Response in atmospheric circulation and sources of Greenland precipitation to glacial boundary conditions

The response in northern hemisphere atmospheric circulation and the resulting changes in moisture sources for Greenland precipitation to glacial boundary conditions are studied in NCAR’s CCM3 atmospheric general circulation model fitted with a moisture tracking functionality. We employ both the CLIMAP SST reconstruction and a modification thereto with reconstructions of glacial ice sheets and land masks. The individual components of the boundary conditions are added first one at a time and, finally, together. These steps show the atmospheric circulation to respond approximately linearly to the boundary condition changes, and the full glacial change may thus be decomposed into contributions from SST and topography changes, respectively. We find that using the CLIMAP SST reconstruction leads to a shift from Atlantic toward Pacific source regions not found with the modified reconstruction having cooler tropics and less sea ice. The occurrence of such a shift depends chiefly on the SST reconstruction and not on the existence of the large northern hemisphere glacial ice sheets. The influence of these circulation changes on important factors for ice core interpretation such as precipitation seasonality, condensation temperatures and source temperatures are assessed.