Publication Date:
2022-05-25
Description:
Author Posting. © The Author(s), 2010. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Geochimica et Cosmochimica Acta 75 (2011): 1594-1607, doi:10.1016/j.gca.2010.12.020.
Description:
Hydrothermal experiments were conducted to evaluate the kinetics of H2(aq)
oxidation in the homogeneous H2-O2-H2O system at conditions reflecting
subsurface/near-seafloor hydrothermal environments (55-250 oC and 242-497 bar). The
kinetics of the water-forming reaction that controls the fundamental equilibrium between
dissolved H2(aq) and O2(aq), are expected to impose significant constraints on the redox
gradients that develop when mixing occurs between oxygenated seawater and high-
temperature anoxic vent fluid at near-seafloor conditions. Experimental data indicate that,
indeed, the kinetics of H2(aq)-O2(aq) equilibrium become slower with decreasing
temperature, allowing excess H2(aq) to remain in solution. Sluggish reaction rates of H2(aq)
oxidation suggest that active microbial populations in near-seafloor and subsurface
environments could potentially utilize both H2(aq) and O2(aq), even at temperatures lower
than 40 oC due to H2(aq) persistence in the seawater/vent fluid mixtures. For these H2-O2
disequilibrium conditions, redox gradients along the seawater/hydrothermal fluid mixing
interface are not sharp and microbially-mediated H2(aq) oxidation coupled with a lack of
other electron acceptors (e.g. nitrate) could provide an important energy source available
at low-temperature diffuse flow vent sites.
More importantly, when H2(aq)-O2(aq) disequilibrium conditions apply, formation
of metastable hydrogen peroxide is observed. The yield of H2O2(aq) synthesis appears to
be enhanced under conditions of elevated H2(aq)/O2(aq) molar ratios that correspond to
abundant H2(aq) concentrations. Formation of metastable H2O2 is expected to affect the
distribution of dissolved organic carbon (DOC) owing to the existence of an additional
strong oxidizing agent. Oxidation of magnetite and/or Fe++ by hydrogen peroxide could
also induce formation of metastable hydroxyl radicals (•OH) through Fenton-type
reactions, further broadening the implications of hydrogen peroxide in hydrothermal environments.
Description:
This research was conducted with partial support from the NSF
OCE-0752221 and the Geophysical Laboratory Postdoctoral Fellowship. We would also
like to acknowledge contributions by the W.M. Keck Foundation and Shell towards
supporting the hydrothermal lab at the Geophysical Lab. SMS acknowledges support
from NSF OCE-0452333 and the Alfried-Krupp Wissenschaftskolleg Greifswald
(Germany), while WES acknowledges support from NSF grants OCE-0549457 and OCE-
0813861.
Keywords:
Knallgas reaction
;
H2 oxidation
;
Metastable hydrogen peroxide
;
Anaerobic chemolithoautotrophic metabolism
;
Fenton reaction
;
Hydrothermal systems
Repository Name:
Woods Hole Open Access Server
Type:
Preprint
Format:
application/pdf
