31 May 2022
 | 31 May 2022
Status: a revised version of this preprint was accepted for the journal TC.

The stability of present-day Antarctic grounding lines – Part B: Possible commitment of regional collapse under current climate

Ronja Reese, Julius Garbe, Emily A. Hill, Benoît Urruty, Kaitlin A. Naughten, Olivier Gagliardini, Gael Durand, Fabien Gillet-Chaulet, David Chandler, Petra M. Langebroek, and Ricarda Winkelmann

Abstract. Observations of ocean-driven grounding line retreat in the Amundsen Sea Embayment in Antarctica give rise to the question of a collapse of the West Antarctic Ice Sheet. Here we analyse the committed evolution of Antarctic grounding lines under present-day climate conditions to locate the underlying steady states that they are attracted to and understand the reversibility of large-scale changes. To this aim, we first calibrate the sub-shelf melt module PICO with observed and modelled melt sensitivities to ocean temperature changes. Using the new calibration, we run an ensemble of historical simulations from 1850 to 2015 with the Parallel Ice Sheet Model to create model instances of possible present-day ice sheet configurations. Then, we extend a subset of simulations best representing the present-day ice sheet for another 10,000 years to investigate their evolution under constant present-day climate forcing. We test for reversibility of grounding line movement if large-scale retreat occurs. While we find parameter combinations for which no retreat happens in the Amundsen Sea Embayment sector, we also find admissible model parameters for which an irreversible retreat takes place. Hence, it cannot be ruled out that the grounding lines – which are not engaged in an irreversible retreat at the moment as shown in our companion paper (Part A, Urruty et al., subm.) – will evolve towards such a retreat under current climate conditions. Importantly, an irreversible collapse in the Amundsen Sea Embayment sector evolves on millennial timescales and is not inevitable yet, but could become so if forcing on the climate system is not reduced in the future. In contrast, we find that allowing ice shelves to regrow to their present geometry means that large-scale grounding line retreat into marine basins upstream of Filchner-Ronne and Ross ice shelves is reversible. Other grounding lines remain close to their current positions in all configurations under present-day climate.

Ronja Reese et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on tc-2022-105', Michele Petrini, 01 Jul 2022
    • AC1: 'Reply on RC1', Ronja Reese, 31 Oct 2022
  • RC2: 'Comment on tc-2022-105', Anonymous Referee #2, 06 Jul 2022
    • AC2: 'Reply on RC2', Ronja Reese, 31 Oct 2022

Ronja Reese et al.

Ronja Reese et al.


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Short summary
We use an ice sheet model to test where current climate conditions in Antarctica might lead. We find that, depending on model parameters, present-day ocean and atmosphere conditions might commit a collapse of parts of West Antarctica which evolves over centuries to millennia. Importantly, this collapse is not yet irreversible as shown in our accompanying study.