The lipid geochemistry of antarctic marine sediments: Bransfield strait

Ten sections of a 10m long sediment core from Bransfield Strait, Antarctic region, have been examined for hydrocarbons, fatty acids, fatty alcohols, sterols, hopanoic acids, lignins and stable isotope ratios. The resolvable lipid compound classes generally occur in the following order of abundance: n-fatty acids > n-alkanes > n-alcohols > sterols > PAH with n-fatty acids comprising 50–80% of the lipids. The distribution of various lipid components indicate that they are principally from marine autochthonous sources, largely from diatoms and bacteria and to a lesser extent from dinoflagellates. There is no evidence from the lipid fraction of significant terrestrial plant input, which was also confirmed by the absence of methoxyphenols of the lignin degradation products. Aeolian transport from other continents appears to be minor or negligible. Minor amounts of epigenetic (mature) triterpenoids and polynuclear aromatic hydrocarbons found in all the samples are probably derived from submarine outcrops of weathered coaliferous shales. Stable carbon isotope ratios fall within a narrow range (−25 to −26‰), characteristic of Antarctic plankton. Coprostanol is the major stanol identified in the sediment core, most probably derived from the excreta of marine mammals, i.e. whales. Perylene, the dominant PAH, appears to be of marine origin in these Antarctic sediments. The presence of labile alkenes, unsaturated fatty acids and diploptene to a depth of 10m implies that little diagenetic alteration of the lipids has occurred. The sub-zero bottom water temperatures and the anoxic environmental conditions of this basin have preserved the total organic matter in the sediments, at least down to a depth of 10m.