Annual accumulation for Greenland updated using ice core data developed during 2000–2006 and analysis of daily coastal meteorological data

Abstract

[1] An updated accumulation map for Greenland is presented on the basis of 39 new ice core estimates of accumulation, 256 ice sheet estimates from ice cores and snow pits used in previous maps, and reanalysis of time series data from 20 coastal weather stations. The period 1950-2000 is better represented by the data than are earlier periods. Ice-sheetwide accumulation was estimated based on kriging. The average accumulation (95% confidence interval, or ±2 times standard error) over the Greenland ice sheet is 30.0 ± 2.4 g cm À2 a À1 , with the average accumulation above 2000-m elevation being essentially the same, 29.9 ± 2.2 g cm À2 a À1 . At higher elevations the new accumulation map maintains the main features shown in previous maps. However, there are five coastal areas with obvious differences: southwest, northwest, and eastern regions, where the accumulation values are 20-50% lower than previously estimated, and southeast and northeast regions, where the accumulation values are 20-50% higher than previously estimated. These differences are almost entirely due to new coastal data. The much lower accumulation in the southwest and the much higher accumulation in the southeast indicated by the current map mean that long-term mass balance in both catchments is closer to steady state than previously estimated. However, uncertainty in these areas remains high owing to strong gradients in precipitation from the coast inland. A significant and sustained precipitation measurement program will be needed to resolve this uncertainty.

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).…”

“…Our mean accumulation estimates are higher than between 1977-89 (Anklin and Stauffer, 1994) at sites above 3100 m, with increases in accumulation of 15% and 22%, but with no significant change at sites below 3000 m (Table 3). The ERA-40 model over-predicts the ASIRAS derived accumulation rates by an average of 16.2%.…”

“…Mean accumulation rates (in m.w.e.) with elevation derived from ASIRAS every 25 km along the transect in conjunction with field data (Fischer et al, 1995;Anklin and Stauffer, 1994) and model results. The observed % change in accumulation are estimated from a comparison between the ASIRAS data and ground observations made by Anklin and Stauffer.…”

“…The calculated mean accumulation rates at 25 km intervals along the transect are presented (Table 3) in conjunction with both the mean annual estimates derived from the ERA-40 data-based model output and estimates made from two previous field based studies (Fischer et al, 1995;Anklin and Stauffer, 1994). Our mean accumulation estimates are higher than between 1977-89 (Anklin and Stauffer, 1994) at sites above 3100 m, with increases in accumulation of 15% and 22%, but with no significant change at sites below 3000 m (Table 3).…”

“…Thus stratigraphically distinct layers in the snowpack, as are commonly formed early in the fall in the dry snow region of the GrIS (Autumn hoar), make it possible to identify widespread internal layers reflecting annual accumulation (Hawley et al, 2006). An advantage in using the Autumn hoar to identify annual layers is that it coincides with the commonly used concept of a mass balance year for an ice sheet, lasting typically from the onset of accumulation (in Autumn) in one year to the cessation of ablation (end-of-summer) the next year (Anklin and Stauffer, 1994). Thus, when referring to the observed accumulation rate in 1999, we are referring to the period from the end-of-summer of 1998 to the end-of-summer of 1999.…”