Extended Data Fig. 6: Sea-floor topography suggests past dynamics influencing the retreat of Thwaites Glacier.

a, Sonar-derived bathymetry from the borehole to the nearest approach made to the GL, coloured by depth, with callouts for panels b and c (after Fig. 2, bathymetry and profiles produced with Qimera and projected in QGIS). b,c, Close-up views showing details of two regions of the survey, after Fig. 2. Red and white lines indicate the position of profiles found in d–g. d,e, Linear profiles of a crosscutting approximately 3-m-tall sinuous ridge are consistent with a past grounding event allowing enhanced sediment deposition in this area. This is the only such feature in the survey data. f,g, Linear profiles across a possible former subglacial channel near the GL. In f, a 5-m-deep U-shaped trough in the sediment begins parallel to ice flow but then cuts perpendicular to ice flow across lineated bed features and then turns sharply, which could be consistent with a channel incised by subglacial outflow into the sediment. In g, the upstream extent of the trough is less conspicuous, suggesting either modification as the ice ungrounded or that the SGW was not routed discretely through this area.