a r t i c l e i n f oArticle history: Available online xxx a b s t r a c tThe origin of Late Pleistocene ice-rich, fine-grained permafrost sequences (Ice Complex deposits) in arctic and subarctic Siberia has been in dispute for a long time. Corresponding permafrost sequences are frequently exposed along seacoasts and river banks in Yedoma hills, which are considered to be erosional remnants of Late Pleistocene accumulation plains. Detailed cryolithological, sedimentological, geochronological, and stratigraphical results from 14 study sites along the Laptev and East Siberian seacoasts were summarized for the first time in order to compare and correlate the local datasets on a large regional scale. The sediments of the Ice Complex are characterized by poorly-sorted silt to fine-sand, buried cryosols, TOC contents of 1.2e4.8 wt%, and very high ground ice content (40e60 wt% absolute). A second large constituent of the Ice Complex are large syngenetic ice wedges, resulting in a total ice content of the Ice Complex of up to 80 vol%. Ice Complex deposits were mostly formed during the Middle Weichselian interstadial and/or during the Late Weichselian stadial periods. A conceptual model of nival lithogenesis of Ice Complex deposits was developed that integrates various other formation hypotheses. A combination of various local and regional paleogeographical, geological, and paleoclimate conditions controlled the formation of Ice Complex sequences during the Late Pleistocene in northern East Siberia. They are chronologically and stratigraphically, but not genetically equivalent to Eurasian and Alaskan loess deposits.
Late Quaternary permafrost deposits on Big Lyakhovsky Island (New Siberian Islands, Russian Arctic) were studied with the aim of reconstructing the palaeoclimatic and palaeoenvironmental conditions of northern Siberia. Hydrogen and oxygen stable isotope analyses are presented for six different generations of ice wedges as well as for recent ice wedges and precipitation. An age of about 200 ka BP was determined for an autochtonous peat layer in ice‐rich deposits by U/Th method, containing the oldest ice wedges ever analysed for hydrogen and oxygen isotopes. The palaeoclimatic reconstruction revealed a period of severe winter temperatures at that time. After a gap in the sedimentation history of several tens of thousands of years, ice‐wedge growth was re‐initiated around 50 ka BP by a short period of extremely cold winters and rapid sedimentation leading to ice‐wedge burial and characteristic ice‐soil wedges (‘polosatics’). This corresponds to the initial stage for the Late Weichselian Ice Complex, a peculiar cryolithogenic periglacial formation typical of the lowlands of northern Siberia. The Ice Complex ice wedges reflect cold winters and similar climatic conditions as around 200 ka BP. With a sharp rise in δ18O of 6‰ and δD of 40‰, the warming trend between Pleistocene and Holocene ice wedges is documented. Stable isotope data of recent ice wedges show that Big Lyakhovsky Island has never been as warm in winter as today. Copyright © 2002 John Wiley & Sons, Ltd.
Ice Complexes, extremely ice-rich permafrost deposits with large ice wedges, are widely distributed in the Arctic region of northeast Siberia. They present excellent archives for the reconstruction of Late Quaternary paleoenvironmental conditions in nonglaciated areas. In 1998, 1999, and 2000 Russian and German scientists worked together on the Bykovsky Peninsula southeast of the Lena Delta in order to investigate the Ice Complex and its associated sediments. Intensive cryolithological and sedimentological studies, Radiocarbon age determinations, paleobotanical studies, micropaleontological investigations, studies of mammal and insect fossils, and stable isotope analyses of ground ice were performed. Radiocarbon data have been obtained from the entire exposed sequence covering approximately the last 60,000 years. The results indicate that compared with modern time the investigated Ice Complex sequence was formed during two cooler and more arid stages of the Late Pleistocene with relatively uniform environmental conditions, separated by a stage with environmental variations and more intensive soil formation caused by climate amelioration. The Late Pleistocene environmental changes were not as strong as those occurring during the Pleistocene/Holocene transition where a sharp break is evident. r
Th/U) were analyzed for pollen and palynomorphs. The records reveal the environmental history for the last ca 200 kyr. For interglacial pollen spectra, quantitative temperature values were estimated using the best modern analogue method. Sparse grass-sedge vegetation indicating arctic desert environmental conditions existed prior to 200 kyr ago. Dense, wet grass-sedge tundra habitats dominated during an interstadial ca 200e190 kyr ago, reflecting warmer and wetter summers than before. Sparser vegetation communities point to much more severe stadial conditions ca 190e130 kyr ago. Open grass and Artemisia communities with shrub stands (Alnus fruticosa, Salix, Betula nana) in more protected and moister places characterized the beginning of the Last Interglacial indicate climate conditions similar to present. Shrub tundra (Alnus fruticosa and Betula nana) dominated during the middle Eemian climatic optimum, when summer temperatures were 4e5 C higher than today. Early-Weichselian sparse grass-sedge dominated vegetation indicates climate conditions colder and dryer than in the previous interval. Middle Weichselian Interstadial records indicate moister and warmer climate conditions, for example, in the interval 40e32 kyr BP Salix was present within dense, grasssedge dominated vegetation. Sedge-grass-Artemisia-communities indicate that climate became cooler and drier after 30 kyr BP, and cold, dry conditions characterized the Late Weichselian, ca 26e16 kyr BP, when grass-dominated communities with Caryophyllaceae, Asteraceae, Cichoriaceae, Selaginella rupestris were present. From 16 to 12 kyr BP, grass-sedge communities with Caryophyllaceae, Asteraceae, and Cichoriaceae indicate climate was significantly warmer and moister than during the previous interval. The presence of Salix and Betula reflect temperatures about 4 C higher than present at about 12e11 kyr BP, during the Allerød interval, but shrubs were absent in the Younger Dryas interval, pointing to a deterioration of climate conditions. Alnus fruticosa, Betula nana, Poaceae, and Cyperaceae dominate early Holocene spectra. Reconstructed absolute temperature values were substantially warmer than present (up to 12 C). Shrubs gradually disappeared from coastal areas after 7.6 kyr BP when vegetation cover became similar to modern. A comparison of proxy-based paleoenvironmental reconstructions with the simulations performed by an Earth system model of intermediate complexity show good accordance between the regional paleodata and model simulations, especially for the warmer intervals.
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