STRATIGRAPHY, DENSITY AND CRYSTAL STRUCTURE OF FIRN-ICE AT DE08-A VERY HIGH ACCUMULATION SITE ON LAW DOME, ANTARCTICA

An approximately 195 mm diameter flrn / ice core, 234 m long, was thermally drilled in 1987 austral summer at DE08 (66°43'S, 113°12'E) on Law Dome, East Antarctica, where the accumulation rate is about 1200kg/(m2-a); 10mice temperature is about-18.8℃. Analysis was mainly made at the site immediately after drilling. The snow stratigraphy at DE08 is characterised by the lack of coarse-grained snow and other distinct visible feature normally corresponding to annual layers. There is a smooth transformation from fine-grained snow at shallow depth to ice at about 80-90m which is greater than that at most other polar locations due to its abnormally high accumulation rate. According to the marked change in the trend of density with depth and in the crystal properties four stages of the transformation of snow to ice and development of crystal structure can be distinguished; settling stage (0-10m); sintering stage (10-90m); rapid crystal growth stage (90-170m); and dynamic metamorphism stage (170-234m). The rates of densification and crystal growth from the surface to the depth of the firn-ice transition closely depend on the general temperature. Below the transition zone, the crystal growth rate is higher by a factor of 4.3 in comparison with that at other sites. The very high vertical strain rate at DE08 compared to that at the other sites suggests that the crystal growth rate in the ice layer may increase by the associated deformation.