Two high-resolution (1 km grid) numerical model simulations of the Amundsen Sea, West Antarctica, are used to study the role of the ocean in the mass loss and grounding line retreat of Pine Island Glacier. The first simulation uses BEDMAP bathymetry under the Pine Island ice shelf, and the second simulation uses NASA IceBridge-derived bathymetry. The IceBridge data reveal the existence of a trough from the ice-shelf edge to the grounding line, enabling warm Circumpolar Deep Water to penetrate to the grounding line, leading to higher melt rates than previously estimated. The mean melt rate for the simulation with NASA IceBridge data is 28 ma–1, much higher than previous model estimates but closer to estimates from remote sensing. Although the mean melt rate is 25% higher than in the simulation with BEDMAP bathymetry, the temporal evolution remains unchanged between the two simulations. This indicates that temporal variability of melting is mostly driven by processes outside the cavity. Spatial melt rate patterns of BEDMAP and IceBridge simulations differ significantly, with the latter in closer agreement with satellite-derived melt rate estimates of ~50ma–1 near the grounding line. Our simulations confirm that knowledge of the cavity shape and its time evolution are essential to accurately capture basal mass loss of Antarctic ice shelves.