Testing the influence of subglacial erosion on the long-term evolution and stability of continental ice sheets using numerical modelling

Focussed erosion beneath continental ice sheets promotes efficient evacuation of ice along fast-flowing marine outlet glacier systems. Theory indicates that bed profiles should tend toward uniformly overdeepened geometries that will reduce ice sheet stability because (a) grounding lines situated on negative slopes are vulnerable to catastrophic retreat and (b) grounding-line stability is sensitive to ice velocity, meaning grounding lines should become unstable as overdeepening causes subglacial water pressures and basal sediment thickness and continuity to increase. This suggests a conceptual model of ice-bed evolution in which ice sheets are self-destructive, because bed erosion reduces equilibrium ice sheet volume and extent. However, many outlet glacier and ice stream systems possess complex bed topographies, raising questions about the nature of subglacial landscape evolution that have major implications for our understanding of ice sheet evolution and stability. For example, a contrasting model of ice-bed evolution in which strong ice-erosion feedbacks produce multiple overdeepenings might enhance ice sheet stability, because numerous bed undulations should resist fast ice flow and impede grounding line retreat. We therefore explore the possible glaciological significance of contrasting models of subglacial landscape evolution using a higher-order ice sheet model (iSOSIA) and assess the implications for the evolution and stability of continental ice sheets. The results will also aid understanding of contemporary ice sheet stability and identify weaknesses in process understanding that will aid further development of ice-erosion models.