Ice shelf Basal Melt Parameterisations for Ice-Ocean Boundary Layers over Dynamically Stable Pycnoclines: Case studies using a Boundary Current Model

Models are reported to overestimate basal melting under warm water ice shelves. Hence, ice-ocean heat exchange and its parameterisation are investigated using an ice-ocean boundary current model (IOBCM).  Using the simplified case of a horizontal ice-ocean interface (IOI), we demonstrate how parameterizations in z-coordinate ocean models can significantly overestimate melt rates in boundary layers over dynamically stable pycnoclines when far-field ocean currents are weak.

We propose a simple physics-based parameterisation framework for this specific case. Two case studies are presented: 1) a horizontal IOI with uniform far-field currents; and 2) a sloped IOI with density-driven, sheared currents. We use this parameterisation framework to formulate a hybrid model for the general case of density-driven currents under ice shelves. The hybrid model is a combination of the classic plume model for dynamically unstable regimes and the parameterized version of the IOBCM for dynamically stable regimes. In the hybrid model, for stable regimes, the melt rate as well as its response to warming are significantly reduced when compared with the regime-independent treatment in the classic plume model.

Our findings highlight the importance of careful consideration of the ocean stratification and flow conditions when parameterizing ice-ocean interactions, especially in regions with weak currents and stable stratification.