Abstract. Due to global warming and particularly high regional ocean warming, both Thwaites and Pine Island glaciers in the Amundsen region of the Antarctic Ice Sheet could lose their buttressing ice shelves over time. We analyze the possible consequences using the Parallel Ice Sheet Model (PISM), applying a simple cliff-calving parameterization and an ice-mélange-buttressing model. We find that the instantaneous loss of ice-shelf buttressing, due to enforced ice-shelf melting, initiates grounding line retreat and triggers the marine ice sheet instability (MISI). As a consequence, the grounding line progresses into the interior of the West Antarctic Ice Sheet and leads to a sea level contribution of 0.6 m within 100 a. By subjecting the exposed ice cliffs to cliff calving using our simplified parameterization, we also analyze the marine ice cliff instability (MICI). In our simulations it can double or even triple the sea level contribution depending on the only loosely constraint parameter which determines the maximum cliff-calving rate. The speed of MICI depends on this upper bound on the calving rate which is given by the ice mélange buttressing the glacier. However, stabilization of MICI may occur for geometric reasons. Since the embayment geometry changes as MICI advances into the interior of the ice sheet, the upper bound on calving rates is reduced and the progress of MICI is slowed down. Although we cannot claim that our simulations bear relevant quantitative estimates of the effect of ice-mélange buttressing on MICI, the mechanism has the potential to stop the instability. Further research is needed to evaluate its role for the past and future evolution of the Antarctic Ice Sheet. TC - Peer review - Stabilizing effect of mélange buttressing on the marine ice-cliff instability of the West Antarctic Ice Sheet Articles | Volume 16, issue 5 Article Assets Peer review Metrics Related articles Articles | Volume 16, issue 5 https://doi.org/10.5194/tc-16-1979-2022 © Author(s) 2022. This work is distributed under the Creative Commons Attribution 4.0 License. Special issue: Improving the contribution of the land cryosphere to sea level... https://doi.org/10.5194/tc-16-1979-2022 © Author(s) 2022. This work is distributed under the Creative Commons Attribution 4.0 License. Articles | Volume 16, issue 5 Article Assets Peer review Metrics Related articles Research article | 24 May 2022 Research article | | 24 May 2022 Stabilizing effect of mélange buttressing on the marine ice-cliff instability of the West Antarctic Ice Sheet Tanja Schlemm , Johannes Feldmann , Ricarda Winkelmann , and Anders Levermann Tanja Schlemm × Earth System Dynamics, Potsdam Institute for Climate Impact Research, Potsdam, Germany Institute of Physics and Astronomy, University of Potsdam, Potsdam, Germany Johannes Feldmann https://orcid.org/0000-0003-4210-0221 × Earth System Dynamics, Potsdam Institute for Climate Impact Research, Potsdam, Germany Ricarda Winkelmann https://orcid.org/0000-0003-1248-3217 × Earth System Dynamics, Potsdam Institute for Climate Impact Research, Potsdam, Germany Institute of Physics and Astronomy, University of Potsdam, Potsdam, Germany Anders Levermann CORRESPONDING AUTHOR anders.levermann@pik-potsdam.de https://orcid.org/0000-0003-4432-4704 × Earth System Dynamics, Potsdam Institute for Climate Impact Research, Potsdam, Germany Institute of Physics and Astronomy, University of Potsdam, Potsdam, Germany Lamont-Doherty Earth Observatory, Columbia University, New York, USA Download Final revised paper (published on 24 May 2022) Preprint (discussion started on 12 Aug 2021) Interactive discussion Status : closed Comment types : AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse RC1 : 'Comment on The authors use a simple cliff-calving parameterization and a mélange buttressing model that were proposed and tested on idealized cases in their previous papers and apply them to real glacier cases in this paper. MICI is an important mechanism that could lead to large uncertainties in modeling the physics of the ice sheets. Recent theoretical and modeling studies (Ma et al., 2017, Bassis et al., 2017, Mercenier et al., 2018) have investigated and analyzed mechanisms for MICI. Applying a more physically based cliff-calving law on real glaciers setting is the timely step to makes an important contribution to the MICI hypothesis. 
 
 P18L6: “This seasonality can be modelled with a time-dependent …” 
 Does this experiment include melting/freezing of mélange? How are the results affected with melting/freezing of mélange? 
 
 P18L26: “The mélange parameterization assumes a constant calving rate…” 
 Do you mean “the upper bound on calving rates (C_max)? 
 
 P20L2: “The processes by which ice shelves fracture… in an ice sheet model” 
 Add references. The evolving glacier configurations are due to this enforced removal of ice and have little to do with concepts of Marine Ice Sheet and Ice Cliff Instabilities that are instabilities of steady state configurations. The experiments use parameterizations, which main property is simplicity, however, the manuscript does not provide physical justification for their use. The interpretation of the results ignores a large body of studies of marine outlet glacier dynamics (a non-exhaustive list is below). The authors then compare sea-level contributions from the Marine Ice Cliff Instability (MICI) with those from the Marine Ice Sheet Instability (MISI) alone. 
 Overall, the manuscript raises interesting questions and presents a great deal of work toward addressing them. However, I found the organization confusing. Many results appear together with uneven levels of detail in the discussion. One of the major conclusions seems to be about interpreting an upper bound on cliff calving rate; the framing of that analysis in particular confused me.