title: Extreme (13)C depletion of carbonates formed during oxidation of biogenic methane in fractured granite.
abstract: 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.
authors.affiliation: Department of Biology and Environmental Science, Linnæus University, SE-39182 Kalmar, Sweden.
authors.forename: Henrik
authors.initials: H
authors.lastname: Drake
authors.affiliation: Department of Biology and Environmental Science, Linnæus University, SE-39182 Kalmar, Sweden.
authors.forename: Mats E
authors.initials: ME
authors.lastname: Åström
authors.affiliation: Department of Geobiology, Geoscience Centre Göttingen of the Georg-August University, Goldschmidtstrasse 3, 37077 Göttingen, Germany.
authors.forename: Christine
authors.initials: C
authors.lastname: Heim
authors.affiliation: Department of Geological Sciences, Stockholm University, SE-106 91 Stockholm, Sweden.
authors.forename: Curt
authors.initials: C
authors.lastname: Broman
authors.affiliation: CSC-IT Center for Science, PO Box 405, FIN-02101 Esbo, Finland.
authors.forename: Jan
authors.initials: J
authors.lastname: Åström
authors.affiliation: Laboratory for Isotope Geology, Swedish Museum of Natural History, PO Box 50 007, SE-10405 Stockholm, Sweden.
authors.forename: Martin
authors.initials: M
authors.lastname: Whitehouse
authors.affiliation: Department of palaeobiology and the Nordic Center for Earth Evolution (NordCEE), Swedish Museum of Natural History, PO Box 50 007, SE-10405 Stockholm, Sweden.
authors.forename: Magnus
authors.initials: M
authors.lastname: Ivarsson
authors.affiliation: Department of Surfaces, Chemistry and Materials, SP Technical Research Institute of Sweden, PO Box 857, SE-50115 Borås, Sweden.
authors.forename: Sandra
authors.initials: S
authors.lastname: Siljeström
authors.affiliation: Department of Surfaces, Chemistry and Materials, SP Technical Research Institute of Sweden, PO Box 857, SE-50115 Borås, Sweden.
authors.forename: Peter
authors.initials: P
authors.lastname: Sjövall
mesh_terms: D002119:Calcium Carbonate / Q000737:chemistry*; D002247:Carbon Isotopes; D003460:Crystallization; D019015:Geologic Sediments; D060587:Groundwater / Q000737:chemistry; D007501:Iron / Q000737:chemistry; D007553:Isotope Labeling; D008697:Methane / Q000032:analysis*; D010084:Oxidation-Reduction; D012822:Silicon Dioxide / Q000737:chemistry*; D013440:Sulfides / Q000737:chemistry; D013997:Time Factors
chemical_list: D002247:Carbon Isotopes; D013440:Sulfides; C007886:granite; C011342:pyrite; D012822:Silicon Dioxide; D007501:Iron; D002119:Calcium Carbonate; D008697:Methane