Carbon Storage in Quaternary Deposits of the Circum-Arctic Permafrost Region

Abstract: Rapid warming in northern latitudes will lead to permafrost thaw and subsequent carbon remobilisa­tion and release to the atmosphere. To incorporate the permafrost carbon climate feedback in globalEarth System Models, it is of importance to know the carbon stored in the circum­Arctic permafrostregion as accurate and precise as possible. Whereas soil, Yedoma and delta carbon stocks are alreadyquantified, deep carbon stocks for vast areas of the current permafrost region are still unaccountedfor. The aim of this Master thesis project is to estimate the deep carbon stock (>3m) for Quaternarydeposits outside the known reservoirs. Therefore, 363 boreholes and exposures were compiled fromthe scientific literature. 244 sites provide profile descriptions (depositional environment, depth andthickness) and another 119 sites contain data to calculate carbon densities (ground ice content, coarsefraction (>1cm and/or >2mm), bulk density and total organic carbon). Data gaps were filled usinglocal, regional and global average facies values from the compiled dataset. For spatial upscaling,key regions are defined using the permafrost zone, overburden thickness and ice content. The fielddata compiled here shows disagreements with the Circum­Arctic Map of Permafrost and Ground­Iceconditions (Brown et al. 2002), which should be updated especially in thin and ice­poor regions. Atotal C stock of 1698 ±255 PgC is estimated for 3­25m in Quaternary deposits of the circum­Arcitcpermafrost region, next to the Yedoma domain (327 ­ 466 PgC, Strauss et al. 2017) and deltas (41 ­151 PgC, Hugelius et al. 2014). About 70% of the carbon is stored within 3­10m (1200 ±238 PgC).Due to a publication bias towards thick and organic­rich sediments in the literature, C stocks calcualtedhere might be overestimated. Additional to the Yedoma domain, 309 ±99 PgC are stored in ice­richdeposits of the continuous permafrost zone, a regions especially prone to thermokarst and deep carbonremobilisation. Thermokarst, thermo­fluvial erosion along rivers and coasts as well as carbon releasethrough inland water systems presents possible release mechanisms for stored carbon. The permafrostcarbon estimate determined here doubles the known carbon reservoir in the permafrost region and em­phasises the importance for possible deep carbon release with future permafrost thawing.