(a) The repeat flight path of the 2002 and 2009 Operation IceBridge (OIB) campaigns, with the letters S-S′, P-P′ and K-K′ marking the endpoints of the profiles in Figs 2, 3, 4. Colour scale shows bottom ice elevation changes at crossover locations of non-repeating OIB tracks between the years 2009 and 2014. At each crossover location, the bottom elevation of the earlier year is subtracted from that of the latter, hence positive values indicate bottom ice loss. The differences found are then averaged over the length of the time interval to facilitate comparisons. Uncertainty varies between ∼35 m per year for the 1-year interval to ∼7 m per year for the 5-year interval (Methods). Grounding lines are from refs 13 and 19, and background image is from the 2008–2009 MODIS Mosaic of Antarctica50 (MOA). (b) The study area of Fig. 1a located on a map of the ASE region by the white rectangle showing the flight paths analysed here of the 2002 and 2009 OIB campaigns, and the 2004 AGASEA campaign along the Smith-Kohler glacier trunk. (c) Surface lowering rates for the period 2003–2009 adapted from ref. 1. The authors used ICESat-1 measurements with the necessary corrections, with ATM and other data products applied as additional constraints to the surface shape and elevation time series.