Modeling Ice-Crystal Fabric as a Proxy for Ice-Stream Stability

Abstract

The crystal structure within an ice sheet evolves in response to deformation; hence ice- crystal fabric records ice-flow history. However, the complexity of crystal-fabric evolution, and the lack of model results with which to compare data, limit the usefulness of fabric measurements, particularly in areas with complex ice dynamics. Here, we use an ice-flow model to identify characteristic fabrics associated with ice-stream onset, with the goal of aiding interpretation of fabric measurements. Using time-dependent model simulations, we identify how crystal fabric may be used to diagnose changes in an ice stream’s speed or lateral position. Consistent with previous work, we find that fabric within an ice stream is generally a vertical girdle, though horizontal shear can lead to a horizontal single maximum. Transient simulations demonstrate that effects from changes in flow may be recorded in the crystal fabric for thousands of years after an ice stream activates and more than ten thousand years after an ice stream stagnates. Both transient and steady effects on fabric are sufficiently large as to be measurable in ice cores or with polarized radar, suggesting that in certain scenarios fabric could be used to identify past flow changes. These results could be used to design radar surveys in areas where ice streams are known to deactivate, such as the Siple Coast in Antarctica, or where they may migrate laterally or widen, such as in Northeast Greenland.