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the Creative Commons Attribution 4.0 License.
| 08 Sep 2025
Review Article: The Foundation-Patuxent-Academy ice stream system, Antarctica
Abstract. The Foundation-Patuxent-Academy system (FPAS) is a major Antarctic ice stream system with a global sea level potential of ~3 m. Draining both East and West Antarctica, the FPAS has been understudied compared with other major Antarctic ice streams. We provide a holistic catchment-scale overview of the FPAS reviewing its glaciological and hydrological systems, its glacial history, and its modelled response to past and future climate change. FPAS may be vulnerable to future change because of: (i) a deep (~2.4 km below sea level) low-gradient retrograde bed that encourages grounding-zone retreat; (ii) a low-gradient ice surface and high tidal range, which are likely to promote flotation of grounded ice and seawater intrusion; (iii) an active and dynamic subglacial hydrological system; (iv) complex ice-meltwater-ocean interactions at the grounding zone; (v) potential for substantive expansion of the across-flow length – and cross sectional area – of the grounding zone; and (vi) susceptibility to ice flow-switching and water piracy. Despite such potential vulnerabilities, existing numerical model simulations of FPAS grounding-zone retreat produce a wide and divergent range of past and future scenarios. Uncertainties in the future response of the FPAS to a warming climate result from poor constraints on its topography and hydrology, processes of ice-ocean interaction, interlinkages with the surrounding ice sheet and ice shelf, and a shortage of FPAS-specific modelling experiments. This review outlines and evaluates these critical gaps in our knowledge of the FPAS and develops a strategy to address them. This strategy would provide: (i) the first robust and comprehensive evaluation of the FPAS’s vulnerability to current and near-future climate forcing; and (ii) improved constraints on projections of the future contribution of the Antarctic Ice Sheet to sea-level rise.
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Status: final response (author comments only)
- RC1: 'Comment on egusphere-2025-3625', Duncan Young, 14 Oct 2025
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RC2: 'Comment on egusphere-2025-3625', Anonymous Referee #2, 28 Dec 2025
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.
Review of Ross et al. The Cryosphere -
Review Article: The Foundation-Patuxent-Academy ice strea 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.
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.
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.
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).
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.
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);
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;
- 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.
- 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.
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.
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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.
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. 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.
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'.
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).
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)).
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.
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.
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).
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.
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).
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.
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.
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.
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?
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 Hydrogeology section could use some paragraph breaks.
Section 5:
It seems there is a missed opportunity to directly tie the targeted activities in Section 5 to the insights in Section 2.
Figure 9: Put titles of panels on the panels.
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?
Minor issues:
In general - more paragraph breaks. 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.
line 366: sub-iice -> sub-ice
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?
line 696: "Aurora Basin" -> "Aurora Subglacial Basin"
References in this review:
Bingham, R. G., M. J. Siegert, D. A. Young, and D. D. Blankenship (2007), Organized flow from the South Pole to the Filchner-Ronne ice shelf: an assessment of balance velocities in interior East Antarctica using radio-echo sounding data, Journal of Geophysical Research, 112(F03S27), doi:https://doi.org/10.1029/2006JF000556.
Bingham, R. G., J. A. Bodart, M. G. P. Cavitte, A. Chung, R. J. Sanderson, J. Sutter, O. Eisen, N. B. Karlsson, J. A. MacGregor, N. Ross, D. A. Young, D. W. Ashmore, A. Born, W. Chu, R. Drews, S. Franke, V. Goel, J. W. Goodge, A. C. J. Henry, A. Hermant, B. H. Hills, N. Holschuh, M. R. Koutnik, G. J.-M. C. L. Vieli, E. J. MacKie, E. Mantelli, C. Mart´ın, F. S. L. Ng, F. M. Oraschewski, F. Napoleoni, F. Parrenin, S. V. Popov, T. Rieckh, R. Schlegel, D. M. Schroeder, M. J. Siegert, T. O. Teisberg, K. Winter, X. Cui, X. Tang, S. Yan, H. Davis, C. F. Dow, T. J. Fudge, T. A. Jordan, B. Kulessa, K. Matsuoka, C. J. Nyqvist, M. Rahnemoonfar, M. R. Siegfried, S. Singh, V. Viˇsnjevi´c, R. Zamora, and A. Zuhr (accepted), Review Article: Antarctica’s internal architecture: Towards a radiostratigraphicallyinformed age–depth model of the Antarctic ice sheets, The Cryosphere, doi:https://doi.org/10.5194/egusphere-2024-2593.
Blankenship, D., J. Holt, S. Kempf, D. L. Morse, M. Davis, R. Bell, and R. Arko (2025), SOAR PPT (Pensacola-Pole Transect) gridded aerogeophysical observations, doi:https://doi.org/10.18738/T8/QMEWFA. [DiMarzio et al.(2003)DiMarzio, Zwally, Brenner, and Sidel] DiMarzio, J. P., H. J. Zwally, A. C. Brenner, and T. Sidel (2003), Ice Sheet Surface Topography of Greenland and Antarctic from ICESat Altimetry, AGU Fall Meeting Abstracts, pp. A420+.
Gardner, A. S., M. A. Fahnestock, and T. A. Scambos (2019), ITS_LIVE Regional glacier and ice sheet surface velocities: Version1.,doi: https ://doi :10.5067/6II6V W8LLWJ7.
Helm, V., A. Humbert, and H. Miller (2014), Elevation and elevation change of Greenland and Antarctica derived from CryoSat-2, The Cryosphere, 8(2), 1539–1559, doi:https://doi.org/10.5194/tc-8-1539-2014.
Holt, J. W., S. L. Magsino, M. E. Peters, S. D. Kempf, R. R. Giggs, D. D. Blankenship, and R. E. Bell (1999), Soar annual report 1998/99. antarctica, Technical Report 185, University of Texas Institute for Geophysics.
Joughin, I., J. Bamber, T. Scambos, S. Tulaczyk, M. Fahnestock, and D. MacAyeal (2006), Integrating satellite observations with modelling: basal shear stress of the Filcher-Ronne ice streams, Antarctica, Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 364(1844), 1795–1814.
Mouginot, J., E. Rignot, and B. Scheuchl (2019), Continent-wide, interferometric SAR phase, mapping of Antarctic ice velocity, Geophysical Research Letters, 46(16), 9710–9718, doi: https://doi.org/10.1029/2019GL083826.
Siegfried, M. R., and H. A. Fricker (2021), Illuminating active subglacial lake processes with icesat-2 laser altimetry, Geophysical Research Letters, 48(14), e2020GL091,089, doi:https://doi.org/10.1029/2020GL091089, e2020GL091089 2020GL091089.
Studinger, M., R. E. Bell, P. G. Fitzgerald, and W. R. Buck (2006), Crustal architecture of the Transantarctic Mountains between the Scott and Reedy Glacier region and South Pole from aerogeophysical data, Earth and Planetary Science Letters, 250(1-2), 182–199, doi:https://doi.org/10.1016/j.epsl.2006.07.035.
Wessel, B., M. Huber, C. Wohlfart, A. Bertram, N. Osterkamp, U. Marschalk, A. Gruber, F. Reuß, S. Abdullahi, I. Georg, and A. Roth (2021), TanDEM-X PolarDEM 90 m of Antarctica: generation and error characterization, The Cryosphere, 15(11), 5241–5260, doi:https://doi.org/10.5194/tc-15-5241-2021.
Young, D. A., J. D. Paden, J. S. Greenbaum, D. D. Blankenship, M. E. Kerr, S. Singh, S. R. Kaundinya, K. Chan, D. P. Buhl, G. Ng, and S. D. Kempf (2024), COLDEX Open Polar Radar MARFA Airborne Radar Data, doi:https://doi.org/10.18738/T8/J38CO5.
Young, D. A., J. D. Paden, S. Yan, M. E. Kerr, S. Singh, A. Vega Gonzalez, S. R. Kaundinya, J. S. Greenbaum, G. Ng, D. P. Buhl, S. D. Kempf, and D. D. Blankenship (2025), Coupled ice sheet structure and bedrock geology in the deep interior of East Antarctica: Results from Dome A and the South Pole Basin, Geophysical Research Letters, 52(e2025GL115729), doi:https://doi.org/10.1029/2025GL115729.