Solar Forcing of Holocene Sea-Ice Cover Off West Greenland

Arctic sea ice represents an important component of the climate system, since it is an effective insulator between the oceans and the atmosphere, restricting the exchange of heat, mass, momentum and chemical constituents. The ongoing severe reduction of Arctic sea ice is largely ascribed to anthropogenic effects, but the current rate of sea-ice reduction is much faster than predicted by models. Despite its importance, little is known about past changes in sea-ice cover and the underlying forcing mechanisms. The central West Greenland shelf is an area which is very sensitive to climate and in particular sea-ice variability, as it lies right at the boundary between the quite extensive sea-ice cover in the north and almost sea-ice free waters in the south. In this study, we use diatom assemblages from marine sediment cores, GA306-GC3 and GA306-GC4 located off West Greenland, to reconstruct changes in sea-ice cover over the past 6,700 years. In order to test the possible role of solar irradiance on sea ice, the sea-ice reconstruction record was compared with variations in the 14C production rate, a proxy for past solar variability inferred from atmospheric 14C concentrations measured in tree rings. The results show a strong link between sea-ice cover off West Greenland and solar variability over the past 4000 years, in particular during the last millennium. Variations in solar activity may directly drive changes in sea-ice cover in the Arctic region, which would further amplify the variations in sea-ice cover off West Greenland through a sea-ice-ocean-atmosphere feedback mechanism. In contrast, solar forcing appears to have been less important for sea-ice concentrations during earlier millennia, underlining the complex link between solar forcing and sea-ice cover. Improved understanding of the natural sea-ice variability is important for predicting future changes in Arctic sea-ice cover associated with anthropogenic influences on climate.