Ice shelf fracture is responsible for roughly half of Antarctic ice mass
loss in the form of calving and can weaken buttressing of upstream ice
flow. Large uncertainties associated with the ice sheet response to
climate variations are due to a poor understanding of these fracture
processes and how to model them. Here, we address these problems by
developing an anisotropic, nonlocal, creep damage model for large-scale
shallow-shelf ice flow. This model can be used to study the full
evolution of fracture from initiation of crevassing to rifting that
eventually causes tabular calving. While previous ice shelf fracture
models have largely relied on simple expressions to estimate crevasse
depths, our model parameterizes fracture directly in 3-D. We also
develop an efficient supporting numerical framework based on the
material point method, which avoids advection errors. Using an idealized
marine ice sheet, we test our methods in comparison to a damage model
that parameterizes crevasse depths, as well as a modified version of the
latter model that accounts for how necking and mass balance affect
damage. We demonstrate that the creep damage model is best suited for
capturing weakening and rifting, and that anisotropic damage reproduces
typically observed fracture patterns better than isotropic damage.
However, we also show how necking and mass balance can significantly
influence damage on decadal timescales. Because these processes are
currently absent from the creep damage parameterization, we discuss the
possibility for a combined approach between models to best represent
mechanical weakening and tabular calving within long-term simulations.