Plenary Speaker

Dr Christina Hulbe

Rapid change in the Amundsen Sea sector of West Antarctica raises concern that a threshold for unstoppable grounding line retreat has been or is about to be crossed. The grounding line is a transition between ice that is resting on the sea floor and ice that is floating in the ocean. As ice flows across this boundary, water that had been stored away in the ice sheet returns to the global ocean. In its simplest form, the threshold for unstoppable retreat is due to the inland-deepening bed of the glacier together with the power-law relationship between ice thickness and ice flux across the boundary. More completely, stability of the grounding line position depends on the three-dimensional shape of the landscape through which the glacier flows and processes acting at its boundaries. The focus here is the shape of, and spatial variation in, the subglacial bed. Using a dynamical model of ice sheet flow, we show that as the grounding line retreats, the threshold for runaway retreat does not occur a place but through a set of processes and that small differences in forcing lead to large differences in retreat rate and ice discharge across the grounding line. Put another way, there is neither reason to panic when particular geographic waypoints are passed, nor reason to be relieved that they have not. Retreat may be inevitable past a certain dynamical threshold, but the rate at which the retreat proceeds remains in our control.