Methane-derived carbonate build-ups and associated microbial communities at cold seeps on the lower Crimean shelf (Black Sea)

Abstract

In the euxinic waters of the NW' Black Sea shelf, tower-like carbonate build-ups up to several metres in height grow at sites of cold methane seepage. These structures are part of an unique microbial ecosystem that shows a considerable biodiversity and a remarkable degree of organization. The accretion of the build-ups is promoted by the growth of centimetre-sized, methane-filled spheres constructed by calcifying microbial mats. Progressive mineralization of these spheres involves the early precipitation of strongly luminescent high-Mg-calcite rich in iron sulphides, and closely interfingered aragonite phases that finally create the stable (mega-) thrombolithic fabric of the towers. Within the microbial mats, microorganisms occur in distinctive spatial arrangements. Major players among the microbial consortia are the archaea groups ANME-1 and ANME-2, Crenarchaeota, and sulphate-reducing bacteria (SRB) of the Desulfosarcina/Desulfobacterium group. The intracellular precipitation of iron sulphides (greigite) by some of these bacteria, growing in close association with ANME-2, suggests iron cycling as an additional biogeochemical pathway involved in the anaerobic oxidation of methane (AOM).

Latest Permian carbonate carbon isotope variability traces heterogeneous organic carbon accumulation and authigenic carbonate formation

“…This approach has attracted criticism due to the complex multicomponent nature and high potential for diagenetic alteration, which may result in a mixture of primary and secondary diagenetic signals. Major sources of contamination that are known to affect the primary marine carbon isotope signal of bulk-carbonate rock are degradation of organic matter and methane oxidation (Marshall, 1992;Reitner et al, 2005;Wacey et al, 2007;Birgel et al, 2015).…”

“…Foremost, the reactive and biologically active upper section of the sediment column can be envisioned as leaving an imprint on carbonate chemistry, including the carbon isotope composition. This carbon isotope signal will be retained in postdepositional carbonate cements and is controlled by organic carbon (OC) fluxes, pH, alkalinity and the nature of the (sub-)sea-floor microbial communities (Melim et al, 2002;Reitner et al, 2005;Wacey et al, 2007;Birgel et al, 2015;Schobben et al, 2016;Zhao et al, 2016).…”

Macroscopic Biofilms in Fracture-Dominated Sediment That Anaerobically Oxidize Methane

“…For example, members of the ANME-1 clade are typically found in areas with high methane and limited sulfate concentrations (12). Examples include a methane-rich brine pool in the Gulf of Mexico (23) and microbial mats in the Black Sea (20,40). In contrast, members of the ANME-2 and ANME-3 clades are found in areas with more sulfate and lower methane concentrations, such as in the top 10 cm of sediments at cold seeps (19).…”

Late Jurassic–Early Cretaceous hydrocarbon seep boulders from Novaya Zemlya and their faunas

“…Bayon et al, 2009). Calcite is less commonly reported from Recent seep carbonates (Reitner et al, 2005). In contrast, fossil seep carbonates are predominantly calcitic, as fibrous aragonite is not stable during burial, although its former…”