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The collapse of ice shelves could expose tall ice cliffs at ice sheet margins. The marine ice cliff instability (MICI) is a hypothesis that predicts that, if these cliffs are tall enough, ice may fail structurally leading to self-sustained retreat. To date, projections that include MICI have been performed with a single model based on a simple parameterization. Here, we implement a physically motivated parameterization in three ice sheet models and simulate the response of the Amundsen Sea Embayment after a hypothetical collapse of floating ice. All models show that Thwaites Glacier would not retreat further in the 21st century. In another set of simulations, we force the grounding line to retreat into Thwaites' deeper basin to expose a taller cliff. In these simulations, rapid thinning and velocity increase reduce the calving rate, stabilizing the cliff. These experiments show that Thwaites may be less vulnerable to MICI than previously thought, and model projections that include this process should be re-evaluated.

Antarctica's contribution to global mean sea level rise has been driven by an increase in ice discharge into the oceans. The rate of change and the mechanisms that drive variability in ice discharge are therefore important to consider in the context of projected future warming. Here, we report observations of both decadal trends and inter-annual variability in ice discharge across the Antarctic Ice Sheet at a variety of spatial scales that range from large drainage basins to individual outlet glacier catchments. Overall, we find a 37 ± 11 Gt year -1 increase in discharge between 1999 and 2010, but a much smaller increase of 4 ± 8 Gt year -1 between 2010 and 2018. Furthermore, comparisons reveal that neighbouring outlet glaciers can behave synchronously, but others show opposing trends, despite their close proximity. We link this spatial and temporal variability to changes in ice shelf buttressing and the modulating effect of local glacier geometry., (© 2022. The Author(s).)

Stearns and van der Veen (Reports, 20 July 2018, p. 273) conclude that fast glacier sliding is independent of basal drag (friction), even where drag balances most of the driving stress. This conclusion raises fundamental physical issues, the most striking of which is that sliding velocity would be independent of stresses imparted through the ice column, including gravitational driving stress., (Copyright © 2019, American Association for the Advancement of Science.)

Most of the ice lost from the Antarctic ice sheet passes through a few fast-flowing and highly dynamic ice streams. Quantifying temporal variations in flow in these ice streams, and understanding their causes, is a prerequisite for estimating the potential contribution of the Antarctic ice sheet to global sea-level change. Here I show that surface velocities on a major West Antarctic Ice Stream, Rutford Ice Stream, vary periodically by about 20 per cent every two weeks as a result of tidal forcing. Tidally induced motion on ice streams has previously been thought to be limited to diurnal or even shorter-term variations. The existence of strong fortnightly variations in flow demonstrates the potential pitfalls of using repeated velocity measurements over intervals of days to infer long-term change.