Two parameterizations of turbulent boundary layer processes at the interface between an ice shelf and the ocean beneath are investigated in terms of their impact on simulated melt rates and feedbacks. The parameterizations differ in the transfer coefficients for heat and freshwater fluxes. In their simplest form, they are assumed constant and hence are independent of the velocity of ocean currents at the ice shelf base. An augmented melt rate parameterization accounts for frictional turbulence via transfer coefficients that do depend on boundary layer current velocities via a drag law. In simulations with both parameterizations for idealized as well as realistic cavity geometries under Pine Island Ice Shelf, West Antarctica, significant differences in melt rate patterns between the velocity-independent and velocity-dependent formulations are found. While patterns are strongly correlated to those of thermal forcing for velocity-independent transfer coefficients, melting in the case of velocity-dependent coefficients is collocated with regions of high boundary layer currents, in particular where rapid plume outflow occurs. Both positive and negative feedbacks between melt rates, boundary layer temperature, velocities, and buoyancy fluxes are identified. Melt rates are found to increase with increasing drag coefficient inline image, in agreement with plume model simulations, but optimal values of Cd inferred from plume models are not easily transferable. Uncertainties therefore remain, both regarding simulated melt rate spatial distributions and magnitudes.
Helmholtz Research Programs > PACES II (2014-2018) > TOPIC 3: The earth system from a polar perspective > WP 3.3: From process understanding to enabling climate prediction