Improving constraints on the basal ice/bed properties is essential for
accurate prediction of ice-sheet grounding-line positions and stability.
Furthermore, the history of grounding-line positions since the Last
Glacial Maximum has proven challenging to understand due to
uncertainties in bed conditions. Here we use a 3D full-Stokes ice-sheet
model to investigate the effect of differing ocean bed properties on
ice-sheet advance and retreat over a glacial cycle. We do this for the
Ekström Ice Shelf catchment, East Antarctica. We find that predicted ice
volumes differ by >50%, resulting in two entirely
different catchment geometries triggered exclusively by variable ocean
bed properties. Grounding-line positions between simulations differ by
>100% (49 km), show significant hysteresis, and migrate
non-steadily with long quiescent phases disrupted by leaps of rapid
migration. These results highlight that constraints for both bathymetry
and substrate geologic properties are urgently needed for predicting
ice-sheet evolution and sea-level change.