The occurrence of monounsaturated n-C₂₁ and polyunsaturated C₂₅ sedimentary hydrocarbons in the lipids of Antarctic marine organisms

Antarctic zooplankton have been found to be a potential source of sedimentary hydrocarbons. Monounsaturated C21 n-alkenes and highly branched polyunsaturated C25 n-alkenes were analysed in the aliphatic fraction of the lipids of Antarctic pelagic and inshore marine organisms. Cluster analysis of the species-based data set produced four main groups: phytoplankton, epipelagic herbivores, epipelagic carnivores and mesopelagic omnivores. The detailed pattern of alkenes exhibited differences within the groups and also with tissue type (krill, Euphausia superba). The origin of alkenes in Antarctic biota appeared to be either synthesis de novo or due to the condensation of smaller molecules. Formation of alkenes by the decarboxylation of fatty acids was not consistent with the hydrocarbon and fatty acid composition of Antarctic zooplankton. There was no evidence for direct assimilation of C21 and C25 alkenes by zooplankton or higher predators from their diet. Zooplankton C25 alkenes are probably transported unaltered directly to the sediment as detritus or via predators in faecal material. Sedimentary C25 alkenes are proposed as biomarkers of recent zooplankton activity in the water column.