Formation Processes of Ice Fabric Pattern in Ice Sheets

Abstract

Experimental studies on the Formation process of the single maximum fabric of ice from its random fabric were carried out using both Greenland Dye-3 ice cores and artificially grown polycrystalline ice. From the observations of the rotation of c-axes of individual grains in thin specimens, an empirical equation was obtained for describing the rotation process of c-axes. Combined with another empirical equation on the relationship between the uniaxial strain of whole specimen and the uniaxial strain in individual grains of different c-axis direction, an equation was derived which describes the formation of single maximum fabric in bulk ice samples.Computer simulation of the formation process was performed based on an equation starting from an artificially made random fabric pattern. From the results obtained by a stepwise simulation of 2% strain intervals, the degree of concentration expressed by θm, the angle which halves the number of grains in the fabric diagram is correlated with the accumulated strain in bulk ice (Fig. 8). The strain deduced by applying this relationship to the obtained θm for samples of Dye-3 ice core coincided well with actual strain which the samples had experienced. This implies that the equation is valid and the mechanism of c-axis rotation prevails in polar ice sheets.

Flow-law hypotheses for ice-sheet modeling

“…Rotation of existing grains in polycrystals is described to good approxinIation by the results of AZUnla and Higashi (1985) {2} Azuma and Higashi (1985) deformed thin ice specimens uniaxially and found that the strain in each grain was approximately proportional to the resolved shear stress along its basal plane, with the bulk strain equal to the strain of individual grains averaged over the entire sample. They then found that this model predicts the observed fabric development at Dye 3, Greenland, in the region of normal grain growth, where such a model for an existing population of grains should apply.…”

“…They then found that this model predicts the observed fabric development at Dye 3, Greenland, in the region of normal grain growth, where such a model for an existing population of grains should apply. More recently, Lipenkov and others (1989) have found that the Azuma and Higashi (1985 ) model, modified for uniaxial tension following Fujita and others (1987 ), accurately describes fabric observations in the Vostok, East Antarctica, core.…”

“…Either (i) polygonization is occurring, allowing fabric development to continue to follow the Azuma and Higashi ( 1985 ) hypothesis closely; or (ii ) recrystallization is occurring, but is sufficiently slow compared to grain rotation that the rotation dominates the fabric development.…”

“…c-axis fabric development occurs by grain rotation, probably following the Azuma and Higashi (1985) hypothesis as extended by Alley ( 1988). .,., following Budd and Jacka (1989) . Flow-law exponents, fabric controls, grain-growth behavior and microscopic processes are indicated.…”

The microstructure of meteoric ice from Vostok, Antarctica

“…A single-maximum fabric is usually produced by vertical compression (and divergent horizontal tension) (Azuma and Higashi, 1985) or by simple shear near the base of a glacier (Budd and Jacka, 1989). The authors noted that these different fabrics (single maximum and vertical girdle) are characteristic of different stress conditions, and suggested that their interpretation requires an assumption of discontinuity in the recrystallization and deformation processes that may be attributed to structural softening.…”