Modelling snow accumulation on Greenland in Eemian, glacial inception and modern climates in a GCM

Abstract

Abstract. Changing climate conditions on Greenland influence the snow accumulation rate and surface mass balance (SMB) on the ice sheet and, ultimately, its shape. This can in turn affect local climate via orography and albedo variations and, potentially, remote areas via changes in ocean circulation triggered by melt water or calving from the ice sheet. Examining these issues in the IPSL global model requires improving the representation of snow at the ice sheet surface. In this paper, we present the new snow scheme implemented in LMDZ, the atmospheric component of the IPSL coupled model. We analyze surface climate and SMB on the Greenland ice sheet under insolation and oceanic boundary conditions for modern, but also for two different past climates, the last glacial inception (115 kyr BP) and the Eemian (126 kyr BP). While being limited by the low resolution of the GCM, present-day SMB is on the same order of magnitude as recent regional model findings. It is affected by a moist bias of the GCM in Western Greenland and a dry bias in the north-east. Under Eemian conditions, the SMB diminishes largely, and melting affects areas with today high surface altitude including recent ice core drilling sites as NEEM. In contrast, glacial inception conditions lead to a higher mass balance overall due to the reduced melting in the colder summer climate. Compared to the widely applied positive degree day (PDD) parameterization of SMB, our direct modelling results suggest a weaker sensitivity of SMB to changing climatic forcing. In addition, significant differences in surface climate and SMB are found between simulations using monthly climatological mean and actual interannually varying monthly mean forcings for the ocean surface temperature and sea ice cover, in particular for the Eemian.