Abstract
This study investigates the microclimate and hydrology of debris-laden ice surfaces in the Taylor Valley, Antarctica, in early summer, focusing on the onset of melt. Measurements of energy and mass fluxes were made on an outwash fan and in moraines near the terminus of Taylor Glacier. The surface microclimate was strongly controlled by absorbed solar radiation, with a low albedo of 0.17. Seasonal warming of the substrate led to an abrupt shift in thermal and hydrological patterns as temperatures exceeded freezing point. Within a week the Bowen ratio switched from 2.05 to 0.48 and mass losses to the atmosphere increased four-fold from 0.39 to 1.6 mm d-1. Melt onset also produced complex ground temperature patterns with strong diurnal damping below the freezing front. These patterns were caused by phase changes in the freezing front, coupled with an abundant water supply from local runoff. Of secondary importance to the surface energy balance and mass fluxes was the effect of local winds on boundary layer characteristics. This resulted in larger mass losses during the more turbulent, warmer and drier down-valley flows.