| 研究実績の概要 |
Understanding the abiotic methane formation pathways in natural serpentinization systems is of crucial importance as it may support the earliest life on Earth or elsewhere. However, conventional approaches, such as hydrocarbon concentrations, stable carbon and hydrogen isotopes, always have limitation to identify methane source and constrain its formation pathways.
In this project, we firstly established the novel analytical approach, named as methane clumped isotope techniques, to precisely obtain the bulk (δ13C and δD) and clumped isotope (Δ13CH3D and Δ12CH2D2) values in the same sample. We have investigated its application in laboratory synthesized abiotic methane via Fischer-Tropsch Type (FTT) reaction catalyzed by Nickel. The changes of bulk and clumped isotope signatures with reaction time ranging from 20 min to 72 hr have been studied, which present extremely disequilibrium values in Δ12CH2D2 with less disequilibrated values in Δ13CH3D during methane formation. The unique patterns controlled by the specific pathway/parameter have been discussed and verified, which could be applied in understanding the natural abiotic methane formation pathways in the following study.
Besides, we have also applied the methane clumped isotope approach in understanding methane formation pathways and sources in natural samples, such as methane gases recovered from the shallow hydrates in the Japan Sea, and from various mud volcanos located in central Japan.
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