The effect of tides on the basal-melting of an ice shelf: large-eddy simulations with a near-wall model

Catherine Ann Vreugdenhil, University of Cambridge, Cambridge, United Kingdom and John Ryan Taylor, University of Cambridge, DAMTP, Cambridge, United Kingdom
Abstract:
The ocean-driven basal melting of Antarctic ice shelves remains difficult to predict and to parameterise in large-scale ocean models. This is in part due to feedback effects between the small-scale turbulence in the ocean boundary layer and the melt rate. A strong tidal current can increase turbulence near the ice base, which mixes warm water towards the ice and increases the melt rate. But ice melting can freshen and stabilise the stratification, supressing the mixing of warm water to the base of the ice and slowing the melt rate. Recent studies observe both a strong tidal signal and stratification in temperature and salinity in the water column beneath the Larsen C ice shelf (Nicholls et al. 2012; Davis and Nicholls 2019).

Here, we use a large-eddy simulation to model the ocean boundary layer beneath a melting ice shelf under conditions similar to the Larsen C site. The strongest observed tidal constituents are used to force a time-dependent current. A near-wall model with Monin-Obukhov similarity scaling calculates the melt rate at the ice base. A turbulent Ekman layer forms at the ice base and further away the flow is in geostrophic balance. The simulations show a mean melt rate consistent with observations and a developing stratification in temperature and salinity. We find that the tidal cycle is important in setting the instantaneous melt rate.