What can modeling Steady-State Crystal Fabrics of Ice Streams tell Us about their Age?

During the gravity-driven flow of glaciers and ice sheets, polycrystalline ice tends to develop a strain-induced alignment of individual grains. This fabric development can act as a strain marker for understanding the recent-most deformation history, in addition to exerting significant rheological control on ice sheets compared to isotropic ice. We develop a new way to directly solve for depth-average fabric fields using satellite-derived velocities, assuming that velocities are approximately steady and that fabric evolution is dominated by lattice rotation, in a depth-averaged sense. We apply the method to the North East Greenland Ice Stream (NEGIS) and compare results to radar-derived observations of ice fabrics, suggesting the memory of past flow, stored in ice-stream fabrics, might be useful way to independently set bounds on the age of ice streams (assuming recrystallization is negligible in a depth-average sense). Source/sink flux terms for crystal orientations at the surface and basal boundary naturally appear in the problem as fabric-state-space attractors, and we discuss how the effect of ice—bed interactions on fabric evolution may be parameterized using such terms.