Belmonte, Ánchel; Sancho, Carlos; et al. (Quaternary Science Reviews, 2012)
Selected multi-proxy and accurately dated marine and terrestrial records covering the past 2000 years in the Iberian Peninsula (IP) facilitated a comprehensive regional paleoclimate reconstruction for the Medieval Climate Anomaly (MCA: 900–1300 AD). The sequences enabled an integrated approach to land–sea comparisons and, despite local differences and some minor chronological inconsistencies, presented clear evidence that the MCA was a dry period in the Mediterranean IP. It was a period characterized by decreased lake levels, more xerophytic and heliophytic vegetation, a low frequency of floods, major Saharan eolian fluxes, and less fluvial input to marine basins. In contrast, reconstruction based on sequences from the Atlantic Ocean side of the peninsula indicated increased humidity. The data highlight the unique characteristics of the MCA relative to earlier (the Dark Ages, DA: ca 500–900 years AD) and subsequent (the Little Ice Age, LIA: 1300–1850 years AD) colder periods. The reconstruction supports the hypothesis of Trouet et al. (2009), that a persistent positive mode of the North Atlantic Oscillation (NAO) dominated the MCA.
id: 2334

Molecular records of climate variability and vegetation response since the Late Pleistocene in the Lake Victoria basin, East Africa - Berke, Melissa A.; Johnson, Thomas C.; Werne, Josef P.; Grice, Kliti; Schouten, Stefan; Sinninghe Damsté, Jaap S. (Quaternary Science Reviews, 2012)
New molecular proxies of temperature and hydrology are helping to constrain tropical climate change and elucidate possible forcing mechanisms during the Holocene. Here, we examine a ∼14,000 year record of climate variability from Lake Victoria, East Africa, the world's second largest freshwater lake by surface area. We determined variations in local hydroclimate using compound specific δD of terrestrial leaf waxes, and compared these results to a new record of temperature utilizing the TEX86 paleotemperature proxy, based on aquatic Thaumarchaeotal membrane lipids. In order to assess the impact of changing climate on the terrestrial environment, we generated a record of compound specific δ13C from terrestrial leaf waxes, a proxy for ecosystem-level C3/C4 plant abundances, and compared the results to previously published pollen-inferred regional vegetation shifts. We observe a general coherence between temperature and rainfall, with a warm, wet interval peaking ∼10–9 ka and subsequent gradual cooling and drying over the remainder of the Holocene. These results, particularly those of rainfall, are in general agreement with other tropical African climate records, indicating a somewhat consistent view of climate over a wide region of tropical East Africa. The δ13C record from Lake Victoria leaf waxes does not appear to reflect changes in regional climate or vegetation. However, palynological analyses document an abrupt shift from a Poaceae (grasses)-dominated ecosystem during the cooler, arid late Pleistocene to a Moraceae-dominated (trees/shrubs) landscape during the warm, wet early Holocene. We theorize that these proxies are reflecting vegetation in different locations around Lake Victoria. Our results suggest a predominantly insolation-forced climate, with warm, wet conditions peaking at the maximum interhemispheric seasonal insolation contrast, likely intensifying monsoonal precipitation, while maximum aridity coincides with the rainy season insolation and the interhemispheric contrast gradient minima. We interpret a shift in conditions at the Younger Dryas to indicate a limited switch in insolation-dominated control on climate of the Lake Victoria region, to remote teleconnections with the coupled Atlantic and Pacific climate system.
id: 2318

Oxygen control on Holocene cold-water coral development in the eastern Mediterranean Sea - Fink, Hiske G.; Wienberg, Claudia; Hebbeln, Dierk; McGregor, Helen V.; Schmiedl, Gerhard; Taviani, Marco; Freiwald, André (Deep Sea Research Part I: Oceanographic Research Papers, 2012)
Continuous sedimentary records from an eastern Mediterranean cold-water coral ecosystem thriving in intermediate water depths (∼600 m) reveal a temporary extinction of cold-water corals during the Early to Mid Holocene from 11.4–5.9 cal kyr BP. Benthic foraminiferal assemblage analysis shows low-oxygen conditions of 2 ml l−1 during the same period, compared to bottom-water oxygen values of 4–5 ml l−1 before and after the coral-free interval. The timing of the corals' demise coincides with the sapropel S1 event, during which the deep eastern Mediterranean basin turned anoxic. Our results show that during the sapropel S1 event low oxygen conditions extended to the rather shallow depths of our study site in the Ionian Sea and caused the cold-water corals temporary extinction. This first evidence for the sensitivity of cold-water corals to low oceanic oxygen contents suggests that the projected expansion of tropical oxygen minimum zones resulting from global change will threaten cold-water coral ecosystems in low latitudes in the same way that ocean acidification will do in the higher latitudes.
id: 2140

Paleoenvironmental changes on the northeastern and southwestern Black Sea shelves during the Holocene - Ivanova, Elena V.; Murdmaa, Ivar O.; Karpuk, Maria S.; Schornikov, Eugene I.; Marret, Fabienne; Cronin, Thomas M.; Buynevich, Ilya V.; Platonova, Elena A. (Quaternary International, 2012)
Four paleoceanographic events are distinguished during the Holocene based on changes in macro- and microfossil assemblages studied from three sediment cores (Ak 521, 522, 2571) from the outer northeast shelf and from core MAR02-45 situated on the southwest shelf of the Black Sea, west to the Bosphorus. The lithology and fossils were previously studied from cores Ak 521 and Ak 522 and MAR02-45. However, high resolution ostracod analyses from the AMS-14C dated core, Ak 2571, allowed for a revision of the taxonomy and paleoecological interpretation of this microfaunal group on the NE shelf. Downcore changes in the relative abundance of the polyhaline ostracods are found to be contemporaneous in all three cores from the NE shelf. As a result, centennial-millennial scale fluctuations of the bottom-water salinity are resolved in the area. A broader scale examination of paleoenvironmental changes between the NE and SW shelves is also made and the surface to bottom salinity gradient is discussed. An uncalibrated radiocarbon based chronology is used throughout this paper to facilitate comparison with the regional chronostratigraphy of marine transgression and regressions in the Black Sea. The calibrated ages corrected for the changes in reservoir age through the Holocene are also provided. The first paleoceanographic event is associated with the pulse of Mediterranean water previously established at about 9.8–9.3 ka BP. This event is clearly observed in the SW region but not on the NE shelf due to a hiatus in the longest core, Ak 521. The second event is represented on both the NE and SW shelves as a replacement of brackish benthic fauna and surface phytoplankton with marine ones between 8.4 and 6.9 ka BP, indicating a gradual increase in salinity. The third event is marked by opposing trends in surface and bottom-water salinity changes. On the NE shelf, bottom-water salinity rose to modern values by ∼ 6.5 ka BP and then decreased within the interval ∼6.4–5.3 ka BP as recorded by the ostracod assemblages. On the SW shelf, surface-water salinity reached modern values by 5.6 ka BP and remained constant until present day as inferred from the dinoflagellate cyst assemblages. The fourth event is marked by a recurring increase in bottom-water salinity to modern values indicated by the polyhaline ostracod assemblages at ∼ 5.3 ka BP in the NE region, after which only minor salinity fluctuations are observed.
id: 2123

Paleoseismic and geomorphologic evidence of recent tectonic activity of the Pozohondo Fault (Betic Cordillera, SE Spain) - Rodriguez-Pascua, M. A.; Perez-Lopez, R.; Garduno-Monroy, V. H.; Giner-Robles, J. L.; Silva, P. G.; Perucha-Atienza, M. A.; Hernandez-Madrigal, V. M.; Bischoff, J. (JOURNAL OF IBERIAN GEOLOGY, 2012)
Instrumental and historical seismicity in the Albacete province (External Prebetic Zone) has been scarcely recorded. However, major strike-slip faults showing NW-SE trending provide geomorphologic and paleoseismic evidence of recent tectonic activity (Late Pleistocene to Present). Moreover, these faults are consistently well oriented under the present stress tensor and therefore, they can trigger earthquakes of magnitude greater than M6, according to the lengths of surface ruptures and active segments recognized in fieldwork. Present landscape nearby the village of Hellin (SE of Albacete) is determined by the recent activity of the Pozohondo Fault (FPH), a NW-SE right-lateral fault with 90 km in length. In this study, we have calculated the Late Quaternary tectonic slip-rate of the FPH from geomorphological, sedimentological, archaeoseimological, and paleoseismological approaches. All of these data suggest that the FPH runs with a minimum slip-rate of 0.1 mm/yr during the last 100 kyrs (Upper Pleistocene-Holocene). In addition, we have recognized the last two major paleoearthquakes associated to this fault. Magnitudes of these paleoearthquakes were gretarer than M6 and their recurrence intervals ranged from 6600 to 8600 yrs for the seismic cycle of FPH. The last earthquake was dated between the 1st and 6th centuries, though two earthquakes could be interpreted in this wide time interval, one at the FPH and other from a far field source. Results obtained here, suggest an increasing of the tectonic activity of the Pozohondo Fault during the last 10,000 yrs.
Keywords: Geomorphology; Paleoseismology; Prebetic; Quaternary; SE Spain

Radiocarbon evidence that carbon from the Deepwater Horizon spill entered the planktonic food web of the Gulf of Mexico - Chanton, J. P.; Cherrier, J.; Wilson, R. M.; Sarkodee-Adoo, J.; Bosman, S.; Mickle, A.; Graham, W. M. (ENVIRONMENTAL RESEARCH LETTERS, 2012)
The Deepwater Horizon (Macondo) oil spill released large volumes of oil and gas of distinct carbon isotopic composition to the northern Gulf of Mexico, allowing Graham et al (2010 Environ. Res. Lett. 5 045301) to use stable carbon isotopes (delta C-13) to infer the introduction of spilled oil into the planktonic food web. Surface ocean organic production and measured oil are separated by 5-7 parts per thousand in stable carbon isotope (delta C-13) space, while in radiocarbon (Delta C-14) space these two potential sources are separated by more than 1000 parts per thousand. Thus radiocarbon isotopes provide a more sensitive tracer by which to infer possible introduction of Macondo oil into the food web. We measured Delta C-14 and delta C-13 in plankton collected from within 100 km of the spill site as well as in coastal and offshore DIC (dissolved inorganic carbon or Sigma CO2) to constrain surface production values. On average, plankton values were depleted in C-14 relative to surface DIC, and we found a significant linear correlation between Delta C-14 and delta C-13 in plankton. Cumulatively, these results are consistent with the hypothesis that carbon released from the Deepwater Horizon spill contributed to the offshore planktonic food web. Our results support the findings of Graham et al (2010 Environ. Res. Lett. 5 045301), but we infer that methane input may be important.
Keywords: carbon isotope; Gulf oil spill; methane; petroleum hydrocarbon; radiocarbon

Radiocarbon evidence that carbon from the Deepwater Horizon spill entered the planktonic food web of the Gulf of Mexico - Chanton, J P; Cherrier, J; Wilson, R M; Sarkodee-Adoo, J; Bosman, S; Mickle, A; Graham, W M (Environmental Research Letters, 2012)
The Deepwater Horizon (Macondo) oil spill released large volumes of oil and gas of distinct carbon isotopic composition to the northern Gulf of Mexico, allowing Graham et al (2010 Environ. Res. Lett. 5 045301) to use stable carbon isotopes (δ13C) to infer the introduction of spilled oil into the planktonic food web. Surface ocean organic production and measured oil are separated by 5–7‰ in stable carbon isotope (δ13C) space, while in radiocarbon (Δ14C) space these two potential sources are separated by more than 1000‰. Thus radiocarbon isotopes provide a more sensitive tracer by which to infer possible introduction of Macondo oil into the food web. We measured Δ14C and δ13C in plankton collected from within 100 km of the spill site as well as in coastal and offshore DIC (dissolved inorganic carbon or ΣCO2) to constrain surface production values. On average, plankton values were depleted in 14C relative to surface DIC, and we found a significant linear correlation between Δ14C and δ13C in plankton. Cumulatively, these results are consistent with the hypothesis that carbon released from the Deepwater Horizon spill contributed to the offshore planktonic food web. Our results support the findings of Graham et al (2010 Environ. Res. Lett. 5 045301), but we infer that methane input may be important.

A reconstruction of late Pleistocene relative sea level in the south Bohai Sea, China, based on sediment grain-size analysis - Yi, Liang; Yu, Hongjun; Ortiz, Joseph D.; Xu, Xingyong; Qiang, Xiaoke; Huang, Haijun; Shi, Xuefa; Deng, Chenglong (Sedimentary Geology, 2012)
Future anthropogenic sea-level rise and its impact on coastal regions is an important issue facing human civilizations. Due to the short nature of the instrumental record of sea-level change, development of proxies for sea-level change prior to the advent of instrumental records is essential to reconstruct long-term background sea-level changes on local, regional and global scales. Here, we employ numerical methods to partition sediment grain size using a combined database of marine surface and core samples, and to quantitatively reconstruct sea-level variation since the late Pleistocene in the south Bohai Sea, China. Our sea-level reconstruction indicates that relative sea-level changes in the southern Bohai Sea track global sea-level variation for the duration of the record. The results also indicate substantial regression from 70 to 30 cal kyr BP, and potentially subarial exposure from 38 to 20 cal kyr BP. Our results document the feasibility of reconstructing relative sea-level change by numerical partitioning of sediment grain size data, demonstrating the potential for future applications.
id: 2312

Refining the model of barrier island formation along a paraglacial coast in the Gulf of Maine - Hein, Christopher J.; FitzGerald, Duncan M.; Carruthers, Emily A.; Stone, Byron D.; Barnhardt, Walter A.; Gontz, Allen M. (Marine Geology, 2012)
Details of the internal architecture and local geochronology of Plum Island, the longest barrier in the Gulf of Maine, have refined our understanding of barrier island formation in paraglacial settings. Ground-penetrating radar and shallow-seismic profiles coupled with sediment cores and radiocarbon dates provide an 8000-year evolutionary history of this barrier system in response to changes in sediment sources and supply rates as well as variability in the rate of sea-level change. The barrier sequence overlies tills of Wisconsinan and Illinoian glaciations as well as late Pleistocene glaciomarine clay deposited during the post-glacial sea-level highstand at approximately 17 ka. Holocene sediment began accumulating at the site of Plum Island at 7–8 ka, in the form of coarse fluvial channel-lag deposits related to the 50-m wide erosional channel of the Parker River that carved into underlying glaciomarine deposits during a lower stand of sea level. Plum Island had first developed in its modern location by ca. 3.6 ka through onshore migration and vertical accretion of reworked regressive and lowstand deposits. The prevalence of southerly, seaward-dipping layers indicates that greater than 60% of the barrier lithosome developed in its modern location through southerly spit progradation, consistent with a dominantly longshore transport system driven by northeast storms. Thinner sequences of northerly, landward-dipping clinoforms represent the northern recurve of the prograding spit. A 5–6-m-thick inlet-fill sequence was identified overlying the lower stand fluvial deposit; its stratigraphy captures events of channel migration, ebb-delta breaching, onshore bar migration, channel shoaling and inlet infilling associated with the migration and eventual closure of the inlet. This inlet had a maximum cross-sectional area of 2800 m2 and was active around 3.5–3.6 ka. Discovery of this inlet suggests that the tidal prism was once larger than at present. Bay infilling, driven by the import of sediment into the backbarrier environment through tidal inlets, as well as minor sediment contribution from local rivers, led to a vast reduction in the bay tidal prism. This study demonstrates that, prior to about 3 ka, Plum Island and its associated marshes, tidal flats, and inlets were in a paraglacial environment; that is, their main source of sediment was derived from the erosion and reworking of glaciogenic deposits. Since that time, Plum Island has been in a state of dynamic equilibrium with its non-glacial sediment sources and therefore can be largely considered to be in a stable, “post-paraglacial” state. This study is furthermore the first in the Gulf of Maine to show that spit accretion and inlet processes were the dominant mechanisms in barrier-island formation and thus serves as a foundation for future investigations of barrier development in response to backbarrier infilling.
Keywords: barrier-island formation; ground-penetrating radar; inlet processes; inlet-fill sequence; paraglacial; spit accretion

Sea surface temperature variability and sea-ice extent in the subarctic northwest Pacific during the past 15,000 years - Max, Lars; Riethdorf, Jan-Rainer; Tiedemann, Ralf; Smirnova, Maria; Lembke-Jene, Lester; Fahl, Kirsten; ürnberg, Dirk; Matul, Alexander; Mollenhauer, Gesine (Paleoceanography, 2012)
Past changes in North Pacific sea surface temperatures and sea-ice conditions are proposed to play a crucial role in deglacial climate development and ocean circulation but are less well known than from the North Atlantic. Here, we present new alkenone-based sea surface temperature records from the subarctic northwest Pacific and its marginal seas (Bering Sea and Sea of Okhotsk) for the time interval of the last 15 kyr, indicating millennial-scale sea surface temperature fluctuations similar to short-term deglacial climate oscillations known from Greenland ice core records. Past changes in sea-ice distribution are derived from relative percentage of specific diatom groups and qualitative assessment of the IP25biomarker related to sea-ice diatoms. The deglacial variability in sea-ice extent matches the sea surface temperature fluctuations. These fluctuations suggest a linkage to deglacial variations in Atlantic meridional overturning circulation and a close atmospheric coupling between the North Pacific and North Atlantic. During the Holocene the subarctic North Pacific is marked by complex sea surface temperature trends, which do not support the hypothesis of a Holocene seesaw in temperature development between the North Atlantic and the North Pacific.

Seasonal fluxes and source variation of organic carbon transported by two major Chinese Rivers: The Yellow River and Changjiang (Yangtze) River - Wang, Xuchen; Ma, Haiqing; Li, Ronghua; Song, Zhensu; Wu, Jinping (GLOBAL BIOGEOCHEMICAL CYCLES, 2012)
A one-year study was carried out to investigate the seasonal fluxes and source variation of organic carbon transported by two major Chinese rivers, the Yellow River and Changjiang. In 2009, the Yellow River and Changjiang transported 3.20 x 10(10) g and 1.58 x 10(12) g DOC and 3.89 x 10(11) g and 1.52 x 10(12) g POC, respectively. The dominant input of the terrestrial organic matter occurred during the high discharge period from June to July for the Yellow River and from June to August for Changjiang, accounting for 36-44% of the DOC and 72-86% of the POC transported by the two rivers in 2009. The Yellow River transported much higher concentrations of inorganic carbon than organic carbon, while a reverse trend was found in the Changjiang, indicating the different sources of carbon discharged by the two rivers. Using radiocarbon and stable carbon isotope measurements, we identified the different sources and seasonal variations of organic carbon transported by the Yellow River and Changjiang. The Yellow River carried old POC with radiocarbon ages ranging from 4000 to 8000 years, while POC transported by Changjiang had a relatively younger C-14 age ranging from 800 to 1060 years. The C-14 ages of DOC were relatively younger (305-1570 years) and showed less variation between the two rivers. The seasonal variations found in C-14 ages of DOC and POC indicate that a large fraction of recent-fixed labile organic carbon was transported by the two rivers in the spring and summer months. The different sources and seasonal variations in both fluxes and sources of organic carbon transported by the Yellow River and Changjiang could have an important influence on the biogeochemical cycle and ecosystems in the estuaries and adjacent coastal waters of the East China Sea.

Significance of active growth faulting on marsh accretion processes in the lower Pearl River, Louisiana - Yeager, Kevin M.; Brunner, Charlotte A.; Kulp, Mark A.; Fischer, Dane; Feagin, Rusty A.; Schindler, Kimberly J.; Prouhet, Jeremiah; Bera, Gopal (Geomorphology, 2012)
Neotectonic processes influence marsh accretion in the lower Pearl River valley. Active growth faults are suggested by groupings of ponded river channel sections, transverse and linear river channel sections, and down- and across-valley contrasts in channel sinuosity. Seismic profiles identified several likely, fault-induced structural anomalies, two of which parallel the axes of surface distributary networks. Lithostratigraphy and biostratigraphy of six cores from across a suspected fault in the West Middle River, combined with 14C-based age control, yielded evidence of vertical offsets, indicating that this river section is on the plane of a growth fault. These data were used to estimate fault slip rates over two time intervals, 1.2 mm/y over the last 1300 yr, and 0.2 mm yr− 1 over the last 3700 yr, and delineated a sinusoidal pattern of deformation moving distally from the fault, which we interpret as resulting from fault-propagation folding. Higher rates of sediment accumulation (of the order of cm yr− 1 from 210Pbxs and 137Cs activity data) on the down-thrown side are consistent with sedimentary response to increased accommodation space, and mass-based sediment accumulation rates (g cm− 2 yr− 1) exhibit a pattern inverse of that shown by fault-driven sinusoidal deformation. We contend that near-surface growth faults are critically important to driving accretion rates and marsh response to sea-level rise.
id: 2294

Ventilation changes in the western North Pacific since the last glacial period - Okazaki, Y.; Sagawa, T.; Asahi, H.; Horikawa, K.; Onodera, J. (CLIMATE OF THE PAST, 2012)
We reconstructed the ventilation record of deep water at 2100m depth in the mid-latitude western North Pacific over the past 25 kyr from radiocarbon measurements of coexisting planktic and benthic foraminiferal shells in sediment with a high sedimentation rate. The C-14 data on fragile and robust planktic foraminiferal shells were concordant with each other, ensuring high quality of the reconstructed ventilation record. The radiocarbon activity changes were consistent with the atmospheric record, suggesting that no massive mixing of old carbon from the abyssal reservoir occurred throughout the glacial to deglacial periods. margin of the North Pacific, in a deep western boundary current analogous to the present one in the North Atlantic. However, our knowledge of paleo-ventilation, particularly in water deeper than 2000m in the western North Pacific, is limited because of poor preservation of foraminiferal shells in sediment. Here we present a detailed account of ventilation changes in the mid-latitude western North Pacific based on radiocarbon records from coexisting planktic and benthic foraminifera in sediment with high sedimentation rates. Because our ventilation reconstruction is based on radiocarbon data from multiple planktic species in the mid to high-latitude western North Pacific, our record provides robust evidence for the ventilation history in the region.

14C-Based source assessment of soot aerosols in Stockholm and the Swedish EMEP-Aspvreten regional background site - Andersson, August; Sheesley, Rebecca J.; Kruså, Martin; Johansson, Christer; Gustafsson, Örjan (Atmospheric Environment, 2011)
Combustion-derived soot or black carbon (BC) in the atmosphere has a strong influence on both climate and human health. In order to propose effective mitigation strategies for BC emissions it is of importance to investigate geographical distributions and seasonal variations of BC emission sources. Here, a radiocarbon methodology is used to distinguish between fossil fuel and biomass burning sources of soot carbon (SC). SC is isolated for subsequent off-line 14C quantification with the chemothermal oxidation method at 375 °C (CTO-375 method), which reflects a recalcitrant portion of the BC continuum known to minimize inadvertent inclusion of any non-pyrogenic organic matter. Monitored wind directions largely excluded impact from the Stockholm metropolitan region at the EMEP-Aspvreten rural station 70 km to the south-west. Nevertheless, the Stockholm city and the rural stations yielded similar relative source contributions with fraction biomass (fbiomass) for fall and winter periods in the range of one-third to half. Large temporal variations in 14C-based source apportionment was noted for both the 6 week fall and the 4 month winter observations. The fbiomass appeared to be related to the SC concentration suggesting that periods of elevated BC levels may be caused by increased wood fuel combustion. These results for the largest metropolitan area in Scandinavia combine with other recent 14C-based studies of combustion-derived aerosol fractions to suggest that biofuel combustion is contributing a large portion of the BC load to the northern European atmosphere.
id: 2148

Age, growth, and spawning season of red bream (Beryx decadactylus) off the southeastern United States - Friess, C.; Sedberry, G. R. (Fishery Bulletin, 2011)
Red bream (Beryx decadactylus) is a commercially important deep-sea benthopelagic fish with a circumglobal distribution on insular and continental slopes and seamounts. In the United States, small numbers are caught incidentally in the wreckfish (Polyprion americanus) fishery which operates off the southeastern coast, but no biological information exists for the management of the U.S. red bream population. For this study, otoliths (n=163) and gonads (n=161) were collected from commercially caught red bream between 2003 and 2008 to determine life history parameters. Specimens ranged in size from 410 to 630 mm fork length and were all determined to be mature by histological examination of the gonads. Females in spawning condition were observed from June through September, and reproductively active males were found year-round. Sectioned otoliths were difficult to interpret, but maximum age estimates were much higher than the 15 years previously reported for this species from the eastern North Atlantic based on whole-otolith analysis. Estimated ages ranged from 8 to 69 years, and a minimum lifespan of 49 years was validated by using bomb radiocarbon dating. Natural mortality was estimated at 0.06/yr. This study shows that red bream are longer lived and more vulnerable to overfishing than previously assumed and should be managed carefully to prevent over-exploitation.
id: 2211; Source type: scholarlyjournals; Object type: Article; Object type: Feature; CSAUnique: OB-MD-0015408089; AccNum: 14385075; ISSN: 0090-0656; Peer Reviewed: true

Bomb-produced radiocarbon validation of growth-increment crossdating allows marine paleoclimate reconstruction - Kastelle, Craig R.; Helser, Thomas E.; Black, Bryan A.; Stuckey, Matthew J.; C. Gillespie, Darlene; McArthur, Judy; Little, Diana; D. Charles, Karen; Khan, Reziah S. (Palaeogeography, Palaeoclimatology, Palaeoecology, 2011)
The bivalve Pacific geoduck (Panopea generosa) has been used in the eastern North Pacific Ocean to create proxies for environmental factors such as temperature and oceanographic conditions. This type of research depends upon accurate age determination of Pacific geoducks, which historically was based on shell growth-increment counts. A recent study comparing age estimates generated by the dendrochronology (tree-ring science) procedure of crossdating to those estimated from growth-increment counts found a significant difference between the methods for geoduck older than 30 years. Compared to the traditional age determination method of counting growth increments, the crossdating method estimates a greater longevity in this species, with some individuals living in excess of 150 years. In the present study, the accuracy of each method was independently assessed using bomb-produced radiocarbon (14C) techniques. Specimens whose birth years were estimated to be within the era of the bomb-produced marine 14C increase and where the differences between ages estimated by the two methods were greatest were selected for 14C analysis. The difference between age estimates from traditional growth-increment counts and those from crossdating was evaluated using their respective 14C chronologies in comparisons to a reference chronology as a standard. The comparisons relied on Bayesian nonlinear models using Markov Chain Monte Carlo simulation. This method of analysis showed that with a 50% probability geoducks were aged correctly when using the crossdating method, compared to the growth increment counts which had a 50% probability of underestimating the age by 4 years. Therefore, the crossdated age estimates were found to be more accurate than increment counts. Furthermore, these results provide new confidence in using Pacific geoduck biochronologies for paleoclimate and paleoenvironmental reconstruction.
id: 2167

Coastal subsidence in Oregon, USA, during the giant Cascadia earthquake of AD 1700 - Hawkes, A. D.; Horton, B. P.; Nelson, A. R.; Vane, C. H.; Sawai, Y. (Quaternary Science Reviews, 2011)
Quantitative estimates of land-level change during the giant AD 1700 Cascadia earthquake along the Oregon coast are inferred from relative sea-level changes reconstructed from fossil foraminiferal assemblages preserved within the stratigraphic record. A transfer function, based upon a regional training set of modern sediment samples from Oregon estuaries, is calibrated to fossil assemblages in sequences of samples across buried peat-mud and peat-sand contacts marking the AD 1700 earthquake. Reconstructions of sample elevations with sample-specific errors estimate the amount of coastal subsidence during the earthquake at six sites along 400 km of coast. The elevation estimates are supported by lithological, carbon isotope, and faunal tidal zonation data. Coseismic subsidence at Nehalem River, Nestucca River, Salmon River, Alsea Bay, Siuslaw River and South Slough varies between 0.18 m and 0.85 m with errors between 0.18 m and 0.32 m. These subsidence estimates are more precise, consistent, and generally lower than previous semi-quantitative estimates. Following earlier comparisons of semi-quantitative subsidence estimates with elastic dislocation models of megathrust rupture during great earthquakes, our lower estimates for central and northern Oregon are consistent with modeled rates of strain accumulation and amounts of slip on the subduction megathrust, and thus, with a magnitude of 9 for the AD 1700 earthquake.
id: 2143

Contemporary 14C radiocarbon levels of oxygenated polybrominated diphenyl ethers (O-PBDEs) isolated in sponge–cyanobacteria associations - Guitart, Carlos; Slattery, Marc; Ankisetty, Sridevi; Radwan, Mohamed; Ross, Samir J.; Letcher, Robert J.; Reddy, Christopher M. (Marine pollution bulletin, 2011)
Considerable debate surrounds the sources of oxygenated polybrominated diphenyl ethers (O-PBDEs) in wildlife as to whether they are naturally produced or result from anthropogenic industrial activities. Natural radiocarbon (14C) abundance has proven to be a powerful tool to address this problem as recently biosynthesized compounds contain contemporary (i.e. modern) amounts of atmospheric radiocarbon; whereas industrial chemicals, mostly produced from fossil fuels, contain no detectable 14C. However, few compounds isolated from organisms have been analyzed for their radiocarbon content. To provide a baseline, we analyzed the 14C content of four O-PBDEs. These compounds, 6-OH-BDE47, 2′-OH-BDE68, 2′,6-diOH-BDE159, and a recently identified compound, 2′-MeO-6-OH-BDE120, were isolated from the tropical marine sponges Dysidea granulosa and Lendenfeldia dendyi. The modern radiocarbon content of their chemical structures (i.e. diphenyl ethers, C12H22O) indicates that they are naturally produced. This adds to a growing baseline on, at least, the sources of these unusual compounds.
id: 2192

Cryostratigraphy of late Pleistocene syngenetic permafrost (yedoma) in northern Alaska, Itkillik River exposureAbstract - Kanevskiy, M.; Shur, Y.; Fortier, D.; Jorgenson, M.T.; Stephani, E. (Quaternary Research, 2011)
Extremely ice-rich syngenetic permafrost, or yedoma, developed extensively under the cold climate of the Pleistocene in unglaciated regions of Eurasia and North America. In Alaska, yedoma occurs in the Arctic Foothills, the northern part of the Seward Peninsula, and in interior Alaska. A remarkable 33-m-high exposure along the lower Itkillik River in northern Alaska opened an opportunity to study the unmodified yedoma, including stratigraphy, particle-size distribution, soil carbon contents, morphology and quantity of segregated, wedge, and thermokarst-cave ice. The exposed permafrost sequence comprised seven cryostratigraphic units, which formed over a period from > 48,000 to 5,000 14C yr BP, including: 1) active layer; 2) intermediate layer of the upper permafrost; 3–4) two yedoma silt units with different thicknesses of syngenetic ice wedges; 5) buried peat layer; 6) buried intermediate layer beneath the peat; and 7) silt layer with short ice wedges. This exposure is comparable to the well known Mus-Khaya and Duvanny Yar yedoma exposures in Russia. Based on our field observations, literature sources, and interpretation of satellite images and aerial photography, we have developed a preliminary map of yedoma distribution in Alaska.

The detailed palaeoecology of a mid-Wisconsinan interstadial (ca. 32 000 (14)C a BP) vegetation surface from interior Alaska - Wooller, Matthew J.; Zazula, Grant D.; Blinnikov, Misha; Gaglioti, Benjamin V.; Bigelow, Nancy H.; Sanborn, Paul; Kuzmina, Svetlana; La Farge, Catherine (Journal of Quaternary Science, 2011)
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.
id: 2131; PT: J; TC: 1; UT: WOS:000296091300010

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 - Li, Chao; Sessions, Alex L.; Valentine, David L.; Thiagarajan, Nivedita (Organic Geochemistry, 2011)
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
id: 2050; PT: J; UT: WOS:000286995900002

Drilling predation and taphonomy in modern mollusk death assemblages, San Salvador Island, Bahamas - Pruss, Sara B.; Stevenson, Marquela; Duffey, Siobhan (Palaeogeography, Palaeoclimatology, Palaeoecology, 2011)
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.
id: 2166

East–West similarities and differences in the surface and deep northern Arabian Sea records during the past 21 Kyr - Gupta, Anil K.; Mohan, K.; Sarkar, Sudipta; Clemens, Steven C.; Ravindra, Rasik; Uttam, Rajesh K. (Palaeogeography, Palaeoclimatology, Palaeoecology, 2011)
This study analyses monsoon proxy Globigerina bulloides from Ocean Drilling Program (ODP) Hole 723A (western Arabian Sea) and Hole ABP-25, 02 (northeastern Arabian Sea) as well as dominant benthic foraminifera, pteropods, total organic carbon (TOC), Inorganic Carbon (IC) and stable isotope values of benthic foraminifera from Hole ABP-25, 02 to understand summer monsoon-driven changes in the western and eastern Arabian Sea and their impacts on deep-sea ventilation during the past 21 Kyr. We have also combined published TOC data from ODP Hole 724B to understand if deep-sea conditions in the Arabian Sea were same throughout the region during the studied interval. The summer monsoon was generally weaker during cold intervals including the Last Glacial Maximum, the Younger Dryas and the Bond events of the Holocene. From 20 to 10 Kyr, the deep northeastern Arabian Sea was better oxygenated with less organic carbon supply except during 14–12.5 Kyr when TOC values increased, indicating a weaker summer monsoon and a weak oxygen minimum zone (OMZ). The TOC values and the abundance of the eutrophic benthic foraminiferal species Bulimina aculeata, Melonis barleeanum and Uvigerina peregrina increased during the late Holocene whereas well-oxygenated, low organic carbon benthic species Sphaeroidina bulloides as well as pteropods decreased, indicating an intense OMZ and an increased supply of refractory organic material to the Arabian Sea. It is important to note that although the surface response to monsoon variability was more or less similar in the western and northeastern Arabian Sea, the deep-sea conditions show a marked contrast in the two regions during the past 21 Kyr.
id: 2100

Evidence of slumping/sliding in Krishna–Godavari offshore basin due to gas/fluid movements - Ramprasad, T.; Dewangan, P.; Ramana, M. V.; Mazumdar, A.; Karisiddaiah, S. M.; Ramya, E. R.; Sriram, G. (Occurrence and exploration of gas hydrate in the marginal seas and continental margin of the Asia, India and Oceania region Occurrence and exploration of gas hydrate in the marginal seas and continental margin of the Asia, India and Oceania region, 2011)
The Krishna–Godavari (KG) offshore basin is one of the promising petroliferous basins of the eastern continental margin of India. Drilling in this basin proved the presence of gas hydrate deposits in the shallow marine sediments beyond 750 m water depths, and provided lithologic and stratigraphic information. We obtained multibeam swath bathymetry covering an area of about 4500 km2 in water depths of 280–1800 m and about 1260 line km of high resolution seismic (HRS) records. The general lithology of midslope deposits is comprised of nannofossil-rich clay, nannofossil-bearing clay and foraminifera-bearing clay. The HRS records and bathymetry reveal evidence of slumping and sliding of the upper and midslope sediments, which result in mass transport deposits (MTD) in the northwestern part of the study area. These deposits exhibit 3–9.5 km widths and extend 10–13 km offshore. The boundaries of the MTDs are often demarcated by sharp truncation of finely layered sediments (FLS) and the MTDs are characterized by acoustically transparent zones in the HRS data. Average thickness of recent MTDs varies with depth, i.e., in the upper slope, the thickness is about 45 m, while in the lower slope it is about 60 m, and in deeper offshore locations they attain a maximum thickness of about 90 m. A direct indication for slumping and mass transportation of deposits is provided by the age reversal in 14C AMS dates observed in a sediment core located in the midslope region. Seismic profiling signatures provide indications of fluid/gas movement. We propose that the presence of steep topographic gradients, high sedimentation rates, a regional fault system, diapirism, fluid/gas movement, and neotectonic activity may have facilitated the slumping/sliding of the upper slope sediments in the KG offshore basin.
id: 2163

Geological Society of America Special PapersGeology and Geoarchaeology of the Black Sea Region: Beyond the Flood HypothesisPontic-Baltic pathways for invasive aquatic species: Geoarchaeological implications - Buynevich, Ilya V.; šytė, Aldona; Bitinas, Albertas; Olenin, Sergej; žeika, Jonas; šius, Rimantas (Geological Society of America, 2011)
An accurate chronology for the exchange of aquatic species between water basins is important for paleoenvironmental reconstruction on both regional and continental scales. During the early Holocene, the range of zebra mussels, Dreissena polymorpha, was limited to the Black, Azov, Caspian, and Aral Seas, as well as the estuaries and lower and middle reaches of the Pontic-Caspian rivers. We present new fi ndings that challenge the currently held view that this species migrated into the Baltic Sea watershed during the early 1800s through the canals joining the tributaries of rivers that drain into the Black and Baltic Sea basins. Geological investigations along the southeast Baltic Sea coast (Curonian and Vistula spits and lagoons) have uncovered shells of D. polymorpha that yielded radiocarbon ages older than 1000 radiocarbon yr B.P. We propose two scenarios to explain the new radiocarbon dates for D. polymorpha. The fi rst scenario involves an anomalously large reservoir effect—as large as 600– 800 yr—however, several lines of evidence cast doubt upon the validity of such a large reservoir correction. The second scenario that might explain the old zebra mussel ages is the earlier arrival of Dreissena polymorpha into the Baltic region. Natural exchange may have been facilitated by the proximity of the tributaries draining thePontic and Baltic watersheds. Human-mediated transport is also considered in association with Viking voyages from the Baltic to the Black and Caspian Seas between A.D. 800 and 1000, and the riverine trade exchange during the Lithuanian expansion into the Pontic steppe in subsequent centuries. It is likely that both scenarios played a role, with implications for late Holocene biogeography and paleoecology of the Pontic-Caspian and Baltic basins. Pontic-Baltic pathways for invasive aquatic species: Geoarchaeological implications (PDF Download Available). Available from: https://www.researchgate.net/publication/256375044_Pontic-Baltic_pathways_for_invasive_aquatic_species_Geoarchaeological_implications [accessed May 25, 2017].

Glacial to Holocene swings of the Australian-Indonesian monsoon - Mohtadi, Mahyar; Oppo, Delia W.; Steinke, Stephan; Stuut, Jan-Berend W.; De Pol-Holz, Ricardo; Hebbeln, Dierk; Lueckge, Andreas (Nature Geoscience, 2011)
The Australian-Indonesian monsoon is an important component of the climate system in the tropical Indo-Pacific region(1). However, its past variability, relation with northern and southern high-latitude climate and connection to the other Asian monsoon systems are poorly understood. Here we present high-resolution records of monsoon-controlled austral winter upwelling during the past 22,000 years, based on planktic foraminiferal oxygen isotopes and faunal composition in a sedimentary archive collected offshore southern Java. We show that glacial-interglacial variations in the Australian-Indonesian winter monsoon were in phase with the Indian summer monsoon system, consistent with their modern linkage through cross-equatorial surface winds. Likewise, millennial-scale variability of upwelling shares similar sign and timing with upwelling variability in the Arabian Sea. On the basis of element composition and grain-size distribution as precipitation-sensitive proxies in the same archive, we infer that (austral) summer monsoon rainfall was highest during the Bolling-Allerod period and the past 2,500 years. Our results indicate drier conditions during Heinrich Stadial 1 due to a southward shift of summer rainfall and a relatively weak Hadley cell south of the Equator. We suggest that the Australian-Indonesian summer and winter monsoon variability were closely linked to summer insolation and abrupt climate changes in the northern hemisphere.
id: 2012; PT: J; UT: WOS:000293277100016

Gulf of Maine shells reveal changes in seawater temperature seasonality during the Medieval Climate Anomaly and the Little Ice Age - Wanamaker Jr, Alan D.; Kreutz, Karl J.; Schöne, Bernd R.; Introne, Douglas S. (Reconstructing mid- to high-latitude marine climate and ocean variability using bivalves, coralline algae, and marine sediment cores from the Northern Hemisphere, 2011)
In this study, we use subannually resolved oxygen isotope values of fossil (dead-collected) and modern (live-caught) bivalve shells (Arctica islandica L.) from the northwestern Atlantic (Gulf of Maine, USA) to reconstruct past seasonal changes in seawater temperature. Our results indicate decreased seasonal temperature amplitude of about 1.6 °C (or ∼ 21%) during Medieval times (ca. AD 1033–1062) compared to shells from the early Little Ice Age (ca. AD 1321–1391) and during the late 19th century (AD 1864–1886). Additionally, seasonal oxygen isotope data suggest that summers were cooler and winters were warmer in the Gulf of Maine during the 11th century compared to summers and winters in the 14th century and the late 19th century. The inferred decreased seasonality during Medieval times likely resulted from increased stratification of the coastal waters due to warmer seawater temperatures. As seawater cooled during the Little Ice Age, we suggest that increased vertical mixing of the coastal surface waters was a major driving factor for the observed increase in the amplitude of the seasonal seawater temperature cycle.
id: 2193

Holocene Southern Ocean surface temperature variability west of the Antarctic Peninsula - Shevenell, A. E.; Ingalls, A. E.; Domack, E. W.; Kelly, C. (Nature, 2011)
The disintegration of ice shelves, reduced sea-ice and glacier extent, and shifting ecological zones observed around Antarctica(1,2) highlight the impact of recent atmospheric(3) and oceanic warming(4) on the cryosphere. Observations(1,2) and models(5,6) suggest that oceanic and atmospheric temperature variations at Antarctica's margins affect global cryosphere stability, ocean circulation, sea levels and carbon cycling. In particular, recent climate changes on the Antarctic Peninsula have been dramatic, yet the Holocene climate variability of this region is largely unknown, limiting our ability to evaluate ongoing changes within the context of historical variability and underlying forcing mechanisms. Here we show that surface ocean temperatures at the continental margin of the western Antarctic Peninsula cooled by 3-4 degrees C over the past 12,000 years, tracking the Holocene decline of local (65 degrees S) spring insolation. Our results, based on TEX(86) sea surface temperature (SST) proxy evidence from a marine sediment core, indicate the importance of regional summer duration as a driver of Antarctic seasonal sea-ice fluctuations(7). On millennial timescales, abrupt SST fluctuations of 2-4 degrees C coincide with globally recognized climate variability(8). Similarities between our SSTs, Southern Hemisphere westerly wind reconstructions(9) and El Nino/Southern Oscillation variability(10) indicate that present climate teleconnections between the tropical Pacific Ocean and the western Antarctic Peninsula(11) strengthened late in the Holocene epoch. We conclude that during the Holocene, Southern Ocean temperatures at the western Antarctic Peninsula margin were tied to changes in the position of the westerlies, which have a critical role in global carbon cycling(9,12).
id: 2053; PT: J; UT: WOS:000287144200042

Late Holocene environmental conditions in Coronation Gulf, southwestern Canadian Arctic Archipelago: evidence from dinoflagellate cysts, other non-pollen palynomorphs, and pollen - Pieńkowski, A. J.; Mudie, Peta J.; England, John H.; Smith, John N.; Furze, Mark F. A. (Journal of Quaternary Science, 2011)
Boxcore 99LSSL-001 (68.095°?N, 114.186° W; 211?m water depth) from Coronation Gulf represents the first decadal-scale marine palynology and late Holocene sediment record for the southwestern part of the Northwest Passage. The record was studied for organic-walled microfossils (dinoflagellate cysts, non-pollen palynomorphs), pollen, terrestrial spores, and sediment characteristics. 210Pb, 137Cs, and three accelerator mass spectrometry 14C dates constrain the chronology. Three prominent palaeoenvironmental zones were identified. During the interval AD 1470?1680 (Zone I), the climate was warmer and wetter than at present, and environmental conditions were more favourable to biological activity and northward boreal forest migration, with reduced sea-ice and a longer open-water (growing) season. The interval AD 1680?1940 (Zone II) records sea-ice increase, and generally cool, polar conditions during the Little Ice Age. During AD 1940?2000 (Zone III), organic microfossils indicate an extended open-water season and decreased sea-ice, with suggested amelioration surpassing that of Zone I. Although more marine studies are needed to place this record into an appropriate context, the succession from ameliorated (Zone I) to cooler, sea-ice influenced conditions (Zone II) and finally to 20th-century warming (Zone III) corresponds well with several terrestrial climatic records from the neighbouring mainland and Victoria Island, and with lower-resolution marine records to the west. Copyright © 2011 John Wiley & Sons, Ltd.
id: 2344

The marine record of deglaciation of the South Shetland Islands, Antarctica since the Last Glacial Maximum - Simms, Alexander R.; Milliken, Kristy T.; Anderson, John B.; Wellner, Julia S. (Quaternary Science Reviews, 2011)
The marine geological record of the glacial-retreat history of the South Shetland Islands is derived from the integration of seismic data, core lithofacies, radiocarbon ages and geomorphological data from two study areas. On the northern shelf, we present one of the first published multibeam bathymetric images of the seafloor. This new image combined with descriptions of new and existing short sediment cores and high-resolution seismic data from the continental shelf north of King George Island are used to map a grounding zone wedge that marks the minimum seaward extent of the South Shetland Ice Cap during the Last Glacial Maximum. Seismic data, multibeam bathymetry, and sediment cores from Maxwell Bay, on the opposite side of King George Island, are used to provide further spatial constrains on the history of grounding and retreat of the ice cap along the southern margin of the South Shetland Islands. During the Last Glacial Maximum the South Shetland Ice Cap extended onto the outer continental shelf, some 50 km north of its present location. The ice grounded on the shelf in troughs in present water depths of almost 400 m. It had a minimum thickness of ∼570 m and was also grounded in the deepest part of fjords and straits between the islands. To the south, the ice cap extended seaward of the mouths of fjords and straits to the steep northern boundary of the Bransfield Strait. Sediment eroded from the fjords and straits was deposited in prominent fans that extend into the Bransfield Strait and show evidence for an ice shelf that covered the Bransfield Strait during the Last Glacial Maximum. A long drill core (SHALDRIL) in Maxwell Bay and several jumbo piston cores yielded carbonate material used to constrain the timing and spatial extent of glacial retreat within Maxwell Bay. The oldest glacimarine sediments in the fjord date back to ∼14.1 to ∼14.8 ka and suggest an initial deglaciation earlier than most previous studies of the South Shetland Islands. Upper Maxwell Bay was ice free by 9.1 ka and most of Maxwell Bay proper was ice free by 5.9 ka except for the smaller tributary fjords of Maxwell Bay. These smaller tributary fjords were ice free by 1.7 ka, but may have been ice free earlier but reoccupied by a neoglacial advance that ended approximately 1.7 ka.
id: 2181

Micropaleontologic record of Quaternary paleoenvironments in the Central Albemarle Embayment, North Carolina, U.S.A - Culver, Stephen J.; Farrell, Kathleen M.; Mallinson, David J.; Willard, Debra A.; Horton, Benjamin P.; Riggs, Stanley R.; Thieler, E. Robert; Wehmiller, John F.; Parham, Peter; Snyder, Scott W.; Hillier, Caroline (Palaeogeography, Palaeoclimatology, Palaeoecology, 2011)
To understand the temporal and spatial variation of eustatic sea-level fluctuations, glacio–hydro–isostacy, tectonics, subsidence, geologic environments and sedimentation patterns for the Quaternary of a passive continental margin, a nearly complete stratigraphic record that is fully integrated with a three dimensional chronostratigraphic framework, and paleoenvironmental information are necessary. The Albemarle Embayment, a Cenozoic regional depositional basin in eastern North Carolina located on the southeast Atlantic coast of the USA, is an ideal setting to unravel these dynamic, interrelated processes. Micropaleontological data, coupled with sedimentologic, chronostratigraphic and seismic data provide the bases for detailed interpretations of paleoenvironmental evolution and paleoclimates in the 90 m thick Quaternary record of the Albemarle Embayment. The data presented here come from a transect of cores drilled through a barrier island complex in the central Albemarle Embayment. This area sits in a ramp-like setting between late Pleistocene incised valleys. The data document the episodic infilling of the Albemarle Embayment throughout the Quaternary as a series of transgressive–regressive (T–R) cycles, characterized by inner shelf, midshelf, and shoreface assemblages, that overlie remnants of fluvial to estuarine valley-fill. Barrier island and marginal marine deposits have a low preservation potential. Inner to mid-shelf deposits of the early Pleistocene are overlain by similar middle Pleistocene shelf sediments in the south of the study area but entirely by inner shelf deposits in the north. Late Pleistocene marine sediments are of inner shelf origin and Holocene deposits are marginal marine in nature. Pleistocene marine sediments are incised, particularly in the northern half of the embayment by lowstand paleovalleys, partly filled by fluvial/floodplain deposits and in some cases, overlain by remnants of transgressive estuarine sediments. The shallowing through time of Quaternary sediments reflects the eastward progradational geometry of the continental shelf. The preservation potential of marginal marine deposits (barrier island, shoreface, backbarrier deposits) is not high, except in topographic lows associated with late Pleistocene paleovalleys and inlets because the current interglacial highstand has not yet reached its highest level. Given the documented increase in rate of relative sea-level rise in this region, shallow marine conditions are likely to return to the central Albemarle Embayment in the near future.
id: 2182

The Posidonia oceanica marine sedimentary record: A Holocene archive of heavy metal pollution - Serrano, O.; Mateo, M. A.; Dueñas-Bohórquez, A.; Renom, P.; López-Sáez, J. A.; Martínez Cortizas, A. (Science of The Total Environment, 2011)
The study of a Posidonia oceanica mat (a peat-like marine sediment) core has provided a record of changes in heavy metal abundances (Fe, Mn, Ni, Cr, Cu, Pb, Cd, Zn, As and Al) since the Mid-Holocene (last 4470 yr) in Portlligat Bay (NW Mediterranean). Metal contents were determined in P. oceanica. Both, the concentration records and the results of principal components analysis showed that metal pollution in the studied bay started ca. 2800 yr BP and steadily increased until present. The increase in Fe, Cu, Pb, Cd, Zn and As concentrations since ca. 2800 yr BP and in particular during Greek (ca. 2680–2465 cal BP) and Roman (ca. 2150–1740 cal BP) times shows an early anthropogenic pollution rise in the bay, which might be associated with large- and short-scale cultural and technological development. In the last ca. 1000 yr the concentrations of heavy metals, mainly derived from anthropogenic activities, have significantly increased (e.g. from ~ 15 to 47 μg g− 1 for Pb, ~ 23 to 95 μg g− 1 for Zn and ~ 8 to 228 μg g− 1 for As). Our study demonstrates for the first time the uniqueness of P. oceanica meadows as long-term archives of abundances, patterns, and trends of heavy metals during the Late Holocene in Mediterranean coastal ecosystems.
id: 2098

Precipitation as the main driver of Neoglacial fluctuations of Gualas glacier, Northern Patagonian Icefield - Bertrand, S.; Hughen, K. A.; Lamy, F.; Stuut, J. B. W.; Torrejon, F.; Lange, C. B. (Climate of the Past, 2011)
Glaciers are frequently used as indicators of climate change. However, the link between past glacier fluctuations and climate variability is still highly debated. Here, we investigate the mid- to late-Holocene fluctuations of Gualas Glacier, one of the northernmost outlet glaciers of the Northern Patagonian Icefield, using a multi-proxy sedimentological and geochemical analysis of a 15 m long fjord sediment core from Golfo Elefantes, Chile, and historical documents from early Spanish explorers. Our results show that the core can be sub-divided in three main lithological units that were deposited under very different hydrodynamic conditions. Between 5400 and 4180 cal yr BP and after 750 cal yr BP, sedimentation in Golfo Elefantes was characterized by the rapid deposition of fine silt, most likely transported by fluvio-glacial processes. By contrast, the sediment deposited between 4130 and 850 cal yr BP is composed of poorly sorted sand that is free of shells. This interval is particularly marked by high magnetic susceptibility values and Zr concentrations, and likely reflects a major advance of Gualas glacier towards Golfo Elefantes during the Neoglaciation. Several thin silt layers observed in the upper part of the core are interpreted as secondary fluctuations of Gualas glacier during the Little Ice Age, in agreement with historical and dendrochronological data. Our interpretation of the Golfo Elefantes glaciomarine sediment record in terms of fluctuations of Gualas glacier is in excellent agreement with the glacier chronology proposed for the Southern Patagonian Icefield, which is based on terrestrial (moraine) deposits. By comparing our results with independent proxy records of precipitation and sea surface temperature, we demonstrate that the fluctuations of Gualas glacier during the last 5400 yr were mainly driven by changes in precipitation in the Andes.
id: 2119

The provenance of vegetation and environmental signatures encoded in vascular plant biomarkers carried by the Ganges–Brahmaputra rivers - Galy, Valier; Eglinton, Timothy; France-Lanord, Christian; Sylva, Sean (Earth and Planetary Science Letters, 2011)
Organic matter carried by rivers and deposited in continental and marine sediments contains valuable information on past environmental conditions and their impact on the terrestrial biosphere. In order to use sedimentary records to reconstruct past environmental conditions on the continents, such as vegetation cover and type, or precipitation intensity, we need to understand the provenance of the organic signatures and how they are transferred, and potentially modified, by fluvial transport to the sedimentary reservoir. In particular, we need to understand how environmental conditions are imprinted in the composition of riverine particulate organic carbon. Here we investigate the stable carbon and hydrogen isotopic signatures of vascular plant leaf wax biomarkers in the modern-day Ganges and Brahmaputra river complex, one of the largest fluvial systems on Earth. The distribution of n-alkanes and n-alkanoic acids in Ganges–Brahmaputra river sediments suggests that vascular plant inputs are consistently a significant component of the organic carbon pool. Molecular δ13C measurements reveal that C3 vegetation inputs delivered by the Himalayan rivers are partly degraded and replaced by mixed C3/C4 vegetation input in the floodplain. The hydrogen isotopic composition of long-chain (C24+) n-alkanoic acids, in combination with their stable C isotopic composition, provides constraints on the isotopic composition of the environmental water used by higher plants within the drainage basin. Calculated compositions compare well with the depleted δD isotopic ratios of the river water during the summer monsoon, suggesting that H-isotopic compositions of long-chain alkanoic acids are a valuable proxy for the composition of summer monsoon moisture in the Ganges–Brahmaputra basin. Detailed studies of the “isotopic anatomy” of modern river systems are critical for informed interpretation of marine sedimentary records in river-influenced continental margins.
id: 2187

Pulleniatina Minimum Events in the Andaman Sea (NE Indian Ocean): Implications for winter monsoon and thermocline changes - Sijinkumar, A. V.; Nath, B. Nagender; Possnert, G.; Aldahan, A. (Marine Micropaleontology, 2011)
The late Quaternary record of Pulleniatina obliquiloculata was investigated from two well dated sediment cores from the Andaman Sea (NE Indian Ocean) to examine its paleoceanographic significance and the presence of the Pulleniatina Minimum Events (PME) in the western North Pacific. As in the Pacific, our study shows that PMEs exist in the Indian Ocean albeit with a lower intensity. The Holocene PME occurs between 4.5 and 3.0 cal ka BP with a considerable reduction in P. obliquiloculata abundance, and which matches well with the Pacific records influenced by the Kuroshio Current. Additionally, two significant minimum events of P. obliquiloculata are also seen during the Younger Dryas (YD) and late Last Glacial Maximum (LGM, 20–18 cal ka BP). Overall, the PMEs of the Andaman Sea are not current driven events like in the western Pacific margin either by the weakening of the Kuroshio Current or reduced winter SSTs. The PMEs of the Andaman Sea are characterised by lower abundances of thermocline species indicating the increased depth of the thermocline (DOT) and reduced winter SSTs mainly during the minimum events of the YD and late LGM. The high SSTs during the Holocene PME make this event a mystery. However, the presence of PMEs in the Andaman Sea suggests that these events are not confined to areas influenced by the Kuroshio Current but may be responding to a broad scale oceanographic–climatic process or mechanism which needs to be explored with a detailed study.
id: 2159

Radiocarbon chronology of the late-glacial Puerto Bandera moraines, Southern Patagonian Icefield, Argentina - Strelin, J. A.; Denton, G. H.; Vandergoes, M. J.; Ninnemann, U. S.; Putnam, A. E. (Quaternary Science Reviews, 2011)
We report radiocarbon dates that constrain the timing of the deposition of the late-glacial Puerto Bandera moraine system alongside the western reaches of Lago Argentino adjacent to the Southern Patagonian Icefield. Close maximum-limiting radiocarbon ages (n = 11) for glacier advance into the outer moraines, with a mean value of 11,100 +/- 60 (14)C yrs BP (12,990 +/- 80 cal yrs BP), were obtained from wood in deformation (soft) till exposed beneath flow and lodgment till in Bahia del Quemado on the northeast side of Brazo Norte (North Branch) of western Lago Argentino. Other exposures of this basal deformation till in Bahia del Quemado reveal incorporated clasts of peat, along with larger inclusions of deformed glaciofluvial and lacustrine deposits. Radiocarbon dates of wood included in these reworked peat clasts range from 11,450 +/- 45 (14)C yrs BP to 13,450 +/- 150 (14)C yrs BP (13,315 +/- 60 to 16,440 +/- 340 cal yrs BP). The implication is that, during this interval, glacier fronts were situated inboard of the Puerto Bandera moraines, with the peat clasts and larger proglacial deposits being eroded and then included in the basal till during the Puerto Bandera advance. Minimum-limiting radiocarbon ages for ice retreat come from basal peat in cores sampled in spillways and depressions generated during abandonment of the Puerto Bandera moraines. Glacier recession and subsequent plant colonization were initiated close behind different frontal sectors of these moraines prior to: 10,750 +/- 75 (14)C yrs BP (12,660 +/- 70 cal yrs BP) east of Brazo Rico, 10,550 +/- 55 (14)C yrs BP (12,490 +/- 80 cal yrs BP) in Peninsula Avellaneda, and 10,400 +/- 50 (14)C yrs BP (12,280 +/- 110 cal yrs BP) in Bahia Catalana. In addition, a radiocarbon date indicates that by 10,350 +/- 45 (14)C yrs BP (12,220 +/- 110 cal yrs BP), the Brazo Norte lobe (or former Upsala Glacier) had receded well up the northern branch of Lago Argentino, to a position behind the Herminita moraines. Furthermore, glacier termini had receded to just outboard of the outer Holocene moraines at Lago Frias and Lago Pearson (Anita) prior to 10,400 +/- 40 (14)C yrs BP (12,270 +/- 100 cal yrs BP) and 9040 +/- 45 (14)C yrs BP (10,210 +/- 50 cal yrs BP), respectively. The most extensive recession registered during the early Holocene was in Agassiz Este Valley, where the Upsala Glacier had pulled back behind the outer Holocene moraine, reaching close to the present-day glacier terminus before 8290 +/- 40 (14)C yrs BP (9300 +/- 80 cal yrs BP). The radiocarbon-dated fluctuations of the Lago Argentino glacier in late-glacial time, given here, are in accord with changes in ocean mixed layer properties, predominately temperature, derived from the isotopic record given here of ODP Core 1233, taken a short distance off shore of the Chilean Lake District. It also matches recently published chronologies of late-glacial moraines in the Southern Alps of New Zealand on the opposite side of the Pacific Ocean from Lago Argentino. Finally, the timing of the late-glacial reversal of the Lago Argentino glacier fits the most recent chronology for the culmination of the Antarctic Cold Reversal (ACR) in the deuterium record of the EPICA Dome C ice core from high on the East Antarctic Plateau. Therefore, we conclude that the climate signature of the ACR was widespread in both the ocean and the atmosphere over at least the southern quarter of the globe. (C) 2011 Elsevier Ltd. All rights reserved.
id: 1954; PT: J; UT: WOS:000295387000014

Rapid Holocene coastal change revealed by high-resolution micropaleontological analysis, Pamlico Sound, North Carolina, USA - Grand Pre, Candace; Culver, Stephen J.; Mallinson, David J.; Farrell, Kathleen M.; Corbett, D. Reide; Horton, Benjamin P.; Hillier, Caroline; Riggs, Stanley R.; Snyder, Scott W.; Buzas, Martin A. (Quaternary Research, 2011)
Foraminiferal analyses of 404 contiguous samples, supported by diatom, lithologic, geochronologic and seismic data, reveal both rapid and gradual Holocene paleoenvironmental changes in an 8.21-m vibracore taken from southern Pamlico Sound, North Carolina. Data record initial flooding of a latest Pleistocene river drainage and the formation of an estuary 9000 yr ago. Estuarine conditions were punctuated by two intervals of marine influence from approximately 4100 to 3700 and 1150 to 500 cal yr BP. Foraminiferal assemblages in the muddy sand facies that accumulated during these intervals contain many well-preserved benthic foraminiferal species, which occur today in open marine settings as deep as the mid shelf, and significant numbers of well-preserved planktonic foraminifera, some typical of Gulf Stream waters. We postulate that these marine-influenced units resulted from temporary destruction of the southern Outer Banks barrier islands by hurricanes. The second increase in marine influence is coeval with increased rate of sea-level rise and a peak in Atlantic tropical cyclone activity during the Medieval Climate Anomaly. This high-resolution analysis demonstrates the range of environmental variability and the rapidity of coastal change that can result from the interplay of changing climate, sea level and geomorphology in an estuarine setting.
id: 2164

Rates and Mechanisms of Mineral Carbonation in Peridotite: Natural Processes and Recipes for Enhanced, in situ CO 2 Capture and Storage - Kelemen, Peter B.; Matter, Juerg; Streit, Elisabeth E.; Rudge, John F.; Curry, William B.; Blusztajn, Jerzy (Annual Review of Earth and Planetary Sciences, 2011)
Near-surface reaction of CO2-bearing fluids with silicate minerals in peridotite and basalt forms solid carbonate minerals. Such processes form abundant veins and travertine deposits, particularly in association with tectonically exposed mantle peridotite. This is important in the global carbon cycle, in weathering, and in understanding physical-chemical interaction during retrograde metamorphism. Enhancing the rate of such reactions is a proposed method for geologic CO2 storage, and perhaps for direct capture of CO2 from near-surface fluids. We review, synthesize, and extend inferences from a variety of sources. We include data from studies on natural peridotite carbonation processes, carbonation kinetics, feedback between permeability and volume change via reaction-driven cracking, and proposed methods for enhancing the rate of natural mineral carbonation via in situ processes ("at the outcrop") rather than ex situ processes ("at the smokestack").

A regional-scale climate reconstruction of the last 4000 years from lakes in the Nebraska Sand Hills, USA - Schmieder, J.; Fritz, S.C.; Swinehart, J.B.; Shinneman, A.L.C.; Wolfe, A.P.; Miller, G.; Daniels, N.; Jacobs, K.C.; Grimm, E.C. (Quaternary Science Reviews, 2011)
High-resolution paleohydrological reconstructions were carried out in five shallow lakes in the Nebraska Sand Hills across an eastewest transect in order to 1) determine whether long-term droughts of the past 4000 years were spatially and temporally coherent across the region, 2) distinguish local variation in climate or hydrology from regional patterns of change, and 3) compare the paleolimnological results with the existing dune-inferred drought records. Diatom-inferred lake-level was reconstructed for all sites and compared with other regional records. Alterations between high and low lake-levels were frequent during the past 4000 years, which suggests that shifts between dry and wet periods were prevalent across the Sand Hills. Extended multi-decadal to centennial-scale droughts were more common prior to 2000 years BP, while the last two millennia were hydrologically more variable and climate conditions alternated on shorter timescales. Despite some discrepancies among the five records, the paleohydrological reconstructions refine the Holocene drought history of the Nebraska Sand Hills, particularly between w2200 and 4000 cal a BP. Many of the observed drought events are contemporaneous with severe droughts documented at sites in the northern Great Plains and Rocky Mountains, lending support for the severity and regional significance of these events in western North America.
Keywords: diatoms; Droughts; Great Plains; Holocene; lakes; Nebraska Sand Hills; paleolimnology

Repeated century-scale droughts over the past 13,000 yr near the Hudson River watershed, USA - Newby, Paige E.; Shuman, Bryan N.; Donnelly, Jeffrey P.; MacDonald, Dana (Quaternary Research, 2011)
Long-term sediment and ground-penetrating radar data from Davis Pond, a small lake near the Hudson River valley, reveal past droughts in a historically humid region that presently supplies water to millions of people in and around New York City. A minimum of eleven sandy paleoshoreline deposits in the lake date from 13.4 to 0.6 cal ka BP. The deposits span 1500 to 200 yr between bracketing radiocarbon ages, and intrude into lacustrine silts up to 9.0 m below the modern lake surface in a transect of six sediment cores. Three low stands, ca. 13.4–10.9, 9.2 and 8.2 cal ka BP indicate low regional moisture balance when low temperatures affected the North Atlantic region. Consistent with insolation trends, water levels rose from ca. 8.0 cal ka BP to present, but five low stands interrupted the rise and are likely associated with ocean–atmosphere interactions. Similar to evidence from other studies, the data from Davis Pond indicate repeated multi-century periods of prolonged or frequent droughts super-imposed on long-term regional trends toward high water levels. The patterns indicate that water supplies in this heavily populated region have continuously varied at multiple time scales and confirm that humid regions such as the northeastern United States are more prone to severe drought than historically expected.
id: 2183

Response of Jakobshavn Isbrae, Greenland, to Holocene climate change - Young, N. E.; Briner, J. P.; Stewart, H. A. M.; Axford, Y.; Csatho, B.; Rood, D. H.; Finkel, R. C. (Geology, 2011)
Rapid fluctuations in the velocity of Greenland Ice Sheet (GIS) outlet glaciers over the past decade have made it difficult to extrapolate ice-sheet change into the future. This significant short-term variability highlights the need for geologic records of preinstrumental GIS margin fluctuations in order to better predict future GIS response to climate change. Using 10Be surface exposure ages and radiocarbon-dated lake sediments, we constructed a detailed chronology of ice-margin fluctuations over the past 10 k.y. for Jakobshavn Isbræ, Greenland's largest outlet glacier. In addition, we present new estimates of corresponding local temperature changes using a continuous record of insect (Chironomidae) remains preserved in lake sediments. We find that following an early Holocene advance just prior to 8 ka, Jakobshavn Isbræ retreated rapidly at a rate of ∼100 m yr−1, likely in response to increasing regional and local temperatures. Ice remained behind its present margin for ∼7 k.y. during a warm period in the middle Holocene with sustained temperatures ∼2 °C warmer than today, then the land-based margin advanced at least 2–4 km between A.D. 1500–1640 and A.D. 1850. The ice margin near Jakobshavn thus underwent large and rapid adjustments in response to relatively modest centennial-scale Holocene temperature changes, which may foreshadow GIS response to future warming.

Sea level controls sedimentation and environments in coastal caves and sinkholes - van Hengstum, Peter J.; Scott, David B.; Groecke, Darren R.; Charette, Matthew A. (Marine Geology, 2011)
Quaternary climate and sea-level research in coastal karst basins (caves, cenotes, sinkholes, blueholes, etc.) generally focuses on analyzing isotopes in speleothems, or associating cave elevations prior sea-level highstands. The sediments in coastal karst basins represent an overlooked source of climate and sea-level information in the coastal zone, but to accurately interpret these sediments first requires an understanding of the forcing mechanisms that emplace them. In this study, we hypothesize that coastal karst basins transition through vadose, littoral, anchialine, and finally into submarine environments during sea-level rise because groundwater and sea level oscillate in near synchrony in the coastal zone, causing each environment to deposit a unique sedimentary facies. To test this hypothesis, the stratigraphy in twelve sediment cores from a Bermudian underwater cave (Green Bay Cave) was investigated and temporally constrained with twenty radiocarbon dates. The results indicate that we recovered the first succession spanning the entire Holocene from an underwater cave (similar to 13 ka to present). The sediments were characterized with X-radiography, fossil remains, bulk organic matter, organic geochemistry (delta(13)C(org), C:N), and grain size analysis. Four distinct facies represent the four depositional environments: (i) vadose facies (>7.7 ka, calcite rafts lithofacies), (ii) littoral facies (7.7 to 7.3 ka: calcite rafts and mud lithofacies), (iii) anchialine facies (7.3 to 1.6 ka: slackwater and diamict lithofacies), and (iv) submarine facies (
id: 2058; PT: J; UT: WOS:000295104800003

Siliceous productivity changes in Gulf of Ancud sediments (42°S, 72°W), southern Chile, over the last ∼150 years - Rebolledo, Lorena; González, Humberto E.; Muñoz, Praxedes; Iriarte, José L.; Lange, Carina B.; Pantoja, Silvio; Salamanca, Marco (Fjord Oceanography of the Chilean Patagonia, 2011)
We evaluated changes in siliceous export production and the source of organic matter preserved in sediment core MD07-3109H recovered from the Gulf of Ancud, Chiloé Inner Sea (42°S, 72°W, water column depth: 328 m), southern Chile. We analyzed the abundance of siliceous microfossils (diatoms, silicoflagellates, sponge spicules, Chrysophyte cysts, phytoliths), geochemical proxies (weight percent silicon %SiOPAL, organic carbon, total nitrogen, C/N molar), and sediment stable isotopes (δ13Corg, δ15N). Chronology based on 210Pb and 14C provided an accumulated age of 144 years at the base of the core. Sediments of core MD07-3109H are predominantly marine in origin, averaging δ13Corg=–20.75‰±0.82, δ15N=8.7±0.35‰, and C/N=8.76±0.36. Marine diatoms compose 94% of the total assemblage of siliceous microfossils. Our record of productivity based on the mass accumulation rates of organic carbon, total nitrogen, SiOPAL, and total diatoms showed high values between 1863 and 1869 AD followed by a declining trend until 1921 AD, a transition period from 1921 to 1959 AD with fluctuating values, and a clear decreasing pattern from 1960 AD to the present. This marked reduction in productivity was associated with decreased precipitation and Puelo River streamflow (41°S), as well as a warmer and more stratified water column, especially since the 1980s.
id: 2191

Solar modulation of North Atlantic central Water formation at multidecadal timescales during the late Holocene - Morley, Audrey; Schulz, Michael; Rosenthal, Yair; Mulitza, Stefan; Paul, André; Rühlemann, Carsten (Earth and Planetary Science Letters, 2011)
Understanding natural climate variability in the North Atlantic region is essential not only to assess the sensitivity of atmosphere–ocean climate signal exchange and propagation, but also to help distinguish between natural and anthropogenic climate change. The North Atlantic Oscillation is one of the controlling modes in recent variability of atmosphere–ocean linkages and ice/freshwater fluxes between the Polar and North Atlantic Ocean. Through these processes the NAO influences water mass formation and the strength of the Atlantic Meridional Overturning circulation and thereby variability in ocean heat transport. However, the impact of the NAO as well as other forcing mechanisms on multidecadal timescales such as total solar irradiance on Eastern North Atlantic Central Water production, central water circulation, and climate signal propagation from high to low latitudes in the eastern subpolar and subtropical basins remains uncertain. Here we use a 1200 yr long benthic foraminiferal Mg/Ca based temperature and oxygen isotope record from a ~ 900 m deep sediment core off northwest Africa to show that atmosphere–ocean interactions in the eastern subpolar gyre are transferred at central water depth into the eastern boundary of the subtropical gyre. Further we link the variability of the NAO (over the past 165 yrs) and solar irradiance (Late Holocene) and their control on subpolar mode water formation to the multidecadal variability observed at mid-depth in the eastern subtropical gyre. Our results show that eastern North Atlantic central waters cooled by up to ~ 0.8 ± 0.7 °C and densities decreased by σθ = 0.3 ± 0.2 during positive NAO years and during minima in solar irradiance during the Late Holocene. The presented records demonstrate the sensitivity of central water formation to enhanced atmospheric forcing and ice/freshwater fluxes into the eastern subpolar gyre and the importance of central water circulation for cross-gyre climate signal propagation during the Late Holocene.
id: 2175

Sources of n-alkanes in an urbanized estuary: Insights from molecular distributions and compound-specific stable and radiocarbon isotopes - Ahad, Jason M. E.; Ganeshram, Raja S.; Bryant, Charlotte L.; Cisneros-Dozal, Luz M.; Ascough, Philippa L.; Fallick, Anthony E.; Slater, Greg F. (Marine Chemistry, 2011)
Diagnostic molecular ratios and compound-specific 13C and 14C analyses were used to identify n-alkane sources in surface sediments collected along a transect from an urbanized estuary draining a peat-rich catchment (Tyne, UK). The most abundant homologues were generally C29 or C31, and the carbon preference index (CPI; 1.8 to 6.4) and average chain length (ACL; 28.5 to 29.5) of C25–C33 n-alkanes became progressively lower in samples closer to the mouth of estuary. δ13C signatures of C19–C31 n-alkanes ranged from − 37.1 to − 29.3‰ and in general became more depleted with increasing carbon number. Δ14C values for C21 (− 945 to − 738‰) were significantly more depleted compared to C29 (− 591 to − 65‰) and C31 (− 382 to − 96‰), pointing to a much higher component of fossil (i.e., 14C-free) carbon in the shorter homologue. The radiocarbon contents for these three n-alkanes decreased toward the North Sea, which in conjunction with an up to 4‰ seaward 13C-enrichment in C29 and C31 and seaward decreases in CPI and ACL pointed to petrogenic hydrocarbon contamination in lower estuarine sediments. Independent 13C and 14C mass balances used to calculate the relative proportions of modern (i.e., plant wax) and fossil (i.e., petrogenic) n-alkanes yielded similar results and demonstrated that mixing with marine-derived organic matter (OM) or microbial degradation during estuarine transport led to a seaward decline in modern, longer-chain homologues, resulting in an increasingly larger fossil carbon contribution toward the mouth of estuary. The ability to clearly distinguish anthropogenic from natural inputs suggests that compound-specific radiocarbon analysis can successfully delineate the age of terrigenous OM delivered to the coastal zone even near historically polluted systems such as the Tyne.
id: 2169

Stable isotope analysis of dog, fox, and human diets at a Late Holocene Chumash village (CA-SRI-2) on Santa Rosa Island, California - Rick, Torben C.; Culleton, Brendan J.; Smith, Carley B.; Johnson, John R.; Kennett, Douglas J. (Journal of Archaeological Science, 2011)
Stable carbon (δ13C) and nitrogen (δ15N) isotope analyses of dog (Canis familiaris), island fox (Urocyon littoralis), and human bone collagen from CA-SRI-2 (AD 130–1830) on Santa Rosa Island, California provide a proxy of diet and the relationships between humans and these animals. Carbon isotopic signatures indicate that Native Americans and their dogs at CA-SRI-2 subsisted almost exclusively on marine resources, while the island fox ate primarily terrestrial foods. Nitrogen isotopes and archaeofaunal remains indicate that humans and dogs also ate higher trophic level foods, including finfishes, marine mammals, and seabirds with smaller amounts of shellfish. The CA-SRI-2 island foxes appear to have eaten higher amounts of terrestrial foods, similar to the diets observed in modern fox populations. These data generally confirm the commensal relationship assumed to exist between domesticated dogs and people, but the carbon isotopic composition of dogs is enriched ∼2‰ compared to humans. We hypothesize that the difference in carbon isotopes between dogs and humans may have resulted from a higher consumption of C3 plants with lower δ13C values by humans, or less likely from the ingestion by dogs of significant amounts of bone collagen, which is enriched by ∼4‰ over associated muscle.
id: 2180

Trace metal enrichments in Lake Tanganyika sediments: Controls on trace metal burial in lacustrine systems - Brucker, Rebecca Poulson; McManus, James; Severmann, Silke; Owens, Jeremy; Lyons, Timothy W. (Geochimica et Cosmochimica Acta, 2011)
We investigate the distributions of several key diagenetic reactants (C, S, Fe) and redox-sensitive trace metals (Mo, Cd, Re, U) in sediments from Lake Tanganyika, East Africa. This study includes modern sediments from a chemocline transect, which spans oxygenated shallow waters to sulfidic conditions at depth, as well as ancient sediments from a longer core (∼2 m) taken at ∼900 m water depth. Modern sediments from depths spanning ∼70–335 m are generally characterized by increasing enrichments of C, S, Mo, Cd, and U with increasing water depth but static Fe distributions. It appears that the sedimentary enrichments of these elements are, to varying degrees, influenced by a combination of organic carbon cycling and sulfur cycling. These modern lake characteristics contrast with a period of high total organic carbon (Corg), total sulfur (STot), and trace metal concentrations observed in the 900 m core, a period which follows the most recent deglaciation (∼18–11 ky). This interval is followed abruptly by an interval (∼11–6 ky) that is characterized by lower C, S, U, and Mo. Consistent with other work we suspect that the low concentrations of S, Mo, and U may indicate a period of intense lake mixing, during which time the lake may have been less productive and less reducing as compared to the present. An alternative, but not mutually exclusive, hypothesis is that changes in the lake’s chemical inventory, driven by significant hydrological changes, could be influencing the distribution of sedimentary trace elements through time.
id: 2144

U-series dating of co-seismic gypsum and submarine paleoseismology of active faults in Northern Chile (23°S) - Vargas, Gabriel; Palacios, Carlos; Reich, Martin; Luo, Shangde; Shen, Chuan-Chou; González, Gabriel; Wu, Yi-Chen (Tectonophysics, 2011)
The convergence of the Nazca and South American plates along the subduction margin of the central Andes results in large subduction earthquakes and tectonic activity along major fault systems. Despite its relevance, the paleoseismic record of this region is scarce, hampering our understanding about the relationship between the Andes building and earthquake occurrence. In this study, we used the U-series disequilibrium method to obtain absolute ages of paleoearthquake events associated with normal displacements along the active Mejillones and Salar del Carmen faults in the Coastal Range of the Atacama Desert of northern Chile. The 230Th–234U disequilibrium ages in co-seismic gypsum salts sampled along the fault traces together with marine evidences indicate that earthquakes occurred at ca. 29.7 ± 1.7 ka, 11 ± 4 ka and 2.4 ± 0.8 ka. When coupled with paleoseismic marine and radiocarbon (14C) records in the nearby Mejillones Bay evidencing large dislocations along the Mejillones Fault, the geochronological dataset presented here is consistent with the notion that gypsum salts formed during large earthquakes as a result of co-seismic dilatancy pumping of saline waters along the major faults. Based on maximum observed cumulative vertical offsets in the studied faults, this phenomena could have occurred episodically at a rate in the order of 1:40 to 1:50 with respect to the very large subduction earthquakes during the latest Pleistocene–Holocene period. The results presented here reveal that the U-series disequilibrium method can be successfully applied to date the gypsum salts deposited along faults during seismic events, and therefore directly constrain the age of large paleoearthquakes in hyperarid and seismically active zones.
id: 2147

Application of bacterial glycerol dialkyl glycerol tetraethers (GDGTs) to develop modern and past temperature estimates from New Zealand lakes - Zink, Klaus- G.; Vandergoes, Marcus J.; Mangelsdorf, Kai; Dieffenbacher-Krall, Ann C.; Schwark, Lorenz (Organic Geochemistry, 2010)
Branched isoalkyl glycerol dialkyl glycerol tetraethers (GDGTs) of bacterial origin have been found in high abundance in both modern and glacial sediments of New Zealand South Island freshwater lakes covering a wide range of altitude (101-2000 m). Like isoprenoid GDGTs of archaeal origin, they provide excellent potential for temperature assessment. For this study, their distribution patterns (MBT, methylation ratio and CBT, cyclisation ratio of branched GDGTs) have been successfully used to develop an initial temperature calibration for the study area and to provide preliminary (palaeo)environmental interpretations. MBT data from modern lake sediments correlate well with measured annual air temperature (R(2) 0 74), enabling a regional calibration for reconstructing palaeotemperatures for fossil samples. MBT-derived palaeotemperatures for Alpine Lake, calibrated against mean annual temperature, were determined for the Last Glacial during an early cold phase (between 29,000 and 26,000 years BP) and for later less cold phases (between 23,000 and 18,000 years BP). Compared with the modern temperature regime, the MBT data indicate a decrease of ca 56 and 2 8 degrees C respectively, during this time Modern and past MBT-derived temperatures correlate with chironomid-based temperature reconstructions in the area Archaeal GDGTs, commonly used for the TEX(86) index, are abundant in fossil sediments (Alpine Lake) but scarce in modern sediments, hindering a new local calibration for this palaeotemperature proxy. (C) 2010 Elsevier Ltd All rights reserved
id: 1955; PT: J; CT: 24th International Meeting on Organic Geochemistry; CY: SEP 06-11, 2009; CL: Bremen, GERMANY; UT: WOS:000282671500040

Asphalt volcanoes as a potential source of methane to late Pleistocene coastal waters - Valentine, D. L.; Reddy, C. M.; Farwell, C.; Hill, T. M.; Pizarro, O.; Yoerger, D. R.; Camilli, R.; Nelson, R. K.; Peacock, E. E.; Bagby, S. C.; Clarke, B. A.; Roman, C. N.; et al. (Nature Geoscience, 2010)
Every year, natural petroleum seepage emits 0.2-2 Tg of oil to the ocean(1). Significant oil seepage can build large underwater mounds, consisting of tar deposits with morphologies similar to volcanic lava flows, known as asphalt volcanoes(2,3). Such events are typically accompanied by large fluxes of the greenhouse gas methane(4,5). Marine sediments from the Santa Barbara basin, California, contain a record of elevated methane concentrations(6), anoxia and tar deposition(7) during the Pleistocene epoch that had been attributed to dissolution of methane hydrates. However, the region is known to have exhibited oil seepage in the past(7). Here, we document the discovery of seven extinct asphalt volcanoes off the coast of southern California. The morphology of the deposits and geochemistry of samples taken from the two largest structures supports their classification as asphalt volcanoes, derived from a common source. We estimate that the two structures resulted from seepage of 0.07-0.4 Tg of oil, accompanied by the emission of 0.35-1.8 Tg of methane. Radiocarbon dating of carbonate deposits entrained with the asphalt indicates formation of the volcanoes between 44 and 31 kyr ago. The timing and volume of erupted hydrocarbons from the asphalt structures can explain some or all of the documented methane release and tar accumulation in the Santa Barbara basin during the Pleistocene.
id: 1866; Sp. Iss. SI 589XW Times Cited:0 Cited References Count:28; YY

Assessing Microbial Uptake of Petroleum Hydrocarbons in Groundwater Systems Using Natural Abundance Radiocarbon - Ahad, Jason M. E.; Burns, Leanne; Mancini, Silvia; Slater, Greg F. (ENVIRONMENTAL SCIENCE & TECHNOLOGY, 2010)
Carbon sources utilized by the active microbial communities in shallow groundwater systems underlying three petroleum service stations were characterized using natural abundance radiocarbon ((14)C). Total organic carbon (TOC) Delta(14)C values ranged from -314 to -972 parts per thousand and petroleum-extracted residues (EXT-RES) ranged from -293 to -971 parts per thousand. Phospholipid fatty acids (PLFAs)-biomarkers for active microbial populations-ranged from -405 to -885 parts per thousand and a comparison of these values with potential carbon sources pointed to significant microbial assimilation of (14)C-free fossil carbon. The most (14)C depleted PLFAs were found in the samples with the highest concentrations of total petroleum hydrocarbons (TPHs). A radiocarbon mass balance indicated up to 43% of the carbon in microbial PLFAs was derived from TPHs, providing direct evidence for biodegradation at two of three sites. At lower levels of TPHs. Delta(14)C values of PLFAs were generally similar to or more enriched than all other carbon in the system indicating microbial utilization of a more (14)C-enriched carbon source and no resolvable evidence for microbial incorporation of petroleum-derived carbon. Results from this study suggest that it is possible to delineate petroleum biodegradation in groundwater systems using these techniques even in complex situations where there exists a wide range in the ages of natural organic matter (i.e., EXT-RES).

Coastal New England pilot study to determine fossil and biogenic formaldehyde source contributions using radiocarbon - Shen, Haiwei; Heikes, Brian G.; Merrill, John T.; McNichol, Ann P.; Xu, Li (JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES, 2010)
Compound specific radiocarbon analyses of atmospheric formaldehyde are reported as fraction modern (Fm) for a limited number of winter and summer air samples collected in coastal southern New England in 2007. The 11 of 13 samples with Fm < 0.2 were collected under the influence of the semipermanent Bermuda high-pressure system with transport from the Washington, D. C., to New York City urban corridor. The two samples with Fm > 0.2 (max similar to 0.35) were collected on days with strong northwesterly flow and the least urban impact. The Fm data were combined with VOC observations from the Rhode Island Department of Environmental Management, estimates of oxygenated VOC (OVOC), and back trajectories to interpret the relative contributions of biogenic and fossil carbon sources. It is argued that CH2O sources were dominated by pollutant VOCs and OVOCs from upwind coastal cities as opposed to more local biogenic VOCs at the times of sample collection.

Controls on the age of terrigenous organic matter in Black Sea sediments - Kusch, Stephanie; Rethemeyer, Janet; Schefuß, Enno; Mollenhauer, Gesine (Geochimica et Cosmochimica Acta, 2010)
id: 885

Determination of Microbial Carbon Sources and Cycling during Remediation of Petroleum Hydrocarbon Impacted Soil Using Natural Abundance (14)C Analysis of PLFA - Cowie, Benjamin R.; Greenberg, Bruce M.; Slater, Gregory F. (Environmental science & technology, 2010)
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.
id: 2054; PT: J; UT: WOS:000275993700017

Developing graminoid cuticle analysis for application to Beringian palaeoecology - Gaglioti, B. V.; Severin, K.; Wooller, M. J. (Review of palaeobotany and palynology, 2010)
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.
id: 2132; PT: J; TC: 3; UT: WOS:000281181100009

From ice age to modern: a record of landscape change in an Andean cloud forest - Valencia, B. G.; Urrego, D. H.; Silman, M. R.; Bush, M. B. (Journal of Biogeography, 2010)
Aim
id: 869; 639ND Times Cited:5 Cited References Count:63Y

Geology of Lonar Crater, India - Maloof, A. C.; Stewart, S. T.; Weiss, B. P.; Soule, S. A.; Swanson-Hysell, N. L.; Louzada, K. L.; Garrick-Bethell, I.; Poussart, P. M. (Geological Society of America Bulletin, 2010)
Lonar Crater, India, is one of the youngest and best preserved impact structures on Earth. The 1.88-km-diameter simple crater formed entirely within the Deccan traps, making it a useful analogue for small craters on the basaltic surfaces of the other terrestrial planets and the Moon. In this study, we present a meter-scale-resolution digital elevation model, geological map of Lonar Crater and the surrounding area, and radiocarbon ages for histosols beneath the distal ejecta. Impact-related deformation of the target rock consists of upturned basalt flows in the upper crater walls and recumbent folding around rim concentric, subhorizontal, non-cylindrical fold axes at the crater rim. The rim-fold hinge is preserved around 10%-15% of the crater. Although tearing in the rim-fold is inferred from field and palcomagnetic observations, no tear faults are identified, indicating that large displacements in the crater walls are not characteristic of small craters in basalt. One significant normal fault structure is observed in the crater wall that offsets slightly older layer-parallel slip faults. There is little fluvial erosion of the continuous ejecta blanket. Portions of the ejecta blanket are overlain by aerodynamically and rotationally sculpted glassy impact spherules, in particular in the eastern and western rim, as well as in the depression north of the crater known as Little Lonar. The emplacement of the continuous ejecta blanket can be likened to a radial ground-hugging debris flow, based on the preserved thickness distribution of the ejecta, the efficient exchange of clasts between the ejecta flow and the underlying histosol, and the lack of sorting and stratification in the bulk of the ejecta. The ejecta profile is thickened at the distal edge and similar to fluidized ejecta structures observed on Mars.
id: 1846; 539YI Times Cited:0 Cited References Count:100Y

Holocene changes in Proboscia diatom productivity in shelf waters of the north-western Antarctic Peninsula - Willmott, V.; Rampen, S. W.; Domack, E.; Canals, M.; Damste, J. S. S.; Schouten, S. (Antarctic Science, 2010)
Diatoms are important primary producers in present day Antarctic waters but their relative significance in the past is less clear. In this Study We used long-chain diols to reconstruct Proboscia diatom productivity in shelf waters of the western Antarctic Peninsula over the last 8500 yr. Biomarker lipid analysis revealed the presence of a suite of long-chain diols in the sediments, mainly comprising the C-28 and C-30 1,14-diol isomers derived from Proboscia diatoms and C-28 and C-30 1,13-diols derived from other unknown algae. The relative importance of Proboscia diatoms was assessed using the relative abundances of 1, 14-diols versus 1, 13-diols, which showed that Proboscia diatoms were relatively more abundant during the Late Holocene, suggesting that stronger upwelling of circumpolar waters Occurred at that time. The variations in the diol index strongly correlate with melt events in the Siple Dome ice core, Suggesting that the climatic processes responsible for changes in mean summer temperature, open marine influence and atmospheric cyclonic activity recorded at Siple Dome, also controlled the productivity of Proboscia diatoms on the western Antarctic Peninsula region.
id: 789; 559YJ Times Cited:0 Cited References Count:51Y