Fig. 2

Radar transects revealing subglacial landforms in grounded ice and basal channels incised upwards beneath floating ice. a A–A’, b B–B’, d C–C’, d D–D’, e E–E’, f F–F’, g G–G’, h H–H’, i i-i', j j-j', k k-k', l L–L’, m M–M’, n N–N’, and o O–O’, as located in Fig. 1. Extended versions of i-i' (I-I'), j-j' (J-J') and k-k' (K-K') can be found in Supplementary Figure 2. Also for these three transects, basal reflectivity (relative values, zero mean) and the echo abruptness are provided. For transect N–N’, the echo abruptness is provided (revealing a step change between grounded and floating ice) with the thickness of ice above the level of flotation (with a tidal range of 0 m, black line; and +5 m, pink line). The identification of three flow-parallel bedforms and U-channels, described in Supplementary Figure 5, are also shown (see Supplementary Figure 6 for locations). Separation between ice sourced from East versus West Antarctica is noted by the dashed black line. Surface elevation profiles (from the aircraft altimeter) are also shown