Variability of organic carbon along the ice-covered polar continental margin of East Greenland

Abstract

The Nordic Seas play an important role in the global climate system. The detailed knowledge and comprehension of recent processes is essential for predicting future climate as well as for reconstructing paleoenvironmental conditions. In order to examine these processes controlling, among other things, the variability of organic carbon in modern sediments of the ice-covered polar continental margin of East Greenland, organic-geochemical bulk parameters(C/N-ratios, hydrogen- and oxygen-index values, Tmax-values) and specific biomarkers (n-alkanes,fatty acids, sterols) in marine surface sediments, onshore sediments originating from Greenland, and sea-ice sediments were determined. Based on literature and compound-specific stable carbon isotope measurements, the investigated biomarkers were assigned tothree different groups representing (a) primary production (phytoplankton, sea-ice algae),(b) secondary input (zooplankton, bacteria), and (c) terrestrial production (higher plants). Primary production- and secondary input-derived biomarkers showed highest concentrations in the shallow fjord and shelf sediments. Degradation processes in the water column and at the sediment-water interface mainly control their distribution as in slope and deep-sea sediments only low concentrations were detected. The higher marine production rate of the marginal ice zone was not reflected in surface sediments. The amounts of higher plant-derived biomarkers were highest in sediments of the marginal ice zone indicating the predominant input of these compounds by melting sea ice. The lowest concentrations of higher plant-derived biomarkers were measured in the fjord and shelf sediments pointing to a negligible input of terrigenous organic carbon direct from Greenland. This study has shown that the distribution and composition of organic carbon in modern sediments of the East Greenland continental margin is primarily controlled by degradation. In addition to the investigation of surface sediments, the organic-carbon records of selected sediment cores were determined todevelop a rough model for the variability of organic carbon during the Late Quaternary.