the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 23 Jul 2026
Estimating the impact of ice sheet surface height and ice divide variability on ice core based climate reconstructions
Abstract. Antarctic ice cores are a unique invaluable archive of past climatic changes over the Antarctic ice sheet. However, as reconstructions are based on the history of surface climate at the ice core site, variations of the surface geometry and the ice flow patterns might result in biases within those reconstructions. In this study, we use results from three transient ice sheet model simulations covering the last two million years to investigate surface height and ice divide variability for major Antarctic ice core sites and ongoing prospective future drilling locations. We find that East Antarctic ice-core site elevations varied by up to 240 m over the glacial cycles of the last 800 kyr, whereas glacial–interglacial surface elevation variability is substantially smaller during earlier periods relevant to prospective oldest ice sites. Simulations using different ice sheet models and climate-forcing approaches produce substantially different long-term surface elevation trends. We further investigate the synchronicity between Antarctic climatic change and simulated surface height variability and find a substantial shift between the timing of maximum interglacial temperature and ice surface elevation. Further, we quantify the variability of the ice divide and ice dome position throughout the time period of the individual ice cores and up to 2 Ma before present for prospective oldest ice cores which varies by up to 120 km. Our study suggests that uncertainty, in ice surface height has to be taken into account when investigating ice core-based Antarctic temperature reconstructions. Further, the results presented in this study serve as initial constraints for further simplified (e.g. 1D) and higher resolution regional simulations of Antarctic ice sheet dynamics at ice core locations.
Competing interests: At least one of the (co-)authors is a member of the editorial board of The Cryosphere.
Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors. Views expressed in the text are those of the authors and do not necessarily reflect the views of the publisher.- Preprint
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Status: open (until 07 Sep 2026)
- RC1: 'Comment on egusphere-2026-4275', Anonymous Referee #1, 22 Aug 2026 reply
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RC2: 'Comment on egusphere-2026-4275', Fuyuki Saito, 25 Aug 2026
reply
Review Report for egusphere-2026-4275
General Comments
This paper presents a set of numerical simulations of the Antarctic ice sheet over the past 2 million years, utilizing two independent ice sheet models. The main focus is to evaluate variations in the elevation and position of major ice core sites to investigate their possible influence on paleo-climate reconstructions. Overall, I find the paper to be fairly well-written, with a few exceptions noted below, and I recommend that it be accepted for publication following minor revisions.
Major Point
The motivation for this study is clear. As described at the beginning of the abstract—"as reconstructions are based on the history of surface climate at the ice core site, variations of the surface geometry and the ice flow patterns might result in biases within those reconstructions"—the goal is to evaluate the influence of the evolution of ice-sheet topography on core-based reconstructions. However, I feel that the discussion of ice flow patterns and their subsequent impacts is somewhat lacking in the current manuscript.
As far as I understand, there are two major sources of uncertainty in reconstructions due to ice-sheet variations: one is what is deposited on the ice-sheet surface, and the other is what is transported within the ice sheet. This paper primarily focuses on the former, while the latter is only briefly mentioned in limited sections (e.g., the abstract, Figure 1, and briefly in Sections 4.3 and 4.4).
I do not request the inclusion of a detailed study of flow patterns in this manuscript. Rather, I suggest carefully excluding the latter topic from the main focus and instead explicitly mentioning both aspects in the introduction to clarify the scope. As described in Section 4.4, a high-resolution nesting model will be necessary to properly address the latter topic, and this study indeed provides the regional constraints for such a sub-model. Furthermore, the simulated divide migration only highlights the potential for bias in the reconstructions, as the transient dome may not actually be a source of ice in the core, as described in the paper. Therefore, I suggest explicitly stating that the evaluation of the influence of flow pattern variations is postponed to future studies.
Nevertheless, I strongly suggest including references to past studies regarding divide positions and their influence on flow, either in the introduction or the discussion. There is a substantial body of literature on this topic that is currently not introduced in the paper. For example:
* Dahl-Jensen (1989) demonstrates that the horizontal scale of the ice divide is on the order of one ice thickness, and that depth profiles of vertical velocity and stress closely approach a profile computed in the shallow ice approximation at a distance of twice the ice thickness from the divide. This study illustrates the scale and magnitude of the influence of divide migration on flow patterns, which is particularly relevant since the present paper shows up to 120 km of variability in position—much larger than the theoretical perspective provided above.
* Weertman (1973) investigated the effect of changes in the ice sheet span and the spatial pattern of the accumulation rate on the divide's position, concluding that the steady-state position of a divide is much more sensitive to the span than to the spatial pattern of accumulation. This aspect directly links to your paper (e.g., how variations in grounded area can impact divide migration).
* Hindmarsh (1996) investigated the sensitivity of a divide position to stochastic, anti-symmetric accumulation distributions near the divide, showing that the time constant for divide relaxation to such a forcing is about 1/16 of the typical time scale (thickness divided by accumulation rate). This could be compared with the time lag presented in your paper.
* Anandakrishnan et al. (1994) estimated that lateral migration of the divide in Central Greenland is between 10 km and 50 km in response to changes in ice sheet margin positions and accumulation rates on glacial/interglacial time scales. This sensitivity is sufficiently large to affect simulated depth-to-age profiles.
* Nereson et al. (1998) estimated that even small changes in the accumulation pattern and lateral boundary elevations may have caused the Siple Dome divide to migrate by 0.05–0.50 m/yr over the past 1,000 years.
* Martin et al. (2009) presented the impact of divide migration on isochrone structures, which would also be an interesting point of discussion for this paper.
You do not necessarily need to cite all of these papers, but they are listed here for your reference as they are foundational to the topic. You may easily start your literature review from these publications:
* Weertman, J. (1973). Position of ice divides and ice centers on ice sheets. Journal of Glaciology, 12(66), 353-360.
* Dahl-Jensen, D. (1989). Steady thermomechanical flow along two-dimensional flow lines in large grounded ice sheets. Journal of Geophysical Research, 94(B8), 10355-10362.
* Anandakrishnan, S., et al. (1994). Sensitivity of the ice-divide position in Greenland to climate change. Geophysical Research Letters, 21(6), 441-444.
* Hindmarsh, R. C. A. (1996). Stochastic perturbation of divide position. Annals of Glaciology, 23, 94-104.
* Nereson, N. A., et al. (1998). Sensitivity of the divide position at Siple Dome, West Antarctica, to boundary forcing. Annals of Glaciology, 27, 143-148.
* Martin, C., et al. (2009). On the effects of anisotropic rheology on ice flow, internal structure, and the age-depth relationship at ice divides. Journal of Geophysical Research: Earth Surface, 114(F4).
Minor Points
* Table 1: It would be much better to summarize these data with a series of bar graphs. I have attached an example of such a graph that I generated for this review.
* L19 ("orbital scale"): Providing a rough guide for the time scale (e.g., ~100 kyrs) would be helpful here.
* L37 ("at ice core sites closer...."): I understand the point, but there is a slight conceptual gap between the core site and ocean dynamics. I suggest rephrasing to something like, "surface height may be influenced by changes in grounded area due to ocean dynamics..."
* Eq. (3): The symbol phi used here conflicts with the phase symbol shown later in the discussion section. Please use distinct symbols.
* L113 ("The model was forced with time-evolving Northern Hemisphere ice sheet....."): What about the Antarctic ice sheet? If it was kept fixed throughout the climate-model simulation, it would be better to mention this explicitly.
* Fig A3 & A4: It might be better to move the axis annotations (Delta T and the scale) to the right side of the figures for better readability.
* Divide migration throughout the text: I am very interested in a systematic view of the divide migration. In the current figures, only the possible ranges of the dome positions are presented without any timing information. Is there any relationship between the position and forcing characteristics? For example, it would be quite interesting to know if the mean positions of a Dome over glacial and interglacial periods are fundamentally different. Adding this context may also help improve the interpretation of the results shown in Figures A5 and A6.
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This manuscript uses three transient ice-sheet-model simulations (PISM-CI, PISM-CESM, and PSUISM) spanning the last two million years to quantify how surface elevation and ice-divide/dome migration at major Antarctic ice-core sites could bias ice-core-based climate reconstructions. The study finds substantial glacial–interglacial elevation variability at East Antarctic sites, a lag between simulated surface-height changes and Antarctic climate signals, and ice-divide/dome displacements of up to ~120 km, with implications for both existing ice cores and prospective "oldest ice" drilling sites. The topic is timely, and the three-model comparison is a genuine strength, but the manuscript would benefit from a number of clarifications, additional justifications, and presentation improvements detailed below. I recommend that the authors address the following comments before the manuscript is considered ready for publication.