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 is controlled by small-scale processes; therefore ice shelf-ocean models rely on parameterisations to predict basal melt. However, most currently used basal melt parameterisations represent melting as a shear-driven process and do not adequately include the effects of stratification by accumulation of buoyant meltwater beneath flat and weakly sloped ice interfaces. We implement an improved three-equation melt parameterisation that accounts for the stratified suppression of turbulence into two ocean models. This stratification feedback parameterisation is based on the results of large eddy simulation (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 % under warm-cavity conditions and 50 % under cold conditions. The stratification feedback also modifies melt rate patterns in a high-resolution regional Pine Island Glacier simulation. However, unconstrained boundary layer parameters, inter-model differences and unresolved processes continue to present challenges for accurately modelling basal melt in ocean models.