Publication Date:
2022-10-26
Description:
© The Author(s), 202. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in McDermott, J. M., Sylva, S. P., Ono, S., German, C. R., & Seewald, J. S. Abiotic redox reactions in hydrothermal mixing zones: decreased energy availability for the subsurface biosphere. Proceedings of the National Academy of Sciences of the United States of America, 117(34), (2020): 20453-20461, doi:10.1073/pnas.2003108117.
Description:
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.
Description:
Financial support was provided by the National Aeronautics and Space Administration (NASA) Astrobiology program (Awards NNX09AB75G and 80NSSC19K1427 to C.R.G. and J.S.S.) and the NSF (Award OCE-1061863 to C.R.G. and J.S.S.). Ship and vehicle time for cruise FK008 was provided by the Schmidt Ocean Institute. We thank the ROV Jason II and HROV Nereus groups, and the captain, officers, and crew of R/V Atlantis (AT18-16) and R/V Falkor (FK008) for their dedication to skillful operations at sea. We thank our scientific colleagues from both cruises, as well as Meg Tivey, Frieder Klein, and Scott Wankel for insightful discussions. We are grateful to the editor and two anonymous reviewers for providing helpful comments and suggestions.
Keywords:
Hydrothermal vent
;
Subsurface biosphere
;
Bioenergetics
;
Biogeochemistry
Repository Name:
Woods Hole Open Access Server
Type:
Article
