Regional setting. (a) Subglacial topography from new PolarGAP survey (strong colours), ICEGRAV56,57 and BEDMAP258. Yellow outline marks region of enhanced basal melting. Pink outlines are Recovery Lake shorelines26, dark and pale blue triangles mark ‘static’ radar-detected and ‘dynamic’ satellite-detected subglacial lakes, respectively17. Foundation Ice Stream (FIS) and Beardmore Glacier (BG) catchments marked in red and blue respectively. N/BD indicates Nimrod/Byrd Glacier catchments. Black box locates Fig. 2. (b) Present ice velocity map19. Thick and thin black contours show 100 and 25 m a−1 flow velocities respectively. Orange lines mark FIS and BG catchments. Note region of former enhanced flow to FIS13 (grey hash) extending ~250 km further inland and black dashed line close to South Pole marking a relic shear margin16.