- Earth and Planetary Sciences; limiting factor; concentration effect; microstructures; grain boundary migration; grain growth; recrystallization; experimental studies; ice crystals; impurity effect; polar region; drill cores; historical reconstruction; investigation method; paleoclimatology; Earth Sciences; Glaciology; Physical Sciences and Mathematics
In order to examine the effects of solutes on recrystallization and subsequent grain growth in ice, both doped and undoped ice single crystals were extruded through a 120° equal-channel angular extrusion jig, in order to impart a large shear strain (∼1.15). Upon subsequent annealing at -3°C, the original single crystals recrystallized, in most cases to a new single crystal with a different orientation. Increasing the solute concentration (for HSO to ∼200-300 ppb, and for NaCl, KCl and MgSO to >5 ppm) was found to significantly retard the growth and possibly, for HSO-doped ice, the nucleation of new grains in the strained ice single crystals. This is indicative of how soluble impurities can retard grain growth in ice cores. It was also found that the migrating grain boundaries surrounding the newly formed grains contained large concentrations of impurities, often observed as filaments. These could have formed by the grain boundaries sweeping up impurities from the lattice into the boundary or by their diffusion to the boundary - mechanisms whereby impurities could be concentrated into the grain boundaries in ice cores - although the latter mechanism seems unlikely since it would require very high diffusion rates.