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Fossil Organic Carbon in Arctic Permafrost Sequences of Northern East Siberia Contents and Characteristics

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Schirrmeister, L. , Wetterich, S. , Grosse, G. , Siegert, C. , Overduin, P. P. and Hubberten, H. W. (2010): Fossil Organic Carbon in Arctic Permafrost Sequences of Northern East Siberia Contents and Characteristics , Third European Conference on Permafrost, Longyearbyen, Svalbard, Norway, June 13-17 .
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Abstract:

Permafrost deposits constitute a large carbon poolhighly sensitive to degradation and potential carbonrelease due to global warming. However, only a fewdetailed analyses have been made on the character ofthis carbon pool, its spatial variability, and its availabilityfor decomposition. Most important andhighly sensitive to degradation are the ice-rich deposits(Ice Complex) of the Yedoma Suite. Fifteenpermafrost sections at coast and river bank sectionson the Laptev and East Siberian seas, in the LenaRiver Delta and in the IndigirkaKolyma lowlandregion were studied for carbon contents (TC; TOC)and organic matter (OM) parameters (C/N, δ13C).The studied permafrost sequences were formed underdifferent climate and landscape conditions duringthe Late Quaternary climate cycles including theSaalian Glacial (Ice Complex deposits), the EemianInterglacial (thermokarst lagoon, lacustrine andboggy alas deposits), the Weichselian Glacial (fluvial,flood plain and Ice Complex deposit), and theHolocene Interglacial (lacustrine and boggy alas deposits).Therefore, OM stored in these sequencesgrew, froze, partly decomposed and refroze underdifferent periglacial environments reflected in specificcryolithological features and organic matter andcarbon signatures.The vertical distribution of TOC in 10 m to up to100 m thick permafrost profiles is highly variableand TOC contents vary from 0.1 up to 40 wt% of thedry sediment. The frozen organic matter consists ofwell preserved plant remains like wood fragments ofshrub twigs, roots, leafs, moss peat inclusions andlayers as well as tree stems in interglacial deposits.In addition, numerous small filamentous grass rootsand loosely distributed fine organic detritus arecommon.The survival of pre-Holocene and sometimes evenpre-Eemian ice wedges and their surrounding icerichsediments proves that despite sometimes highice contents near surface permafrost was not totallydegraded during the Eemian warm period and theearly Holocene thermal maximum.Variations in TOC, C/N, and δ13C are connected tochanges in bioproductivity, intensity and characterof cryosol formation, in OM decomposition, sedimentationrates, as well as in plant associations.High TOC, high C/N, and low δ13C reflect lessdecomposedOM under anaerobic conditions that ischaracteristic of interglacial and interstadial periods.Glacial and stadial periods are characterised by lessvariable, low TOC, low C/N, and high δ13C indicatingstable environments with reduced bioproductivity,stronger OM decomposition under relatively dry,aerobic conditions.Due to the inhomogeneous vertical distribution oforganic carbon and poorly mapped spatial distributionof organic-rich deposits estimations of carbonrelease from permafrost are somewhat speculative.The variable vulnerability of permafrost-stored carbonunder warming climate conditions complicatesmodeling and quantification of climate change feedbackswith the permafrost carbon pool.

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