Publication Date:
2021-03-29
Description:
Precipitation of exceptionally 13C-depleted authigenic carbonate is a result of, and thus a tracer for, sulphate-dependent anaerobic methane oxidation, particularly in marine sediments. Although these carbonates typically are less depleted in 13C than in the source methane, because of incorporation of C also from other sources, they are far more depleted in 13C (δ13C as light as -69‰ V-PDB) than in carbonates formed where no methane is involved. Here we show that oxidation of biogenic methane in carbon-poor deep groundwater in fractured granitoid rocks has resulted in fracture-wall precipitation of the most extremely 13C-depleted carbonates ever reported, δ13C down to -125‰ V-PDB. A microbial consortium of sulphate reducers and methane oxidizers has been involved, as revealed by biomarker signatures in the carbonates and S-isotope compositions of co-genetic sulphide. Methane formed at shallow depths has been oxidized at several hundred metres depth at the transition to a deep-seated sulphate-rich saline water. This process is so far an unrecognized terrestrial sink of methane.
Keywords:
carbonates; biogenic methane; fractured granite
;
551
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Calcium Carbonate
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Carbon Isotopes
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Crystallization
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Geologic Sediments
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Groundwater
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Iron
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Isotope Labeling
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Methane
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Oxidation-Reduction
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Silicon Dioxide
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Sulfides
;
Time Factors
Language:
English
,
English
Type:
article
,
publishedVersion
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