Fatty-acids and their δ 13C characteristics of seep carbonates from the northern continental slope of Gulf of Mexico

Here we reported the fatty-acids and their delta C-13 values in seep carbonates collected from Green Canyon lease block 185 (GC 185; Sample GC-F) at upper continental slope (water depth:similar to 540 m), and Alaminos Canyon lease block 645 (GC 645; Sample AC-E) at lower continental slope (water depth: similar to 2200 m) of the Gulf of Mexico. More than thirty kinds of fatty acids were detected in both samples. These fatty acids are maximized at C-16. There is a clear even-over-odd carbon number predominance in carbon number range. The fatty acids are mainly composed of n-fatty acids, iso-/anteiso-fatty acids and terminally branched odd-numbered fatty acids (iso/anteiso). The low delta C-13 values (-39.99aEuro degrees to.32.36aEuro degrees) of n-C-12:0, n-C-13:0, i-C-14:0 and n-C-14:0 suggest that they may relate to the chemosynthetic communities at seep sites. The unsaturated fatty acids n-C-18:2 and C-18:1 Delta(9) have the same delta C-13 values, they may originate from the Beggiatoa/Thioploca. Unlike other fatty acids, the terminally branched fatty acids (iso/anteiso) show lower delta C-13 values (as low as -63.95aEuro degrees) suggesting a possible relationship to sulfate reducing bacteria, which is common during anaerobic oxidation of methane at seep sites.