Anaerobic methane oxidation inducing carbonate precipitation at abiogenic methane seeps in the Tuscan archipelago (Italy)

Sun, Xiaole, Meister, Patrick, Wiedling, Johanna, Lott, Christian, Bach, Wolfgang, Kuhfuß, Hanna, Wegener, Gunter, Böttcher, Michael E., Deusner, Christian, Lichtschlag, Anna, Bernasconi, Stefano M. and Weber, Miriam (2018) Anaerobic methane oxidation inducing carbonate precipitation at abiogenic methane seeps in the Tuscan archipelago (Italy) PLoS ONE, 13 (12). e0207305. DOI 10.1371/journal.pone.0207305.

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Abstract

Seepage of methane (CH4) on land and in the sea may significantly affect Earth's biogeochemical cycles. However processes of CH4 generation and consumption, both abiotic and microbial, are not always clear. We provide new geochemical and isotope data to evaluate if a recently discovered CH4 seepage from the shallow seafloor close to the Island of Elba (Tuscany) and two small islands nearby are derived from abiogenic or biogenic sources and whether carbonate encrusted vents are the result of microbial or abiotic processes. Emission of gas bubbles (predominantly CH4) from unlithified sands was observed at seven spots in an area of 100 m(2) at Pomonte (Island of Elba), with a total rate of 234 ml m(-2) d(-1). The measured carbon isotope values of CH4 of around -18 parts per thousand (VPDB) in combination with the measured delta H-2 value of -120 parts per thousand (VSMOW) and the inverse correlation of delta C-13-value with carbon number of hydrocarbon gases are characteristic for sites of CH4 formation through abiogenic processes, specifically abiogenic formation of CH4 via reduction of CO2 by H-2. The H-2 for methanogenesis likely derives from ophiolitic host rock within the Ligurian accretionary prism. The lack of hydrothermal activity allows CH4 gas to become decoupled from the stagnant aqueous phase. Hence no hyperalkaline fluid is currently released at the vent sites. Within the seep area a decrease in porewater sulphate concentrations by ca. 5 mmol/l relative to seawater and a concomitant increase in sulphide and dissolved inorganic carbon (DIC) indicate substantial activity of sulphate-dependent anaerobic oxidation of methane (AOM). In absence of any other dissimilatory pathway, the delta C-13-values between -17 and -5 parts per thousand in dissolved inorganic carbon and aragonite cements suggest that the inorganic carbon is largely derived from CH4. The formation of seep carbonates is thus microbially induced via anaerobic oxidation of abiotic CH4.

Document Type: Article
Keywords: ANGLE NORMAL FAULTS; ELBA ISLAND; MICROBIAL COMMUNITIES; SULFATE REDUCTION; ISOTOPE FRACTIONATION; ORGANIC-COMPOUNDS; ABIOTIC METHANE; MONTEREY BAY; MUD VOLCANO; FLUID-FLOW
Research affiliation: NOC
MARUM
OceanRep > GEOMAR > FB2 Marine Biogeochemistry > FB2-MG Marine Geosystems
IOW
Refereed: Yes
DOI etc.: 10.1371/journal.pone.0207305
ISSN: 1932-6203
Projects: GRASP, TRIADOL
Date Deposited: 07 Jan 2019 12:20
Last Modified: 07 Jan 2019 12:20
URI: http://eprints.uni-kiel.de/id/eprint/45117

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