Turbulence-enhanced bottom melting of a horizontal glacier--lake interface

Abstract:

We use laboratory tank experiments and direct numerical simulations to investigate the meltrates of a horizontal bottom glacier--lake interface as a function of lake temperature. Existing parameterisations of such meltrates are usually based on empirical fits to field observations. To understand the meltrates of an ice--water interface more systematically we study an idealised system in terms of its temperature-driven buoyancy forcing. In such systems, the meltrate can be expressed analytically for a stable stratification. Here we investigate the unstable case and present how the meltrate depends on the lake temperature when the water beneath the ice is overturning and turbulent.

We use laboratory tank experiments and direct numerical simulations to study an idealised ice--water boundary. The laboratory tank experiments provide robust observation-based mean-temperature profiles. The numerical simulations provide the full three-dimensional structure of the turbulent flow down to scales not accessible in the laboratory, with a minimum 0.2mm gridspacing.

Our laboratory mean-temperature profiles agree well with the numerical simulations and lend credibility to our numerical setup. The structure of the turbulent flow in our simulations is well described by two self-similar subregions, a diffusion-dominated inner layer close to the ice and a turbulence-dominated outer layer far from the ice. We provide an explicit expression for the parameterisation of the meltrate of a horizontal glacier--lake interface as a function of lake temperature.