c-axes measurements with the automated fabric analyser (Graphic: Ilka Weikusat, Alfred-Wegener-Institut)

Crystal orientations (also called fabrics or lattice orientations) represent an important subject of microstructure studies on the ice found on Earth. Due to the high mechanical anisotropy of hexagonal ice, crystal orientations influence the material response to stresses and thus have an immense impact on the ice flow. The distribution of c-axis orientations of polycrystalline ice develops with increasing depth from an almost random distribution close to the surface of ice sheets or glaciers to preferred crystal orientation patterns (girdle fabric or single/multiple maxima fabrics) in deeper parts of the ice core.

The Fabric Analyzer used here at AWI is an automated polarized-light microscope measuring crystal c-axis orientations of thin sections. Automatic control of polarizers, lambda-quarter plate and viewing direction by a computer software, as well as automatic sample positioning enables fast acquisition of data. Hence, investigations of physical properties of long ice cores are possible including large sample numbers (several hundreds of thin sections). FA provides scan images at a resolution of up to 5 μm. Applying digital image processing to the fabric data allows studying c-axis distributions of the polycrystal, as well as the inter- and intragranular lattice orientation changes.