TY - JOUR T1 - Relative sea-level change in South Florida during the past ~5000 years JF - Global and Planetary Change Y1 - 2022 A1 - Khan, Nicole S. A1 - Ashe, Erica A1 - Moyer, Ryan P. A1 - Kemp, Andrew C. A1 - Engelhart, Simon E. A1 - Brain, Matthew J. A1 - Toth, Lauren T. A1 - Chappel, Amanda A1 - Christie, Margaret A1 - Kopp, Robert E. A1 - Horton, Benjamin P. KW - Holocene KW - mangrove KW - Proxy reconstruction KW - Reproducibility KW - sea level AB - A paucity of detailed relative sea-level (RSL) reconstructions from low latitudes hinders efforts to understand the global, regional, and local processes that cause RSL change. We reconstruct RSL change during the past ~5 ka using cores of mangrove peat at two sites (Snipe Key and Swan Key) in the Florida Keys. Remote sensing and field surveys established the relationship between peat-forming mangroves and tidal elevation in South Florida. Core chronologies are developed from age-depth models applied to 72 radiocarbon dates (39 mangrove wood macrofossils and 33 fine-fraction bulk peat). RSL rose 3.7 m at Snipe Key and 5.0 m at Swan Key in the past 5 ka, with both sites recording the fastest century-scale rate of RSL rise since ~1900 CE (~2.1 mm/a). We demonstrate that it is feasible to produce near-continuous reconstructions of RSL from mangrove peat in regions with a microtidal regime and accommodation space created by millennial-scale RSL rise. Decomposition of RSL trends from a network of reconstructions across South Florida using a spatio-temporal model suggests that Snipe Key was representative of regional RSL trends, but Swan Key was influenced by an additional local-scale process acting over at least the past five millennia. Geotechnical analysis of modern and buried mangrove peat indicates that sediment compaction is not the local-scale process responsible for the exaggerated RSL rise at Swan Key. The substantial difference in RSL between two nearby sites highlights the critical need for within-region replication of RSL reconstructions to avoid misattribution of sea-level trends, which could also have implications for geophysical modeling studies using RSL data for model tuning and validation. VL - 216 UR - https://www.sciencedirect.com/science/article/pii/S0921818122001692 ER - TY - JOUR T1 - Younger Dryas and early Holocene climate in south Greenland inferred from oxygen isotopes of chironomids, aquatic Moss, and Moss cellulose JF - Quaternary Science Reviews Y1 - 2022 A1 - Puleo, Peter J. K. A1 - Masterson, Andrew L. A1 - Medeiros, Andrew S. A1 - Schellinger, Grace A1 - Steigleder, Regan A1 - Woodroffe, Sarah A1 - Osburn, Magdalena R. A1 - Axford, Yarrow KW - Chironomids KW - Deglaciation KW - diatoms KW - Greenland KW - Holocene KW - Micropaleontology KW - paleoclimatology KW - paleolimnology KW - Stable isotopes KW - Younger Dryas AB - Ice core records have long indicated that the Younger Dryas began and ended with large, abrupt climate shifts over Greenland. Key climatic features remain unknown, including the magnitude of warming during the Younger Dryas-Holocene transition along with the seasonality and spatial variability of Younger Dryas climate changes across Greenland. Here, we use geochemical and paleoecological proxies from lake sediments at Lake N14 in south Greenland to address these outstanding questions. Radiocarbon dating and diatom assemblages confirm early deglaciation and isolation of Lake N14 before ∼13,600 cal yr BP, consistent with previous work. Oxygen isotope ratios (δ18O) of chironomid head capsules, bulk aquatic moss, and aquatic moss-derived cellulose are used to reconstruct oxygen isotopes of past lake water and annual precipitation. Oxygen isotope proxies indicate annual precipitation δ18O values increased by 5.9–7.7‰ at the end of the Younger Dryas. Following the Younger Dryas, moss and cellulose δ18O values show a clear decline in precipitation δ18O values of 2–3‰ from ∼11,540–11,340 cal yr BP that may correspond with the Preboreal Oscillation. Reconstructed precipitation δ18O values then gradually increased from 11,300–10,100 cal yr BP. All three aquatic organic materials register similar shifts in precipitation δ18O values over time, and they closely parallel the δ18O shifts observed in ice cores. This evidence strongly supports the utility of these methods for reconstructing lake water δ18O, and furthermore precipitation δ18O values where lake water reflects precipitation. The relatively large shift in isotopic composition of precipitation at Lake N14 suggests that shifts in temperature, precipitation seasonality, and/or moisture sources at the end of the Younger Dryas were even larger in south Greenland than they were in central Greenland, most likely because of the proximity to major changes in North Atlantic Ocean circulation. The annual air temperature change estimated at Lake N14 at the end of the Younger Dryas is also very large (∼18 ± 7 °C) compared to the summer warming previously inferred from chironomid species assemblages there (∼6 °C). This indicates that the strongest warming at the end of the Younger Dryas occurred in the winter season, consistent with past observations of intensified Younger Dryas seasonality at Lake N14 and elsewhere in Greenland. VL - 296 UR - https://www.sciencedirect.com/science/article/pii/S0277379122004413 ER - TY - JOUR T1 - Asian summer monsoon influence on chemical weathering and sediment provenance determined by clay mineral analysis from the Indus Submarine Canyon JF - Quaternary Research Y1 - 2020 A1 - Li, Yuting A1 - Clift, Peter D. A1 - Murray, Richard W. A1 - Exnicios, Elise A1 - Ireland, Thomas A1 - Böning, Philipp KW - Clay minerals KW - Holocene KW - monsoon KW - Provenance KW - Reworking KW - Submarine canyon AB - Clay minerals from the Indus Canyon and eastern clinoform since ~12 ka are uniformly rich in smectite and illite, similar to those from the Holocene Indus flood plains. A systematic enrichment of smectite in the proximal delta compared to the canyon and eastern clinoform argues for preferential capture of smectite close to the river mouth since ~12 ka. There is a rapid shift to a more smectite-rich assemblage in the canyon and eastern clinoform after ~5 ka. This change is probably caused by a change in sediment source, with less direct flux from the Himalaya and more erosion of older, weathered, smectite-rich sediment from the Indus River flood plains, driven by incision of the Indus and its tributaries into the floodplain as summer monsoon rains weakened. This influx of smectite is consistent with lower kaolinite/smectite values since ~5 ka. The onset of large-scale agricultural activities since ~5 ka, especially starting with the Harappan Civilization, may also have enhanced incision and erosion of floodplain sediments over the same time period. This study reports for the first time how monsoon strength variations since ~12 ka affected the clay mineral assemblages and sediment provenance in a major submarine canyon. VL - 93 UR - https://www.cambridge.org/core/journals/quaternary-research/article/asian-summer-monsoon-influence-on-chemical-weathering-and-sediment-provenance-determined-by-clay-mineral-analysis-from-the-indus-submarine-canyon/AA11F458BD5924C1BD9EC9901D1F2941 ER - TY - JOUR T1 - Insolation and greenhouse gases drove Holocene winter and spring warming in Arctic Alaska JF - Quaternary Science Reviews Y1 - 2020 A1 - Longo, William M. A1 - Huang, Yongsong A1 - Russell, James M. A1 - Morrill, Carrie A1 - Daniels, William C. A1 - Giblin, Anne E. A1 - Crowther, Josue KW - Alkenone KW - Beringia KW - Continental biomarkers KW - Holocene KW - North America KW - paleoclimatology KW - paleolimnology KW - Proxy data-model comparison KW - seasonality KW - Temperature reconstruction AB - Global surface temperature changes and their drivers during the Holocene Epoch remain controversial. Syntheses of proxy data indicate that global mean annual temperature declined from the mid-Holocene until the Pre-industrial Era, a trend linked to decreasing Northern Hemisphere summer insolation. In contrast, global climate models simulate increasing mean annual temperatures driven by retreating ice sheets and increasing greenhouse gas concentrations. This proxy-model disagreement may originate from a warm season bias in Northern Hemisphere proxy reconstructions, highlighting the need for new proxies that quantify cold season temperature, especially in Arctic regions that were devoid of continental ice sheets during the Holocene. Here, we present a new 16,000-year winter-spring temperature reconstruction derived from the unsaturation ratio of alkenones (U-3(7)K) in a continuous sedimentary sequence from Lake E5, northern Alaska. We employ a thermodynamic lake model to convert alkenone-inferred lake temperatures into winter-spring air temperature anomalies and we contextualize our proxy reconstruction with climate model output from the region. Our reconstruction shows that winter-spring temperatures warmed rapidly during the deglaciation at 16 and 14 thousand years before present and continued to warm gradually throughout the middle and late Holocene (0.12-0.28 degrees C/thousand years) in concert with regional sea surface temperature and sea ice records. Our results are consistent with climate model simulations and we attribute Holocene warming to rising winter-spring insolation, radiative forcing from rising greenhouse gas concentrations and regional feedbacks. Our reconstructed cold season warming equaled or exceeded summer cooling according to a regional synthesis of temperature records, suggesting that seasonal biases in temperature reconstructions may account for proxy-model disagreements in Holocene temperature trends from Eastern Beringia. (C) 2020 Elsevier Ltd. All rights reserved. VL - 242 UR - https://linkinghub.elsevier.com/retrieve/pii/S0277379120304005 ER - TY - JOUR T1 - Late glacial and Holocene paleoenvironments in the midcontinent United States, inferred from Geneva Lake leaf wax, ostracode valve, and bulk sediment chemistry JF - Quaternary Science Reviews Y1 - 2020 A1 - Puleo, Peter J.K. A1 - Axford, Yarrow A1 - McFarlin, Jamie M. A1 - Curry, B. Brandon A1 - Barklage, Mitchell A1 - Osburn, Magdalena R. KW - Holocene KW - Inorganic geochemistry KW - Loess KW - North America KW - Organic geochemistry KW - paleoclimatology KW - paleolimnology KW - Pleistocene KW - sedimentology KW - Stable isotopes AB - Geneva Lake in Wisconsin, USA, is > 20,000 years old and contains a 30-m thick lacustrine sediment record of mid-continent North American climate and environmental change. Here we describe a sediment record from Geneva Lake spanning the past 14,500 years. From scanning X-ray fluorescence, organic C and N concentrations and isotopes, X-ray diffraction, magnetic susceptibility, and grain size of bulk sediments, we infer changes in sediment sources over time including: abrupt decline in inputs of remobilized loess ∼13,400 cal yr BP followed by a gradual transition to organic-rich marl deposition by ∼10,400 cal yr BP as the landscape stabilized following a period of permafrost thaw and vegetation development; deposition of a minerogenic unit at ∼8,200 cal yr BP that may record enhanced eolian activity during the widespread “8.2 ka event; ” and elevated zinc, lead, and arsenic from human activities following regional industrialization. Within the Holocene marl, we also use isotopic (δ18O and δ13C) and trace metal ratio (Sr/Ca and Mg/Ca) analyses of ostracode valves paired with concentrations and hydrogen isotopic composition (δ2H) of leaf wax n-alkanes to infer climate and hydrological change. Groundwater had a large but declining influence on lake water chemistry from 11,800 to 9,700 cal yr BP, precluding inferences of regional climate from our lacustrine proxies during this period. δ2H values of terrestrial n-C29 alkanes show little variability from 9,700 to present, indicating the average isotopic composition of local precipitation was relatively stable, reflecting stable condensation temperatures and source. In contrast, a gradual trend towards more δ18O- and δ2H-depleted lake water and lower lake water Sr/Ca from 9700 cal yr BP to present suggest decreasing evaporation of lake water and increasing precipitation amounts throughout the Holocene and resulting shorter lake water residence times. Lake water Mg/Ca variations over the past 9,700 years broadly parallel regional pollen-based reconstructions of summer temperatures. Neither Mg/Ca nor terrestrial leaf wax δ2H suggest long-term directional shifts in temperature at this site through the middle to late Holocene, as climate became wetter. It appears that precipitation isotopes did not track local temperatures on millennial timescales in this part of mid-continent North America through the Holocene, and instead may have covaried with changes in Northern Hemisphere latitudinal temperature gradients driven by large Arctic temperature changes. VL - 241 UR - https://www.sciencedirect.com/science/article/pii/S0277379120303462 ER - TY - JOUR T1 - A late Holocene subfossil Atlantic white cedar tree-ring chronology from the northeastern United States JF - Quaternary Science Reviews Y1 - 2020 A1 - Pearl, Jessie K. A1 - Anchukaitis, Kevin J. A1 - Donnelly, Jeffrey P. A1 - Pearson, Charlotte A1 - Pederson, Neil A1 - Lardie Gaylord, Mary C. A1 - McNichol, Ann P. A1 - Cook, Edward R. A1 - Zimmermann, George L. KW - coastal KW - Geomorphology KW - Holocene KW - North America KW - paleoclimatology KW - radiogenic isotopes KW - Tree-rings AB - Tree-rings provide precise annually dated climate information, but their application can be limited by the relatively short lifespan of many trees. To overcome this limitation, tree-ring records can be extended over longer time periods by connecting living trees with older “sub-fossil” trees, which can provide information on longer timescales throughout the Holocene. These long chronologies are proxy records of past climate, provide precise chronological information for extreme events, and give insight into the range of natural climate variability prior to the instrumental period. In the densely populated northeastern United States, few tree-ring records are longer than 500 years, and there are no millennial-length tree-ring chronologies for the region. Here, we use a combination of standard dendrochronological and radiocarbon techniques, including use of the 774 CE radiocarbon excursion, to generate an absolutely dated 2500 year-long tree ring record from living, archaeological, and subfossil Atlantic white cedar (Chamaecyparis thyoides) found in the coastal northeastern United States. Our chronology demonstrates the potential to develop multi-millennial Chamaecyparis thyoides tree-ring records to address previously unanswered questions regarding late Holocene hydroclimate, extreme events, and temperature variability in New England. VL - 228 UR - https://linkinghub.elsevier.com/retrieve/pii/S0277379119308108 ER - TY - JOUR T1 - RADIOCARBON RESERVOIR AGES IN THE HOLOCENE DEAD SEAABSTRACT JF - Radiocarbon Y1 - 2020 A1 - Weber, Nurit A1 - Lazar, Boaz A1 - Stern, Ofra A1 - Burr, George A1 - Gavrieli, Ittai A1 - Roberts, Mark A1 - Kurz, Mark D A1 - Yechieli, Yoseph A1 - Stein, Mordechai KW - aragonite KW - Dead Sea KW - Holocene KW - radiocarbon KW - reservoir ages AB - The sources and fate of radiocarbon (C-14) in the Dead Sea hypersaline solution are evaluated with C-14 measurements in organic debris and primary aragonite collected from exposures of the Holocene Ze'elim Formation. The reservoir age (RA) is defined as the difference between the radiocarbon age of the aragonite at time of its precipitation (representing lake's dissolved inorganic carbon pig) and the age of contemporaneous organic debris (representing atmospheric radiocarbon). Evaluation of the data for the past 6000 yr from Dead Sea sediments reveal that the lake's RA decreased from 2890 yr at 6 cal kyr BP to 2300 yr at present. The RA lies at similar to 2400 yr during the past 3000 yr, when the lake was characterized by continuous deposition of primary aragonite, which implies a continuous supply of freshwater-bicarbonate into the lake. This process reflects the overall stability of the hydrological-climate conditions in the lake's watershed during the late Holocene where bicarbonate originated from dissolution of the surface cover in the watershed that was transported to the Dead Sea by the freshwater runoff. An excellent correlation (R-2=0.98) exists between aragonite ages and contemporaneous organic debris, allowing the estimation of ages of various primary deposits where organic debris are not available. VL - 62 UR - https://apps.webofknowledge.com/InboundService.do?product=WOS&Func=Frame&DestFail=http%3A%2F%2Fwww.webofknowledge.com&SrcApp=search&SrcAuth=Alerting&SID=8AkJOJLKFU3j5nkGaRI&customersID=Alerting&mode=FullRecord&IsProductCode=Yes&AlertId=4d48b20a-7d27-4fa2- IS - 5 ER - TY - JOUR T1 - A refined age calibrated paleosecular variation and relative paleointensity stack for the NW Barents Sea: Implication for geomagnetic field behavior during the Holocene JF - Quaternary Science Reviews Y1 - 2020 A1 - Caricchi, C. A1 - Sagnotti, L. A1 - Campuzano, S.A. A1 - Lucchi, R.G. A1 - MacrÌ, P. A1 - Rebesco, M. A1 - Camerlenghi, A. KW - Arctic region KW - Barents Sea KW - Geomagnetic paleosecular variation KW - Holocene KW - marine sediment cores KW - Paleomagnetism KW - Relative paleointensity AB - Reconstruction of Paleomagnetic Secular Variation (PSV) of the geomagnetic field is fundamental both to assess geodynamo models and to obtain age constraints for rocks, sediments and archaeological material. We present refined age-calibrated Holocene PSV and relative paleointensity (RPI) stack curves derived from Arctic marine sediments (Northwestern Barents Sea). The Holocene sections of four sedimentary cores were correlated on the basis of paleomagnetic trends and age models, and stacked. The resultant composite PSV and RPI Holocene records (NBS stack) and the reconstructed Holocene Virtual Geomagnetic Pole (VGP) path were evaluated in comparison with the most recent paleomagnetic stack curves and geomagnetic field models. The data indicate that during the Holocene time, the VGPs moved within the superficial projection of the inner core tangent cylinder, with the exception of short time intervals around 5600 and 3200 cal yr BP when VGPs extended to lower latitudes. These deviations might reflect regional geomagnetic features, such as persistent geomagnetic flux lobes at core-mantle boundary. Our data confirm that the large VGP shift observed around 5600 cal yr BP is the result of an increased radial magnetic field at the core-mantle boundary over North America, whilst the VGP shift around 3200 cal yr BP represents a major swing to middle latitudes toward the Middle East and might be associated to a regional high paleointensity peak, known as Levantine Iron Age Anomaly (LIAA). VL - 229 UR - https://linkinghub.elsevier.com/retrieve/pii/S0277379119306869 ER - TY - JOUR T1 - Stable source of Holocene spring precipitation recorded in leaf wax hydrogen-isotope ratios from two New York lakes JF - Quaternary Science Reviews Y1 - 2020 A1 - Schartman, Anna K. A1 - Diefendorf, Aaron F. A1 - Lowell, Thomas V. A1 - Freimuth, Erika J. A1 - Stewart, Alexander K. A1 - Landis, Joshua D. A1 - Bates, Benjamin R. KW - Holocene KW - Hydrogen isotopes KW - late glacial KW - Leaf wax KW - North America KW - Organic geochemistry KW - paleoclimatology KW - Precipitation sourcing AB - Changes in synoptic atmospheric circulation patterns are thought to play a role in establishing millennial scale climate periods during the end of the late glacial and the Holocene. In the northeastern United States, multi-proxy evidence documents fluctuations in effective moisture and temperatures for this time period, but constraining the relationship between atmospheric processes and these climate regimes is not straightforward. Because the hydrogen-isotope ratios of sedimentary terrestrial leaf waxes can reflect precipitation δD, these long-chain hydrocarbon compounds are an excellent tool to investigate moisture sourcing. Here we present lake sediment and leaf wax carbon- and hydrogen-isotope records that span the past ∼14.0 thousand years from Heart Lake and Moose Pond in the Adirondack Mountains (ADK), New York. High initial lake productivity after basin inception is reflected in low C:N ratios (<15), and higher relative short chain n-alkane (n-C17, n-C19, and n-C21) to long chain n-alkane (n-C27, n-C29 and n-C31) concentration ratios. The Holocene record is characterized by low bulk and n-alkane δ13C (∼ −28‰, ∼ −31‰, respectively), high ACL25-35 (∼28), and high relative concentrations of long chain n-alkane homologues, indicating a dominantly terrestrial source of organic matter for this time period. Hydrogen-isotope ratios of n-C29 n-alkane from both lake basins range only ∼20‰ through the Holocene and reconstructed precipitation δD (δDprecip) from both basins is in good agreement with that of modern modeled spring precipitation. This suggests there may have been no major changes in the sourcing of spring precipitation for the ADK throughout the time of record. VL - 240 UR - https://linkinghub.elsevier.com/retrieve/pii/S027737912030319X ER - TY - JOUR T1 - A 12,700-year history of paleolimnological change from an Andean microrefugium JF - The Holocene Y1 - 2019 A1 - de Novaes Nascimento, Majoi A1 - Laurenzi, Anne Gail A1 - Valencia, Bryan G A1 - Van, Robert A1 - Bush, Mark KW - Andes KW - diatoms KW - drought KW - enso KW - Holocene KW - limnology KW - microrefugia KW - mid-Holocene dry event KW - paleoecology AB - We present a 12,6700-yr limnological history of Lake Miski, a high-elevation lake in a wet section of the Peruvian Andes. While many shallow Andean lakes dried up during the mid-Holocene, loss-on-ignition, magnetic susceptibility, and diatom analysis showed that Lake Miski was a constant feature in the landscape. Overall, fluctuations in the fossil diatom communities of Lake Miski tracked changes in insolation, but this was not the only mechanism influencing observed variability. We identify periods when insolation and interactions with the Pacific Ocean may have played a role in structuring local climate and diatom assemblages. The true mid-Holocene Dry Event (MHDE) is manifested in this record between 8000 and 5000 cal BP, but the carbonate stratigraphy and the diatom community indicated that although the level of the lake decreased, it never completely dried out, instead there was higher availability of planktic habitat and stronger mixing than in much of the Holocene. High rates of biological change observed during the late-Holocene in other records from Peru associated with human amplification of climatic signals were not observed in Lake Miski, as this lake may have been too wet and remote to be strongly influenced by human activity. Because of the presence of a woodland microrefugium, Lake Miski was suggested to have been an unusually climatically stable and wet location during the regional drying associated with the MHDE. Our new limnological information provides additional insights relating to this discussion. The presence of the observed woodland apparently withstood fluctuations that induced state changes in the lake and diatom flora, underscoring that microrefugia do not equate to ‘unchanging’ hydrologies or climates. VL - 29 UR - http://journals.sagepub.com/doi/10.1177/0959683618810400 IS - 2 ER - TY - JOUR T1 - Abrupt mid-Holocene ice loss in the western Weddell Sea Embayment of Antarctica JF - Earth and Planetary Science Letters Y1 - 2019 A1 - Johnson, Joanne S. A1 - Nichols, Keir A. A1 - Goehring, Brent M. A1 - Balco, Greg A1 - Schaefer, Joerg M. KW - Antarctica KW - cosmogenic dating in situ 14C KW - Holocene KW - Weddell Sea ice sheet AB - The glacial history of the westernmost Weddell Sea sector of Antarctica since the Last Glacial Maximum is virtually unknown, and yet it has been identified as critical for improving reliability of glacio-isostatic adjustment models that are required to correct satellite-derived estimates of ice sheet mass balance. Better knowledge of the glacial history of this region is also important for validating ice sheet models that are used to predict future contribution of the Antarctic ice sheet to sea level rise. Here we present a new Holocene deglacial chronology from a site on the Lassiter Coast of the Antarctic Peninsula, which is situated in the western Weddell Sea sector. Samples from 12 erratic cobbles and 18 bedrock surfaces from a series of presently-exposed ridges were analysed for cosmogenic Be-10 exposure dating, and a smaller suite of 7 bedrock samples for in situ C-14 dating. The resulting Be-10 ages are predominantly in the range 80-690 ka, whereas bedrock yielded much younger in situ C-14 ages, in the range 6.0-7.5 ka for samples collected from 138-385 m above the modern ice surface. From these we infer that the ice sheet experienced a period of abrupt thinning over a short time interval (no more than 2700 years) in the mid-Holocene, resulting in lowering of its surface by at least 250 m. Any late Holocene change in ice sheet thickness - such as re-advance, postulated by several modelling studies - must lie below the present ice sheet surface. The substantial difference in exposure ages derived from Be-10 and C-14 dating for the same samples additionally implies ubiquitous Be-10 inheritance acquired during ice-free periods prior to the last deglaciation, an interpretation that is consistent with our glacial-geomorphological field observations for former cold-based ice cover. The results of this study provide evidence for an episode of abrupt ice sheet surface lowering in the mid-Holocene, similar in rate, timing and magnitude to at least two other locations in Antarctica. VL - 518 UR - https://www.sciencedirect.com/science/article/pii/S0012821X19302638 ER - TY - JOUR T1 - Comparing and improving methods for reconstructing peatland water-table depth from testate amoebae JF - The Holocene Y1 - 2019 A1 - Nolan, Connor A1 - Tipton, John A1 - Booth, Robert K A1 - Hooten, Mevin B A1 - Jackson, Stephen T KW - Bayesian statistics KW - compositional data KW - Holocene KW - hydrology KW - North America KW - Northeast United States KW - Paleoclimate KW - peatlands KW - statistical methods KW - testate amoebae AB - Proxies that use changes in the composition of ecological communities to reconstruct temporal changes in an environmental covariate are commonly used in paleoclimatology and paleolimnology. Existing methods, such as weighted averaging and modern analog technique, relate compositional data to the covariate in very simple ways, and different methods are seldom compared systematically. We present a new Bayesian model that better represents the underlying data and the complexity in the relationships between species’ abundances and a paleoenvironmental covariate. Using testate amoeba–based reconstructions of water-table depth as a test case, we systematically compare new and existing models in a cross-validation experiment on a large training dataset from North America. We then apply the different models to a new 7500-year record of testate amoeba assemblages from Caribou Bog in Maine and compare the resulting water-table depth reconstructions. We find that Bayesian models represent an improvement over existing methods in three key ways: more complete use of the underlying compositional data, full and meaningful treatment of uncertainty, and clear paths toward methodological improvements. Furthermore, we highlight how developing and systematically comparing methods lead to an improved understanding of the proxy system. This paper focuses on testate amoebae and water-table depth, but the framework and ideas are widely applicable to other proxies based on compositional data. VL - 29 UR - https://journals.sagepub.com/doi/10.1177/0959683619846969 IS - 8 ER - TY - JOUR T1 - Holocene and Last Interglacial climate of the Faroe Islands from sedimentary plant wax hydrogen and carbon isotopes JF - Quaternary Science Reviews Y1 - 2019 A1 - Curtin, Lorelei A1 - D'Andrea, William J. A1 - Balascio, Nicholas A1 - Pugsley, Genevieve A1 - de Wet, Gregory A1 - Bradley, Raymond KW - Holocene KW - interglacial KW - North Atlantic KW - Organic geochemistry KW - paleoclimatology KW - Stable isotopes AB - The Last Interglacial period (LIG) is Earth's most recent globally warm period and is analogous in some ways to projected future global warming. However, questions remain regarding the state of the climate during the LIG in the North Atlantic, a region that is extremely sensitive to changes in oceanic and atmospheric circulation. Here, we present hydrogen and carbon isotope (δD and δ13C) records from a suite of plant wax biomarkers preserved in Holocene and LIG lacustrine sediments from the North Atlantic Faroe Islands and interpret them as qualitative proxies for temperature and hydroclimate variability. These data are used to directly compare LIG and Holocene climate using the same proxy approaches from the same terrestrial location. Measuring multiple isotopes on multiple types of waxes elucidates the sources of homologous plant waxes. We deduce that the δD values of long-chain n-alkanes (C27–C33) and mid-chain n-alkanes (C23–C25) in these sedimentary archives reflect leaf water and lake water δD values, respectively, while the δD values for both long-chain (C28–C30) and mid-chain n-alkanoic acids (C24–C26) primarily represent lake water δD values. Plant wax-inferred δD values of precipitation during the early Holocene (10,100 to 8,200  cal  yr BP) are ∼35‰ more positive than late Holocene values, and decline over the Holocene. δD-inferred hydrologic change and δ13C -inferred plant water use efficiency both indicate that the Faroe Islands became drier throughout the Holocene. Comparison with measurements from LIG plant waxes indicates that late LIG in the Faroe Islands was hydrologically similar to the early-to mid-Holocene (8,200 to 4,000  cal  yr BP), with enriched precipitation isotopes and reduced evapotranspiration indicating a warmer, wetter environment. VL - 223 UR - https://www.sciencedirect.com/science/article/pii/S0277379119304251 ER - TY - JOUR T1 - Holocene sea-level variability from Chesapeake Bay Tidal Marshes, USA JF - The Holocene Y1 - 2019 A1 - Cronin, Thomas M A1 - Clevenger, Megan K A1 - Tibert, Neil E A1 - Prescott, Tammy A1 - Toomey, Michael A1 - Hubeny, J Bradford A1 - Abbott, Mark B A1 - Seidenstein, Julia A1 - Whitworth, Hannah A1 - Fisher, Sam A1 - Wondolowski, Nick A1 - Ruefer, Anna KW - chesapeake bay KW - Foraminifera KW - Holocene KW - sea level KW - tidal marsh KW - US East Coast AB - We reconstructed the last 10,000 years of Holocene relative sea-level rise (RSLR) from sediment core records near Chesapeake Bay, eastern United States, including new marsh records from the Potomac and Rappahannock Rivers, Virginia. Results show mean RSLR rates of 2.6 mm yr−1 from 10 to 8 kilo-annum (ka) due to combined final ice-sheet melting during deglaciation and glacio-isostatic adjustment (GIA subsidence). Mean RSLR rates from ~6 ka to present were 1.4 mm yr−1 due mainly to GIA, consistent with other East Coast marsh records and geophysical models. However, a progressively slower mean rate (<1.0 mm yr−1) characterized the last 1000 years when a multi-century-long period of tidal marsh development occurred during the ‘Medieval Climate Anomaly’ (MCA) and ‘Little Ice Age’ (LIA) in the Chesapeake Bay region and other East Coast marshes. This decrease was most likely due to climatic and glaciological processes and, correcting for GIA, represents a fall in global mean sea level (GMSL) near the end of Holocene Neoglacial cooling. These pre-historical climate- and GIA-driven Chesapeake Bay sea-level changes contrast sharply with those based on Chesapeake Bay tide-gauge rates (3.1–4.5 mm yr−1) (back to 1903). After subtracting the GIA subsidence component, these rates can be attributed to long-term (millennial) global factors of accelerated ocean thermal expansion (~1.0 mm yr−1) and mass loss from alpine glaciers and Greenland and Antarctic Ice Sheets (1.5–2.0 mm yr−1). VL - 29 UR - http://journals.sagepub.com/doi/10.1177/0959683619862028 IS - 11 ER - TY - JOUR T1 - Millennial-scale fluctuations in water volume transported by the Tsushima Warm Current in the Japan Sea during the Holocene JF - Global and Planetary Change Y1 - 2019 A1 - Horikawa, Keiji A1 - Kodaira, Tomohiro A1 - Ikehara, Ken A1 - Murayama, Masafumi A1 - Zhang, Jing KW - Holocene KW - Mg/Ca-derived KW - Neogloboquadrina incompta KW - sea-surface temperature KW - Solar forcing KW - The Japan Sea KW - Tsushima KW - Warm Current AB - Cyclic changes in volume transport of the Tsushima Warm Current (TWC) have been argued from diatom records in the southern Japan Sea off the Japanese islands during the Holocene. Although this phenomenon has not yet been confirmed by various proxy data, determining whether or not these oceanographic changes occurred is crucial for clarifying the nature of oceanographic changes in the southern Japan Sea. Here, we conducted a coupled analysis of Mg/Ca ratios and oxygen isotopes (δ18O) in shallow-dwelling Neogloboquadrina incompta from 13 core-top sediments in southern Japan, and developed a new equation for Mg/Ca temperature calibration (Mg/Ca = 0.311 × exp (0.07 × T)) as a proxy for spring sea surface temperature (SST). Using the newly developed, species-specific Mg/Ca-paleothermometry, we reconstructed SST variability for the past 6800 years from core YK10-7-PC09 in the southern Japan Sea. The Mg/Ca-derived SST record clearly represented five warmer periods at 6200–6000, 4900–4500, 4200–3800, 2600–2100, and 900–400 cal. year BP, almost consistent with previously published diatom records. These warmer events also corresponded to the periods in which warm molluscan assemblages increased at the northern end of the TWC, suggesting that periods of higher SST can be seen as reflecting the increased volume transport of the TWC. We interpreted the results of a model study showing that higher solar irradiance provoked positive Arctic Oscillation (AO)-like spatial patterns and the negative phase of the Pacific Decadal Oscillation (PDO) to mean that increased (reduced) TWC volume transport on the multi-centennial to millennial time scales was caused by high (low) solar insolation via a potential link between AO and PDO. Given that larger and more frequent volcanic eruptions occurred in the mid Holocene than in the late Holocene, volcanic forcing on the TWC volume transport changes would have been more significant during the former, as seen in the highly variable SST from this period and distinct decreases in SST around ~5900 cal. year BP and ~6400 cal. year BP. The millennial-scale fluctuations seen in SSTs in the southern Japan Sea would have had a large impact on the evolution of vegetation and human adaptation in the northern Japanese islands, adjacent to the Japan Sea, over the last 6800 years. VL - 183 UR - https://linkinghub.elsevier.com/retrieve/pii/S0921818118306465 ER - TY - JOUR T1 - Multiple independent records of local glacier variability on Nuussuaq, West Greenland, during the Holocene JF - Quaternary Science Reviews Y1 - 2019 A1 - Schweinsberg, Avriel D. A1 - Briner, Jason P. A1 - Licciardi, Joseph M. A1 - Bennike, Ole A1 - Lifton, Nathaniel A. A1 - Graham, Brandon L. A1 - Young, Nicolás E. A1 - Schaefer, Joerg M. A1 - Zimmerman, Susan H. KW - Cosmogenic 10Be KW - Cosmogenic in situ 14C KW - Greenland KW - Holocene KW - lake sediment KW - Mountain glaciers KW - Neoglaciation AB - The sensitivity of mountain glaciers to small-scale climate fluctuations makes records of their past extent among the best proxies for identifying spatio-temporal climate variability. Here we build on the few existing Holocene records of local glacier change in Greenland by using three independent geochronological methods—proglacial lake sediment analysis, cosmogenic 10Be surface-exposure dating, and in situ 14C burial modeling—to reconstruct continuous records of Holocene glacier variability on Nuussuaq, West Greenland. 10Be ages of perched boulders indicate eastern Nuussuaq was deglaciated between ∼11.0 and 10.5 ka. Radiocarbon-dated sediments from two lakes on Nuussuaq contain mineral-rich layers between ∼9.6 and 9.0 and ∼8.7–8.0 cal ka BP that may be correlative with nearby ice sheet moraines deposited in the early Holocene. Multiple proxies for glacier size indicate frequent, high-amplitude glacier fluctuations superimposed on net glacier growth during the late Holocene, with significant ice expansion phases at ∼3.7 ka, 2.8 ka, and throughout the past ∼2 ka. Mean 10Be ages from five nested moraine crests confirm that local glacier extents on Nuussuaq culminated during both the Little Ice Age [∼1470 C.E. (n = 3) and 1750 C.E. (n = 3)] and the preceding centuries (∼520–1320 C.E.; n = 11). Results reveal that local glaciers on Nuussuaq episodically advanced and retreated at centennial timescales throughout the Holocene, most likely in response to regional climate changes in West Greenland superimposed on the progressive insolation-driven cooling trend in the Northern Hemisphere. Our new 10Be moraine chronologies coupled with other glacier-size proxies corroborate an emerging pattern of significant summer cooling and glacier expansion in the centuries prior to the Little Ice Age in the Arctic. VL - 215 UR - https://www.sciencedirect.com/science/article/pii/S0277379118308771 ER - TY - JOUR T1 - Sediment accumulation and sedimentation rates in playas on the High Plains of western Kansas, USA JF - Geomorphology Y1 - 2019 A1 - Bowen, Mark W. A1 - Johnson, William C. KW - 210Pb KW - Agricultural KW - chronology KW - Holocene KW - Radiocarbon dating KW - sedimentation AB - Grassland ecosystems are some of the most modified ecosystems in the world, largely due to conversion to cropland, and the High Plains of the central United States is no exception. Playa wetlands are ubiquitous features of the High Plains and have experienced increased sediment accumulation, which is the primary cause of reduced playa ecosystem function. Seven playas on the High Plains of western Kansas, five with cropland-dominated watersheds and two with grassland-dominated watersheds, were examined to quantify the amount of recent (past ~100–175 yr) sediment accumulated within playas and to establish chronologies of playa filling. Thicknesses of recent sediment were determined in the field, and soil cores were extracted from study playas. Four playa cores were analyzed for 210Pb to establish the chronology of recent sediment accumulation and sedimentation rates. Chronologies of pre-agricultural sediments and sedimentation rates were calculated by 14C dating of buried soils preserved within playa cores. Radiocarbon ages indicate playa stratigraphic records span the Holocene and that these playas have persisted on the landscape since at least the Late Pleistocene. Long-term, natural sedimentation rates were highest during the Pleistocene-Holocene transition and early Holocene, at ~2–4 cm/century. During the middle and late Holocene, sedimentation rates averaged ~1 cm/century. Cropland playas accumulated ~10–15 cm of recent sediment at average rates of ~6.5–10 cm/century, while grassland playas accumulated only ~2 cm of recent sediment. Conversion of watersheds to cropland has greatly accelerated sediment accumulation within playas, which is generally resulting in a decline in critical playa ecosystem functions. VL - 342 UR - https://linkinghub.elsevier.com/retrieve/pii/S0169555X19302612 ER - TY - JOUR T1 - Sortable silt records of intermediate-depth circulation and sedimentation in the Southwest Labrador Sea since the Last Glacial Maximum JF - Quaternary Science Reviews Y1 - 2019 A1 - Hoffmann, Sharon S. A1 - Dalsing, Risa E. A1 - Murphy, Sarah C. KW - Holocene KW - labrador sea KW - paleoceanography KW - Sedimentology-marine cores AB - The Labrador Sea is a vital region for the Atlantic Meridional Overturning Circulation (AMOC), where overflow waters from the Nordic Seas mix with locally produced Labrador Sea Water (LSW), before exiting to the interior of the Atlantic Ocean. The dynamical sedimentary proxy of mean sortable silt size () can give information on past changes in deep water circulation speed and the strength of AMOC. We have produced records from two core sites at depths between 1500 and 2000 m on the continental slope east of Newfoundland, to reconstruct changes in intermediate depth water circulation speed, including Glacial North Atlantic Intermediate Water and Labrador Sea Water over the past 22,000 years. Increases in appear to coincide with much of the deglaciation as well as the mid-late Holocene. End-member modeling suggests that ice-rafted debris (IRD) is an important factor in interpreting during the deglaciation. We find that a robust increase in is likely unrelated to IRD during the past 5 ka, and probably reflects increased flow at intermediate depths due to local production of LSW strengthening as Nordic Seas overflows weakened at this depth. Our results highlight both the complications of producing records in IRD-rich, slope environments and the promise that this proxy nevertheless has for reconstructing dynamical changes in deep ocean currents. VL - 206 UR - https://linkinghub.elsevier.com/retrieve/pii/S0277379118306449 ER - TY - JOUR T1 - Breaching of Mustang Island in response to the 8.2 ka sea-level event and impact on Corpus Christi Bay, Gulf of Mexico: Implications for future coastal change JF - The Holocene Y1 - 2018 A1 - Ferguson, Shannon A1 - Warny, Sophie A1 - Anderson, John B A1 - Simms, Alexander R A1 - White, Crawford KW - barrier island KW - dinoflagellates KW - Gulf of Mexico KW - Holocene KW - North America KW - Sea-level changes AB - The results from an investigation of the coupled Mustang Island–Corpus Christi Bay complex, Gulf of Mexico, shows that the island was eliminated as an effective salinity barrier between 8.86 and 8.17 ka. This event is recorded by a 5-fold increase in dinoflagellate cysts within Corpus Christi Bay. During this time, the bay-head delta shifted 15 km landward and oyster reefs within the bay died off. Our age model indicates that this event most likely resulted from the most rapid period of eustatic rise of the Holocene, which peaked at 8.18–8.31 ka. This event is attributed to late-stage ice sheet disintegration, particularly in North America, by the rapid draining of Lake Agassiz–Ojibway. Local glacial-isostatic factors resulted in a sea-level rise of only 0.2–0.56 m in the western Gulf of Mexico, which was less than needed to submerge the barrier. Rather, it was the marked nature of this sea-level rise that led to the virtual destruction of Mustang Island as an effective salinity barrier. These results provide an analog for predicting coastal morphodynamic response to accelerated sea-level rise and emphasize the need for better understanding of barrier response to sea-level rise and developing improved numerical models for predicting future changes to coastal barrier shorelines. VL - 28 UR - http://journals.sagepub.com/doi/10.1177/0959683617715697 IS - 1 ER - TY - JOUR T1 - Ecological history of a long-lived conifer in a disjunct population JF - Journal of Ecology Y1 - 2018 A1 - Herring, Erin M. A1 - Gavin, Daniel G. A1 - Dobrowski, Solomon Z. A1 - Fernandez, Matias A1 - Hu, Feng Sheng ED - Gill, Jacquelyn KW - climate KW - disjunction KW - dispersal KW - Holocene KW - Idaho KW - mertensiana KW - Palaeoecology KW - pollen KW - refugia KW - Tsuga AB - In northern Idaho (USA), more than 100 vascular plant species are disjunct >160 km from their main distribution along the Pacific Northwest coast. It remains unclear whether most species within this interior forest disjunction, including Tsuga mertensiana, survived the last glacial period in a north‐Idaho refugium or whether these species colonized the region via long‐distance dispersal during the Holocene. Sediment cores were extracted from three mid‐ to high‐elevation lakes within T. mertensiana‐dominated forests in the Northern Rocky Mountains of Idaho. Pollen and macrofossils were used to reconstruct forest composition, determine the timing of T. mertensiana establishment, examine the hypothesis that the region was a glacial refugium, and contrast how climate, competition and/or dispersal limitation have influenced its modern distribution. The modern distribution of T. mertensiana was analysed by constructing a range map and modelling the potential species distribution. The presence of outlier populations surrounding the Idaho disjunction along with broad areas of unoccupied suitable habitat indicates that the range of T. mertensiana is currently expanding. To assess the accuracy of T. mertensiana pollen at detecting its range limit, a network of pollen surface samples was used to analyse the probability of detecting T. mertensiana pollen as a function of distance from its geographical range limit. Consistent T. mertensiana pollen occurrence at ≥1% abundance is likely only within 42 km of its range limit. Tsuga mertensiana first appears in the pollen and macrofossil record at the highest‐elevation site at c. 4,100 cal year bp, then at the next highest‐elevation site at c. 1,600 cal year bp, and last at the mid‐elevation site at 800 cal year bp. Tsuga mertensiana pollen occurs continuously at ≥1% at all three sites by c. 300 cal year bp suggesting regional presence. The timing of arrival suggests that T. mertensiana is a recent component of the forests of Idaho, having arrived during the Holocene via long‐distance dispersal from coastal populations over 160 km away. Synthesis. Comparison with palaeoclimate reconstructions from the broader region suggests that climate was a greater limiting factor than dispersal in the Holocene establishment in the interior, indicating little difficulty overcoming a large dispersal barrier. However, T. mertensiana remained at low abundances for millennia until Little Ice Age climates promoted its recent increase in abundance. Unoccupied areas of suitable habitat suggest that competition, rather than climate or dispersal, is a limiting range infilling in the interior mesic forests today. VL - 106 UR - https://besjournals.onlinelibrary.wiley.com/doi/full/10.1111/1365-2745.12826 IS - 1 ER - TY - JOUR T1 - Effects of the Younger Dryas climate event recorded in sediment near the western Irish seaboard JF - Geological Journal Y1 - 2018 A1 - Wood, Bill L. A1 - Williams, D. Michael A1 - Murray, John ED - Somerville, I. KW - Atlantic Ocean KW - Foraminifers KW - Holocene KW - ice rafted debris KW - Ireland KW - sediment core KW - Younger Dryas AB - Results of analyses of a shallow marine sediment vibrocore from the Atlantic seafloor just west of the Aran Islands, western Ireland, are presented. The sediments range from ~16,000 to younger than 9,000 cal BP in age, based on 14C dating of foraminifers and molluscs. One sample within the core is dated at 12804 ± 125 cal BP and lies a very short distance stratigraphically below a conspicuous horizon containing isolated pebbles and sand‐size clasts, in what is an otherwise fine‐grained sequence of sediment. These outsized clasts are interpreted to be ice‐rafted debris. Approximately coeval with this horizon, the diversity and abundance of foraminifers decrease significantly and the foraminifer Nonionellina labradorica makes its first appearance in the core sediment. Stable isotope analysis shows a significant increase in values of δ18O approaching the horizon containing ice‐rafted debris. These results show the effects of a relatively sudden cooling of this part of the Atlantic Ocean at middle latitudes coincident with, or just after, the onset of the Younger Dryas event and demonstrate the extent of floating icebergs and probable later pack ice as a result of this temperature decrease. VL - 53 UR - https://onlinelibrary.wiley.com/doi/10.1002/gj.2918 IS - 2 ER - TY - JOUR T1 - Holocene mountain glacier history in the Sukkertoppen Iskappe area, southwest Greenland JF - Quaternary Science Reviews Y1 - 2018 A1 - Schweinsberg, Avriel D. A1 - Briner, Jason P. A1 - Miller, Gifford H. A1 - Lifton, Nathaniel A. A1 - Bennike, Ole A1 - Graham, Brandon L. KW - Cosmogenic in situ 14C KW - Glacier fluctuations KW - Greenland KW - Holocene KW - lake sediment KW - Neoglaciation AB - Mountain glaciers and ice caps (GIC) independent of the Greenland Ice Sheet respond rapidly to climate variations and records of their past extent provide information on the natural envelope of climate variability. Here, we use a multi-proxy approach that combines proglacial lake sediment analysis, cosmogenic nuclide surface-exposure dating (in situ 10Be and 14C), and radiocarbon dating of recently ice-entombed moss to generate a centennial-scale record of Holocene GIC fluctuations in southwestern Greenland. Following local deglaciation ∼10-9 ka, sediments from proglacial Crash Lake record a glacier advance at ∼9 ka that is indistinguishable from nearby ice sheet moraines, implying a synchronous response of GIC and the Greenland Ice Sheet to a centennial-scale climate event. Following this local glacier advance, GIC experienced net recession until ∼4.6 ka. Radiocarbon ages of in situ moss (n = 29) and Crash Lake sediments reveal intervals of glacier expansion at ∼1.8, 1.2 and 0.7 ka that are superimposed on an overall trend of net glacier expansion throughout the late Holocene. In situ 14C concentrations from bedrock adjacent to radiocarbon-dated moss samples further constrain the duration of ice cover through the Holocene in this region. We find that our glacier-size proxy records during the past ∼4 ka are broadly consistent with relatively lower temperatures recorded in GISP2 and occur during, or following, intervals of volcanic perturbations. Thus, we speculate that volcanic activity, although less frequent and intense than in the early Holocene and during the Little Ice Age, may have led to centennial-scale variability imprinted on net glacier expansion due to decreasing summer insolation through the late Holocene. VL - 197 UR - https://www.sciencedirect.com/science/article/pii/S0277379118302531 ER - TY - JOUR T1 - Changes in glacial meltwater alter algal communities in lakes of Scoresby Sund, Renland, East Greenland throughout the Holocene: Abrupt reorganizations began 1000 years before present JF - The Holocene Y1 - 2017 A1 - Slemmons, Krista EH A1 - Medford, Aaron A1 - Hall, Brenda L A1 - Stone, Jeffery R A1 - McGowan, Suzanne A1 - Lowell, Thomas A1 - Kelly, Meredith A1 - Saros, Jasmine E KW - climate KW - Diatom KW - East Greenland KW - glacier KW - Holocene KW - Lake level AB - We investigated the response of lake algal communities to changes in glacial meltwater from the Renland Ice Cap (Greenland) through the Holocene to assess whether influxes always elicit consistent responses or novel responses. We measured sedimentary algal pigments in two proximal lakes, snow-fed Raven and glacier- and snow-fed Bunny Lake, and diatom community structure and turnover in Bunny Lake. Diatom data were not available in Raven Lake. We also modeled lake-level change in Bunny Lake to identify how glacial meltwater may have altered diatom habitat availability through time. Through a series of glacier advances and retreats over the Holocene, the algal response in Bunny Lake was relatively constant until approximately 1015 yr BP, after which there were major changes in sedimentary algal remains. Algal pigment concentrations sharply declined, and diatom species richness increased. Diatom community structure underwent three reorganizations. Until 1015 yr BP, assemblages were dominated by Pinnularia braunii and Aulacoseira pffaffiana. However, approximately 1015–480 yr BP, these species declined and Tabellaria flocculosa and Hannaea arcus became a significant component of the assemblage. Approximately 440 yr BP, A. pfaffiana increased along with species indicating elevated nitrogen. In contrast, the algal pigment records from nearby snow-fed Raven Lake showed different and minimal change through time. Our results suggest that changes in the magnitude and composition of meltwater in our two study lakes were unique over the last 1000 yr BP and elicited a non-linear threshold response absent during other periods of glacier advance and retreat. Deciphering the degree to which glaciers structure algal communities over time has strong implications for lakes as glaciers continue to recede. VL - 27 UR - http://journals.sagepub.com/doi/10.1177/0959683616678468 IS - 7 ER - TY - JOUR T1 - Equilibrium line altitudes along the Andes during the Last millennium: Paleoclimatic implications JF - The Holocene Y1 - 2017 A1 - Sagredo, Esteban A A1 - Lowell, Thomas V A1 - Kelly, Meredith A A1 - Rupper, Summer A1 - Aravena, Juan Carlos A1 - Ward, Dylan J A1 - Malone, Andrew GO KW - Andes KW - equilibrium line altitude KW - glacial fluctuations KW - glacial reconstruction KW - Holocene KW - last millennium AB - Deciphering the climate changes that influenced the glacial fluctuations of the last millennium requires documenting the spatial and temporal patterns of these glacial events. Here, we estimate the change in equilibrium line altitudes (ELAs) between the most prominent glacial advance of the last millennium and the present for four alpine glaciers located in different climatic regimes along the Andes. For each glacier, we reconstruct scenarios of climatic conditions (temperature and precipitation anomalies) that accommodate the observed ELA changes. We focus on the following glaciers: an alpine glacier in the Cordillera Vilcanota (13°S), Tapado glacier (30°S), Cipreses glacier (34°S), and Tranquilo glacier (47°S). Our results show that the range of possible temperature and precipitation anomalies that accommodate the observed ELA changes overlap significantly at three of the four sites (i.e. Vilcanota, Cipreses, and Tranquilo). Only Tapado glacier exhibits a set of climate anomalies that differs from the other three sites. Assuming no change in precipitation, the estimated ELA changes require a cooling of at least 0.7°C in the Cordillera Vilcanota, 1.0°C at Tapado glacier, 0.6°C at Cipreses glacier, and 0.7°C at Tranquilo glacier. Conversely, assuming no change in temperature, the estimated ELA changes are explained by increases in precipitation exceeding 0.52 m yr−1 (64% of the annual precipitation) in the Cordillera Vilcanota, 0.31 m yr−1 (89%) at Tapado glacier, 0.22 m yr−1 (27%) at Cipreses glacier, and 0.3 m yr−1 (27%) at Tranquilo glacier. By mapping the ELA changes and modeling the potential climate forcing across diverse climate settings, we aim to contribute toward documenting the spatial variability of climate conditions during the last millennium, a key step to decipher the mechanisms underlying the glacial fluctuation that occurred during this period. VL - 27 UR - http://journals.sagepub.com/doi/10.1177/0959683616678458 IS - 7 ER - TY - JOUR T1 - Holocene climate and environmental history of East Greenland inferred from lake sediments JF - Journal of Paleolimnology Y1 - 2017 A1 - Lusas, Amanda R. A1 - Hall, Brenda L. A1 - Lowell, Thomas V. A1 - Kelly, Meredith A. A1 - Bennike, Ole A1 - Levy, Laura B. A1 - Honsaker, William KW - De Vries cycle KW - Glacially fed lakes KW - Greenland KW - Holocene KW - Paleoclimate AB - Prediction of future Arctic climate and environmental changes, as well as associated ice-sheet behavior, requires placing present-day warming and reduced ice extent into a long-term context. Here we present a record of Holocene climate and glacier fluctuations inferred from the paleolimnology of small lakes near Istorvet ice cap in East Greenland. Calibrated radiocarbon dates of organic remains indicate deglaciation of the region before ~10,500 years BP, after which time the ice cap receded rapidly to a position similar to or less extensive than present, and lake sediments shifted from glacio-lacustrine clay to relatively organic-rich gyttja. The lack of glacio-lacustrine sediments throughout most of the record suggests that the ice cap was similar to or smaller than present throughout most of the Holocene. This restricted ice extent suggests that climate was similar to or warmer than present, in keeping with other records from Greenland that indicate a warm early and middle Holocene. Middle Holocene magnetic susceptibility oscillations, with a ~200-year frequency in one of the lakes, may relate to solar influence on local catchment processes. Following thousands of years of restricted extent, Istorvet ice cap advanced to within 365 m of its late Holocene limit at ~AD 1150. Variability in the timing of glacial and climate fluctuations, as well as of sediment organic content changes among East Greenland lacustrine records, may be a consequence of local factors, such as elevation, continentality, water depth, turbidity, and seabirds, and highlights the need for a detailed spatial array of datasets to address questions about Holocene climate change. VL - 57 UR - http://link.springer.com/10.1007/s10933-017-9951-5 IS - 4 ER - TY - JOUR T1 - Holocene temperatures and isotopes of precipitation in Northwest Greenland recorded in lacustrine organic materials JF - Quaternary Science Reviews Y1 - 2017 A1 - Lasher, G. Everett A1 - Axford, Yarrow A1 - McFarlin, Jamie M. A1 - Kelly, Meredith A. A1 - Osterberg, Erich C. A1 - Berkelhammer, Max B. KW - Chironomids KW - Greenland KW - Holocene KW - paleoclimatology KW - paleolimnology KW - Stable isotopes AB - Reconstructions of Holocene lake water isotopic composition based upon subfossil aquatic organic material offer new insights into Arctic climate. We present quantitative estimates of warmth during the Holocene Thermal Maximum in northwest Greenland, inferred from oxygen isotopes of chironomid head capsules and aquatic moss preserved in lake sediments. delta O-18 values of chironomids from surface sediments of multiple Greenland lakes indicate that these subfossil remains record the delta O-18 values of the lake water in which they grow. Our lake water delta O-18 reconstruction is supported by downcore agreement with delta O-18 values in aquatic moss and chironomid remains. delta O-18 of both organic materials from Secret Lake decrease after 4 ka (ka = thousands of years ago) by 3 parts per thousand into the Neoglacial. We argue that lake water at Secret Lake primarily reflects precipitation delta O-18 values, which is strongly correlated with air temperature in NW Greenland, and that this signal is biased towards summer and early autumn conditions. Other factors may have influenced Secret Lake delta O-18 values through the Holocene, including evaporation of lake water and changing seasonality and source of precipitation. The maximum early Holocene summer and early autumn-biased temperature anomaly at Secret Lake is 2.5-4 degrees C warmer than present from 7.7 (the beginning of our record) to similar to 6 ka. The maximum late Holocene cold anomaly (which includes the Little Ice Age) is 1.5-3 degrees C colder than present. These ranges of possible temperature anomalies reflect uncertainty in the delta O-18 temperature relationship for precipitation at the study site through the Holocene. (C) 2017 Elsevier Ltd. All rights reserved. VL - 170 UR - http://linkinghub.elsevier.com/retrieve/pii/S0277379116305650http://api.elsevier.com/content/article/PII:S0277379116305650?httpAccept=text/xmlhttp://api.elsevier.com/content/article/PII:S0277379116305650?httpAccept=text/plain ER - TY - JOUR T1 - Records of continental slope sediment flow morphodynamic responses to gradient and active faulting from integrated AUV and ROV data, offshore Palos Verdes, southern California Borderland JF - Marine Geology Y1 - 2017 A1 - Maier, Katherine L. A1 - Brothers, Daniel S. A1 - Paull, Charles K. A1 - McGann, Mary A1 - Caress, David W. A1 - Conrad, James E. KW - Deep-water channel KW - Gradient KW - Holocene KW - Sediment waves KW - Turbidite Fault AB - Variations in seabed gradient are widely acknowledged to influence deep-water deposition, but are often difficult to measure in sufficient detail from both modern and ancient examples. On the continental slope offshore Los Angeles, California, autonomous underwater vehicle, remotely operated vehicle, and shipboard methods were used to collect a dense grid of high-resolution multibeam bathymetry, chirp sub-bottom profiles, and targeted sediment core samples that demonstrate the influence of seafloor gradient on sediment accumulation, depositional environment, grain size of deposits, and seafloor morphology. In this setting, restraining and releasing bends along the active right-lateral Palos Verdes Fault create and maintain variations in seafloor gradient. Holocene down-slope flows appear to have been generated by slope failure, primarily on the uppermost slope (~ 100–200 m water depth). Turbidity currents created a low relief (< 10 m) channel, up-slope migrating sediment waves (λ = ~ 100 m, h ≤ 2 m), and a series of depocenters that have accumulated up to 4 m of Holocene sediment. Sediment waves increase in wavelength and decrease in wave height with decreasing gradient. Integrated analysis of high-resolution datasets provides quantification of morphodynamic sensitivity to seafloor gradients acting throughout deep-water depositional systems. These results help to bridge gaps in scale between existing deep-sea and experimental datasets and may provide constraints for future numerical modeling studies. VL - 393 UR - https://linkinghub.elsevier.com/retrieve/pii/S0025322716302304 ER - TY - JOUR T1 - Two phases of the Holocene East African Humid Period: Inferred from a high-resolution geochemical record off Tanzania JF - Earth and Planetary Science Letters Y1 - 2017 A1 - Liu, Xiting A1 - Rendle-Bühring, Rebecca A1 - Kuhlmann, Holger A1 - Li, Anchun KW - African Humid Period KW - Congo Air Boundary KW - Holocene KW - Intertropical Convergence Zone KW - X-ray fluorescence scanner AB - During the Holocene, the most notably climatic change across the African continent is the African Humid Period (AHP), however the pace and primary forcing for this pluvial condition is still ambiguous, particularly in East Africa. We present a high-resolution marine sediment record off Tanzania to provide insights into the climatic conditions of inland East Africa during the Holocene. Major element ratios (i.e., log-ratios of Fe/Ca and Ti/Ca), derived from X-Ray Fluorescence scanning, have been employed to document variations in humidity in East Africa. Our results show that the AHP is represented by two humid phases: an intense humid period from the beginning of the Holocene to 8 ka (AHP I); and a moderate humid period spanning from 8 to 5.5 ka (AHP II). On the basis of our geochemical record and regime detection, the termination of the AHP initiated at 5.5 ka and ceased around 3.5 ka. Combined with other paleoclimatic records around East Africa, we suggest that the humid conditions in this region responded to Northern Hemisphere (NH) summer insolation. The AHP I and II might have been related to an eastward shift of the Congo Air Boundary and warmer conditions in the western Indian Ocean, which resulted in additional moisture being delivered from the Atlantic and Indian Oceans during the NH summer and autumn, respectively. We further note a drought event throughout East Africa north of 10°S around 8.2 ka, which may have been related to the southward migration of the Intertropical Convergence Zone in response to the NH cooling event. VL - 460 UR - https://linkinghub.elsevier.com/retrieve/pii/S0012821X16307294 ER - TY - JOUR T1 - 10Be dating reveals early-middle Holocene age of the Drygalski Moraines in central West Greenland JF - Quaternary Science Reviews Y1 - 2016 A1 - Sandra L. Cronauer A1 - Jason P. Briner A1 - Samuel E. Kelley A1 - Susan R.H. Zimmerman A1 - Mathieu Morlighem KW - Holocene AB - Abstract We reconstruct the history of the Greenland Ice Sheet margin on the Nuussuaq Peninsula in central West Greenland through the Holocene using lake sediment analysis and cosmogenic 10Be exposure dating of the prominent Drygalski Moraines. Erratics perched on bedrock outboard of the Drygalski Moraines constrain local deglaciation to ∼9.9 ± 0.6 ka (n = 2). Three Drygalski Moraine crests yield mean 10Be ages of 8.6 ± 0.4 ka (n = 2), 8.5 ± 0.2 ka (n = 3), and 7.6 ± 0.1 ka (n = 2) from outer to inner. Perched erratics between the inner two moraines average 7.8 ± 0.1 ka (n = 2) and are consistent with the moraine ages. Sediments from a proglacial lake with a catchment area extending an estimated 2 km beneath (inland of) the present ice sheet terminus constrain an ice sheet minimum extent from 5.4 ka to 0.6 ka. The moraine chronology paired with the lake sediment stratigraphy reveals that the ice margin likely remained within ∼2 km of its present position from ∼9.9 to 5.4 ka. This unexpected early Holocene stability, preceded by rapid ice retreat and followed by minimum ice extent between ∼5.4 and 0.6 ka, contrasts with many records of early Holocene warmth and the Northern Hemisphere summer insolation maximum. We suggest ice margin stability may instead be tied to adjacent ocean temperatures, which reached an optimum in the middle Holocene. VL - 147 UR - http://www.sciencedirect.com/science/article/pii/S0277379115301050 N1 - Special Issue: \{PAST\} Gateways (Palaeo-Arctic Spatial and Temporal Gateways) ER - TY - JOUR T1 - Comparison of eastern tropical Pacific TEX 86 and Globigerinoides ruber Mg/Ca derived sea surface temperatures: Insights from the Holocene and Last Glacial Maximum JF - Earth and Planetary Science Letters Y1 - 2016 A1 - Hertzberg, Jennifer E. A1 - Schmidt, Matthew W. A1 - Bianchi, Thomas S. A1 - Smith, Richard W. A1 - Shields, Michael R. A1 - Marcantonio, Franco KW - Foraminifera KW - Holocene KW - LGM; Pacific Ocean KW - Mg/Ca KW - TEX86TEX86 AB - 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. VL - 434 UR - http://linkinghub.elsevier.com/retrieve/pii/S0012821X15007542http://api.elsevier.com/content/article/PII:S0012821X15007542?httpAccept=text/xmlhttp://api.elsevier.com/content/article/PII:S0012821X15007542?httpAccept=text/plain ER - TY - JOUR T1 - Micropaleontologic record of Pliocene and Quaternary paleoenvironments in the southern Albemarle Embayment, North Carolina, U.S.A JF - Palaeogeography, Palaeoclimatology, Palaeoecology Y1 - 2016 A1 - Stephen J. Culver A1 - Kathleen M. Farrell A1 - David J. Mallinson A1 - Debra A. Willard A1 - Benjamin P. Horton A1 - Stanley R. Riggs A1 - E. Robert Thieler A1 - John F. Wehmiller A1 - Peter R. Parham A1 - Jessica Pierson Moore A1 - Scott W. Snyder A1 - Caroline Hillier KW - Holocene AB - 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. VL - 457 UR - http://www.sciencedirect.com/science/article/pii/S0031018216301572 ER - TY - JOUR T1 - Relative sea-level change in northeastern Florida (USA) during the last ∼8.0 ka JF - Quaternary Science Reviews Y1 - 2016 A1 - Hawkes, Andrea D. A1 - Kemp, Andrew C. A1 - Donnelly, Jeffrey P. A1 - Horton, Benjamin P. A1 - Peltier, W. Richard A1 - Cahill, Niamh A1 - Hill, David F. A1 - Ashe, Erica A1 - Alexander, Clark R. KW - Foraminifera KW - Georgia KW - Holocene KW - Salt marsh KW - St. Marys River AB - An existing database of relative sea-level (RSL) reconstructions from the U.S. Atlantic coast lacked valid sea-level index points from Georgia and Florida. This region lies on the edge of the collapsing forebulge of the former Laurentide Ice Sheet making it an important location for understanding glacio-isostatic adjustment and the history of ice-sheet melt. To address the paucity of data, we reconstruct RSL in northeastern Florida (St. Marys) over the last ∼8.0 ka from samples of basal salt-marsh sediment that minimize the influence of compaction. The analogy between modern salt-marsh foraminifera and their fossil counterparts preserved in the sedimentary record was used to estimate paleomarsh surface elevation. Sample ages were determined by radiocarbon dating of identifiable and in-situ plant macrofossils. This approach yielded 25 new sea-level index points that constrain a ∼5.7 m rise in RSL during the last ∼8.0 ka. The record shows that no highstand in sea level occurred in this region over the period of the reconstruction. We compared the new reconstruction to Earth-ice models ICE 6G-C VM5a and ICE 6G-C VM6. There is good fit in the later part of the Holocene with VM5a and for a brief time in the earlier Holocene with VM6. However, there are discrepancies in model-reconstruction fit in the early to mid Holocene in northeastern Florida and elsewhere along the Atlantic coast at locations with early Holocene RSL reconstructions. The most pronounced feature of the new reconstruction is a slow down in the rate of RSL rise from approximately 5.0 to 3.0 ka. This trend may reflect a significant contribution from local-scale processes such as tidal-range change and/or change in base flow of the St. Marys River in response to paleoclimate changes. However, the spatial expression (local vs. regional) of this slow down is undetermined and corroborative records are needed to establish its geographical extent. VL - 142 UR - http://linkinghub.elsevier.com/retrieve/pii/S0277379116301275http://api.elsevier.com/content/article/PII:S0277379116301275?httpAccept=text/xmlhttp://api.elsevier.com/content/article/PII:S0277379116301275?httpAccept=text/plain ER - TY - JOUR T1 - Accretion history of mid-Holocene coral reefs from the southeast Florida continental reef tract, USA JF - Coral Reefs Y1 - 2015 A1 - Stathakopoulos, A. A1 - Riegl, B. M. KW - Backstepping KW - Holocene KW - Reef accretion KW - Relict reef KW - SE Florida continental reef tract AB - 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. VL - 34872624292351278520242597237061293327511611519362751494811122751520228638172349513073526222412724 UR - http://link.springer.com/10.1007/s00338-014-1233-3http://link.springer.com/content/pdf/10.1007/s00338-014-1233-3 IS - 11 ER - TY - JOUR T1 - Climate forcing of unprecedented intense-hurricane activity in the last 2000 years JF - EARTHS FUTURE Y1 - 2015 A1 - Donnelly, Jeffrey P. A1 - Hawkes, Andrea D. A1 - Lane, Philip A1 - MacDonald, Dana A1 - Shuman, Bryan N. A1 - Toomey, Michael R. A1 - van Hengstum, Peter J. A1 - Woodruff, Jonathan D. KW - Climate change KW - common era KW - Holocene KW - sea surface temperature KW - tropical cyclones AB - 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. VL - 3 ER - TY - JOUR T1 - Marine record of Holocene climate, ocean, and cryosphere interactions: Herbert Sound, James Ross Island, Antarctica JF - Quaternary Science Reviews Y1 - 2015 A1 - Minzoni, Rebecca Totten A1 - Anderson, John B. A1 - Fernandez, Rodrigo A1 - Wellner, Julia Smith KW - Antarctic Peninsula KW - diatoms KW - Holocene KW - paleoceanography KW - paleoclimatology AB - The sediment record offshore James Ross Island, northeast Antarctic Peninsula presents an unparalleled opportunity to directly compare marine and terrestrial climate records spanning the Holocene in maritime Antarctica. An 11 m drill core was collected between Herbert Sound and Croft Bay as part of the SHALDRIL NBP-0502 initiative and produced the southernmost sediment record from the eastern side of the AP. Thirty-eight radiocarbon ages are used to construct an age model of centennial-scale resolution. Multi-proxy records, including magnetic susceptibility, pebble content, particle size, total organic carbon, and diatom assemblages, were interrogated in the context of nearby Holocene-age ice core, lake, and drift records from James Ross Island. Differences in the timing and expression of Holocene events reflect marine controls on tidewater glaciers, such as water mass configurations and sea ice. Glacial behavior mimics ice core paleotemperatures during the Holocene, with the exception of distinct ocean warming events. Herbert Sound was fully occupied by grounded ice during the Last Glacial Maximum, and experienced rapid lift-off, followed by a floating ice phase. The canopy of floating ice receded by 10 ± 2.4 cal kyr BP, presumably in response to Early Holocene warming. Herbert Sound and Croft Bay fully deglaciated by 7.2 cal kyr BP, when the Mid Holocene Hypsithermal commenced and the sound became open and productive. An extreme peak in productivity ∼6.1 cal kyr BP indicates an oceanic warming event that is not reflected in atmospheric temperature or lacustrine sediment records. Increase in sea ice cover and ice rafting mark the onset of the Neoglacial ∼2.5 cal kyr BP, when pronounced atmospheric cooling is documented in the James Ross Island ice core. Our comparison facilitates more holistic understanding of atmosphere-ocean-cryosphere interactions that may aid predictions of glacial response to future warming and sea-level scenarios. VL - 129 UR - https://doi.org/10.1016/j.quascirev.2015.09.009 ER - TY - JOUR T1 - A sea-level database for the Pacific coast of central North America JF - Quaternary Science Reviews Y1 - 2015 A1 - Engelhart, Simon E. A1 - Vacchi, Matteo A1 - Horton, Benjamin P. A1 - Nelson, Alan R. A1 - Kopp, Robert E. KW - Cascadia subduction zone KW - Glacial isostatic adjustment KW - Holocene KW - Pacific North America KW - Sea-level database AB - A database of published and new relative sea-level (RSL) data for the past 16 ka constrains the sea-level histories of the Pacific coast of central North America (southern British Columbia to central California). Our reevaluation of the stratigraphic context and radiocarbon age of sea-level indicators from geological and archaeological investigations yields 600 sea-level index points and 241 sea-level limiting points. We subdivided the database into 12 regions based on the availability of data, tectonic setting, and distance from the former Cordilleran ice sheet. Most index (95%) and limiting points (54%) are <7 ka; older data come mainly from British Columbia and San Francisco Bay. The stratigraphic position of points was used as a first-order assessment of compaction. Formerly glaciated areas show variable RSL change; where data are present, highstands of RSL occur immediately post-deglaciation and in the mid to late Holocene. Sites at the periphery and distant to formerly glaciated areas demonstrate a continuous rise in RSL with a decreasing rate through time due to the collapse of the peripheral forebulge and the reduction in meltwater input during deglaciation. Late Holocene RSL change varies spatially from falling at 0.7 ± 0.8 mm a−1 in southern British Columbia to rising at 1.5 ± 0.3 mm a−1 in California. The different sea-level histories are an ongoing isostatic response to deglaciation of the Cordilleran and Laurentide Ice Sheets. VL - 113 UR - https://doi.org/10.1016/j.quascirev.2014.12.001 ER - TY - JOUR T1 - A depth refugium from catastrophic coral bleaching prevents regional extinction JF - Ecology Y1 - 2014 A1 - Smith, Tyler B. A1 - Glynn, Peter W. A1 - é, Juan L. A1 - Toth, Lauren T. A1 - Gyory, Joanna KW - Coral bleaching KW - Coral mortality KW - Depth refuge KW - Eastern Tropical Pacific KW - El Nino-Southern Oscillation KW - Extinction KW - Holocene KW - Millepora KW - Refuge AB - Species intolerant of changing climate might avoid extinction within refugia buffered from extreme conditions. Refugia have been observed in the fossil record but are not well documented or understood on ecological time scales. Using a 37-year record from the eastern Pacific across the two most severe El Nin o events on record (1982-1983 and 1997- 1998) we show how an exceptionally thermally sensitive reef-building hydrocoral, Millepora intricata, twice survived catastrophic bleaching in a deeper-water refuge (.11 m depth). During both events, M. intricata was extirpated across its range in shallow water, but showed recovery within several years, while two other hydrocorals without deep-water populations were driven to regional extinction. Evidence from the subfossil record in the same area showed shallow-water persistence of abundant M. intricata populations from 5000 years ago, through severe El Nin o-Southern Oscillation cycles, suggesting a potential depth refugium on a millennial timescale. Our data confirm the deep refuge hypothesis for corals under thermal stress. © 2014 by the Ecological Society of America. VL - 95 UR - http://doi.wiley.com/10.1890/13-0468.1 IS - 6 ER - TY - JOUR T1 - Holocene paleoclimatic variation in the Schirmacher Oasis, East Antarctica: A mineral magnetic approach} JF - POLAR SCIENCE Y1 - 2014 A1 - Phartiyal, Binita KW - Holocene KW - Lacustrine sediments KW - Mineral remanent magnetism KW - Paleoclimate KW - Schirmacher Oasis AB - An analysis of remanent magnetism and radiocarbon ages in the dry lacustrine/sediment fills of the Schirmacher Oasis (SO) in East Antarctica was conducted to reconstruct past climatic condition. The statistically run mineral magnetic data on paleontological statistics software package (multivariate cluster analysis) placed on accelerator mass spectrometer radiocarbon chronology of the three sediment sections, trace 6 phases of climatic fluctuation between 13 and 3 ka, (Phases 1, 3 and 5 represent cold periods while Phases 2, 4, and 6 represent warm periods). One short warm period (Phase 2, ca. 12.5 ka) occurred in the late Pleistocene, and two marked warm periods (Phase 4, 11-8.7 ka; Phase 6, 4.4-3 ka) occurred in the Holocene. High magnetic susceptibility (chi), saturation isothermal remanent magnetism (SIRM), and soft isothermal remanent magnetism (soft IRM) values correspond to colder periods and low values reflect comparatively warmer lacustrine phases. Holocene Optima (Phase 4) and Mid Holocene Hypsithermal (Phase 6) are distinguished by decreased values of concentrations dependent parameters. Remanence is preserved in the low-coercive minerals. Heavy metals in the sediments include, Fe, Rb, Zn, Mo, Co, Pb, Mn, Cu, and As in order of decreasing abundance. (C) 2014 Elsevier B.V. and NIPR. All rights reserved. VL - 8 ER - TY - BOOK T1 - Treatise on Geomorphology8.26 Climate Change Impacts on Cold Climates Y1 - 2013 A1 - Baroni, C. KW - Adélie penguins KW - Antarctica KW - Arctic KW - Cenozoic KW - Climate change KW - Elephant seals KW - glacial history KW - Holocene KW - Icehouse AB - Since the onset of Cenozoic ice sheets, cold climate regions have played a leading role in planetary energy balance, atmospheric and global oceanic circulations. Glacial and periglacial processes in polar regions act as morphogenetic agents for landscape sculpting providing landforms and deposits that represent valuable records for investigating the amplitude of key phases of Cenozoic glacial history. Glacio-eustatic sea-level variations induce revolutionary environmental changes across the entire planet. Changes in periglacial processes also influence cold region hydrology, ecosystems, and soil carbon storage. Climatic and environmental changes in cold regions cause adaptation through ecological and evolutionary responses by organisms. PB - Elsevier SN - 9780080885223 UR - https://doi.org/10.1016/B978-0-12-374739-6.00222-0 ER - TY - JOUR T1 - A decadally-resolved paleohurricane record archived in the late Holocene sediments of a Florida sinkhole JF - Marine Geology Y1 - 2011 A1 - Lane, Philip A1 - Donnelly, Jeffrey P. A1 - Woodruff, Jonathan D. A1 - Hawkes, Andrea D. KW - Apalachee Bay KW - Gulf of Mexico KW - Holocene KW - hurricane KW - paleohurricane KW - Paleotempestology KW - sinkhole KW - SLOSH KW - storm surge KW - tropical cyclone AB - A 4500-year record of hurricane-induced storm surges is developed from sediment cores collected from a coastal sinkhole near Apalachee Bay, Florida. Recent deposition of sand layers in the upper sediments of the pond was found to be contemporaneous with significant, historic storm surges at the site modeled using SLOSH and the Best Track, post-1851 A.D. dataset. Using the historic portion of the record for calibration, paleohurricane deposits were identified by sand content and dated using radiocarbon-based age models. Marine-indicative foraminifera, some originating at least 5 km offshore, were present in several modern and ancient storm deposits. The presence and long-term preservation of offshore foraminifera suggest that this site and others like it may yield promising microfossil-based paleohurricane reconstructions in the future. Due to the sub-decadal (~ 7 years) resolution of the record and the site's high susceptibility to hurricane-generated storm surges, the average, local frequency of recorded events, approximately 3.9 storms per century, is greater than that of previously published paleohurricane records from the region. The high incidence of recorded events permitted a time series of local hurricane frequency during the last five millennia to be constructed. Variability in the frequency of the largest storm layers was found to be greater than what would likely occur by chance alone, with intervals of both anomalously high and low storm frequency identified. However, the rate at which smaller layers were deposited was relatively constant over the last five millennia. This may suggest that significant variability in hurricane frequency has occurred only in the highest magnitude events. The frequency of high magnitude events peaked near 6 storms per century between 2800 and 2300 years ago. High magnitude events were relatively rare with about 0–3 storms per century occurring between 1900 and 1600 years ago and between 400 and 150 years ago. A marked decline in the number of large storm deposits, which began around 600 years ago, has persisted through present with below average frequency over the last 150 years when compared to the preceding five millennia. VL - 287 UR - http://linkinghub.elsevier.com/retrieve/pii/S0025322711001472http://api.elsevier.com/content/article/PII:S0025322711001472?httpAccept=text/xmlhttp://api.elsevier.com/content/article/PII:S0025322711001472?httpAccept=text/plain IS - 1-4 ER - TY - JOUR T1 - A regional-scale climate reconstruction of the last 4000 years from lakes in the Nebraska Sand Hills, USA JF - Quaternary Science Reviews Y1 - 2011 A1 - Schmieder, J. A1 - Fritz, S.C. A1 - Swinehart, J.B. A1 - Shinneman, A.L.C. A1 - Wolfe, A.P. A1 - Miller, G. A1 - Daniels, N. A1 - Jacobs, K.C. A1 - Grimm, E.C. KW - diatoms KW - Droughts KW - Great Plains KW - Holocene KW - lakes KW - Nebraska Sand Hills KW - paleolimnology AB - 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. VL - 30 UR - http://linkinghub.elsevier.com/retrieve/pii/S0277379111001132http://api.elsevier.com/content/article/PII:S0277379111001132?httpAccept=text/xmlhttp://api.elsevier.com/content/article/PII:S0277379111001132?httpAccept=text/plain IS - 13-14 ER - TY - JOUR T1 - Calibrating a sedimentary record of overwash from Southeastern New England using modeled historic hurricane surges JF - Marine Geology Y1 - 2010 A1 - Boldt, Katherine V. A1 - Lane, Philip A1 - Woodruff, Jonathan D. A1 - Donnelly, Jeffrey P. KW - Holocene KW - hurricane KW - Paleotempestology KW - Salt marsh KW - storm surge KW - tropical cyclone AB - We present a 2000-year record of overwash deposits preserved in a backbarrier salt marsh from southeastern New England. The timing of recent deposits matches well with large hurricane-induced storm surge events documented by local tide gauges in 1991, 1960, 1954, and 1938. Storm surge modeling is used to evaluate the flooding history at the site as well as to assess the pre-instrumental historical record. Storms in 1815, 1727, and 1635 likely caused significant surge that overtopped the barrier, with the timing of coarse-grained overwash deposition correlating well with these events. We infer that twenty-three prehistoric layers mapped across the site were likely also deposited by landfalling hurricanes. Additional records from the area will help to evaluate whether or not temporal trends at the site are a robust representation of hurricane activity for the region. The frequency of overwash at Mattapoisett Marsh, on average 1.5 events per century, is significantly higher than many other overwash-based reconstructions from the western North Atlantic. Further, the Mattapoisett Marsh record does not contain significant multi-centennial gaps in overwash layers. This initial comparison of the data from Mattapoisett marsh with other reconstructions from the western North Atlantic may point toward relatively constant tropical cyclone frequency over the last 2000 years with significant variation in the number of intense tropical cyclones. VL - 275 UR - http://linkinghub.elsevier.com/retrieve/pii/S0025322710001702http://api.elsevier.com/content/article/PII:S0025322710001702?httpAccept=text/xmlhttp://api.elsevier.com/content/article/PII:S0025322710001702?httpAccept=text/plain IS - 1-4 ER - TY - JOUR T1 - In situ cosmogenic Be-10 production-rate calibration from the Southern Alps, New Zealand JF - QUATERNARY GEOCHRONOLOGY Y1 - 2010 A1 - Putnam, A. E. A1 - Schaefer, J. M. A1 - Barrell, D. J. A. A1 - Vandergoes, M. A1 - Denton, G. H. A1 - Kaplan, M. R. A1 - Finkel, R. C. A1 - Schwartz, R. A1 - Goehring, B. M. A1 - Kelley, S. E. KW - Be-10 KW - C-14 KW - Cosmogenic nuclide KW - Debris flow KW - Holocene KW - Last glacial maximum KW - Moraine KW - Production rate KW - South Island AB - We present a Be-10 production-rate calibration derived from an early Holocene debris-flow deposit at about 1000 m above sea level in the central Southern Alps, New Zealand, in the mid-latitude Southern Hemisphere. Ten radiocarbon ages on macrofossils from a soil horizon buried by the deposit date the deposit to 9690 +/- 50 calendar years before AD2008. Surface Be-10 concentrations of seven large boulders partially embedded in the stable surface of the deposit are tightly distributed, yielding a standard deviation of similar to 2%. Conversion of the Be-10 measurements to sea level/high-latitude values using each of five standard scaling methods indicates Be-10 production rates of 3.84 +/- 0.08, 3.87 +/- 0.08, 3.83 +/- 0.08, 4.15 +/- 0.09, and 3.74 +/- 0.08 atoms g(-1) a(-1), relative to the `07KNSTD' Be-10 AMS standard, and including only the local time-integrated production-rate uncertainties. When including a sea level high-latitude scaling uncertainty the overall error is similar to 2.5% (1 sigma) for each rate. To test the regional applicability of this production-rate calibration, we measured Be-10 concentrations in a set of nearby moraines deposited before 18060 +/- 200 years before AD2008. The Be-10 ages are only consistent with minimum-limiting C-14 age data when calculated using the new production rates. This also suggests that terrestrial in situ cosmogenic-nuclide production did not change significantly from Last Glacial Maximum to Holocene time in New Zealand. Our production rates agree well with those of a recent calibration study from northeastern North America, but are 12-14% lower than other commonly adopted values. The production-rate values presented here can be used elsewhere in New Zealand for rock surfaces exposed during or since the last glacial period. (C) 2009 Elsevier B.V. All rights reserved. VL - 5 ER - TY - JOUR T1 - Late Quaternary benthic foraminifera from Ocean Drilling Program Hole 716A, Maldives Ridge, southeastern Arabian Sea JF - Micropaleontology Y1 - 2009 A1 - Sarkar, S. A1 - De, S. A1 - Gupta, A. K. KW - benthonic foraminifera KW - equatorial indian-ocean KW - Holocene KW - late neogene KW - monsoon KW - Oxygen minimum zone KW - productivity KW - red-sea KW - south atlantic-ocean KW - Water masses AB - A study on deep-sea benthic foraminifera from the interval similar to 445 ka BP to the Present of the Ocean Drilling Program (ODP) Hole 716A (4 degrees 56.0'N, 73 degrees 17.0'E; preser t water depth 533.3m), Maldives Ridge. southeastern Arabian Sea, documented 201 species belonging to 105 genera. These taxa were examined under scanning electron microscope (SEM) to illustrate their interspecific morphological variations. Several of these species are dominant showing significant down core fluctuations in their abundances whereas some are rare and sporadic. VL - 55 SN - 0026-2803 IS - 1 N1 - 424cdTimes Cited:5 Cited References Count:47 JO - Micropaleontology ER - TY - JOUR T1 - Recently exposed vegetation reveals Holocene changes in the extent of the Quelccaya Ice Cap, Peru JF - QUATERNARY RESEARCH Y1 - 2009 A1 - Buffen, Aron M. A1 - Thompson, Lonnie G. A1 - Mosley-Thompson, Ellen A1 - Huh, Kyung In KW - 14C dating KW - Andes KW - Climate change KW - Glacier retreat KW - Holocene KW - Peru KW - Quelccaya Ice Cap KW - South America KW - Tropical glaciers AB - Radiocarbon dating of well-preserved, in-place vegetation exposed by the retreating Quelccaya Ice Cap of southeastern Peru constrains the last time the ice cap's extent was smaller than at present. Seventeen plant samples from two sites along the central western margin collectively date to 4700 and 5100 cal yr BP and strongly indicate that current ice cap retreat is unprecedented over the past similar to 5 millennia. Seventeen vegetation samples interbedded in a nearby clastic sedimentary sequence suggest ice-free conditions at this site from similar to 5200 to at least similar to 7000 cal yr BP, and place minimum constraint on early- to mid-Holocene ice cap extent. (C) 2009 University of Washington. Published by Elsevier Inc. All rights reserved. VL - 72 ER - TY - CONF T1 - Environmental Factors Controlling Community Structure, Morphology and Linear Extension of Mid-Holocene Reef Corals from Cañada Honda, Southwestern, Dominican Republic T2 - Proceedings of the 11th International Coral Reef Symposium, Ft. Lauderdale, Florida Y1 - 2008 A1 - Cuevas, D. A1 - Sherman, C. A1 - Ramírez, W. A1 - Hubbard, D. KW - Caribbean KW - Holocene KW - ICRS11 KW - Lessons from the past KW - linear extension KW - siltation AB - The Cañada Honda (CH) fossil coral reef, located in SW Dominican Republic, provides a unique opportunity to examine reef accretion in a high-sedimentation environment between 9.0-5.0 ky ago. Annual linear extension of fossil corals was determined for comparison with data from modern coral reefs. The reef is characterized by the high abundance of sediment-tolerant coral species, their tendency to form almost monospecific stands and grow as domes-cones with ragged margins. Also, colonies of Montastraea faveolata commonly contain bands of sediment incorporated within their skeletons. Calibrated radiocarbon ages of fossil corals range from 9,256±137 to 6,737±94.5 BP. Correlation with Holocene sea-level curves indicates that most corals on CH developed at depths greater than 15m. Growth rates varied from 0.09-0.44 cm/yr and suggest reduced light penetration caused by coral growth at such depths. Reef sediment is characterized by more than 85% carbonate material. A significant portion of the carbonate is allochtonous and was derived from nearby Neogene limestones. The reef was able to survive under these conditions because of the high carbonate content of incoming terrigenous sediment and that storms probably occurred sporadically providing intervening lowsedimentation periods during which reef corals could respond and grow back, “keeping-up” with sedimentation. JF - Proceedings of the 11th International Coral Reef Symposium, Ft. Lauderdale, Florida N1 - id: 1979 ER - TY - JOUR T1 - Oxygen and carbon isotope records of calcareous nannofossils from the west Philippine Sea during the last 190ka JF - Earth Science.Journal of China University of Geoscience Y1 - 2008 A1 - Jingtao, Zhao A1 - Li, Tiegang A1 - Chang, Fengming A1 - Li, Jun KW - 02D KW - 24 KW - algae KW - biochemistry KW - C-13/C-12 KW - carbon KW - Cenozoic KW - Foraminifera KW - Geochemistry KW - Holocene KW - Invertebrata KW - Isotope geochemistry KW - isotope ratios KW - isotopes KW - Last glacial maximum KW - microfossils KW - nannofossils KW - north pacific KW - Northwest Pacific KW - O-18/O-16 KW - oxygen KW - Pacific Ocean KW - paleo-oceanography KW - Philippine Sea KW - Plantae KW - Pleistocene KW - productivity KW - Protista KW - Quaternary KW - Quaternary geology KW - Stable isotopes KW - upper Pleistocene KW - West Pacific AB - The piston core Ph05-5 recovered from the West Philippine Sea(16.049 degrees N, 124.344 degrees E, water depth 3382m) was used to study the delta (super 18) O and delta (super 13) C variations of calcareous nannofossils. The delta (super 18) O values of calcareous nannofossils were obviously lower in Holocene and the last interglaciation than those in the last and the penultimate glaciation. During the last 190 ka the nannofossil delta (super 18) O values were positively correlated with those of planktonic and benthic foraminifera from the same core. But the average delta (super 18) O value of nannofossils was 0.431X10 (super -3) , higher than that of planktonic foraminifera Globigerinoides rubber, and was 0.410X10 (super -3) , lower than that of planktonic foraminifera Neogloboquadrina dutertrei. All the above three average delta (super 18) O values were much lower than those of benthic foraminifera Cibicides wullerstorfi. The change of nannofossil delta (super 13) C values showed similar trends with the absolute abundance of calcareous nannofossils in core Ph05-5, which also indicates the primary productivity variations in the West Philippine Sea. The primary productivity stayed at a stable but relatively low level at MIS 6 and MIS 5e.There was an abrupt rise at the beginning of MIS 5d for the primary productivity which retained high value until 25 ka BP. The primary productivity showed a slight decline during MIS 2 and MIS 1, but still higher than that of MIS 6 and MIS 5e. VL - 33 SN - 1000-2383, 1000-2383 IS - 2 N1 - id: 1933; NO: Source type: scholarlyjournals; Object type: Article; Copyright: GeoRef in Process, Copyright 2011, American Geosciences Institute. After editing and indexing, this record will be added to Georef.; CSAUnique: 570969-5; AccNum: 570969-5; ISSN: 1000-2383; Peer Reviewed: true ER - TY - THES T1 - Paleotsunami History Recorded in Holocene Coastal Lagoon Sediments, Southeastern Sri Lanka T2 - Marine Geology and Geophysics (Marine) Y1 - 2008 A1 - Jackson, Kelly KW - Coastal Lagoons KW - Holocene KW - Paleotsunamis KW - Sri Lanka KW - Tsunami Deposits KW - Tsunami Sediments KW - Tsunamis AB - Tsunamis are low amplitude, large wavelength waves that can significantly impact coastal regions. Although their destructive impacts are clear from recent events, the frequency with which tsunamis occur is less well constrained. To better understand the tsunami history and coastal impacts in Sri Lanka, this study compares sediments deposited by the December 26, 2004, tsunami to older lagoon sediments in search of evidence for paleotsunami deposits. Results from this study illustrate that the coastal lagoons in Sri Lanka preserve tsunami deposits and can provide the first steps towards constraining the paleotsunami history of the Indian Ocean. Because Sri Lanka is a far field location relative to the Sumatra-Andaman subduction zone, the preserved tsunami deposits are likely mega-tsunami events similar in size and destruction to the December 26, 2004, tsunami. The December 26, 2004, M 9.1?9.3 Sumatra-Andaman earthquake generated a massive tsunami that propagated throughout the Indian Ocean, causing extreme coastal inundation and destruction. The southeastern coastline of Sri Lanka was impacted by the 2004 tsunami where between one and three waves inundated coastal villages, lagoons, and lowlands, killing more than 35,000 people. Karagan Lagoon, located on the southeastern coast of Sri Lanka, was impacted by two waves from this tsunami. Although the lagoon commonly is dominated by organic-rich, siliciclastic clays, silts, and fine sands, the 2004 tsunami deposited a distinct layer of coarse quartz-dominated sand between 1 and 22 cm thick. The base of the 2004 deposit is sharp and erosional and some layers feature faint subparallel laminations. The 2004 tsunami deposit is generally continuous, fines landward, and is confined to the eastern portion of Karagan Lagoon, in the direction from which the tsunami arrived. Sri Lankan lore, in conjunction with reconstructed historical earthquake data, suggests that other tsunamis likely affected Sri Lanka in the past. To test this, twenty-two 1?4 m sediment cores were collected from Karagan Lagoon, providing key information for unraveling the pre-2004 tsunami history of southeastern Sri Lanka. At depth, sixteen cores from Karagan Lagoon contain as many as ten distinct sand layers, including the deposit from the 2004 tsunami. These cores feature siliciclastic clays, silts, and fine sands that dominate the background lagoonal sedimentation that are punctuated by coarse sand layers. These sand-rich layers feature sharp, erosional bases, coarsen and fine upwards, vary in thickness from 1 to 22 cm, and include varying percentages of fine to very coarse sand, with a low-abundance of silt and clay. In the best constrained interval, three coarse sand layers include composition, grain size, grading, and sedimentary structures similar to the sediments deposited by the December 26, 2004, tsunami. The layers are identified in five of the twenty-two cores, although the thicknesses vary. Six additional less well constrained sand layers are present in four of the twenty-two cores. Cores located closer to the lagoon mouth and the eastern coastline (the direction from which the 2004 tsunami arrived) contain more sand layers than cores farther away from the tsunami wave entry point. On the basis of their sedimentary structures, geometry, and extent, these sandy layers are interpreted to represent paleotsunami deposits. AMS radiocarbon dating was used to date the bulk organic sediment from above, between, and below the ten paleotsunami layers in sediment cores from Karagan Lagoon to constrain the timing of events in southeastern Sri Lanka. Material from within the deposit was not dated because it was likely transported from various sources during the event and thus does not represent the age of the tsunami. AMS radiocarbon dates from above and below the paleotsunami layers were calibrated from radiocarbon years before present to calendar years before present (Cal YBP) using OxCal v. 4.0 (Bronk Ramsey, 1995; Bronk Ramsey, 2001) with calibration curve IntCal04 (Reimer et al., 2004). The constraining time intervals of tsunami deposits II?VI were averaged to yield deposits of ages 226, 1641, 4198, 4457, 4924 Cal YBP. Tsunamis VII?X only had sediment dated immediately below the deposit and therefore were deposited prior to 6249, 6455, 6665, and 6840 Cal YBP. In total, ten tsunami deposits, including the 2004 event, are preserved in Karagan Lagoon on the southeastern coast of Sri Lanka. The Karagan Lagoon paleotsunami deposits provide constraints on the recurrence interval of tsunamis similar in magnitude to the 2004 event. The uppermost paleotsunami units were deposited 226, 1641, 4198, 4457, and 4924 Cal YBP, based on AMS radiocarbon dating. Thus, including the 2004 event, six tsunamis affected Karagan Lagoon in the past 5500 years, yielding a recurrence interval of approximately 916 years. Three of the six events, however, occur between ~4000 and 5500 years yielding a recurrence interval of approximately 500 years for this 1500 year period. Four additional older paleotsunami deposits occur in the deeper sections of the cores and were deposited prior to 6249, 6455, 6665, and 6840 Cal YBP, yielding a recurrence interval of approximately 200 years for this time period. Assuming that Karagan Lagoon contains a complete record of tsunami events, the recurrence of tsunamis similar in magnitude to the December 26, 2004, event can occur as often as 200 years. This ?recurrence interval? is illustrated by our data for the time period with increased tsunami activity from ~4000 to 7000 Cal YBP. Tsunamis may potentially affect Sri Lanka at relatively high frequency during certain time intervals though the overall recurrence pattern of these events displays a highly irregular distribution. This extreme variability needs to be taken into consideration when such events are related to earthquake recurrence intervals. Prior to the December 26, 2004, tsunami, paleotsunami deposits in the Indian Ocean were largely unstudied and consequently, Holocene tsunami chronology was incompletely understood for the Indian Ocean. The results from this study represents the first geologic evidence of paleotsunami deposits in Sri Lanka generated by tsunamis during the past 7000 years. The identification of these paleotsunami deposits illustrates that the 2004 tsunami was not a ?one-time event,? but in fact has ancient counterparts. JF - Marine Geology and Geophysics (Marine) PB - University of Miami CY - Miami, FL VL - Master of Science (MS) UR - http://scholarlyrepository.miami.edu/oa_theses/171 ER - TY - CONF T1 - Taphonomy and ages of bivalve shells from San Salvador Island, Bahamas Y1 - 2008 A1 - Pruss, Sara B. KW - 10 KW - abrasion KW - absolute age KW - Bahamas KW - beachrock KW - Bivalvia KW - C-14 KW - carbon KW - carbonate rocks KW - Caribbean region KW - Cenozoic KW - Chione KW - dates KW - Gastropoda KW - Glycymeris KW - Heterodonta KW - Holocene KW - interpretation KW - Invertebrata KW - Invertebrate paleontology KW - isotopes KW - lithification KW - living taxa KW - Mollusca KW - Quaternary KW - radioactive isotopes KW - San Salvador KW - sedimentary rocks KW - sediments KW - shells KW - taphonomy KW - upper Holocene KW - Veneridae KW - Veneroida KW - West Indies AB - Paleontological interpretations of taphonomic processes can be complimented by examining abrasion and age of shells in modern settings. A preliminary analysis of the ages of bivalves from Haitian Boat Beach (just east of Barkers Point, northwest coast of San Salvador Island, Bahamas) provides a range of ages of shell material exposed on modern beaches of San Salvador Island and provides estimates of the timing of beach rock lithification. At Haitian Boat Beach Beach, bivalves and gastropods were collected from shell accumulations preserved on the beach as well as within a single 3 to 5-cm thick horizon of beach rock. The ages of 2 valves (Genus Chione) from the beach and 4 valves (Genus Chione and Genus Glycymeris) from the beach rock were analyzed. Two of the most abraded shells were selected for analysis from the beach in an attempt to get a maximum age of beach shell material. These shells were radiocarbon dated by measuring carbon-14 at NOSAMS and converted to calendar years using the CALIB program of Stuiver and Reimer (1993). Two abraded valves collected from the beach yielded calendar year ages BP of 512 and 549 years. The beach rock valves yielded calendar year ages BP of 143, 129, and 1628. These results suggest lithification of beach rock was initiated PB - Geological Society of America (GSA), Boulder, CO, United States (USA) CY - United States (USA) VL - 40 N1 - id: 2219; Source type: conferencepapers&proceedings; Object type: Article; Object type: Conference Paper; Copyright: GeoRef, Copyright 2008, American Geological Institute. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States; CSAUnique: 2010-024085; AccNum: 2010-024085; ISSN: 0016-7592; CODEN: GAAPBC ER - TY - CONF T1 - The Environmental Anomalies in the Northeastern East China Sea during the Last 3000 Years: Implications for El Nino Activity in the Holocene T2 - 9th International Conference on Paleoceanography (ICP 9) Y1 - 2007 A1 - Chang, F. A1 - Zhuang, L. A1 - Li, T. A1 - Yan, J. A1 - Li, Q. ED - Shanghai International Convention Center, Shanghai KW - Donghai Sea KW - Holocene KW - Multidisciplinary KW - Paleo studies KW - Paleoenvironments KW - U 7000 JF - 9th International Conference on Paleoceanography (ICP 9) N1 - id: 1935; TY: CPAPER; NO: Source type: conferencepapers&proceedings; Object type: Conference Paper; CSAUnique: CPI-4728602; AccNum: 4728602(China) ER - TY - JOUR T1 - Late Holocene barrier island collapse; Outer Banks, North Carolina, USA JF - The Sedimentary Record Y1 - 2007 A1 - Culver, Stephen J. A1 - Grand Pre, Candace A. A1 - Mallinson, David J. A1 - Riggs, Stanley R. A1 - Corbett, D. Reide A1 - Foley, Jennifer A1 - Hale, Michael A1 - Metger, Lauren A1 - Ricardo, John A1 - Rosenberger, Jeb A1 - Smith, Christopher G. A1 - Smith, Curtis W. A1 - Snyder, Scott W. A1 - Twamley, David A1 - Farrell, Kathleen A1 - Horton, Benjamin KW - 24, Quaternary geology KW - algae KW - assemblages KW - barrier islands KW - Cenozoic KW - changes KW - clastic sediments KW - cores KW - diatoms KW - erosion KW - Foraminifera KW - geologic hazards KW - Holocene KW - hurricanes KW - Invertebrata KW - landform evolution KW - lithofacies KW - littoral KW - microfossils KW - North Carolina KW - Outer Banks KW - Pamlico Sound KW - Plantae KW - preservation KW - Protista KW - Quaternary KW - salinity KW - sand KW - sea-level KW - sediments KW - United States KW - upper Holocene KW - Vibroseis AB - We document here the threat of large scale destruction (collapse) of barrier islands based on the study of many cores taken along the Outer Banks and in Pamlico Sound, North Carolina.Around 1,100 cal yr BP, probably as the result of hurricane activity, portions of the southern Outer Banks must have collapsed to allow normal salinity waters to bathe southern Pamlico Sound for several hundred years. Such collapse could occur again during our current regime of global warming, rising sea level and increased tropical cyclone activity. The economic effect of barrier island break collapse on Outer Banks communities would be devastating. VL - 5 IS - 4 N1 - id: 1887; ISSN: 1543-8740 Language: English References: 16; illus. incl. strat. col., geol. sketch map United States (USA) Latitude:N350000,N353000 Longitude:W0753000,W0760000 ER - TY - JOUR T1 - Aspartic acid racemization dating of Holocene brachiopods and bivalves from the southern Brazilian shelf, South Atlantic JF - Quaternary Research Y1 - 2006 A1 - Barbour-Wood, S. L. A1 - Krause R.A, Jr. A1 - Kowalewski, M. A1 - Wehmiller, J. F. A1 - Simoes, M. G. KW - Amino acid racemization KW - Aspartic KW - Bouchardia KW - Brachiopods KW - Brazil KW - Holocene KW - Mollusks KW - Radiocarbon dating KW - Semele KW - Ubatuba Bay AB - The extent of racemization of aspartic acid (Asp) has been used to estimate the ages of 9 shells of the epifaunal calcitic brachiopod Bouchardia rosea and 9 shells of the infaunal aragonitic bivalve Semele casali. Both taxa were collected concurrently from the same sites at depths of 10 m and 30 m off the coast of Brazil. Asp D/L values show an excellent correlation with radiocarbon age at both sites and for both taxa (r2Site 9 B. rosea = 0.97, r2Site 1 B. rosea = 0.997, r2Site 9 S. casali = 0.9998, r2Site 1 S. casali = 0.93). The Asp ratios plotted against reservoir-corrected AMS radiocarbon ages over the time span of multiple millennia can thus be used to develop reliable and precise geochronologies not only for aragonitic mollusks (widely used for dating previously), but also for calcitic brachiopods. At each collection site, Bouchardia specimens display consistently higher D/L values than specimens of Semele. Thermal differences between sites are also notable and in agreement with theoretical expectations, as extents of racemization for both taxa are greater at the warmer, shallower site than at the cooler, deeper one. In late Holocene marine settings, concurrent time series of aragonitic and calcitic shells can be assembled using Asp racemization dating, and parallel multi-centennial to multi-millennial records can be developed simultaneously for multiple biomineral systems. VL - 66 IS - 2 N1 - id: 1168 JO - Aspartic acid racemization dating of Holocene brachiopods and bivalves from the southern Brazilian shelf, South Atlantic ER - TY - JOUR T1 - Postglacial climate reconstruction based on compound-specific D/H ratios of fatty acids from Blood Pond, New England JF - Geochemistry Geophysics Geosystems Y1 - 2006 A1 - Hou, J. Z. A1 - Huang, Y. S. A1 - Wang, Y. A1 - Shuman, B. A1 - Oswald, W. W. A1 - Faison, E. A1 - Foster, D. R. KW - atmospheric processes : paleoclimatology KW - eastern north-america KW - fatty acids KW - geochemistry : organic and biogenic geochemistry KW - geochemistry : stable isotope geochemistry KW - Holocene KW - hydrogen isotope KW - hydrogen isotope ratios KW - lacustrine organic-matter KW - lake-sediments KW - Paleoclimate KW - record KW - Stable isotopes KW - united-states KW - vegetation history KW - younger-dryas AB - We determined hydrogen isotope ratios of individual fatty acids in a sediment core from Blood Pond, Massachusetts, USA, in order to reconstruct climate changes during the past 15 kyr. In addition to palmitic acid (C-16 n-acid), which has been shown to record lake water D/H ratios, our surface sediments and down core data indicate that behenic acid (C-22 n-acid), produced mainly by aquatic macrophytes, is also effective for capturing past environmental change. Calibration using surface sediments from two transects across eastern North America indicates that behenic acid records delta D variation of lake water. Down core variations in delta D values of behenic acid and pollen taxa are consistent with the known climate change history of New England. By evaluating the hypothesis that D/H fractionations of long chain even numbered fatty acids (C-24-C-32 n-acids) relative to lake water provide independent estimates of relative humidity during the growing season, we find that differences between lake-level records and isotopically inferred humidity estimates may provide useful insight into seasonal aspects of the hydrologic cycle. Combined analyses of D/H of short and long chain fatty acids from lake sediment cores thus allow reconstructions of both past temperature and growing season relative humidity. Comparison of delta D records from two lakes in New England provides critical information on regional climate variation and abrupt climate change, such as the 8.2 ka event. VL - 7 SN - 1525-2027 IS - 3 N1 - 031uaTimes Cited:32 Cited References Count:43 JO - Geochem Geophy Geosy ER - TY - JOUR T1 - Evidence of past intense tropical cyclones from backbarrier salt pond sediments: A case study from Isla de Culebrita, Puerto Rico, USA JF - Journal of Coastal Research Y1 - 2005 A1 - Donnelly, J. P. KW - Caribbean KW - climate KW - coast KW - deposits KW - florida KW - grain-size analysis KW - Holocene KW - hurricane KW - hurricanes KW - new-jersey KW - record KW - south-carolina KW - storm KW - tsunami AB - Tropical cyclones pose a significant threat to lives and resources in heavily-populated regions and can extensivelymodify coastal landforms. In appropriate depositional environments a sedimentological record of past tropical cyclones can be preserved. Given the relative rarity of landfalling tropical cyclones and the shortness of the instrumental record, little is known about past patterns of hurricane activity. The development of long-term records of tropical cyclone activity will make it possible to examine how past climate change may have influenced the frequency, intensity, and locations (origin, tracks) of hurricanes. Previous work has shown that intense hurricane strikes produce a distinctive sedimentary signature that can be used to reconstruct long-term records of these events. Numerous coastal salt ponds and lagoons in eastern Puerto Rico and the U.S. Virgin Islands are well situated to receive allocthonous sediments during intense tropical cyclone landfalls. Coastal salt ponds, normally low-energy environments, are dominated by fine-grained organic sediments, with the exception of episodic deposition of coarser-grained mineral sediments from the beach and nearshore during extreme storms. Sediment obtained from a series of cores taken from Big Culebrita Salt Pond on the Isla de Culebrita, Puerto Rico reveal a record of flooding-induced sedimentation within mangrove and salt-pond sediments dating back more than 2000 years. Reconstructing the history of storm-surge deposition from backbarrier salt-pond sediments may allow for the reconstruction of a millennial-scale record of tropical cyclones for the northeastern Caribbean and other regions. VL - SI42 SN - 0749-0208 UR - http://www.jstor.org/stable/25736985 N1 - Sp. Iss. 42947fu Times Cited:16 Cited References Count:40 JO - J Coastal Res ER - TY - JOUR T1 - Mangrove ecocystem dynamics and elemental cycling at Twin Cays, Belize, during the Holocene JF - Journal of Quaternary Science Y1 - 2004 A1 - Wooller, M. J. A1 - Behling, H. A1 - Smallwood, B. J. A1 - Fogel, M. KW - Holocene KW - isotopes;pollen KW - mangroves KW - Palaeoecology AB - Existing at the transition between the terrestrial environment and hydrosphere, mangroves are sensitive to environmental change (e.g. sea-level rise). We present pollen and stable isotope data from a core (TCC1) of continuous (10 m) mangrove peat from Twin Cays, ∼12 km off of the coast of Belize, Central America. Radiocarbon dates on fragments of mangrove leaves preserved in TCC1 show that the core provides an 8600 14C year record of mangrove ecosystem changes. Variation in the stable carbon and nitrogen isotope composition (δ13C = ∼−30 to −25‰; δ15N = ∼−6 to 2‰) of mangrove leaves imply that the stand structure and nutrient status of the mangroves at the site have changed during the Holocene. Pollen data from the same core show that the floral composition of the site has changed at points during the Holocene, most notably a brief (∼240 years) switch at ∼3860 14C yr BP to dominance by a species of Myrsine (not currently present at the site). Our results are consistent with significant environmental changes (either marked disturbance from hurricanes or fluctuations in sea-level) through the Holocene. VL - 19 IS - 7 N1 - id: 1149 JO - Mangrove ecocystem dynamics and elemental cycling at Twin Cays, Belize, during the Holocene ER - TY - JOUR T1 - Late-Quaternary lowstands of Lake Titicaca: evidence from high-resolution seismic data JF - Palaeogeography Palaeoclimatology Palaeoecology Y1 - 2002 A1 - D'Agostino, K. A1 - Seltzer, G. A1 - Baker, P. A1 - Fritz, S. A1 - Dunbar, R. KW - Andes KW - bolivian altiplano KW - central andes KW - climatic-change KW - Holocene KW - lacustrine KW - lake level change KW - lake titicaca KW - level KW - malawi KW - Peru KW - record KW - seismic reflection data KW - tropical paleoclimate KW - tropical south-america AB - Approximately 600 km of high-resolution seismic reflection data were collected to investigate the late-Quaternary stratigraphic development of Lake Titicaca. The focus of this report is on two seismic sequence boundaries, which are interpreted as erosional surfaces formed at times of low lake level. The younger erosional surface occurs as much as 90 in below the present lake level and up to 8 in below the present sediment-water interface. This erosional surface is interpreted to be coeval with a well-documented early- to mid-Holocene lowstand, dated between similar to 8000 and 3600 cal yr BP. An earlier and previously unknown erosional surface occurs at a sub-bottom depth of approximately 30 m, and as much as 240 in below the present lake level, which implies a major late-Pleistocene lowstand of Lake Titicaca. By extrapolation of sedimentation rates from the upper similar to 14 in of sediment, we estimate the age of this older lowstand at > 90 000 cal yr BP. Both lowstands of Lake Titicaca indicated by the seismic data are likely to have been a response to climatic change in the region. (C) 2002 Elsevier Science B.V. All rights reserved. VL - 179 SN - 0031-0182 IS - 1-2 N1 - 560qxTimes Cited:31 Cited References Count:33 JO - Palaeogeogr Palaeocl ER - TY - JOUR T1 - Ocean ventilation and sedimentation since the glacial maximum at 3 km in the western North Atlantic JF - Geochemistry Geophysics Geosystems Y1 - 2002 A1 - Keigwin, L. D. A1 - Schlegel, M. A. KW - abyssal circulation KW - benthic foraminifera KW - c-14 ages KW - Calibration KW - climate-change KW - deep-water KW - Holocene KW - Last glacial maximum KW - ocean ventilation KW - radiocarbon KW - radiocarbon age KW - sea KW - sediment drifts KW - Younger Dryas AB - [1] Stable isotope, sedimentological, and radiocarbon data from cores at similar to 3 km water depth on the Blake Ridge, western subtropical North Atlantic, reveal the history of deep water ventilation since the last glacial maximum (LGM). Bulk sediment accumulation rates varied locally by a factor of 2 under the influence of bottom currents in this sediment drift environment, but the sand flux, mostly foraminifera, was nearly identical at a given time. This suggests that the rain rate of foraminifera (mostly planktonic) was constant, that transport of foraminifera was negligible, and that current-controlled differences in clay and silt transport drive bulk accumulation. In two of the cores, flux peaks in the benthic foraminifera Cibicidoides and Uvigerina peregrina occurred during the Younger Dryas (YD) cold event, and at 18.2, 19.6, 21.1, 25.0, and 28.1 ka. Radiocarbon measurements on those benthic foraminifera show the ventilation age of bottom waters was similar to 1000 years during the YD, and for older events it was as great as 2000 years. These results contrast with Holocene ventilation, which was similar to 500 years and 700 years at 1500 years and similar to 7100 years before present, respectively. VL - 3 SN - 1525-2027 IS - 6 N1 - 565rlTimes Cited:26 Cited References Count:43 JO - Geochem Geophy Geosy ER - TY - JOUR T1 - Stable isotope composition of Littoridina australis from the coast of Buenos Aires province, Argentina, during Holocene climatic fluctuations JF - Geobios Y1 - 2002 A1 - Aguirre, M. L. A1 - Zanchetta, G. A1 - Fallick, A. E. KW - Argentina KW - Holocene KW - Littoridina australis KW - Molluscs KW - Palaeoenvironments KW - Stable isotopes AB - Stable isotope (carbon and oxygen) analyses were performed on Littoridina australis shells collected from molluscan concentrations within Holocene littoral deposits along the Bonaerensian coastal area of Argentina (south-western Atlantic). Isotope data allow us to define two very different areas: the Samborombon Bay, where isotope composition of shells was mainly governed by mixing between marine and freshwater, and the Mar Chiquita lagoon, where the original brackish environment was dominated by evaporation of water that originated high isotope shell values. In both areas some isotope profiles show short and quite large oscillations in delta(18)O. Their origin may be tentatively explained as due to the changes in moisture regime that control freshwater supply. The results suggest that these deposits can represent natural archives potentially useful for palaeoclimate reconstruction. (C) 2002 Editions scientifiques et medicales Elsevier SAS. All rights reserved. VL - 35 IS - 1 N1 - 563lxTimes Cited:9Cited References Count:27 JO - Stable isotope composition of Littoridina australis from the coast of Buenos Aires province, Argentina, during Holocene climatic fluctuations ER - TY - JOUR T1 - Holocene lake sediment records of Arctic hydrology JF - Journal of Paleolimnology Y1 - 2000 A1 - MacDonald, G. M. A1 - Felzer, B. A1 - Finney, B. P. A1 - Forman, S. L. KW - Arctic KW - Climate change KW - Holocene KW - paleohydrology KW - paleolimnology AB - Although paleoclimatic research in the Arctic has most often focused on variations in temperature, the Arctic has also experienced changes in hydrologic balance. Changes in Arctic precipitation and evaporation rates affects soils, permafrost, lakes, wetlands, rivers, ice and vegetation. Changes in Arctic soils, permafrost, runoff, and vegetation can influence global climate by changing atmospheric methane and carbon dioxide concentrations, thermohaline circulation, and high latitude albedo. Documenting past variations in Arctic hydrological conditions is important for understanding Arctic climate and the potential response and role of the Arctic in regards to future climate change. Methods for reconstructing past changes in Arctic hydrology from the stratigraphic, isotopic, geochemical and fossil records of lake sediments are being developed, refined and applied in a number of regions. These records suggest that hydrological variations in the Arctic have been regionally asynchronous, reflecting the impacts of different forcing factors including orbitally controlled insolation changes, changes in geography related to coastal emergence, ocean currents, sea ice extent, and atmospheric circulation. Despite considerable progress, much work remains to be done on the development of paleohydrological proxies and their application to the Arctic. VL - 24 IS - 1 N1 - id: 375 JO - S. L. Holocene lake sediment records of Arctic hydrology ER - TY - JOUR T1 - Identification of a novel alkenone in Black Sea sediments JF - Organic Geochemistry Y1 - 2000 A1 - Xu, L. A1 - Reddy, C. M. A1 - Farrington, J. W. A1 - Frysinger, G. S. A1 - Gaines, R. B. A1 - Johnson, C. G. A1 - Nelson, R. K. A1 - Eglinton, T. I. KW - Alkenone KW - Black Sea KW - Haptophytes KW - Holocene KW - Sediment KW - Structure characterization AB - We report the identification of a novel long-chain ketone in Holocene Black Sea sediments. Based on chemical properties, and chromatographic and mass spectrometric characteristics, this compound has been identified as a di-unsaturated C36 ethyl ketone. Further analyses indicated the position and configuration of the double bonds, and the novel alkenone was determined to be hexatriaconta-(16E,21E)-dien-3-one. While this compound is present in only trace quantities in Unit I sediments, it is the most abundant alkenone in portions of Unit II. Its presence thus apparently pre-dates the invasion of Emiliania huxleyi in the Black Sea. The down-core profiles and isotopic compositions suggest that the precursor for the C36:2 alkenone may be distinct from that of the C37-39 alkenones, however the biological origin of this novel compound is presently unknown. VL - 32 N1 - id: 1719 JO - Identification of a novel alkenone in Black Sea sediments ER - TY - JOUR T1 - Postglacial climate and vegetation history, north-central Kola Peninsula, Russia: pollen and diatom records from Lake Yarnyshnoe-3 JF - Boreas Y1 - 2000 A1 - Snyder, J. A. A1 - MacDonald, G. M. A1 - Forman, S. L. A1 - Tarasov, G. A. A1 - Mode, W. N. KW - atlantic KW - finnish lapland KW - Holocene KW - late pleistocene KW - norway KW - sea KW - sediments KW - varanger-peninsula KW - western part KW - younger-dryas AB - A sediment core from Lake Yamyshnoe-3 (69 degrees 04'N; 36 degrees 04'E), an emerged coastal lake from the tundra of the north-central Kola Peninsula, has been analyzed for fossil pollen and diatoms. The pollen record shows the Younger Dryas event marked by increasing Artemisia coupled with decreases in Poaceae, Cyperaceae and Salix at c. 10 700 to 10 000 BP. This core provides the first well-defined palynological record of the Younger Dryas event on the Kola Peninsula. Stomates from Pinus were recovered from the core interval between 8000 and 6000 BP. The stomates, coupled with elevated values of pine pollen, indicate that Pinus sylvestris grew near the arctic coastline of the central Kola Peninsula in the middle Holocene. However, the small number of stomates suggests that pines were not plentiful. The diatom record from the core reflects basin isolation from the sea and indicates additional limnological changes during the climate transition between c. 5000 and 4000 BP. The broadly similar climate and vegetation history on the north-central Kola Peninsula and in Fennoscandia demonstrates the propagation of late glacial and Holocene climate events from the North Atlantic region into the Eurasian Arctic. VL - 29 SN - 0300-9483 IS - 4 N1 - 378dxTimes Cited:28 Cited References Count:82 JO - Boreas ER - TY - JOUR T1 - Marine and meteoric diagenesis of Pleistocene carbonates from a nearshore submarine terrace, Oahu, Hawaii JF - Journal of Sedimentary Research Y1 - 1999 A1 - Sherman, C. E. A1 - Fletcher, C. H. A1 - Rubin, K. H. KW - barrier-reef KW - calcite KW - corals KW - fringing-reef KW - Holocene KW - oxygen isotopes KW - platform KW - recrystallization KW - sea-level KW - stabilization AB - The nearshore slope of Oahu consists of a shallowly dipping shelf extending from the shoreline out to the similar to -20 m contour, where there is a sharp break in slope down to similar to -30 m, Limestones recovered in a series of short cores taken from this nearshore terrace are typical of shallow-marine reef environments and comprise either a branching-coral or massive-coral facies, The composition as well as shoreward zonation of facies suggests that the terrace represents an in situ fossil reef complex. Th-U ages of in situ corals are all Pleistocene and suggest that the bulk of the feature formed during marine oxygen isotope stage 7. Later accretion along the seaward front of the terrace occurred during marine oxygen isotope substages 5a and/or 5c. Deposition during these interglacial highstands has not previously been documented in the sea-level record on Oahu,Although the diagenetic record in the cored samples is incomplete, three periods of diagenesis are identified: early shallow marine, meteoric, and post-meteoric shallow marine. Early shallow-marine diagenesis includes cementation by aragonite and Mg calcite in an active marine phreatic zone and predominantly micritization in a stagnant marine phreatic zone. Meteoric processes occurred in the vadose zone and include precipitation of calcite (needle fibers, meniscus cements, micritic networks), neomorphism, and dissolution. All limestones are now in an active marine phreatic zone. Evidence of post-meteoric shallow-marine diagenesis is found in last-generation Mg calcite cements and internal sediments occurring directly on limestone substrates that have otherwise been stabilized to calcite. The present seafloor is undergoing extensive biological and physical erosion. No Holocene limestones were recovered. Petrographic and geochemical signatures of subaerial exposure and meteoric diagenesis are recognized within the upper several centimeters of all cores. Thus, the present seafloor in the study area is a flooded Pleistocene subaerial exposure surface. VL - 69 SN - 1073-130x IS - 5 N1 - A237cq Times Cited:42 Cited References Count:79 JO - J Sediment Res ER - TY - JOUR T1 - Sea-level rise on eastern China's Yangtze delta JF - Journal of Coastal Research Y1 - 1998 A1 - Chen, Z. Y. A1 - Stanley, D. J. KW - delta flooding KW - Holocene KW - neolithic sites KW - peat KW - radiocarbon dates KW - relative sea level KW - sea-level curve KW - subsidence KW - taihu lake KW - yangtze delta AB - The Yangtze delta is a densely populated, low-lying region highly vulnerable to flooding, high tides and typhoons. All previous studies indicated that relative sea level was higher from similar to 7500-4000 yrs. BP, then lowered and stabilized at about present msl during the past 3000 yrs. To the contrary, we find that sea level has been rising relative to the southern Yangtze delta plain based on new sea-level data derived from dated peats, reassessment of earlier sea-level curves and measurement of delta plain subsidence and analysis of prehistoric habitat bases from similar to 7000 to 3000 yrs. BP. Consequences of this relative rise include difficulty in expelling water from the low-lying delta plain to the coast and associated flood damage. Emplacement of the 3-Gorges Dam on the Yangtze will control flooding of the Yangtze river but decrease sediment accumulation on the delta plain that, in turn, is likely to accelerate saline inundation of this vital breadbasket. VL - 14 SN - 0749-0208 IS - 1 N1 - Yt592Times Cited:46 Cited References Count:27 JO - J Coastal Res ER - TY - JOUR T1 - Biogenic Silica in Lake Baikal Sediments - Results from 1990-1992 American Cores JF - Journal of Great Lakes Research Y1 - 1994 A1 - Carter, S. J. A1 - Colman, S. M. KW - accumulation KW - Holocene KW - Lake Baikal KW - marine-sediments KW - opal KW - Paleoclimate KW - sediments KW - silica AB - The Lake Baikal Paleoclimate Project is a joint Russian-American program established to study the paleoclimate of Central Asia. During three summer field seasons, duplicate Russian and American coves were taken at a number of sites in different sedimentary environments in the lake. Eight cores returned to the U.S. were quantitatively analyzed for biogenic silica using a single-step 5-hour alkaline leach, followed by dissolved silicon analysis by inductively-coupled-plasma atomic-emission spectroscopy. Sediments of Holocene age in these cores have biogenic silica maxima that range from about 15 to 80 percent. An underlying zone in each core with low biogenic-silica concentrations (0 to 5 percent) dates from the last glacial maximum. The transition from the last glaciation to the present interglaciation, recorded by biogenic silica, began about 13,000 years ago. Biogenic silica profiles from these cores appear to be a good measure of past diatom productivity and a useful basis for paleoclimatic interpretations. VL - 20 SN - 0380-1330 IS - 4 N1 - Px453Times Cited:46 Cited References Count:20 JO - J Great Lakes Res ER - TY - JOUR T1 - A Sediment Budget for Southern Lake-Michigan - Source and Sink Models for Different Time Intervals JF - Journal of Great Lakes Research Y1 - 1994 A1 - Colman, S. M. A1 - Foster, D. S. KW - deposition KW - erosion KW - Holocene KW - lake michigan KW - sediment budget KW - sediments AB - We have constructed a sediment budget for the southern Lake Michigan basin for sand and for mud during three time periods: the past 100, 5,000, and 10,000 years. For the modern (100-year) sediment budget, accountable sediment sources add up to 93 percent of the calculated sinks. The mud budget has a source deficit of about 40%, probably due to errors in mu&sand ratios and (or) to other sources not included in our model, especially erosion of the lake floor, which accompanies bluff recession. Two terms dominate the modem sediment-budget equation: (1) bluff erosion, which is an order of magnitude larger than either rivers or aerosols as a source, and (2) deposition in the deep basin, which is more than two orders of magnitude greater as a sink than suspended sediment transport out of the basin. About half of the sand derived from bluff erosion is deposited in the deep lake; the other half must be deposited in nearshore sand bodies, beaches, and dunes. Despite the uncertainties in our estimates of sediment sources and sinks, the attempt to reconstruct sediment budgets for time intervals of 100, 5,000, and 10,000 years leads to important insights about erosion and sedimentation processes. Bluff erosion is the dominant source of both sand and mud in the basin. The deep lake floor is the primary sink for mud, whereas both the deep lake and nearshore areas are important sinks for sand. On a long-term basis, rates of bluff erosion have progressively decreased and are apparently independent of anthropogenic effects. Rates of sediment accumulation in the lake basin mirror the decrease in rates of bluff erosion for prehistoric time, but have increased markedly since human settlement, probably because of anthropogenic effects on river and aerosolic inputs. VL - 20 SN - 0380-1330 IS - 1 N1 - Nl348Times Cited:17 Cited References Count:29 JO - J Great Lakes Res ER - TY - JOUR T1 - A synthesis of post-glacial diatom records from Lake Baikal JF - Journal of Paleolimnology Y1 - 1994 A1 - Bradbury, J. Platt A1 - Bezrukova, Ye V. A1 - Chernyaeva, G. P. A1 - Colman, S. M. A1 - Khursevich, G. A1 - King, J. W. A1 - Likoshway, Y. V. KW - Climate change KW - diatoms KW - Holocene KW - Lake Baikal KW - paleolimnology KW - palynology AB - The biostratigraphy of fossil diatoms contributes important chronologic, paleolimnologic, and paleoclimatic information from Lake Baikal in southeastern Siberia. Diatoms are the dominant and best preserved microfossils in the sediments, and distinctive assemblages and species provide inter-core correlations throughout the basin at millennial to centennial scales, in both high and low sedimentation-rate environments. Distributions of unique species, once dated by radiocarbon, allow diatoms to be used as dating tools for the Holocene history of the lake. Diatom, pollen, and organic geochemical records from site 305, at the foot of the Selenga Delta, provide a history of paleolimnologic and paleoclimatic changes from the late glacial (15 ka) through the Holocene. Before 14 ka diatoms were very rare, probably because excessive turbidity from glacial meltwater entering the lake impeded productivity. Between 14 and 12 ka, lake productivity increased, perhaps as strong winds promoted deep mixing and nutrient regeneration. Pollen evidence suggests a cold shrub — steppe landscape dominated the central Baikal depression at this time. As summer insolation increased, conifers replaced steppe taxa, but diatom productivity declined between 11 and 9 ka perhaps as a result of increased summer turbidity resulting from violent storm runoff entering the lake via short, steep drainages. After 8 ka, drier, but more continental climates prevailed, and the modern diatom flora of Lake Baikal came to prominence. On Academician Ridge, a site of slow sedimentation rates, Holocene diatom assemblages at the top of 10-m cores reappear at deeper levels suggesting that such cores record at least two previous interglacial (or interstadial?) periods. Nevertheless, distinctive species that developed prior to the last glacial period indicate that the dynamics of nutrient cycling in Baikal and the responsible regional climatic environments were not entirely analogous to Holocene conditions. During glacial periods, the deep basin sediments of Lake Baikal are dominated by rapidly deposited clastics entering from large rivers with possibly glaciated headwaters. On the sublacustrine Academician Ridge (depth = 300 m), however, detailed analysis of the diatom biostratigraphy indicates that diastems (hiatuses of minor duration) and (or) highly variable rates of accumulation complicate paleolimnologic and paleoclimatic reconstructions from these records. VL - 10 IS - 3 N1 - id: 16 JO - A synthesis of post-glacial diatom records from Lake Baikal ER -