Isotopic variation of molecular hydrogen in 20°-375°C hydrothermal fluids as detected by a new analytical method

Shinsuke Kawagucci, Tomohiro Toki, Junichiro Ishibashi, Ken Takai, Michihiro Ito, Tamotsu Oomori, Toshitaka Gamo

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Abstract

Molecular hydrogen (H2) is one of the most important energy sources for subseafloor chemolithoautotrophic microbial ecosystems in the deep-sea hydrothermal environments. This study investigated stable isotope ratios of H2 in 20°-375°C hydrothermal fluids to evaluate usefulness of the isotope ratio as a tracer to explore the H2- metabolisms. Prior to the observation, we developed an improved analytical method for the determination of concentration and stable isotope ratio of H 2. This method achieved a relatively high sensitivity with a detection limit of 1 nmol H2 within an analytical error of 10‰ in the δDH2 value. The δDH2 values in the high-temperature fluids were between -405‰ and -330‰, indicating the achievement of the hydrogen isotopic equilibrium between H2 and H2O at around the hydrothermal end-member temperature. In contrast, several low-temperature fluids showed apparently smaller δDH2 values than those in the high-temperature fluids in spite of a negligible δDH2 change due to fluid-seawater mixing, suggesting the possibility of δDH2 change in the low-temperature fluids and the surrounding environments. Since the δDH2 change in low-temperature environments is not well explained by the very sluggish abiotic thermal isotopic equilibrium between H2 and H2O, it could be associated with (micro)biological H2-consuming and/or H 2-generating metabolisms that would strongly promote the isotopic equilibrium at low temperatures. Our first detection of the δD H2 variation in deep-sea hydrothermal systems presents the availability of the δDH2 value as a new tracer for microbes whose enzymes catalyze D/H exchange in H2.

Original languageEnglish
Article numberG03021
JournalJournal of Geophysical Research: Biogeosciences
Volume115
Issue number3
DOIs
Publication statusPublished - Sep 1 2010

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All Science Journal Classification (ASJC) codes

  • Geophysics
  • Forestry
  • Oceanography
  • Aquatic Science
  • Ecology
  • Water Science and Technology
  • Soil Science
  • Geochemistry and Petrology
  • Earth-Surface Processes
  • Atmospheric Science
  • Earth and Planetary Sciences (miscellaneous)
  • Space and Planetary Science
  • Palaeontology

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