The effect of fluctuations in surface density, accumulation and compaction on elevation change rates along the EGIG line, central Greenland

Repeated measurements of density profiles and surface elevation along a 515 km section of the Greenland ice sheet have been used to determine elevation change rates and the error in determining mass balance from these rates which arises from short-term fluctuations in mass input, compaction and surface density. Over the 28 months from spring 2004 to summer 2006 the average error over 100 km sections of the traverse ranged from -0.006 to 0.100 m a(-1). The lowest values, comparable with the system accuracy of the CryoSat radar altimeter (0.033 m a(-1)), were found below 3000 m. The surface density required to translate the elevation change into mass change decreased from 0.40 g cm(-3) at an elevation of 2348 m to 0.33 g cm(-3) at an elevation of 3264 m. From the density profiles the equivalent values for a time period of 10 years were found to be 0.48 and 0.38 g cm(-3), respectively.