The huge ice masses stored in the polar ice sheets are the main fresh water reservoirs and thus have potentially huge effects on sea level evolution. Especially the role and development of ice streams, such as the NEGIS, are still under debate. IPCC specified the estimates of the dynamic flow of polar ice sheets and the insufficient understanding of ice sheet physics as major error sources on predictions of sea level change. One of two main components governing the dynamic flow of ice is the internal deformation of the ice body.
Any large-scale plastic flow of even huge bodies of any material is actually conducted by deformation on smaller scales; down to crystallite and subgrain as well as atomic scales. As these deformation mechanisms significantly control the rheology of the material, knowledge on these processes is essential to understand and predict ice dynamics seriously. Depending on the conditions (e.g. depth in the ice sheet, speed of deformation, temperature) different mechanisms mobilize smallest volumes of the ice (e.g. molecule groups, crystal lattice planes, crystal boundaries) whose movements in total lead to the shape change of the ice sheet.
These small scale deformation mechanisms leave behind traces in the grain morphologies and orientations (microstructures) which can be used to identify the relevant mechanisms. These traces are e.g. grain sizes, grain shapes, crystal orientation distributions (fabrics), subgrain boundary occurrence, subgrain boundary misorientations and types, dislocation densities and types.
The mechanical properties of the ice are furthermore modified by recrystallisation processes induced mainly by deformation energy and temperature changes, which again can be traced in the microstructure.
We study deformation microstructures in ice core samples from Greenland and Antarctica with the following experimental methods: