The distribution of methane on the Siberian Arctic shelves: Implications for the marine methane cycle

The seepage of methane (CH₄) through the seabed of the world's shelves is considered to be ubiquitous. Although numerous observations of methane seepages from shallow marine sources have been reported, there were only a very few observations made over the Arctic shelves and none for the East-Siberian Sea (ESS) or Laptev Sea (LS). We present two years of data obtained during the late summer period (September 2003 and September 2004) for both the ESS and LS shelves. According to our data, the surface layer of shelf water was supersaturated up to 2500% relative to the present average atmospheric methane content of 1.85 ppm. Anomalously high concentrations (up to 154 nM or 4400% supersaturation) of dissolved methane in the bottom layer of shelf water suggest that the bottom layer is somehow affected by near-bottom sources. Considering the possible formation mechanisms of such plumes, we favor thermo-abrasion and the effects of shallow gas or gas hydrates release.