Continuously accelerating ice loss over Amundsen Sea catchment, West Antarctica, revealed by integrating altimetry and GRACE data

Satellite altimetry and Gravity Recovery and Climate Experiment (GRACE) measurements have provided contemporary, but substantially different Antarctic ice sheet mass balance estimates. Altimetry provides no information about firn density while GRACE data is significantly impacted by poorly constrained glacial isostatic adjustment signals. Here, we combine Envisat radar altimetry and GRACE data over the Amundsen Sea (AS) sector, West Antarctica, to estimate the basin-wide averaged snow and firn column density over a seasonal time scale. Removing the firn variability signal from Envisat-observed ice-sheet elevation changes reveals more rapid dynamic thinning of underlying ice. We report that the net AS sector mass change rates are estimated to be - 47 \textpm 8 Gt yr- 1 between 2002 and 2006, and - 80 \textpm 4 Gt yr- 1 between2007 and 2009, equivalent to a sea level rise of 0.13 and 0.22 mm yr- 1, respectively. The acceleration is due to a combination of decreased snowfall accumulation (+ 13 Gt yr- 1 in 2002\textendash2006, and - 6 Gt yr- 1 in 2007\textendash2009) and enhanced ice dynamic thinning (- 60 \textpm 10 Gt yr- 1 in 2002\textendash2006, and - 74 \textpm 11 Gt yr- 1 in 2007\textendash2009) after 2007. Because there is no significant snowfall trend over the past 21 yr (1989\textendash2009) and an increase in ice flow speed (2003\textendash2010), the accelerated mass loss is likely to continue.