Fatty-acids and their C-13 signatures in seep carbonates from hydrocarbon seeps on the upper (GC 185) and lower (AC 645) continental slope of the Gulf of Mexico

Here we reported the fatty-acids and their δ 13C values in seep carbonates collected from Green Canyon lease block 185 (GC 185; Sample GC-F) at upper continental slope (water depth: ∼540 m), and Alaminos Canyon lease block 645 (GC 645; Sample AC-E) at lower continental slope (water depth: ∼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 C16. 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 δ 13C values (−39.99‰ to.32.36‰) of n-C12:0, n-C13:0, i-C14:0and n-C14:0 suggest that they may relate to the chemosynthetic communities at seep sites. The unsaturated fatty acids n-C18:2 and C18:1Δ9 have the same δ 13C values, they may originate from theBeggiatoa/Thioploca. Unlike other fatty acids, the terminally branched fatty acids (iso/anteiso) show lowerδ 13C values (as low as −63.95‰) suggesting a possible relationship to sulfate reducing bacteria, which is common during anaerobic oxidation of methane at seep sites.

Relationship between precipitation and the infiltration depth over the middle and lower reaches of the Yellow River and Yangtze-Huaihe River Valley

National Natural Science Foundation of China [40701021, 40625002, 40331013]; National Knowledge Innovation Program of Chinese Academy of Sciences [KZCX2-YW-315-2]