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Organic Carbon in Ice Complex deposits - characteristics and origin of the Yedoma Suite in East Siberian Arctic lowlands

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Schirrmeister, L. , Wetterich, S. , Grosse, G. , Siegert, C. , Overduin, P. P. and Hubberten, H. W. (2009): Organic Carbon in Ice Complex deposits - characteristics and origin of the Yedoma Suite in East Siberian Arctic lowlands , 2nd CAPP Workshop, Carbon Pools in Permafrost Regions, Stockholm University, June 3-5 .
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Abstract:

Ongoing climate change and global warming may change the Ice Complex formation of the Yedoma Suite from a long-term carbon sink to a major carbon source due to thawing of organic-rich sediments and the subsequent release of greenhouse gases.The origin of Late-Pleistocene ice-rich, fine-grained permafrost sequences (Ice Complex deposits) in arctic and subarctic Siberia has been disputed for over a century. Corresponding permafrost sequences are frequently exposed along sea coasts and river banks in so-called Yedoma hills, which are considered to be the erosional remnants of Late Pleistocene accumulation plains. We have summarized cryolithological, sedimentological, geochronological, and stratigraphical results from 14 study sites along the Laptev and East Siberian Sea coasts in order to compare and correlate the local datasets. The Ice Complex was predominantly formed under subaerial conditions in polygonal tundra landscapes. Ice Complex deposits at all sites are sequences of buried cryosols. Separate cryosol horizons are characterized by brownish organic-rich patches, peat nests, and numerous individual plant remains ranging from well-preserved grass roots to twigs and leaves. Cryoturbation patterns of 0.5 to 1 m thickness are very common. The average total organic carbon content (TOC) is relative high for individual sites (1.2 to 4.8 wt%), but strongly varies for individual horizons within a sequence (0.5 to 27 wt%). Such variation in TOC is caused by alternation of mineral- and organic-rich horizons and the presence of irregular patches where organic remains concentrated during deposition. The TOC variations are similar to modern typical Aquiturbels in polygon walls (0.5-3.5 wt%) and typical Historthels in polygon centers (1 to >20 wt%), and therefore its occurrence represents a massive permafrost carbon reservoir. According to several paleo-botanical analyses, herbs (e.g. Artemisia, Carophyllaceae, Asteraceae), grasses (e.g. Poacea, Cyperacea), and partly some dwarf shrubs (e.g. Salix, Alnus, Betula) predominate within the Ice Complex sequences. d13C values range between -24 and -29 and indicate only freshwater aquatic and subaerial terrestrial environments. The values reflect the dominance of terrestrial C3 plants within the composition of organic matter. Variations in TOC content, C/N ratio, and d13C values are connected to changes in the bioproductivity, intensity and character of cryosol formation, different degrees of organic matter decomposition as well as variations in plant associations. High TOC contents, high C/N ratios, and low d13C values reflect less-decomposed organic matter under anaerobic conditions, which is characteristic for Middle Weichselian interstadial periods. Stadial or glacial periods are characterized by less variable, generally low TOC contents, which indicate stable environments with reduced bioproductivity an by low C/N ratios. High d13C values reflect relatively dry, aerobic condition.

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