Organic matter characteristics of a rapidly eroding permafrost cliff in NE Siberia (Lena Delta, Laptev Sea region)

• Published in: Biogeosciences
• Main Authors: Haugk, Charlotte, Jongejans, Loeka, Mangelsdorf, Kai, Fuchs, Matthias, Ogneva, Olga, Palmtag, Juri, Mollenhauer, Gesine, Mann, Paul, Overduin, Pier Paul, Grosse, Guido, Sanders, Tina, Tuerena, Robyn, Schirrmeister, Lutz, Wetterich, Sebastian, Kizyakov, Alexander, Karger, Cornelia, Strauss, Jens
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: Zenodo 2022
• Subjects: laptev; Laptev Sea; lena delta; lena river; permafrost; Siberia
• Online Access: https://doi.org/10.5194/bg-19-2079-2022; https://bg.copernicus.org/articles/19/2079/2022/

Organic carbon (OC) stored in Arctic permafrost represents one of Earth's largest and most vulnerable terrestrial carbon pools. Amplified climate warming across the Arctic results in widespread permafrost thaw. Permafrost deposits exposed at river cliffs and coasts are particularly susceptible to thawing processes. Accelerating erosion of terrestrial permafrost along shorelines leads to increased transfer of organic matter (OM) to nearshore waters. However, the amount of terrestrial permafrost carbon and nitrogen as well as the OM quality in these deposits is still poorly quantified. We define the OM quality as the intrinsic potential for further transformation, decomposition and mineralisation. Here, we characterise the sources and the quality of OM supplied to the Lena River at a rapidly eroding permafrost river shoreline cliff in the eastern part of the delta (Sobo-Sise Island). Our multi-proxy approach captures bulk elemental, molecular geochemical and carbon isotopic analyses of Late Pleistocene Yedoma permafrost and Holocene cover deposits, discontinuously spanning the last ∼52 kyr. We showed that the ancient permafrost exposed in the Sobo-Sise cliff has a high organic carbon content (mean of about 5 wt %). The oldest sediments stem from Marine Isotope Stage (MIS) 3 interstadial deposits (dated to 52 to 28 cal ka BP) and are overlaid by last glacial MIS2 (dated to 28 to 15 cal ka BP) and Holocene MIS1 (dated to 7–0 cal ka BP) deposits. The relatively high average chain length (ACL) index of n -alkanes along the cliff profile indicates a predominant contribution of vascular plants to the OM composition. The elevated ratio of iso- and anteiso-branched fatty acids (FAs) relative to mid- and long-chain (C ≥ 20) n -FAs in the interstadial MIS3 and the interglacial MIS1 deposits suggests stronger microbial activity and consequently higher input of bacterial biomass during these climatically warmer periods. The overall high carbon preference index (CPI) and higher plant fatty acid (HPFA) values as well as high ...