Modelled behaviour of subglacial drainage systems near the ice-ocean boundary

Melting at the ice-ocean interface exerts a critical control on ice sheet response to climate change. It is controlled by the temperature and salinity of the ocean water, but is also strongly influenced by discharge of meltwater from beneath the ice. This fresh water source initiates a buoyant plume that rises up the ice face, entraining heat from the ocean to melt the ice. To fully understand ocean melting it is necessary to understand how meltwater emerges from beneath the ice sheet. In this work, we use recent models of the subglacial drainage system to examine the likely mode of melt water delivery across the grounding line. Rothlisberger channels are expected to 'trumpet' out as the ocean is approached, due to a lack of confining stress to counteract wall melting. We calculate the expected size of these channels at the grounding line. More detailed theory suggests that the channels may in fact become drained close to the grounding line, the water being dispersed laterally into a distributed system. We calculate the resulting distribution of melt water delivery across the grounding line. Implications of the results for the melting rate of the ice front will also be discussed.