Fig. 4: Summary of flow mechanics and evolution of the crystal orientation fabric (COF) in the ice-stream onset region.

The COF distribution in the Northeast Greenland ice stream (NEGIS) is a result of the deformation history. The dominant vertical compression outside the ice stream leads to a vertical single maximum, which rotates into the horizontal plane towards the ice-stream margins, where horizontal shear is the dominant deformation mechanism. In the upstream part of the NEGIS, ice-flow channelling and along-flow acceleration create a vertical girdle with a superimposed horizontal single maximum. Downstream of the East Greenland ice-core project (EGRIP), divergent flow and stagnant flow velocities lead to a reversed deformation, so c-axes rotate back into vertical symmetry. By the downstream end of the survey region, stagnant ice-stream width and increased flow velocities again cause along-flow extension and the transition into a girdle-type COF. The COF affects the ice viscosity, e.g. leading to considerable stiffening for pure-shear deformation in parts of the ice stream.