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Structure and composition of Late Quaternary permafrost sequences at Cape Mamontov Klyk, Northern Siberia, and the palaeoenvironmental and palaeoclimate implications

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Magens, D. , Meyer, H. , Schirrmeister, L. , Derevyagin, A. Y. and Hubberten, H. W. (2005): Structure and composition of Late Quaternary permafrost sequences at Cape Mamontov Klyk, Northern Siberia, and the palaeoenvironmental and palaeoclimate implications , EUCOP II, 2nd European Conference on Permafrost, Potsdam, Germany, 12-16 June 2005. .
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Abstract:

Research at Cape Mamontov Klyk, Northern Siberia, was carried out to reconstruct the palaeoclimatic and palaeoenvironmentalhistory in this remote region. The investigated area is located in the Lena-Anabar lowland at the LaptevSea coast. Generally, the cliff of Cape Mamontovy Klyk (73° 36? N; 117° 10? E) consists of ice-rich sediments witha complicated depositionary and cryolithological situation.Samples of sediments and ice wedges of different generations were taken over the whole vertical profile of the cliff forsedimentological, hydrochemical and isotope-geochemical analyses. These include analyses of grain size, and C andN content in order to get information about the conditions of deposition. With the ice wedge samples hydrochemicalanalyses (major ions) and Æ18O and ÆD analyses were carried out for information about hydrological and palaeoclimaticconditions. A clear stratification of four units outcropping at the cliff can be found regarding the differentsedimentological parameters. About 4 m thick bottom sands with ice-sand-wedges represent the oldest unit in thissection (IRSL dated between 31:34:2 and 56:26:7 ka). It is overlain by a 5 m thick peat-sand-complexwith smallice wedges radiocarbon dated 30 to 45 ka 14C BP. Above that the Late Pleistocene Ice Complex as the main unit (about9 to 20 m thick) is one of the most peculiar cryolithological formations in this region characterised by silty sands withhuge syngenetic ice wedges. The Ice Complex is partly covered by a 2 m thick horizon of peat-rich, silty sedimentsof Holocene age. Besides this, two more subunits of Holocene age can be distinguished: deposits of thermoerosionalvalleys as well as fluvial deposits. First interpretations of these units indicate changing depositionary conditions froma rather fluvial to an alluvial environment in the Pleistocene and thermoerosional destruction in the Holocene.Recent ice wedges of the profile seem to be genetically correlated with snow patches as their isotopic composition isin the same range. Ice wedge growth is caused by the repeated cracking of the frozen ground, followed by penetrationand refreezing of melt water of winter snow. Thus, the isotopic signal of wedge ice may reflect winter temperatures.Assuming this, results of the isotopic composition of the ice wedges indicate that today?s climate seems to be thewarmest for that area since recent ice wedges show the heaviest isotopic composition of all units. Winter conditionsduring the Holocene were similar, but slightly colder than today.The Pleistocene ice wedges show a clear transition in the isotopic compositions which separate them clearly fromthe Holocene units ( 5? in Æ18O less) pointing to colder winter temperatures at that time. The peat-sand-complexshows extreme variations in the isotopic composition. It has to be solved if these variations can only be explained byfluctuations in the winter temperatures. The lowermost unit (bottom sands) represents a period that is characterised bycold temperatures and low climatic variability in the winter season.Hydrochemical results for the ice wedges show that Holocene ice wedges are characterised by higher sodium andchloride contents and may therefore point to a stronger maritime influence whereas ice wedges of Pleistocene ageshow higher contents of calcium and hydrogen carbonate and may therefore be associated with a rather continentallyaffected environment.

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