Evidence of Vast Methane Release Over the East Siberian Arctic Shelf

The East Siberian Arctic Shelf (ESAS), which includes the Laptev Sea, the East-Siberian Sea and the Russian part of the Chukchi Sea, has not been considered to be a methane (CH₄) source to hydrosphere or atmosphere because sub-sea permafrost, which underlies most of the ESAS was believed first, not to be conducive to methanogenesis and second, to act as an impermeable lid, preventing CH₄ escape through the seabed. Here, recent observational data obtained during summer (2005–2009) and winter (2007) expeditions indicate the ubiquitous presence of elevated dissolved CH₄and the atmospheric CH₄ mixing ratio, and evidence of strong ebullition through shallow water column. The methane data were analyzed together with sonar measurements of bubble flow using a seabed lander, ship-based hydro-acoustical bubble observation and geophysical investigation of the seafloor. Available data suggest the ESAS subsea permafrost is leaking substantial CH₄. This points permafrost failure to further conserve CH₄ deposits in the ESAS, from which shallow hydrates are believed to be involved the most likely.

The ESAS is a unique area of World Ocean for a range of reasons: 1) As a marine ecosystem, the ESAS is markedly oligotrophic, which could limit microbial methane consumption (or production); 2) No comparable region has such an extensive continental shelf area; the ESAS shelf accounts for ~10% of the global continental shelf area; 3) The ESAS is very shallow, which provides a short conduit for seabed CH₄ transfer to the atmosphere. 4) ESAS seabed CH₄emissions are geologically controlled; specifically, by subsea permafrost, which for thousands of years was stable and impermeable. Permafrost failure uncorks the huge gas reservoirs, leading to large-scale releases. 5) The ESAS is a major reservoir for shallow arctic hydrates and subsea permafrost (more than 80% of existing subsea permafrost), thus potential CH₄ release from the ESAS is enormous.