5:15 PM - 6:30 PM
[MIS09-P09] Geochemistry of dissolved gas around gas chimney structures in the Mogami Trough, Japan
Distributions of methane (C1) and ethane (C2) concentrations and C1/C2 ratios show gradual increase toward the center of gas chimney particularly in shallow sections, reflecting higher biogenic methane production in the higher gas migration zone within the chimney. The stable carbon isotopic compositions of methane are also high in the center of the chimney due to higher contribution of thermogenic gas derived from deep section. The higher concentration and upward flux of gas are observed in the mound area rather than pockmark area, reflecting that the activity of gas chimney may control the distribution of gas hydrate responsible for shallow topographic anomalies.