| 03 Mar 2026
Parameterizing tidal-water intrusions in long-term Antarctic ice-sheet projections
Abstract. The Antarctic Ice Sheet is expected to be the dominant contributor to sea-level rise in the coming centuries. However, this contribution is deeply uncertain due to the lack of understanding of some fundamental processes influencing ice-sheet dynamics. A key question is the extent to which submarine melting takes place at the transition between grounded and floating ice. Traditionally, in continental-scale ice-sheet modelling, this area has been treated as an abrupt transition or grounding line with suppressed or strongly limited submarine melting upstream. However, several lines of evidence challenge this view. In many places, changes in ocean tides lead to back and forth migrations of the grounding line over a broad grounding zone and can cause intrusion of warm ocean waters several kilometres upstream of the grounding line, allowing for submarine melting there. Here, we propose a simple parameterization to represent the effect of tidally-controlled migrations of the grounding line and tidal-water intrusion in submarine melting in continental-scale ice-sheet models. We calibrate the magnitude of the parameter controlling the extent of oceanic water intrusions against the observational evidence as inferred from differential interferometry synthetic aperture radar. We use a three-dimensional ice-sheet model to investigate the impact of this parameterization on Antarctic ice-sheet projections under a high-emission climate scenario extending to the year 3000. Our results show that increasing the extent of tidal intrusion, reinforced by dynamic feedbacks, leads to stronger and more widespread grounding-zone retreat under warming scenarios, and consequently ice-stream acceleration, ice-shelf thinning and debuttressing. This implies larger sea-level contributions compared to the usual treatment of melt at the grounding line and should be accounted for in future projections.
Competing interests: At least one of the (co-)authors is a member of the editorial board of The Cryosphere.
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The manuscript “Parametrizing tidal-water intrusions in long-term Antarctic ice-sheet projections” by Antonio Juarez-Martinez and coauthors presents a set of future simulations of the Antarctic ice sheet using Yelmo as ice-sheet model. The authors introduce melting beneath grounded ice by modifying the sub-grid melt parameterization with the goal of reproducing the concept of the grounding zone. I previously reviewed this manuscript for GRL and felt that its format was better suited to a technical journal such as The Cryosphere. I am pleased to see that the authors have addressed most of my earlier comments. Overall, I believe the paper requires significant revisions. I still have concerns about the methodology as well as some results. Please find my line-to-line comments below.
Line 24: This line seems a bit off here perhaps worth incorporating it with the previous paragraph.
Line 89: Eq. 22 in this manuscript or in Robel et al 2022? Also, I am not sure this equation is referenced anywhere else in the manuscript, so please consider removing.
Line 104: If the resolution is 16 km, how can you represent km-scale intrusions?
Line 160-161, ‘seems to be consistent’, ‘observations in the broad sense’. These statements are somewhat vague and lack quantification. Given the importance of this assumption, it should be supported by a clear and logical argument. I apologize if I have overlooked this point, but if so, I believe the authors should expand their discussion. It is not clear why the intrusion length would be expected to scale inversely with the gradient. From the figures, there seems to be a dependency to the inverse of H_af? Why the gradient?
Line 187: While I have no objection to the use of Bedmap3, it is important to note that this dataset represents an average of bed elevations derived from multiple interpolation techniques across varying time scales. In contrast, the DInSAR product from Rignot’s group is tied to specific timeframes (typically days to weeks/months). As such, a direct comparison between thickness inferred from Bedmap and grounding zone extent derived from Rignot’s group should be carefully qualified, with the associated limitations clearly discussed.
Line 189: H_t = [15, 130] m. I think this is a very important result, but it is only introduced in the methodology. I am not aware of any other work that has quantified grounding zone in a similar, pan-Antarctic, fashion. If this is indeed the first study, please consider putting this finding in the results (followed by a discussion) and stress out the importance, also noting the limitation I expressed above.
Line 203: It appears that you are using BedMachine v2 to initialize the model. While this version is somewhat dated (a more recent v4.1 release is now available), it would be helpful to clarify this choice. How does this approach compare with the use of Bedmap for the parameterization described above?
Line 234: While this statement may hold by the year 3000, the results do not show significant changes in WAIS even by 2100, differently than Robel et al 2022, for example. Does this imply that seawater intrusion is not a key factor for WAIS, despite its rapid retreat and grounding zone expansion over the past decade? If so, does this suggest that thermal forcing plays a more dominant role with respect to intrusion length? I feel the discussion around these points needs to be expanded.
Line 270: Rignot 2024 and Robel 2022 report estimates of roughly a twofold increase in sea-level contribution for Thwaites and the Amundsen Sea Embayment when introducing actively melting grounding zones. In contrast, your results suggest that this sector of Antarctica is more strongly influenced by climate warming than by intrusion length, leading to a different conclusion. Could you clarify how these findings can be reconciled, as they appear contradictory?
Line 272: This result is only valid for EAIS only, right? WAIS seems to show no impact from tidal intrusion.
Line 281: This paragraph is somewhat confusing, particularly regarding the interpretation for WAIS. It is not clear whether WAIS is considered vulnerable to seawater intrusion or not. If not, this is in direct contrast to Robel et al 2022 and Rignot 2024. As written, the discussion seems ambiguous. Could this be related to the choice of initial conditions (e.g., ice thickness)? Clarifying this point would help strengthen the overall argument.
Line 286: I am still unclear about the rationale behind the parameterization and its dependence on the inverse of the H_af gradient. Could the authors clarify why the gradient is used as the parameter rather than the simple height above flotation? What is the physical or conceptual reason for this choice?
Line 299: As in my previous review, I am not sure if ‘calibrated; is a correct term here. I’d rather say ‘compared’ to observations.
Line 301: I do not see a discussion of the Greenland glacier comparison in the main text. Figure A1 is included, but without accompanying explanation, it is difficult for the reader to interpret its relevance. Including two Greenland glaciers seems unusual given that the study focuses on Antarctica, as Greenland fjords have different ocean circulation, thermal forcing, bed topography, and other properties. Could the authors clarify the purpose of this comparison and how it supports the main message of the study?
Line 310: Like my earlier comment. How does a 16 km model resolution allow you to draw conclusions regarding ocean-induced melt over km-scale intrusions? I understand that sub-grid melt parameterizations are used, but it is important to quantify the associated errors. Simply stating that “coarse resolutions tend to produce higher estimates” is insufficient—can the authors provide a more detailed assessment of the limitations and uncertainties introduced by the coarse resolution?
Line 317: The statement “For this reason …” is somewhat misleading. The very large climate forcing you are using may effectively mask the impact of intrusion lengths on WAIS. In that case, can you be confident that the effect of intrusion length is truly being isolated?
Line 320: The final paragraph appears to be off-topic and does not contribute to the main argument. Its relevance to the study is unclear and may need to be removed or substantially revised.
Line 326: The quantification of H_t between [15-130] m This is a very important result, but it is currently given too little attention in the text. I recommend moving its discussion from the Methods and Conclusion sections directly into the Results section, where it can be properly highlighted and interpreted.