Complex motion of Greenland Ice Sheet outlet glaciers with basal temperate ice

Abstract

Uncertainty associated with ice-sheet 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. Here, we model isolated 3D domains from fast-moving (Sermeq Kujalleq/Store Glacier) and slow-moving (Isunnguata Sermia) ice-sheet settings in Greenland. By incorporating realistic geostatistically simulated topography, we show that a spatially highly variable layer of temperate ice (much softer ice at the pressure-melting point) forms naturally in both settings, alongside ice-motion patterns which diverge substantially from those obtained using smoothly varying BedMachine topography. Temperate ice is vertically extensive (>100 m) in deep troughs, but thins notably (<5 m) over bedrock highs, with basal-slip rates reaching >90% or <5% of surface velocity dependent on topography and temperate-layer thickness. Developing parameterizations of the net effect of this complex motion can improve the realism of predictive ice-sheet models