Sea-floor fissures, biological communities and sediment fatty acids of theNorthern Okushiri Ridge, Japan Sea: Implications for possible methane seepage

A biological community was discovered in the Northern Okushiri Ridge, north eastern Japan Sea. The community Twas closely associated with sea-floor fis sures, and presumed to be supported by methanotrophic and/or thiotrophic ba cterial production. Sediments inside of and in the vicinity of the fissures were collected, and the short-chain (C9-20) sediment fatty acids were anal yzed for amounts and compositions. The fatty acid compositions were compare d with those fi sm a known methane seep and a submarine volcano in the Saga mi Bay, central Japan, and from a whale skeleton at the Torishima Seamount, northwestern Pacific Ocean. As a result, a close relationship between the sediments from the Northern Okushiri Ridge, the known methane-seep, and the whale skeleton was found. This finding represents the first discovery of m ethane seepage and associated biological communities in the Japan Sea. This also supports the hypothesis that the eastern margin of the northern Japan Sea is at the early stage of new subduction.