Preprints
https://doi.org/10.5194/bg-2021-167
https://doi.org/10.5194/bg-2021-167

  23 Jun 2021

23 Jun 2021

Review status: this preprint is currently under review for the journal BG.

Hydrogen and carbon isotope fractionation factors of aerobic methane oxidation in deep-sea water

Shinsuke Kawagucci1,2, Yohei Matsui3,4, Akiko Makabe1, Tatsuhiro Fukuba5, Yuji Onishi1,6, Takuro Nunoura7, and Taichi Yokokawa1 Shinsuke Kawagucci et al.
  • 1Super-cutting-edge Grand and Advanced Research (SUGAR) Program, Institute for Extra-cutting-edge Science and Technology Avant-garde Research (X-star), Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Yokosuka 237-0061, Japan
  • 2Institute of Geochemistry and Petrology, ETH Zürich, Zürich 8092, Switzerland
  • 3Advanced Science-Technology Research (ASTER) Program, X-star, JAMSTEC, Yokosuka 237-0061, Japan
  • 4Department of Engineering Mechanics and Energy, University of Tsukuba, Tsukuba 305-0006, Japan
  • 5Institute for Marine-Earth Exploration and Engineering (MarE3), JAMSTEC, Yokosuka 237-0061, Japan
  • 6The Center for Ecological Research, Kyoto University, Otsu 520-2113, Japan
  • 7Research Institute for Marine Resources Utilization (MRU), JAMSTEC, Yokosuka 237-0061, Japan

Abstract. Isotope fractionation factors associated with various biogeochemical processes are important in ensuring the practicality of isotope tracers in biogeosciences at large. Methane is a key component of the subsurface biosphere and a notable greenhouse gas, making the accurate evaluation of methane cycles, including microbial methanotrophy, imperative. Although the isotope fractionation factors associated with methanotrophy been examined under various conditions, the dual-isotope fractionation factors of aerobic methanotrophy in oxic seawater column remain unclear. Here, we investigated hydrogen and carbon isotope ratios of methane as well as the relevant biogeochemical parameters and microbial community compositions in hydrothermal plumes in the Okinawa Trough. Methanotrophs were found to be abundant in plumes above the Hatoma Knoll vent site, and we succeeded in simultaneously determining hydrogen and carbon isotope fractionation factors associated with aerobic oxidation of methane (εH = 49.4 ± 5.0 ‰, εC = 5.2 ± 0.4 ‰) – the former being the first of its kind ever reported. This εH value is comparable with reported values from terrestrial ecosystems but clearly lower than those from aerobic and anaerobic methanotroph enrichment cultures, as well as incubations of methanotrophic isolates. The covariation factor between δ13CCH4 and δDCH4, Λ (9.4/8.8 determined using two different methods), was consistent with those from methanotrophic isolate incubations. These values determined herein are valuable for understanding dynamics of methane cycling in the marine realm, and future applications of the approach used herein to other habitats with methanotrophic activity will help reveal whether the small εH value observed herein is a ubiquitous feature across all marine systems.

Shinsuke Kawagucci et al.

Status: open (until 14 Aug 2021)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on bg-2021-167', Carsten Vogt, 12 Jul 2021 reply

Shinsuke Kawagucci et al.

Shinsuke Kawagucci et al.

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Here, we investigated hydrogen and carbon isotope ratios of methane as well as the relevant biogeochemical parameters and microbial community compositions in hydrothermal plumes in the Okinawa Trough. We succeeded in simultaneously determining hydrogen and carbon isotope fractionation factors associated with aerobic oxidation of methane in seawater (εH = 49.4 ± 5.0 ‰, εC = 5.2 ± 0.4 ‰) – the former being the first of its kind ever reported.
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