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

Abstract

A biological community was discovered in the Northern Okushiri Ridge, northeastern Japan Sea. The community was closely associated with sea‐floor fissures, and presumed to be supported by methanotrophic and/or thiotrophic bacterial production. Sediments inside of and in the vicinity of the fissures were collected, and the short‐chain (C9–20) sediment fatty acids were analyzed for amounts and compositions. The fatty acid compositions were compared with those from a known methane seep and a submarine volcano in the Sagami 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 methane 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.