Abstract
Strong and unusual BSRs (e.g. High-Amplitude reflections below the BSR) and gas chimneys have been revealed by seismic profiling survey off Shimokita peninsula. These observations suggest anomalously high flux of upward migrating methane and subsurface methane production. This study aims to examine the methane activity in shallow sediments and methane concentration of seawater in this unique area. Piston cores and seawater samples were collected at this area during KT05-7 cruise, April 2005. After cruise, sulfate and chloride concentrations in pore-water, methane concentration and carbon isotopic composition of pore-water and seawater were determined.High methane concentration and 13C-depleted methane (δ13C∼δ-90‰) proved that the study area are characterized by high methane flux and active microbial methane production in shallow sediments. Moreover, seawater has high concentration methane suggesting the possibility of methane release at sea floor.
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