biostudies-literatureWild BEuropean Research Council5057https://www.ebi.ac.uk/biostudies/studies/S-EPMC9420143biostudies-literatureUnknown13(1)Subsea permafrost represents a large carbon pool that might be or become a significant greenhouse gas source. Scarcity of observational data causes large uncertainties. We here use five 21-56 m long subsea permafrost cores from the Laptev Sea to constrain organic carbon (OC) storage and sources, degradation state and potential greenhouse gas production upon thaw. Grain sizes, optically-stimulated luminescence and biomarkers suggest deposition of aeolian silt and fluvial sand over 160 000 years, with dominant fluvial/alluvial deposition of forest- and tundra-derived organic matter. We estimate an annual thaw rate of 1.3 ± 0.6 kg OC m^-2 in subsea permafrost in the area, nine-fold exceeding organic carbon thaw rates for terrestrial permafrost. During 20-month incubations, CH<sub>4<Nature communicationsOrganic matter composition and greenhouse gas production of thawing subsea permafrost in the Laptev Sea.PMC9420143695331Wild BDudarev OJakobsson MTesi TNybom IMazurov AShakhova NAlexanderson HKosmach DMatsubara FSemiletov IRuban AGrimm HGustafsson OTumskoy VfalseOrganic matter composition and greenhouse gas production of thawing subsea permafrost in the Laptev Sea.Subsea permafrost represents a large carbon pool that might be or become a significant greenhouse gas source. Scarcity of observational data causes large uncertainties. We here use five 21-56 m long subsea permafrost cores from the Laptev Sea to constrain organic carbon (OC) storage and sources, degradation state and potential greenhouse gas production upon thaw. Grain sizes, optically-stimulated luminescence and biomarkers suggest deposition of aeolian silt and fluvial sand over 160 000 years, with dominant fluvial/alluvial deposition of forest- and tundra-derived organic matter. We estimate an annual thaw rate of 1.3 ± 0.6 kg OC m^-2 in subsea permafrost in the area, nine-fold exceeding organic carbon thaw rates for terrestrial permafrost. During 20-month incubations, CH<sub>4<2022-01-01T00:00:00Z2022 Aug2025-04-04T13:46:47.147Z2025-04-04T13:46:47.147ZS-EPMC94201433603026910.1038/s41467-022-32696-0