Nested modeling of high-order ice dynamics in outlet glaciers of the Greenland Ice Sheet

Classical shallow-ice approximation models of ice sheet dynamics are adequate and efficient for large parts of the continental ice sheets, but they are theoretically questionable at high resolutions (ca. 1 km). Perhaps more importantly, the shallow-ice approximation does not give a good representation of ice flow in important sectors of the ice sheet, such as the ice sheet margins and in marine-based outlet glaciers, which appear to be most sensitive to interannual and decadal-scale climate variability. We couple a high-order, finite-element model of glacier dynamics with a 3D, thermomechanical ice sheet model to provide an improved representation of Greenland Ice Sheet outlet glaciers. The large-scale ice sheet model provides boundary conditions for ice velocity, thickness, and effective viscosity at the upstream boundary of the finite element model. The boundary location is determined by the inland position at which vertical shear becomes the dominant deformation mechanism, at which point a full Stokes solution is unnecessary. The coupled model better resolves the dynamics and high velocities that characterize the major outlet glaciers of the Greenland Ice Sheet.