Robert Law , Poul Christoffersen, Emma MacKie, Samuel James Cook , Marianne Haseloff, Olivier Gagliardini

Uncertainty associated with ice motion plagues sea-level rise predictions. Much of this uncertainty arises from imperfect representations of physical processes including basal slip and internal ice deformation, with ice-sheet models largely incapable of reproducing borehole-based observations. To investigate further, we model isolated 3D domains from fast-moving (Sermeq Kujalleq or Store Glacier) and slow-moving (Isunnguata Sermia) ice-sheet settings in Greenland. By incorporating realistic geostatistically simulated topography, we show that a layer of basal temperate ice (much softer ice at the pressure-melting point) with spatially highly variable thickness forms naturally in both settings, alongside ice-motion patterns which are far more complex than previously considered. Temperate ice is vertically extensive in deep troughs, but thins notably over bedrock highs. Basal-slip rates are interconnected with this variability, reaching >90% or <5% of surface velocity dependent on setting. This realistic representation of ice-sheet motion opens new pathways for improving parameterizations in large-scale ice-sheet models.