REVIEWER 1

Review of Ross et al., 2025 (doi:10.5194/egusphere-2025-3625)

"Review Article: The Foundation-Patuxent-Academy ice stream system, Antarctica"

Overview:  

This review paper is a call to arms to focus on the sprawling Foundation-Patuxent-Academy System, a collection of ice stream catchments that flow from Dome A into the intersection of the Filchner and Ronne Ice Shelves.  In general, it is a fine and timely overview, but there are gaps, and places where things could be clearer.  There are elements of a proposal in here, so forgive me if I approach it with that mindset.

We are grateful to reviewer 1 for the positive comments about the manuscript. We very much appreciate their suggestions for gaps to fill and their guidance on where to make the manuscript clearer. We do have one eye on future research with this review article, but it was not the primary reason for us writing it. We are however pleased that reviewer 1 has identified “elements of a proposal” within it.

Major issues:

Section 1: 

It appears a key point this paper is trying to make is a shift from an ice shelf oriented view to a grounded ice point of view of the system (the historical priority of the ice shelf is a natural outcome of the evolution in satellite remote sensing described in the discussion of Section 3 below). Authors could be more explicit in why they want to make this contrast.  

We would be happy to make this point clearer in a revised version of the manuscript. The focus towards grounded ice was deliberate and stemmed from the research interests of the authors, efforts to distinguish future research activities in this system from relatively recent (ocean-oriented) research on the Filchner Ice Shelf System, and the fact that factors other than ice-ocean interactions can determine glaciological change. For example, there is Holocene-age evidence for non-ocean driven changes to parts of the Antarctic Weddell Sea Sector, and multiple examples of where water and/or ice piracy has driven major reorganisation of Antarctic ice sheet flow. Our manuscript was deliberately set up to embody a broader focus than the ice-shelf/ocean oriented viewpoint. We would be happy to make this perspective/argument more prominent in a revised manuscript.

Figure 1 is not clear.  The forest of overlapping red boxes with letter pointers to numeric pointers to other figures does not add much value.  You could combine a simple insert map of all Antarctica, showing simply the major subcatchments you describe here, with Figure 10 (the block diagram), and it would be clearer what you are talking about.  There is talk of flux gates which are not shown.

We agree with reviewer 1 here and would be happy to revise the figure. There is an annotation to a flux gate (FG) in 1b but it is admittedly tricky to display at the scale of the map and resolution of the image. We could either remove the reference to fluxgates in the caption or display them more effectively on the revised figure. Either option is acceptable to us.

Section 2: 

The numbered 'insights' (eg "Bed geometry near the grounding zone" here are titled as generic targets.  I think those targets could be phrased as actual insights. Why do we care about the bed geometry near the grounding zone? etc etc.  Frame them as a provocation. A pithier version of the first sentence of each section.  Alternatively, you could refer to them as 'targets of investigation' instead of 'insights'.

Our preference here would be to adopt the suggestion to refer to the numbered ‘insights’ as ‘targets of investigation’. We would retain ‘insights’ in Line 78 but make the alteration in line 86. 

Section 3: 

There is a good historical section that goes into the detail of the early exploration of this issue.  However, it is missing a discussion an element that has profoundly shaped the understanding of this region - the remote sensing 'pole hole' that meant we didn't have good topography of much of this region before IceSat-1 in 2003 (DiMarzio et al., 2003), which was significantly, but not totally advanced by Cryosat-2 in 2014 (Helm et al., 2014), and then it wasn't until TanDEM-X (Wessel et al., 2021) that we managed to fill in the key intersection between Foundation and Academy (and event then there are issues with the accessibility of that dataset).  

We agree with reviewer 1 here and would be happy to introduce some text in a revised manuscript to describe the ‘pole hole’ and its influence on FPAS research. We appreciate the useful suggestions for literature to include.

Surface velocity is a similar story: image based velocity tracking (Gardner et al., 2019) - the only data we have for much of the system is from Radarsat-2 coverage from ~ 2015 (Mouginot et al 2019), with significant errors in key parts of the onset of this system.  NiSAR should address a lot of the surface velocity issues.  The role of intuition on this system from balance velocities derived from incomplete surface topography data is a key part of the story (which was acknowledged as an issue at the time (eg Bingham et al. 2007)). 

We would be happy to include additional text to cover this aspect too. The challenges associated with ice velocity errors in this region is certainly something that has become more apparent to the author team since the submission of this manuscript, and is important to record in the revised manuscript. NiSAR data certainly provides many opportunities to address the current surface velocity issues, and we can make reference to its potential in the manuscript.

On the airborne geophysics side, it's probably worth mentioning the SOAR/Pensacola-Pole Transect (Studinger et al., 2006, Holt et al., 1998, Blankenship et al., 2025) which first traversed this system at the South Pole.

Apologies to reviewer 1 that the SOAR/Pensacola-Pole Transect (PPT) isn’t already reflected in section 3 of the manuscript. This was an oversight. An earlier version of the manuscript did include reference to SOAR/PPT here, and its absence in the submitted version likely occurred during final editing prior to submission. We will rectify this in a revised version.

The value of Figure 3 is not clear, especially panels c-e. It might be clearer just to show the various bedmaps (including bedmap1) to show synoptic scale changing in configuration.  To make the point about poorly optimized collection, maybe using the ILCI figure (Fig 6 in Bingham, Bodart, Cavitte, Chung, Sanderson and Sutter et al., in press) might make the point better.

Reviewer 2 has made a similar comment about Figure 3. We would be happy to deploy reviewer 1’s solution of showing the various bed topographies. There are two other potential options for addressing this issue with figure 3: (1) we move the figure in its entirety to SI; or (2) we reduce the number of subplots (i.e. reduce c-e to a single subplot). We would prefer to retain subplots a, b and f in the main text as they demonstrate how poorly sampled some parts of FPAS are, as well as the substantive differences that exist even between Bedmap3 and BedMachine v3. This is despite these data products using similar (if not identical) input data across FPAS. 

Lastly, there now has been an very extensive recent survey of the onset region of this system through NSF COLDEX; data has been out for a while (Young, Paden et al., 2024), and now actually a paper (Young et al., 2025), which has implications for how this system is initiating (obviously this came out after the paper was submitted, but is relevant to this review paper).

We were aware of a few COLDEX papers that were available as preprints at the time we submitted our review but thought it wise to wait until they had been published to include. We will cite the newly published papers in the revised manuscript.

Section 4: 

This section starts with two paragraphs which are a half page long, which makes it a little hard to parse.  Names are introduced that are not in the Antarctic Gazette (eg "Foundation Trough") - the authors should make it clear what is official and what is not, and maybe consider a plan for getting them approved if not.

We will explore options for breaking up the two paragraphs that start section 4. We can make clear which place names are official or not. We note that ‘Foundation Trough’ (or ‘Foundation-Thiel Trough’) has been in informal usage for some time, having been referred to in previously published papers (e.g. https://doi.org/10.1016/j.quascirev.2016.09.028 & https://doi.org/10.1029/2018GL077504). As the Foundation Trough is within the geographic remit of the UK Antarctic Place-names Committee, we can liaise with that committee about formal approval. 

The discussion of Joughin et al 2006 in the context of in Academy roughness is a little indirect, since that paper does not explicitly mention Academy Ice Stream or roughness. It does seem that what Joughin's inversion is picking up is the prominent cross flow ridges visible in MOA imagery, which the FISS and Polargap survey lines in Figure 4 are not well oriented to detect (which does go to the authors' point on coverage in Section 3).  

Joughin et al. (2006) envelope the entirety of FPAS into a single ‘Foundation Ice Stream’ catchment and therefore do not mention Academy Glacier directly (see their Fig. 1), although their Figures 2, 3 and 6, and Section ‘e’ do show and describe all the major FPAS components (Foundation, Patuxent and Academy). Definitions of the FPAS catchment as solely Foundation Ice Stream like this example were one of the initial motivations for this review article, as they have masked the details and intricacies of the system. We propose that the solution here would be to make clear that Joughin et al. (2006), do cover FPAS, it’s just that they defined the system as ‘Foundation’-only.

We agree that Joughin’s inversion seems to be picking up, or at least has features coincident with, the prominent cross flow ridges visible in MOA etc. imagery. Although the FISS/Polargap RES survey lines are not well oriented for capturing these landforms, they are fairly well represented in more recent compilations of bed topography (e.g. Bedmap3), and likely control the locations of recently discovered potential active subglacial lakes (Wilson et al., 2025 https://doi.org/10.1038/s41467-025-63773-9) 

On the roughness trend inland - at least with the color map in Figure 4a, it's still looking fairly smooth on the rebounded bed >0 elevation topography.

This is a fair comment from reviewer 1, as the roughness deep into the Pensacola-Pole Basin (i.e. proximal to South Pole) is certainly still relatively smooth. However, there are clearly abrupt lateral contrasts in roughness around Patuxent Ice Stream and the mid-parts of Academy Glacier that warrant further (future) investigation. We thought it was important to highlight: (i) these ‘contrasts’ in the review - as to the best of our knowledge this pattern of roughness has not been shown previously, and (ii) the apparent spatial coincidence with the topography below the 0 m rebounded contour in many areas of FPAS.

Figure 4.  Using consistent colours between panels a and b for the bed contours will make it easier to compare.  For FAIR purposes, include the granule/flight information for the radargram in the caption.

We can explore options for consistent bed contour colours. We originally had black contours on 4a but they got a little lost because of the colour pallet used to display the roughness. The suggestion from reviewer 1 to include the granule/flight information for the radargram is an excellent one. We will implement this suggestion.

Figure 6 has some issues. In a) The higher discharge values are hard to distinguish from the background color map. In the legend the text Subglacial Lakes bleeds directly into Channel Discharge.  6a also needs a scalebar. 6b (directly taken from Siegfried and Fricker, 2021) should be located on 6a, not on a separate figure on a separate page.  The box for 6d should be shown on 6a, or the catchment boundaries should be added to 6d for reference.

We are happy to amend figure 6 to address most of these comments. We note that 6a does have a scalebar – located within the figure legend – which we can move to a more visible location. However, we don’t fully comprehend the comment “6b (directly taken from Siegfried and Fricker, 2021) should be located on 6a, not on a separate figure on a separate page.”. We wonder if reviewer 1 is referring to figure 7 here?

The Jordan 2018 downdraw is shown on Figure 5, but not fully discussed in the text until after the subglacial hydrology section - I would suggest adding it to the subglacial hydrology figures.  Would it be possible to add the Jordan flow routes (yellow line their Fig 3) to these figures?

We can add the downdraw zone to figure 6a, but the zone is outwith the extent of figure 7. We could consider including the Jordan hydropotential flow routes (or a more updated version of this analysis) on figure 6a. However, given the assumptions (e.g. warm bed throughout) and uncertainties (e.g. in bed topography etc.) associated with that type of analysis, our preference would be to simply retain the hydropotential contours currently included in Fig. 6a. These indicate the broad potential pattern of basal water flow, rather than potentially unrealistic details. The model output from Ehrenfeucht et al., 2025 in 6a and 7b is likely a better estimate of where water is present at the FPAS bed than a simple Shreve-type analysis because it accounts for basal thermal temperature. 

line 426: It’s not clear that the dynamic summit migration seen at Dome C, which is solely a function of velocity, would have any direct bearing on ice sheet geometry.

The inclusion of this information and reference was simply to demonstrate that ice sheet interior geometries are not static and can change at quite rapid rates. However, we can simply delete the sentence and associated reference if appropriate.

The Hydrogeology section could use some paragraph breaks.

We will explore how we might do this. We note that reviewer 2 has made some suggestions for new paragraph breaks throughout the manuscript too.

Section 5:

It seems there is a missed opportunity to directly tie the targeted activities in Section 5 to the insights in Section 2.

We are not in favour of rewriting section 5 in this way, but we can explore options if necessary. We originally had this approach in a draft of the manuscript, but it: (1) resulted in a series of very similar ‘lists’ repeated throughout the manuscript; and (2) did not facilitate a flowing section 5 where several of the subsections overlap the ‘targets of investigation’/’insights’ that are listed in section 2. In any revised version of the manuscript, we will need to account for suggestions made by reviewer 2 around section 5 and a potential, reviewer 2-proposed, section 6. As a result, we will await editorial input before deciding on how to adapt section 5, if adaptation is required.

Figure 9: Put titles of panels on the panels.

We will action this. It will help readers distil the information in the figure more readily. Thank you.

line 678: "For example, some reported ‘Academy Glacier’ active subglacial lakes (i.e. A14 and A16) could be located beneath Support Force Glacier instead. "  This does not make sense as written. You have defined the margins of these features in this paper, and the locations of the active lakes is well determined. Are you suggesting that there are Academy Glacier and Support Force Glacier hydrological catchments that do not correspond to the ice declared ones?

There is considerable complexity in accurately defining the boundaries between the ice flow and hydrological catchments of Academy Glacier and Support Force Glacier. This is because of uncertainties in the ice velocity and ice thickness/bed topography datasets, as well as errors that propagate into derived products such as hydrological flowpaths etc. When the active lakes were categorised in the late 2000s, that uncertainty was even greater because of the datasets available at the time, so that some of the active lakes designated as ‘Academy’ lakes are actually beneath ice within the Support Force Glacier catchment (as defined by ice flow). This can be seen in figure 7b, where A14 and A16 are either below (A14), or to the (geographic) north east (A16) of the IMBIE ice-catchment boundary between Academy and Support Force Glacier. Of course, which ‘side of the lines’ these potential active lakes reside on is highly dependent on the accuracy of the defined mass balance catchments, which is why we opted for a conservatively worded sentence, i.e. “For example, some reported ‘Academy Glacier’ active subglacial lakes (i.e. A14 and A16) could be located beneath Support Force Glacier instead.”. A solution to the comment from reviewer 1 here would be to explain this point in the manuscript in greater detail, based on the text we have written in response to reviewer 1 here.

Minor issues:

In general - more paragraph breaks.  

Yes, we can do this – reviewer 2 has suggested the same and has pointed us to some possible locations to introduce them.

Also for radargrams add more granularity to the reference - allow readers to go directly to the Polar Airborne Geophysics Data Portal or equivalent and look at the same radargram at full resolution.

This is an excellent suggestion. We will do this.

line 366: sub-iice -> sub-ice

We will amend this. Reviewer 2 also spotted this.

line 373: "Based on overburden hydraulic potential calculations, but not model results (Dow et al.,2022),"  Awkwardly phrased - does Dow and GLADS imply that water-route switching is unlikely?

Yes, the model output from Dow et al. does not support the idea of water-route switching, though we understand that this was not explicitly explored in the model runs. We can explore how to reword this sentence in a revised article to improve the phrasing.

line 696: "Aurora Basin" -> "Aurora Subglacial Basin"

We will amend this.

REVIEWER 2

The questions listed above do not fit well with a review paper. The paper is fine, an excellent review of the literature and most of the aspects of importance to this part of Antarctica. But as a review paper of the state of knowledge, how can it be, e.g., 'excellent' in (1) originality? or (3), 'changing our scientific understanding of a subject'? Editors may with to reconsider the questions for a paper of this type.

We are very appreciative of the positive comments from reviewer 2 about the manuscript here. Thank you. We will leave the issues with the questions listed to the TC editorial team.

Review of Ross et al. The Cryosphere -  

Review Article: The Foundation-Patuxent-Academy ice stream system, Antarctica

The paper presents an overview of the observations and some of the potential processes of this multi-channel ice-stream system, with a strong focus on the bedrock geometry and potential for marine ice sheet instability processes to take hold in the century-scale future.

There are numerous comments in the attached .pdf mark-up.

We have extracted those comments from the marked-up PDF and included them at the bottom of this response.

This is well-written, not hard to follow, and fairly thorough for the aspects that are covered.  It could be published as it is, but as it is, it will fall a bit short of stimulating the kind of community push to work in the area that it seems to be calling for.

We appreciate the positive comments about our review paper here, and that it “could be published as it is”. However, we are keen to stimulate a community push to work in the FPAS and surrounding region so we would be happy to develop the manuscript to deliver this goal.

The top comment is that much more should be said, from the beginning, about the ocean side of the story and the potential for warm deep water to enter the Filchner-Ronne cavity and cause retreat along the entire grounding zone discussed here (and the Institute-Möller too). I wasn’t sure this had been expanded upon since Hellmer et al., 2012’s work, but I see that several papers, and not just from Hellmer, have discussed this possibility more recently. This should be the main driver of a push to understand the system now, and model how it might behave in the 22nd – 23rd century.

We were wary of pinning the justification for the manuscript on Hellmer et al., (2012) because it is likely a high-impact, low-likelihood end-member scenario. Because of the location and configuration of the FPAS grounding zone, it would likely take a long time for changes in cavity circulation to propagate to it from the Filchner Ice Shelf edge. We therefore took a cautious approach in our justification for why FPAS is important, avoiding possibly unrealistic ‘alarmist’ statements for this part of the Antarctic Ice Sheet, where glaciological change on the scale of the Amundsen Sea Sector is not currently occurring. We were also keen – as reviewer 1 identified – to pivot the research in this area towards the grounded ice, rather than the ice shelf. 

However, as suggested by reviewer 2 (see comment below associated with ~Line 78), we could weave in some ice-ocean/ice shelf justification into the text (in sections 1 or 2 of the current manuscript). This additional content (likely 1-2 sentences in introduction, perhaps with further content in section 4.4) would focus on introducing the potential for the cavity to become warm and contribute to future sea level rise. We can see that adding this is relevant given: (1) the ocean is inherently part of the major forcing for potential future sea level rise from the region; and (2) that one of the future research directions (number 4) is "observations of ice-ocean-hydrology interactions". For the latter any reader will need some context earlier in the manuscript as to why ice-ocean interactions are important.

If we implement such changes then we would prefer to balance any additional ocean-related content with a clear statement that despite the recent work on the ocean/ice-shelf side (e.g. Hellmer et al, 2012; Filchner Ice Shelf System programme etc.), the primary aim of the current manuscript is to focus on the grounded parts of the catchment & to explain why (see also comments in response to reviewer 1). We would also want to ensure that any such additional content on this topic didn’t further widen the scope of the manuscript (e.g. encroaching into discussing other large Weddell Sea Sector ice streams that flow into the Filchner Trough).

A second high-level comment is that the paper might consider including the Support Force Glacier as well, since there are several strong links at the regional scale between the areas discussed and SFG. This would entail a significant re-write, but really, most of the data sets and figures already include this area, and the strong likelihood of water piracy and ice flow re-direction make it logical to include it (e.g., Figure 7).

The consideration of adding Support Force Glacier to the review more explicitly (e.g. including it in the title of the manuscript) was discussed within the authorship team prior to submission of the manuscript. In the end we opted not to do this because of: (i) FPAS is a single system that shares a single flux gate; (ii) there has been relatively little research done on Support Force Glacier (although we note some excellent recent work by AWI/BAS); and (iii) the unwieldiness of adding another glacier into the mix and extending the manuscript even further/longer.

Support Force Glacier may well be key to future research understanding how the glaciology of FPAS and the wider Weddell Sea Sector might evolve (and has evolved in the past). However, we do wonder just different any revised manuscript including more Support Force content would look. This is because of the relatively small amount of research completed to date on Support Force, and that much of that existing published research is already included, albeit slightly indirectly, in the current manuscript. Possible solutions here would be either to make more prominent and direct reference to Support Force Glacier in the manuscript (e.g. in the abstract and introduction), or to state more clearly in the introduction section the reasons why we focus on FPAS but not Support Force. We disagree with Reviewer 2 that any such changes would “entail a significant re-write” though.

At the end of the paper (Section 5 and sub-sections, Figure 10), the authors list what is not known about the system, and what might be done. The items listed are indeed not well-known, but a similar case could be made for virtually any large ice stream system in Antarctica --- the posed questions are not drivers for research in this area. The points made are valid, but they are broad, geographically wide-ranging, and not focused into a logistically efficient and fundable set of objectives.

We disagree with Reviewer 2 here, as we feel that that the items listed in section 5 and subsections are FPAS (&Support Force)-specific. The manuscript is not intended, nor designed, to provide “a logistically efficient and fundable set of objectives”. Instead, it is intended as a broad inspiration for future, more specific, funding proposals. The focused, logistically efficient and fundable set of objectives is a later (i.e. post review paper) step in the development of future FPAS (&Support Force) research.

As noted, the paper could be published more or less as it is. It’s not wrong, it has a comprehensive bibliography (but missing ocean conditions and circulation in the Filchner-Ronne cavity);

Thank you. We are delighted to hear that “the paper could be published more or less as it is” and that the reviewer reinforces that point again here.

But if the goal is to motivate a major research program, for example, for the upcoming International Polar Year 2032-2033, then I would suggest the following;

    Include the possibility of a large increase in ocean-driven melting as per Hellmer and other papers; this is probably an additional section discussing the oceanography of the Weddell generally, and the drivers that might lead to warm-water intrusion into the Filchner cavity;

As stated in an earlier response to Reviewer 2, we can insert a short section early in the manuscript about the potential for ocean-driven melting and include the Hellmer et al., 2012 reference. However, because it will pivot the manuscript away from the ‘grounded ice’ focus identified by reviewer 1, and will further extend an already long manuscript, we would prefer not to add a substantive section or sections on ocean-driven melting/ice-ocean interactions to the manuscript.

    Shorten Section 5 to be a concise general setting out of the regional questions (adding ocean and sub-shelf cavity ones). I would add in Support Force, since both the basal topography, hydrology, and surface flow are all potentially connected, in the past or in the future.

We can explore how to shorten section 5, and to make it more geographically/regionally focused; however, as we argue above, we feel that it is quite concise already. The addition of content on Support Force would require only minor changes to the text (e.g. changing references to ‘FPAS’ to ‘FPAS and SFG’) as Support Force is already discussed comprehensively in section 5 (e.g. section 5.2 has 5-6 explicit mentions of Support Force).

    Create a new Section and describe an efficient, integrated research program – ocean cruises here, two logistical camps here and here, with the key science questions addressed by this and that set of observations located in these selected locations, reachable from the camps; point out how the key locations you have identified for camps and for measurments are the best ones to address the questions; describe the goals and data sets of a continuing remote sensing effort; and describe how, e.g., new airborne data and the field data might feed into new modelling by the skills represented in the author list. Talk about the high potential for a UK-European-US collaboration.

We do not wish to include a new ‘Section 6’ describing “an efficient, integrated research program….”. This is because: (i) the manuscript is a review paper, not a proposal –  it is not a manuscript that pre-empts a large special research programme akin to ITGC; (ii) the FPAS community is not yet at the stage of research development where we can provide these level of details; (iii) at this point in time, we do not necessarily envisage a full ITGC-style programme to undertake future FPAS/SFG research; and (iv) we feel that there are ethical/research governance issues relating to us delivering the requested level of detail at this stage (i.e. when proposals are not yet initiated). 

We note that reviewer 2 has twice stated above that the manuscript “could be published as it is” so we would therefore argue that the creation of a new section 6 is unnecessary.  Such information is appropriate for future research proposals, but not for inclusion within this review article.

But don’t make the mistakes ITGC did: be efficient, stay within the logistical realities; keep the field teams a bit smaller, UK-style, and have a phased field work plan that doesn’t overwhelm the capabilities in any given year. Don’t get me wrong – ITGC is a magnificent accomplishment, but it could have been easier to accomplish.

This is helpful guidance and input from reviewer 2 and will be a useful steer for any future (potential) science on FPAS. Thank you.

Specific comments from PDF

Title: As I note later, consider adding the Support Force Glacier to the review. The manuscript already dwells on it quite a bit, and the high possibility of water piracy links the systems.

Please see response to reviewer 2’s general comments on Support Force Glacier above. 

L25: This sentence isn't necessary -- a small justification for the paper, yes, but really everything in science can claim a need for further study.

We can do this but would want to retain the “draining both East and West Antarctica” part by incorporation into the opening sentence of the abstract. This part is particularly important to retain if we are guided to amplify the importance (and visibility) of Support Force Glacier in the manuscript (see responses to reviewer 2 above).

L26: just noting -- this list of vulnerabilities mixes those that might have a big impact on net ice flux and sea level with those that are just dynamically interesting but don't pose the same level of threat.

Yes, we note this too, and think that this is philosophically a good approach, for both FPAS and for Glaciology/Antarctic Science in general. We should ensure that we investigate both ‘threats’ and aspects of the ice sheet that are ‘just dynamically interesting’. We don’t know when the latter might become the former (or vice-versa!).

L35: seems like this last point is different from the others, and not needed. Uncertainties result from fewer available model runs... doesn't seem logical somehow. I'd just drop the last point.

We’d prefer to retain this point if we can, as it reflects content within the review article (i.e. section 4.4).

L78: A major driver for increased interest in this area (and for your earlier Institute-Möller I.S. review) is the model result by Hellmer, 2012 and related follow-on papers indicating the possibility of warm water intruding the Filchner - Ronne cavity in the 22nd century. This shoudl lead off your justifications.

Please see our response to reviewer 2’s general comments above regarding using Hellmer et al., 2012 to justify the review article.

L86: start new para here

Happy to implement this.

L88: maybe make these italicized headings rather than the (i), (ii) listings -- a bit over-used here?

Happy to implement this.

L102: ...all linked to the presence / absence of warm deep water in the cavity -- ?

Happy to implement this.

L105: break sentence in two here.

Happy to implement this.

L109: nesting of the i, ii organization style - can't do that.

Good spot. This issue will be addressed if we opt for italicized headings as suggested above (L88).

L113: Cite Walker, 2013 et al here

Happy to implement this.

Figure 2: this might be better presented as two figures, or a large single figure -- in particular, the radar profiles deserve more space and perhaps more interpretive annotation. Consider a layout of (a) as a full width map (or nearly full-width), (f-i) below right, and (b-e) arranged more in a rectangular overall shape below left.

Thanks for the suggestion. We are happy to revise this figure to give the radar profiles more space and to add interpretive annotation.

Figure 3:  this seems like a lot of space for a review of improvements relative to older data. Could (a) and (b) be combined? Then perhaps just keep (d) and (f). Then perhaps a fourth panel could be the current best topography, which I think is Bedmachine v3. I think this would support your three points (i,ii,iii).

Reviewer 1 also commented that Figure 3 took up a lot of space, and we suggested some options to address this (see comments in response to reviewer 1). We think that combining a&b would make the combined single figure very complex. We would be happy to reduce c-e down to one figure, at least in the main manuscript. Whether Bedmachine v3 is better than Bedmap3 is open to debate, and probably subject to individual views on the manual modifications that were made to Bedmap3 along deep subglacial troughs. We felt that it was important to highlight the large differences between Bedmap3 and BedMachine v3 in this area, as it has important implications for model boundary conditions, particularly along the Foundation Trough.

Figure 5: add other aspects of the geology? what is the geology of the Dufek Massif, Patuxent Range, or the bounding rocks (if known) for the PolarGap Highlands?

We could incorporate a second panel with other aspects of the geology here. Our deliberate plan for this review article was to focus on glaciology (and hence why we opted to submit to TC), but we can certainly adapt figure 5 to include geological information if it is necessary.

L347: Start new paragraph here

We are not sure about this suggestion here as it would leave a single sentence paragraph immediately before. We could move the sentence “Subglacial lakes are present….” to earlier in the section (e.g. line 322)?

L348: ...to refreezing at the ice base over subglacial...

Happy to implement this.

L350: start new sentence

Happy to implement this.

L367: sp

Happy to implement this. Also spotted by reviewer 1.

Figure 6: The color map of elevation change is featureless... is there another mapping, maybe 2018-2020 or later that shows the drainage better?

We will explore this and can make a bespoke subplot for the figure that shows the drainage more effectively.

Figure 6: add " A ---- A' " to the graph.

Happy to implement this.

Figure 6: where is (d) located? can you add a surface map to this panel?

Happy to implement this.

L454: suggesting a reference for this, makes a better case for the eastern Peninsula's LGM extent: http://dx.doi.org/10.5194/tc-9-613-2015

Happy to consider the inclusion of this reference here.

L497: This is also a scenario for the Thwaites region - late re-advance after the Holocene optimum-ish period.

No change required.

Figure 9: change to '...under Pliocene conditions..'

Happy to implement this.

L574: New paragraph here

Happy to implement this.

L601: Without the impetus of a potential intrusion of warm water (if the Hellmer projection is still viable) these questions pertain to nearly any region of Antarctica.

Please see our response to general comments from reviewer 2 regarding ice-ocean interactions and Hellmer et al. 2012.

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ADDITIONAL AUTHOR COMMENT NOT RELATED TO REVIEWS 1 or 2

Since the submission of our manuscript in summer 2025, we have become aware of (a) relevant research publications that we overlooked in our initial manuscript; and (b) research publications that have been published since then. We propose that we will include them in the revised manuscript. They are:

Hills et al. 2025 Radar‐Derived Crystal Orientation Fabric Suggests Dynamic Stability at the Summit of Hercules Dome  https://doi.org/10.1029/2023JF007588 

Lucas et al., 2023 Tidally Modulated Glacial Seismicity at the Foundation Ice Stream, West Antarctica  https://doi.org/10.1029/2023JF007172 

Rosier et al., 2017. Strong tidal variations in ice flow observed across the entire Ronne Ice Shelf and adjoining ice streams https://doi.org/10.5194/essd-9-849-2017

Summers et al., 2024 Evidence for and Against Temperate Ice in Antarctic Shear Margins From Radar‐Depth Sounding Data https://doi.org/10.1029/2023GL106893

Wilson et al., 2025. Detection of 85 new active subglacial lakes in Antarctica from a decade of CryoSat-2 data https://doi.org/10.1038/s41467-025-63773-9