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. Permafrost ground is one of the largest repositories ofterrestrial organic carbon and might become or already is a carbon source inresponse to ongoing global warming. With this study of syngeneticallyfrozen, ice-rich and organic carbon (OC)-bearing Yedoma and associated alasdeposits in central Yakutia (Republic of Sakha), we aimed to assess the local sedimentdeposition regime and its impact on permafrost carbon storage. For thispurpose, we investigated the Yukechi alas area (61.76495 ∘  N,130.46664 ∘  E), which is a thermokarst landscape degrading into Yedoma incentral Yakutia. We retrieved two sediment cores (Yedoma upland, 22.35 mdeep, and alas basin, 19.80 m deep) in 2015 and analyzed the biogeochemistry,sedimentology, radiocarbon dates and stable isotope geochemistry. Thelaboratory analyses of both cores revealed very low total OC (TOC) contents(  wt %) for a 12 m section in each core, whereas theremaining sections ranged from 0.1 wt % to 2.4 wt % TOC. The core sectionsholding very little to no detectable OC consisted of coarser sandy material wereestimated to be between 39 000 and 18 000 BP (years before present) in age. For thisperiod, we assume the deposition of organic-poor material. Pore water stableisotope data from the Yedoma core indicated a continuously frozen stateexcept for the surface sample, thereby ruling out Holocene reworking. Inconsequence, we see evidence that no strong organic matter (OM)decomposition took place in the sediments of the Yedoma core until today.The alas core from an adjacent thermokarst basin was strongly disturbed bylake development and permafrost thaw. Similar to the Yedoma core, somesections of the alas core were also OC poor (  wt %) in 17 outof 28 samples. The Yedoma deposition was likely influenced by fluvialregimes in nearby streams and the Lena River shifting with climate. With itscoarse sediments with low OC content (OC mean of 5.27 kg m −3 ), the Yedoma deposits in the Yukechi area differ from other Yedoma sites inNorth Yakutia that were generally characterized by silty sediments withhigher OC contents (OC mean of 19 kg m −3 for the non-icewedge sediment). Therefore, we conclude that sedimentary composition anddeposition regimes of Yedoma may differ considerably within the Yedomadomain. The resulting heterogeneity should be taken into account for futureupscaling approaches on the Yedoma carbon stock. The alas core, stronglyaffected by extensive thawing processes during the Holocene, indicates apossible future pathway of ground subsidence and further OC decompositionfor thawing central Yakutian Yedoma deposits.

Organic carbon characteristics in ice-rich permafrost in alas and Yedoma deposits, central Yakutia, Siberia