Variability of unusual distributions of alkenones in the surface waters of the Nordic seas

Samples of filtered particulate organic matter (POM) were obtained during the summers of 1999 and 2000 from the surface waters of the Nordic seas to monitor the spatial distribution of long-chain alkenones. The aim of the study was to appraise existing alkenone-based climatic proxies in northern high latitudes. Unusually high percentages of the tetraunsaturated alkenone were measured in the polar waters of the East Greenland Current, with C_37:4 of up to 77% in 80% of sea-ice cover. Values of percent C_37:4 across the Nordic seas showed a strong association with water mass type. Analysis of coccoliths in filters indicated that calcified Emiliania huxleyi could not be discounted as the biological precursor of alkenones in all the water masses. A combined data set of 69 samples of POM revealed a stronger correlation of percent C_37:4 to sea surface salinity (SSS; R² = 0.72) than to sea surface temperature (SST; R² = 0.50). Values of percent C_37:4 in sea surface POM were much higher than those in surficial sediments of the northern North Atlantic. To explain the discrepancy in sedimentary and surface water column percent C_37:4, we propose that the alkenone contents in surface sediments underlying arctic and polar waters are a combination of autochthonous and allochthonous inputs of alkenones. Our results show that percent C_37:4 can be used to reconstruct the relative extension of arctic/polar water masses in the North Atlantic. However, the results prevent confirmation of percent C_37:4 as a paleo-SSS proxy in the Nordic seas, given its multivariate nature in our data set and the decoupling between its range of values in surface waters and sediments.