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Accessing the subsurface biosphere within rocks undergoing active low-temperature serpentinization in the Samail ophiolite (Oman Drilling Project)
  • +15
  • Alexis S Templeton,
  • Eric T Ellison,
  • Clemens Glombitza,
  • Yuki Morono,
  • Kaitlin R. Rempfert,
  • Tori Hoehler,
  • Spencer D Zeigler,
  • Emily Kraus,
  • John Spear,
  • Daniel Nothaft,
  • Elizabeth M Fones,
  • Eric Boyd,
  • Mason Munro-Ehrlich,
  • Lisa Mayhew,
  • Dawn Cardace,
  • Juerg Matter,
  • Peter B Kelemen,
  • the Oman Drilling Project Science Party
Alexis S Templeton
University of Colorado Boulder

Corresponding Author:[email protected]

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Eric T Ellison
University of Colorado
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Clemens Glombitza
ETH Zürich
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Yuki Morono
Kochi Institute for Core Sample Research, Japan Agency for Marine-Earth Science and Technology
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Kaitlin R. Rempfert
University of Colorado
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Tori Hoehler
NASA Ames Research Center
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Spencer D Zeigler
University of Colorado
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Emily Kraus
Colorado School of Mines
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John Spear
Colorado School of Mines
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Daniel Nothaft
University of Colorado - Boulder
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Elizabeth M Fones
Montana State University
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Eric Boyd
Montan State University
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Mason Munro-Ehrlich
Montana State University
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Lisa Mayhew
University of Colorado Boulder
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Dawn Cardace
University of Rhode Island
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Juerg Matter
University of Southampton
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Peter B Kelemen
Columbia University
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the Oman Drilling Project Science Party
University of Southampton
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Abstract

The Oman Drilling Project established an “Active Alteration” multi-borehole observatory in dunite and harzburgite undergoing low-temperature serpentinization in the Samail ophiolite. The highly serpentinized rocks are in contact with strongly reducing fluids. Distinct hydrological regimes, governed by differences in rock porosity and fracture density, give rise to steep redox (Eh +200 to -750 mV) and pH (pH range 8.5 to 11.2) gradients within the 300 to 400 meter deep boreholes. The serpentinites and fluids host an active subsurface ecosystem. Microbial cell abundances vary at least 6 orders of magnitude, from ≤3.5*101 cells/g to 2.9*107 cells/gram. Low levels of biological sulfate reduction (2-1000 fmol/cm3/day) can be detected in rock cores, particularly in rocks in contact with reduced groundwaters with pH <10.5. Thermodesulfovibrio is the predominant sulfate reducer identified via metagenomic sequencing of adjacent groundwater communities. We infer that transport and reaction of microbially generated sulfide with the serpentine and brucite assemblages gives rise to optical darkening and sulfide overprinting, including the formation of tochilinite-vallerite group minerals, potentially serving as an indicator that this system is inhabited by microbial life. Olivine mesh-cores replaced with ferroan brucite and minor awaruite, abundant veins containing hydroandradite garnet and polyhedral serpentine, and late-stage carbonate veins are suggested as targets for future spatially-resolved life-detection investigations. The high-quality whole-round core samples that have been preserved can be further probed to define how life distributes itself and functions within a system where chemical disequilibria are sustained by low-temperature water/rock interaction, and how biosignatures of in-situ microbial activity are generated.
Oct 2021Published in Journal of Geophysical Research: Biogeosciences volume 126 issue 10. 10.1029/2021JG006315