Greenland Ice Sheet surface mass-balance modelling and freshwater flux for 2007, and in a 1995-2007 perspective

The freshwater flux from the Greenland Ice Sheet (GrIS) to the ocean is of considerable importance to the global eustatic sea level rise. A physical modelling approach using SnowModel, a state-of-the-art snow-evolution modelling system that includes four submodels (MicroMet, EnBal, SnowPack, and SnowTran-3D), was used to quantify the 1995–2007 GrIS surface massbalance (SMB), including freshwater flux. Meteorological observations from 26 meteorological stations located on the GrIS (Greenland Climate Network; GC-Net stations) and in coastal Greenland (Danish Meteorological Institute (DMI) WMOstations) were used as model inputs. The GrIS minimum surface melt extent of 29% occurred in 1996, while the greatest extent of 51% was present in 2007. The 2007 melt extent was 20% greater than the average for 1995–2006. The year 2007 had the highest GrIS surface runoff (523 km3 y 1) and the lowest SMB ( 3 km3 y 1); the only year with a negative GrIS SMB. Runoff in 2007 was approximately 35% greater than average for 1995–2006. From 1995 through 2007 overall, precipitation decreased while ablation increased, leading to an increased average SMB loss of 127 km3. The modelled GrIS SMB was merged with previous estimates of GrIS subglacial runoff (from geothermal melt) and GrIS calving to quantify GrIS freshwater flux to the ocean, indicating an average negative mass-balance of 265 (š83) km3 y 1. This study further suggests an average GrIS freshwater flux of approximately 786 km3 y 1 to the ocean, of which 45% occurs from iceberg calving and geothermal bottom melting. The average annual GrIS freshwater flux equals 2Ð1 š 0Ð2 mm w.eq. y 1 in eustatic sea level rise, indicating a cumulative flux of 28 mm w.eq. from 1995 through 2007. The average GrIS net loss contributes to a net sea level rise of 0Ð7 š 0Ð2 mm w.eq. y 1, and a cumulative net increase of 10 mm w.eq. Copyright  2009 John Wiley & Sons, Ltd.