the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 04 Jul 2025
The elusive 8.2 ka event in speleothems from southern France
Abstract. The Holocene is generally considered a climatically stable period, yet a prominent perturbation occurred around 8.2 ka BP. Evidence of its impacts has been identified in many palaeoclimate archives across Europe. However, outside the Atlantic seaboard, no clear high-resolution signal for this event has emerged from southwestern Europe. Here, we investigate the potential impact of the 8.2 ka event in southern France through high-resolution multiproxy analyses of two speleothems from the Ardèche region. Variations in Mg/Ca and Sr/Ca of the speleothem calcite are attributed to the prior calcite precipitation (PCP) effect and indicate switches between drier and wetter conditions. The δ13C signal is likely influenced by soil development and biological activity, integrating both regional climate conditions and local geomorphology. The pattern of speleothem δ18O changes do not correlate with regional palaeotemperature reconstructions and is therefore more likely related to hydrology, such as variations in the seasonality of karst recharge and/or the moisture source. During the 8.2 ka event, no distinct geochemical anomaly is recorded by the Ardèche speleothems, suggesting either a limited climatic impact in southern France or a lack of sensitivity of these speleothem proxies to an event of this magnitude. While the muted δ18O response may be explained by a decoupling from temperature and buffering by Mediterranean influences at the time, the absence of a clear hydrological response in Mg/Ca, Sr/Ca and δ13C remains unresolved. Therefore, despite a likely southward displacement of the westerlies induced by the 8.2 ka event, the Ardèche region may have remained under their influence, preventing a marked shift towards drier conditions. Consistent with other records from southern France, our results showing no significant changes around 8.2 ka challenge the spatial extent and uniformity of its climatic impacts across western Europe.
Competing interests: At least one of the (co-)authors is a member of the editorial board of Climate of the Past.
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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RC1: 'Comment on egusphere-2025-2945', Anonymous Referee #1, 29 Jul 2025
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This manuscript presents first data from two stalagmites in southern France covering the Holocene period with the main aim of understanding why the 8.2 ka event is not present in paleoclimate records from the Mediterranean, particularly in those from southern France. The authors obtain the data to support this hypothesis from two stalagmites with robust chronologies and high-resolution isotopic profiles (trace elements are analyzed in one of the two stalagmites) from two different caves: Orgnac and St Marcel. The objective is sound and the methodology is adequate but the study lacks support from other Mediterranean records to the central hypothesis. In my opinion, major changes are required before publication (see below) and obtaining some monitoring data may be of interest too to better understand the response of these two caves to current climate.
INTRODUCTION AND MAIN HYPOTHESIS. the introduction should be completed with more references, particularly from marine cores from W Mediterranean. Evidences of the 8.2 ka event have been found in marine sediments from W Mediterranean, both in the Balearic Sea (Frigola et al., 2007) and in the Alboran Sea (Cacho et al., 2002), indicating a clear signal of a cold event and with intensified dry westerly winds. In fact, it has been proposed that this event interrupted the sapropel 1 (ORL in W Med) since the Western Mediterranean deep-water convection was reactivated. This idea should be incorporated in the introduction and later in the discussion because it contradicts the main hypothesis of the manuscript about the lack of signal of the 8.2 ka event in the Mediterranean realm. It is also very important to show the records compared to the two stalagmites; Fig. 1 with the map including so many records is really nice and informative but the records themselves should be also incorporated as a final figure, clearly indicating which records are under the influence of Atlantic climates, which are under Mediterranean and which show an annual signal versus those biased towards one season. In that different way of incorporating the climate signal may be the key to understand the 8.2 ka event in a regional scale. The manuscript, as it is now, lacks the comprehensive view required to explore the proposed hypothesis.
MONITORING. I understand that the drip-water was monitored in a cave that was close to Orgnac cave (line 105) but that does not guarantee the same pattern in drip-water or the same infiltration processes in the two studied caves, not over the two different stalagmites. The amount of soil, the thickness of the host rock or even the type of rock and its fracturation pattern are other important factors that may condition drip water dynamics in Orgnac cave that may not be the same in St Marcel cave.
In fact, the authors use those factors related to soil processes to justify the different pattern in d13C in both stalagmites (line 200). Both caves may be under different environmental conditions, i.e. soil activity, epikarst PCP, etc, that lead to such diverse isotopic profiles (d13C). Similarly, those different conditions may require conducting monitoring surveys in the cavities to fully understand dripwater processes, relation with rainfall patterns, etc.
INTERPRETATION OF PROXIES. Comparison of the two d18O or the two d13C profiles does not help too much to interpret the meaning of those proxies in these particular caves and time period. I wonder if providing trace elements for the two stalagmites may be of further help. Now, both trace elements (Mg and Sr) are quite different and they do not compare well with d13C to be explained all proxies in terms of hydrological variations. In general, my feeling is that the two stalagmites are well-dated but they do not respond in a similar way to past climate/environment conditions. The reasons remain elusive but the authors may want to explore more and complete the section about proxy interpretation (section 4.1) with more ideas or more data. As it is now, it is not very convincing.
Cited references:
- Frigola, J., Moreno, A., Cacho, I., Canals, M., Sierro, F.J., Flores, J.A., Grimalt, J.O., Hodell, D.A., Curtis, J.H., 2007. Holocene climate variability in the western Mediterranean region from a deepwater sediment record. Paleoceanography 22.- Cacho, I., Grimalt, J.O., Canals, M., 2002. Response of the Western Mediterranean Sea to rapid climate variability during the last 50,000 years: a molecular biomarker approach. Journal of Marine Systems 33–34, 253–272.Citation: https://doi.org/10.5194/egusphere-2025-2945-RC1 -
RC2: 'Comment on egusphere-2025-2945', Anonymous Referee #2, 01 Aug 2025
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The 8.2 ka event is widely regarded as the most significant climate shift in the N Hemisphere since the end of the Younger Dryas. And it is probably the best studied event in the Holocene whose timing and origin as well understood. Still, there are regions, in particular close to the Mediterranean Sea, where this events has not been recorded, even in high-resolution archives. The present ms. adds new observational evidence from two cave sites in S France showing no significant proxy response to this N Atlantic cooling and drying event.
The ms. is well written and the proxy evidence is fairly convincing. I regret, however, that depite the authors’ claim about the importance of multiproxy analyses (line 376) they do not present trace element data for the second stalagmite. If possible, I recommend to add Mg+Sr data at least across the critical time range of the 8.2 ka event.
Another aspect that could/should be improved is the nearly complete lack of petrographic information. The reader is shown the scans of the slabs and somewhere I read a sentence about the fabric, but nothing else.
Minor:
- Line 49: Herbstlabyrinth Cave
- Line 53: Schleinsee
- Fig. 2A: explain dashed lines
Citation: https://doi.org/10.5194/egusphere-2025-2945-RC2 -
RC3: 'Comment on egusphere-2025-2945', Anonymous Referee #3, 28 Aug 2025
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Review of the manuscript “The elusive 8.2 ka event in speleothems from southern France” by Passelergue et al., submitted to Climate of the Past
General comment:
Passelergue et al. present proxy data for two speleothems from southern France, which do not show any obvious peaks during the 8.2 ka event, which is considered as one of the major climate anomalies of the Holocene. They interpret this pattern as evidence that the 8.2 event did not have a major impact in southern France or at least as the absence of a clear hydrological response.
The paper is interesting and well written, and I agree with the general conclusion and can recommend publication in CP. However, I do not fully agree with the interpretation of the proxies (e.g., the Mg and Sr data in terms of PCP, see detailed comments below). In addition, I think that the authors may have a bit more to offer. Based on the references, it is clear that they compiled all the literature for the 8.2 ka event in Europe. (i) It would be good to see at least some of these records in a figure to highlight the (regionally consistent?) similarities and differences, which are currently only described in the text. (ii) This comparison may allow to draw some more general conclusions about the expression of the 8.2 ka event in proxy records from Europe (i.e., in which archives/proxies does it occur?) and its (general or spatially variable?) climatic features (cold, dry, wet, etc.).
Detailed comments:
Fig. 1: See my general comment. The figure shows various sites/proxy records that obviously were compiled for the paper. It would be really useful to see a comparison with at least a few of those in a figure. Furthermore, it may be possible to derive some more general information about the expression of the 8.2 ka event in Europe, beyond southern France.
Line 63: ‘However, some records suggest that the presence of sapropel S1, which occurred at the same time, masks the possible influence of the 8.2 ka event in some regions (e.g. Magny et al., 2007; Siani et al., 2013; Zanchetta et al., 2007). More generally, there are no high-resolution records in the western Mediterranean region showing significant changes that can be clearly attributed to the 8.2 ka event (e.g. d’Oliveira et al., 2023; Jalali et al., 2016; McDermott et al., 1999; Fig. 1a, b).’ Should the order of these two sentences be changed? Otherwise, I do not get the meaning of the first one.
Line 107: ‘Since the host rock and fracture network are similar at all sites, we can expect the same mixing of infiltration waters at St Marcel and Orgnac Caves. This implies that the δ¹⁸O of the calcite represents at least an intra-annual, if not an inter-annual, average of the δ¹⁸O of recharge precipitation.’ Although I agree with the reasonable conclusion in the second sentence, It think, the interpretation in the first sentence is too ‘optimistic'. It is well known that even two nearby drip sites in the same cave can have very different characteristics.
Table 1: Please provide the uncertainties for the (230Th/232Th) activity ratios. In addition, it would be good to report a consistent number of significant digits.
Line 172: ‘The empirically derived (230Th/232Thinitial) corrections applied were 0.48±0.32 for SM1-A and 0.48±0.24 for OR09-A.’ Why are the uncertainties different? I guess this is related to the method used to derive the corrections, but a brief explanation would be good.
Section 3.2: ‘Isotopic Equilibrium Conditions’ I think the header is misleading because other aspects influencing the isotope data are discussed here as well. In addition, this section should in my opinion be moved into the discussion section or at least not be discussed prior to the general description of the data (section 3.3). I would suggest to integrate the whole section into section 4.1.
Line 181: ‘However, the absence of consistent covariation between δ¹³C and δ¹⁸O in each of the stalagmites (Fig. 3) indicates that calcite precipitation was not associated with significant kinetic fractionation.’ The d18O and d13C values of stalagmite SM1-A are significantly correlated (Table 3), so this statement is not correct. However, there are numerous speleothem studies showing highly correlated d18O and d13C values due to climatic reasons rather than disequilibrium isotope fractionation that the absence of a correlation should – in my opinion – not be interpreted as evidence for the lack of in-cave effects. PCP, for instance, would also result in a correlation between d18O and d13C values. In general, I do not understand why this topic is discussed in such detail. The major point of the paper is that there is not strong signal during the 8.2 ka event. This interpretation does not require equilibrium isotope fractionation. Quite the contrary, very dry conditions, for instance, could result in low drip rates supporting disequilibrium fractionation and positive peaks in d13C and d18O, which would even be useful.
Line 193: ‘For most of the growth interval, the δ¹⁸O signals of these stalagmites show similar trends with a limited amplitude (Fig. 4a). … Indeed, besides some discrepancy during the periods 9.7–9.3 ka and 8.0–7.6 ka, the two δ¹⁸O patterns are very similar.’ I agree. To further support this statement, it may be useful to calculate (running) correlations between the two curves.
Line 195: ‘This is in spite of an offset for much of the period, with OR09-A having generally higher values (Fig. 4a and b).’ Looking at Fig. 4, which is very useful, it seems to me that there is not just an offset, but also some centennial scale differences of more than 0.5 permil. This may be related to dating uncertainties, but could also be due to local effects occurring at the surface or in the karst aquifers and caves.
Table 3: The high correlation coefficient between Mg/Ca and Sr/Ca is really surprising to me, not only from Fig. 3, but in particular considering Fig. A.3, which just shows a point cloud.
Line 247: The introductory paragraph to the discussion section can be deleted.
Line 262: ‘Magnesium and strontium concentrations in calcite generally reflect hydrological variations in the vadose environment above the cave or aerosol contributions (Dredge et al., 2013; Regattieri et al., 2014; Verheyden et al., 2000).’ I strongly disagree with this statement. There are many speleothem trace element records, where both Mg and Sr do not show a robust relationship with any climate parameter. I agree that – if e.g. PCP can be demonstrated to have an effect – both elements are powerful hydrological proxies. However, this is not ‘generally’ the case, and then, the interpretation in terms of palaeoclimate is often very difficult.
Line 268: ‘Alternatively, PCP may explain the variations in magnesium concentrations.’ Yes, if the effect can be demonstrated, for instance with a positive Sinclair test (see below). If this test is negative, PCP does probably not have a major influence and other processes need to be considered. Since the Sinclair test is negative, I think that the interpretation in terms of PCP (and hydrology) goes to far. However, as stated above, this is not a problem for the major conclusion of the paper about the 8.2 ka event.
Line 287: ‘The Sr and Mg of SM1-A show a significant positive correlation (Table 3), and although the slope is below 0.7 (Fig. A3), the similar long-term trend between the two elemental ratios supports the hypothesis of an increase of moisture balance through the first part of the Holocene.’ It would be good to demonstrate this ‘similar long-term trend’, e.g., by calculating the correlation between two strongly smoothed curves or linear fits through both proxies.
Line 297: ‘In summary, the evidence suggests that the variations in Mg/Ca and Sr/Ca of SM1-A are mainly linked to changes in site moisture balance.’ I do not agree with this statement (see above). However, this interpretation of the Mg and Sr data is not crucial for the major conclusion of the paper.
Line 310: ‘Considering the general trend of SM1-A and OR09-A δ¹⁸O and the information provided by the other proxies, it is more likely that the δ¹⁸O variations were related to hydrological changes.’ Or they are not at all sensitive to climate change, at least during the Holocene when climate conditions at the surface were rather stable. Even the largest event of the Holocene, the 8.2 ka event (if so), was not recorded.
Section 4.2: See my general comment. I agree with everything in this section, but I believe that the authors may have more to offer. As the state in their last sentence, there is a ‘… need for complementary approaches through the cross comparison of multiple archives in order to decipher regional palaeoclimatic responses to the 8.2 ka event.’ It seems to me that they already compiled this information and have everything available to perform such a cross comparison. The paper would strongly benefit from making more use of these data.
Line 373: ‘… but it does not explain the absence of a hydrological response from the Mg/Ca and Sr/Ca.’ See my comment above. If Mg/Ca and Sr/Ca are not affected by PCP (as suggested by the negative Sinclair test), they do not reflect hydrological changes above the cave. Maybe, they are not sensitive to climate change (of this scale) at all. This statement is too ambitious to me.
Line 373: ‘Whilst it is well known that these ratios do not always yield meaningful hydrological information at all cave sites, the positive covariance of Mg/Ca and δ¹³C over the whole 11-5.5 ka interval suggests SM1-A was sensitive to hydrological change during its growth history, at least over the long term.’ I absolutely agree with the first part of the sentence (see my previous comments). With the second part, I do not agree considering the negative Sinclair test, Fig. A.3 and Fig. 3.
Citation: https://doi.org/10.5194/egusphere-2025-2945-RC3
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