Evaluation of Modeled Subglacial Discharge From the Antarctic Ice Sheet to the Southern Ocean
Courtney Shafer, University at Buffalo
Ice shelf basal melting from relatively warm ocean water has a major effect on ice-shelf and glacier evolution. Subglacial discharge, the outflow of meltwater across the grounding zone of the ice sheet, can contribute to ice shelf basal melting by introducing fresh meltwater into the ice shelf cavity. The density and temperature differences between the subglacial discharge and ocean water work together to create a buoyant plume that captures and pulls the warm ocean water with it across the ice shelf base, enhancing ocean-driven melting. While this phenomenon is known, the interaction between subglacial discharge and ocean water on ice shelf basal melting is rarely accounted for within earth system and ocean modeling, in part because subglacial discharge around Antarctica is poorly known. In this work, we create a map of subglacial discharge across Antarctica using a distributed subglacial hydrology model within the MPAS-Albany Land ice Model (MALI). The fidelity of the map is evaluated by its ability to replicate (1) subglacial lake locations and (2) locations of unexplained locally high ice-shelf basal melt rates. We perform sensitivity experiments for key subglacial hydrology model parameters, such as hydraulic conductivity. Results show concentrated subglacial flow pathways along ice streams and outlet glaciers, corresponding with many locations of anonymously high ice-shelf basal melt rates at the grounding line. The model tends to form large, extensive subglacial lakes in ice streams rather than the networks of small lakes observed by altimetry and radar echo sounding. Results also show that the hydraulic conductivity of water through the hydrologic system controls the width of the concentrated flow pathways. While results to date only consider distributed subglacial drainage, ongoing work is investigating the impact of including channelized subglacial discharge within the model. Our final subglacial discharge product will be made available for ocean modelers to incorporate into simulations of ice-shelf basal melting in the future.