Multicomponent modelling of summer acceleration at the margin of the Greenland Ice Sheet

Increasing surface runoff from the Greenland Ice Sheet due to a warming climate not only accelerates ice mass loss by altering surface mass balance, but may also lead to increased dynamic losses. This is because surface melt draining to the bed can reduce ice-bed coupling, leading to faster ice flow. Understanding the impact of surface melt on ice dynamics is important for constraining the contribution of the Greenland Ice Sheet to sea level rise. The aim of this research is to numerically model the influence of surface runoff on ice velocities during the summer melt season. A multicomponent model integrating the main components of the ice sheet system is presented and applied to the Russell Glacier Area. This model consists of a surface hydrology model, interfaced with a coupled subglacial hydrology model/ice flow model. A key challenge for simulations applying a coupled ice-flow/hydrology model is state and parameter initialization. This challenge is addressed by a workflow for incorporating modelled subglacial water pressures into inversions of basal drag. The subglacial hydrology model is run for a winter season, and the output is used to invert for basal drag at the start of the melt season. The coupled ice-flow/hydrology model is initialized using this workflow and driven using output from the supraglacial hydrology model. Three recent melt seasons are modelled. To a first order, predicted ice velocities match measured velocities at multiple GPS sites. This affirms the conceptual model that summer velocity patterns are driven by transitions between distributed and channelized subglacial hydrological systems.