[MIS21-P11] Geochemical behavior of carbon in shallow sediment within the gas chimney in Hidaka Trough, offshore Hokkaido
Keywords:SMI, gas chimney, Hidaka Trough
In the area of calyptogena community, the SMI locates at shallow depth and indicates reductive environment is established because of sulfate depletion. The sulfate is depleted at shallower depth in the area with carbonates near the seafloor, where the concentration of calcium ion is also lower than other areas. These results indicate carbonate formed at higher rate in the area with higher methane flux. Total organic carbon amount decrease with depth above the SMI, the residual organic matter in sediment generates methane at depth and enhances the methane flux toward the seafloor. Based on the composition of dissolved hydrocarbons and δ13C of methane, although the methane is generally of biogenic origin over the research areas in the Hidaka Trough, the δ13C of methane increase rapidly with depth on the mound center, indicating thermogenic methane predominantly migrate from deeper sediments at the site. Biogeochemical behavior of carbon varies not only among sampling sites but also among relative locations on the single gas chimney structure.