Below-surface ice melt on the coastal Antarctic ice sheet

In the Jutulgryta area of Dronning Maud Land, Antarctica, subsurface meltin g of the ice sheet has been observed. The melting takes place during the su mmer months in blue-ice areas under conditions of below-freezing air and su rface temperatures. Adjacent snow-covered regions, having the same meteorol ogical and climatic conditions, experience little or no subsurface melting. To help explain and understand the observed melt-rate differences in the b lue-ice and snow-covered areas, a physically based numerical model of the c oupled atmosphere, radiation, snow and blue-ice system has been developed. The model comprises a heat-transfer equation which includes a spectrally de pendent solar-radiation source term. The penetration of radiation into the snow and blue ice depends on the solar-radiation spectrum, the surface albe do and the snow and blue-ice grain-sizes and densities. In addition, the mo del uses a complete surface energy balance to define the surface boundary c onditions. It is run over the full annual cycle, simulating temperature pro files and melting and freezing quantities throughout the summer and winter seasons. The model is driven and validated using field observations collect ed during the Norwegian Antarctic Research Expedition (NARE) 1996-97. The s imulations suggest that the observed differences between subsurface snow an d blue-ice melting can be explained largely by radiative and heat-transfer interactions resulting from differences in albedo, grain-size and density b etween the two mediums.