Modelling the behaviour of Greenland outlet glaciers

Rapid ice-sheet changes such as thinning and flow acceleration originate in, and spread from restricted regions of fast flow such as ice streams and outlet glaciers. Such rapid changes as observed for several Greenland outlet glaciers cannot be explained by the existing large-scale ice-sheet models that are based on the Shallow Ice Approximation, as they lack the necessary spatial resolution, an adequate treatment of the grounding line motion and do not consider the longitudinal transfer of stresses. The aim of this study is, firstly, to develop an adequate numerical model that can simulate this behaviour of outlet glaciers, in particular, to include longitudinal stresses and grounding line migration into a flowline model. Secondly, such a model is then used to investigate the interaction between ice-marginal processes and discharge from the interior through upstream transmission of perturbations. We use remotely sensed data (e.g. changes of surface elevation, velocity and front position) from Helheim Glacier, East Coast Greenland to refine and validate the model. We compare model response to perturbations in the frontal region and evaluate the role of longitudinal stresses in the retreat-thinning feedback. Such a comparison gives us important insights on the requirements for numerical models to improve our ability to predict future ice-sheet change.