A spatially calibrated model of annual accumulation rate on the Greenland Ice Sheet (1958-2007)

Past estimates of Greenland Ice Sheet accumulation rates have been multiyear climatologies based on ice/firn cores and coastal precipitation records. Existing annually resolved estimates have incompletely quantified uncertainty, owing primarily to incomplete spatial coverage. This study improves upon these shortcomings by calibrating annual (1958-2007) solid precipitation output from the Fifth Generation Mesoscale Model modified for polar climates (Polar MM5) using firn core and meteorological station data. The calibration employs spatial interpolation of regionally derived linear correction functions. Residual uncertainties exhibit coherent spatial patterns, which are modeled via spatial interpolation of root mean squared errors. Mean 1958-2007 Greenland Ice Sheet annual accumulation rate is 337 +/- 48 mm/yr water equivalent (w.e.) or 591 +/- 83 Gt/yr. Annual estimates contain one standard deviation uncertainties of 74 mm/yr w.e., 22%, or 129 Gt/yr. Accumulation rates in southeast Greenland are found to exceed 2000 mm/yr w.e. and to dominate interannual variability in Greenland Ice Sheet total accumulated mass, representing 31% of the whole. Accumulation rates in the southeast are of sufficient magnitude to affect the sign of Greenland mass balance during some years. The only statistically significant temporal change in total ice sheet accumulation in the 1958-2007 period occurred between 1960 and 1972, when a simultaneous accumulation increase and decrease occurred in west and east Greenland, respectively. No statistically significant uniform change in ice sheet-wide accumulation is evident after 1972. However, regional changes do occur, including an accumulation increase on the west coast post-1992. The high accumulation rates of 2002-2003 appear to be confined to the southeast.