Ice Shelf Basal Melt Sensitivity to Tide-Induced Mixing Based on the Theory of Subglacial Plumes

Abstract

Tidal currents are known to influence basal melting of Antarctic ice shelves through two types of mechanisms: local processes taking place within the boundary current adjacent to the ice shelf-ocean interface and far-field processes influencing the properties of water masses within the cavity. The separate effects of these processes are poorly understood, limiting our ability to parameterize tide-driven ice shelf-ocean interactions. Here we focus on the small-scale processes within the boundary current. We apply a one-dimensional plume model to a range of ice base geometries characteristic of Antarctic ice shelves to study the sensitivity of basal melt rates to different representations of tide-driven turbulent mixing processes. Our simulations demonstrate that tides can either increase or decrease melt rates depending on the approach chosen to parameterize entrainment of ambient water into the turbulent plume layer, a process not yet well constrained by observations. A theoretical assessment based on an analogy with tidal bottom boundary layers suggests that tide-driven shear at the ice shelf-ocean interface enhances mixing through the pycnocline. Under this assumption our simulations predict a tide-induced increase in melt and freeze rates along the base of the ice shelf, with the strongest plume path-integrated effects for cold cavities (up to +400% in the realistic set up). An approximation is provided to account for this response in basal melt rate parameterizations that neglect the effect of tide-induced turbulent mixing.