DIAGENESIS OF MARINE LIPIDS IN OCEAN SEDIMENTS

Piston cores from a northwest African upwelling area, the Mid-Atlantic Ridge, and the open western Atlantic were analyzed by gas chromatography to investigate the distribution and diagenesis of fatty acids, isoprenoid alcohols, and hydrocarbons in Recent and ancient marine sediments. 14C and 234U/230Th analyses were obtained on two of these cores to provide information on the time scale of the alteration of these lipids. The recent input of anthropogenic hydrocarbons was observed in the upwelling and Mid-Atlantic Ridge cores although an unresolved complex mixture of hydrocarbons was also found over much longer time periods (≅120,000 yr). The predominant hydrocarbons in all cores were nC25, nC29, and nC31, which are believed to be continentally derived. The fatty acids and isoprenoid alcohols in the cores were of marine origin. While the concentration of biogenic hydrocarbons and the hydrocarbon/organic carbon (OC) ratios remained essentially constant down the core, the fatty acids and isoprenoid alcohols (and their ratios to OC) both decreased in concentration with depth. Unbound lipids appeared to be degraded more rapidly than bound lipids. Investigation of the stereochemistry of monounsaturated fatty acids and isoprenoid alcohols indicated that they may serve as useful indicators of source material. No conversion of cis to trans geometric fatty acid isomers was detected but the relative absence of the Δ11 positional may be correlated with the small bacterial populations in the sediments. The dominance of the RRR isomer of dihydrophytol over the SRR isomer indicated that the reduction of phytol to dihydrophytol was microbially mediated in these cores. © 1979.