Authigenic carbonate mounds from active methane seeps on the southern Aquitaine Shelf (Bay of Biscay, France): evidence for anaerobic oxidation of biogenic methane and submarine groundwater discharge during formation
|Author(s)||Pierre Catherine1, Demange Jerome1, Blanc-Valleron Marie-Madeleine2, Dupre Stephanie3|
|Affiliation(s)||1 : UPMC, Sorbonne Univ, LOCEAN, 4 Pl Jussieu, F-75252 Paris 05, France.
2 : MNHN, Sorbonne Univ, CR2P, 57 Rue Cuvier, F-75005 Paris, France.
3 : IFREMER, Unite Geosci Marines, BP 70, F-29280 Plouzane, France.
|Source||Continental Shelf Research (0278-4343) (Pergamon-elsevier Science Ltd), 2017-02 , Vol. 133 , P. 13-25|
|WOS© Times Cited||10|
|Keyword(s)||Aquitaine Shelf, Methane-derived authigenic carbonates, Oxygen isotopes, Carbon isotopes, Submarine groundwater discharge, Anaerobic oxidation of methane, Aerobic oxidation of methane|
|Abstract||The widespread methane emissions that were discovered in 2013 on the Aquitaine Shelf at water depth between 140 and 220 m are associated with authigenic carbonate crusts that cover meter-high subcircular reliefs of 10 to 100 m in diameter. These authigenic carbonates are primarily aragonite plus calcite and dolomite, which cement the fine- to medium-grained sandy sediment. The carbonate cement is often pierced by numerous circular cavities of 5 to 10 µm in diameter that are considered to be moulds of gas bubbles. Conversely, micron-sized cavities in the aragonite crystals are attributed to dissolution features, in relation to the production of CO2 during the aerobic oxidation of methane. The oxygen isotopic compositions of bulk carbonate (+1.7 to +3.7‰) and aragonite cements obtained from microsampling (-0.1 to +1.4‰) indicate that these carbonates were precipitated in mixtures of seawater and freshwater, i.e., in the context of submarine groundwater discharge at the seafloor. The carbon isotopic compositions of authigenic carbonates (-51.9 to -38.1‰) and of aragonite cements (-49.9 to -29.3‰) show that the dissolved inorganic carbon of pore fluids was mostly produced by the anaerobic oxidation of biogenic methane and also partly from the groundwater system.|