Extreme firn metamorphism: impact of decades of vapor transport on near-surface firn at a Sow-accumulation glazed site on the East Antarctic plateau

摘要

Snow and firn properties control the transport of vapor, gases and water between the atmosphere and the underlying strata. An understanding of this transport and the properties that control it is important for predicting air-snow transfer of chemical species and for interpreting ice cores. Remote-sensing images of East Antarctica show large areas of alternating light and dark bands. These low-amplitude, long-wavelength features have glazed downwind faces and rough upwind faces and are called megadunes. The first linked measurements of the permeability and the associated microstructure for a glazed area within a well-defined megadune area are reported in this paper. Permeability and density were measured, along with grain-scale properties derived from digital image processing of preserved thick sections, at this cold, low-accumulation glazed site. A clear layering pattern exists. In the top meter the firn density ranges from 0.24 to 0.50gem"3. Permeability measurements range from 50 x 10~10 to 200 x 10~10m2, several times greater than corresponding profiles from warmer, higher-accumulation sites like Siple Dome, Antarctica. It is shown that buoyancy-driven natural convection may be important in post-depositional processes in very cold, low-accumulation sites like this.