Extreme (13)C depletion of carbonates formed during oxidation of biogenic methane in fractured granite.

Medientyp: E-Artikel

Titel: Extreme (13)C depletion of carbonates formed during oxidation of biogenic methane in fractured granite

Beteiligte: Drake, Henrik [Verfasser:in]; Åström, Mats E [Verfasser:in]; Heim, Christine [Verfasser:in]; Broman, Curt [Verfasser:in]; Åström, Jan [Verfasser:in]; Whitehouse, Martin [Verfasser:in]; Ivarsson, Magnus [Verfasser:in]; Siljeström, Sandra [Verfasser:in]; Sjövall, Peter [Verfasser:in]

Erschienen: GEO-LEOe-docs (FID GEO), 2015

Sprache: Englisch

DOI: https://doi.org/10.1038/ncomms8020

ISSN: 2041-1723

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Beschreibung: 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.

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