A thermo-hydrodynamic modelling study of an idealized low-elevation blue-ice area in Antarctica

Abstract

Low-elevation blue-ice areas in Antarctica can contain significant amounts of subsurface liquid water during summer and may experience internal melt-freeze cycles due to absorption of shortwave radiation. An existing 2-D (x-z) model has been used to study the phenomenon and this is improved by changing the lower boundary condition from a no-flux condition to one that lets heat through, and by changing the bulk optical properties to spectral values. Both changes made the model more realistic. The optical and thermal boundary conditions, together with the optical attenuation coefficient, have a large effect on the amount of water produced in the ice. Our results show that if the lower boundary condition is changed from no flux to radiating, subsurface melting is reduced dramatically. Using a spectral albedo produces less melting than using a corresponding bulk albedo, the other variables left unchanged. If optical properties are changed to spectral values, the melting is different than using bulk values. If the linear extent of the blue-ice area is <0.6 m, subsurface melting is diminished. We found the spatial variability of snow has a significant effect on subsurface melting. Subsurface melting was found to be impossible for albedos >0.7 and the subsurface ponds can persist over the winter if the albedo is <0.4.