4:10 PM - 4:30 PM
[BGM02-08] Origin of deep methane from pull-apart basin on the Itoigawa-Shizuoka Tectonic Line: Impacts between deep carbon and surface ecosystem in Lake Suwa
★Invited Papers
Keywords:Methane-specific stable carbon and radiocarbon profiles, Active seep gas, Dissolved inorganic carbon, Pull-apart basin
In summary, there are three origins of methane emission in Lake Suwa: 1) from the surface hydrosphere, 2) from deep sedimentary layers, and 3) from the mantle. In this study, we are investigating the interaction of these methane sources on the hydrosphere ecosystem using radiocarbon measurement. Methane and carbon dioxide collected at seep sites, where gas inflow was regularly observed in Lake Suwa, were 14C-depleted (Δ14CCH4 = −989.8 ±0.3‰, Δ14CCO2 = −951.2 ±1.0‰). The results clearly indicated that the origin of methane is different from that of methane released from the benthic sediments (Δ14CCH4 = +21.7 ±3.8‰). The Δ14C values of dissolved inorganic carbon (DIC) in surface lake water collected at seep sites (Δ14CDIC = −103.1 to −630.6‰) and near the lakeshore (Δ14CDIC = −100.9 ±3.5‰) suggested that the influence of deep carbon occurred not only around the seep sites but also at the lakeshore. Using the application of the new analytical method [5, 6], we confirmed that the signal of deep carbon is transmitted to algae and fish through DIC, and succeeded in quantitatively evaluating the picture of the utilization of deep-derived carbon including methane as a carbon source in the lake ecosystem.
This study was supported in part by the Japan Society for the Promotion of Science (JSPS) with the joint research between the JAMSTEC and Shinshu University.
References:
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