the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 31 Aug 2026
Stability and basal thermal conditions of East Antarctic divide regions during the last glacial cycle
Abstract. Ice domes and divides of the East Antarctic Ice Sheet (EAIS) are primary targets for deep ice core drilling because of their presumed stability and cold basal conditions. These characteristics are essential for preserving undisturbed and continuous stratigraphy, which is critical for interpreting climate proxies from ice core records. Here, we conduct an ensemble of transient thermomechanical simulations of the Antarctic ice sheet over the last glacial cycle to evaluate the stability of six regions identified as potential candidates for deep ice core drilling. The evolution of the basal thermal regime and its response to climate forcing are also assessed. Results indicate that domes and divides of the EAIS remained relatively stable throughout the last glacial cycle, with displacements occurring primarily within 20 to 40 km of their initial positions and elevation changes ranging from 50 to 150 m between glacial and interglacial periods. Dome migration is primarily driven by changes in local accumulation patterns and large-scale grounding-line migration. Basal temperatures and melt rates exhibit a lagged response to climate forcing of approximately 17 to 35 ka, suggesting that present-day basal thermal conditions still reflect the cooler climate of the Last Glacial Maximum. Finally, we find favourable thermodynamic conditions for the preservation of ancient ice at the base in all but one of the studied regions, and use this information to identify and map potential drilling sites across Antarctica. However, estimates of the thermal state are highly sensitive to geothermal heat flow and even minor inaccuracies in modelled ice thickness, indicating that local constraints are required to better decipher conditions at the ice-bedrock interface.
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Status: final response (author comments only)
- RC1: 'Comment on egusphere-2026-5136', Frédéric Parrenin, 24 Sep 2026
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RC2: 'Review of Raspoet et al.', Anonymous Referee #2, 19 Oct 2026
Review of Raspoet et al.,
Raspoet et al. assess variations in Antarctic ice sheet geometry and basal thermal state. They perform a large ensemble of forcings, weighting the results based on the fits to modern and paleo constraints. The research builds on previous methods and results and finds, generally, that ice divide positions are stable, basal thermal condition changes are relatively unimportantly on glacial-interglacial timescales although they lag surface forcings by tends of thousands of years, and locations suitable for drilling old ice remain largely similar. The paper is well written with a good use of supplementary information and appendices to keep the main paper concise while provided more detail. The results, while largely supporting previous work, are quite useful by providing greater confidence.
I have a variety of minor points as described below. The only more major point I have is that I found the discussion of the impact on old ice sites to be middling – there is neither enough analysis to really add quantitative information about potential old ice sites yet the authors continue past the qualitative analysis that would be more appropriate. My major complaint is that the authors focus only on ice thickness, surface velocity, and basal thermal state, when the body of literature has evolved such that depth-age relationships are really the primary metric of evaluation. I recommend that either the authors restrict their analysis to qualitative implications of previous work, or add estimate of depth-age relations as support.
Minor comments
- I have trouble following the timing and direction of the described divide migrations. It’s often unclear to me which way time is going – that is, is the migration being defined from the start of the model run and going forward to present day, or is it the current position and going back in time. Also, the directions in Antarctica are always confusing because true directions being different than map directions. Being specific throughout this section and laying out the convention at the start would be helpful.
- Figure 4 – I can’t follow what is in the plots. I will list some specific issues, but I think a more general revision of this figure could be more helpful than just small tweaks. The circles are ice thickness? I think this would be better as a thickness anomaly, since with a range of 2000-3000m, ~100m changes are washed out and not visible. Is this for the current divide location? Or are you tracking the divide through time and plotting that? Or is this some average for the region? And what is the PMP for each site? The legend says that the temperatures are relative to the PMP, but Dome Fuji is consistently below 0C, yet always has basal melting. I’m just confused. I think you should also label both the left and right y-axes since they are the same units but different things. The legend also refers to a “scatter plot”, which I don’t what is being referred to.
- I think more information about RP2025 is necessary in the text. Beyond the 8km and 25km resolution, I don’t understand the difference in the ensembles. Maybe this info is buried somewhere in the Intro or Methods (I didn’t find it when scanning) but it should be front and center in this section if it’s important enough to warrant a large figure.
- In multiple sections, the authors describe that the lag in thermal response is related to the ice thickness; this is undoubtably true, yet I wonder if the accumulation rate is an equal or more important factor. For instance, the accumulation rate at Herc Dome is a factor of 4 greater than Dome C, which allows a change in surface temperature to be advected into the ice sheet at about a factor of 4 faster.
- I’m concernedabout Section 4.3 and Figure 6 as written. The depth-age relationship is the fundamental constraint on old ice preservation, while Figure 6 focused only on ice thickness, basal thermal state, and surface velocities. Given all the work that has been done on old ice preservation, this feels limited to the point of being misleading. I think the authors should do one of two things: 1) keep to a qualitative description of how the new results impact previous work, which could mean removing Figure 6, or limiting it to show changes in cold basal conditions, and 2) expand this section and provide depth-age relationships.
- Figure 6 – if this figure is kept, showing ice thickness rather than bedrock elevation would be more informative, particularly since you don’t provide surface elevations. And it would be helpful to have the surface elevation contour intervals.
Citation: https://doi.org/10.5194/egusphere-2026-5136-RC2
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Stability and basal thermal conditions of East Antarctic divide regions during the last glacial cycle Olivia Raspoet, Violaine Coulon, Frank Pattyn https://doi.org/10.5281/zenodo.22047132
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Summary
This manuscript studies the problem of domes migration, elevation changes and basal thermal state in the East Antarctic ice sheet. This is of primary importance for the definition of potential old ice drilliing sites or for the interpretation of already drilled ice cores such EDC, DF, etc. The tool used is the Kori-ULB model, which is an hybrid SIA-SSA ice sheet model, used at 25 km resolution (although some limited 8 km simulations are used for comparison). The different unknowns of the modeling, such as the GHF or climate forcings, are investigated using an ensemble simulations with a scoring that measures the agreement with present-day or past ice sheet observations.
It is found that domes stayed relatively stable in the past, with movements primarily of 20-40 km from their initial position. Moreover, elevation changes range from 50 to 150 m, in agreement with previous studies such as Ritz et al. (2001). It is also found that basal temperatures and basal melting lag the climate forcing by 17 to 35 kyr. Finally, a updated map of potential drilling sites is given.
This subject is of primary importance for ice core scientists. The study is generally well crafted, the manuscript reads well and the figures are rich (sometimes maybe even too rich!) and well designed. I recommend the publication of the manuscript but I have some minor comments that I hope the authors will find useful.
Important comments:
- the maps of the potential drilling sites are interesting, but they rely heavily on parameters such as the GHF forcing which is poorly known. These maps therefore provide a general overview but of course smaller scale studies are needed, which is clearly stated in the manuscript, so this is ok.
- one limitation is that the study focuses on domes. These are not the only interesting targets for old ice sites. There are interesting locations all along the ridge swith minimal horizontal displacements. I do not ask to redo the study, but maybe this limitation should be stated somewhere.
- regarding the climate forcing, Parrenin, Fujita et al. (JG, 2016) found, from the volcanic synchronisation between EDC and DF, that the SMB_DF/SMB_EDC ratio was strongly varying during the last climatic cycle. Hence, the accumulation pattern is not stable in the past. I am wondering how the precipitation forcing used in the present study agrees with this ice core observation. I think this comparison should be made somewhere in the manuscript because it is an important point.
- Basal melting is quantified at Dome C (see, e.g., Figure 5). We actually have fairly accurate estimates of basal melting at EDC based on the ice core age scale. Parrenin et al. (CP, 2007, "1D ice flow modeling...") found 0.66 ice-mm/yr while the more recent Jeaumot et al. (TC, submitted) study found 0.68 ice-mm/yr. It would be good to cite at least one of these studies for comparison.
- Parrenin et al. (2017) and Chung et al. (PAGES, 2023) found elevated isochrones around North Patch (also called Dome C North by the Australian MYIC project) and made the hypothesis that it could be diluted Raymand arches due to the more Northern dome position during the past. Your reconstruction of the Dome C position during the past seems to confirm this hypothesis. It is an interesting outcome of this study that could be stated.
- p. 19, it is explained that the thermal equation is not solved in the bedrock, neglecting the propagation of thermal waves underneath the ice. I am wondering if this would be a big work to implement this. I am not asking to do it for the current study because this would imply redoing all the simulations. But I do hope this will be implemented for a future study.
More technical points:
- p. 2, l. 46: regarding flow band modeling, note that the Chung et al. (2025) study uses the recently published forward model of Parrenin et al. (2025).
- p. 8, l. 219: "by widespread retreat during _the last_ deglaciation..."
- p. 11, Figure 2: note that Ridge B is now called Dome B (because there is actually a dome here!) and the previous Dome B (which was actually on a ridge!) is now called Old Dome B.
- p. 11, Figure 2 (again): the dome maps with the 3 colors superimposed are really difficult to read.