Anaerobic oxidation of methane in a cold-water coral carbonate mound from the Gulf of Cadiz

Abstract

The Gulf of Cadiz is an area of mud volcanism and gas venting through the seafloor. In addition, several cold-water coral carbonate mounds have been discovered at the Pen Duick escarpment amidst the El Arraiche mud volcano field on the Moroccan margin. One of these mounds -named Alpha mound-has been studied to examine the impact of the presence of methane on pore-water geochemistry, potential sulphate reduction (SR) rate and dissolved inorganic carbon (DIC) budget of the mound in comparison with off-mound and off-escarpment locations. Pore-water profiles of sulphate, sulphide, methane, and DIC from the on-mound location showed the presence of a sulphate to methane transition zone at 350 cm below the sea floor. This was well correlated with an increase in SR activity. 13 C-depleted DIC at the transition zone (-21.9% vs. Vienna Pee Dee Belemnite) indicated that microbial methane oxidation significantly contribute to the DIC budget of the mound. The Alpha mound thus represents a new carbonate mound type where the presence and anaerobic oxidation of methane has an important imprint on both geochemistry and DIC isotopic signature and budget of this carbonate mound.

Evidence of Active Methanogen Communities in Shallow Sediments of the Sonora Margin Cold Seeps

“…Enrichment steps are generally required for the detection and identification of Methanococcoides lineages in cold seep sediments (13,14,42,50,51). The presence and activity of these methanogens in these sulfate-rich sediments (22 to 5 mM sulfate) (23), as observed previously in other marine sediments (14,47,50,52,53), were probably a consequence of utilization of noncompetitive methanogenic substrates, such as methylamines (17,19,54). Methylated amines were presumably available in the surface sediments of WM14 and EWM14, as marine invertebrates, observed in high densities over these sediments, can accumulate large amounts of osmolytes (e.g., betaine and trimethylamine N-oxide) and choline (widespread in cell membranes) in their tissues that can be subsequently released in the sediments and degraded to smaller methylated amines (e.g., (Fig.…”

Microbial community composition and biogeochemical processes in cold-water coral carbonate mounds in the Gulf of Cadiz, on the Moroccan margin

“…Extensive fields of seep-related carbonates have been unveiled in offreef regions (Maldonado and Uriz, 1999;Nelson and Maldonado, 1999;Pinheiro et al, 2003;Somoza et al, 2003;Van Rensbergen et al, 2005b). Recent studies documented a shallow sulfate-methane transition zone (at~3.5 m sediment depth) in Alpha Mound, one of the first mounds on the ridge of the Pen Duick Escarpment and a possible linkage between methane-driven diagenetic processes and coral dissolution, as well as carbonate production in this mound was suggested (Foubert et al, 2008;Maignien et al, 2010;Wehrmann et al, this issue).…”

Carbonate mounds: From paradox to World Heritage

“…Second, where giant carbonate mound provinces occur, surface expressions of deep-sourced, advective fluxes of geofluids have been repeatedly reported, in proximal or in remote position, including pockmark fields (Porcupine Seabight, Van Rensbergen et al, 2007), mud volcanoes (Alboran Sea, Comas et al, 2009;Gulf of Cadiz, Van Rensbergen et al, 2005), sulfate-methane transition zones, both within a mound (Alpha Mound, Pen Duick Escarpment, Morocco, Maignien et al, 2010) and below a mound (Challenger Mound, IODP Exp. 307, Frank et al, 2010).…”

“…water coral dissolution and carbonate precipitation Foubert and Henriet, 2009). The Alpha Mound on Pen Duick Escarpment, featuring a shallow zone of anoxic oxidation of methane (AOM) (Maignien et al, 2010), comprises up to 40% of microbial dolomite Wehrmann et al, 2011;Pirlet et al, 2012). …”