Melting of Antarctic ice shelves has a large impact on ocean circulation, future sea level rise and the global climate. Most of the ice-shelves in Antarctica are sloped forward into the ocean forming an ice cavity underneath. The turbulent transport of heat and salt into the ice interface melts the ice and drives convective wall plumes that play a crucial role in the basal melting. Ice-bathymetry and various ambient flows like tides, waves and sub-mesoscale eddies further modify the plumes. The regional and global ocean models work at scales over 100 metres and rely on crude sub-grid scale parameterization of convection and turbulent processes at the ice-ocean boundary layer, causing uncertainties in the estimation of the melt rate.
Over the course of my dissertation I have examined the role of micro scale turbulent processes at the ice ocean boundary using Direct Numerical Simulation (fully resolving convection and turbulence, see figure). We carry out simulations by varying the slope of the ice shelves, changing the strength of ambient flow and including sub glacial discharge. Our results show that the melt rate is controlled by the slope of the ice-face with decreasing melt rate at shallower slopes. Over the geophysical flow regime, convection is the key parameter that controls the heat and salt transfer into the ice-face and hence the melt rate. The results from this study significantly widen our present understanding of the basal melting and can improve the ice-ocean parameterizations for large-scale models.
Figure: Schematic of a sloping Antarctic ice shelf along with an enlarged snapshot of the boundary layer flow field (inset figure). The along-slope velocity (ζ – η plane) and cross-slope convective velocity (y- η plane) and spatial distribution of melt rate (ζ – y plane) at the ice-interface is shown here at ambient temperature, Tb= 1° C and ambient current, Ub= 0.05 m/s.