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Origin of short-chain organic acids in Serpentinite Mud Volcanoes of the Mariana Convergent Margin

Origin of short-chain organic acids in Serpentinite Mud Volcanoes of the Mariana Convergent Margin
Origin of short-chain organic acids in Serpentinite Mud Volcanoes of the Mariana Convergent Margin
Serpentinitic systems are potential habitats for microbial life due to frequently high concentrations of microbial energy substrates, such as hydrogen (H2), 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°C). To elucidate the possibility of microbial life in deep serpentinitic crustal environments, International Ocean Discovery Program (IODP) Expedition 366 drilled into the Yinazao, Fantangisña, and Asùt Tesoru serpentinite mud volcanoes on the Mariana Forearc. These mud volcanoes differ in temperature (80, 150, 250°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 H2 concentrations, indicate a serpentinization-related origin. Thermodynamic calculations suggest that formate is produced by equilibrium reactions with dissolved inorganic carbon (DIC) + H2, and that equilibration continues during fluid ascent at temperatures below 80°C. By contrast, the mechanism(s) of acetate production are not clear. Besides formate, acetate, and H2 data, we present concentrations of other SCOAs, methane, carbon monoxide, and sulfate, δ13C-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.
1664-302X
Eickenbusch, Philip
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Takai, Ken
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Sissman, Olivier
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Suzuki, Shino
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Menzies, Catriona
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Sakai, Sanae
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Sansjofre, Pierre
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Tasumi, Eiji
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Bernasconi, Stefano M.
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Glombitza, Clemens
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Jørgensen, Bo Barker
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Morono, Yuki
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Lever, Mark Alexander
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Eickenbusch, Philip
9e98b8fb-175d-4438-a993-9855ff9a6d91
Takai, Ken
ab7b7a53-c1c2-4005-a646-8e9472147011
Sissman, Olivier
4f1af22b-b5b9-4be5-a09f-4f73b0f5da03
Suzuki, Shino
0b2bc3b1-6ffb-4c37-b094-e3441dbc9f0d
Menzies, Catriona
04bc2a62-064d-4911-9c45-17b47f3005de
Sakai, Sanae
44f8114f-defa-4b67-87a3-c24617d6b861
Sansjofre, Pierre
b74e8158-2818-494e-a479-2da7a9b12574
Tasumi, Eiji
e4d7773c-d591-470d-b358-396fbf0a9141
Bernasconi, Stefano M.
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Glombitza, Clemens
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Jørgensen, Bo Barker
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Morono, Yuki
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Lever, Mark Alexander
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Eickenbusch, Philip, Takai, Ken, Sissman, Olivier, Suzuki, Shino, Menzies, Catriona, Sakai, Sanae, Sansjofre, Pierre, Tasumi, Eiji, Bernasconi, Stefano M., Glombitza, Clemens, Jørgensen, Bo Barker, Morono, Yuki and Lever, Mark Alexander (2019) Origin of short-chain organic acids in Serpentinite Mud Volcanoes of the Mariana Convergent Margin. Frontiers in Microbiology, 10. (doi:10.3389/fmicb.2019.01729).

Record type: Article

Abstract

Serpentinitic systems are potential habitats for microbial life due to frequently high concentrations of microbial energy substrates, such as hydrogen (H2), 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°C). To elucidate the possibility of microbial life in deep serpentinitic crustal environments, International Ocean Discovery Program (IODP) Expedition 366 drilled into the Yinazao, Fantangisña, and Asùt Tesoru serpentinite mud volcanoes on the Mariana Forearc. These mud volcanoes differ in temperature (80, 150, 250°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 H2 concentrations, indicate a serpentinization-related origin. Thermodynamic calculations suggest that formate is produced by equilibrium reactions with dissolved inorganic carbon (DIC) + H2, and that equilibration continues during fluid ascent at temperatures below 80°C. By contrast, the mechanism(s) of acetate production are not clear. Besides formate, acetate, and H2 data, we present concentrations of other SCOAs, methane, carbon monoxide, and sulfate, δ13C-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.

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Accepted/In Press date: 12 July 2019
Published date: 26 July 2019

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Local EPrints ID: 435031
URI: https://eprints.soton.ac.uk/id/eprint/435031
ISSN: 1664-302X
PURE UUID: 3a423455-6cab-400f-a107-cce7cc5f00de

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Date deposited: 18 Oct 2019 16:30
Last modified: 18 Oct 2019 16:30

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