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
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 -