Sediment Melt-Migration Dynamics in Perennial Antarctic Lake Ice

We examined sediment melt-migration dynamics in the ice cover of Lake Fryxell, Taylor Valley, McMurdo Dry Valleys, Antarctica, using a combination of laboratory experiments, field observations, and modeling. The specific objectives were to determine the thermal conditions required for sediment melt and how sediment migration rates vary with meteorological forcings and ice microstructure. These characteristics are relevant to the influence of climate change on lake ice structure and ecosystem processes in polar regions. Sediment began melting through laboratory ice at -2 degrees C in simulated summer conditions, with warmer ice producing faster melt rates. An energy balance model, supported by our laboratory experiments, demonstrated that subsurface sediment can melt down to an equilibrium depth of similar to 2 m in two years. Field experiments and modeling revealed that surficial sediment melts at about half the rate of subsurface sediment because of heat losses to shallow, cold ice and the cold, dry atmosphere. Gravity flow of sediment along grain boundaries was pronounced in laboratory ice warmer than -1 degrees C. This mechanism produced a flux of 0.1 g m(-2) hr(-1), a significant value relative to published benthic sedimentation rates for these lakes indicating an important sediment sorting mechanism.