Methane flux, seafloor gas hydrates, chloride anomalies and sulfate reduction : Joetsu regions, eastern margin of Japan Sea

Abstract

The Umitaka (UT) spur in Japan Sea is characterized by methane-induced features such as Bottom-simulating reflectors (BSRs), pockmarks, mounds and ∼600 m high plumes in the water column (Aoyama et al., 2004). These features seem to indicate active fluid and/or gas venting on the UT spur. In order to estimate methane flux and gas hydrate existence, we measured sulfate and chloride ion concentration of pore water. Sulfate ion concentration has revealed much stronger methane flux than Brake Ridge and chloride anomaly seems to result of recent gas hydrate formation and past dissociation.