the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 25 Jun 2026
Sensitivity of grounding zone melting to subglacial discharge configuration and sediment dynamics across contrasting ice shelf cavity regimes
Abstract. Subglacial freshwater discharge plays a critical role in modulating basal melting and ocean circulation beneath ice shelves, yet the combined influence of discharge configuration, cavity thermal state, and sediment-driven morphodynamics remains poorly constrained. Using idealised ocean simulations following the ISOMIP+ framework, we investigate how subglacial discharge location, configuration (channelised versus distributed), and sediment load interact with contrasting warm and cold cavity regimes, and how these processes influence the circulation, melt, and seabed evolution at the grounding zone. Melt rates differ markedly between warm and cold regimes, with values in the warm cavity an order of magnitude higher than in the cold cavity. However, relative to no-discharge control experiments, subglacial discharge induces substantially greater local melt anomalies at the grounding line in the cold cavity, where localised melt rate increases up to ~955 %, compared to ~173 % in the warm regime. Discharge location and configuration further control the spatial extent of the response, with channelised inputs driving strong, localised melting, and distributed inputs producing weaker but more spatially extensive melt across the grounding zone. Sediment-laden subglacial discharge consistently reduces localised melt under channelised configurations (~13 % reduction in the warm regime and ~16 % in the cold regime), whereas its influence is negligible (<1 %) when discharge is distributed. These reductions arise primarily through morphodynamic feedbacks, as sediment modifies seabed structure and circulation near the grounding zone. In the cold regime, reduced circulation promotes sediment accumulation and episodic erosion, leading to seabed and circulation changes. These results demonstrate that the impact of subglacial discharge on basal melt depends on the combined effects of cavity regime, discharge configuration, and sediment dynamics, with implications for representing grounding zone processes and basal melt parametrisations in ice-ocean models, and ultimately for ice shelves vulnerability and Antarctic Ice Sheet stability.
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Status: final response (author comments only)
- RC1: 'Comment on egusphere-2026-3435', Anonymous Referee #1, 14 Sep 2026
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RC2: 'Comment on egusphere-2026-3435', Anonymous Referee #2, 17 Sep 2026
Review of Sensitivity of grounding zone melting to subglacial discharge configuration and sediment dynamics across contrasting ice shelf cavity regimes
The paper by Papapetros et al examines various aspects of subglacial drainage into an idealized ice shelf cavity based on the ISOMIP+ experiments. Different thermal regimes, set by far field ocean conditions, are examined, as is the position of the drainage (and distributed vs channelized). The ROMS model is also utilized to look at the impacts of sediment inflow and mobilization using a multi-grain size sediment model and parameterization for density effects of sediment load.
Introducing subglacial drainage into an ice-shelf cavity model is not a new development at this point; the study does investigate position of inflow which is somewhat novel for ice-shelf cavities, but what I think is new is the investigation of sediment load and transport in the water, and the effects of input from subglacial sources. As such I do think that the paper could be suitable for TC, but there are a number of somewhat major issues relating to presentation and clarity, which will certainly need addressing.
General comments:
1. I did not find this an easy paper to get through, unfortunately, and I think to some extent this can be addressed by better presentation of results. Each new results section presents a rather LARGE array of figures to look at. The reader is then invited to visually pick apart differences e.g. in figures of circulation cells, some of which are not side by side (eg when we are asked to compare 2cd, and 6cd). In figures where an array of raster plots are shown i would prefer to see comparison of some sort of metric -- for instance, the strength (and maybe position) of circulation cells in fig 2a and similar. I would ask the authors to really think about how to do this, as it is difficult to take much away from e.g. most rows of Fig 3. Alternatively or additionally readers should not need to visually compare such images, but should instead be shown anomalies where appropriate. The text in turn is quite a dense description of the figures and I wonder if Sections 3.1 and 3.2 can be shortened by taking some of these suggestions on board, and instead trying to give an overarching message.
2. There are numerous instances with figures not being suitably described in the text or in the caption -- please look out for these in specific comments below.
NOTE ABOUT ABOVE COMMENTS: due to limited time I was not able to look over the Appendix in detail -- but I maintain that a reader should not need to do so. And so even if it turns out that some of my concerns are addressed in appendix, my comments stand.
3. As I said, I believe the sediment load aspect is the unique aspect of this paper. In the final results section we see how it affects melt, but I would like to know whether this is due to density changes or bathymetry changes, neither is really addressed; and I would like in general to better understand how sediment load impacts circulation.
4. The method of introducing subglacial drainage, a momentum flux at the boundary of cells, is a somewhat standard approach at this point, as shown by the sources cited. The flux of 73 cumbers is actually not unheard of, Gourmelen et al (2025) infer that for brief periods, runoff into thwaites cavity may have reached 10x this value. Subglacial channels, however, are not likely to be substantially less than 2km wide (and likely not as tall as the grounding line water column, which is not stated..) meaning that the input momentum is quite diffuse and current effects are due to salinity gradients. As I expect sediment mobilization is nonlinear in current speed, this may not have the same effect as current speeds associated with a 20-50m wide opening. I invite the authors to discuss this in the manuscript.
Line by line CommentsLine 119-120 - can you justify the load assumption from literature
Line 165 - I did not follow, can you reword
FIg 2f: I think change from initial baths would be better to show here
Fig 2g: caption says "grounding line geometry" which I don't think is true. Im guessing this is the bed initially (black line) and after X years simulation (blue/red line) in the southernmost cells? Please define more carefully.
Line 173: Do you mean SGW has a stronger impact in the cold regime?
Line 194: "relative to the warm regime.." They look the same to me.
Fig 3: this is far too much. I would prefer to see where possible for each row some metric comparing with the relevant figure in 2a (1st or 2nd column?) or a difference with this column. Similar with Fig 4.
Line 225, "This generates" it is hard to see any pattern or signal from the figures
Line 240-241: how can we see this from 3g and 4g? Tell us what to look for (and I don't think we should need to refer to the appendix, per the definition of "appendix")
Fig 5f: please do not truncate the erosional stress plot.
Line 254, "thereby": it would be nice to see more clearly how the bed depth and suspended sediment influences heat transport.
Fig 270: you should be showing an anomaly figure, not asking us to compare.
Section 3.4: There are numerous issues with the presentation of these results -- which are interesting -- and so I don't think I will be able to list them all.
* My principal concern is that the lines in Fig 7 are not sufficiently explained (***which needs addressing***) so I needed to infer them. In figs. 6a and 6e, I believe this shows the melt rate in the ocean grid cell where SGW is entering, so that e.g. at point 34, we see the melt rate in x=34 *when the SGW enters x=34*, and not otherwise. This of course explains why the mean melt rate in 6c,g is so much smaller. (I also infer that the "grounding zone mean" is the average over all these cells (which is not quite the definition of a "grounding zone"). One issue I have is that this is taken later as evidence that channelized runoff at a given location greatly increases melt.. where really, we need to take the mean into account. As such, I do not like the comparison here, and I also feel isolated melt and distributed melt should not be compared. I *think* it is, but to be honest I found the text in this section confusing. I suggest the authors take a clean approach at writing this section (which is thankfully not very long) as it communicates useful messages.
Also in fig 6: all axes where there are values shown should be labeled. Say that the dashed lines correspond to right hand axes. And (if it is true) say that rows 2 and 4 show GZ average.
Line 298, 173%. this is only where the melt is released no? do we even see what happens to melt elsewhere? or are you now actually talking about 7c, not 7a?
Line 306-7: indicating that changes outwith the location of runoff are VERY different, which you don't make clear.
Line 320, 37% increase: in the mean, or locally?
Line 326: please cite slater 2015 here and elsewhere where this result is discussed, as it is relevant even if it applies to a tidewater glacier (both have a theoretical scaling from Jenkins 2011 which basically makes this argument). and this is not quite true for COLD, x=54
Lines 332-333: .. if you only consider where the SGW is released. please make this clear.
Line 339, Lebrocq et al 2013. If you cite this, then you should also cite Gourmelen et al, 2025.
Line 340: "However..." LeBrocq focused primarily on cold cavities.
Line 353-355: you should comment on what position is most likely from a glacial perspective.
Lines 373-4: i would argue that one must look at GZ-averaged results here. while it can have a large effect on mean melt, it does not raise melt by 2 orders of magnitude.
Line 389: the current paper does not distinguish between the influence due to density change and that due to bathymetry change.
Line 392: i thought the wedges were constructed similarly to moraines (sediment being pushed by ice) -- if you are going to bring this point up perhaps you should include this as a source? or compare source magnitudes?
Sources
Gourmelen, N., Jakob, L., Holland, P. R., Dutrieux, P., Goldberg, D., Bevan, S., ... & Malczyk, G. (2025). The influence of subglacial lake discharge on Thwaites Glacier ice-shelf melting and grounding-line retreat. Nature Communications, 16(1), 2272.
Jenkins, A. (2011). Convection-driven melting near the grounding lines of ice shelves and tidewater glaciers. Journal of Physical Oceanography, 41(12), 2279-2294.
Slater, D. A., Nienow, P. W., Cowton, T. R., Goldberg, D. N., & Sole, A. J. (2015). Effect of near‐terminus subglacial hydrology on tidewater glacier submarine melt rates. Geophysical Research Letters, 42(8), 2861-2868
Citation: https://doi.org/10.5194/egusphere-2026-3435-RC2
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I have reviewed the paper by Paola Papapetrous et al called "The Sensitivity of Grounding Zone Melting to Subglacial Discharge Configuration and Sediment Dynamics Across Contrasting Ice Shelf Cavity Regimes". I have thoroughly enjoyed reading this paper. I really appreciated the structure of each of the sections and the clarity of the results presented. I absolutely recommend this paper for publication after minor revisions.
Minor comments in order of appearance in the paper:
Overall, very nice paper!