Radiostratigraphy and surface accumulation history of the Amundsen-Weddell Ice Divide, West Antarctica

Napoleoni, Felipe; Bentley, Michael J.; Ross, Neil; Jamieson, Stewart S. R.; Uribe, José A.; Oberreuter, Jonathan; Zamora, Rodrigo; Rivera, Andrés; Smith, Andrew M.; Bingham, Robert G.; Matsuoka, Kenichi

doi:10.5194/egusphere-2025-4670

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https://doi.org/10.5194/egusphere-2025-4670

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12 Nov 2025

| 12 Nov 2025

Status: this preprint is open for discussion and under review for The Cryosphere (TC).

Radiostratigraphy and surface accumulation history of the Amundsen-Weddell Ice Divide, West Antarctica

Felipe Napoleoni, Michael J. Bentley, Neil Ross, Stewart S. R. Jamieson, José A. Uribe, Jonathan Oberreuter, Rodrigo Zamora, Andrés Rivera, Andrew M. Smith, Robert G. Bingham, and Kenichi Matsuoka

Abstract. Recent ground-based radio-echo sounding (RES) surveys across the Ellsworth Subglacial Highlands (ESH), a topographically complex region near the Amundsen–Weddell ice divide, reveal new insights into Holocene accumulation and ice dynamics in West Antarctica. We traced seven internal reflection horizons (IRHs) across approximately 2000 km of RES data spanning a 13,000 km² area in the upper catchments of Pine Island Glacier, and the Rutford and Institute Ice Streams. Two of these IRHs intersect dated airborne radar lines tied to the WAIS Divide 2014 ice-core chronology. Applying the Dansgaard–Johnsen model with local accumulation rates from stake measurements and satellite-derived value we estimated ages of up to ~ 17.6 kyr for the deepest horizon (IRH7). Internal stratigraphy is well preserved in the slow-flowing alpine terrain of the ESH but becomes disrupted in areas of relatively fast flow and tributary convergence, such as the southern Ellsworth and CECs troughs. Despite these localised disturbances, IRHs remain traceable across most of the region, highlighting the potential for radiostratigraphic continuity in complex settings. Modern and Holocene accumulation patterns reveal a persistent asymmetry across the AWID, with consistently higher accumulation in the CECs Trough, supporting long-term ice divide stability since at least the mid-Holocene. Our study extends the spatial coverage of dated radiostratigraphy in West Antarctica and provides new linkage between the Weddell and Amundsen Sea Embayments. These results support several core goals of the AntArchitecture initiative of the Scientific Committee on Antarctic Research, including the expansion of a continent-wide IRH framework, improved Holocene accumulation reconstructions, identification of palaeoclimate archive targets, and enhanced boundary conditions for numerical ice-sheet models.

Received: 22 Sep 2025 – Discussion started: 12 Nov 2025

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Felipe Napoleoni, Michael J. Bentley, Neil Ross, Stewart S. R. Jamieson, José A. Uribe, Jonathan Oberreuter, Rodrigo Zamora, Andrés Rivera, Andrew M. Smith, Robert G. Bingham, and Kenichi Matsuoka

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RC1: 'Comment on egusphere-2025-4670', Ella Wood & Tun Jan Young (co-review team), 10 Dec 2025 reply

Review: Napoleoni et al. Radiostratigraphy and surface accumulation history of the Amundsen-Weddell Ice Divide, West Antarctica

Manuscript #: egusphere-2025-4670

Ella Wood and TJ Young

This manuscript extends the age-depth radiostratigraphy of the Amundsen-Weddell Ice Divide through the incorporation of 2000 km long of Centro de Estudios Cientificos (CECs) ground-based RES survey. In this dataset, seven internal reflection horizons dating to the last ~17.6 kyr were traced of which two were linked to wider mapped radiostratigraphy datasets in this region.

Overall, this paper is well written and clearly structured with nicely presented figures showing interesting findings on the accumulation history of the Amundsen-Weddell Ice Divide. We have minor comments to improve the clarity of certain points and emphasise and contextualise the significance of the findings.

General comments

In general, the contextual scope of the manuscript is currently positioned between a paper describing a dataset and an analysis of the larger flow stability of the region—these were defined in the study aims (L74-75). Though the former aim was clearly accomplished and detailed, the latter aim was only discussed in a broad scope in Section 4.2, with regards to the overall lack of disturbance of ice flow in the wider region of study. We suggest redefining the secondary aim to be more focused and reframing Section 4.2 in terms of tying in where this study extends in interpretation from the previous work done in the region.
Though the statement of a stable ice divide is indeed evidenced across multiple past studies (an addition to the list would be Conway and Rasmussen 2009 for WAIS Divide), there is little mention of how this study extends / expands beyond the understanding of complex flow dynamics present in certain sections of the regions, particularly at the boundaries of the Institute-Moller ice streams. Here, there will be benefits in contextualising the study and positing interpretations where appropriate in relation to previous work done in the region (in particular Siegert et al. 2019, Ross et al. 2020). Potentially, addressing this point will also in part address comment (a).
For someone less familiar with the region, the use of the CECs abbreviation was at times confusing in that it was sometimes referring to the region and sometimes to the source of your radar data. It would be beneficial to add a sentence early on to clarify these differences. Occasionally the final S in CECS is also capitalised (line 84, figure 1 caption), I assume this is a typo. The reference to the Subglacial Lake CECs (SLC) was slightly confusing, consider adding a short statement to clarify that the lake has been previously identified and also why it is referred to as CECs.
Figure 8 is only very briefly mentioned in the text, perhaps this figure doesn’t need to be in the main text body or could be discussed more detail.
Paragraph (L385) here you talk about high and low accumulation scenarios. This is not previously mentioned, please provide further information to clarify what is meant by this and why contrasting high / low scenarios are relevant here.
Table 3 showcases significantly larger minimum / maximum bounds for Area 3, especially in comparison with bounds of corresponding IRHs in the other two Areas. Although it is understandable that the lowest IRH (7) will have substantially large bounds, there is scope to contextualise why these errors are so much larger in the discussion.

Specific comments

L7	Satellite derived values
L13	New linkages or a new linkage
L19	Revealed significant and ongoing mass loss - no a?
L22	“a-1” à a^-1”
L23	Geological records indicating
Figure 1	Suggest visualising the locations of the three sites of study (potentially here or in Figure 5): CECs Trough, (Ellsworth?) Subglacial Highlands and Alpine Terrain, and Ellsworth Trough. These sites are included in Figure 2 but it is difficult to georeference these locations alongside physical features, in particular the Ellsworth Trough which is not actually pinpointed.
L129	“internal layer continuity index”
L132	“as a consequence of—for example—topography…”
L136-7	Quantitatively constrain what defines the “upper part” and the “lower end” of the ice column—from Eq. 1 this is defined as the surface to 200 m and 400m to the bed, but then Figure 3 suggests the lower bounds to be much deeper. Regardless—these definitions need to be much more explicit and clear.
L184	Suggestion to elaborate on the constraints in which Nye-style modelling was found to yield comparable results to D-J modelling. Such conditions are implicitly given in L192-193 but could be made much more explicit.
L192-202	This paragraph seems to repeat several points multiple times—it could be condensed to be much more precise and succinct.
L248-251	A remnant clause still exists in this paragraph that will need to be removed.
L263	Equation reference to be pointed to Eq. 7 (I think, but am not sure). Potentially some additional explanation needs to be provided as to exactly how this specific uncertainty component has been defined and propagated.
L303	Suggest also providing additional offsets between IRH4 and H2, or if H2 and R2 are equivalent, then make this explicit.
Figure 7	Suggest to mark IRHs on this figure. Figure caption mentioned a red arrow in panel f that doesn’t appear in the figure.
Table 3	Could include headings for much better signposting to indicate the upper and lower bounds for each IRH and area. Are the alpha values representing snow-equivalent or (as referenced in L402) ice-equivalent depth-rate estimates? For L402, is this then the midpoint between the bracketed alpha values shown in Table 3?
L403-4	I am unsure as to how matching IRH4 to the equivalent age-depth reflector in Bodart et al. (2021) will produce accumulation rates—would this not be determined independently through the D-J model?
L427	“At least two” As far as I am aware, only two reflectors (IRH4 and IRH6) were discussed, so I am not sure there were more than two that were actually of note.
L473	Typo Arthem et al. (2006)
L476	Statement is quite vague “rates vary over short distances”. Can you quantify magnitude and distance in some way to make this statement more explicit.
L486	Consider including reference for broader WA climate trends.

References

Conway H and Rasmussen LA (2009) Recent thinning and migration of the Western Divide, central West Antarctica. Geophysical Research Letters, 36(L12502). doi: https://doi.org/10.1029/2009GL038072

Siegert, M.J., Kingslake, J., Ross, N., Whitehouse, P.L., Woodward, J., Jamieson, S.S.R., Bentley, M.J., Winter, K., Wearing, M., Hein, A.S., Jeofry, H. and Sugden, D.E. (2019). Major Ice Sheet Change in the Weddell Sea Sector of West Antarctica Over the Last 5,000 Years. Reviews of Geophysics, 57(4), pp.1197–1223. doi: https://doi.org/10.1029/2019rg000651.

Ross, N., Corr, H. and Siegert, M. (2020). Large-scale englacial folding and deep-ice stratigraphy within the West Antarctic Ice Sheet. The Cryosphere, 14(6), pp.2103–2114. doi: https://doi.org/10.5194/tc-14-2103-2020.

Citation: https://doi.org/10.5194/egusphere-2025-4670-RC1

Felipe Napoleoni, Michael J. Bentley, Neil Ross, Stewart S. R. Jamieson, José A. Uribe, Jonathan Oberreuter, Rodrigo Zamora, Andrés Rivera, Andrew M. Smith, Robert G. Bingham, and Kenichi Matsuoka

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https://doi.org/10.5194/egusphere-2025-4670-supplement

Felipe Napoleoni, Michael J. Bentley, Neil Ross, Stewart S. R. Jamieson, José A. Uribe, Jonathan Oberreuter, Rodrigo Zamora, Andrés Rivera, Andrew M. Smith, Robert G. Bingham, and Kenichi Matsuoka

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Short summary

We mapped buried layers inside West Antarctic ice using ice penetrating radar across 13,000 km² near the Amundsen–Weddell divide. Some layers may be as old as 17k years. They appear neat in slow ice and warped where ice speeds up, yet can be followed across most of the area. Snowfall has long been higher on one side, suggesting the divide has remained stable for millennia. Our work links records from the Weddell and Amundsen seas and helps target future climate archives and models.


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