the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 07 Jul 2026
Annual-resolution hydroclimate variability during the MCA–LIA transition in southern Iberia: insights into the role of cut-off lows (DANAs) from a speleothem record in Ardales Cave
Abstract. High-resolution paleoclimate records from southern Iberia remain scarce, limiting the understanding of hydroclimatic variability during the transition from the Medieval Climate Anomaly (MCA) to the Little Ice Age (LIA). Here, we present an annually resolved multiproxy reconstruction based on the laminated Zerolín stalagmite from Ardales Cave, a climatically sensitive site influenced by both Atlantic and Mediterranean moisture sources. The chronology is constrained through the integration of U–Th dating, lamina counting, and color-based modelling. Hydroclimatic variability was investigated using a combined analysis of trace elements, stable isotopes, petrography, and forward geochemical modelling. The results reveal alternating humid and arid phases, with four major drought intervals (~1125, 1250, 1500, and 1560 CE) and wetter periods consistent with increased recharge and higher growth rates. Two additional intervals (1320–1450 and 1600–1700 CE) display increased variability and are interpreted as reflecting an increased influence of Mediterranean convective precipitation (cut-off lows) during transitional atmospheric conditions. At the regional scale, the main hydroclimatic phases are consistent with North Atlantic Oscillation variability, while these transitional periods show a weaker correspondence with large-scale Atlantic forcing. Overall, the record highlights the interplay between Atlantic and Mediterranean dynamics in shaping southern Iberian hydroclimate during the last millennium.
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Status: open (until 01 Sep 2026)
- RC1: 'Comment on egusphere-2026-3717', Anonymous Referee #1, 16 Jul 2026 reply
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RC2: 'Comment on egusphere-2026-3717', Anonymous Referee #2, 17 Jul 2026
reply
General Comments
This paper uses a speleothem as a climate archive, providing a rare high-resolution (seasonal to multiannual) record of climate, particularly hydroclimate, conditions in southern Iberia during a period for which there is a lack of information, the MCA-LIA transition. The location is influenced by both the full Atlantic and Mediterranean atmospheric circulations, adding another layer of importance to the study by enabling the isolation of periods of Atlantic vs Mediterranean influence. To achieve the objectives, the authors develop an age model using both U/Th dating and lamina counting, and integrate a layer analysis of the speleothem's petrographic characteristics with trace elements (measured using different ICP-MS methods, depending on whether the elements are associated with insoluble or colloidal phases), O and C isotopes, and forward modeling.
Combining different methodological approaches is certainly the right way to enable the definition of seasonal-scale processes and multiannual hydroclimatic variability in this Mediterranean karst area. Furthermore, comparing their archive results with other archives is of high importance for a better understanding of the climatic processes in the area and should lend robustness to the conclusions. That is, the scientific approach to the problem is correct and well explained.
The paper is well structured; the methodology is clear and well explained, and the data treatment and results are clearly outlined.
The figures are informative and, in most cases, readable.
The supplementary material is justified and important, with part of it related to the modern calibration study, which is essential for each proxy interpretation.
Two main problems arise in the interpretation and discussion of the results:
- We all know that each proxy reflects a combination of effects from different processes, with the importance of each varying over time; as such, these multi-process and/or multi-factor controls need to be clearly stated or presented in a table format, and the dominant process/ factor identified and justified, in part by integrating and comparing information from independent proxies. If this is not clearly presented, the sequence of processes invoked to explain trace-metal information at any given time, or to reconcile trace-metal data with isotope data, becomes difficult to follow, and the interactions invoked become doubtful.
- In terms of atmospheric circulation, it has been shown that the NAO is not the sole explanation for the climate conditions observed in the Iberian Peninsula records during the last 2000 years, with the EA and SCAND also playing important roles. Their effects on the record should also be exploited.
Detailed Notes
Figure 2 – The y-axis in the figure is expressed in mm, but in the figure caption you use cm;
…the red line indicates the boundary where annual resolution is lost - Not sure it can be seen. I was not able to identify it.
U–Th dates are plotted directly on the speleothem image; - Impossible to see. Consider increasing the size.
The approximate growth rate, as derived from the slope of each age model, is shown on the right-hand side of the graph. - To guarantee a clear relation between the model and the growth rate, consider using the same color as the one used to identify the model in this figure.
Figure 7 – Lines 370 to 374 in the figure caption - Does this paragraph really belong in a figure caption? I would include this information in the main text.
Lines 422 – 427 - line 422 should read "... distinct in-cave and environmental processes govern d13C and d18O respectively.
Figure 8 - summer–autumn temperature reconstruction from Lake Redon (orange; Catalán et al., 2009)
This temperature is indicated as being diatom-derived (Diatom alq – what does the alq stand for?); however, I have investigated the paper you refer to and could not find it. The reference should be Catalan et al., 2002 (Journal of Paleolimnology); the Temperature is derived from assemblage composition and is expressed in ºC.
Figure A2 – Line 732 – Y-axis scale and figure caption values for concentration do not coincide, although
Citation: https://doi.org/10.5194/egusphere-2026-3717-RC2
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This manuscript presents a high-resolution (annual to sub-annual), multi-proxy speleothem reconstruction covering the last millennium, supported by modern cave monitoring. The density of the dataset, the meticulous chronological framework, and the effort to integrate active monitoring data are highly commendable. The record has great potential to contribute significantly to our understanding of Western Mediterranean paleoclimate during the last millennia. The study combines U-Th chronology, lamina counting, trace elements, stable isotopes, petrography, and forward modelling to reconstruct hydroclimate variability and proposes changes in Atlantic versus Mediterranean climatic forcing, including variations in DANA activity. The manuscript is generally well written and presents an impressive amount of high-quality data, the chronology appears carefully developed, and the site has clear potential to provide an important high-resolution record for southern Iberia. The annual lamination, modern cave monitoring, and multiproxy approach are valuable contributions. All these together would support publication in a well-known journal like Climate of the Past.
However, the manuscript currently suffers from critical geochemical contradictions, circular reasoning regarding the decoupling of its main paleohydrological proxies, and a speculative, over-simplistic connection to the North Atlantic Oscillation (NAO). In its current form, many interpretations are not sufficiently supported by the presented data and appear internally contradictory. I recommend a revision to resolve these fundamental issues before the paper can be considered for publication.
Comments and suggestions
Geochemical Inconsistencies and Proxy Decoupling (δ¹³C vs. Mg/Ca)
The authors heavily rely on Prior Calcite Precipitation (PCP), longer residence times, and dolomite dissolution to explain their proxy variations, but their arguments contain a major thermodynamic contradiction:
The authors should resolve this contradiction more clearly and present a coherent mechanistic framework for the reader. If they maintain that PCP is the driver, they must explain the decoupling in a quantitative geochemical way (e.g., ln (Mg/Ca) vs. ln (Sr/Ca) systematics, verify if there are higher or lower correlations between the sections where δ¹³C and Mg are visually correlated or not). Otherwise, they must temper their claims and explore alternative drivers for δ¹³C and Mg/Ca variations. Overall, the trace-element discussion should be substantially simplified and focused on mechanisms that are directly supported by the observations.
Contradictions between observations and interpretations
Several interpretations presented in the manuscript appear inconsistent with the data. For example:
Although the authors attempt to reconcile these observations through multiple interacting processes, the final conceptual model remains difficult to follow and is not fully convincing. The discussion would benefit from explicitly acknowledging the limitations of interpreting trace elements in such a complex hydrological system rather than proposing several simultaneous explanations.
What is truly an extreme event in Mg/Ca changes?
In the chapter explaining changes in Mg concentrations when monitoring cave drips, it states that during abrupt transitions that show changes between wet and dry years, the concentrations can increase up to 17 times the normal Mg/Ca concentration. The appendix clearly shows how the concentrations of the dripping water on the stalagmite can be compared, making it clear that an event of the magnitude of those between 2016 and 2018 has not been recorded on the stalagmite. Do all of the inferred dry events represent statistically or geochemically significant excursions? At least the transition from the beginning of the dry medieval period to its second phase shows a decrease of at least 3 to 4 times in Mg/Ca concentrations, but the others do not differ in the same way. For example, is the shift around 1500 CE statistically distinguishable from background variability?
Speculative Atmospheric Dynamics and the NAO
The manuscript attempts to frame the regional climate evolution entirely through the lens of the North Atlantic Oscillation (NAO), but the dynamic mechanisms presented are weak:
The authors should compare their record against existing high-resolution continental archives from the Iberian Peninsula (e.g., other NAO records, speleothems from northern Spain or the Pyrenees, or high-resolution lake records). Here, the rainfall record of Andalusia (Rodrigo et al., 1999) is very helpful in arguing the changes from wet to dry during 1520 to 1560 AD, unlike records from Portugal and Morocco, which show clear differences with the record of the Ardales cave in several sections during the last millennium. This comparative spatial analysis is required to robustly demonstrate if the regional NAO signature actually breaks down during these transitional centuries or if local cave/karst routing effects are dominating the signal.
Analytical Discrepancy in Colloidal Elements
In Section 4.3, the authors mention that elements typically associated with detrital or colloidal fractions (such as Al and Y) yielded concentrations up to 400% higher when measured via laser ablation (LA-ICP-MS) compared to conventional wet-chemistry solution ICP-MS (which used a weak nitric acid digestion).
It would be useful to provide the exact details of the standard materials used for the LA-ICP-MS calibration, quantify the analytical uncertainty, and justify why the LA-ICP-MS Al/Ca and Y/Ca spikes can be reliably interpreted as paleo-environmental "extreme events" rather than analytical artifacts.
Terminology and Figures
Recommendation
This manuscript presents an important new annually resolved speleothem record from southern Iberia with considerable potential to improve our understanding of hydroclimate variability during the MCA–LIA transition. The chronology, cave monitoring, and high-resolution analyses represent valuable contributions.
However, the interpretation of the trace-element proxies requires revision. The current discussion invokes multiple competing geochemical mechanisms without adequately distinguishing their relative contributions, resulting in several internal inconsistencies. Likewise, the climatic interpretation, particularly regarding NAO and DANA variability, is based on limited supporting evidence and should be significantly strengthened through comparison with additional regional reconstructions and a more cautious interpretation of the proxy data.
With a more rigorous and internally consistent treatment of the proxy system and a more balanced climatic interpretation, this manuscript has the potential to become a valuable contribution to Mediterranean paleoclimatology.
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Rodrigo, F. S., Esteban-Parra, M. J., Pozo-Vázquez, D., and Castro-Díez, Y., 1999. A 500-year precipitation record in Southern Spain, Int. J. Climatol., 19, 1233–1253, https://doi.org/10.1002/(SICI)1097-0088(199909)19:11%3C1233::AID-JOC413%3E3.0.CO;2-L.
Trouet, V., Esper, J., Graham, N.E., Baker, A., Scourse, J.D., Frank, D.C., 2009. Persistent positive North Atlantic oscillation mode dominated the Medieval climate anomaly. Science 324, 78e80. https://doi.org/10.1126/science.1166349.