Organic matter quality of deep permafrost carbon – a study from Arctic Siberia

• Main Authors: Strauss, Jens, Schirrmeister, Lutz, Mangelsdorf, Kai, Eichhorn, Luise, Wetterich, Sebastian, Herzschuh, Ulrike
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: Copernicus Publications 2014
• Subjects: Arctic; Ice; permafrost; Thermokarst; Siberia
• Online Access: https://epic.awi.de/id/eprint/36668/; https://epic.awi.de/id/eprint/36668/1/Strauss_BGD_print_suppl.pdf; http://www.biogeosciences-discuss.net/11/15945/2014/bgd-11-15945-2014.html; https://hdl.handle.net/10013/epic.44440; https://hdl.handle.net/10013/epic.44440.d001

The organic carbon (OC) pool accumulated in Arctic permafrost (perennially frozen ground) equals the carbon stored in the recent atmosphere. To give an idea of how Yedoma region permafrost could respond under future climatic warming, we conducted a study to quantify the organic matter quality for future decomposition of late Pleistocene (Yedoma) and Holocene (thermokarst) deposits on the Buor Khaya Peninsula, northeast Siberia. The objective of this study was to develop a stratigraphic classified organic matter quality characterization. For this purpose the degree of organic matter decomposition was estimated by using a multiproxy approach. We applied sedimentological (grain-size analyses, bulk density, ice content) and geochemical parameters (total OC, stable carbon isotopes (δ13C), carbon : nitrogen (C / N) ratios) as well as lipid biomarkers (n-alkanes, n-fatty acids, hopanes, triterpenoids, and biomarker proxies/indices: average chain length, carbon preference index (CPI), and higher plant fatty acid index (HPFA)). Our results show that the Yedoma and thermokarst organic matter qualities exhibit no obvious degradation – depth trend. The C / N, δ13C, and hop-17(21)-ene values and the HPFA index show a better quality of the organic matter stored in thermokarst deposits compared to Yedoma deposits, but the CPI points in the other direction. As the ranges of the proxies mostly overlap, we interpret this as to indicate similar quality for both kind of deposits with perhaps slightly better thermokarst organic matter quality. Supported by principal component analyses, the sediment parameters and quality proxies of Yedoma and thermokarst deposits could not be clearly separated from each other. This lack of clear quality differences revealed that the organic matter vulnerability is heterogeneous, independent from radiocarbon age and depends on different decomposition trajectories and the previous decomposition and preservation history. Elucidating this was one of the major novelties of our multiproxy study. With the ...