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Abiotic redox reactions in hydrothermal mixing zones: Decreased energy availability for the subsurface biosphere
Name
20453.full.pdf
Description
Published version
Size
947.76 KB
Format
Adobe PDF
Checksum (MD5)
e2512d4c6c27d969dd0da16067847b93
Author(s)
McDermott, Jill M
Sylva, Sean P
Ono, Shuhei
German, Christopher R
Seewald, Jeffrey S
Date Issued
2020
Journal
Proceedings of the National Academy of Sciences of the United States of America
Publisher
Proceedings of the National Academy of Sciences
Version
Final published version
Abstract
© 2020 National Academy of Sciences. All rights reserved. Subseafloor mixing of high-temperature hot-spring fluids with cold seawater creates intermediate-temperature diffuse fluids that are replete with potential chemical energy. This energy can be harnessed by a chemosynthetic biosphere that permeates hydrothermal regions on Earth. Shifts in the abundance of redox-reactive species in diffuse fluids are often interpreted to reflect the direct influence of subseafloor microbial activity on fluid geochemical budgets. Here, we examine hydrothermal fluids venting at 44 to 149 °C at the Piccard hydrothermal field that span the canonical 122 °C limit to life, and thus provide a rare opportunity to study the transition between habitable and uninhabitable environments. In contrast with previous studies, we show that hydrocarbons are contributed by biomass pyrolysis, while abiotic sulfate (SO42-) reduction produces large depletions in H2. The latter process consumes energy that could otherwise support key metabolic strategies employed by the subseafloor biosphere. Available Gibbs free energy is reduced by 71 to 86% across the habitable temperature range for both hydrogenotrophic SO42- reduction to hydrogen sulfide (H2S) and carbon dioxide (CO2) reduction to methane (CH4). The abiotic H2 sink we identify has implications for the productivity of subseafloor microbial ecosystems and is an important process to consider within models of H2 production and consumption in young oceanic crust.
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Creative Commons Attribution-NonCommercial-NoDerivs License
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DOI of Published Version
10.1073/PNAS.2003108117
