TY - JOUR
T1 - Origin of methane in serpentinite-hosted hydrothermal systems
T2 - The CH4-H2-H2O hydrogen isotope systematics of the Hakuba Happo hot spring
AU - Suda, Konomi
AU - Ueno, Yuichiro
AU - Yoshizaki, Motoko
AU - Nakamura, Hitomi
AU - Kurokawa, Ken
AU - Nishiyama, Eri
AU - Yoshino, Koji
AU - Hongoh, Yuichi
AU - Kawachi, Kenichi
AU - Omori, Soichi
AU - Yamada, Keita
AU - Yoshida, Naohiro
AU - Maruyama, Shigenori
N1 - Funding Information:
We thank Mr. Sejima (Happoone Development Company) for his cooperation and assistance in the field study. We also thank the managers of the Kurashita, Renge, Wakakuri and Tsugaike hot springs for their cooperation. This research was supported by a grant for the Global COE Program entitled “From the Earth to “Earths” ”, MEXT , Japan. Y.U. is supported partly by the Funding Program for Next Generation World-Leading Researchers from the Japanese Society for Promotion of Science (JSPS) .
PY - 2014/1/15
Y1 - 2014/1/15
N2 - 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.
AB - 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.
KW - Abiotic methane
KW - Hydrogen isotope
KW - Serpentinization
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U2 - 10.1016/j.epsl.2013.11.001
DO - 10.1016/j.epsl.2013.11.001
M3 - Article
AN - SCOPUS:84888039100
VL - 386
SP - 112
EP - 125
JO - Earth and Planetary Sciences Letters
JF - Earth and Planetary Sciences Letters
SN - 0012-821X
ER -