the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 09 Dec 2024
Geochronological reconstruction of the glacial evolution in the Ésera valley (Central Pyrenees) during the last deglaciation
Abstract. The last deglaciation period in the Pyrenees was distinguished by intricate glacier dynamics, encompassing a multitude of advances and rapid glacier retreats that did not always align with the fluctuations observed in other European glaciers. The Ésera valley, located in the Central Pyrenees (northern Spain), provides a distinctive opportunity to reconstruct past climate in high-mountain regions during the last deglaciation period. Previous studies of glacial evolution in this area have employed a variety of methods, including the analysis of glacial lake sediments and detailed geomorphological studies of glacial landforms. This paper presents measurements of cosmogenic 10Be exposure ages from glacial deposits and a polished bedrock surface in the Ésera valley, together with calculations of the equilibrium line altitude (ELA), with the objective of reconstructing the evolution of the Ésera glacier and the associated environmental implications during the last deglaciation. Following the Pyrenean Last Glacial Maximum, at approximately 75 ka in the Ésera valley, the Ésera glacier commenced a period of retreat during the Marine Isotopic Stage (MIS) 3, reaching a point of stabilisation at approximately 47 ka at the location of the Pllan d’Están proglacial lake. Subsequently, a new glacial advance resulted forming the Llanos del Hospital moraine (~16 ka), a glacial deposit located a lower altitude in the valley than Pllan d’Están lake. During that time interval, we suggest that sediment deposition at Pllan d’Están took place in a subglacial environment. Following the conclusion of the Oldest Dryas period (~16 ka) and continuing into the Early Holocene, the Ésera glacier underwent a rapid retreat. The Little Ice Age (LIA) represented the last cold period documented in the Ésera valley, after which the glacier has exhibited a persistent retreatment. The ELA analyses indicate that the temperature in the Ésera valley increased by 3.6 ± 0.45 °C over the past 16 ka, which resulted in the retreat of the glacier front from 1750 metres above sea level (m a.s.l.) to 3000 m a.s.l.
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Status: final response (author comments only)
- RC1: 'Comment on cp-2024-75', Anonymous Referee #1, 07 Jan 2025
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RC2: 'Comment on cp-2024-75', Anonymous Referee #2, 04 Sep 2025
Review of the manuscript cp-2024-75 “Geochronological reconstruction of the glacial evolution in the Ésera valley (Central Pyrenees) during the last deglaciation” by Vidaller et al.
This manuscript deals with the reconstruction of different stages of glacier retreat and readvances (here called last deglaciation) in northern Spain. The authors use cosmo nuclide dating, as well as isotope ratios to constrain the glaciation history. The methods are robust, even though paleoELA is subject to quite some uncertainties in terms of interpretation of impacts of temperature versus precipitation changes. It would be good to defend this point in a more convincing manner – with this being said, it is a standard practice in the geomorphological community and is thus acceptable. One very interesting discovery is the subglacial paleolake that existed under the glacier during the glacier readvance prior to its final, relatively smooth retreat.
I enjoyed reading the manuscript – it is relatively well written, presents a nice story and new, previously non-existent data that are high quality and well-aligned in chronology as opposed to earlier studies in the same area characterized by a large scattering. I particularly liked the discussion in light of existing proxy data in the region and globally. Nicely done. I recommend publication after minor revisions that are listed below.
Please, edit for typos. There are quite many of them. I will pass the file with some typos marked through the editorial system.
The title with “last deglaciation” is a bit misleading because the authors also discuss the PLGM conditions at 75 ka and MIS3 evidence of glacier shrinking. I understand that it could be inferred that the last deglaciation actually started at 75 ka and continued until now but this is not commonplace to state something like this and besides the choice of a journal (CP, which is focusing on the climate reconstructions, not on paleoglaciology or glacial geomorphology as such) requires that the authors make their messages very clear and use generic language. I therefore suggest that the authors simplify their narrative for the cross-discipline communities.
The snow shielding effect is parameterized using quite an old methodology. I am not an expert in this subject, so I am asking whether there are any other recent publications that would introduce a more up-to-date parameterization and how the choice of methodology impacts your conclusions. Please, elaborate and include a comparison in the appendix.
Again, for PaleoELA calculations – a very old publication. I understand that everyone is using ELA approach but the authors could at least add a discussion of how alternative methods could differ in terms of climate interpretation and how robust it is.
The glacier has been retreating since the LIA. Why didn´t you use more robust, recent observations to validate your ELA calculations? There are plenty of remote-sensed studies, aerial surveys, and maybe even some repeat photography. Besides, there are climate reanalysis data and observations to validate your choices of parameters.
In the line 255 you mention equations. What equations are we talking about? There are no eq. numbers, neither do I find many equations in this work. Namely it is just one it seems. Please, clarify.
Temperature lapse rate does not only depend on elevation but also on the season (can go from 4.5C/km in summer to 10C/km in winter) and even on the background climate. Please, add it in your discussion of limitations. I think such a section might need to be introduced in the appendix. Since this is part of a PhD study, such section is anyway needed in the thesis.
Line 260: Not obvious that the formation of moraines is marking the onset of glacier retreat. Aren´t they accumulate during stillstands? Also, “ablation zone” seems out of context here. Further discussion/explanations are needed here.
Line 272: I don´t understand these calculations. Please, explain in a better way.
Table 2: Correct “Period - 2023”. It is the other way around. Clarify if it is a summer temperature difference or mean annual?
In section 5.1 you use a sediment core record dated by the OSL method. Was it not possible to cross-correlate temperature anomalies?
The statements about the early PLGM in section 5.1 are not inclusive. For example, the Barents-Kara Sea ice sheet reached its local LGM during MIS5. A lot of glaciers in Asia did too. The Patagonian ice sheet did so during MIS3, as well as glaciers in New Zealand.
Line 325: Misleading sentence – In many parts of the world glaciers during the Penultimate LGM were more extensive. Indicate that this is only for the last glacial period.
Lines 356-357: Why is that? How do you justify that your choice of parameters is more reliable?
Uncertainties in delta T estimates should be explicitly discussed
Line 403: I am not sure I understand this sentence. Rock or debris-covered glaciers or both?
Lines 408 – 411: How do you explain such a disparity? What about the role of precipitation change?
Line 420: The formulation is weird.
Line 431: I agree regarding biological indicators but isn´t it the same for ELA to some extent?
Lines 439-440: Why so?
Line 462: What mechanism can explain such an early local LGM?
How reliable are reconstructions of glacier retreat followed by a readvance? What makes your methodology trustworthy? Explain for paleoclimatologists.
Citation: https://doi.org/10.5194/cp-2024-75-RC2
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Comment on “Geochronological reconstruction of the glacial evolution in the Ésera valley (Central Pyrenees) during the last deglaciation” by Ixeia Vidaller, Toshiyuki Fujioka, Juan Ignacio López-Moreno, Ana Moreno, ASTER Team.
This paper presents a serie of 14 surface exposure datings on boulders and polished bedrock in Esera valley (Central Pyrenees, Spain). These new data are cross-checked with OSL and 14C datings previously published (Vidaller et al., 2024) and obtained from a sedimentary sequence located at Plan d’Estan, ~ 7 km downstream of the LIA moraines and the current glaciers of the Maladeta massif. The Plan d’Estan sequence records three successive units: (i) a sub-glacial till at the bottom of the core, (ii) a proglacial lacustrine deposit in the middle of the sequence, (iii) sub-glacial lacustrine deposit at the top of the sequence. Both series of data allow the Late Pleistocene fluctuations of the Esera glacier to be reconstructed. Additionally, authors quantify changes in ELA position and in temperature anomalies (with respect to present) for 6 glacial stades respectively dated at 47ka, 16 ka, 13.9 ka, 12.8 ka, 11 ka and 0.4 ka.
General comments
The most interesting (and innovative) result of this work is the evidence of a major deglaciation of the Esera valley during MIS 3. Indeed, around 47 ka, the terminal position of the Esera glacier was located upstream of the Plan d'Estan, as indicated by an OSL dating at 46.7±2.9 ka within the proglacial unit that overlies the basal till. This result gives a substantial advance on Late Pleistocene glacier fluctuations in the Pyrenees because, until now, most of the data produced in this mountain were obtained from moraines ridges or paleolakes close to the PLGM and, therefore, they provided informations on the maximum glacial advances and very scarcely on episodes of glacial retreat.
Beyond this major result, two other issues should be addressed more explicitly in this paper.
Overall, in order to enable readers to make up their own minds on the subject, it would be useful to provide in this paper a figure that summarizes informations contained in the Plan d'Estan sequence that are essential for reasoning about the chronology of glacial fluctuations (thickness and content of each sedimentary unit, location of OSL and 14C datings within the sequence, all 14C with their error bar and not only those retains by the bayesian model age…).
Moreover, it would be interesting to analyze the TCN results with respect to they location within the sequence of moraines ridges (hospital moraine, plan de llanos moraine, aigualluts moraine, etc...) because these frontal and lateral moraines ridges delineate the ice extent of the Esera glacier for several glacial stillstand stadials. TCN datings from boulders located on frontal and/or lateral moraines ridges allow these events (these glacial stillstand stadials) to be dated.
In the same way, you should describe more accuractey the geomorphological markers used to reconstruct ELAs. Each ELA must correspond to a specific frontal and/or lateral moraine ridge because this kind of deposit (and landform), and only this one, is able to delineate the ice margin position of a specific glacial stade. You do that accurately for LIA but not for older glacial stade. Please, do it for ALL glacial stades.
Together, the two previous comments should help readers to better understand the chronological milestones at 13.9, 12.8 and 11 ka reported in Table 2. Indeed, because ice margin deposits used to reconstruct ice extent at several time of the Late Pleistocene is not well explained and because TCN datings are not clearly located with respect to moraines ridges, we miss information to understand how did you produce milestones at 13.9, 12.8 and 11 ka associated to ELA reconstructions.
Please, see PDF file in attached for detailed comments
Note that the concept of “deglaciation” used numerously in the manuscript (even in the title) is not enough clear in term of time. It does not allow to identify the period covers by the paper. I think you should use conventional stratigraphic terminology such as “Late Pleistocene”.
Details comments in PDF file suggest you add the following references to the manuscript.
Andrés, N. de, Gómez‐Ortiz, A., Fernández‐Fernández, J.M., Tanarro, L.M., Salvador‐Franch, F., Oliva, M., Palacios, D., 2018. Timing of deglaciation and rock glacier origin in the southeastern Pyrenees: a review and new data. Boreas 47, 1050–1071.
Delmas, M., Calvet, M., Gunnell, Y., Braucher, R., Bourlès, D., 2012. Les glaciations quaternaires dans les Pyrénées ariégeoises : approche historiographique, données paléogéographiques et chronologiques nouvelles. Quaternaire 23, 61–85.
Delmas, M., Gunnell, Y., Calvet, M., Reixach, T., Oliva, M., 2022. The Pyrenees: glacial landforms prior to the Last Glacial Maximum (chapter 40). In: Palacios, D., Hughes, P., García-Ruiz, J.M., Andrés, A. (Eds.), European Glacial Landscapes (volume 1): Maximum Extent of Glaciations. Elsevier, 295–307.
Delmas, M., Gunnell, Y., Calvet, M., Reixach, T., Oliva, M., 2022. The Pyrenees: glacial landforms from the Last Glacial Maximum (chapter 59). In: Palacios, D., Hughes, P., García-Ruiz, J.M., Andrés, A. (Eds.), European Glacial Landscapes (volume 1): Maximum Extent of Glaciations. Elsevier, 461–472.
Delmas, M., Gunnell, Y., Calvet, M., Reixach, T., Oliva, M., 2023. The Pyrenees: environments and landforms in the aftermath of the LGM (chapter 21). In: Palacios, D., Hughes, P., García-Ruiz, J.M., Andrés, A. (Eds.), European Glacial Landscapes (volume 2): Last Deglaciation. Elsevier, 185–200.
Delmas, M., Oliva, M., Gunnell, Y., Reixach, T., Fernandes, M., Fernández-Fernández, J.M., Calvet, M., 2023c. The Pyrenees: glacial landforms from the Younger Dryas (chapter 56). In: Palacios, D., Hughes, P., García-Ruiz, J.M., Andrés, A. (Eds.), European Glacial Landscapes (volume 2): Last Deglaciation. Elsevier 441–452.
Delmas, M., Oliva, M., Gunnell, Y., Fernández-Fernández, J.M., Reixach, T., Fernandes, M., Chapron, E., René, P., Calvet, M., 2024. The Pyrenees: glacial landforms from the Holocene (chapter 21). In: Palacios, D., Hughes, P., Jomelli, V., Tanarro, L.M., (Eds.), European Glacial Landscapes during the Holocene (volume 3). Elsevier, 419–443.
Pallàs, R., Rodés, A., Braucher, R., Bourlès, D., Delmas, M., Calvet, M., Gunnell, Y., 2010. Small, isolated glacial catchments as priority targets for cosmogenic surface exposure dating of Pleistocene climate fluctuations, southeastern Pyrenees. Geology 38, 891–894.
Reixach, T., Delmas, M., Braucher, R., Gunnell, Y., Mahé, C., Calvet, M. 2021. Climatic conditions between 19 and 12 ka in the eastern Pyrenees, and wider implications for atmospheric circulation patterns in Europe. Quaternary Science Reviews 260, 106923
I hope these comments we help you to improve the manuscript.
Magali Delmas