Fig. 2: Sea-floor bathymetry shows smooth retreat and ice–bed interactions near the TEIS GL.

The sea-floor bathymetry near the TEIS GL is characterized by along-flow ridged bedforms having several different wavelengths, as well as evidence for two possible former GL positions (white and red boxes) and channelized subglacial outflow (black box). Data in a–d are from downward-facing bathymetric sonar and e from forward sonar on Icefin. Reworked sediments (white box) are observed near the borehole (yellow circle). b, A single sinuous 2–3-m-tall slope consistent with a GL sediment wedge is found about 200 m north of the 2016 GL estimated from remote sensing (red boxed region from a; red arrows denote wedge). The wedge crosscuts the 2–5-m wavelength along-flow bedforms (Extended Data Figs. 5 and 6). c, An isolated 4-m-deep channel cut into the sea floor makes two sharp turns and includes a segment that cuts perpendicular to most bedforms, suggesting that this feature formed from rerouting of subglacial water as the GL retreated (Extended Data Fig. 5). d, The bedform topography near the GL of T2 shows evidence of linear ridges striking north (Extended Data Fig. 4). e, Forward-looking sonar data of the ice base near the GL shows that the ice has the same 2–5-m-wavelength ridges as the shortest-wavelength features on the sea floor. These data together suggest that GL retreat has been largely continuous over the observable period, since at least 2011 based on remote sensing. Moreover, the similarities between the bed and ice morphology at the GL suggest that the ice–bed interactions set up slopes that are then progressively melted by the intruding seawater. Bathymetric sonar, a–d, was processed in Qimera and projected using QGIS. Forward sonar are projected using the Oculus ViewPoint software.