the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 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.
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.- Preprint
(10675 KB) - Metadata XML
- BibTeX
- EndNote
Status: open (until 15 Jun 2026)
- RC1: 'Comment on egusphere-2026-248', Anonymous Referee #1, 29 Mar 2026 reply
-
RC2: 'Comment on egusphere-2026-248', Anonymous Referee #2, 13 May 2026
reply
See attached pdf.
-
RC3: 'Comment on egusphere-2026-248', Anonymous Referee #3, 11 Jun 2026
reply
The manuscript shows an interesting way to parameterize GZ melt rates using a single parameter, height above flotation, computed from existing datasets (BedMap3 and BedMachine). They compare the range of values this parameter can take using recent DinSAR observations from various sources. Using the range space, they run multiple projection scenarios using GCM output from SSP5-8.5 (SMB anomalies and ocean forcing) until 2300, keeping it constant thereafter until 3000. They compare the outputs of all these scenarios and show that by 3000, across all scenarios, the collapse of the WAIS and the spread of the EAIS sea-level contribution. They conclude by saying that incorporating melt within the IGZ, can increase the SLC by around 20%. While this work shows an interesting way to incorporate the GZ melt, I would like the authors to address some concerns before suggesting it for a publication:
Major Concerns:
The authors use the BedMap3 to estimate Ht (the threshold for height above flotation). When running the projection simulations, they use model data to update the length L (if I understood it correctly). While this seems to be good, as this is the 1st time something like that is done, the authors do not talk about the assumptions that go in using this method such as using the criteria of floatation to pick the grounding line (and not the contact condition), use of stream/shelf model instead of stokes flow model as in the GZ all terms in the stress tensor are important. While I understand that it is not easy to quantify the impact of these assumptions, it is strongly advised to state them in a couple of sentences in the discussion section.
As someone who has worked on Operation IceBridge (OIB) data on Thwaites Glacier and Petermann Glacier, I note that as ice moves through the ice grounding zone, it falls below flotation and then rises above flotation (refer to Gadi et al., 2025) before reaching flotation. This deflection is a permanent feature of the ice shelf, in addition to short-term fluctuations in surface elevation (±1 m) caused by changes in sea surface height (oceanic tides and atmospheric pressure). Figure 1 is a very simplified representation of this, and it is important to write this somewhere clearly and state the same. And I am not sure whether they see the same kind of behavior using their model data or BedMap3 (I have not used these datasets for this purpose). Using this criteria and defining the weighing function may work for this pertaining study as they do not use a full stokes system, but if you do, from my collection of talking to a colleague (long ago), the model also shows that ice falls below flotation by 1m and then rises by 1m in the flexure zone. Once again, I am not asking the authors to do more runs, I would advise them to write this either in Section 2.2 where they describe the approach or add a paragraph or couple of sentences on this as I think this is important to be said.
Gadi, et al. "Contrasting melt regime in the Ice Grounding Zone of Thwaites Glacier, West Antarctica." Proceedings of the National Academy of Sciences 122.48 (2025): e2512626122.I have read through the discussion section to see whether the authors address many of the things that were missing. While they seem to write about the subglacial environment, the authors do not discuss the missing ice-ocean feedback, such as changes in ice-shelf shape due to melting and their impact on ocean circulation, which would further affect melting. Once again, I understand it is hard to quantify the impact of leaving these, but a sentence or two on this would be great to caution the readers about the limitations.
The authors state that, in 193-195, the approach works for Greenland glaciers (two of them). I would like them to caution that Greenland has stronger seasonality than Antarctica and that the approach does not assume any subglacial environmental conditions. It is fine to keep this sentence, but maybe add a statement on this.
Minor Concerns:
75-85 It is important to note that the work of Wilson or Robel et al address the intrusions of seawater but not the tidal pumping mechanism; whereas the lines that follow up with observational studies are tidal migrations of GL. A sentence to differentiate this would be good.
Section 2.1 has many knobs within the equations 2-3, it would be great if the authors can state which of these they are the most dominant and, how would they think that might influence the projections so that the community can learn from their expertise.
In equation (3), I do not understand why an all-drainage-based averaged forcing is added to the thermal forcing. Could the authors state a sentence explaining why? Also the choice of constant gamma_0 seems like a constant exchange coefficient, and in literature, it has been noted that this predicts larger melting than velocity dependent parameterization, in which case (if I understand correctly), a sentence on this would be nice
203 I am not sure why BedMap3 was used in Figure 1, and while computing the basal friction coefficient, the BedMachine dataset is used. Is there any specific reason why this was done?
200 If I understand correctly, the ice sheet model runs using climatological monthly mean values of atmospheric fields and climatological ocean fields for the run 1979-2019?
215-220 While the atmospheric values are provided as anamolies, the ocean forcing is derived from GCM output annually? If so please rewrite this?213 Please mention that by observations, the authors mean BedMachine dataset and not DinSAR-derived velocities? A4 does not state what observations (use Bedmachine dataset) as in A5
225-226 is perhaps interesting as it shows that the ice-shelves become sensitive when the ocean forcing increases with different H_t values; this is important to state somewhere in the discussion.
232 21% compared to H_t=0 case?
245: FRIS is a cold ice-shelf cavity implying lower melt rates, though it has strong tides. If the authors wanted to show that increasing H_t increases basal melting, why not show a warmer ice-shelf cavity such as PIG or thwaites? This is a suggestion.
248-250 When the authors say that H_t is the most important parameter controlling the evolution, I would suggest that they need to make it clear that this is for the scenario considered and no subglacial environment is considered.
282-284: I am lost with that sentence and would like authors to re-phrase it
306-308: The % reported is for Petermann gletscher, for TGT and TEIS, these numbers are different (50%), so it is important to state that submarine melting does not happen all throughout its length than the %; instead if the authors want to use the %, it would be nice to state the glacier name in that sentence.
Figure A1: The mean and median for H_af values are…
Figure A3: Adding labels b-g in panel (a) would make it clear where these locations are in (same as Figure 1)
Figure A4: Please write Bedmachine dataset instead of observations
Figure A7: Write the location FRIS in the caption
Citation: https://doi.org/10.5194/egusphere-2026-248-RC3
Viewed
| HTML | XML | Total | BibTeX | EndNote | |
|---|---|---|---|---|---|
| 880 | 639 | 83 | 1,602 | 78 | 88 |
- HTML: 880
- PDF: 639
- XML: 83
- Total: 1,602
- BibTeX: 78
- EndNote: 88
Viewed (geographical distribution)
| Country | # | Views | % |
|---|
| Total: | 0 |
| HTML: | 0 |
| PDF: | 0 |
| XML: | 0 |
- 1
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.