Stratified suppression of turbulence in an ice shelf basal melt parameterisation

Abstract. Ocean-driven basal melting of Antarctic ice shelves is an important process that affects the Antarctic Ice Sheet, global climate and sea level. Basal melting occurs within ice shelf cavities, which are not represented in most global ocean or climate models. Models targeted for studying ice-ocean interactions include ice shelf cavities and are critical tools for understanding basal melt and the ocean circulation beneath ice shelves but rely on parameterisations to predict basal melt. Most currently used basal melt parameterisations best represent shear-driven melting occurring in a limited parameter space of ice shelf cavity conditions. In other conditions, stratification of buoyant meltwater against the ice interface suppresses melt and diffusive convection plays a role, both processes that are not adequately included in existing melt parameterisations. We implement an improved three-equation melt parameterisation in two ocean models, which accounts for stratification suppressing the turbulence that drives basal melting. This stratification feedback parameterisation is based on the results of LES studies, which suggest a functional dependence of heat and salt transfer coefficients on the viscous Obukhov scale. Changes in melting and circulation due to the stratification feedback are regime-dependent: melt rates in idealised, quiescent simulations decrease by 80 % in warm cavity conditions and 50 % in cold conditions. The stratification feedback also suppresses melt rates in a high-resolution regional Pine Island Glacier simulation by 60 %, suggesting that much of the ice shelf boundary layer is affected by stratification. However, unconstrained boundary layer parameters, inter-model differences and unresolved processes continue to present challenges for accurately modelling basal melt in ocean models.