Abstract
Abstract. Understanding the processes that govern ice shelf extent is important to improving estimates of future sea-level rise. In present-day Antarctica, ice shelf extent is most commonly determined by the propagation of through-cutting fractures called ice shelf rifts. Here, I present the first three-dimensional analysis of ice shelf rift propagation. I model rifts using the assumptions of linear elastic fracture mechanics (LEFM). The model predicts that rifts may be stabilized (i.e., stop propagating) when buoyant flexure results in the partial contact of rift walls. This stabilizing tendency may be overcome, however, by processes that act in the ice shelf margins. In particular, loss of marginal strength, modeled as a transition from zero tangential displacement to zero tangential shear stress, is shown to favor rift propagation. Rift propagation may also be triggered if a rift is carried with the ice flow (i.e., advected) out of an embayment and into a floating ice tongue. I show that rift stability is closely related to the transition from uniaxial to biaxial extension known as the compressive arch. Although the partial contact of rift walls is fundamentally a three-dimensional process, I demonstrate that it may be parameterized within more numerically efficient two-dimensional calculations. This study constitutes a step towards a first-principle description of iceberg calving due to ice shelf rift propagation.
Highlights
Introduction and backgroundDespite decades of progress, it remains unclear whether Antarctica will gain or lose mass by the year 2100
The ice front, rift walls, and top and bottom ice shelf surfaces are loaded by a depth-varying normal stress that is equal to the water pressure below the waterline and equal to zero above the waterline
The partial contact of rift walls is a nonlinear phenomenon because it involves solving for the shape of the contacting region and changing the region over which different boundary conditions are applied (Johnson and Johnson, 1987)
Summary
It remains unclear whether Antarctica will gain or lose mass by the year 2100. Further observation of a relationship between ice shelf retreat, rifting, and marginal thinning has been noted in the Amundsen Sea Embayment (MacGregor et al, 2012) and Jakobshavn Glacier, Greenland (Joughin et al, 2008). I consider the hypothesis that the forces that drive rift propagation are entirely described by the instantaneous ice shelf geometry and boundary conditions. This hypothesis requires three-dimensional calculations in order to directly calculate – rather than parameterize or approximate – the role of gravitational driving forces.
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