Realistic ice-shelf/ocean state estimates (RISE) of Antarctic basal melting and drivers

Galton-Fenzi, Benjamin Keith; Porter-Smith, Richard; Cook, Sue; Cougnon, Eva; Gwyther, David E.; Huneke, Wilma G. C.; Rosevear, Madelaine G.; Asay-Davis, Xylar; Boeira Dias, Fabio; Dinniman, Michael S.; Holland, David; Kusahara, Kazuya; Naughten, Kaitlin A.; Nicholls, Keith W.; Pelletier, Charles; Richter, Ole; Seroussi, Helene L.; Timmermann, Ralph

doi:10.5194/egusphere-2024-4047

Preprints

https://doi.org/10.5194/egusphere-2024-4047

Preprints

18 Feb 2025

| 18 Feb 2025

Realistic ice-shelf/ocean state estimates (RISE) of Antarctic basal melting and drivers

Benjamin Keith Galton-Fenzi, Richard Porter-Smith, Sue Cook, Eva Cougnon, David E. Gwyther, Wilma G. C. Huneke, Madelaine G. Rosevear, Xylar Asay-Davis, Fabio Boeira Dias, Michael S. Dinniman, David Holland, Kazuya Kusahara, Kaitlin A. Naughten, Keith W. Nicholls, Charles Pelletier, Ole Richter, Helene L. Seroussi, and Ralph Timmermann

Abstract. Societal adaptation to rising sea levels requires robust projections of the Antarctic Ice Sheet’s retreat, particularly due to ocean-driven basal melting of its fringing ice shelves. Recent advances in ocean models that simulate ice-shelf melting offer an opportunity to reduce uncertainties in ice–ocean interactions. Here, we compare several community-contributed, circum-Antarctic ocean simulations to highlight inter-model differences, evaluate agreement with satellite-derived melt rates, and examine underlying physical processes. All but one simulation use a melting formulation depending on both thermal driving (T ^⋆) and friction velocity (u^⋆), which together represent the thermal and ocean current forcings at the ice–ocean interface. Simulated melt rates range from 650 to 1277 Gt year⁻¹ (m = 0.45 − 0.91 m year⁻¹), driven by variations in model resolution, parameterisations, and sub-ice shelf circulation. Freeze-to-melt ratios span 0.30 to 30.12 %, indicating large differences in how refreezing is represented. The multi-model mean (MMM) produces an averaged melt rate of 0.60 m year⁻¹ from a net mass loss of 842.99 Gt year⁻¹ (876.03 Gt year⁻¹ melting and 33.05 Gt year⁻¹ refreezing), yielding a freeze-to-melt ratio of 3.92 %. We define a thermo-kinematic melt sensitivity, ζ = m/(T ^⋆u^⋆) = 4.82 × 10⁻⁵ °C⁻¹ for the MMM, with individual models spanning 2.85 × 10⁻⁵ to 19.4 × 10⁻⁵ °C⁻¹. Higher melt rates typically occur near grounding zones where both T ^⋆ and u^⋆ exert roughly equal influence. Because friction velocity is critical for turbulent heat exchange, ice-shelf melting must be characterised by both ocean energetics and thermal forcing. Further work to standardise model setups and evaluation of results against in situ observations and satellite data will be essential for increasing model accuracy, reducing uncertainties, to improve our understanding of ice-shelf–ocean interactions and refine sea-level rise predictions.

Received: 23 Dec 2024 – Discussion started: 18 Feb 2025

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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Journal article(s) based on this preprint

04 Dec 2025

Multi-model estimate of Antarctic ice-shelf basal mass budget and ocean drivers

Benjamin K. Galton-Fenzi, Richard Porter-Smith, Sue Cook, Eva Cougnon, David E. Gwyther, Wilma G. C. Huneke, Madelaine G. Rosevear, Xylar Asay-Davis, Fabio Boeira Dias, Michael S. Dinniman, David Holland, Kazuya Kusahara, Kaitlin A. Naughten, Keith W. Nicholls, Charles Pelletier, Ole Richter, Hélène Seroussi, and Ralph Timmermann

The Cryosphere, 19, 6507–6525, https://doi.org/10.5194/tc-19-6507-2025,https://doi.org/10.5194/tc-19-6507-2025, 2025

Short summary

Interactive discussion

Status: closed

RC1:
'Comment on egusphere-2024-4047', Anonymous Referee #1, 20 Mar 2025

The authors present the multi-model mean (MMM) of ice shelf melt rates and other parameters that determine ice shelf melt rates. They claim that the MMM provides a useful comparison between different models and serves as a guideline for observations and modeling. However, I believe that the simulated ice shelf melt rate is a parameter that can be easily tuned by selecting appropriate coefficients, and the multi-model comparisons presented here are somewhat overstating and misleading. I believe more analyses can make this manuscript much more useful for the community. I suggest a major revision.

Major Comments
1. The authors discuss, for example, the comparison of simulated total melt with satellite-based estimates (e.g., between lines 325 and 337 and in Table 2). However, in global simulations like this, integrated melt rates are easily tunable parameters. I question the significance of this study's comparison of model outputs that are easily adjustable, rather than focusing on parameters that are more challenging to tune and simulate. I suggest that the authors add a paragraph explaining how the drag coefficients and heat and salt transfer coefficients are determined in all simulations.
2. To enhance the usefulness of the comparisons, I suggest addressing the following aspects (a-d). In the current version of the manuscript, the authors discuss bottom or vertically integrated ocean hydrography, which is not the best metric for determining ice shelf melt rates. I recommend presenting thermocline depths and vertical sections under major ice shelf cavities to illustrate how variations in hydrography lead to differences in simulated melt rates. Additionally, it is important to examine interannual and seasonal variability, discussing the extent of differences in these aspects.
(a) Integrated ice shelf melt rates for each individual ice shelf.

(b) Hydrographic conditions, particularly vertical sections within the ice shelf cavity or at the ice shelf front.

(c) Temporal variability of thermocline depth and its relationship to ice shelf melt rates.

(d) The processes governing ice shelf melt rates, such as thermocline depth variations, temperature changes, and other factors influencing ocean velocity.
Minor Comments
1. I find that Antarctica's wide mean melt rate is not very intuitive. I suggest adding an integrated melt rate in Gt/yr.
2. Lines 79-82: Considering that the Antarctic ice shelf melt rate is an easily tuned parameter, I feel this is somewhat overstating the presented findings here "allows us to constrain both present and future ocean-driven impacts on Antarctica, and provide much needed evaluation with both satellite-derived and in situ estimates of ice shelf basal melt rates".
3. Lines 403–412: One of the main conclusions of this multi-model comparison is the strong dependence of both thermal driving and friction velocity on the melt rate—concepts that have already been well established in numerous previous studies. While this study represents a first attempt at presenting a multi-model mean, I do not believe that there are more useful comparisons metrics that are not presented in the current version of the manuscript.

Citation: https://doi.org/10.5194/egusphere-2024-4047-RC1
- AC1: 'Reply on RC1', Ben Galton-Fenzi, 10 Jun 2025
  
  Please see the uploaded document detailing our response to the review.
  
  Citation: https://doi.org/10.5194/egusphere-2024-4047-AC1
RC2:
'Comment on egusphere-2024-4047', Anonymous Referee #2, 04 Apr 2025
General Comments
This study compares several circum-Antarctic ocean simulations that include sub-ice-shelf cavities to highlight inter-model differences and evaluate results against satellite-derived melt rates. The approach is to take the ocean simulations “as is,” without following a particular protocol. Both model outputs and satellite-derived melt rates are remapped to a common grid to facilitate comparison. This represents the first attempt to provide a Multi-Model Mean estimate of Antarctic ice shelf basal melting, while also highlighting areas of agreement and divergence among models. The work has the potential to serve as a valuable reference for future modeling efforts and to help guide targeted observational strategies.
However, I have a major concern that the comparison is overly focused on melt rate and its primary drivers (friction velocity and thermal driving) while giving limited or no attention to the underlying ocean and sea ice state. These parameters are often highly tunable, which reduces the robustness and generalizability of the findings. As a result, the comparison has limited utility for informing future modeling or observation-based studies. A broader focus on key oceanographic and sea ice metrics would strengthen the study’s relevance and impact.
Here are several suggested comparisons that I believe would significantly strengthen the manuscript. While I do not expect the authors to include all of these, incorporating at least some would enhance the study's depth and utility:
Cross-sections (y–z) of mean temperature and salinity in key regions, particularly where Circumpolar Deep Water intrusions occur;

T/S diagrams over individual ice shelves, including adjacent continental shelves;

Heat transport across individual ice shelf fronts;

Mean mixed layer depth (e.g., July to September), based on a clearly defined criterion;

Annual cycle of sea ice area and volume;

Maps of sea ice concentration and sea ice thickness.

For metrics where observation-based estimates are available (e.g., sea ice properties), I encourage the authors to include these in the comparisons as well.
The manuscript is overall well-written and clear. However, in addition to my main concern noted above, there are also significant issues with several figures, as outlined below. For these reasons, my recommendation is major revision.

Specific Comments
Table 1: I suggest including (1) a column indicating whether the model is “regional” or “global”; (2) a column specifying the atmospheric forcing used to drive the model (e.g., JRA-55, CORE); and (3) for regional models, a column identifying the product used to drive open boundary conditions.
Lines 142–143: “The thermal driving…” – Please modify this sentence to reflect that thermal driving can be negative (i.e., T* < 0), in which case the water is colder than the freezing point.
Section 2.2 “Remapping approach to a common grid”:
I was not familiar with the Voronoi tessellation approach, which I believe is not commonly used in the geophysical sciences. What are the advantages of this method compared to more widely used techniques such as bilinear or nearest-neighbor interpolation? It is mentioned that this approach results in “lower total melt estimates than previous studies” (lines 199–200), and later that “discrepancies likely arise from differences in the areas used to compute melt rates” (lines 252–253). Is this because the Voronoi tessellation is non-conservative? Would it make more sense to convert melt rates to a mass flux, apply a conservative remapping to the common grid, and then convert the flux back to a melt rate? This might avoid the bias toward lower melt estimates. Lastly, please include other specific reasons for selecting this approach over more conventional alternatives.
Table 2: Are the mean melt rates area-weighted? If so, please clarify this in both the table caption and the main text.
Figure 1: I suggest that the comparison with satellite observations be moved from the supplementary material to the main text.
Lines 316–317: “The Multi-Model Mean (MMM) estimate of Antarctic ice shelf basal melting surpasses the performance of any individual model in our ensemble.” The rationale for this statement is unclear. No analysis is provided to support it. Please clarify the basis for this claim or include supporting evidence.
Line 399: “Comprehensive” may be too strong in this context. I suggest using a softer term such as “extensive.”
Code and Data Availability: Please make the code used in this study publicly available to enhance transparency and reproducibility.

Editorial / Typographical Comments
Line 55: “IUGG, WCRP, SCAR” – Please define these acronyms in full for readers who may not be familiar with them.
Line 60: Please define MISOMIP and MISOMIP2.
Line 83: “...the project” – Since the RISE Project is introduced in the next paragraph, I suggest changing “the project” to “this work” or a more neutral phrasing.
Lines 90–91: Please define ICESat, ApRES, NECKLACE, and SOOS.
Table 1: The phrase “...reference for each model” is redundant. I suggest deleting “for each model.” Also, please define u* in the caption.
Lines 149–150: “Thermal driving …” – This is unnecessarily repetitive, as thermal driving was already defined in line 142. I recommend combining the two definitions to avoid duplication.
Line 228: Correct “at teh” → “at the.”
Figure 1: Please define “ISMR” and “SD.” The coordinates are difficult to read; consider increasing the font size of the x and y axes.
Figures 2 and 3: Same comments as for Figure 1.
Line 261: Correct “is suggests” → “suggests.”
Line 375: Fix formatting error in “e.g.,[” – likely a LaTeX code issue.
Supplementary Material: In some figures, the legend text is difficult to read. Please ensure all text is legible at standard PDF viewing size.
Citation: https://doi.org/10.5194/egusphere-2024-4047-RC2
- AC2: 'Reply on RC2', Ben Galton-Fenzi, 10 Jun 2025
  
  Please see the uploaded document detailing our response to the review.
  
  Citation: https://doi.org/10.5194/egusphere-2024-4047-AC2

Interactive discussion

Status: closed

RC1:
'Comment on egusphere-2024-4047', Anonymous Referee #1, 20 Mar 2025

The authors present the multi-model mean (MMM) of ice shelf melt rates and other parameters that determine ice shelf melt rates. They claim that the MMM provides a useful comparison between different models and serves as a guideline for observations and modeling. However, I believe that the simulated ice shelf melt rate is a parameter that can be easily tuned by selecting appropriate coefficients, and the multi-model comparisons presented here are somewhat overstating and misleading. I believe more analyses can make this manuscript much more useful for the community. I suggest a major revision.

Major Comments
1. The authors discuss, for example, the comparison of simulated total melt with satellite-based estimates (e.g., between lines 325 and 337 and in Table 2). However, in global simulations like this, integrated melt rates are easily tunable parameters. I question the significance of this study's comparison of model outputs that are easily adjustable, rather than focusing on parameters that are more challenging to tune and simulate. I suggest that the authors add a paragraph explaining how the drag coefficients and heat and salt transfer coefficients are determined in all simulations.
2. To enhance the usefulness of the comparisons, I suggest addressing the following aspects (a-d). In the current version of the manuscript, the authors discuss bottom or vertically integrated ocean hydrography, which is not the best metric for determining ice shelf melt rates. I recommend presenting thermocline depths and vertical sections under major ice shelf cavities to illustrate how variations in hydrography lead to differences in simulated melt rates. Additionally, it is important to examine interannual and seasonal variability, discussing the extent of differences in these aspects.
(a) Integrated ice shelf melt rates for each individual ice shelf.

(b) Hydrographic conditions, particularly vertical sections within the ice shelf cavity or at the ice shelf front.

(c) Temporal variability of thermocline depth and its relationship to ice shelf melt rates.

(d) The processes governing ice shelf melt rates, such as thermocline depth variations, temperature changes, and other factors influencing ocean velocity.
Minor Comments
1. I find that Antarctica's wide mean melt rate is not very intuitive. I suggest adding an integrated melt rate in Gt/yr.
2. Lines 79-82: Considering that the Antarctic ice shelf melt rate is an easily tuned parameter, I feel this is somewhat overstating the presented findings here "allows us to constrain both present and future ocean-driven impacts on Antarctica, and provide much needed evaluation with both satellite-derived and in situ estimates of ice shelf basal melt rates".
3. Lines 403–412: One of the main conclusions of this multi-model comparison is the strong dependence of both thermal driving and friction velocity on the melt rate—concepts that have already been well established in numerous previous studies. While this study represents a first attempt at presenting a multi-model mean, I do not believe that there are more useful comparisons metrics that are not presented in the current version of the manuscript.

Citation: https://doi.org/10.5194/egusphere-2024-4047-RC1
- AC1: 'Reply on RC1', Ben Galton-Fenzi, 10 Jun 2025
  
  Please see the uploaded document detailing our response to the review.
  
  Citation: https://doi.org/10.5194/egusphere-2024-4047-AC1
RC2:
'Comment on egusphere-2024-4047', Anonymous Referee #2, 04 Apr 2025
General Comments
This study compares several circum-Antarctic ocean simulations that include sub-ice-shelf cavities to highlight inter-model differences and evaluate results against satellite-derived melt rates. The approach is to take the ocean simulations “as is,” without following a particular protocol. Both model outputs and satellite-derived melt rates are remapped to a common grid to facilitate comparison. This represents the first attempt to provide a Multi-Model Mean estimate of Antarctic ice shelf basal melting, while also highlighting areas of agreement and divergence among models. The work has the potential to serve as a valuable reference for future modeling efforts and to help guide targeted observational strategies.
However, I have a major concern that the comparison is overly focused on melt rate and its primary drivers (friction velocity and thermal driving) while giving limited or no attention to the underlying ocean and sea ice state. These parameters are often highly tunable, which reduces the robustness and generalizability of the findings. As a result, the comparison has limited utility for informing future modeling or observation-based studies. A broader focus on key oceanographic and sea ice metrics would strengthen the study’s relevance and impact.
Here are several suggested comparisons that I believe would significantly strengthen the manuscript. While I do not expect the authors to include all of these, incorporating at least some would enhance the study's depth and utility:
Cross-sections (y–z) of mean temperature and salinity in key regions, particularly where Circumpolar Deep Water intrusions occur;

T/S diagrams over individual ice shelves, including adjacent continental shelves;

Heat transport across individual ice shelf fronts;

Mean mixed layer depth (e.g., July to September), based on a clearly defined criterion;

Annual cycle of sea ice area and volume;

Maps of sea ice concentration and sea ice thickness.

For metrics where observation-based estimates are available (e.g., sea ice properties), I encourage the authors to include these in the comparisons as well.
The manuscript is overall well-written and clear. However, in addition to my main concern noted above, there are also significant issues with several figures, as outlined below. For these reasons, my recommendation is major revision.

Specific Comments
Table 1: I suggest including (1) a column indicating whether the model is “regional” or “global”; (2) a column specifying the atmospheric forcing used to drive the model (e.g., JRA-55, CORE); and (3) for regional models, a column identifying the product used to drive open boundary conditions.
Lines 142–143: “The thermal driving…” – Please modify this sentence to reflect that thermal driving can be negative (i.e., T* < 0), in which case the water is colder than the freezing point.
Section 2.2 “Remapping approach to a common grid”:
I was not familiar with the Voronoi tessellation approach, which I believe is not commonly used in the geophysical sciences. What are the advantages of this method compared to more widely used techniques such as bilinear or nearest-neighbor interpolation? It is mentioned that this approach results in “lower total melt estimates than previous studies” (lines 199–200), and later that “discrepancies likely arise from differences in the areas used to compute melt rates” (lines 252–253). Is this because the Voronoi tessellation is non-conservative? Would it make more sense to convert melt rates to a mass flux, apply a conservative remapping to the common grid, and then convert the flux back to a melt rate? This might avoid the bias toward lower melt estimates. Lastly, please include other specific reasons for selecting this approach over more conventional alternatives.
Table 2: Are the mean melt rates area-weighted? If so, please clarify this in both the table caption and the main text.
Figure 1: I suggest that the comparison with satellite observations be moved from the supplementary material to the main text.
Lines 316–317: “The Multi-Model Mean (MMM) estimate of Antarctic ice shelf basal melting surpasses the performance of any individual model in our ensemble.” The rationale for this statement is unclear. No analysis is provided to support it. Please clarify the basis for this claim or include supporting evidence.
Line 399: “Comprehensive” may be too strong in this context. I suggest using a softer term such as “extensive.”
Code and Data Availability: Please make the code used in this study publicly available to enhance transparency and reproducibility.

Editorial / Typographical Comments
Line 55: “IUGG, WCRP, SCAR” – Please define these acronyms in full for readers who may not be familiar with them.
Line 60: Please define MISOMIP and MISOMIP2.
Line 83: “...the project” – Since the RISE Project is introduced in the next paragraph, I suggest changing “the project” to “this work” or a more neutral phrasing.
Lines 90–91: Please define ICESat, ApRES, NECKLACE, and SOOS.
Table 1: The phrase “...reference for each model” is redundant. I suggest deleting “for each model.” Also, please define u* in the caption.
Lines 149–150: “Thermal driving …” – This is unnecessarily repetitive, as thermal driving was already defined in line 142. I recommend combining the two definitions to avoid duplication.
Line 228: Correct “at teh” → “at the.”
Figure 1: Please define “ISMR” and “SD.” The coordinates are difficult to read; consider increasing the font size of the x and y axes.
Figures 2 and 3: Same comments as for Figure 1.
Line 261: Correct “is suggests” → “suggests.”
Line 375: Fix formatting error in “e.g.,[” – likely a LaTeX code issue.
Supplementary Material: In some figures, the legend text is difficult to read. Please ensure all text is legible at standard PDF viewing size.
Citation: https://doi.org/10.5194/egusphere-2024-4047-RC2
- AC2: 'Reply on RC2', Ben Galton-Fenzi, 10 Jun 2025
  
  Please see the uploaded document detailing our response to the review.
  
  Citation: https://doi.org/10.5194/egusphere-2024-4047-AC2

Peer review completion

AR – Author's response | RR – Referee report | ED – Editor decision | EF – Editorial file upload

ED: Publish subject to revisions (further review by editor and referees) (11 Jul 2025) by Nicolas Jourdain

Dear Ben Galton-Fenzi and co-authors,

First of all, I thank the two experts for their careful review of the initial manuscript. I also thank you for your point-by-point responses.

Both reviewers recommended to reconsider the manuscript after major revisions. Their major concerns are related to (i) the absence of analyses of temperature and salinity in front of the ice shelf cavities, and (ii) the lack of evidence for the claim that such a multi-model mean is more interesting than individual models.

On the first point, more analyses and disussions about the T,S properties in front of ice shelves is needed. Melt rates in regions with warm cavities can be adjusted by tuning the heat exchange coefficient (Jourdain et al., 2017), even though such adjustment is indeed more difficult for circum-Antarctic simulations. Regardless of the tuning, both reviewers find that the study would be much more useful if it included more assessment of temperature and salinity. Looking at the multi-model mean temperature and salinity at a given depth (or profiles averaged over a given region) would indicate whether biases are actually weak in the multi-model mean, and whether realistic melt rates are obtained for realistic conditions near the ice shelf fronts. The new table in the manuscript that will include "the average temperature and salinity on the continental shelf in the front of each of the seven ice shelves" may partly address this concern if it is enough described and discussed.

Regarding the second point, Reviewer #1 was not convinced by the interest of the multi-model mean. I consider that the use of the multi-model mean is well justified and is an interesting aspect of this manuscript. However, the provided references are related to climate models under a common forcing framework (CMIP), while the models partaking to RISE were run under very different forcings. In particular, I am not sure that averaging ocean models forced by reanalyses over the recent period together with a coupled ocean–atmosphere model in pre-industrial conditions can be expected to reduce the overall bias. I therefore expect a slightly more nuanced presentation of the added value of a multi-model mean in the revised manuscript.

In the revised version, please also provide an explicit link to the data and code shared through the AAD data center.

Once the system lets you do so, please upload the revised manuscript.

Best regards

Nicolas Jourdain

Hide

AR by Ben Galton-Fenzi on behalf of the Authors (11 Aug 2025) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (18 Aug 2025) by Nicolas Jourdain

RR by Anonymous Referee #2 (04 Sep 2025)

RR by Anonymous Referee #1 (24 Sep 2025)

Suggestions for revision or reasons for rejection

The authors present the multi-model mean (MMM) of ice shelf melt rates and other parameters that determine ice shelf melt rates. They claim that the MMM provides a useful comparison between different models and serves as a guideline for observations and modeling. I appreciate the effort of the authors in assembling the model outputs and attempting to draw general conclusions about ice shelf melt rates. However, I have concerns about the interpretation of the results and the framing of the conclusions. I suggest a major revision or rejection.

Major comment
1.On the claim that MMM is a state estimate
I disagree with the characterization of the MMM as a “state estimate.”The MMM, in contrast, is a purely statistical average of model outputs with no observational constraint. If the authors wish to maintain this terminology, they must provide clear justification and distinguish it from formal state estimation approaches.

2. On the interpretation of melt rates
The authors state: “The melt rate is therefore the end result of many complex oceanic processes, and relationships and feedbacks with those and the shape of the geometry and forcing, that provide for the resulting ocean heat supply underneath the ice shelf.” I find this statement problematic. While melt rate is indeed a diagnostic outcome of coupled processes, it is also highly sensitive to tunable parameterizations. This makes it less of an “end result” in the sense of being emergent, and more of a model-dependent quantity that reflects chosen parameterizations. For example, I think ice shelf melt rate is an end product if ice shelf melt rate is calculated using an ice sheet-ocean coupled simulation with an evolving ice shelf cavity. I believe ocean model cavity temperature or MMM of vertical section showing cavity hydrography is a much more important result than ice shelf melt rate.

3. On the use of the multi-model mean (MMM)
The manuscript presents the MMM as a robust estimate of basal melt rates. However, the MMM is only powerful under certain conditions—for example, when model physics are approximately correct and the variable of interest is an emergent system property. Basal melt rate does not meet these criteria. The underlying parameterizations are still debated, and the variable is highly tunable. Melt rate is highly sensitive to the ice shelf geometries, which are also not the same for all model simulations. While it may not be straightforward to tune melt directly, it can be easily adjusted through choices of heat-transfer coefficients, mixing parameters, and cavity geometry assumptions. This undermines the statistical argument that the MMM provides a more reliable estimate.

4. I recommend that the authors reframe the manuscript away from emphasizing the MMM as a robust estimate achieving better agreement with observations. Instead, the strength of this work lies in evaluating model differences and highlighting the physical and parametric reasons behind them. I again highly recommend to include (a) examining hydrographic conditions (e.g., vertical sections within cavities and at ice shelf fronts), (b) exploring temporal variability of thermocline depth and its relationship to melt, and (c) analyzing the processes governing melt rates (thermocline shifts, temperature variability, and ocean circulation drivers). I believe MMM of these parameters are more important the ice shelf melt rates.

Minor comment :
Lines 102-105: I think you need add additional explanation if it is the case (see major comments).

Hide

ED: Publish subject to minor revisions (review by editor) (14 Oct 2025) by Nicolas Jourdain

Dear Ben Galton-Fenzi and co-authors,

First of all, I thank the two reviewers for their second evaluation of your manuscript. Reviewer #1 recommends accepting your manuscript as it is. In contrast, Reviewer #2 still thinks that the manuscript is problematic and that there were more interesting things to analyse in this model ensemble than the multi-model mean melt rate. I doubt that you will be willing to follow this direction and entirely change the content of your manuscript. Based on my own review and Reviewer #1’s evaluation, I do think that there is value in presenting the RISE results through the multi-model mean melt rate. Several points raised by Reviewer #2 are nonetheless very relevant, and I am asking you to revise your manuscript as detailed below.

1- “realistic ice-shelf/ocean state estimate [...]” may not be the most appropriate title, as (i) “realistic state estimate” is usually dedicated to ocean simulations with some kind of data assimilation, which is quite far from this ensemble that even includes a pre-industrial simulation, and (ii) “Realistic” is a claim that is not supported by a thorough evaluation of the model outputs in comparison to observations (e.g., 3D temperature and salinity). As such, the title of this manuscript and the name of the RISE project may sound somewhat problematic. Please consider changing the title to something like “Ice-shelf/ocean multi-model state estimates of Antarctic basal melting and drivers”? Then you can still mention the RISE project in the abstract and/or introduction because this name has been widely advertised in the community.

2- These sentences in section 4 are still overselling the method (see Reviewer #2’s comments and my previous review): “The MMM thus serves to reduce individual biases and smooth out uncertainties, likely resulting in a more reliable representation of the State Estimate of basal melting and ocean-drivers. The Multi-Model Mean (MMM) estimate of Antarctic ice shelf basal melting therefore likely surpasses the performance of any individual model in our ensemble”. Please specify that only a part of the uncertainty can be expected to be removed here. The structural uncertainty shared by models, like an inappropriate physical parameterisation of ice-shelf basal melting or common biases in the bathymetry or ice topography, will of course remain problematic in the MMM. Furthermore, the last sentence of the quote should be either removed or supported by analyses as there could still be a few models that are better tuned than the others and that therefore surpass the MMM.

3- In Tab.1, add a footnote near the “150 years” of E302 to indicate “pre-industrial conditions” (currently, it is hidden in the supplementary material, and this appears to me as an important piece of information).

Best regards

Nicolas Jourdain

Hide

AR by Ben Galton-Fenzi on behalf of the Authors (28 Oct 2025) Author's response Manuscript

EF by Katja Gänger (30 Oct 2025) Author's tracked changes

ED: Publish as is (02 Nov 2025) by Nicolas Jourdain

AR by Ben Galton-Fenzi on behalf of the Authors (05 Nov 2025) Manuscript

Journal article(s) based on this preprint

04 Dec 2025

Multi-model estimate of Antarctic ice-shelf basal mass budget and ocean drivers

The Cryosphere, 19, 6507–6525, https://doi.org/10.5194/tc-19-6507-2025,https://doi.org/10.5194/tc-19-6507-2025, 2025

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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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Short summary

Melting beneath Antarctica’s floating ice shelves is key to future sea-level rise. We compare several different ocean simulations with satellite measurements, and provide the first multi-model average estimate of melting and refreezing driven by both ocean temperature and currents beneath ice shelves. The multi-model average can provide a useful tool for better understanding the role of ice shelf melting in present-day and future ice-sheet changes and informing coastal adaptation efforts.


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