Preprints
https://doi.org/10.5194/bg-2021-331
https://doi.org/10.5194/bg-2021-331

  13 Dec 2021

13 Dec 2021

Review status: this preprint is currently under review for the journal BG.

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

Charlotte Haugk1,2,a, Loeka Laura Jongejans1,2, Kai Mangelsdorf3, Matthias Fuchs1, Olga Ogneva1,4,5, Juri Palmtag6, Gesine Mollenhauer4,5, Paul James Mann6, Pier Paul Overduin1, Guido Grosse1,2, Tina Sanders7, Robyn Elizabeth Tuerena8, Lutz Schirrmeister1, Sebastian Wetterich1,b, Alexander Kizyakov9, Cornelia Karger3, and Jens Strauss1 Charlotte Haugk et al.
  • 1Permafrost Research Section, Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Potsdam, 14473 Germany
  • 2Institute of Geosciences, University of Potsdam, Potsdam, 14476, Germany
  • 3Section of Organic Geochemistry, Helmholtz Centre Potsdam GFZ German Research Centre for Geosciences, Potsdam, 14473, Germany
  • 4Marine Geochemistry Section, Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Bremerhaven, 27570, Germany
  • 5Faculty of Geosciences, University of Bremen, Bremen, 28359, Germany
  • 6Department of Geography and Environmental Sciences, Northumbria University, Newcastle-upon-Tyne, NE1 8ST, UK
  • 7Institute for Carbon Cycles, Helmholtz-Zentrum Hereon, Geesthacht, 21502, Germany
  • 8Scottish Association for Marine Science, Oban, PA37 1QA, UK
  • 9Cryolithology and Glaciology Department, Faculty of Geography, Lomonosov Moscow State University, Moscow, 119234, Russia
  • anow at: Department of Environmental Science and Analytical Chemistry, Stockholm University, Stockholm, 11418, Sweden
  • bnow at: Institute of Geography, Technische Universität Dresden, Dresden, 01069, Germany

Abstract. 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 are still poorly quantified. 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 ka. We show that the ancient permafrost exposed in the Sobo-Sise cliff has a high organic carbon content (mean of about 5 wt%).We found that the OM quality, which we define as the intrinsic potential to further transformation, decomposition, and mineralization, is also high as inferred by the lipid biomarker inventory. The oldest sediments stem from Marine Isotope Stage (MIS) 3 interstadial deposits (dated to 52 to 28 cal kyr BP) and is overlaid by Last Glacial MIS 2 (dated to 28 to 15 cal ka BP) and Holocene MIS 1 (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 FAs relative to long chain (C ≥ 20) n-FAs in the interstadial MIS 3 and the interglacial MIS 1 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 C / N ratios point to a good quality of the preserved OM and thus to a high potential of the OM for decomposition upon thaw. A decrease of HPFA values downwards along the profile probably indicates a relatively stronger OM decomposition in the oldest (MIS 3) deposits of the cliff. The characterisation of OM from eroding permafrost leads to a better assessment of the greenhouse gas potential of the OC released into river and nearshore waters in future, which is important to understand the consequences of a warming climate in Arctic environments on the global carbon cycle.

Charlotte Haugk et al.

Status: open (until 07 Feb 2022)

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  • RC1: 'Comment on bg-2021-331', Anonymous Referee #1, 20 Jan 2022 reply

Charlotte Haugk et al.

Charlotte Haugk et al.

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Short summary
Buried animal and plant remains (carbon) from the last ice age were freeze-locked in permafrost. At an extremely fast eroding permafrost cliff in the Lena Delta (Siberia), we found this formerly frozen carbon well preserved. Our results show that ongoing degradation releases substantial amounts of this carbon, making it available for future carbon emissions. This mobilisation at the studied cliff but also similarly eroding sites bear the potential to affect rivers and oceans negatively.
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