Estimate of Greenland and Antarctic ice-sheet total discharge from multiple GRACE solutions

Abstract. In this work a method for the estimation of 2003–2010 monthly-mean total discharge from Greenland and Antarctica is presented. We show that measurements of time-variable gravity from GRACE when combined with estimates of precipitation and sublimation can realistically reconstruct the total discharge from the ice-sheets into the ocean. In particular, the total discharge has been calculated as a 8-member ensemble-mean obtained by combining multiple GRACE solutions with water fluxes from both an high resolution regional atmospheric climate model (RACMO2) and a global reanalysis (ERA-Interim). The gravimetric measurements of mass variations and the precipitation and sublimation atmospheric fields have been combined in the ice-sheets water mass balance equation, according to the main drainage basin systems. The use of the combined land-atmosphere water mass balance has also been tested, which however led to a large underestimation of total discharge. A comparison among the different GRACE solutions is also performed, highlighting similarities and differences and analyzing the possible causes. GRACE datasets show similar ice-sheet mass trends on Antarctica and over the majority of the Greenland basins, while significant differences (up to a factor of 1.9) have been found in mass-loss areas characterized by strongly negative water height trends. This is likely primarily caused by the different pre-processing techniques applied to the raw gravimetric data.