Publication Date:
2022-05-25
Description:
Author Posting. © The Author(s), 2014. This is the author's version of the work. It is posted here by permission of National Academy of Sciences for personal use, not for redistribution. The definitive version was published in Proceedings of the National Academy of Sciences of the United States of America 111 (2014): 5474-5479, doi:10.1073/pnas.1400643111.
Description:
Simple alkyl thiols such as methanethiol (CH3SH) are widely speculated to form in
seafloor hot spring fluids. Putative CH3SH synthesis by abiotic (non-biological) reduction of
inorganic carbon (CO2 or CO) has been invoked as an initiation reaction for the emergence of
proto-metabolism and microbial life in primordial hydrothermal settings. Thiols are also
presumptive ligands for hydrothermal trace metals and potential fuels for associated microbial
communities. In an effort to constrain sources and sinks of CH3SH in seafloor hydrothermal
systems, we determined for the first time its abundance in diverse hydrothermal fluids emanating
from ultramafic, mafic and sediment-covered mid-ocean ridge settings. Our data demonstrate that
the distribution of CH3SH is inconsistent with metastable equilibrium with inorganic carbon,
indicating production by abiotic carbon reduction is more limited than previously proposed.
CH3SH concentrations are uniformly low (~10-8 M) in high-temperature fluids (〉200°C) from all
unsedimented systems, and in many cases suggestive of metastable equilibrium with CH4 instead.
Associated low-temperature fluids (〈200°C) formed by admixing of seawater, however, are
invariably enriched in CH3SH (up to ~10-6 M) along with NH4+ and low molecular weight
hydrocarbons relative to high-temperature source fluids, resembling our observations from a
sedimented system. This strongly implicates thermogenic interactions between upwelling fluids
and microbial biomass or associated dissolved organic matter during subsurface mixing in crustal
aquifers. Widespread thermal degradation of subsurface organic matter may be an important
source of organic production in unsedimented hydrothermal systems, and may influence
microbial metabolic strategies in cooler near-seafloor and plume habitats.
Description:
2014-09-27
Keywords:
Methanethiol
;
Hydrothermal systems
;
Biogeochemistry
Repository Name:
Woods Hole Open Access Server
Type:
Preprint
Format:
application/pdf
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