Lipid geochemistry of methane-seep-related Black Sea carbonates

Carbonates recovered front anoxic waters between 235 and 1555 in depth in the northwestern Black Sea were analyzed for lipid biomarkers and stable carbon isotopic compositions. [it addition, a methane-seep-related microbial ruat and a sample Of Surface sediment recovered from a non-seep site were studied for comparison. High concentrations of strongly C-13-depleted lipids attributed to bacteria and archaca mediating the anaerobic oxidation of methane (AOM) were found in all samples except for the sediment. Differences of the dominant AOM-performing communities between the carbonates indicated by specific lipid patterns appear to be caused by the respective biogeochemical settings. High proportions of ANME-2 consortia are found at sites of assumingly high partial pressures of methane while ANME-1 associations dominate at locations of moderate methane Supply. In the sedimentary concretion, a complex mixture of biomarkers for terrestrial and planktonic organisms was found. Different molecular Structures along with strong variations in the stable carbon isotopic compositions (delta C-13 = -20.2 parts per thousand to -94.3 parts per thousand) allow for an estimation of the proportions of tetraether-bound biphytanes derived front planktonic Crenarchaeota and methanotrophic Euryarchaeota. Our data imply that the shape of AOM-derived carbonate precipitates in Black Sea environments is crucially influenced by the respective methane supply. Active AOM-driven chimney-like bioherins, similar to those previously observed on the Ukrainian shelf, might also develop in the deep euxinic zone at 1555 in water depths. (c) 2005 Elsevier B.V. All rights reserved.