Variability in lipid flux and composition of particulate matter in the Peru upwelling region

Abstract

Particulate matter samples were collected with free-drifting sediment traps and in situ filtration systems in the Peruvian upwelling area to study the organic geochemistry of particulate organic matter in the water column and its relationship to source organisms and sediments. A variety of lipids—fatty acids, wax esters, steryl esters, triacylglycerols, sterols, fatty alcohols, stanones, unsaturated C 37 and C 38 methyl ketones, and hydrocarbons—were analyzed by capillary gas chromatography and gas chromatography—mass spectrometry. Diel and depth-related variation in lipid composition and flux of an order of magnitude were not uncommon in the sediment trap samples. Two samplings of a single site four days apart produced significantly different results. Flux and composition patterns varied depending on lipid class, collection time and depth, and source. The lipid composition of the suspended particles collected by in situ filtration was quite different from that of sinking particles collected in sediment traps, reflecting complexities in differentiating between source, transport, and transformation processes affecting the two particle size fractions. The data provide estimates of the range of fluctuations in composition of material contributing to the sedimentary record, which integrates over time periods of years to centuries.