[MIS16-P07] Methanogenesis and methane consumption within the gas chimney structure in Hidaka Trough, offshore Hokkaido: implications from pore water and gas geochemistry
Sulfate is depleted strongly near the seafloor at the sulfate-methane interface (SMI), indicating the domination of reductive environment near the seafloor. Sharp negative peak of δ13C of dissolved inorganic carbon (DIC) locates at the SMI, indicating the anaerobic methane oxidation predominates for the sulfate consumption at this interval. We examined δ13C of methane and dissolved hydrocarbon composition to distinguish the gas source. Although the biogenic methane is transported from deep sediments, it receives a certain amount of methane of thermogenic origin. In addition, by comparing δ13C of methane with DIC, biogenic methane produced by microbial mediated CO2 reduction pathway is also significant. Methane produced by microbial mediated CO2 reduction within upper methanogenesis zone and biogenic and/or thermogenic methane derived from deep sediments contributes to the shallow reductive environment within gas chimney structures in Hidaka Trough.
This study used data collected during the academic researches and expeditions conducted under the commission from AIST as a part of the methane hydrate research project funded by the Ministry of Economy, Trade and Industry, Japan.