Origin of Short-Chain Organic Acids in Serpentinite Mud Volcanoes of the Mariana Convergent Margin

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DOI

  • Philip Eickenbusch, ETH Zürich
  • ,
  • Ken Takai, Japan Agency for Marine Earth Science and Technology
  • ,
  • Olivier Sissman, IFP Energies Nouvelles, IFP Energies Nouvelles
  • ,
  • Shino Suzuki, Japan Agency for Marine Earth Science and Technology
  • ,
  • Catriona Menzies, University of Southampton, University of Aberdeen
  • ,
  • Sanae Sakai, Japan Agency for Marine Earth Science and Technology
  • ,
  • Pierre Sansjofre, Université de Bretagne Occidentale
  • ,
  • Eiji Tasumi, Japan Agency for Marine Earth Science and Technology
  • ,
  • Stefano M. Bernasconi, ETH Zürich
  • ,
  • Clemens Glombitza, ETH Zürich, NASA Ames Research Center
  • ,
  • Bo Barker Jorgensen
  • Yuki Morono, Japan Agency for Marine-Earth Science and Technology
  • ,
  • Mark Alexander Lever, ETH Zurich

Serpentinitic systems are potential habitats for microbial life due to frequently high concentrations of microbial energy substrates, such as hydrogen (H-2), methane (CH4), and short-chain organic acids (SCOAs). Yet, many serpentinitic systems are also physiologically challenging environments due to highly alkaline conditions (pH > 10) and elevated temperatures (>80 degrees C). To elucidate the possibility of microbial life in deep serpentinitic crustal environments, International Ocean Discovery Program (IODP) Expedition 366 drilled into the Yinazao, Fantangisfia, and Asut Tesoru serpentinite mud volcanoes on the Mariana Forearc. These mud volcanoes differ in temperature (80, 150, 250 degrees C, respectively) of the underlying subducting slab, and in the porewater pH (11.0, 11.2, 12.5, respectively) of the serpentinite mud. Increases in formate and acetate concentrations across the three mud volcanoes, which are positively correlated with temperature in the subducting slab and coincide with strong increases in H(2 )concentrations, indicate a serpentinization-related origin. Thermodynamic calculations suggest that formate is produced by equilibrium reactions with dissolved inorganic carbon (DIC) + H-2, and that equilibration continues during fluid ascent at temperatures below 80 degrees C. By contrast, the mechanism(s) of acetate production are not clear. Besides formate, acetate, and H-2 data, we present concentrations of other SCOAs, methane, carbon monoxide, and sulfate, delta C-13-data on bulk carbon pools, and microbial cell counts. Even though calculations indicate a wide range of microbial catabolic reactions to be thermodynamically favorable, concentration profiles of potential energy substrates, and very low cell numbers suggest that microbial life is scarce or absent. We discuss the potential roles of temperature, pH, pressure, and dispersal in limiting the occurrence of microbial life in deep serpentinitic environments.

Original languageEnglish
Article number1729
JournalFrontiers in Microbiology
Volume10
Number of pages21
ISSN1664-302X
DOIs
Publication statusPublished - Jul 2019

    Research areas

  • limits of life, deep biosphere, serpentinization, abiotic synthesis, formate, acetate, methane, International Ocean Discovery Program, VOLATILE FATTY-ACIDS, THERMOCHEMICAL SULFATE REDUCTION, DEEP SUBSEAFLOOR SEDIMENTS, FORE-ARC, MICROBIAL COMMUNITIES, ACTIVITY-COEFFICIENTS, HYDROTHERMAL REACTIVITY, HYDROGEN GENERATION, ANAEROBIC-BACTERIA, REDUCING BACTERIA

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