the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 24 Apr 2026
West Antarctic Ice Retreat Temporarily Halted with Transient Rheology in Future Climate Projections
Abstract. Projections of sea-level change and Antarctic Ice Sheet (AIS) stability under anthropogenic climate change hinge upon accurately describing physical feedbacks that link ice dynamics (marine and terrestrial) with the gravitational, rotational and deformational response of the solid Earth to ice and ocean loading changes. In turn, the rate of AIS melting can lower the rate of global mean temperature rise, by promoting sea ice growth and amplifying Earth’s albedo. The marine West Antarctic Ice Sheet (WAIS) is vulnerable to runaway grounding line retreat. However, the rapid viscoelastic rebound of the bedrock in response to ice retreat has been shown to stabilize its grounding line, aided by the low-viscosity mantle beneath the WAIS. Such bedrock deformation is typically modelled with idealized Maxwell viscoelasticity, despite that rock deformation experiments show that additional “transient” creep mechanisms occur over societally relevant (~decadal-centennial) timescales that are missing from the Maxwell model. Here, we simulate future AIS evolution, coupled with self-consistent solid Earth deformation and sea level change, for various emissions scenarios (RCP 2.6, 4.5, 8.5), incorporating transient deformation. This more complete treatment of solid Earth deformation delays grounding line retreat as compared to Maxwell projections, with differences of tens of kilometres persisting for decades at Pine Island and Thwaites Glaciers. Though transient deformation slows glacier retreat, it is unable to prevent the bulk of ice loss and sea-level rise on longer, centennial timescales. Even still, deviations in AIS meltwater flux with transient deformation could affect the pace of global temperature rise in climate model predictions.
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RC1: 'Comment on egusphere-2026-2172', Maria Zeitz, 15 Jun 2026
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AC1: 'Reply on RC1', Allie Coonin, 06 Aug 2026
Dear Dr. Zeitz,
Thank you very much for your constructive feedback. You brought up several valuable points that we think will significantly improve the manuscript. Please see below for our response to each comment and how we plan to address them in the revised manuscript. We have formatted your comments in italics to distinguish your original text from our responses. Any proposed revisions to the text of the manuscript are embedded in quotations and bolded.
Summary
The manuscript studies the interaction between climate change, ice sheet dynamics and the solid earth in West Antarctica. The authors introduce a new modeling approach to the solid earth rheology – a transient viscoelastic rheology, which responds on decadal to centennial time scales relevant to modern ice loss due to anthropogenic climate change – and compare it to the established Maxwell rheology. They find that the retreat of the West Antarctic Ice Sheet in different climate scenarios is consistently slower in simulations with the transient model and the bedrock uplift is stronger. This effect is less pronounced for scenarios with little ice loss and increases for higher ice loss scenarios. However, the long-term response of the ice sheet to a changing climate does not seem to be affected.
General comments
In my opinion the paper is already very good. The topic is of scientific interest and relevant to the community. The methods seem appropriate for the question at hand. The presentation of the research is clear and well structured. The visual representation is compelling. I also appreciate the sensitivity analyses in the supplement.
There are a few points I would like to address:
l13: the feedbacks promoting sea ice growth and amplifying albedo are not part of the study and only a minor point in the discussion. I would delete the sentence from the abstract, to avoid false expectations.
Done. We agree this sentence is unwarranted and have removed it from the abstract.
The introductory paragraph (l40-l56) gives a very short introduction to the marine ice sheet instability. In a realistic, 3-dimensional ice sheet with time-variable boundary conditions, the onset of unstable collapse can be moderated by many factors. For the sake of completeness, it would be helpful to expand the discussion here a bit.
Thank you for this comment. We agree this discussion should be expanded to emphasize the other processes that trigger unstable collapse. We have revised the first paragraph, and it now reads as follows:
“Predictions of ice sheet and sea-level change in response to various trajectories of atmospheric carbon emissions have demonstrated the potential for dramatic ice retreat in West Antarctica (Kopp et al., 2017; Robel et al., 2019). This vulnerability to extreme ice loss is in large part because the bedrock underneath the marine-based West Antarctic Ice Sheet (WAIS) deepens from the margins toward the ice sheet interior, which predisposes the WAIS to runaway retreat via the Marine Ice Sheet Instability (Schoof, 2007; Thomas, 1979; Weertman, 1974). The flux through the grounding line, the location at which the ice sheet begins to float because it is too thin to displace the entire weight of the water column, has strong sensitivity to the thickness of ice at the grounding line (with outflow proportional to ice thickness to the power ~5, Schoof, 2007.) Therefore, on such retrograde bed slopes, even a small perturbation can trigger unstable collapse as the grounding line retreats to a location with deeper bedrock and greater ice thickness. This greater grounding line ice thickness heightens ice loss through the grounding line, promoting continued retreat. Bedrock topography is one of many factors that can trigger ice sheet retreat; grounding line migration is a complex process modulated by time-evolving boundary conditions relating to ocean forcing, downstream ice shelf stability, variable ice mass accumulation, ice rheology, and basal friction and heat flow, which are spatially heterogenous (Caillet et al., 2023; Hudson et al., 2023; Sergienko et al., 2026). These unsteady phenomena enable irregular oscillations between advance and retreat and allow for unstable conditions to exist on prograde as well as retrograde slopes (Sergienko & Wingham, 2024).”
Caillet, J., Jourdain, N. C., Mathiot, P., Hellmer, H. H., & Mouginot, J. (2023). Drivers and reversibility of abrupt ocean state transitions in the Amundsen Sea, Antarctica. Journal of Geophysical Research: Oceans, 128, https://doi.org/10.1029/2022JC018929
Hudson, T.S., Kufner, S.K., Brisbourne, A.M. et al. Highly variable friction and slip observed at Antarctic ice stream bed. Nat. Geosci. 16, 612–618 (2023). https://doi.org/10.1038/s41561-023-01204-4
Sergienko, O., Haseloff, M., Robel, A. et al. A new paradigm for understanding Earth’s marine ice sheets. Nat. Geosci. 19, 374–383 (2026). https://doi.org/10.1038/s41561-026-01941-2
As far as I understand the Schoof parameterization for grounding line ice flux fails for heavily buttressed ice shelves (see Reese et al., 2018). As buttressing is important for the ice shelves studied, I would appreciate a short discussion on how the choice of this parameterization might affect the results.
Reese, R., Winkelmann, R., and Gudmundsson, G. H.: Grounding-line flux formula applied as a flux condition in numerical simulations fails for buttressed Antarctic ice streams, The Cryosphere, 12, 3229–3242, https://doi.org/10.5194/tc-12-3229-2018, 2018.
Thank you for bringing this up – we failed to include an important citation for a paper that describes the updated treatment of the grounding line parametrization in the most recent version of the PSU3D ice model (Pollard and Deconto, 2020), which addresses the comments raised by Reese et al. (2018) for the case of heavily buttressed ice shelves. In Appendix B1, Pollard and DeConto explain that when the buttressing factor, θ falls to zero (i.e. in situations where there is high compressive horizontal deviatoric stress normal to the grounding line and high compressive strain in the direction of ice flow), the Schoof parametrization predicts unrealistically low velocities at the grounding-line and acknowledge that the equation is invalid for θ<0. However, such conditions of strong buttressing are not prevalent in simulations of future Antarctic retreat because the grounding lines readily retreat into wide interior basins, so there is not much ice shelf buttressing acting upon the upstream ice. Such strong buttressing conditions would be even less likely if a major ice shelf break up, e.g., via hydrofracturing, were to occur. Failure of the parametrization under strong buttressing conditions would be more of a concern for paleo simulations of the Antarctic ice sheet during glacial periods, when the grounding line and ice shelves were more expansive.
We have added the following discussion in Section 2.2 to address this limitation of the parameterization and emphasize that it would not likely impact the results:
“The Schoof (2007) grounding line flux parametrization has been shown to fail in cases where ice shelves are heavily buttressed (Reese et al., 2018). However, such conditions are not prevalent in simulations of future West Antarctic ice sheet retreat with the PSU 3D ice sheet-shelf model because of ice shelf thinning due to oceanic melting and grounding zones readily retreat into wide interior basins, which are less sensitive to buttressing than are narrower embayments (Pollard and DeConto, 2020).”
Pollard, D. and R. M. Deconto (2020). "Improvements in one-dimensional grounding-line parameterizations in an ice-sheet model with lateral variations (PSUICE3D v2.1)." Geoscientific Model Development 13(12): 6481-6500.
The authors use a realistic climate scenario and model the time period from 1950 CE – 2500 CE. The initial state and the history of the ice sheet and the solid earth play an important role on these time scales. I would like to know more about the spin-up procedure for both, the ice sheet model (in section 2.2) and the solid earth model (in section 2.3). In addition, I would like to see a brief analysis of the initial state, comparing the ice thickness and ice velocities observations.
We agree that sensitivity to initial state and spin up are important issues, however, since our study is focused on isolating the impact of transient rheology, we feel it would be beyond the scope of this study to perform a detailed analysis of this factor and instead adopt initial conditions from previous work. The PSU 3D ice sheet model spin-up is identical to that of DeConto et al. (2021) and Gomez et al. (2024) and we have edited the text to direct the reader to the original papers for greater detail on this procedure in Section 2.2 (see below). We already plot the initial ice thickness of the spun-up Antarctic Ice Sheet model in Figure 1(a), and we will also provide a more complete set of ice sheet model outputs than is shown in figures, including initial ice velocities and thicknesses, within a data repository linked in the Data Availability Section, so that future work can explore these comparisons in more detail.
We have added the following to Section 2.2:
“The dynamic ice component is a hybrid ice sheet-shelf model employing the shallow ice and shallow shelf approximations for ice flow (which account for vertical shearing and longitudinal stretching respectively), ensuring computational feasibility for continental-scale simulations (Pollard & DeConto, 2012). The ice sheet model setup is identical to that of DeConto et al. (2021) and Gomez et al. (2024), with a 100,000-year spin-up of the ice sheet model using observed climate forcing and Antarctic bathymetry from Bedmap2 (Fretwell et al., 2013).”
With respect to the solid Earth model in section 2.3, we do not consider the effects of loading prior to the year 1950 and utilize the modern bathymetry from Bedmap 2 (Fretwell et al., 2013) as is done in Gomez et al. (2024). The entire history of loading, including the last deglaciation, can impact Antarctic sea level projections, though it will have a smaller signal than the drastic modern loading changes arising from the coupled model. Since the purpose of this study is to demonstrate the impacts of the consideration of transient solid Earth deformation in dynamic ice sheet-sea level feedbacks, we believe this is sufficient in representing the physics involved. Given the computational requirements of the coupled model, we only consider two 1D Earth models with transient and Maxwell rheology (4 total solid Earth models). Thus, we do not claim to present these results as the most accurate or realistic forecast of future Antarctic sea level change and ice loss. A more accurate and realistic projection should also consider laterally-varying Earth structure, given the complexity of the mantle beneath Antarctica, which we note in Section 4.3 Moving to a more realistic Earth rheology. We have clarified the text in section 2.2 above and in 2.3:
“As in Gomez et al. (2024), the sea level model begins in equilibrium at the start of the simulations in 1950 and we do not consider the ongoing effects of loading prior to the year 1950, which will be relatively small compared to the GIA driven by ongoing ice mass changes during the simulation. In order to model the entire continent self-consistently in a way that captures the East-West dichotomy, we would require a 3D model of GIA (as in Gomez et al., 2024). As mentioned, such 3D GIA model simulations are computationally expensive and we emphasize that our approach (i.e., to run full simulations with two distinct 1D Earth models) is a reasonable approximation to model the impact of transient deformation on each side of the continent, since our focus, as we shall see, will be on deformation in the direct vicinity of each region.”
A clear description of the basal- and sub-shelf melt is missing in Section 2.2.
We agree that we could have included a more detailed description of the basal- and sub-shelf melt in the methods section. We originally thought there was no need to go into further depth, since we cite the model papers which describe these parametrizations in great detail. However, it would certainly be helpful to the reader to provide them directly, so readers do not have to refer to the other papers. We have revised the text and Section 2.2 now reads as follows:
“The dynamic ice component is a hybrid ice sheet-shelf model employing the shallow ice and shallow shelf approximations for ice flow (which account for vertical shearing and longitudinal stretching respectively), ensuring computational feasibility for continental-scale simulations (Pollard & DeConto, 2012). The ice sheet model setup is identical to that of DeConto et al. (2021) and Gomez et al. (2024), with a 100,000-year spin-up of the ice sheet model using observed climate forcing and Antarctic bathymetry from Bedmap2 (Fretwell et al., 2013). A modified version of the Schoof (2007) parametrization for ice flux through the grounding line is adopted, allowing for evolving grounding line position and self-consistency with the basal shear stress condition at the grounding line (Pollard & DeConto, 2012; Pollard & DeConto, 2020; Schoof, 2007). Surface mass balance is calculated by a positive-degree day scheme using RCP temperature and precipitation forcings. The parametrization for basal melting accounts for frictional heating due to shear, and sub-ice oceanic melting closely follows the parametrization of Martin et al. (2011) and is described in Pollard and DeConto (2012).
Calving of floating ice, though still poorly understood, is also an important mass balance consideration for tidewater glaciers and ice shelves because floating ice can stabilize grounded ice upstream by means of buttressing at the grounding line (Gudmundsson, 2013; Sergienko, 2025). We consider two endmembers to describe ice loss through calving – a parametrization based on the large–scale stress field of the ice sheet where calving is related to the thickness of the ice shelf and is proportional to the positive divergence of floating ice velocity for thicker ice shelves (Nick et al., 2010) and the highly debated Marine Ice Cliff Instability (MICI), with the parametrization of Pollard et al. (2015), which accounts for hydrofracturing due to surface melt and failure of vertical cliff faces (Bassis et al., 2021; Golledge & Lowry, 2021; Pollard et al., 2015). The main results presented in this paper reflect the former, though we explore a possible scenario of accelerated retreat due to the MICI (see Section 4.2). The Schoof (2007) grounding line flux parametrization has been shown to fail in cases where ice shelves are heavily buttressed (Reese et al., 2018). However, such conditions are not prevalent in simulations of future West Antarctic ice sheet retreat with the PSU 3D ice sheet-shelf model because of ice shelf thinning due to oceanic melting and grounding zones readily retreat into wide interior basins, which are less sensitive to buttressing than are narrower embayments (Pollard and DeConto, 2020). “
Figure 2 (e) uses a different scale than the other figures, which might be misleading. Please consider using the same scale or adding a note in the caption.
Thank you for mentioning this. We understand how the change in scale for only panel (e) could be confusing, but we intended to demonstrate the difference in the magnitude of uplift deviation across RCP 8.5, compared to the other scenarios. We have added the following text in the caption to point out the scale difference in panel (e):
"Figure 2. Bedrock and Ice Thickness Deviation (Transient minus Maxwell) (a),(c),(e) Difference between bedrock elevation of transient and Maxwell Earth rheology simulations at 2500 CE in West Antarctica for (a) RCP 2.6 and (c) RCP 4.5, and (e) RCP 8.5 respectively. Note that the scale bar for Fig. 2 (e) is distinct from that of 2 (a) and 2 (c), to illustrate that there is a larger magnitude of uplift deviation under the RCP 8.5 projection than under RCP 2.6 or 4.5. (b),(d),(f) Difference between final ice thickness of transient and Maxwell Earth rheology simulations at 2500 CE in West Antarctica for (b) RCP 2.6 and (d) RCP 4.5, and (f) RCP 8.5 respectively."
The representation in figures 3, 4, and 7 (and similar figures in the SI) is on the one hand very rich in information, but hard to read on the other hand. After having watched the movies I wonder if the times highlighted in these figures for comparison are representative of the general dynamics or chosen to illustrate the largest differences between the Maxwell model and the transient model.
To add clarity, I would suggest some additional figures with grounding line position along the transect versus time. This might allow the reader to see at once how much slower the grounding line retreats in the transient viscosity model.This is a fair point. The times highlighted in the figures for comparison are more representative of the largest differences between the Maxwell model and the transient model. We believe there is still value in representing the lateral scale of grounding line position deviations in Figures 3, 4, and 7. To address your comment, we have created new supplementary figures plotting the grounding line position along the transect versus time as suggested, to better represent the general grounding line dynamics in the simulations. Readers are also encouraged to view the supplemental movies to interpret the pace and lateral scale of grounding line deviations altogether. We also have revised the text in Section 3.1 to avoid misleading the reader about the dynamics of grounding line retreat:
“Fig. 3 compares the relative deviation of grounding line position through time in Maxwell versus transient models under RCP 8.5 (IPCC, 2014) at Pine Island (vertical lines, Fig. 3a,c) and Thwaites Glaciers (Fig. 3b,d).”
We have also added the following text after line 307:
“We emphasize that the marine outlet glaciers of the WAIS are broad spatial features, and we only show the grounding line migration through time along the transects described in Fig. 1 in the cross-sections (Figures 3 and 4). The deviations in the spatial pattern of retreat of marine outlet glaciers are more complex, as illustrated by the areas where the grounded ice margins vary between the transient and Maxwell models off-transect in Figs 1 and 2 (yellow fill) and Figures S17-22. The vertical lines in Figures 3 and 4 highlight instances of time with the largest differences in the grounding line position between the Maxwell and the transient model. Figure S15 plots the timeseries of grounding line position along the glacier transects from Figures 3 and 4 for the Maxwell versus transient models.”
Please see the attached pdf for drafts of the suggested grounding-line position time series figures (new Figures S15 and S16).
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AC1: 'Reply on RC1', Allie Coonin, 06 Aug 2026
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RC2: 'Comment on egusphere-2026-2172', Anonymous Referee #2, 03 Jul 2026
In this study, the authors perform coupled ice sheet-sea level simulations to investigate the evolution of the Antarctic ice sheet under RCP climate scenarios. Rather than adopting the standard Maxwell viscoelastic rheology, they consider a transient rheology to represent mantle deformation. They show that, although transient rheology does not prevent long-term ice loss, it delays grounding-line retreat and the associated West Antarctic ice loss compared to simulations using Maxwell rheology. This is an important study which highlights the stabilizing influence of Glacial Isostatic Adjustment (GIA) feedbacks on Antarctic ice sheet retreat. The manuscript is overall well written and should be suited for publication in The Cryosphere after the following points have been addressed.
Specific commentsl.13-15. I suggest deleting this sentence, as the feedback described is not directly relevant to this study and is only one of several feedback mechanisms associated with Antarctic ice sheet melting. Alternatively, rephrase it to state that the rate of Antarctic melting has multiple impacts on the Earth system.
l.17-20: I suggest rephrasing as follows: “Such bedrock deformation is typically modelled using idealised Maxwell viscoelasticity. However, rock deformation experiments show that additional 'transient' creep mechanisms, which are not captured by the Maxwell model, occur over societally-relevant timescales (~decadal to centennial).”
l.27-28: Adjust according to how you decide to address my comment regarding lines 13-15 above.
l.42: DeConto & Pollard, 2016 and Deconto et al., 2021 illustrate the role of MICI in triggering extreme Antarctic ice loss rather than the role of MISI. I am not sure these are the most appropriate references to illustrate marine ice sheet instability mechanisms.
l.40-56. Sergienko et al., 2026 (https://doi.org/10.1038/s41561-026-01941-2) stress how reality is much more complex than Weertman’s and Schoof’s original definitions. It would be worth acknowledging this here. In fact, the influence of bedrock deformation on Antarctic marine ice loss does not necessarily need to be framed through the MISI perspective.
l.63-65: See my previous comment. Could be simply phrased as: “Sea-level rise at a marine grounding line (e.g. from far-field ice loss) promotes further grounding-line retreat.”
l.87: Please clarify what is meant by the ‘bulk mantle’.
l.93: Please clarify what is meant by ‘modern cases’.
l.97: Replace ‘While they assume’ by ‘Assuming a’.
l.101: I would suggest removing ‘even’.
l.101-111: I think the manuscript would benefit from a simple explanation of the fundamental difference between Maxwell viscoelastic rheology and the transient rheology considered here. Since this distinction is central to the paper, it should be introduced more clearly.
l.113: Please clarify what is meant by ‘compliant’.
l.121: I suggest rephrasing as ‘Here, we modify the coupled framework of Gomez et al. (2024) by incorporating transient viscoelastic deformation’.
l.123-127: I suggest splitting this long sentence into two for clarity.
l.133: I suggest ending the sentence after ‘emissions scenarios’, and removing ‘namely’.
l.139-143: I suggest splitting this long sentence for clarity.
l.152: Remove ‘-as just mentioned-’.
l.155: What exactly is meant by ‘a prescribed loading history’ here? Does this refer to Ice-sheet evolution prior to the start of the coupled simulations? Please clarify and specify which loading history is used.
l.180: I suggest removing ‘according to MISI’ here. Evolving grounding line position occurs even without any MISI. I also recommend citing Pollard and DeConto (2020; https://doi.org/10.5194/gmd-13-6481-2020) here.
l.182-184: It would be good to provide more information, or at least a reference, for the PDD scheme used (e.g., parameter values, etc). Similarly, no information is provided on how sub-shelf melting is calculated, while it is a key driver of Antarctic ice loss, nor about the initialisation procedure. How do you initialise such a coupled framework? This should be clarified.
l.188: Is this the calving parameterization of Pollard et al. (2015)? If so, please state this explicitly. Also, does this parameterization include hydrofracturing, or is hydrofracturing turned off?
l.192: What do you mean by ‘in the Main Text’? I suggest rephrasing to avoid confusion.
l.198-199: Please add appropriate references.
l.226-231: This is a very long sentence. I suggest splitting it for clarity.
l.247: I suspect there is a ‘with’ missing in this sentence.
Figure1: It would be helpful to delineate the calving front on the figure to better visualise the ice shelves' extent.
l.263-265: I find the yellow regions somewhat confusing. If, as stated in the caption of Figure 1, the final grounded ice extent for the transient model is contoured in yellow, it means that the yellow regions indicate places where the Maxwell model extends further than the transient one, right? Perhaps consider an alternative way of comparing the two extents.
l.265-269: Please split this sentence after ‘4.5’.
l.275: I am not sure where to visualise the subtle subsidence in East Antarctica. Could you refer to a figure?
Figure 3: For clarity, I would suggest displaying the ice draft as well on those figures. Also, while I clearly see the added value of glacier transects, I would be interested in comparing the spatial pattern of grounding line evolution for both rheologies.
l.295-297: What about RCP8.5? Was the total grounding line retreat identical for both models? If so, please clarify.
l.301: Clarify ‘compared to the Maxwell rheology’.
l.304-307: As mentioned above, I think a 2D comparison of grounding-line evolution between the two rheologies would be valuable, even if only included in the Supplement.
l.328: It would be good to explicitly state that this corresponds to only a few centimetres of sea-level contribution by 2300, compared with a total contribution of approximately 0.6–2.5 m (i.e., only a few percent of the total).
l.332: How do you explain that the reduction in WAIS contribution under transient rheology is larger for eta_high than eta_low under RCP2.6, but the opposite occurs under RCP4.5?
l.334: I find this a little misleading, as 5% is in fact the maximum reduction. It would also be worth clarifying that the highest reductions occur for the lower-emission scenarios.
l.341: Do you observe any influence at all in East Antarctica? It might be interesting to comment somewhere about that, given that you do simulate the whole ice sheet.
l.343-344: Please clarify what is meant by different sensitivities. My interpretation of the Results section is that both cases exhibit delayed grounding-line retreat relative to the Maxwell simulations.
l.345-347: Again, I do not think the simulations demonstrate that grounding-line retreat is driven by marine ice sheet instability. Instead, I believe that retreat is simply driven by the imposed climate forcing. Yet, this does not change the stabilizing influence of GIA. I would suggest reformulating and avoiding explicit reference to MISI.
l.347-349: This point is not entirely clear from the Results section. Please be more specific about the timescales over which rheology influences the simulations. Does this apply across all scenarios? Why does the influence diminish with time? Is it because the climate forcing eventually dominates, or is it an intrinsic property of the rheological model?
l.356: It may be interesting to point out here that any reduction in the rate of sea-level rise resulting from transient rheology is directly relevant for coastal adaptation planning. From the results, I suspect transient rheology has a noticeable effect on the rate of sea-level rise, and this deserves discussion.
l.364: Again, please clarify whether the retreat is inevitable under all forcing scenarios.
l.367-368: Is there a way to verify this interpretation? For example, could bedrock uplift predicted by the two rheologies be compared directly over the relevant period?
l.370: Replace ‘MISI’ with ‘grouding-line retreat’(cf comments above).
l.372: It is not clear to me why I should look specifically at the continuous lines in Fig.6 here.
l.380-383: In line with my earlier comments on the Introduction, I think that this requires a little more information for readers who are not familiar with the Yamauchi and Takei model.
l.387: Please add a reference here.
l.402-405: In line with one of my earlier comments, do you observe this behaviour in your simulations, given that the entire Antarctic Ice Sheet is represented? If so, it would be useful to comment on it.
Figure 7: Are both panels shown for RCP4.5 with MICI enabled? If so, Figure 7b appears to contain a typo, as the title refers to RCP8.5.
l.453: I am not entirely sure what is meant by static ice loading change. Please clarify this so that readers do not need to consult Lau et al.
l.456-460: This is an important point and, in my opinion, could already be introduced in the Introduction as part of the motivation for the study.
l.467: Are you referring to the present study or to Lau et al.? Please clarify.
l.475-481: I agree with the general point, but I believe the situation is more nuanced. For example, Antarctic freshwater input has also been shown to have the potential to enhance Antarctic mass loss by inducing subsurface ocean warming (e.g., Bronselaer et al., 2018; https://www.nature.com/articles/s41586-018-0712-z). It would therefore be worth acknowledging that freshwater feedbacks can act in both directions.
Citation: https://doi.org/10.5194/egusphere-2026-2172-RC2 -
AC2: 'Reply on RC2', Allie Coonin, 06 Aug 2026
Dear Reviewer,
We greatly appreciate your writing suggestions and comments. We believe we have addressed all your specific comments and respond to each comment individually below. These changes significantly improve the manuscript. Thank you! We have formatted your comments in italics to distinguish your original text from our responses. Any proposed revisions to the text of the manuscript are embedded in quotations and bolded.
Summary
In this study, the authors perform coupled ice sheet-sea level simulations to investigate the evolution of the Antarctic ice sheet under RCP climate scenarios. Rather than adopting the standard Maxwell viscoelastic rheology, they consider a transient rheology to represent mantle deformation. They show that, although transient rheology does not prevent long-term ice loss, it delays grounding-line retreat and the associated West Antarctic ice loss compared to simulations using Maxwell rheology. This is an important study which highlights the stabilizing influence of Glacial Isostatic Adjustment (GIA) feedbacks on Antarctic ice sheet retreat. The manuscript is overall well written and should be suited for publication in The Cryosphere after the following points have been addressed.
Specific commentsl.13-15. I suggest deleting this sentence, as the feedback described is not directly relevant to this study and is only one of several feedback mechanisms associated with Antarctic ice sheet melting. Alternatively, rephrase it to state that the rate of Antarctic melting has multiple impacts on the Earth system.
Done. Dr. Zeitz also pointed this out. We agree and have removed the sentence from the abstract.
l.17-20: I suggest rephrasing as follows: “Such bedrock deformation is typically modelled using idealised Maxwell viscoelasticity. However, rock deformation experiments show that additional 'transient' creep mechanisms, which are not captured by the Maxwell model, occur over societally-relevant timescales (~decadal to centennial).”
Done. We appreciate this suggestion and believe it has improved the clarity of the statement.
l.27-28: Adjust according to how you decide to address my comment regarding lines 13-15 above.
Done. We deleted lines 13-15 as suggested in your earlier comment and have revised the final sentence in the abstract to note the broader implications on climate modeling without unnecessary specificity. The final sentence in the abstract now reads as follows:
“Even still, deviations in AIS meltwater flux with transient deformation could impact climate model predictions.”
l.42: DeConto & Pollard, 2016 and Deconto et al., 2021 illustrate the role of MICI in triggering extreme Antarctic ice loss rather than the role of MISI. I am not sure these are the most appropriate references to illustrate marine ice sheet instability mechanisms.
Thank you for bringing this up. Originally, we included these references as examples of studies predicting major ice sheet retreat and sea level change from Antarctica to make the more general point, as opposed to specifically referencing the role of MISI. However, you are correct that we go on to discuss the MISI in greater detail. We have replaced the citation of DeConto and Pollard (2016) and Deconto et al. (2021) with a study by Robel et al. (2019). We have also added Gomez et al. (2024) since they show their results with and without invoking MICI. While much of DeConto et al., 2021 focuses on the role of MICI, they also ran simulations without MICI for comparison (see Extended Data Figure 8; DeConto et al., 2021). Our “no MICI” coupled model simulations follow the setup from DeConto et al. (2021). We agree that the MICI simulations predict more extreme Antarctic ice loss than those without.
A.A. Robel, H. Seroussi, & G.H. Roe, Marine ice sheet instability amplifies and skews uncertainty in projections of future sea-level rise, Proc. Natl. Acad. Sci. U.S.A. 116 (30) 14887-14892, https://doi.org/10.1073/pnas.1904822116 (2019).
l.40-56. Sergienko et al., 2026 (https://doi.org/10.1038/s41561-026-01941-2) stress how reality is much more complex than Weertman’s and Schoof’s original definitions. It would be worth acknowledging this here. In fact, the influence of bedrock deformation on Antarctic marine ice loss does not necessarily need to be framed through the MISI perspective.
Thank you for this comment – The other reviewer also expressed similar sentiments. We have revised the introductory paragraph to acknowledge the complexity of ice sheet instability beyond the simplified framework of Schoof and Weertman, and in doing so, we cite Sergienko et al. (2026) and others. We hope that this addresses your concerns. The first paragraph of the introduction now reads as follows:
“Predictions of ice sheet and sea-level change in response to various trajectories of atmospheric carbon emissions have demonstrated the potential for dramatic ice retreat in West Antarctica (Kopp et al., 2017; Robel et al., 2019). This vulnerability to extreme ice loss is in large part because the bedrock underneath the marine-based West Antarctic Ice Sheet (WAIS) deepens from the margins toward the ice sheet interior, which predisposes the WAIS to runaway retreat via the Marine Ice Sheet Instability (Schoof, 2007; Thomas, 1979; Weertman, 1974). The flux through the grounding line, the location at which the ice sheet begins to float because it is too thin to displace the entire weight of the water column, has strong sensitivity to the thickness of ice at the grounding line (with outflow proportional to ice thickness to the power ~5, Schoof, 2007.) Therefore, on such retrograde bed slopes, even a small perturbation can trigger unstable collapse as the grounding line retreats to a location with deeper bedrock and greater ice thickness. This greater grounding line ice thickness heightens ice loss through the grounding line, promoting continued retreat. Bedrock topography is one of many factors that can trigger ice sheet retreat; grounding line migration is a complex process modulated by time-evolving boundary conditions relating to ocean forcing, downstream ice shelf stability, variable ice mass accumulation, ice rheology, and basal friction and heat flow, which are spatially heterogenous (Caillet et al., 2023; Hudson et al., 2023; Sergienko et al., 2026). These unsteady phenomena enable irregular oscillations between advance and retreat and allow for unstable conditions to exist on prograde as well as retrograde slopes (Sergienko & Wingham, 2024).”
Caillet, J., Jourdain, N. C., Mathiot, P., Hellmer, H. H., & Mouginot, J. (2023). Drivers and reversibility of abrupt ocean state transitions in the Amundsen Sea, Antarctica. Journal of Geophysical Research: Oceans, 128, https://doi.org/10.1029/2022JC018929
Hudson, T.S., Kufner, S.K., Brisbourne, A.M. et al. Highly variable friction and slip observed at Antarctic ice stream bed. Nat. Geosci. 16, 612–618 (2023). https://doi.org/10.1038/s41561-023-01204-4
Sergienko, O., Haseloff, M., Robel, A. et al. A new paradigm for understanding Earth’s marine ice sheets. Nat. Geosci. 19, 374–383 (2026). https://doi.org/10.1038/s41561-026-01941-2
l.63-65: See my previous comment. Could be simply phrased as: “Sea-level rise at a marine grounding line (e.g. from far-field ice loss) promotes further grounding-line retreat.”
Done. Thank you for this suggestion - we agree this wording is much clearer.
l.87: Please clarify what is meant by the ‘bulk mantle’.
Thank you for pointing this out. We meant “bulk” as in the average of the whole mantle, but we have revised it for clarity. The sentence now reads as follows:
“For ice mass changes associated with modern climate change, this is often the case since for the mantle on average ranges between approximately 500 to 10,000 years (K. Hansen et al., 2021; Spada et al., 2012; Whitehouse et al., 2012).”
l.93: Please clarify what is meant by ‘modern cases’.
This is a good point. We have revised the sentence and it now reads as follows:
“And thus, even for some modern ice loading calculations, the viscoelastic deformation must be considered.”
l.97: Replace ‘While they assume’ by ‘Assuming a’.
Done.
l.101: I would suggest removing ‘even’.
Done.
l.101-111: I think the manuscript would benefit from a simple explanation of the fundamental difference between Maxwell viscoelastic rheology and the transient rheology considered here. Since this distinction is central to the paper, it should be introduced more clearly.
We agree that a simple, intuitive explanation would be helpful and we have chosen to add this to the Introduction. We have added the text below prior to line 112:
“Where the Maxwell viscoelastic model is characterized by a single relaxation time, , any transient viscoelastic model is one that includes additional relaxation times, or a continuous spectrum of relaxation times, which results in non-elastic behavior at time scales even shorter than the Maxwell time. In these models, the elastic, transient viscous, and Maxwell steady state components of strain add together to describe the total deformation response.”
l.113: Please clarify what is meant by ‘compliant’.
By ‘compliant’ we mean softer or weaker. We have adjusted the language and the sentence now reads as follows:
“Hence, if the Earth is weaker over shorter timescales, regardless of the assumed viscosity structure of the mantle, the magnitude and timing the solid Earth response to ice and ocean load changes and consequently, sea level and topography will differ by as much as meters (Coonin et al., 2025; Lau, 2023).”
l.121: I suggest rephrasing as ‘Here, we modify the coupled framework of Gomez et al. (2024) by incorporating transient viscoelastic deformation’.
Done. Thank you for this suggestion – it reads much more clearly now.
l.123-127: I suggest splitting this long sentence into two for clarity.
This is a good point – we have split up the long sentence, and it now read as follows:
“While Gomez et al. (2024) showed that laterally varying properties clearly play an important role in coupled global sea level–Antarctic ice sheet evolution, such models with 3D earth structure require significantly greater computational power. We do not take this route, instead opting for 1D (i.e., depth dependent only) mantle viscoelastic structure. Not only is this computationally more feasible, but it also allows us to isolate the effect that transient deformation alone has in modulating the solid Earth’s response to modern timescales of ice loss.”
l.133: I suggest ending the sentence after ‘emissions scenarios’, and removing ‘namely’.
Done.
l.139-143: I suggest splitting this long sentence for clarity.
Done - we appreciate this suggestion. We have split the sentence it now reads as follows:
“We run forward simulations of Antarctic Ice Sheet evolution using the PSU 3D ice sheet shelf model (Pollard & Deconto, 2012; Pollard et al., 2015) coupled with the gravitationally self-consistent sea-level algorithm outlined in Kendall et al. (2005) and expanded upon in Gomez et al. (2010) for use in projections. The sea level component of the model accounts for the gravitational, deformational and rotational effects from glacial isostatic adjustment, assuming a radially-varying Earth.”
Gomez, N., Mitrovica, J., Huybers, P. et al. Sea level as a stabilizing factor for marine-ice-sheet grounding lines. Nature Geosci 3, 850–853 (2010). https://doi.org/10.1038/ngeo1012
l.152: Remove ‘-as just mentioned-’.
Done.
l.155: What exactly is meant by ‘a prescribed loading history’ here? Does this refer to Ice-sheet evolution prior to the start of the coupled simulations? Please clarify and specify which loading history is used.
The standalone sea level model from Kendall et al. (2005) requires ice thickness maps throughout the time period being simulated. There is no loading history applied prior to 1950. In the coupled model, the dynamic ice sheet-shelf component is run for an interval of time and the associated ice changes are then fed into the sea level algorithm to calculate the associated sea level change (which is in turn fed back into the ice model for the following time step). We have adjusted this language and the sentence now reads as follows:
“Required inputs for the sea level model include the initial bedrock topography, the ice mass distribution changes (here, generated by the PSU 3D ice model), and the Love numbers corresponding to the chosen radially varying viscoelastic Earth model (see Fig. S2; Kendall et al., 2005).”
We have also clarified that we do not consider any loading changes prior to the year 1950 in section 2.3:
“As in Gomez et al. (2024), the sea level model begins in equilibrium at the start of the simulations in 1950 and we do not consider the ongoing effects of loading prior to the year 1950, which will be relatively small compared to the GIA driven by ongoing ice mass changes during the simulation.”
l.180: I suggest removing ‘according to MISI’ here. Evolving grounding line position occurs even without any MISI. I also recommend citing Pollard and DeConto (2020; https://doi.org/10.5194/gmd-13-6481-2020) here.
Done. We agree that Pollard and DeConto (2020) should be cited here.
l.182-184: It would be good to provide more information, or at least a reference, for the PDD scheme used (e.g., parameter values, etc). Similarly, no information is provided on how sub-shelf melting is calculated, while it is a key driver of Antarctic ice loss, nor about the initialisation procedure. How do you initialise such a coupled framework? This should be clarified.
With respect to the sub-shelf melting procedure and the initialization procedure, we have added important clarifications (Dr. Zeitz also made this comment). The ice sheet model setup we use is identical to that of DeConto et al. (2021). The same goes for the PDD scheme, we use the same parameter values as DeConto et al. 2021, which assumes 0.005m of melt per degree day. The first paragraph of Section 2.2 now reads as follows:
“The dynamic ice component is a hybrid ice sheet-shelf model employing the shallow ice and shallow shelf approximations for ice flow (which account for vertical shearing and longitudinal stretching respectively), ensuring computational feasibility for continental-scale simulations (Pollard & DeConto, 2012). The ice sheet model setup is identical to that of DeConto et al. (2021) and Gomez et al. (2024), with a 100,000-year spin-up of the ice sheet model using observed climate forcing and Antarctic bathymetry from Bedmap2 (Fretwell et al., 2013). A modified version of the Schoof (2007) parametrization for ice flux through the grounding line is adopted, allowing for evolving grounding line position and self-consistency with the basal shear stress condition at the grounding line (Pollard & DeConto, 2012; Pollard & DeConto, 2020; Schoof, 2007). Surface mass balance is calculated by a positive-degree day scheme using RCP temperature and precipitation forcings (DeConto et al., 2021). The parametrization for basal melting accounts for frictional heating due to shear, and sub-ice oceanic melting closely follows the parametrization of Martin et al. (2011) and is described in Pollard and DeConto (2012).”
l.188: Is this the calving parameterization of Pollard et al. (2015)? If so, please state this explicitly. Also, does this parameterization include hydrofracturing, or is hydrofracturing turned off?
We apologize that this was unclear. Yes, the calving parameterization is that of Pollard et al. (2015). We cited this reference at the end of the sentence, but we see how it was unclear that we used Pollard et al.’s MICI parameterization. The MICI parameterization from Pollard et al. (2015) also includes hydrofracturing. The MISI-only simulations do not include hydrofracturing and utilize the calving parametrization of Nick et al. (2010). The second paragraph of Section 2.2 now reads as follows:
“Calving of floating ice, though still poorly understood, is also an important mass balance consideration for tidewater glaciers and ice shelves because floating ice can stabilize grounded ice upstream by means of buttressing at the grounding line (Gudmundsson, 2013; Sergienko, 2025). We consider two endmembers to describe ice loss through calving – a parametrization based on the large–scale stress field of the ice sheet where calving is related to the thickness of the ice shelf and is proportional to the positive divergence of floating ice velocity for thicker ice shelves (Nick et al., 2010) and the highly debated Marine Ice Cliff Instability (MICI), with the parametrization of Pollard et al. (2015), which accounts for hydrofracturing due to surface melt and failure of vertical cliff faces (Bassis et al., 2021; Golledge & Lowry, 2021; Pollard et al., 2015). The main results presented in this paper reflect the former, though we explore a possible scenario of accelerated retreat due to the MICI (see Section 4.2). The Schoof (2007) grounding line flux parametrization has been shown to fail in cases where ice shelves are heavily buttressed (Reese et al., 2018). However, such conditions are not prevalent in simulations of future West Antarctic ice sheet retreat with the PSU 3D ice sheet-shelf model because of ice shelf thinning due to oceanic melting and grounding zones readily retreat into wide interior basins, which are less sensitive to buttressing than are narrower embayments (Pollard and DeConto, 2020).”
l.192: What do you mean by ‘in the Main Text’? I suggest rephrasing to avoid confusion.
We have rephrased this below to fix the confusing language. The sentence now reads as follows:
“While we focus on West Antarctica here, we considered two distinct 1D Earth models to represent the geological dichotomy of the Antarctic continent, where East Antarctica is characterized by cold cratonic structure and West Antarctica is characterized by thin lithosphere underlain by relatively warm mantle.”
l.198-199: Please add appropriate references.
We have added the citations for Lloyd et al. 2020 and Lucas et al. (2024) that we use in our first reference to the low viscosity mantle in West Antarctica within the Introduction.
l.226-231: This is a very long sentence. I suggest splitting it for clarity.
Thank you for this suggestion. We have split the sentence as follows:
“An Earth with transient solid Earth rheology will be more sensitive to the pace of ice melting over timescales smaller than typical Maxwell relaxation times. Given that our planet’s actual trajectory of radiative forcing is unknown, we explore multiple climate change scenarios and further modify the rate of ice loss in each climate scenario further by invoking the rapid ice loss via MICI.”
l.247: I suspect there is a ‘with’ missing in this sentence.
Thank you for bringing this to our attention. Yes, there was a missing ‘with.’ The sentence now reads as follows:
“Figure 1 shows the initial ice configuration for all simulations (1950 CE; Fig. 1a) and the change in ice thickness between 1950 and 2500 CE across West Antarctica with the steady state viscosity with Maxwell solid Earth rheology, our reference case (Fig. 1b.i RCP 2.6; Fig. 1b.ii RCP 4.5; Fig. 1b.iii RCP 8.5).”
Figure 1: It would be helpful to delineate the calving front on the figure to better visualise the ice shelves' extent.
Figure 1 already includes gray shading over all shelf ice, so the calving front is simply the boundary of the gray shading.
l.263-265: I find the yellow regions somewhat confusing. If, as stated in the caption of Figure 1, the final grounded ice extent for the transient model is contoured in yellow, it means that the yellow regions indicate places where the Maxwell model extends further than the transient one, right? Perhaps consider an alternative way of comparing the two extents.
We apologize that it appears confusing. The fact that the final grounded ice extent transient model is visible beyond the Maxwell model shows that the transient one extends further. We have adjusted the caption to read:
“The final grounded ice extent in the transient model is contoured in yellow, which extends further from the solid black line, indicating areas of additional grounded ice extent in the transient model, compared to the maxwell model (b.iii).”
l.265-269: Please split this sentence after ‘4.5’.
Done.
l.275: I am not sure where to visualise the subtle subsidence in East Antarctica. Could you refer to a figure?
We did not include a figure illustrating the subsidence pattern in East Antarctica in the text, though we have a supplementary figure illustrating the ice thickness retained in the simulation with the transient Earth model but not the Maxwell Earth model. We will add supplementary figures like Figure 2(a),(c),(e) that illustrate the bed elevation change in East Antarctica across the simulations and point to them here in the text (see new Figures S12 and S13 in attached pdf).
Figure 3: For clarity, I would suggest displaying the ice draft as well on those figures. Also, while I clearly see the added value of glacier transects, I would be interested in comparing the spatial pattern of grounding line evolution for both rheologies.
While we appreciate the suggestion, we feel that the glacier transect figures (3, 4, and 7) are already very busy. We feel that adding more traces of the ice draft on those figures will reduce the readability/interpretability of the figures.
l.295-297: What about RCP8.5? Was the total grounding line retreat identical for both models? If so, please clarify.
Yes, the total grounding line retreat by the year 2500 along the Pine Island transect is identical for both models under RCP 8.5. We have added a sentence for clarification here:
“In fact, the total distance of grounding line retreat by the year 2500 along the Pine Island glacier transect in the transient model is less than that of the Maxwell model (by ~10 km and 20 km for RCPs 2.6 and 4.5, respectively). This is distinct from the RCP 8.5 simulations, where the total grounding line retreat by the year 2050 is identical for both rheology models.”
l.301: Clarify ‘compared to the Maxwell rheology’.
Thank you for pointing this out. We have added the context that was missing:
“The same is true at Thwaites Glacier in RCP 8.5, though in the more moderate emissions scenarios there is little to no deviation in Thwaites Glacier grounding line retreat with transient rheology, compared to the Maxwell rheology simulation (Supplementary Movie 1).”
l.304-307: As mentioned above, I think a 2D comparison of grounding-line evolution between the two rheologies would be valuable, even if only included in the Supplement.
We appreciate this suggestion and will add figures along these lines for the Supplement (see attached pdf, Fig. S17-22, which will be cited in Section 3.1).
l.328: It would be good to explicitly state that this corresponds to only a few centimetres of sea-level contribution by 2300, compared with a total contribution of approximately 0.6–2.5 m (i.e., only a few percent of the total).
This is a good point – we have revised the sentence as follows:
“Examining the deviation in the total WAIS GMSL contribution throughout the simulation (Fig. 6, right vertical axis), we see that transient deformation causes the cumulative GMSL rise from the WAIS by the year 2500 to be smaller than that of the Maxwell model by centimetres (~2 cm in RCP 2.6, ~3 cm in RCP 4.5, and ~5 cm in RCP 8.5), compared with a total contribution of approximately 0.6–2.5 m.”
l.332: How do you explain that the reduction in WAIS contribution under transient rheology is larger for eta_high than eta_low under RCP2.6, but the opposite occurs under RCP4.5?
That is a very good question. The process is very non-linear, in that the rate at which the forcing (i.e., change in ice sheet mass) will activate different time scales of relaxation and at any given point in time, the previous loading history also contributes depending on how quickly those contributions are relaxed away. So, there is no easy answer. Upon some more thought, we would say that RCP 2.6 simulations first show much smaller difference between low and high viscosity. Earlier in the simulation, the high viscosity shows much more deviation, until the low viscosity simulation takes over. So depending on when we would have “paused” the simulation, either conclusion could have been drawn, with RCP 4.5 at the point before this inflexion still showing the same trend. Sadly, it might not be as simple as saying that one is behaving in the opposite fashion. But in order to emphasize this, we have added the text:
“We note that between the high and low viscosity deviations (i.e., comparing solid and dashed lines) between different RCP scenarios does not show a clear pattern. That is, in RCP 4.5, the simulation deviates less than , whereas in RCP 8.5 they both track each other very well and in RCP 2.6, the deviation is greater than before switching around 2400. This reflects the different ways the time scale of forcing interacts with the deformational properties of the planet at the time of load, but also the inherited load from viscous relaxation. The two RCP 8.5 traces align because the loading is so rapid that both and behave near-elastically. However, the other two models show more complicated interactions.”
l.334: I find this a little misleading, as 5% is in fact the maximum reduction. It would also be worth clarifying that the highest reductions occur for the lower-emission scenarios.
We appreciate your comment. The original text you refer to says the reduction is ~5% or less for all times in the simulation, which we thought implies that it was a maximum of 5%. We have revised the sentence as follows, including a discussion of why the largest reductions occur for the lower-emission scenarios:
“Even so, the WAIS and AIS GMSL contributions are reduced with transient deformation by only a few percent, with a maximum value of ~5% (see SM-5 for absolute and percent deviations in WAIS GMSL contribution.) Interestingly, the largest percent reductions in GMSL contribution are associated with the lower-emissions scenarios, RCP 2.6 and 4.5. This reflects how the timescale of uplift in the transient Earth model can more readily compete with the timescale of the climate forcing in RCP 2.6 and 4.5 than RCP 8.5. as the climate forcing becomes increasingly rapid, eventually the climate forcing will dominate the response because even the accelerated solid Earth uplift from transient deformation will struggle to keep pace.”
l.341: Do you observe any influence at all in East Antarctica? It might be interesting to comment somewhere about that, given that you do simulate the whole ice sheet.
We already comment on the influence of transient rheology in East Antarctica in Section 4.2 lines 435-438 and direct the reader to SM-6, Fig. S12 for more on this matter.
Since the MICI is still heavily debated, we choose to focus on our “no-MICI” simulations. In our simulations without MICI, our results in West Antarctica are more pronounced because there is more dramatic ice loss in West Antarctica than East Antarctica.
l.343-344: Please clarify what is meant by different sensitivities. My interpretation of the Results section is that both cases exhibit delayed grounding-line retreat relative to the Maxwell simulations.
Thank you for noting this. We meant to express that the reduction in the pace of grounding-line retreat with transient deformation differs at Pine Island vs. Thwaites glacier, for the same climate forcing. We recognize that the language here could be much clearer and have revised/added more explanation. We believe the new language is more effective:
“For a given climate forcing, the offset in the grounding line position with transient rheology relative to Maxwell rheology is sustained for a larger portion of the simulation at Pine Island Glacier than at Thwaites Glacier (e.g., compare Supplementary Movies 1 and 2 or 5 and 6). In other words, grounding-line retreat in the transient model more readily catches up with the Maxwell model at Thwaites Glacier than Pine Island glacier under the same RCP scenario. This reflects the distinct bathymetry profiles along each selected glacier transect; there are a greater number of pinning points in the Pine Island transect than the Thwaites transect that the grounding line can get stuck on due to the small deviation in bedrock uplift with transient deformation, exacerbating the lag from the Maxwell model.”
l.345-347: Again, I do not think the simulations demonstrate that grounding-line retreat is driven by marine ice sheet instability. Instead, I believe that retreat is simply driven by the imposed climate forcing. Yet, this does not change the stabilizing influence of GIA. I would suggest reformulating and avoiding explicit reference to MISI.
Thank you for the suggestion. We have removed the explicit reference to the MISI. The sentence now reads as follows:
“Overall, the local effects of transient rheology are stabilizing to the WAIS by counteracting grounding-line retreat.”
l.347-349: This point is not entirely clear from the Results section. Please be more specific about the timescales over which rheology influences the simulations. Does this apply across all scenarios? Why does the influence diminish with time? Is it because the climate forcing eventually dominates, or is it an intrinsic property of the rheological model?
There is no one timescale over which transient rheology influences the simulations – observations from rock deformation experiments (e.g. Yamauchi and Takei, 2016 used here) indicate energy dissipation in the elastic timescale regime of the idealized Maxwell model over a broad continuum. In other words, a transient Earth will deform with viscosities other than the steady state viscosity and there is not a single characteristic loading timescale akin to the Maxwell time that will trigger non-elastic deformation.
The deviation in behavior between the transient and Maxwell models diminishes with time for multiple reasons. It is an intrinsic property of the rheological model that the long-term (steady-state) viscosity of the Maxwell and the transient model are identical (as they should be). There are, however, scenarios in which the climate forcing is so rapid that not even a transient Earth model can keep pace so the climate forcing dominates the behavior. We believe this is clarified with our revisions to address your above comment about line 334. We also point you to lines 415-422 where we feel that this point has been made for the case of the simulations with MICI.
l.356: It may be interesting to point out here that any reduction in the rate of sea-level rise resulting from transient rheology is directly relevant for coastal adaptation planning. From the results, I suspect transient rheology has a noticeable effect on the rate of sea-level rise, and this deserves discussion.
This is a great point. We will add the following text:
“Although transient deformation cannot counteract the magnitude of projected global sea level rise, any reduction in the predicted rate of sea-level rise from transient rheology compared to Maxwell predictions has implications on coastal adaptation planning for concerns such as amplified storm surge flooding and saltwater intrusion of aquifers (Panthi et al., 2022; Tahvildari and Castrucci, 2021).”
Tahvildari, N. & Castrucci, L. (2021). Relative sea level rise impacts on storm surge flooding of transportation infrastructure. Natural Hazards Review, 22(1). https://doi.org/10.1061/(ASCE)NH.1527-6996.000041
Panthi, J., Pradhanang S.M., et al. (2022). Saltwater intrusion into coastal aquifers in the contiguous United States — A systematic review of investigation approaches and monitoring networks. Science of The Total Environment, 836: 155641.
l.364: Again, please clarify whether the retreat is inevitable under all forcing scenarios.
In Line 364, “inevitable retreat” refers to grounding line retreat that is predisposed by the climate forcing. We have removed “the inevitable” from the sentence.
l.367-368: Is there a way to verify this interpretation? For example, could bedrock uplift predicted by the two rheologies be compared directly over the relevant period?
We apologize for the imprecise language. The early positive deviations in GMSL with transient rheology relative to the Maxwell model are the result of increased water expulsion because both rheology models are subjected to the same climate forcing and there are negligible differences in ice volume loss so early on in the simulation. We have removed the “we interpret this to be” and the lines now read as follows:
“This early opposing trend reflects enhanced far field sea level rise due to increased water expulsion in the transient simulations relative to the Maxwell, since there are negligible transient–Maxwell deviations in ice loss so early in the simulation (Fig 6; red fill). Despite this water expulsion effect, there is a net reduction in GMSL rise from Antarctica.”
l.370: Replace ‘MISI’ with ‘grounding-line retreat’ (see comments above).
Done.
l.372: It is not clear to me why I should look specifically at the continuous lines in Fig.6 here.
We meant to point out how there is a time delay before the cumulative GMSL deviations begin to increase in magnitude. We have added some clarification:
“The ability for solid Earth uplift to counteract grounding-line retreat in West Antarctica builds with time as the simulation progresses, owing to the time delay between the loading change and the associated strain contribution from non-elastic deformation (see how the continuous lines for cumulative GMSL deviation begin to depart from zero around 2150, Fig. 6).”
l.380-383: In line with my earlier comments on the Introduction, I think that this requires a little more information for readers who are not familiar with the Yamauchi and Takei model.
We agree that this is somewhat difficult to contextualize. Upon reflection we do not believe that the details of the Yamauchi and Takei model (or any other transient model) are very important in this context but agree that we need to add something more conceptual. Along with the text added in the Introduction, we will add the following text:
“As aforementioned, transient deformation affects the magnitude and timing of the solid Earth response to loading changes, causing an apparent softening of Earth’s mechanical properties over relevant loading timescales and an effective reduction in time delay for viscous deformation. Our transient rheology model (Yamauchi and Takei, 2016) is based on taking a Maxwell viscoelastic model and adding a continuous spectrum transient dissipation in proportion to the Maxwell steady state viscosity. If a given transient rheological model has a Maxwell time of 1000 years, the transient dissipation will be activated on timescales faster than the Maxwell time. If instead, the Maxwell time is 10,000 years, the transient dissipation will be proportionally stretched over a broader bandwidth at timescales faster than 10,000 years. As such, different steady state viscosity profiles will have a distinct transient viscoelastic behavior and will therefore have a different sensitivity to the timescale of the forcing than another transient Earth model scaled to a different steady state viscosity profile.”
l.387: Please add a reference here.
We will now cite Barletta et al. (2018) at the end of the sentence in question.
Barletta, V. R., Bevis, M., Smith, B. E., Wilson, T., Brown, A., Bordoni, A., Willis, M., Khan, S. A., Rovira-Navarro, M., Dalziel, I., Smalley, R., Kendrick, E., Konfal, S., Caccamise, D. J., Aster, R. C., Nyblade, A., & Wiens, D. A. (2018). Observed rapid bedrock uplift in Amundsen Sea Embayment promotes ice-sheet stability. Science, 360(6395), 1335-1339. https://doi.org/10.1126/science.aao1447
l.402-405: In line with one of my earlier comments, do you observe this behaviour in your simulations, given that the entire Antarctic Ice Sheet is represented? If so, it would be useful to comment on it.
In response to this comment and your earlier comment, we already describe the impacts for East Antarctica in Section 4.2 Impact of the Marine Ice Cliff Instability. We have added some context and point the reader to the following section for more detail on the East Antarctic behaviour:
“There are several marine-terminating outlet glaciers through which East Antarctica loses considerable ice mass, and they have been suggested to exhibit considerable grounding line retreat (Favier et al., 2016; Jones et al., 2015; Picton et al., 2023; Stokes, 2022). In our simulations, the East Antarctic deviations in behaviour between transient and Maxwell models are most notable when MICI is invoked because it expedites the early ice loss timescales in East Antarctica before the ice shelves are completely collapsed, regardless of the RCP scenario. We discuss these East Antarctic deviations in the following section.”
Figure 7: Are both panels shown for RCP4.5 with MICI enabled? If so, Figure 7b appears to contain a typo, as the title refers to RCP8.5.
Yes, this is a typo! Thank you for catching this. Both panels in Figure 7 should be labeled as RCP 4.5. We will update the figure in the revised manuscript.
l.453: I am not entirely sure what is meant by static ice loading change. Please clarify this so that readers do not need to consult Lau et al.
We meant to express that the Lau et al. study is not a coupled dynamic ice sheet-sea level model, but rather a sea level model that takes into account lateral variations in Earth structure and transient deformation in response to the redistribution of surface mass loads. The ice mass distribution through time imposed in the Lau et al. model does not have any dynamic feedback with sea level changes. We have removed this language, since we already note that the Lau et al. sea level model is not dynamically coupled to an ice sheet model.
l.456-460: This is an important point and, in my opinion, could already be introduced in the Introduction as part of the motivation for the study.
We agree it is an important point and is powerful motivation for the study. The Lau et al. paper was still in review when the manuscript was submitted, so we originally thought it best to keep the mention of it in the conclusion. Since the paper has now been accepted, we have revised the introduction to incorporate the Lau et al. study as motivation for this manuscript. The introduction now includes the following after line 118:
“Lau et al. (2026) model the GIA response to Antarctic ice loss under future projections, accounting for lateral variations in both steady state mantle viscosity and transient rheology without consideration of dynamic ice sheet-sea level feedbacks. They find that deviations in near field sea level from transient solid Earth deformation are on the order of or larger than the effects of 3D Earth structure, suggesting that transient Earth rheology is an important consideration in modelling modern and future marine grounding line dynamics.”
There will still be a reference to the Lau et al. study in Section 4.3 Moving to a more realistic Earth rheology:
“As noted earlier, the Lau et al. (2026) GIA model accounts for lateral variations in both steady state mantle viscosity and transient rheology (using the Yamauchi and Takei, 2016 model, as applied here though only to 1D Earth models). Though the two distinct 1D steady state viscosity profiles used here are consistent in terms of the magnitude of GMSL reduction in the transient Earth model relative to that of the reference Maxwell model, future coupled ice sheet-sea level modelling studies should incorporate laterally varying Earth structure (as in Gomez et al., 2024) in conjunction with transient deformation behaviour, since East Antarctica and West Antarctica evolve simultaneously and there is potential for covariance across the regions within the context of solid Earth-ice sheet feedbacks (Gomez et al., 2018; Gomez et al., 2024; Lucas et al., 2024; van Calcar et al., 2025).”
l.467: Are you referring to the present study or to Lau et al.? Please clarify.
We meant to refer to the present study. Please see our response to the previous comment for the revised language that clarifies this concern.
l.475-481: I agree with the general point, but I believe the situation is more nuanced. For example, Antarctic freshwater input has also been shown to have the potential to enhance Antarctic mass loss by inducing subsurface ocean warming (e.g., Bronselaer et al., 2018; https://www.nature.com/articles/s41586-018-0712-z). It would therefore be worth acknowledging that freshwater feedbacks can act in both directions.
Thank you for this suggestion – you make a great point. We have expanded upon the discussion of meltwater feedbacks to address the complexity of the potential climate response. The final paragraph of Section 4.3 now read as follows:
“Transient solid Earth deformation is unable to thwart the inevitable Antarctic ice loss and sea level rise predisposed by the climate forcing in this coupled model of ice sheet-sea level-solid Earth interactions. However, transient deformation has the potential to slow the pace of ice retreat and influence the rate at which freshwater discharge from the Antarctic Ice Sheet is delivered to the ocean. Some studies from the atmospheric and oceanic modelling community (e.g. Sadai et al. 2020) have shown that freshwater outflux from the AIS can delay global temperature rise, concurrently with increasing sea level rise, by driving the expansion of sea ice. Earth’s albedo, or reflectivity of the surface against solar radiation, is highly sensitive to sea ice extent and this feedback has been shown to reduce predictions of global mean temperature between 0.3 and 1°C by 2100 CE (Sadai et al., 2025). At the same time, Antarctic freshwater input may also enhance local ice mass loss by inducing subsurface warming (Bronselaer et al., 2018). As the atmosphere warms over time, the uppermost portion of the coastal water column becomes trapped due to meltwater-induced changes in ocean stratification, enabling heat to accumulate beneath the ice shelf, though a recent study suggests that this positive meltwater stratification feedback may become saturated under amplified climate forcing (Kreuzer et al., 2026). If we predict AIS evolution and contribution to sea-level rise within the framework of transient solid Earth rheology, it remains unclear how the deviations in meltwater flux from Maxwell model predictions will impact competing ocean and atmospheric feedbacks. Regardless, transient viscoelastic deformation is a more realistic description of viscoelastic rock deformation behaviour. We demonstrate that transient earth deformation delays AIS retreat, which controls the rate of freshwater discharge, thus it should be a consideration in predicting and interpreting the response of the entire climate system.”
Bronselaer, B., Winton, M., Griffies, S.M. et al. Change in future climate due to Antarctic meltwater. Nature 564, 53–58 (2018). https://doi.org/10.1038/s41586-018-0712-z
Kreuzer, M., Albrecht, T., Huiskamp, W., Petri, S., Feldmann, J., Feulner, G., & Winkelmann, R. (2026). Antarctic meltwater-stratification feedback is less pronounced under high climate forcing. Geophysical Research Letters, 53, e2025GL118643. https://doi.org/10.1029/2025GL118643
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AC2: 'Reply on RC2', Allie Coonin, 06 Aug 2026
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Summary
The manuscript studies the interaction between climate change, ice sheet dynamics and the solid earth in West Antarctica. The authors introduce a new modeling approach to the solid earth rheology – a transient viscoelastic rheology, which responds on decadal to centennial time scales relevant to modern ice loss due to anthropogenic climate change – and compare it to the established Maxwell rheology. They find that the retreat of the West Antarctic Ice Sheet in different climate scenarios is consistently slower in simulations with the transient model and the bedrock uplift is stronger. This effect is less pronounced for scenarios with little ice loss and increases for higher ice loss scenarios. However, the long-term response of the ice sheet to a changing climate does not seem to be affected.
General comments
In my opinion the paper is already very good. The topic is of scientific interest and relevant to the community. The methods seem appropriate for the question at hand. The presentation of the research is clear and well structured. The visual representation is compelling. I also appreciate the sensitivity analyses in the supplement.
There are a few points I would like to address:
To add clarity, I would suggest some additional figures with grounding line position along the transect versus time. This might allow the reader to see at once how much slower the grounding line retreats in the transient viscosity model.
Reese, R., Winkelmann, R., and Gudmundsson, G. H.: Grounding-line flux formula applied as a flux condition in numerical simulations fails for buttressed Antarctic ice streams, The Cryosphere, 12, 3229–3242, https://doi.org/10.5194/tc-12-3229-2018, 2018.