Abstract
We combine estimates of the surface mass balance, SMB, of the Greenland ice sheet for years 1958 to 2007 with measurements of the temporal variability in ice discharge, D, to deduce the total ice sheet mass balance. During that time period, we find a robust correlation (R2 = 0.83) between anomalies in SMB and in D, which we use to reconstruct a continuous series of total ice sheet mass balance. We find that the ice sheet was losing 110 ± 70 Gt/yr in the 1960s, 30 ± 50 Gt/yr or near balance in the 1970s–1980s, and 97 ± 47 Gt/yr in 1996 increasing rapidly to 267 ± 38 Gt/yr in 2007. Multi‐year variations in ice discharge, themselves related to variations in SMB, cause 60 ± 20% more variation in total mass balance than SMB, and therefore dominate the ice sheet mass budget.
Highlights
We find no significant reduction in SMB accuracy in the pre-satellite era, prior to 1978, for Box and Hanna values
[9] Ice discharge, D, for reference year 1996 or 2000, is calculated as the flux, F, at the flux gate plus the reference SMB for the area in between the flux gate and the calving front or grounding line. This assumes that the glacier lower elevations are in balance with the reference SMB on that reference year
North of basin 25, we assume no change in speed since these glaciers did not accelerate in the 2000s
Summary
[2] Airborne altimetry measurements collected in the 1990s showed that the Greenland ice sheet was thinning along its periphery and slightly thickening in the interior [Krabill et al, 1999]. Enhanced melt reduced the annual input of mass at the ice surface and thinned the glaciers in their frontal regions, which caused them to unground and accelerate toward the sea by 150 – 210% [Thomas, 2004; Howat et al, 2007; Rignot and Kanagaratnam, 2006; Luckman et al, 2006]. In comparison, bed lubrication accelerates outlet glaciers by only 8 – 10% during months of peak melting [Rignot and Kanagaratnam, 2006; Joughin et al, 2008].
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