Investigating the stability of Greenland’s outlet glaciers

The Greenland Ice Sheet is the fastest growing contributor to sea level rise, due to loss of ice from its marine-terminating outlet glaciers. One of the largest of these is Helheim Glacier, located in eastern Greenland. Recent observational work suggests that Helheim could be approaching a threshold beyond which it would undergo rapid retreat. Here, we present a modelling study investigating the stability of Helheim Glacier. We seek to establish whether such a threshold exists in the future evolution of this glacier, and whether a rapid retreat event would be reversible. We approach this by initialising the model to a steady state close to the present-day geometry of the glacier, then carrying out a series of experiments to test its stability in relation to changes in atmospheric and ocean forcing. Calving front positions at the ocean interface and mass balance at the surface are perturbed incrementally, and the system allowed to reach a new steady state after each perturbation. The forcing is then reversed in order to assess whether the resulting changes to the glacier’s position and dynamics are reversible. Our methodology is demonstrated in synthetic geometries representative of Greenlandic fjord environments, in which we find a hysteresis behaviour within the system such that after a retreat of the ice front, readvance will not occur along the same pathway when the forcing is reversed. Initial results suggest that such behaviour is also present within the Helheim system.