Is East Antarctica gaining more mass than West Antarctica is losing?

The East Antarctic Ice Sheet (EAIS) has the greatest potential to contribute to sea level rise than any source, including non-glacial contributors. It is, however, the most challenging ice mass to constrain due to the relative paucity of in-situ observations and the poor signal-to-noise ratio of Earth Observation data. The West Antarctic Ice Sheet (WAIS), on the other hand, has been the subject of several investigations and there is relatively good agreement between estimates of its mass loss from different independent techniques. Here we combine GRACE, satellite altimetry and GPS data in a statistical framework to constrain the mass balance of Antarctica over the period 2003-13. We investigate the impact of different assumptions regarding the origin of elevation changes of EA. The statistical framework partitions mass trends between surface mass balance and ice dynamics based on physical principles and measures of statistical likelihood. Without imposing any partition, for EA the model apportions about a third of the mass trend to ice dynamics, +18 Gt/yr, and two thirds, +39 Gt/yr, to SMB, resulting in a total mass trend of 57±20 Gt/yr. The total mass trend for WA over the same period was -112±10 Gt/yr. We then imposed the condition that the surface mass balance is tightly constrained by RACMO2.3 and assumed that residual height changes were due to ice dynamics, replicating the hypothesis of dynamic thickening proposed in a recent study (Zwally et al 2015). By imposing these conditions, results for EA showed a larger dynamic signal, 87±21 Gt/yr, which was partially offset by a negative trend in SMB, resulting in an overall trend of 56±15 Gt/yr. Even after forcing an ice dynamic trendover the EAIS, we are unable to reproduce the large positive trend obtained in Zwally et al (2015). We conclude that, irrespective of any assumption made about the density of surface elevation changes, mass gains in the EAIS do not exceed mass losses in the WAIS over the studied period.