Ninth International Conference on Permafrost ... - IARC Research

Content and Composition of Organic Matter in Quaternary Deposits on the LaptevSea CoastA.L. KholodovGeophysical Institute, University of Alaska Fairbanks, USAInstitute of Physical, Chemical, and Biological Problems of Soil Science, RAS, RussiaL. SchirrmeisterAlfred Wegener Institute for Polar and Marine Research, Potsdam, GermanyH. MeyerAlfred Wegener Institute for Polar and Marine Research, Potsdam, GermanyCh. KnoblauchSoil Science Institute of Hamburg University, GermanyK. FahlAlfred Wegener Institute for Polar and Marine Research, Bremerhaven, GermanyIntroductionBecause of freezing and subsequent preservation ofbiomass after sedimentation, permafrost areas are consideredto be important carbon sinks. Mean TOC contents of frozenQuaternary deposits exposed at the Laptev Sea coast arehigh and vary between 3.2 to 11.9 wt% (Grigoriev et al.2004). The organic matter (OM) is preserved in permafrostin the early diagenetic stage of OM maturation. This stageis characterized by a decreasing N content, depletion ofproducts, which have a biological value (carbohydrates,proteins, etc.) and preservation of biopolymers (Bordenave1993). Deeper thawing caused by climate warming can resultin increased decomposition of organic matter and a releaseof greenhouse gases. This study aims a characterization ofthe organic matter in different types of Quaternary depositsat the Laptev Sea coast.The Study Area and Investigated DepositsPermafrost drilling was carried out on the BykovskyPeninsula (SW of Lena River Delta) and Cape Svyatoy Nos(NE of Yana River mouth) in 2001 and 2003 (Kholodov et al.2006). Various types of Quaternary deposits were analyzedfrom both sampling sites:1. Middle Pleistocene deposits of the KuchchuguySuite composed of well-sorted silty loam with numerous thingrass roots. The ice content is in the range from 30 to 50%.The cryostructure is massive. The genesis of these loess-likedeposits is still under debate.2. Late Pleistocene syncryogenic Ice Complex depositsof silt or silty loam with sand and peat layers, fragmentsof twigs and other plant remains, and peat inclusions arecharacterized by volumetric ice content of up to 80–90%and large wedges (up to 30 m high). The Ice Complexdeposits of the Bykovsky Peninsula can be divided into 2groups: those accumulated due to intensive sedimentationrate and formed under the condition of stable ground surfaceposition. The first group was formed during the MIS-4 andMIS-2 periods. The second group was accumulated duringMIS-3 Interstadial. According to previous investigation(Schirrmeister et al. 2002), several periods existed duringthe MIS-3 time, when rates of sedimentation and freezingdecreased and palaeosol horizons were formed over longperiods during several thousands of years. The Ice Complexsequences are in places covered by Late Holocene deposits.3. Late Pleistocene to Holocene deposits in thermokarstdepressions (alases). The formation of these deposits was aresult of thermokarst processes that took place during theLate Pleistocene to Holocene transition period (13–10 kyrBP). This layer can be subdivided into 2 horizons:a. Taberal deposits, that is, former Ice Complexdeposits which were thawed under thermokarst lakes andrefrozen after lake drainage. Taberal deposits are silty loamswith a volumetric ice content of up to 50%.b. Lacustrine to boggy (alas) deposits were formed inshallow lakes or in bogs. These deposits are characterized bya high peat and ice (up to 60%) content.Materials and MethodsThe described deposits were cored using a rotary drillingdevice. The samples were air dried immediately after drilling.Subsequently the material was milled. For determination ofTOC and isotopic composition, carbonates were removedfrom samples by a 1n solution of HCl at 90°C for 3 hoursand washed with distilled water.The following analyses were done:Water (ice) content and density of soil were determinedusing a weight method. Elemental composition of OM: Totalcarbon (TC), total organic carbon (TOC), and nitrogen (N)were determined using the VARIO II Element analyzer.Isotopic composition (δ 13 C) was determined with a FinniganMAT Delta-S mass spectrometer using a FLASH elementalanalyzer and a CONFLO III gas mixing system for onlinedetermination of the carbon isotopic composition. DissolvedOrganic Carbon (DOC) was extracted from sampleswith a CaCl 2solution (4 mM). Subsequently the sampleswere centrifuged and filtered (0.45 µm) (Zsolnay 2003).Biomarkers, to gain better insights into the geochemicalcomposition of the particulate organic carbon n-alkanes (C15to C37), sterols (sum of 24-Methylcholest-5-en-3ß-ol and133