Sea Ice and Dynamical Controls on Preindustrial and Last Glacial Maximum Accumulation in Central Greenland

Greenland has experienced large changes since the last glacial with its summit warming by approximately 218C, average accumulation rates tripling, and annual amplitudes of temperature and accumulation seemingly declining. The altered seasonal cycle of accumulation has been attributed to a combination of the large-scale dynamical response of the North Atlantic storm track to surface boundary conditions and the modulation of moisture availability due to changes in winter sea ice cover. Using atmospheric simulations of preindustrial and glacial climate, the contributions of these two mechanisms are evaluated. Estimates of moisture source footprintsmake it possible to distinguish between long-range transport related to the storm track and regional transport from the ocean surface near Greenland. It is found that the contribution of both mechanisms varies significantly with the background climate.With greater ice cover and theNorthAtlantic storm track locked to the topographically enhanced stationary wave during the glacial, seasonal migration of the sea ice edge becomes relatively important in controlling moisture availability. In contrast, the preindustrial simulation has relatively greater transient eddy activity and is less moisture limited by sea ice extent, so accumulation is more strongly related to synoptic variability in the North Atlantic. These results highlight how changes in atmospheric circulation and sea ice together explain the shifts in annual mean and seasonal moisture supply to Greenland. Also discussed are some implications of the inferred narrow source distribution of accumulation during the glacial for the interpretation of stable isotopes derived from the central Greenland ice cores.