TY - JOUR T1 - A human role in Andean megafaunal extinction? JF - Quaternary Science Reviews Y1 - 2019 A1 - Raczka, M.F. A1 - Mosblech, N.A. A1 - Giosan, L. A1 - Valencia, B.G. A1 - Folcik, A.M. A1 - Kingston, M. A1 - Baskin, S. A1 - Bush, M.B. KW - Andes KW - Deglaciation KW - Ecuador Extinction KW - Fossil pollen KW - Human arrival KW - Pleistocene megafauna KW - Sporormiella AB - A new fossil pollen, Sporormiella, and sediment chemistry record from Lake Llaviucu, Ecuador, spanning the period from 16,280–9000 years Before Present, provides a high-resolution record of paleoecological change in the high Andes. The deglacial transition from super-páramo through páramo grasslands, to Andean forest is traced, with near-modern systems being established by c. 11,900 years ago. It is suggested that forest elements probably existed in microrefugial populations close to the ice front. Sporormiella is used as a proxy for megafaunal abundance, and its decline to background levels is inferred to indicate a local extinction event at c. 12,800 years ago. About 1800 years prior to the extinction, charcoal becomes a regular sedimentary component in this very wet valley. An early date for human activity in the valley is suggested, with the direct implication of humans in the extinction of the megafauna. VL - 205 UR - https://linkinghub.elsevier.com/retrieve/pii/S0277379118307005 ER - TY - JOUR T1 - Deglacial floods in the Beaufort Sea preceded Younger Dryas cooling JF - Nature Geoscience Y1 - 2018 A1 - Keigwin, L. D. A1 - Klotsko, S. A1 - Zhao, N. A1 - Reilly, B. A1 - Giosan, L. A1 - Driscoll, N. W. AB - A period of cooling about 13,000 years ago interrupted about 2,000 years of deglacial warming. Known as the Younger Dryas (YD), the event is thought to have resulted from a slowdown of the Atlantic meridional overturning circulation in response to a sudden flood of Laurentide Ice Sheet meltwater that reached the Nordic Seas. Oxygen isotope evidence for a local source of meltwater to the open western North Atlantic from the Gulf of St Lawrence has been lacking. Here we report that the eastern Beaufort Sea contains the long-sought signal of O-18-depleted water. Beginning at similar to 12.94 ± 0.15 thousand years ago, oxygen isotopes in the planktonic foraminifera from two sediment cores as well as sediment and seismic data indicate a flood of meltwater, ice and sediment to the Arctic via the Mackenzie River that lasted about 700 years. The minimum in the oxygen isotope ratios lasted similar to 130 years. We suggest that the floodwater travelled north along the Canadian Archipelago and then through the Fram Strait to the Nordic Seas, where freshening and freezing near sites of deep-water formation would have suppressed convection and caused the YD cooling by reducing the meridional overturning. VL - 11 UR - http://www.nature.com/articles/s41561-018-0169-6http://www.nature.com/articles/s41561-018-0169-6.pdfhttp://www.nature.com/articles/s41561-018-0169-6http://www.nature.com/articles/s41561-018-0169-6.pdf IS - 8 ER - TY - JOUR T1 - Composition and origin of authigenic carbonates in the Krishna-Godavari and Mahanadi Basins, eastern continental margin of India JF - Marine and Petroleum Geology Y1 - 2014 A1 - Teichert, B. M. A. A1 - Johnson, J. E. A1 - Solomon, E. A. A1 - Giosan, L. A1 - Rose, K. A1 - Kocherla, M. A1 - Connolly, E. C. A1 - Torres, M. E. AB - The mineralogical and stable isotopic composition of authigenic carbonates from the Krishna-Godavari (KG) and Mahanadi Basin provide a deeper insight into the processes inducing carbonate formation in the sediments of the eastern continental margin of India in the Bay of Bengal. Authigenic carbonate cements, (micro) nodules, bioturbation casts and tubes from 12 core locations drilled during the Indian National Gas Hydrate Program (NGHP) Expedition 01 were investigated for this study. Three main processes responsible for authigenic carbonate precipitation are identified: organoclastic sulfate reduction, anaerobic oxidation of methane and methanogenesis. Evidence of vigorous methane seepage is indicated in carbonates recovered at Sites 7, 10, 12 (KG Basin) and 19 (Mahanadi Basin). These methane-derived carbonates display typical paragenetic carbonate mineralogies (aragonite, high-Mg calcite with >15 Mol% MgCO3, Ca-rich dolomite). Two separate horizons of methane derived-carbonates are correlated between 4 drill holes (up to ∼16 km apart). The upper horizon has been dated with 14C (40,100 – 51,600 a B.P. 1950) clearly indicating that methane seepage has been much more vigorous in the past possibly due to a glacial sea level lowstand. VL - 58 N1 - AAy4wyTimes Cited:5Cited References Count:63 JO - Composition and origin of authigenic carbonates in the Krishna-Godavari and Mahanadi Basins, eastern continental margin of India ER - TY - JOUR T1 - DNA and lipid molecular stratigraphic records of haptophyte succession in the Black Sea during the Holocene JF - Earth and Planetary Science Letters Y1 - 2009 A1 - Coolen, M. J. L. A1 - Saenz, J. P. A1 - Giosan, L. A1 - Trowbridge, N. Y. A1 - Dimitrov, P. A1 - Dimitrov, D. A1 - Eglinton, T. I. AB - Previous studies suggest that the coccolithophorid haptophyte Emiliania huxleyi entered the Black Sea similar to 3400 yrs ago and since then a coccolith ooze defined as Unit I has developed. Unit I sediments contain long-chain alkenones derived from E huxleyi whereas the alkenone distribution of the deeper coccolith-free sapropel (Unit II) is rather unusual. Alkenone-derived past sea surface temperature (SST) estimates suggest a large difference between Unit II and Unit I, which is likely a result of unusual biological precursors of the alkenones in Unit II. Here, we report a high-resolution stratigraphic analysis of ancient haptophyte DNA to establish the Holocene succession of haptophytes as sources of the alkenones in the Black Sea. Haptophytes related to brackish Isochrysis spp. were the initial sources of alkenones, and appeared immediately after the onset of sapropel deposition (similar to 7550 yrs before present [a BP]). As salinity increased, Isochrysis-related haptophytes were slowly replaced by a complex suite of huxleyi strains as sources of alkenones. Our paleogenetic data showed that E. huxleyi colonized the Black Sea shortly after the onset of sapropel deposition, similar to 4000 yrs earlier than previously recognized based on their preserved coccoliths. E. huxleyi strains were the most likely source of the previously reported abundant and unusual C-36 di-unsaturated "Black Sea alkenone". Strong haptophyte species and strain-specific effects were observed on the level of unsaturation of alkenones which resulted in spurious alkenone-derived SST estimates before 5250 a BP. In contrast, from similar to 5250 a BP onwards a relatively stable haptophyte assemblage dominated by a different suite of E. huxleyi strains yielded robust alkenone-SST values and indicated a gradual cooling from 19 degrees C to similar to 15 degrees C at the top of the record (similar to 450 a BP). Published by Elsevier B.V. VL - 284 IS - 3-4 N1 - id: 1853; 487NY Times Cited:1 Cited References Count:78; YY JO - DNA and lipid molecular stratigraphic records of haptophyte succession in the Black Sea during the Holocene ER - TY - JOUR T1 - Sinking deltas due to human activities JF - Nature Geoscience Y1 - 2009 A1 - Syvitski, J. P. M. A1 - Kettner, A. J. A1 - Overeem, I. A1 - Hutton, E. W. H. A1 - Hannon, M. T. A1 - Brakenridge, G. R. A1 - Day, J. A1 - Vorosmarty, C. A1 - Saito, Y. A1 - Giosan, L. A1 - Nicholls, R. J. AB - Many of the world's largest deltas are densely populated and heavily farmed. Yet many of their inhabitants are becoming increasingly vulnerable to flooding and conversions of their land to open ocean. The vulnerability is a result of sediment compaction from the removal of oil, gas and water from the delta's underlying sediments, the trapping of sediment in reservoirs upstream and floodplain engineering in combination with rising global sea level. Here we present an assessment of 33 deltas chosen to represent the world's deltas. We find that in the past decade, 85% of the deltas experienced severe flooding, resulting in the temporary submergence of 260,000 km(2). We conservatively estimate that the delta surface area vulnerable to flooding could increase by 50% under the current projected values for sea-level rise in the twenty-first century. This figure could increase if the capture of sediment upstream persists and continues to prevent the growth and buffering of the deltas. VL - 2 IS - 10 N1 - id: 799; 501BW Times Cited:2 Cited References Count:38; YY JO - Sinking deltas due to human activities ER - TY - JOUR T1 - Was the Black Sea catastrophically flooded in the early Holocene? JF - Quaternary Science Reviews Y1 - 2009 A1 - Giosan, L. A1 - Filip, F. A1 - Constatinescu, S. AB - A catastrophic flooding of the Black Sea basin was proposed to have occurred during its reconnection to the ocean in the early Holocene. Possible cultural consequences of the flood include the migration of Neolithic farmers from around the Black Sea towards central Europe as well as the creation of flood myths. Stratigraphic and paleo-geomorphologic information from Danube delta aided by radiocarbon ages on articulated mollusks constrain the level in the Black Sea before the marine reconnection to ca 30 m below the present sea level rather than 80 m or lower. If the flood occurred at all, the sea level increase and the flooded area during the reconnection were significantly smaller than previously proposed. (C) 2008 Elsevier Ltd. All rights reserved. VL - 28 IS - 1-2 N1 - id: 866; 399HK Times Cited:0 Cited References Count:56; YY JO - Was the Black Sea catastrophically flooded in the early Holocene? ER - TY - JOUR T1 - Holocene erosion of the Lesser Himalaya triggered by intensified summer monsoon JF - Geology Y1 - 2008 A1 - Clift, P. D. A1 - Giosan, L. A1 - Biusztajn, J. A1 - Campbell, I. H. A1 - Allen, C. A1 - Pringle, M. A1 - Tabrez, A. R. A1 - Danish, M. A1 - Rabbani, M. M. A1 - Alizai, A. A1 - Carter, A. A1 - Lueckge, A. AB - Climate is one of the principal controls setting rates of continental erosion. Here we present the results of a provenance analysis of Holocene sediments from the Indus delta in order to assess climatic controls on erosion over millennial time scales. Bulk sediment Nd isotope analysis reveals a number of changes during the late Pleistocene and early Holocene (at 14-20,11-12 and 8-9 ka) away from erosion of the Karakoram and toward more sediment flux from the Himalaya. Radiometric Ar-Ar dating of muscovite and U-Pb dating of zircon sand grains indicate that the Lesser Himalaya eroded relatively more strongly than the Greater Himalaya as global climate warmed and the summer monsoon intensified after 14 ka. Monsoon rains appear to be the primary force controlling erosion across the western Himalaya, at least over millennial time scales. This variation is preserved with no apparent lag in sediments from the delta, but not in the deep Arabian Sea, due to sediment buffering on the continental shelf. VL - 36 IS - 1 N1 - id: 800; 247YL Times Cited:7 Cited References Count:27; YY JO - Holocene erosion of the Lesser Himalaya triggered by intensified summer monsoon ER - TY - JOUR T1 - The last reconnection of the Marmara Sea (Turkey) to the World Ocean: A paleoceanographic and paleoclimatic perspective JF - Marine Geology Y1 - 2008 A1 - McHugh, C. M. G. A1 - Gurung, D. A1 - Giosan, L. A1 - Ryan, W. B. F. A1 - Mart, Y. A1 - Sancar, U. A1 - Burckle, L. A1 - Cagatay, M. N. AB - During the late glacial, marine isotope Stage 2, the Marmara Sea transformed into a brackish lake as global sea-level fell below the sill in the Dardanelles Strait. A record of the basin's reconnection to the global ocean is preserved in its sediments permitting the extraction of the paleoceanographic and paleoclimatic history of the region. The goal of this study is to develop a high-resolution record of the lacustrine to marine transition of Marmara Sea in order to reconstruct regional and global climatic events at a millennia] scale. For this purpose, we mapped the paleoshorelines of Marmara Sea along the northern, eastern, and southern shelves at Cekmece. Prince Islands, and Imrali, using data from multibeam bathymetry, high-resolution subbottom profiling (chirp) and ten sediment cores. Detailed sedimentologic, biostratigraphic (foraminifers, mollusk, diatoms), X-ray fluorescence geochemical scanning, and oxygen and carbon stable isotope analyses correlated to a calibrated radiocarbon chronology provided evidence for cold and city conditions prior to 15 ka BP, warm conditions of the Bolling-Allerod from similar to 15 to 13 ka BP, a rapid marine incursion at 12 ka BP, still stand of Marmara Sea and sediment reworking of the paleoshorelines during the Younger Dryas at similar to 11.5 to 10.5 ka BP, and development of strong stratification and influx of nutrients as Black Sea waters spilled into Marmara Sea at 9.2 ka BR Stable environmental conditions developed in Marmara Sea after 6.0 ka BP as sea-level reached its present shoreline and the basin floors filled with sediments achieving their present configuration. (C) 2008 Elsevier B.V. All rights reserved. VL - 255 IS - 1-2 N1 - id: 801; 370ED Times Cited:4 Cited References Count:104; YY JO - The last reconnection of the Marmara Sea (Turkey) to the World Ocean: A paleoceanographic and paleoclimatic perspective ER - TY - JOUR T1 - Research focus - Tempestuous highs and lows in the Gulf of Mexico JF - Geology Y1 - 2008 A1 - Donnelly, J. P. A1 - Giosan, L. 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Giosan, Liviu Geological soc amer, inc Boulder; YY JO - Research focus - Tempestuous highs and lows in the Gulf of Mexico ER - TY - CHAP T1 - The Geographic, Geological and Oceanographic Setting of the Indus River T2 - Large Rivers Y1 - 2007 A1 - Inam, A. A1 - Clift, P. D. A1 - Giosan, L. ED - Gupta, A. JF - Large Rivers PB - Wiley Press N1 - id: 867; Y ER - TY - CONF T1 - Late Holocene climate variability of South America reconstructed by a multi-proxy analysis of Chilean fjord sediments T2 - Abstracts, EGU General Assembly Y1 - 2006 A1 - Bertrand, S. A1 - Hughen, K. A. A1 - Giosan, L. A1 - Tierney, J. A1 - Sepfulveda, J. A1 - Pantoja, S. JF - Abstracts, EGU General Assembly CY - Vienna, Austria N1 - id: 560 ER - TY - JOUR T1 - Young Danube delta documents stable Black Sea level since the middle Holocene: Morphodynamic, paleogeographic, and archaeological implications JF - Geology Y1 - 2006 A1 - Giosan, L. A1 - Donnelly, J. P. A1 - Constantinescu, S. A1 - Filip, F. A1 - Ovejanu, I. A1 - Vespremeanu-Stroe, A. A1 - Vespremeanu, E. A1 - Duller, G. A. T. AB - New radiocarbon and optical dates show that the Holocene Danube delta started to build out of a Black Sea embayment similar to 5200 yr ago. Delta lobe development phases differ by as much as 5 k.y. from previously proposed ages. The new chronology allows for a better understanding of the Danube delta paleogeography, including the demise of Istria, the main ancient Greek-Roman city in the region. Prior reconstructions of sea level in the Black Sea inferred fluctuations to 15 m in range; however, stratigraphy of beach ridges in the delta shows that the relative Black Sea level for the past 5 k.y. was stable in the Danube delta region within -2 m and +1.5 of the current level. Hydroisostatic effects related to a proposed catastrophic reconnection of the Black Sea to the World Ocean in the early Holocene may have been responsible for the sea level reaching the highstand earlier than estimated by models. The new sea-level data suggest that submergence at several ancient settlements around the Black Sea may be better explained by local factors such as subsidence rather than by basin-wide sea-level fluctuations. VL - 34 IS - 9 N1 - 084aqTimes Cited:63Cited References Count:35 JO - Young Danube delta documents stable Black Sea level since the middle Holocene: Morphodynamic, paleogeographic, and archaeological implications ER - TY - JOUR T1 - Morphodynamics and evolution of Danube delta JF - Journal of Sedimentary Research Y1 - 2005 A1 - Giosan, L. A1 - Vespremeanu, E. A1 - Donnelly, J. P. A1 - Bhattacharya, J. A1 - Buonaiuto, F. VL - SP 83 N1 - id: 499 ER -