Subglacial discharge beneath ice shelves is a source of freshwater, and therefore buoyancy, at the grounding line. Being released at depth, it accelerates an ascending plume along the ice-shelf base, enhancing entrainment of ambient waters, and increasing melt rates. By now it is understood that subglacial discharge is a key control on melt rate variability at the majority of Greenland's glaciers. However, its importance in present-day and future Antarctic melt rates is less clear.
To address this point, we use the Energy Exascale Earth System Model (E3SM) and investigate the effects of subglacial discharge addition in both idealized setups and realistic, global, sea-ice ocean coupled configurations. For realistic Antarctic configurations, we use the subglacial hydrology model from the MALI ice-sheet model run at 4-20 km resolution to calculate steady state subglacial discharge across the grounding line under historical ice-sheet conditions. This subglacial meltwater discharge is implemented as a grounding line freshwater flux in MPAS-Ocean, the ocean component of E3SM.

Results from idealized, rotating ice-shelf configurations show a stronger melt rate dependence on discharge than in previously studied non-rotating Greenland-like fjord scenarios. We also find that the melt-rate response is strongly sensitive to the location of the discharge along the grounding line; the efficiency of subglacial discharge, in terms of total melt-rate increase, grows with distance from the area where meltwater accumulates due to rotational effects. The analysis of subglacial discharge effects in realistic, global configurations focuses on ice-shelf melt rates, cavity circulation, continental shelf properties, and sea-ice conditions around Antarctica. Results from realistic, global configurations indicate that, although some regions are more affected than others, overall the present-day levels of subglacial discharge result only in relatively minor changes in ice-shelf melt rates and continental shelf properties. Significant oceanic changes would require at least an order of magnitude stronger subglacial discharge than present-day estimates.