Organic geochemistry of marine sediments of the Subantarctic Indian Ocean sector: Lipid classes—sources and fate

Abstract

Nine sections of core KTB16 (47°59′98 S, 55°59′74 E, 4240 m) taken from the Indian Ocean sector of the Antarctic Polar Front Zone were analyzed for their lipid class and total chlorin contents using thin-layer chromatography-flame ionisation detection (TLC/FID). The following series were included: hydrocarbons, chlorins and chlorin esters, alcohols, sterols, triacylglycerols, free fatty acids and phospholipids. For these major classes, the distribution of their individual components was determined to evaluate the source and fate of each lipid class. Relationships between the lipid composition of overlying particles and of buried material were investigated. The sediment-water interface was found to be of primary importance in the biogeochemical transformations occurring in organic matter, such as loss of the major part of the lipids, and formation of a notable unresolved complex mixture (UCM), of biological origin. Some classes such as chlorin esters appeared to convey their lipid contents from the upper layers without major alteration. In contrast, several other classes, such as storage lipids, appeared to be degraded during sedimentation, indicating extensive recycling of labile lipids in the water column. The burial efficiency and bacterial inputs downcore were highly variable depending on the class considered. Several novel compounds are reported. They consist of alkyl chlorin esters and include a wide variety of saturated and unsaturated long-chain alcohols. Owing to the lack of lipid data in the study area, these results provide an insight into the various biological and chemical processes occurring in open-sea Antarctic sedimentary environments.