Environmental Science and Engineering Seminar

Glacial melt rates at ice-ocean interfaces are commonly represented as a time-constant shear boundary layer parameterization. However, this assumption has only been deemed reasonable for horizontal ice-ocean boundaries where the exchange of heat and freshwater across the mm-scale diffusive thermal and salinity boundary layers varies proportionally with the strength of external momentum. This is only the case when buoyancy-driven turbulence and the suppression of turbulence by stratification is weak.

Guided by Direct Numerical Simulations (10 micron resolution) of the ice-ocean boundary layer for varying geometric and ocean forcing parameters, I will present an updated understanding of the basic principles of ice-ocean boundary layers (as a diffusive freshwater layer nested within a diffusive thermal layer within a viscous velocity shear layer within a turbulent momentum layer). I will present numerical simulation results that seek to merge the following turbulent ice-ocean boundary layer regimes: (1) meltwater-driven buoyancy, (2) meltwater-driven shear, and (3) externally-driven shear (from both horizontal and vertical sources of momentum). In the absence of externally-driven flow, a dynamical transition from buoyancy-controlled to shear-controlled boundary layers is possible for the thermal layer, but not the freshwater layer. By contrast, externally-driven sources of shear can constrain both the thermal and freshwater layers.

This improved understanding allows us to develop accurate predictions for the turbulently-constrained momentum, thermal, and freshwater boundary layer thicknesses, which is required to predict the ocean-driven melt rate of ice in Greenland and Antarctica.