Palaeo methane-seepage history traced by biomarker patterns in a carbonate crust, Nile deep-sea fan (Eastern Mediterranean Sea)

We investigated lipid biomarkers in three depth-intervals of a methane-derived carbonate crust collected from a pockmark in the Nile Deep-Sea fan sampled during the Nautinil cruise of the R/V l'Atalante. A diverse set of C-13-depleted archaeal and bacterial lipids were detected along this crust with delta C-13 values as low as - 118 parts per thousand. This provides evidence that anaerobic oxidation of methane was the main process that induced the formation of this carbonate crust. Archaeal lipid biomarker distributions revealed the presence of archaea belonging both to the ANME-1 and ANME-2 phylogenetic clusters, with the former predominating. The distribution and compound specific delta C-13 values of AOM-derived lipid biomarkers showed no significant variations with depth. These results infer that the archaeal community structure and thus the local seepage environment remained relatively stable during the 5000 kyr period of the carbonate crust precipitation. (C) 2008 Elsevier B.V. All rights reserved.