溶存メタンを指標に用いた富山湾海底湧出地下水の地球化学的研究(<特集>沿岸海底湧水の地球科学)

概要

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We present here a geochemical study on the SGD in the Toyama Bay using CH4 and its carbon isotope ratio as tracers. We found that all SGD fluids and many of land groundwaters contain less methane than natural water in equilibrium with atmospheric CH4. Theδ13C values of CH4 in the SGD fluids range from -50 to -20‰ VPDB, almost comparable or slightly higher than that of atmospheric CH4. The results suggest that most of methane in the SGD fluids had been derived from the atmosphere and a part of the CH4 is oxidized in the course of groundwater flow through the aquifer, with no CH4 production that is usual in highly anoxic groundwater.This is probably due to little organic matter content in the aquifer and/or a short residence time from recharge to discharge on seafloor. The low concentration and high carbon isotopic ratio of CH4 are similar to those in some of the land groundwaters. The SGD fluid in Uozu should be flowing underground along the Katagai River.
日本地球化学会の論文
2005-08-20