A record negative Greenland ice sheet surface mass balance rate in 2007

Results made with the regional climate model MAR show a record surface melt (592 km³/yr = a global sea level rise of 1.6 mm/yr) of the Greenland ice sheet (GrIS) during summer 2007 compared with 1970-2006. This record melt, detected also in the microwave satellite data, is associated with very low snowfall (508 km³/yr) inducing a negative Surface Mass Balance (SMB) rate of -65 km³/yr. Such a negative simulated SMB rate is unprecedented in the recent Greenland history. The summer 2007 is associated with a positive SST anomaly, a negative 2006-2007 GrIS winter accumulation and anomalous advection of warm air masses over the GrIS. Sensitivity experiments carried out by the MAR model evaluate the impacts of these anomalies on the Greenland climate and SMB. The main impacts of a warmer SST anomaly in the MAR model are more precipitation over Greenland due to an enhanced evaporation above the ocean and, an increase of surface melt induced by the advection of warmer oceanic air (>0°C) into the continent by the atmospheric part of MAR. A negative winter accumulation anomaly exposes ice and old snow (with a lower albedo) earlier than previous years in the ablation zone which significantly increases the melting given the albedo feedback. Finally, changes in the boundaries forcing of the MAR model test the consequence of the anomalous persistent southerly airflow during June and July.