Holocene surface ocean temperatures in the Labrador Sea

The Labrador Sea is a marginal sea in subpolar regions considered important for North Atlantic overturning circulation. It is surrounded by large land masses partly covered by glaciers and continental ice sheets that have and will strongly influence the freshwater/saltwater balance at the surface and thus, next to cooling and freezing processes in winter, control the formation of deep water masses that have strong impact on the deep Western Atlantic return flow in the North Atlantic thermohaline circulation. Reconstructions of centennial to millenial scale climate variability during the Holocene have also documented this complex interaction between inflow of relatively warm surface waters south of Greenland, mixing with meltwater intrusions from land, ice-berg calving and seasonal sea-ice coverage, leading to pronounced changes in the Labrador Current that fuels its surface and deeper water masses into the North Atlantic current systems. However, linking modern observations and historical times series with past records on Labrador Sea climate variability has been hampered by the lack of robust quantitative paleothermometers. Therefore, after re-calibrating the ketone unsaturation index of C37 long-chain hydrocarbon molecules in the temperature range between 0 and 10° C by comparing index values from recent surface sediments with ambient temperatures and salinities from the Greenland and Labrador Margins, we generated Holocene time series of surface temperatures and meltwater events. While sea surface temperatures in the eastern Labrador Sea, Westgreenland Current, have varied between 2 and 10°C, with higher meltwater intrusions leading to cooling in fjords, first results from the western Labrador Sea, Labrador Current, point to on average much colder surface temperatures between -1 and 5° C for the Labrador Basin outflow. This general E-W temperature difference in surface waters manifests the occurence of the modern surface temperature gradient, and thus a circulation pattern similar to modern conditions since the Holocene climate optimum about 7.000 years BP. Furthermore, the new temperature records will allow to infer on interactions between Labrador Sea surface circulation, sea-ice built up and retreat, as well as meltwater intrusions at the terminal stage of the glacial ice-sheet melting.