DYNAMIC RECRYSTALLIZATION AND TEXTURE DEVELOPMENT IN ICE AS REVEALED BY THE STUDY OF DEEP ICE CORES IN ANTARCTICA AND GREENLAND

The preferred c axis orientation of ice from polar ice sheets develops essentially as a result of intracrystalline slip; but dynamic recryst allization appears to alter the kinetics of the development of deforma tion textures and is, at high temperature, at the origin of recrystall ization textures. The purpose of this work is to obtain a better under standing of recrystallization processes that occur in polar ice sheets and to clarify the relationship between dynamic recrystallization and textures. The study was based on two deep ice cores from Greenland an d Antarctica, the GReenland Ice core Project (GRIP) and Vostok ice cor es. The structure along the GRIP core displays normal grain growth in the first 100 m of the ice sheet and rotation recrystallization and mi gration recrystallization near the bottom. Only grain growth and rotat ion recrystallization appear to occur in the Vostok ice core. The tran sition between these recrystallization regimes was studied, estimating , for interglacial ice, the evolution with depth of the dislocation de nsity. This calculation has shown the efficiency of grain boundary mig ration for the absorption of dislocations. At Vostok, the highest valu e of the dislocation density is found at a depth of about 1000 m and t he continuous decrease in the dislocation density below this depth is related to the increase of the grain boundary migration rate. It is sh own that the driving force required to initiate migration recrystalliz ation is not reached in interglacial ice at Vostok. The observed textu res were compared with those predicted by the self-consistent approach . Recrystallization textures are interpreted by assuming that the less stressed grains, i.e., the best oriented for basal slip, are favored by the size advantage of subgrains. The recrystallization textures are compared with those of other materials.