the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Alternating cold and warm periods during the European late-Holocene
Abstract. The decadal to centennial scale climate variability of the past 4000 years consists of colder and warmer periods, potentially initiated by fast varying external forcing, or the lack thereof. These alternating cold and warm periods are most clearly visualized by the waxing and waning of glaciers in the Northern Hemisphere. However, these cold and warm periods are neither spatially nor temporally consistent, and using these defined periods to interpret local variations in climate and society could prove difficult. Here, we use two global earth system models, as well as available proxy reconstructions to examine to which extent the defined warm and cold periods of the last 4000 years before the industrial period are reflected in the climate for Northern, Southern, and Central Europe. We find that on regional scales, the relative role of internal variability appears more pronounced compared to the externally forced signal, thereby decreasing the forcing signal in local climate records. In addition, one model suggests that the climate variability for Northern Europe follows the external forcing more closely than the climate of Central and especially Southern Europe, while the other model shows rather ambiguous results. This study illustrates that periods defined by glacier advances and archaeology have to be carefully used in the interpretation of past events at a local scale, as it is likely that internal variability dominates on such scales.
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RC1: 'Comment on cp-2024-79', Anonymous Referee #1, 17 Dec 2024
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I was quite surprised by the manuscript "Alternating cold and warm periods during the European late-Holocene" written by Evelien J.C. van Dijk and colleagues. The initial idea is quite good and I expected something solid, structured, based on multiple models. But, very quickly, we realize that this manuscript has many weaknesses and that it absolutely does not reflect a potential reality.
The first weakness, which is major, is based on the number of sites considered. The map (Figure 1) perfectly shows the extent of the problem. Only one site for the south, four for the center and four for the north. How can we draw conclusions about "southern Europe" from a single site in Spain? How is this site representative of the whole of southern Europe? The same is true for central Europe, four more or less agglomerated sites. How are these sites representative? How can the authors justify this? In the literature, there are many sites for each of these geographical areas that one wonders how this tiny selection was made.
The authors also mix annual data with summer data (Table 2). How can the two be combined? Especially since we have known for a long time that seasonality is a key element in ancient climates and that annual data are not conducive to this kind of exercise. So, mixing the two is meaningless (see the abundant literature on this subject).
Another major point is the temporal resolution. Basically, one point every 100 years. This gives smoothed curves (Figure 2; without any 1σ or 2 σ error!) that inevitably miss all the climatic variations between two consecutive and smoothed points. So, these curves are not even long-term trends [which result from multiple points (present on a graph) that are used to produce a smoothed curve with a maximum sampling step of 30 or even 50 years].
Finally, how can we evoke a potential link between these curves and societies when the foundation is so erroneous?
I suggest that the authors redo their entire study, incorporate multiple sites for each geographical area, justify why they have chosen particular sites, have a very precise temporal resolution and above all, work on seasonality. From there, they will be able to compare their reconstructions with archaeological and historical data. At present, this is absolutely not the case and this manuscript should be rejected.
Citation: https://doi.org/10.5194/cp-2024-79-RC1 -
AC1: 'Reply on RC1', Evelien JC van Dijk, 31 Jan 2025
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Thank you for your helpful comments.
Concerning your first major concern, we agree that we have not a lot of proxy records used for the paleo reconstruction part of the paper. The reason for this is twofold: (i) we decided to include only reconstructions which have an adequate temporal resolution to capture the high-frequency climate variability, and (ii) the reconstructions must span the entire period considered in the manuscript. In a revised version of the manuscript, we will better motivate the choice made. In the meantime we try to find more proxy records which fulfill the two criteria above and will add them to the revised manuscript.
The point about seasonality is fair and we realize that we need to better discuss the seasonality of the different proxy records. Fortunately, we can combine this also with the modelling results presented. The revised version of the manuscript will thus include such a discussion and elaborate the difference in seasonality of the proxy reconstructions but also the modeling results.
Another concern was the low temporal resolution used for display reasons. We agree with the reviewer that not showing the full resolution can be confusing. We will add the full resolution to the paleo proxy figures, as well the 2-sigma threshold for uncertainty.
Lastly, the concern about the potential link between these curves and societies. We are bit puzzled as our aim was not to link climate variability to societal changes. Our aim we are trying to convey with this paper, is that the warm and cold periods as defined from glacier fluctuations is a lot more nuanced than it is sometimes perceived. These periods were not spatially or temporally homogeneous throughout Europe, and that caution is therefore advised when drawing conclusions about these time periods in very localized studies (like for example archeological studies). The paleo proxy reconstructions are a part of this, but a large part of our arguments also come from model simulations.
We are of the opinion that with major revisions, we can address these points and improve the manuscript so that our main point becomes clear.
Citation: https://doi.org/10.5194/cp-2024-79-AC1
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AC1: 'Reply on RC1', Evelien JC van Dijk, 31 Jan 2025
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CC1: 'Comment on cp-2024-79', Melaine Le Roy, 05 Feb 2025
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Dear authors,
I'd like to comment on this paper concerning the sections dealing with glacier fluctuations over the Holocene and particularly the Neoglacial, which concern my area of expertise.
Title
I’m a bit confused by the title and it should be rewritten to be more specific and less vague, as the reader would like to have a glimpse of main results from here.
Introduction
I found it not well-written, disjointed and confusing. More importantly, the introduction doesn’t reflect current state of knowledge on the glacier/climate topic. There is no progression nor link between the paragraphs and some of the glacier-related evidence reported here sounds anecdotical. This makes it difficult to follow the progression of reasoning and hampers understanding the problematic of the paper.
Nomenclature used in the Introduction
On this nomenclature issue, we orient the authors to our recent work who represent the most up to date review on Holocene glacier variations in the Alps and where we introduced a novel nomenclature for glacier advances in the Alps for the entire Holocene (Le Roy et al., 2024). This should be therefore quoted in such a study. A number of terms are introduced in this paper for the climate and glacier advance periods to express an Alpine-wide view. This departs from the regional-based nomenclature used in earlier publications. As far as possible, it's best to get rid of local names (e.g. Löbben, Göschenen). It is equally important to remain consistent : e.g., why using here names belonging to a local morphostratigraphy (e.g. Löbben), together with hemispheric/global terms like the ‘2.8 ka event’ or the ‘RWP’ ?
In my opinion the Table I is problematic. There's a mixture of different types of study (paeoclimatology, archaeology, geomorphology), all put on the same level, which shouldn't be the case. How to justify that meta-analyses can be found alongside local case studies? Clearly, the results are not the same when it comes to the periods that the authors wish to define here.
More, the span of the different period as shown in Table 1 is at odd with the actual evidence and the nomenclature used is outdated. Tree-ring data exist and should be better integrated here, instead of loosely defined intervals. The way in which the bounds are defined is not clearly explained in the paper
- A summary about the 4.2 ka event is made here, concluding that consequences are contrasting and not global. But the authors didn’t mention the increase in humidity around the Alps with rising of lake level (Magny et al., 2011 ; 2012a ; 2012b ) and glacier advances (e.g Le Roy et al., 2017) at that time.
- The Löbben oscillation (now called BAAP) is represented on Fig 2 as spanning 1700 to 1200 BCE, while it has been shown to span 1700-1400 BCE and that glacier peaked at 1500 BCE during this period and then retreated markedly afterwards (Le Roy et al., 2024). The coldest interval of the BAAP lasted from ca 1660 to 1500 BCE (with cold peaks centered on ca 1625 and ca 1530 BCE) (Le Roy et al., 2015). There is extensive evidence for that advance (and especially tree-ring dates, which are far more precise than the TCN dates the authors quoted here) available at multiple sites all over the Alps, and it should be therefore better acknowledged. On the contrary, the Löbben advance is defined in the Introduction of the paper as having manifested (only) in the Tyrol (!)
- ‘The BWP was less pronounced’ (line 54) : Less pronounced than what? On the contrary, it was a lengthy period of marked retreat that spanned 1400 to 1000 BCE (see review in Le Roy et al., 2024).
- The 2.8 ka event is represented on Tab. 1/Fig 2 as spanning 1000 to 300 BCE. More, it is described in the text by a ‘cooling’ only. This is obviously misleading. How this name (‘2.8 ka event’), which has been defined in raised bogs from NW Europe (e.g. van Geel et al., 2014) as an abrupt shift to extremely wet conditions over a short time period centered on 800 BCE, could be used here to encompass this broad interval (700 yr-long) ?
- The RWP is shown as spanning 250 BCE to 400 CE in Table1/Fig. 2, being ‘stable warm and dry’ during the whole interval. This is overly simplistic and does not conform to available glacier/climate evidence. Indeed, LIA-like glacier extent is attested (i) around 2.1 ka and (ii) around 300 CE, which means RWP is de facto restricted to ~1-250 CE (Le Roy et al., 2024), as shown also by available temperature reconstructions (e.g. Luterbacher et al, 2016).
In short, the COLD/WARM periods defined it Table I/Fig. 2 do not conform to the current state of knowledge (palaeoclimatology and palaeoglaciology), which is far more nuanced. It is therefore not a suitable starting point for this study.
Line 108/109: We recently demonstrate that the Alpine Little Ice Age spans precisely 1260 to 1860 CE based on tree-ring dated evidence, both from glacier kill dates and from tree-ring summer tempereture reconstruction (Nicolussi et al., 2022). This is a significant update of Grove’s work.
- Methods
Line 133: The Mer de Glace record is entirely based on tree-ring dated wood samples (absolute calendar dates) and not radiocarbon dating as stated here (14C was only used at early stages).
General remarks
- Use of ‘archaeological periods’
I really don’t understand what is the point to use it here, apart from confusing the reader (as Reviewer 1 mentionned it). The authors use archaeological records only to bound the time periods here. However, this can be done better with palaeoclimatological reconstructions. There is no need in my opinion to go looking for a little added value from another disciplinary field (that is not used in the rest of the paper).
2) Synchronism of glacier advances in Europe :
Your main reply to #Reviewer1 was ‘ that the warm and cold periods as defined from glacier fluctuations is a lot more nuanced than it is sometimes perceived’
I agree with that. However, there is still need to use the right glacial records to show that. The authors made extensive use of glacier data but only for three of the largest glaciers in Europe. The largest Alpine glaciers are notoriously known to lag climate, especially Aletsch glacier. But this lag is barely mentionned (briefly evocated at the line 197), but not quantified in the paper. And the Figure 2 compares both glacier length curves with an ELA record. So why not using the ELA values deduced from the glacier length curve for Alpine glaciers, as it has already been done before (e.g Luthi, 2014) to mitigate this problem and use a more direct (annual) climate proxy? Moreover, in Scandinavia numerous ELAs reconstruction based on lake sediment exist and could be merged to obtain a regional composite record, rather than the single local record used here. This could be done also in the Alps with available length variations, instead of using only three local records.
When looking at all available glacier data in Europe (Please see the book about ‘Holocene glaciation in Europe’ recently released, and the different chapters relating to northern/central/southern Europe (https://www.sciencedirect.com/book/9780323997126/european-glacial-landscapes), we can see that despite different resolution, a common pattern emerges as for the glacier advances during the Neoglacial (last 4 ka ). Temporal resolution is far better in the Alps because of ancient and widespread use of tree-ring dating, but apparent synchronism is strong, modulated, of course, by (i) the different glacier response times and by (ii) the uncertainties of the various dating methods.
Conclusion
I don’t find the Conclusion convincing and bringing something new to our current understanding of the Late Holocene climate in Europe. How the results drawn here could be considered robusts given the low number of included proxy records, especially for southern Europe (i.e., only one speleothem in northern Spain, see Fig. 1). This corpus should be enriched also be including high resolution lake sediment record (e.g. Zander et al., 2024), which are well distributed across the area of interest.
Minor points
Moran et al 2005 (Tab. 1) => this should read ‘Moran et al 2017’
‘Spannagel’ cave is mispelled in (Tab. 1)
All the best,
Melaine Le Roy
References
Le Roy, M., Nicolussi, K., Deline, P., Astrade, L., Edouard, J.L., Miramont, C., et al., 2015. Calendar-dated glacier variations in the western European Alps during the Neoglacial: the Mer de Glace record, Mont Blanc massif. Quaternary Science Reviews 108, 1-22. https://doi.org/10.1016/j.quascirev.2014.10.033
Le Roy, M., Deline, P., Carcaillet, J., Schimmelpfennig, I., Ermini, M., ASTER Team, 2017. 10Be exposure dating of the timing of Neoglacial glacier advances in the Ecrins-Pelvoux massif, southern French Alps. Quat. Sci. Rev. 178, 118–138. https://doi.org/10.1016/j.quascirev.2017.10.010
Le Roy, M., Ivy-Ochs, S., Nicolussi, K., Monegato, G., Reitner, J.M., Colucci, R.R., Ribolini, A., Spagnolo, M., Stoffel, M., 2024. Chapter 20 - Holocene glacier variations in the Alps. In: Palacios, D., Hughes, P.D., Jomelli, V., Tanarro, L.M. (Eds.) European Glacial Landscapes: The Holocene. Elsevier, Amsterdam. 367-418. https://doi.org/10.1016/B978-0-323-99712-6.00018-0
Luterbacher, J., Werner, J.P., Smerdon, J.E., Fernandez-Donado, L., Gonzalez-Rouco, F.J., Barriopedro, D., et al., 2016. European summer temperatures since Roman times. Environmental Research Letters 11, 024001. https://doi.org/10.1088/1748-9326/11/2/024001
Lüthi, M.P., 2014. Little Ice Age climate reconstruction from ensemble reanalysis of Alpine glacier fluctuations. Cryosphere 8, 639-650. https://doi.org/10.5194/tc-8-639-2014
Magny, M., Bossuet, G., Ruffaldi, P., Leroux, A., Mouthon, J., 2011. Orbital imprint onHolocene palaeohydrological variations in west-central Europe as reflected by lake level changes at Cerin (Jura Mountains, eastern France). J. Quat. Sci. 26 (2),171-177. https://doi.org/10.1002/jqs.1436
Magny, M., Joannin, S., Galop, D., Vanni_ere, B., Haas, J.N., Bassetti, M., Bellintani, P.,Scandolari, R., Desmet, M., 2012a. Holocene palaeohydrological changes in thenorthern Mediterranean borderlands as reflected by the lake-level record of Lake Ledro, northeastern Italy. Quat. Res. 77, 382-396. https://doi.org/10.1016/j.yqres.2012.01.005
Magny, M., Arnaud, F., Billaud, Y., Marquet, A., 2012b. Lake-level fluctuations at Lake Bourget (eastern France) around 4500-3500 cal. BP and their palaeoclimatic and archaeological implications. J. Quat. Sci. 27 (5), 494-502. https://doi.org/10.1002/jqs.2546
Nicolussi, K., Le Roy M., Schlüchter, C., Wacker L., Stoffel M., 2022. The glacier advance at the onset of the Little Ice Age in the Alps – new evidence from Mont Miné and Morteratsch glaciers. The Holocene. https://doi.org/10.1177/09596836221088247
van Geel, B., Heijnis, H., Charman, D. J., Thompson, G., & Engels, S. (2014). Bog burst in the eastern Netherlands triggered by the 2.8 kyr BP climate event. The Holocene, 24(11), 1465-1477. https://doi.org/10.1177/0959683614544066
Zander, P. D., Żarczyński, M., Tylmann, W., Vogel, H., & Grosjean, M. (2024). Subdecadal Holocene warm-season temperature variability in central Europe recorded by biochemical varves. Geophysical Research Letters, 51, e2024GL110871. https://doi.org/10.1029/2024GL110871
Citation: https://doi.org/10.5194/cp-2024-79-CC1
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