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

Abstract

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.

Spatially extensive estimates of annual accumulation in the dry snow zone of the Greenland Ice Sheet determined from radar altimetry

“…A clear gradient in the thickness of each layer and in the associated estimates of annual accumulation is seen along the transect, with a 33.6% ± 16% mean decrease in accumulation from west to east each year. This trend has been observed in previous studies (Fischer et al, 1995;Anklin and Stauffer, 1994;Burgess et al, 2010) and reflects the dominant transport of water vapour in the region from west to east. Inter-annual variability in accumulation has also been observed previously (Fischer et al, 1995).…”

“…Meanwhile, there are reports of an increase in the surface elevation at higher altitudes since 1990 (Krabill et al, 2000;Nghiem et al, 2005;Hanna et al, 2006), supporting calibrated climate models which show that some regions of the ice sheet have experienced higher than average accumulation rates, especially in the south (Burgess et al, 2010). A recent modelling study found larger than average accumulation rates across the GrIS between 1958 and 2007, and that the surface mass balance over the same period is between 32-63% higher than previous estimates (Ettema et al, 2009).…”

Dynamically and Observationally Constrained Estimates of Water-Mass Distributions and Ages in the Global Ocean

“…cs.umt.edu/isis/index.php/SeaRISE_Assessment), which is fairly similar to our inversion setup. The datasets include mean annual surface temperature from Fausto et al [2009], precipitation rates from Burgess et al [2010], basal heat flux from Shapiro and Ritzwoller [2004], and bedrock topography, ice thickness and surface elevation from Bamber et al [2001]. Observed surface velocities are also provided by Joughin et al [2010] and filled with balance velocities [see, e.g., Bamber et al, 2000] in the areas where observations are not available.…”

Changes in the firn structure of the western Greenland Ice Sheet caused by recent warming

“…Cores 6945 and 6943 (named for the coordinates where they were acquired) are ∼ 18 m long and extend back to 1976 while core 6941 is 11.7 m long and extends to a depth equating to 1985's accumulation. The thickness of the different annual layers is affected by annual snowfall, deflation and redeposition by wind, compaction, and melting, and varies on the order of tens of cm from year to year in western Greenland (McConnell et al, 2000;de la Peña et al, 2010;Burgess et al, 2010). Small amounts of ice are commonly found in the core, but are not present on an annual basis.…”