Improving model representation of freshwater flux and glacial processes in ocean models

Modern observations revealing accelerated mass loss across the Greenland Ice Sheet have raised concern regarding the impact of increased freshwater flux on global circulation. Specifically, ocean models display strong sensitivity to freshwater runoff in the Arctic (both in distribution and magnitude) that can lead to rapid changes in overturning circulation and heat transport in the North Atlantic. For the Greenland Ice Sheet, freshwater flux into the ocean arises from surface melt, melting of marine terminating glaciers, and calving of the glacier’s ice front. Surface melt that is routed to the ice-bedrock interface and enters the ocean at depth (i.e. subglacial runoff) can dramatically increase melt rates at the ice front by forming a turbulent buoyant plume that enhances mixing and entrains warmer ambient water.

In light of the importance of freshwater flux on global ocean circulation, careful treatment of surface runoff and glacial processes (i.e. calving and submarine melting) is critical for ocean models. Here, we present work focused on improving the representation of freshwater flux in a regional Arctic-subpolar North Atlantic simulation and state estimation framework by transitioning from climatological estimates to updated observations of freshwater runoff and simulating additional freshwater production from submarine melting of Greenland’s largest glaciers. Since the computational cost of resolving fjord-scale systems in global ocean models is prohibitive, we leverage sub-gridscale plume models within our ocean model to simulate submarine melting of the glacial systems. This model retains key aspects of the fine-scale configuration, namely the ice draft and sill depth along the fjord, and is forced by estimates of subglacial flux. Based on these results, we aim to develop parameterizations of submarine melt rates and transfer functions for the Greenland Ice Sheet that can be used for climate projection.