Potential greenhouse gas production by organic matter decomposition in thawing subsea permafrost

Subsea permafrost extends over vast areas across the East Siberian Arctic Ocean shelves and might harbor a large and vulnerable organic matter pool. Field campaigns have observed strongly elevated concentrations of CH₄ in seawater above subsea permafrost that might stem from microbial degradation of thawing subsea permafrost organic matter, from release of CH₄ stored within subsea permafrost, from shallow CH₄ hydrates or from deeper thermogenic/petrogenic CH₄ pools. We here assess the potential production of CH₄, as well as CO₂ and N₂O by organic matter degradation in subsea permafrost after thaw. To that end, we employ a set of subsea permafrost drill cores from the Buor-Khaya Bay in the south-eastern Laptev Sea where previous studies have observed a rapid deepening of the ice-bonded permafrost table. Preliminary data from an ongoing laboratory incubation experiment suggest the production of both CH₄ and CO₂ by decomposition of thawed subsea permafrost organic matter, while N₂O production was negligible. These data will be combined with detailed biomarker analysis to constrain the vulnerability of subsea permafrost organic matter to degradation to greenhouse gases upon thaw.