Origin of methane in serpentinite-hosted hydrothermal systems: The CH4-H2-H2O hydrogen isotope systematics of the Hakuba Happo hot spring

Konomi Suda, Yuichiro Ueno, Motoko Yoshizaki, Hitomi Nakamura, Ken Kurokawa, Eri Nishiyama, Koji Yoshino, Yuichi Hongoh, Kenichi Kawachi, Soichi Omori, Keita Yamada, Naohiro Yoshida, Shigenori Maruyama

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    Abstract

    Serpentinite-hosted hydrothermal systems have attracted considerable attention as sites of abiotic organic synthesis and as habitats for the earliest microbial communities. Here, we report a systematic isotopic study of a new serpentinite-hosted system: the Hakuba Happo hot spring in the Shiroumadake area, Japan (36°42 'N, 137°48 'E). We collected water directly from the hot spring from two drilling wells more than 500 m deep; all water samples were strongly alkaline (pH > 10) and rich in H2 (201-664 μmol/L) and CH4 (124-201 μmol/L). Despite the relatively low temperatures (50-60°C), thermodynamic calculations suggest that the H2 was likely derived from serpentinization reactions. Hydrogen isotope compositions for Happo #1 (Happo #3) were found to be as follows: δD-H2 = - 700‰ (-710‰), δD-CH4 = - 210‰ (-300‰), and δD-H2O = - 85‰ (-84‰). The carbon isotope compositions of methane from Happo #1 and #3 were found to be δC13=-34.5‰ and -33.9‰, respectively. The CH4-H2-H2O hydrogen isotope systematics indicate that at least two different mechanisms were responsible for methane formation. Happo #1 has a similar hydrogen isotope compositions to other serpentinite-hosted systems reported previously. The elevated δD-CH4 (with respect to the equilibrium relationship) suggests that the hydrogen of the Happo #1 methane was not sourced from molecular hydrogen but was derived directly from water. This implies that the methane may not have been produced via the Fischer-Tropsch-type (FTT) synthesis but possibly by the hydration of olivine. Conversely, the depleted δD-CH4 (with respect to the equilibrium relationship) in Happo #3 suggests the incorporation of biological methane. Based on a comparison of the hydrogen isotope systematics of our results with those of other serpentinite-hosted hydrothermal systems, we suggest that abiotic CH4 production directly from H2O (without mediation by H2) may be more common in serpentinite-hosted systems. Hydration of olivine may play a more significant role in abiotic methane production than previously thought.

    Original languageEnglish
    Pages (from-to)112-125
    Number of pages14
    JournalEarth and Planetary Science Letters
    Volume386
    DOIs
    Publication statusPublished - Jan 15 2014

    Keywords

    • Abiotic methane
    • Hydrogen isotope
    • Serpentinization

    ASJC Scopus subject areas

    • Geophysics
    • Geochemistry and Petrology
    • Earth and Planetary Sciences (miscellaneous)
    • Space and Planetary Science

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  • Cite this

    Suda, K., Ueno, Y., Yoshizaki, M., Nakamura, H., Kurokawa, K., Nishiyama, E., Yoshino, K., Hongoh, Y., Kawachi, K., Omori, S., Yamada, K., Yoshida, N., & Maruyama, S. (2014). Origin of methane in serpentinite-hosted hydrothermal systems: The CH4-H2-H2O hydrogen isotope systematics of the Hakuba Happo hot spring. Earth and Planetary Science Letters, 386, 112-125. https://doi.org/10.1016/j.epsl.2013.11.001