the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 26 Mar 2025
Modelling the sensitivity of ice loss to calving front retreat rates in the Amundsen Sea Embayment, West Antarctica
Abstract. Ice-flow modelling studies of the Amundsen Sea Embayment (ASE) in West Antarctica have provided estimates of its future impacts on sea level rise. However, many of these studies have not considered the impacts of calving, a key process in the dynamics of marine-terminating glaciers. Sensitivity to calving front retreat is not well understood, so we set out to investigate it in systematic manner. In this study, we quantify the sensitivity of modelled future mass loss to ice front retreat in the ASE, including Pine Island and Thwaites Glaciers. We find that prescribing constant frontal retreat rates from 0.1 to 1 km a-1 progressively increases the contribution to sea level rise when compared to experiments with a fixed ice front. The result with our highest rate of retreat is up to 21.4 mm additional sea level contribution by 2100, and 239 mm by 2300. We identify specific buttressing thresholds where loss of contact with bedrock features causes changes in the ice dynamics. These are reached at different times depending on the retreat rate, and are the main cause of sensitivity to movement of the ice front. We compare variability in the range of our results using different retreat rates to that in the range of ISMIP6 ocean forcing products, as ocean-induced melt is known to be a major factor in determining the future evolution of the Antarctic ice sheet. We find that the variability due to these two factors is similar. We also find that the additional loss of ice due to a prescribed retreat rate is not heavily dependent on ocean forcing, so can be quantified independently of the ocean-induced melt. Our results demonstrate the importance of accurately representing calving processes in models, showing that they can be as important as ocean forcing and therefore deserve a similar amount of attention in future model development work.
Competing interests: At least one of the (co-)authors is a member of the editorial board of The Cryosphere.
Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors. Views expressed in the text are those of the authors and do not necessarily reflect the views of the publisher.-
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The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
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Preprint
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The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
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- Final revised paper
Journal article(s) based on this preprint
Interactive discussion
Status: closed
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RC1: 'Comment on egusphere-2025-328', Anonymous Referee #1, 12 May 2025
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2025/egusphere-2025-328/egusphere-2025-328-RC1-supplement.pdfCitation: https://doi.org/
10.5194/egusphere-2025-328-RC1 - AC1: 'Response to RC1', Jowan Barnes, 26 Jun 2025
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RC2: 'Comment on egusphere-2025-328', Anonymous Referee #2, 15 May 2025
In this study, the authors address a simple yet important question: What is the sensitivity of ice loss to constant, uniform calving front retreat rates in the Amundsen Sea Embayment? Calving is a major source of uncertainty in ice-sheet model projections due to the lack of robust and consistent calving laws. However, this question had not been addressed yet. By filling this gap and helping to assess the influence of calving on the loss of ice shelf buttressing capacity and, consequently, on ice sheet ice loss, this study makes a highly relevant and valuable contribution to the community.
One of the strengths of the study is the 'simplicity' of its experimental design. By prescribing constant retreat rates using the ice sheet model Ua, the authors are able to identify key features of the ice sheet response, such as specific buttressing thresholds, and demonstrate how the magnitude of the retreat modulates mass loss. The paper is very well written, concise, and easy to follow. The authors have a clear objective, which is clearly stated from the beginning, and address it in a consistent and coherent way.Â
My only concern relates to one of the study’s key messages. By comparing simulations forced by ISMIP6-2300 Tier 1 ocean/atmosphere coupled model outputs with the range obtained by varying the prescribed retreat rate, the authors conclude that accurately representing calving front retreat may be as important as accurately representing sub-shelf melt rates. However, if I understand correctly, the simulations are forced using both atmospheric and oceanic outputs following the ISMIP6-2300 protocol. Therefore, the spread in simulations forced by different ESMs cannot be attributed only to ocean forcing, as it also reflects changes in surface mass balance. Typically, by 2300 under high emission scenarios, some ESMs project significant increases in both snow accumulation and surface runoff. Moreover, by accounting for a range of ESM forcing, it seems to me that the authors are addressing the variability in climate forcings themselves, rather than isolating the influence of the way ocean-induced melt is accounted for in ice-sheet models. Either the message should be reformulated to something like ‘the variability in the range of ice sheet response using different retreat rates is similar to the spread resulting from a range of ESM forcings’, or the methodology applied to compare the impact of retreat rate and ocean-induced variability should be adjusted. This could be done, for example, by comparing to the spread in ice sheet response obtained using different sub-shelf melt parameterisations, or varying the gamma0 value within a given parameterisation (such as the local quadratic one used here).
Once this point is addressed, along with the minor comments listed below, I believe this study will make a very valuable contribution to the community.
Specific comments
l.10-12: As explained above, I find the comparison between variability attributed to retreat rates and the one attributed to ocean-induced melt misleading.
l.76-77: It would be helpful to provide more details on this adjustment of the Bedmachine dataset, perhaps in the supplementary materials.
l.110-115: Consider adding a table summarising the experiments, for clarity.
Figure 1: Since Figures 1a–b and 1c–i convey different messages, you might consider splitting them into two separate figures: one introducing the study area and another focused on the results.
Figure 2: You could try making the figure more self-explanatory, for example, by highlighting in panels (b) and (d) the regions zoomed in by panels (a) and (c).
l.165: You refer to the ESM forcings as ‘ocean forcing’, but I believe that you also include atmospheric forcing through anomalies in SMB following the ISMIP6 protocol? If so, the term ‘ocean forcing’ may be misleading, as changes in SMB also have quite a significant influence on the ice sheet response.
l.181-182: Do you mean here that the ~70 mm range for RR0 in Figure 3a is larger than the ranges shown by the green and red shaded areas in Figure 3b? If so, it would be helpful to specify that explicitly for clarity.
l.198-201: Could this be explained by increases in SMB post-2100 in UKESM as compared to UKESMrep?
l.209: replace ‘sensitivity’ by ‘SLR-RR-sensitivity’ for clarity.
l.220-221: I’m not sure where to visualise that the threshold is reached even for the smallest prescribed retreat rate. Clarification or reference to a figure would be useful.
l.255-258: In line with my previous comments, I think that this statement should be revised to something like ‘greater than the range of forcing from the ISMIP6-2300 Tier 1 experiments’. It does not seem to me that the current experiments allow for direct comparison between the influence of calving front retreat variability and variability in sub-shelf melt representation in ice sheet models. Instead, you account for variability in climate forcings, including ocean and atmospheric forcings.
l.286-296: Same as above.
Citation: https://doi.org/10.5194/egusphere-2025-328-RC2 - AC2: 'Response to RC2', Jowan Barnes, 26 Jun 2025
Interactive discussion
Status: closed
-
RC1: 'Comment on egusphere-2025-328', Anonymous Referee #1, 12 May 2025
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2025/egusphere-2025-328/egusphere-2025-328-RC1-supplement.pdf
- AC1: 'Response to RC1', Jowan Barnes, 26 Jun 2025
-
RC2: 'Comment on egusphere-2025-328', Anonymous Referee #2, 15 May 2025
In this study, the authors address a simple yet important question: What is the sensitivity of ice loss to constant, uniform calving front retreat rates in the Amundsen Sea Embayment? Calving is a major source of uncertainty in ice-sheet model projections due to the lack of robust and consistent calving laws. However, this question had not been addressed yet. By filling this gap and helping to assess the influence of calving on the loss of ice shelf buttressing capacity and, consequently, on ice sheet ice loss, this study makes a highly relevant and valuable contribution to the community.
One of the strengths of the study is the 'simplicity' of its experimental design. By prescribing constant retreat rates using the ice sheet model Ua, the authors are able to identify key features of the ice sheet response, such as specific buttressing thresholds, and demonstrate how the magnitude of the retreat modulates mass loss. The paper is very well written, concise, and easy to follow. The authors have a clear objective, which is clearly stated from the beginning, and address it in a consistent and coherent way.Â
My only concern relates to one of the study’s key messages. By comparing simulations forced by ISMIP6-2300 Tier 1 ocean/atmosphere coupled model outputs with the range obtained by varying the prescribed retreat rate, the authors conclude that accurately representing calving front retreat may be as important as accurately representing sub-shelf melt rates. However, if I understand correctly, the simulations are forced using both atmospheric and oceanic outputs following the ISMIP6-2300 protocol. Therefore, the spread in simulations forced by different ESMs cannot be attributed only to ocean forcing, as it also reflects changes in surface mass balance. Typically, by 2300 under high emission scenarios, some ESMs project significant increases in both snow accumulation and surface runoff. Moreover, by accounting for a range of ESM forcing, it seems to me that the authors are addressing the variability in climate forcings themselves, rather than isolating the influence of the way ocean-induced melt is accounted for in ice-sheet models. Either the message should be reformulated to something like ‘the variability in the range of ice sheet response using different retreat rates is similar to the spread resulting from a range of ESM forcings’, or the methodology applied to compare the impact of retreat rate and ocean-induced variability should be adjusted. This could be done, for example, by comparing to the spread in ice sheet response obtained using different sub-shelf melt parameterisations, or varying the gamma0 value within a given parameterisation (such as the local quadratic one used here).
Once this point is addressed, along with the minor comments listed below, I believe this study will make a very valuable contribution to the community.
Specific comments
l.10-12: As explained above, I find the comparison between variability attributed to retreat rates and the one attributed to ocean-induced melt misleading.
l.76-77: It would be helpful to provide more details on this adjustment of the Bedmachine dataset, perhaps in the supplementary materials.
l.110-115: Consider adding a table summarising the experiments, for clarity.
Figure 1: Since Figures 1a–b and 1c–i convey different messages, you might consider splitting them into two separate figures: one introducing the study area and another focused on the results.
Figure 2: You could try making the figure more self-explanatory, for example, by highlighting in panels (b) and (d) the regions zoomed in by panels (a) and (c).
l.165: You refer to the ESM forcings as ‘ocean forcing’, but I believe that you also include atmospheric forcing through anomalies in SMB following the ISMIP6 protocol? If so, the term ‘ocean forcing’ may be misleading, as changes in SMB also have quite a significant influence on the ice sheet response.
l.181-182: Do you mean here that the ~70 mm range for RR0 in Figure 3a is larger than the ranges shown by the green and red shaded areas in Figure 3b? If so, it would be helpful to specify that explicitly for clarity.
l.198-201: Could this be explained by increases in SMB post-2100 in UKESM as compared to UKESMrep?
l.209: replace ‘sensitivity’ by ‘SLR-RR-sensitivity’ for clarity.
l.220-221: I’m not sure where to visualise that the threshold is reached even for the smallest prescribed retreat rate. Clarification or reference to a figure would be useful.
l.255-258: In line with my previous comments, I think that this statement should be revised to something like ‘greater than the range of forcing from the ISMIP6-2300 Tier 1 experiments’. It does not seem to me that the current experiments allow for direct comparison between the influence of calving front retreat variability and variability in sub-shelf melt representation in ice sheet models. Instead, you account for variability in climate forcings, including ocean and atmospheric forcings.
l.286-296: Same as above.
Citation: https://doi.org/10.5194/egusphere-2025-328-RC2 - AC2: 'Response to RC2', Jowan Barnes, 26 Jun 2025
Peer review completion
Journal article(s) based on this preprint
Video supplement
Modelling the sensitivity of ice loss to calving front retreat rates - Video 1 Jowan Barnes https://doi.org/10.5446/69727
Modelling the sensitivity of ice loss to calving front retreat rates - Video 2 Jowan Barnes https://doi.org/10.5446/69728
Modelling the sensitivity of ice loss to calving front retreat rates - Video 3 Jowan Barnes https://doi.org/10.5446/69729
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Jowan M. Barnes
G. Hilmar Gudmundsson
Daniel N. Goldberg
Sainan Sun
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
- Preprint
(1534 KB) - Metadata XML