Fig. 4: Ocean currents and ice topography contribute to variable melting in terraces and crevasses.

Here the Icefin vehicle track is shaded by relative along-track distance from downstream (white) to upstream (black) and current velocities are shaded from slowest (white) to fastest (purple). a, Horizontal and vertical trends near a corner of a wide terrace (1,900 m downstream in T1 near the borehole) show freshening and cooling water inside the terrace and slowing currents as the water feels the influence of the ice interface. The grey lines denote the bottom of the terrace. Vertical profiles of ocean-current speed (U), thermal driving (Θ − Θ_f), absolute salinity (S_A) and dissolved oxygen (DO) binned with distance from the ice base show that, although the water is warm close to the interface, the current velocity slows in the boundary layer, suggesting breaking from friction at the interface²⁸. b,c, As in a for the furthest crevasse from the GL, observed along both T1 (b) and T2 (c). The panels on the right are binned with distance from the top of a step in the crevasse sidewall along T1 marked with the upper grey line. The lower grey line indicates the elevation of the bottom of the crevasse in T1. Stars in b relate to the location in the left panel. These panels show warm water with thermal driving of nearly 1.8 °C (Θ − Θ_f) reaching the crevasse walls accompanied by very slight freshening and oxygen increase that indicate melting (S_A and DO) that would then rise into the crevasse.