Early to Middle Holocene aridification trend in southeastern Iberia and the termination of the last North African Humid Period revealed by a multi-proxy speleothem record

Gázquez, Fernando; Vonhof, Hubert; Pérez-Mejías, Carlos; Columbu, Andrea; Giesche, Alena; Cheng, Hai; Martínez-García, Alfredo; DiMento, Brian; Iriarte, Eneko; Calaforra, José María

doi:10.5194/egusphere-2026-4435

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https://doi.org/10.5194/egusphere-2026-4435

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07 Aug 2026

| 07 Aug 2026

Status: this preprint is open for discussion and under review for Climate of the Past (CP).

Early to Middle Holocene aridification trend in southeastern Iberia and the termination of the last North African Humid Period revealed by a multi-proxy speleothem record

Fernando Gázquez, Hubert Vonhof, Carlos Pérez-Mejías, Andrea Columbu, Alena Giesche, Hai Cheng, Alfredo Martínez-García, Brian DiMento, Eneko Iriarte, and José María Calaforra

Abstract. During the Early Holocene, relatively humid conditions prevailed across northern Africa, transitioning to a drier climate by the end of the mid-Holocene. While the timing and nature of this climatic shift are well-established in the Maghreb region of Africa, uncertainties remain regarding the pace of the wet-to-dry transition in the southern Iberian Peninsula. We present a multi-proxy stalagmite record from Simarrón II cave, spanning 9.7 to 4.4 ka BP. The dataset combines stable carbon and oxygen isotopes in calcite (δ¹⁸O_carb, δ¹³C), Mg/Ca ratios, petrographic observations, fluid inclusion isotopes (δ¹⁸O_fi, δ²H) and TEX₈₆-derived paleotemperatures to reconstruct paleohydrological and climatic changes. From 9.7 to 4.4 ka, progressively higher δ¹⁸Ofi and δ²H values, coupled with decreasing deuterium excess, are consistent with a gradual shift in rainfall seasonality and/or moisture sources (i.e., frontal Atlantic-type precipitation regime during the early Holocene to a more convective Mediterranean regime). This trend could be overprinted by enhanced soil and in-cave water evaporation during the late Mid-Holocene because of climate aridification. Lower δ¹⁸O_carb, δ¹³C, and Mg/Ca values between 9.7 and 6.0 ka also indicate relatively wet conditions during the early Holocene and part of the middle Holocene. From ~6.0 ka onward, these proxies show a progressive increase, stabilizing after ~5.5 ka, consistent with a climate shift toward more arid conditions that occurred within ~500 yrs. This is interpreted as reflecting enhanced prior calcite precipitation rates and kinetic isotope effects associated with intensified in-cave CO₂ degassing, due to the dry climate during the termination of the last North African Humid Period. Paired δ¹⁸O_carb– δ¹⁸O_fipaleotemperature estimates yield unrealistically high values (20–30 °C) for most of the investigated period, further supporting non-equilibrium fractionation processes and likely in-cave water evaporation. In contrast, TEX₈₆-based temperatures (13–17 °C) suggest that early–mid Holocene cave temperatures were higher than present-day values in the cave (11.7 °C).

Received: 23 Jul 2026 – Discussion started: 07 Aug 2026

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Fernando Gázquez, Hubert Vonhof, Carlos Pérez-Mejías, Andrea Columbu, Alena Giesche, Hai Cheng, Alfredo Martínez-García, Brian DiMento, Eneko Iriarte, and José María Calaforra

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RC1:
'Comment on egusphere-2026-4435', Anonymous Referee #1, 30 Sep 2026 reply
This manuscript presents a new multi-proxy speleothem record from Simarrón II cave in southeastern Iberia, covering an important interval of Early-to-Middle Holocene hydroclimatic change. The combination of carbonate stable isotopes, fluid-inclusion water isotopes, Mg/Ca ratios, petrography, U–Th dating, and TEX₈₆ measurements is potentially valuable. The high-elevation setting and comparison with records from Iberia and northern Africa are also of considerable interest to Climate of the Past.
The manuscript is generally well structured and the dataset has the potential to make a useful contribution. However, several of the main conclusions;particularly those concerning fluid-inclusion isotope trends, quantitative temperature changes, the timing of North African Humid Period termination, and the role of high-elevation areas as climatic refugia; are currently stated with greater confidence than the available evidence permits. The chronology and analytical uncertainties also need to be documented more completely.
The chronology needs substantially more documentation. Eleven U–Th ages are reported, but the supplement contains only one petrographic figure and no table of dating results. A complete table should report sample depth, 238U and 232Th concentrations, isotope activity ratios, initial 234U/238U, uncorrected and detrital-corrected ages, correction assumptions, and analytical uncertainties. There also appears to be an inconsistency in lines 240–244. The youngest age is said to be 4,621 ± 12 yr BP at 70 mm from the top, whereas Figure 2 appears to place this date much closer to the top. This should be checked carefully. Furthermore, the manuscript states that the record spans 9.7–4.4 ka, although the directly dated interval is reported as 9.244–4.621 ka. The authors should explain how the end ages were extrapolated and report their model uncertainties. The possible hiatus at approximately 30 mm must be explicitly incorporated into the age modelling. Interpolating a continuous COPRA model across a physical hiatus could produce misleading ages and growth rates. The authors should clarify whether the sections above and below the hiatus were modelled separately, quantify the possible duration of the hiatus, and show the complete age-model uncertainty envelope. Growth-rate uncertainties should also be presented.

The interpretation of the fluid-inclusion isotope record is presently ambiguous. The measured relationship, δ²H = 4.2 × δ¹⁸O − 15.8, has a slope considerably lower than either the GMWL or the reported Almería LMWL. This strongly indicates evaporation and/or analytical fractionation. It is therefore difficult to reconcile this result with the statement that most samples plot along the GMWL. More importantly, the uncorrected δ¹⁸O, δ²H, and d-excess values are subsequently used to infer changes in moisture source and rainfall seasonality. If evaporation during crushing, soil/epikarst evaporation, and in-cave evaporation are all plausible, the present data cannot uniquely distinguish among these mechanisms.
The authors should report the absolute water yield for every analysis, not only water content per gram, provide the five replicate results individually, test δ¹⁸O, δ²H, and d-excess against water yield and sample mass, state the validated water-volume range and any data-exclusion criteria for the analytical system, quantify the temporal trends with slopes, confidence intervals, and significance tests, apply and discuss the evaporation correction consistently, not only for paleotemperature calculations. Unless these tests provide stronger discrimination, the shift from Atlantic frontal precipitation toward Mediterranean convective precipitation should be presented as one hypothesis among several, rather than as a principal conclusion.

The interpretation of higher δ¹³C and Mg/Ca as evidence of increased prior calcite precipitation and aridity is plausible, but not unique. Mg/Ca may also respond to water–rock interaction, residence time, source-rock variability, and temperature-dependent partitioning. Similarly, δ¹³C can be influenced by vegetation, soil productivity, cave-air CO₂, degassing, and PCP. The proposed relationship between dry conditions and faster stalagmite growth also requires more careful justification. Reduced infiltration may increase degassing and PCP, but it may simultaneously reduce drip supply and stalagmite growth. Growth rate should not be treated as independent confirmation of aridity without a more explicit process-based argument. The reported δ¹⁸O–δ¹³C correlation over the 240–140 mm interval may partly reflect two variables sharing the same temporal trend. The authors should test correlations after detrending or using first differences and account for serial autocorrelation. Correlations among Mg/Ca, δ¹³C, δ¹⁸O, growth rate, and water content should be reported quantitatively. If kinetic fractionation is central to the interpretation, along-layer measurements or another independent kinetic test would be valuable. If such analyses are not possible, the limitations should be stated explicitly.

Only six TEX₈₆ measurements are available, yet the manuscript uses them to infer a 2.5 °C warming, rapid climate oscillations, and warming associated with termination of the humid period. These conclusions are too strong for the current sampling density and uncertainty treatment. The authors should provide the individual GDGT abundances, TEX₈₆ values, analytical replicates, error estimates, and relevant quality-control indices. Potential changes in GDGT source or microbial community should also be discussed, because hydroclimatic changes may influence TEX₈₆ independently of cave temperature. The statement that calibration uncertainty is approximately ±1 °C at 2 SD needs to be reconciled with the uncertainties reported for the intercept and slope of the calibration equation. Repeatability of the in-house standard is analytical precision and should not be presented as total paleotemperature accuracy. Errors should be propagated and displayed in Figures 5 and 6. Until this is done, the inferred 2.5 °C variation cannot be evaluated robustly. The TEX₈₆ results should probably be presented as tentative evidence for temperature variability rather than a quantitative demonstration of rapid warming.

The regional comparison is useful, but Figure 7 combines records with different temporal resolutions, age uncertainties, and proxy sensitivities. The authors should explain the common interval used for z-score calculation, whether the records were resampled, and how chronological uncertainty was considered. Positive δ¹⁸O z-scores do not necessarily have an identical hydroclimatic meaning at every site. The conclusion that aridification was delayed at high elevations; and that mountain areas acted as climatic refugia; is based primarily on an approximately 500-year difference between Simarrón II and Cueva Victoria. This difference could also result from age-model uncertainty, cave hydrology, proxy-specific responses, or local climatic variability. The refugium interpretation should therefore be presented as a hypothesis unless it can be supported by additional high and low elevation records. Similarly, hydroclimatic change in southeastern Iberia should not automatically be equated with termination of the African Humid Period. The authors should distinguish between the African monsoon phenomenon itself and its possible western Mediterranean expression or teleconnection.

The final archaeological paragraph is not adequately connected to the preceding analyses and appears to contain a chronological mismatch. The mid-sixth millennium cal BC corresponds to approximately 7.5 ka BP, whereas the main aridification discussed in the manuscript culminates around 5.8–5.3 ka BP, approximately 3850–3350 BC. These events are therefore separated by well over a millennium. The claimed “close temporal correspondence” between the Mesolithic–Neolithic transition and the reconstructed aridification is not supported as currently presented. This paragraph should either be removed or developed into a properly referenced discussion using consistent BP/BC chronologies and a clearly defined archaeological transition.

Specific comments
Line 41: “García-Alix et., 2022” should be “García-Alix et al., 2022.”

Line 74: “alpine area” may not be the most appropriate description for a cave entrance at approximately 1,493 m. “High-elevation” or “montane” may be more accurate.

Line 79: The longitude appears to be incorrect. Sierra de Gádor is west of Greenwich, so “2°48′33″ E” should presumably be “W.”

Lines 103–105: Correct “southeaster Iberia” to “southeastern Iberia.”

Lines 109–115: Provide the source of the 1997–2025 precipitation estimate and identify whether 250 mm refers to the cave elevation or a broader regional average. Reconcile the reported summer RH of 65–75% with the later statement that RH can fall below 65%.

Line 114: Replace “relative humidity is attested” with “relative humidity was measured” or similar wording.

Lines 228–229: “Can be excluded” is too categorical. Petrography indicates no evidence of pervasive diagenesis but cannot necessarily exclude all alteration.

Lines 240–243: Distinguish clearly between activity ratios and atomic ratios. “232Th-corrected age” should be described more precisely as a detrital-thorium-corrected age.

Lines 260–261: Change “d-excess values … varies” to “d-excess values … vary.”

Lines 272–274: Differences of approximately 1.2‰ in δ¹⁸O and 9‰ in δ²H are not merely “slightly higher.” The altitude explanation is also not unique and should be qualified.

Figure 5 caption: “oxygen and carbonate isotopes in carbonate” should be “oxygen and carbon isotopes in carbonate.” The caption states that Mg/Ca was z-score standardized, but the plotted axis appears to show mmol mol⁻¹.

Line 361: Add “and” in “the Mg/Ca ratios and δ¹³C values.”

Line 392: The cave latitude is approximately 36.85° N, not 36.5°.

Lines 395–408: The failure of corrected paired-isotope temperatures to match expected cave temperature does not uniquely demonstrate in-cave evaporation. Kinetic carbonate fractionation, pre-infiltration evaporation, and limitations of the fractionation equation remain difficult to separate.

Lines 445–446: The study does not cover the entire Holocene, so “the driest Holocene conditions” should be replaced by wording restricted to the investigated interval.

Lines 478–480: Correct “the some of the lowest” to “some of the lowest.”

Line 493: Correct “norther Africa” to “northern Africa.”

Line 508: The text states that increasing δ¹⁸O and δ²H were accompanied by an increase in d-excess, whereas the rest of the manuscript and the figures indicate a decrease.

Lines 545–546: Correct “may result in in local cooling/warming.”

The timing of the main transition varies between approximately 6.0–5.5 ka in the abstract and approximately 5.8–5.3 ka in the conclusions. Use a consistent interval and incorporate age-model uncertainty.

Figure 8: Use the standard notation for the UK′₃₇ index. The caption should say “δ¹⁸O and δ¹³C,” not “δ¹⁸O/δ¹³C.”

Line 589: Correct “may have not the primary driver” to “may not have been the primary driver.”

Line 595: Correct the data DOI formatting to https://doi.org/10.5281/zenodo.21498781 and ensure that the repository record is active and contains all data required to reproduce the figures and analyses.

Author contributions: “AD” does not correspond to an author and may need to be “BD.” Similarly, “FGS” should presumably be “FG.”

Check the reference list systematically. Apparent inconsistencies include García-López et al. (2022/2023), Carrión et al. (2003/2010), Stachnik et al. (2016/2026), Luppichini et al. (2025/2026), IAEA/WMO (2026), and Zanchetta et al. (2026).

Reply
Citation: https://doi.org/10.5194/egusphere-2026-4435-RC1
RC2: 'Comment on egusphere-2026-4435', Anonymous Referee #2, 16 Oct 2026 reply

The manuscript by Gazquez et al. investigates the transition between wet and dry climate in the southern Iberian Peninsula based on a multi-proxy stalagmite record from Simarron Cave that grew between 9.7 and 4.4 ka BP. The study gives new climate information for this region and makes links with North African and western Mediterranean climate. Overall, the manuscript is well structured and easy to follow and is fully within the scope of Climate of the Past. My main concern is about the temperature reconstruction from both proxies, that seems hardly reliable, and the use of speleothem fluid inclusion d-excess as a witness for aridification (Section 5.2). The presented values seem sometimes fragile to support the conclusion made by the authors. For instance, the 2.5°C shift based on TEX86 analyses is not robust, especially regarding the uncertainty in the absolute temperature reconstruction from the data (+4°C compared to modern). Only little explanations are given for the offsets of temperatures.
Specific comments
To reconstruct temperature, a correction is applied to speleothem fluid inclusion water isotope values, which assume a constant evaporation slope. To me, it is not clear why the authors are doing this correction. First, the isotope data seems to be in a cloud rather than on a pure evaporation line (Fig. 4), however with a very slight trend that seems not significant and probably related to the heating phase during analyses. Temperature results based on the correction (Fig. 6) tends indeed to show that correction does not improve data, and consequently, that this step can be skipped. A second assumption that is made for the correction is that the “original” drip water fell on the LMWL, which may also add new uncertainty to the calculation, since the LMWL may have changed between the wetter early Holocene and the drier Mid-Holocene. Overall, applying this correction does not at all improve the data and temperature reconstruction, especially because the FI values seem to not be affected by evaporation, which is also supported by the fact that all d-excess values range (0-15 ‰) in the range of modern precipitation. Then, the link between aridification and fluid inclusions d-excess becomes fragile. I think that this section 5.2 is not essential for the manuscript and it can be easily shortened, since it raises more questions than it solves. Furthermore, the drying trend observed in carbonate from 6.5 to 5.3 ka BP (Fig. 5) is not reproduced in d-excess. However, this link is used to support the drying conditions (Lines 566-570). Why?
The statement made in line 397-399 is not correct. The fact that the correction fails to provide realistic temperatures is not a proof that analytical artefact is not the primarily cause for the offset in temperature. The authors mention also the work of Warken et al. (2022), but Warken provides d-excess values that are much more negative and consequently display a much shallower slope, which may be due to analytical artefact. Here, the range of d-excess values is within the range of modern precipitation.
Regarding the reconstructed temperature, it is not clear to me how the authors assess the relevance of their reconstructed paleotemperatures, since both FIT and TEX seem far too warm compared to modern temperature (Fig. 6). Moreover, they display a different trend compared to the SST. This raises several questions: Are FIT and TEX temperatures significant? Can you use them to interpret the past temperature variability? What are the reasons for the very high FIT? TEX86 temperatures are in average ~4°C warmer than modern temperature (Line 419), which seems also unrealistic. How do you justify the use of TEX temperature, since they document too high temperature? Would that mean that TEX86 temperatures are biased towards summer? Can the authors expand a bit on why the variation between samples is robust, since the absolute values does not seem so (Line 423).
Line 43: Give the age of nAHP.
Line 130: Delete entirely.
Line 210: The equation differs slightly from the one given in Wassenburg et al. (2021, Nature Geoscience).
Line 383-385: Rewrite. There is no proof that the corrected value corresponds to the original drip water value. Correcting may be simply adding new uncertainty.
Line 400: Rapid CO₂ degassing seems to not be an issue; on the contrary, longer CO₂ degassing would be problematic (Deininger et al., 2012, Geochimica et Cosmochimica Acta).
Lines 403-409: Do the data show this? I think, we should see it in d-excess, which is not the case.
Lines 568-573: What change do you expect between Mediterranean and Atlantic sources? What will the isotope and the d-excess look like? Could the trend observed in the stable isotopes from fluid inclusions be linked to a source change instead of aridification? More explanations would be useful to support this section.
The captions would benefit from more detailed descriptions.
Fig. 2: there is no legend for the colours, letter, etc.
Figs. 3 and 5: it seems that on the d-excess profile, the record is not the same on the left side of both figures (on sides 0 mm or 4000 BP).
Fig. 4 Groundwater and LMWL have a similar grey colour, which is confusing.

Reply

Citation: https://doi.org/10.5194/egusphere-2026-4435-RC2
CC1: 'Comment on egusphere-2026-4435', Giacomo Medici, 28 Oct 2026 reply

General comments
Very good research on paleoclimate with an angle on spleothems. Please, consider the specific comments to improve the final version of the manuscript.

Specific comments
Lines 39-76. Highlight better the novelty of your research.
Lines 54-55. Insert recent literature on the capacity of speleothems that captures hydological and geological events related to specific chronological intervals:
- Medici G, Marianelli D, Cornacchia I, Gori F, Brandano M (2026) Multi-disciplinary approach to paleokarst occurrence in the Eocene–Oligocene succession of the Apulia Carbonate Platform (Salento, Italy). Facies, 72(2), 17.
- Wong CI, Breecker DO (2015) Advancements in the use of speleothems as climate archives." Quaternary Science Reviews 127, 1-18.
Line 76. Describe the specific objectives of your research by using numbers (e.g., i, ii, and iii).
Line 85. Which type of carbonate rocks? Dolostones or limestones of Triassic age?
Line 85. Specify the depositional paleoenvironment for the Triassic carbonates.
Lines 80-90. Describe better the potential link between the presence of faults and the cave.
Line 210. Each equation should be associated to a number.
Line 210. Refer to the equations in the text using numbers.
Line 559. Highlight the novelty of your research also in this last section.

Figures and tables
Figure 1. These three figures can be in vertical position so you can make them larger.
Figure 1. The map of the cave really needs to be larger.
Figure 3. Increase the graphic resolution by rising the number of dpi.
Figure 4. Insert three equations on the plots.
Figure 5. Increase the graphic resolution by rising the number of dpi also for this figure.

Reply

Citation: https://doi.org/10.5194/egusphere-2026-4435-CC1

Fernando Gázquez, Hubert Vonhof, Carlos Pérez-Mejías, Andrea Columbu, Alena Giesche, Hai Cheng, Alfredo Martínez-García, Brian DiMento, Eneko Iriarte, and José María Calaforra

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https://doi.org/10.5194/egusphere-2026-4435-supplement

Fernando Gázquez, Hubert Vonhof, Carlos Pérez-Mejías, Andrea Columbu, Alena Giesche, Hai Cheng, Alfredo Martínez-García, Brian DiMento, Eneko Iriarte, and José María Calaforra

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Short summary

By studying mineral deposits formed in a cave in southern Spain, we reconstructed how climate changed between about 9,700 and 4,400 years ago. We found that a humid climate gradually gave way to much drier conditions, with the main transition occurring between 6,000 and 5,500 years ago. These results show how the end of a wet period in North Africa also affected southern Europe, improving our understanding of how regional climates respond to large-scale environmental change.


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