Aliphatic lipids in recent sediments of the Fram Strait/Yermak Plateau (Arctic Ocean)

Surface sediments (n=39) from the western Fram Strait and across the Yermak Plateau (Arctic Ocean) were investigated by molecular and isotopic organic geochemical methods to determine the composition, distribution and origin of extractable aliphatic lipids (n-alkanes, n-alkanols, fatty acids). Bulk geochemical parameters (TOC-content, d13Corg) were also determined, including additional samples nearby. Enhanced organic carbon contents of up to 1.6% along the western slope of the Yermak Plateau and north off Spitsbergen, corroborated by an average d13Corg value of -22.3 per mil, indicated most of the organic material to be of a marine origin, despite ice-cover. The extractable aliphatic lipids contributed up to 1% of the sedimentary organic carbon and were dominated by fatty acids (0.7-9.1 mg/g TOC), whereas n-alkanes and n-alkanols contributed only minor amounts (0.1-0.4 mg/g TOC). The detailed molecular and carbon isotopic characterisation of the studied aliphatic compounds enabled assignments of most components to three lipid pools, representing: (a) primary production (marine phytoplankton, sea-ice algae), (b) secondary inputs (by feeding of zooplankton, benthic organisms and bacteria on the former) and (c) terrestrial-derived contributions. The first two compound groups dominated, but varied significantly in relation to the environment and were highest at the MIZ (Marginal Ice Zone), and along the permanently ice-covered western flank of the Yermak Plateau. In contrast, compounds attributable to a terrestrial source were of only minor importance in terms of absolute concentrations and less variable, but showed increasing relative proportions from an average of 8-14% at and southwards of the MIZ up to 27-33% on the Yermak Plateau and towards the central Arctic Ocean as a consequence of the weakening signal of primary and secondary production. This study provides further insights into the Arctic Ocean carbon dynamics, but also an example of the impact of ocean-currents on the deposition and composition of organic matter.