Characterization of organic matter stored in frozen Yedoma and thermokarst basin deposits on Sobo-Sise Island, Lena Delta

Jens.Strauss [ at ]


The permafrost region approximately makes up one quarter of the land surface of the Northern Hemisphere. Its soil organic carbon pool is estimated to be about twice the size of carbon in the modern atmosphere (Hugelius et al., 2014). In the context of climate warming, understanding the processes that are linked to permafrost thaw and its effects on the organic carbon pool is of major concern (Schuur et al., 2015). In particular, permafrost carbon quality characteristics are of interest since they determine availability of carbon to microbial decomposition and may significantly influence the outcome of permafrost carbon feedbacks to climate. We analyzed organic-matter quality of Late Pleistocene (Yedoma) and Holocene (thermokarst basin) permafrost deposits with regard to the degree of decomposition by applying a multi-proxy approach. Samples were taken from two exposures, one located in a thermokarst depression and the other on a Yedoma-to-thermokarst slope on Sobo-Sise Island in the Lena Delta (northeast Siberia). Additionally, a four meters long frozen core was taken from a baydzerakh hill on a Yedoma slope. In our approach, building on Strauss et al. (2015), we used sedimentological (ice content, bulk density) and geochemical parameters (total organic carbon (TOC), dissolved organic carbon (DOC), stable isotopes (δ13C, δ18O), total organic carbon total nitrogen (C/N) ratios), as well as molecular biomarkers (n-alkanes, n-fatty acids, and biomarker indices, i.e., average chain length (ACL), carbon preference index (CPI), and higher-plant fatty-acid index (HPFA)). Our results indicated higher concentrations of organic carbon in Yedoma when compared to thermokarst basin deposits. Concentrations of DOC were clearly higher for Yedoma, with values ranging from 200 mg/l to above 1000 mg/l, compared to DOC concentrations in thermokarst basin deposits of under 200 mg/l (Fig. 1, a). With values between 5-15 wt%, TOC was also higher for Yedoma, while in thermokarst basin deposits it only ranged from 4-6 wt% (Fig. 1, b). However, C/N ratio and δ13C showed no clear difference between data from Yedoma or thermokarst (Fig. 1, b, c). TOC and DOC measured in this study suggest both less degradation of organic-matter stored in Yedoma deposits as in thermokarst. However, in Strauss et al. (2015) organic-matter from both Yedoma and thermokarst deposits showed no relation between degradation and depth, while C/N ratio and δ13C values suggested a better conservation of organic matter from thermokarst deposits compared to Yedoma deposits. Hence, Strauss et al. (2015) concluded that organic-matter vulnerability is heterogeneous and depends on different decomposition trajectories and previous decomposition and preservation history. Furthermore, biomarker data suggested that degradation rather occurs as a combination of degradation processes than a simple linear function of age or sediment facies. In this context, our study approach of combining lipid biomarkers and δ18O, together with our sedimentological and geochemical data, is promising to deliver valuable information about decomposition processes and trajectories of organic-matter in the Lena Delta. References Hugelius, G., Strauss, J., Zubrzycki, S., Harden, J.W., Schuur, E.A.G., Ping, C.-L., Schirrmeister, L., Grosse, G., Michaelson, G.J., Koven, C.D., O’Donnell, J.A., Elberling, B., Mishra, U., Camill, P., Yu, Z., Palmtag, J., Kuhry, P., 2014. Estimated stocks of circumpolar permafrost carbon with quantified uncertainty ranges and identified data gaps. Biogeosciences 11, 6573–6593. doi:10.5194/bg-11-6573-2014 Schuur, E.A.G., McGuire, A.D., Schädel, C., Grosse, G., Harden, J.W., Hayes, D.J., Hugelius, G., Koven, C.D., Kuhry, P., Lawrence, D.M., Natali, S.M., Olefeldt, D., Romanovsky, V.E., Schaefer, K., Turetsky, M.R., Treat, C.C., Vonk, J.E., 2015. Climate change and the permafrost carbon feedback. Nature 520, 171–179. doi:10.1038/nature14338 Strauss, J., Schirrmeister, L., Mangelsdorf, K., Eichhorn, L., Wetterich, S., Herzschuh, U., 2015. Organic-matter quality of deep permafrost carbon – a study from Arctic Siberia. Biogeosciences 12, 2227–2245. doi:10.5194/bg-12-2227-2015

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Conference (Poster)
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XI. International Conference on Permafrost, 20 Jun 2016 - 24 Jun 2016, Potsdam, Germany.
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Neubauer, D. , Strauss, J. , Mangelsdorf, K. and Grosse, G. (2016): Characterization of organic matter stored in frozen Yedoma and thermokarst basin deposits on Sobo-Sise Island, Lena Delta , XI. International Conference on Permafrost, Potsdam, Germany, 20 June 2016 - 24 June 2016 .

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