the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 26 May 2026
Can multi-glacier moraine analysis constrain paleoclimate reconstructions? Evidence from 3D glacier modeling in the Cordillera Real, Bolivia
Abstract. Glacier moraines are widely used as proxies for past climate, as they are interpreted to reflect near-equilibrium glacier extents. However, a single glacier geometry can arise from multiple temperature–precipitation combinations and their quantification relies on glacier modeling that introduce additional uncertainties. Here, we investigate how this non-uniqueness can be constrained from a 3D full-Stokes ice-flow model (Elmer/Ice), applied to neighboring coeval glaciers in the Zongo–Charquini area of the Bolivian Cordillera Real. Using synthetic experiments, in which Temperature-Precipitation (T-P) anomaly curves are derived from several glacier extents generated under prescribed climate conditions, we show that differences in glacier geometry and hypsometry cannot be used to distinguish between temperature and precipitation conditions. However, we also show that glacier thickness may provide a way to dissociate temperature and precipitation but with a limited sensitivity that would require highly accurate past volume estimates to be useful in practice, which is often not feasible. Using real moraine records, our results show that single-glacier reconstructions are strongly influenced by both, methodological choice (melt model), and site-specific uncertainties, resulting in a range of T-P anomaly curves describing the same climate. In this context, using a multi-glacier framework allows to better assess the temperature-precipitation condition and its associated uncertainties. Using this approach combined with independent tree-ring and hydrological lake-balance precipitation reconstruction in the region, we estimate temperature anomalies of -0.8+-0.3°C for the Little Ice Age and -1.3+-0.4°C for the Early Holocene (∼10 ka BP), relative to a present-day reference climate (1950–2023).
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Status: open (until 30 Jul 2026)
- RC1: 'Comment on egusphere-2026-2638', Anonymous Referee #1, 30 Jun 2026 reply
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RC2: 'Comment on egusphere-2026-2638', Anonymous Referee #2, 06 Jul 2026
reply
Summary:
This is an interesting paper which I enjoyed reading. Although previous studies have used glacier models to reconstruct past climate from moraine evidence, relatively few have examined the underlying assumptions in detail. This manuscript therefore addresses an important gap.
When I first started reading, I was not fully convinced by the methodological choices. Why use a full Stokes model for a problem that is fundamentally about climate–ice interactions? It is well established that mass-balance forcing is the dominant control on mountain glacier response to climate. Similarly, I initially questioned the use of synthetic experiments based on real glaciers. Would a purely synthetic glacier geometry have provided a clearer framework for testing these ideas?
However, after reading the manuscript in full and thinking further on the approach, I am more convinced that the authors have made a valuable contribution to the literature. Therefore I do not recommend changes to the methodology or request additional experiments. There is value in the progression from synthetic to realistic experiments, and although a full Stokes model is arguably more sophisticated than necessary, it is useful to demonstrate that this additional complexity does not improve the climate reconstruction. People in this field regularly receive critical proposal reviews from glaciologists who argue against the use of simpler flowline models (e.g., OGGM) for climate reconstruction, so this result is useful.
Major issues:
The background and articulation of the scientific problem are underdeveloped. Citations are concentrated within a relatively small research group, and several important studies are missing. Here are some suggested citations which include a range of approaches previously taken with models of different complexity, as well as a review of reconstructing past climates from glaciers.
Reconstructing spatially variable mass balances from past ice extents by inverse modelling https://www.cambridge.org/core/journals/journal-of-glaciology/article/reconstructing-spatially-variable-mass-balances-from-past-ice-extents-by-inverse-modeling/D05D2D15D5DE670D0D86ECCA653E1891
A 2-D numerical model of snow/ice energy balance and ice flow for paleoclimatic interpretation of glacial geomorphic features. https://www.sciencedirect.com/science/article/abs/pii/S0277379103000817
Constraints on Southern Hemisphere tropical climate change during the Little Ice Age and Younger Dryas based on glacier modeling of the Quelccaya Ice Cap, Peru. https://www.sciencedirect.com/science/article/pii/S0277379115300676
Reconstruction of Past Glacier Changes with an Ice-Flow Glacier Model: Proof of Concept and Validation https://www.frontiersin.org/journals/earth-science/articles/10.3389/feart.2021.595755/full
Reconstructing Climate from Glaciers. https://doi.org/10.1146/annurev-earth-063016-020643
A specific omission is citation of the influence of interannual climate variability on glacier mass balance and the potential for glaciers to undergo a "random walk" in response to stochastic climate forcing, as developed by Hans Oerlemans and then extended by Gerard Roe. These findings have implications for the steady state reconstruction of glaciers from moraine positions and this should be briefly discussed.
For example:
The response of glaciers to intrinsic climate variability: observations and models of late-Holocene variations in the Pacific Northwest https://doi.org/10.3189/002214309790152438
An exercise in glacier length modeling: Interannual climatic variability alone cannot explain Holocene glacier fluctuations in New Zealand. https://www.sciencedirect.com/science/article/abs/pii/S0012821X17302170?via%3Dihub
Holocene glacier fluctuations: is the current rate of retreat exceptional? https://www.cambridge.org/core/journals/annals-of-glaciology/article/holocene-glacier-fluctuations-is-the-current-rate-of-retreat-exceptional/B8B127380CB133A11533CDE1A451F67E
Because models have different sensitivity to temperature and precipitation, precipitation variability can be used to provide a uncertainty window of past temperature reconstructions. And the bounds can be reasonably tight. More could be said about this in the introduction.
Also the effect of precipitation field on inversion results has been considered by Ann Rowan and should be cited.
Late Quaternary glacier sensitivity to temperature and precipitation distribution in the Southern Alps of New Zealand
https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2013JF003009Minor issues:
Line 33. ‘In contrast, SEB models aim for greater accuracy’.
SEB models have more complete representation of physical processes but are not necessarily more accurate. Rewrite this.
Line 34. ‘the limited availability of past meteorological data leads to an underdetermined problem in paleoclimate studies.’
Not sure what this means. Underutilised? Please clarify. Another issue is lack of data to constrain model parameters (not just meteorological forcings).
Line 35. A key challenge in using ice-marginal moraines as paleoclimate proxies is that a single glacier extent can result from different combinations of precipitation and temperature.
While this is true, it is worth adding some nuance. Temperature and precipitation have different sensitivities and this could be cited. E.g. how much temperature change is needed to offset a % chance in precipitation. Also, one should remind the reader that temperature affects melt AND precipitation phase.
Also, other meteorological variables can also have an effect even though their influence is smaller. E.g. cloud cover influencing incoming solar radiation, and wind speed and humidity affecting turbulent exchange. This should be mentioned prior to moving on to temp and precip.
Figure 2. Typical climatic conditions in the upper reaches of the Zongo-Charquini area. The red curve shows the mean monthly temperature,
and the light blue bars show the mean monthly precipitation at 5050 m a.s.l.
- Is this at about the terminus elevation? State how this elevation relates to nearby glaciers.
L 79. ‘flowing meltwaters’,
meltwater – should be singular
Table 1. Characteristics of the four study glaciers
- Add terminus elevation
Table 2. How were assumptions made about past precipitation levels?
‘This approach is currently among the most accurate for simulating ice flow’
Comprehensive does not necessarily mean accurate
L 154. Oerlemans (2001)and Hock (1999) models,
Needs gap
L 400. ‘The limited sensitivity of the results to the ice-flow formulation is likely because, in mountain glacier settings, topography strongly guides and confines ice flow, so in a steady state simulation, glacier geometry is primarily controlled by mass-balance distribution rather than by the specific ice-flow approximation.’
This is a long-held understanding dating back to at least Oerlemans but there is no citation.
L 423. In this context, multi-glacier approaches provide a robust framework
for estimating regional climate. I agree and you could cite work that has previously done this.
E.g. Last Glacial Maximum climate in New Zealand inferred from a modelled Southern Alps icefieldhttps://www.sciencedirect.com/science/article/abs/pii/S0277379112001850
Citation: https://doi.org/10.5194/egusphere-2026-2638-RC2
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- 1
The manuscript by Reyes et al., presents a timely investigation into the long-standing problem of non-uniqueness in glacier-based paleoclimate reconstructions. The combination of synthetic experiments, full-Stokes glacier modelling, and multi-glacier analysis represents a valuable contribution to glacier paleoclimatology. The manuscript is well written but, several aspects require clarification and further development before publication.
Major comments:
First, the novelty of the study should be articulated more clearly in both the Introduction and the Discussion. While the manuscript demonstrates that combining multiple coeval glaciers reduces uncertainties in temperature-precipitation reconstructions, it is not sufficiently explained how this framework advances beyond previous studies that have already used multiple glaciers or multiple climate proxies. I would recommend authors to explicitly identify the conceptual and methodological innovations of their approach, distinguish it from earlier work, and clarify the specific scientific questions that can now be addressed because of the full-Stokes modelling framework
Second, the uncertainty analysis remains incomplete. The manuscript discusses uncertainties arising from the choice of melt model and glacier-specific responses, but other important sources of uncertainty are only mentioned qualitatively or not evaluated at all. These include moraine age uncertainties, errors in moraine mapping, calibration parameter uncertainty, assumptions regarding equilibrium conditions, precipitation lapse rates, and climate forcing. A more systematic assessment of these uncertainties, either through a sensitivity analysis or an uncertainty propagation framework, would considerably strengthen the robustness of the reconstructed temperature estimates and provide readers with greater confidence in the conclusions.
Third, the justification for excluding the maximum Little Ice Age Zongo moraine from the final multi-glacier reconstruction requires further support. Although the proposed explanation involving topographic controls and serac collapse is plausible, it remains largely speculative. My advice would be to provide additional geomorphological or modelling evidence supporting this interpretation, or alternatively present quantitative sensitivity tests demonstrating how inclusion or exclusion of this glacier affects the reconstructed regional climate.
Fourth, the manuscript would benefit from a clearer discussion of the broader applicability and limitations of the proposed methodology. The study is conducted in a relatively small tropical mountain range where neighbouring glaciers experience similar climatic forcing. It remains unclear how transferable the proposed multi-glacier framework is to other glaciated regions with stronger climatic gradients, different precipitation regimes, larger glacier size variability, or more complex topographic settings. Expanding the Discussion to identify the conditions under which the proposed approach is expected to perform well, and where it may be less reliable, would significantly increase the impact of the paper and its relevance to a broader paleoclimate audience.
Minor comments:
P2 L18-19 - Glaciers continuously grow and shrink in response to climate variations, reshaping the landscape beneath them and leaving behind characteristic features of glacial erosion and deposition.
Citation is missing here. Please add:
https://doi.org/10.4324/9780203785010
P2 L22-23 - Such moraines provide valuable information about former glacier boundaries, and their distribution in the present-day landscape is often assumed to reflect ice positions during climatically stable periods.
Citation is missing here. Please add:
https://doi.org/10.1016/j.geomorph.2014.07.030
P2 L35-36 - A key challenge in using ice-marginal moraines as paleoclimate proxies is that a single glacier extent can result from different combinations of precipitation and temperature.
Citations are missing here. Please add:
https://doi.org/10.3390/rs17091486
https://doi.org/10.1080/04353676.2025.2521180
The scale bar is missing from Figure 3.
The scale bar and the coordinates from Figure 5.