Tipping point behaviour of submarine melting at ice sheet grounding zones

Ice sheets are highly sensitive to melting in their grounding zones, where they transition from grounded ice to floating. Recent models of the interaction between warm salty ocean water and cold fresh subglacial discharge in the grounding zone suggest that warm water can intrude kilometres beneath the ice sheet, with important consequences for ice dynamics.

Here, we couple a model for warm water intrusion to a simple model of melting and, in doing so, capture a previously ignored feedback between geometry and subglacial water flow that occurs as the grounding zone responds to melting. This feedback enhances the potential for warm water to intrude beneath the grounded ice sheet, and therefore makes high melting in grounding zones more likely.

Intriguingly, our results also suggest that increases in ocean temperature can lead to a tipping point being passed, beyond which ocean water intrudes indefinitely beneath the ice sheet by a process of runaway melting, suggesting a candidate mechanism for dramatic changes in grounding-zone behaviour that are not currently included in ice sheet models, and which may enable them to reproduce previous high warm-period sea levels.