Estimation of Arctic organic matter degradability in ice-rich permafrost using lipid biomarkers

Permafrost organic matter is becoming increasingly mobilized by thaw with ongoing climate warming. The huge amount of carbon stored in pan-arctic perennially frozen soils and deposits (estimated to 822 Gt) is comparable in size with the current atmospheric carbon stock (860 Gt). About 327 to 466 Gt of this permafrost carbon are stored in the yedoma domain, a region covering much of East Siberia and parts of Alaska and NW Canada which contains thick ice-rich Pleistocene and Holocene permafrost deposits. We hypothesize that a substantial amount of the Pleistocene and Holocene permafrost contain organic carbon of good quality for future microbial degradability upon thaw. To test this hypothesis, we sampled yedoma permafrost in the circum-arctic region from Siberia (Sobo Sise: 72.5426°N, 128.2681°E; Buor Khaya Peninsula: 71.38361°N, 132.08397°E; Yukechi: 61.7649° N, 130.466° E; Duvanny Yar: (68.6342°N; 159.0875°E) to Alaska (Baldwin Peninsula: 66.7326°N, 162.4945°W; Itkillik River: 69.5676°N, 150.8658°W). We measured state-of-the-art biomarker and sedimentological proxies to assess the potential for future organic matter degradability. At all study sites, we used the following parameters: carbon to nitrogen ratio, stable carbon isotope ratios, radiocarbon ages, carbon preference index, average chain length, total n-alkane, n-fatty acid, and n-alcohol concentration. Our findings indicate that the organic matter in the Pleistocene yedoma deposits is at least as well preserved as in the Holocene deposits, and in some cases even better (Baldwin Peninsula). We conclude that rapid preservation of OM in permafrost locks the quality of OM in for extensive times (millennia to tens of millennia) and thus results in high potential for easy degradability upon thaw. The next step in our study is the combination of the applied degradation proxies measured and reported here with experimental incubation experiments (Jongejans et al., this conference), which is part of our ongoing research