海底下地殻内流体系のメタンの起源(<特集>有機物・微生物・生態系の地球化学)

概要

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Geofluids venting from the seafloor have been regarded as window to view the invisible subseafloor environment where vast fuels, unique biosphere, and active faults causing terrible disasters are present. Because methane originates from hot, chemical reactions and cool, microbial metabolisms in reductive subseafloor environment, an understanding of the contributors to methanogenesis in geofluid systems can provide valuable insights into microbial activity and geochemical processes in the subseafloor environment. Interpretation of the origin of methane has relied heavily on the use of geochemical tracers, such as carbon and hydrogen isotope ratios. However, the currently used geochemical tracers to distinguish each methane source are problematic in some cases and should be revised to avoid the misunderstanding of the geofluid systems. Here, the principle defining the magnitude of the change of values of the geochemical tracers is reviewed. Improved knowledge to evaluate the origin of methane in the venting geofluids will promote to illustrate what goes on in the invisible subseafloor environment.
2010-12-25