Ice fabric evolution process understood from anisotropic distribution of a-axis orientation on the GRIP (Greenland) ice core

Annals of Glaciology, Vol. 42, Number 1, pp. 47-52(6), 2005

A. Miyamoto, A. Hori and T. Hondoh
Institute of Low Temperature Science, Hokkaido University, Sapporo 060-0819, Japan.
H. Shoji
Kitami Institute of Technology, Koen-cho 165, Kitami 090-8507, Japan.
H.B. Clausen
Ice and Climate, The Niels Bohr Institute, Juliane Maries Vej 30, DK-2100 Copenhagen, Denmark
O. Watanabe
National Institute of Polar Research, Kaga, Itabashi-ku, Tokyo 173-8515, Japan.

To better understand how ice fabric evolves in polar ice sheets, we use X-ray diffraction to measure ice crystal orientations. X-ray measurement equipment which can measure the orientation of the c-axis and a-axis of each crystal in a thin section with high measurement accuracy was developed. In this study, we present a-axes orientation distribution of the deep part of the GRIP (Greenland summit) ice core. At some depths, we find an anisotropic distribution of a-axes orientation. Long-term uniaxial compression tests are also carried out on the GRIP ice core to investigate the ice fabric evolution process. The c-axis orientation distribution develops into a stronger single maximum as the strain increases up to about 20% strain. We find that the a axes of each grain also tend to cluster close to nearly a mutual direction. We discuss the development process of ice fabrics, taking into consideration the distribution of the a-axis orientations. It is suggested that these fabrics may be attributed to a local simple shear deformation in the deep part of an ice sheet.