ALBERT

Description: Variability of mass changes at basin scale for Greenland and Antarctica The Cryosphere Discussions, 6, 3397-3446, 2012 Author(s): V. R. Barletta, L. S. Sørensen, and R. Forsberg During the last decade, the GRACE mission has provided valuable data for determining the mass changes of the Greenland and Antarctic ice sheets. Yet, discrepancies still exist in the published mass balance results, and analyses on the sources of errors and discrepancies are lacking. Here, we present monthly mass changes together with trends derived from GRACE data at basin scale for both the Greenland and Antarctica ice sheets and we assess, for the first time systematically, the variability and errors for each of the possible sources of discrepancies: mass inference methods, data sets and background models. We find a very good agreement between the monthly mass change results derived from two independent methods, which represents a cross validation. For the monthly solutions, we find that most of the variability is caused by the use of different data sets rather than different methods. Besides the well-known GIA trend uncertainty, we find that the degree-1 variability and the recent de-aliasing corrections have significant impact on monthly time series and trends respectively. We also show the remarkable differences between the use of release RL04 and the new RL05, and how the latter results in smaller mass trends for the majority of the basins. The overall variability of the solutions well exceeds the uncertainties propagated from the data errors and the leakage (as done in the past), hence we calculate new sound total errors for the monthly solutions and the trends. For the whole GRACE period our trend estimate for Greenland is −234 ± 20 Gt yr −1 and −83 ± 36 Gt yr −1 for Antarctica (−111 ± 15 Gt yr −1 in the western part). These trends show a clear (with respect to our errors) increase of mass loss in the last four years.