biostudies-literatureSteinbach JVetenskapsrådetEuropean Research CouncilMinistry of Science and Higher Education of the Russian FederationKnut och Alice Wallenbergs StiftelseRussian Science FoundationEU-H2020National Science Foundatione2019672118https://www.ebi.ac.uk/biostudies/studies/S-EPMC7958249biostudies-literatureUnknown118(10)The East Siberian Arctic Shelf holds large amounts of inundated carbon and methane (CH4). Holocene warming by overlying seawater, recently fortified by anthropogenic warming, has caused thawing of the underlying subsea permafrost. Despite extensive observations of elevated seawater CH4 in the past decades, relative contributions from different subsea compartments such as early diagenesis, subsea permafrost, methane hydrates, and underlying thermogenic/ free gas to these methane releases remain elusive. Dissolved methane concentrations observed in the Laptev Sea ranged from 3 to 1,500 nM (median 151 nM; oversaturation by ∼3,800%). Methane stable isotopic composition showed strong vertical and horizontal gradients with source signatures for two seepage areas of δ13C-CH4 = (-42.6 ± 0.5)/(-55.Proceedings of the National Academy of Sciences of the United States of AmericaSource apportionment of methane escaping the subsea permafrost system in the outer Eurasian Arctic Shelf.PMC7958249ERC-AdG CC-TOP project #6953312011.0027621-2013-5297 and 2017-01601Nunataryuk (contract 773421) and Comfort (contract 820989)0909546075-15-2020-978OPP ARC-102328115-17-20032 and 18-77-10004695331Steinbach JSemiletov IBruchert VNoormets RShcherbakova KShakhova NSalyuk ASapart CJGustafsson OHolmstrand HKosmach DChernykh DfalseSource apportionment of methane escaping the subsea permafrost system in the outer Eurasian Arctic Shelf.The East Siberian Arctic Shelf holds large amounts of inundated carbon and methane (CH4). Holocene warming by overlying seawater, recently fortified by anthropogenic warming, has caused thawing of the underlying subsea permafrost. Despite extensive observations of elevated seawater CH4 in the past decades, relative contributions from different subsea compartments such as early diagenesis, subsea permafrost, methane hydrates, and underlying thermogenic/ free gas to these methane releases remain elusive. Dissolved methane concentrations observed in the Laptev Sea ranged from 3 to 1,500 nM (median 151 nM; oversaturation by ∼3,800%). Methane stable isotopic composition showed strong vertical and horizontal gradients with source signatures for two seepage areas of δ13C-CH4 = (-42.6 ± 0.5)/(-55.2021-01-01T00:00:00Z2021 Mar2025-04-19T15:36:05.1Z2025-04-19T15:36:05.1ZS-EPMC79582493364922610.1073/pnas.2019672118