Dynamic recrystallization and texture development in ice as revealed by the study of deep ice cores in Antarctica and Greenland

Abstract

• appears to alter the kinetics of the development of deformation textures and is, at high temperature, at the origin of recrystallization textures. The purpose of this work is to obtain a better understanding 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 and Antarctica, the GReenland Ice core Project (GRIP) and Vostok ice cores. The structure along the GRIP core displays normal grain growth in the first 100 m of the ice sheet and rotation recrystallization and migration recrystallization near the bottom. Only grain growth and rotation recrystallization appear to occur in the Vostok ice core. The transition between these recrystallization regimes was studied, estimating, for interglacial ice, the evolution with depth of the dislocation density. This calculation has shown the efficiency of grain boundary migration for the absorption of dislocations. At Vostok, the highest value of the dislocation density is found at a depth of about 1000 m and the continuous decrease in the dislocation density below this depth is related to the increase of the grain boundary migration rate. It is shown that the driving force required to initiate migration recrystallization is not reached in interglacial ice at Vostok. The observed textures 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.

The physics of premelted ice and its geophysical consequences

“…This change has been attributed to the emergence of a more temperature-sensitive deformation mechanism that might be associated with an increase in water mobility along grain boundaries at higher temperatures. Further evidence for changes in the mobility of water at grain boundaries comes from the abrupt increases in grain size that are typically seen in polar ice cores at depths where such temperatures are reached ͑Thorsteinsson et al, 1997; de la Chapelle et al, 1998͒. It has yet to be conclusively demonstrated whether or not grain-boundary melting ͑see Sec. II.B.3͒ contributes to the explanation for these phenomena.…”

Fabric development with nearest‐neighbor interaction and dynamic recrystallization

“…where a is a constant >1, K is the grain growth factor, and D is the crystal diameter [De La Chapelle et al, 1998;Montagnat and Duval, 2000]. The first term on the right-hand side represents the increased dislocation density, by work hardening, and the second term represents the absorption of dislocations at grain boundaries (recovery).…”

Comment on “Superplastic deformation of ice: Experimental observations” by D. L. Goldsby and D. L. Kohlstedt

“…The reduction in dislocation density is related to the annihilation of dislocations by moving grain boundaries and to the formation of grain boundaries by the progressive misorientation of subboundaries. Application to ice sheets shows that GBM associated with grain growth or rotation recrystallization is an efficient recovery process and can be considered as the main accommodation mechanism of basal slip [De La Chapelle et al, 1998;Montagnat and Duval, 2000].…”

“…Grain boundary migration (GBM) associated with normal grain growth and recrystallization occurs throughout the whole thickness of ice sheets [Alley, 1992;De La Chapelle et al, 1998]. By reducing the rate of dislocations accumulation at grain boundaries, GBM can be an efficient accommodation mechanism of basal slip [Pimienta and Duval, 1987;Alley, 1992].…”