Serpentinization and associated hydrogen and methane fluxes at slow spreading ridges

Cannat, Mathilde; Fontaine, F. J.; Escartı́n, J.

doi:10.1029/2008gm000760

Cited by 128 publications

(167 citation statements)

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“…The total hydrogen and methane produced by serpentinization are calculated in this work to be 133 × 10 9 mol yr −1 and 14 × 10 9 mol yr −1 . These fluxes are slightly lower than those calculated by Cannat et al [2010] according to the rate of mantle rock exhumation and the stoichiometry of olivine hydration (167 × 10 9 mol yr −1 for H 2 and 25 × 10 9 mol yr −1 for CH 4 ). Although this difference could be due to subsurface consumption of hydrogen by reactions other than CO 2 reduction, all of these results are within the uncertainty of plus/minus a factor of 2 inherent to these estimates.…”

Section: Discussionmentioning

confidence: 55%

“…Three of the 7 ultramafic sites, however, exhibit low-temperature venting (Lost City, Saldanha, Menez Hom). On the basis of gravity anomalies, Cannat et al [1995Cannat et al [ , 2010 suggest that 23% of the seafloor created at slow-spreading ridges contains ultramafic rock. Here I assume the fraction of ultramafic-hosted vent fields on slow-spreading ridges is the average of these percentages.…”

Section: Abiogenic Methane Flux From Mid-ocean Ridgesmentioning

confidence: 99%

“…A starting point for these considerations is the abiogenic source on earth today, but estimates of this flux range over 2 orders of magnitude [Welhan and Craig, 1983;Kasting, 2005;Sorokhtin et al, 2001;Emmanuel and Ague, 2007;Cannat et al, 2010]. In this note, hydrothermal fluxes of abiogenic methane and hydrogen from mid-ocean ridges are estimated on the basis of gas concentrations that have been observed in vent fluids and the dependence of these concentrations on the type of host rock.…”

Section: Introductionmentioning

confidence: 99%

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A note on the fluxes of abiogenic methane and hydrogen from mid‐ocean ridges

Keir¹

2010

Geophysical Research Letters

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[1] The concentrations of methane and hydrogen in hydrothermal vent fluids issuing from mid-ocean ridges tend to fall into two groups, one with high concentrations of these gases in ultramafic-hosted vent fields and a second group with relatively lower concentrations in basalt-hosted vent fluids. Ultramafic-hosted systems, however, appear to be restricted to slow-spreading ridges and constitute only a fraction of the hydrothermal systems found there. In this note, the hydrothermal fluxes of methane and hydrogen have been calculated by estimating the percentages of the total subsurface hydrothermal circulation that circulate through each type of host rock. Even though the percentage of the total subsurface flow that is affected by serpentinization appears to be rather small (8%), it still appears that this process produces about 70% of the total mid-ocean flux of these gases. The total production of methane and hydrogen is calculated to be about 20 × 10 9 mol yr −1 and 190 × 10 9 mol yr −1 , respectively. The hydrogen flux is comparable to that most recently calculated on the basis of the rate of hydration of mantle rock in newly formed crust and the stoichiometry of the serpentinization reaction. This suggests that, except for the production of methane, a major portion of the hydrogen produced in the subsurface is not consumed before venting. Citation: Keir, R. S.(2010), A note on the fluxes of abiogenic methane and hydrogen from mid-ocean ridges, Geophys.

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Section: Discussionmentioning

confidence: 55%

Section: Abiogenic Methane Flux From Mid-ocean Ridgesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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A note on the fluxes of abiogenic methane and hydrogen from mid‐ocean ridges

Keir¹

2010

Geophysical Research Letters

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“…Serpentinization is currently taking place in the shallow forearc of subduction zones, along ultraslow-, slow-, and fast-spreading midocean ridges where oceanic mantle is exposed to water (52)(53)(54)(55). Whether serpentinization is currently taking place along passive margins is unclear, but it certainly occurred in the geological past, as shown in the present study.…”

Section: Serpentinization and Subseafloor Microbial Activitymentioning

confidence: 70%

Fluid mixing and the deep biosphere of a fossil Lost City-type hydrothermal system at the Iberia Margin

Klein

Humphris

Guo

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

100

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Subseafloor mixing of reduced hydrothermal fluids with seawater is believed to provide the energy and substrates needed to support deep chemolithoautotrophic life in the hydrated oceanic mantle (i.e., serpentinite). However, geosphere-biosphere interactions in serpentinite-hosted subseafloor mixing zones remain poorly constrained. Here we examine fossil microbial communities and fluid mixing processes in the subseafloor of a Cretaceous Lost City-type hydrothermal system at the magma-poor passive Iberia Margin (Ocean Drilling Program Leg 149, Hole 897D). Brucite−calcite mineral assemblages precipitated from mixed fluids ca. 65 m below the Cretaceous paleo-seafloor at temperatures of 31.7 ± 4.3°C within steep chemical gradients between weathered, carbonate-rich serpentinite breccia and serpentinite. Mixing of oxidized seawater and strongly reducing hydrothermal fluid at moderate temperatures created conditions capable of supporting microbial activity. Dense microbial colonies are fossilized in brucite−calcite veins that are strongly enriched in organic carbon (up to 0.5 wt.% of the total carbon) but depleted in 13 C (δ 13 C TOC = −19.4‰). We detected a combination of bacterial diether lipid biomarkers, archaeol, and archaeal tetraethers analogous to those found in carbonate chimneys at the active Lost City hydrothermal field. The exposure of mantle rocks to seawater during the breakup of Pangaea fueled chemolithoautotrophic microbial communities at the Iberia Margin, possibly before the onset of seafloor spreading. Lost City-type serpentinization systems have been discovered at midocean ridges, in forearc settings of subduction zones, and at continental margins. It appears that, wherever they occur, they can support microbial life, even in deep subseafloor environments.serpentinization | microfossils | lipid biomarkers | brucite−calcite | passive margin

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“…Constraining the sources of carbon (C) and hydrogen (H) for the production of CH 4 , as well as the depths and temperatures at which CH 4 is generated in these hydrothermal systems, is critical for understanding the origin of methane (Welhan, 1988b;Charlou et al, 2002;Proskurowski et al, 2008;McDermott et al, 2015). The abundance and isotopic composition of methane venting from submarine hydrothermal fields that are relatively free of sediment cover has been described at oceanic spreading centers characterized by a range of spreading rates (e.g., Welhan, 1988b;Charlou et al, 2002;McCollom and Seewald, 2007;Proskurowski et al, 2008;Cannat et al, 2010;Charlou et al, 2010;Proskurowski, 2010;McDermott et al, 2015;McDermott, 2015). In general, fluids that have interacted with ultramafic rocks are substantially enriched in CH 4 relative to fluids that have reacted with mafic rocks (Keir, 2010), although there are exceptions in which high-CH 4 fluids are associated with apparent mafic substrates (e.g., basalt) (Charlou et al, 2000).…”

Section: Introductionmentioning

confidence: 99%

The geochemistry of methane isotopologues

Wang¹

2017

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This thesis documents the origin, distribution, and fate of methane and several of its isotopic forms on Earth. Using observational, experimental, and theoretical approaches, I illustrate how the relative abundances of 12 CH 4 , 13 CH 4 , 12 CH 3 D, and 13 CH 3 D record the formation, transport, and breakdown of methane in selected settings.Chapter 2 reports precise determinations of 13 CH 3 D, a "clumped" isotopologue of methane, in samples collected from various settings representing many of the major sources and reservoirs of methane on Earth. The results show that the information encoded by the abundance of 13 CH 3 D enables differentiation of methane generated by microbial, thermogenic, and abiogenic processes. A strong correlation between clumped-and hydrogen-isotope signatures in microbial methane is identified and quantitatively linked to the availability of H 2 and the reversibility of microbially-mediated methanogenesis in the environment. Determination of 13 CH 3 D in combination with hydrogen-isotope ratios of methane and water provides a sensitive indicator of the extent of C-H bond equilibration, enables fingerprinting of methane-generating mechanisms, and in some cases, supplies direct constraints for locating the waters from which migrated gases were sourced. Chapter 3 applies this concept to constrain the origin of methane in hydrothermal fluids from sediment-poor vent fields hosted in mafic and ultramafic rocks on slow-and ultraslow-spreading mid-ocean ridges. The data support a hypogene model whereby methane forms abiotically within plutonic rocks of the oceanic crust at temperatures above ca. 300• C during respeciation of magmatic volatiles, and is subsequently extracted during active, convective hydrothermal circulation. Chapter 4 presents the results of culture experiments in which methane is oxidized in the presence of O 2 by the bacterium Methylococcus capsulatus strain Bath. The results show that the clumped isotopologue abundances of partially-oxidized methane can be predicted from knowledge of 13 C/ 12 C and D/H isotope fractionation factors alone.: Shuhei Ono, Ph.D. Acknowledgments I fear that this section will not do justice to the people I have not the space to thank individually. Alas, here goes. To those whose names are not specifically listed here, thank you too. I wish first to thank Shuhei Ono. The work this thesis represents could not have happened without his bold vision and the license to explore and question that working in his lab afforded. His unbridled optimism, breadth of scientific curiosity, personal integrity, and accessibility to his personnel are traits I one day hope to emulate. I thank him for his nonjudgmental yet appropriately measured support of many of my ideas-even those that led nowhere-, for believing in me even when I found it difficult to do so myself, and for teaching me to change pump oil, build vacuum lines, and drink Icelandic vodka.I also wish to thank my thesis committee members Jeff Seewald, Roger Summons, and John Pohlman, for their in...

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Serpentinization and associated hydrogen and methane fluxes at slow spreading ridges

Cited by 128 publications

References 99 publications

A note on the fluxes of abiogenic methane and hydrogen from mid‐ocean ridges

A note on the fluxes of abiogenic methane and hydrogen from mid‐ocean ridges

Fluid mixing and the deep biosphere of a fossil Lost City-type hydrothermal system at the Iberia Margin

The geochemistry of methane isotopologues

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