Elevation change of the southern Greenland ice sheet from 1978 to 1988: Interpretation

The spatial pattern of elevation change estimates derived from satellite radar altimeter data for the period from 1978 to 1988 for the southern Greenland ice sheet is examined. As reported previously, the results from 12 ice cores widely distributed in the study area indicate that much of the spatial variability in the elevation change estimates can be explained by temporal variations in accumulation, Most notably, the areas of largest thickening and thinning, east and west of the ice divide around 66degreesN, recently experienced substantial decadal fluctuations in accumulation sufficient to explain the observed elevation change rates that span the range of +/-24 cm yr(-1). Elevation change estimates in the NW of the study area around the 2000-m elevation contour were found to be inconsistent with both short- and long-term changes in accumulation fluctuations. Examination of stratigraphy in several shallow ice cores in the NW indicates that significant melting took place in 1977 and 1978, and this was followed by many years of very little melt activity. This likely resulted in a significant downward bias in the 1978-1988 elevation change estimates in the NW. Comparison of measured surface velocities with those calculated assuming steady state balance show very good agreement overall, but there are many instances in the southeast where the steady state velocities are significantly smaller than measured surface velocities. We cannot rule out the possibility that increased ice flow in lower-elevation outlet glaciers has migrated farther upstream thereby causing negative long-term mass imbalance in southeast Greenland.