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Transition to marine ice cliff instability controlled by ice thickness gradients and velocity

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Science  18 Jun 2021:
Vol. 372, Issue 6548, pp. 1342-1344
DOI: 10.1126/science.abf6271

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Cliff collapse

Tall ice cliffs at the edges of ice sheets can collapse under their own weight in spectacular fashion, a process that can considerably hasten ice sheet mass loss. Bassis et al. used a dynamic ice model to demonstrate that this kind of collapse can be slowed either by upstream thinning of the ice sheet or by the resistive forces from sea ice and calved debris (see the Perspective by Golledge and Lowry). Conversely, when there is upstream ice thickening, a transition to catastrophic collapse can occur.

Science, abf6271, this issue p. 1342; see also abj3266, p. 1266

Abstract

Portions of ice sheets grounded deep beneath sea level can disintegrate if tall ice cliffs at the ice-ocean boundary start to collapse under their own weight. This process, called marine ice cliff instability, could lead to catastrophic retreat of sections of West Antarctica on decadal-to-century time scales. Here we use a model that resolves flow and failure of ice to show that dynamic thinning can slow or stabilize cliff retreat, but when ice thickness increases rapidly upstream from the ice cliff, there is a transition to catastrophic collapse. However, even if vulnerable locations like Thwaites Glacier start to collapse, small resistive forces from sea-ice and calved debris can slow down or arrest retreat, reducing the potential for sustained ice sheet collapse.

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