Sub-surface melting in blue-ice fields in Dronning Maud Land, Antarctica: observations and modelling

Abstract

During the Norwegian Antarctic Research Expedition 1993/94, field studies were conducted on a blue-ice field in Jutulgryta, Dronning Maud Land. Measurements of sub-surface temperatures revealed that temperatures in blue ice were about 6°C higher than in the adjacent snow. Despite the predominantly negative air temperatures, a sub-surface melt layer was discovered within the uppermost metre of the blue ice. Here the temperature maximum was consistent throughout the entire month of observations, and resulted in both internal melt and water transport. The melting is a consequence of solar radiative penetration and absorption within the ice, i.e. the “solid-state greenhouse”. Sensitivity experiments using a non-stationary combined radiative and thermodynamic model reveal that the physical properties (here extinction coefficient, radiation transmittance and albedo) strongly control the formation and vertical extent of the melt layer. The persistence of the sub-surface melt layer increases the runoff volume from blue-ice fields, which otherwise might be restricted to a few yearly events when air temperatures reach or exceed the freezing point. The conditions required for melting activity are marginal in Jutulgryta. Hence, this phenomenon may serve as an indicator of climate fluctuations in the area.