Tephra data from varved lakes of the last Glacial-Interglacial transition: towards a global inventory and better chronologies

Beckett, Anna; Blanchet, Cecile; Brauser, Alexander; Kearney, Rebecca; Martin-Puertas, Celia; Matthews, Ian; Mittelbach, Konstantin; Palmer, Adrian; Ramisch, Arne; Brauer, Achim

doi:https://doi.org/10.5194/essd-2023-154

Preprints

https://doi.org/10.5194/essd-2023-154

Preprints

13 Jun 2023

| 13 Jun 2023

Status: this preprint is currently under review for the journal ESSD.

Tephra data from varved lakes of the last Glacial-Interglacial transition: towards a global inventory and better chronologies

Anna Beckett, Cecile Blanchet, Alexander Brauser, Rebecca Kearney, Celia Martin-Puertas, Ian Matthews, Konstantin Mittelbach, Adrian Palmer, Arne Ramisch, and Achim Brauer

Abstract. The Varve Database (VARDA) was launched in 2020 and aimed to establish a community database for annually-resolved chronological archives with their associated high-resolution proxy records. This resource would support reproducibility through accessible data for the paleoclimate and modelling communities. In this paper, we used VARDA to assemble an extensive dataset of European tephra geochemical data and metadata to enable the synchronisation of varve records during the Last Glacial Interglacial Transition (here defined as 25 ka BP to 8 ka BP). Geochemical data from 49 known individual tephra layers across 19 varve lake records have been included, with Lago di Grande Monticchio being the single biggest contributor of geochemical data with 28 tephra layers. The Vedde Ash and Laacher See tephra are the most common layers being found in 6 different varve records and highlights the potential of refining the absolute age estimates for these tephra layers using varve chronologies and for synchronising regional paleoclimate archives. This is the first stage in a 5 year plan funded by the Past Global Changes (PAGES) Data Stewardship Scholarship to incorporate a global dataset of tephra geochemical data in varve records. Further stages of this project will focus on different regions and timescales.

Received: 21 Apr 2023 – Discussion started: 13 Jun 2023

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Anna Beckett et al.

Status: final response (author comments only)

CC1:
'Comment on essd-2023-154', Carl Regnéll, 19 Jun 2023

Dear authors,

I have a few comments on your preprint which I point out below:

General comments:

It is important not to consider databases like RESET and VARDA as complete and not critically review the data one uses from them, as it might lead to the propagation of misinformation.

Also, when referring to specific sites and studies included in these databases I would consider it only fair to cite the original references for these studies and not only the databases.

More specific:

P.7, Lines 152-154: “Furthermore, the location of seven additional sites with robust varve chronologies, which have high potential for cryptotephra investigations are identified (Figure 4).”

Comments: Potential tephra site “a” (Aspevatnet) is included in the VARDA-database but is not varved, or at least no varves are reported in the reference given in VARDA (Bakke et al. 2005).
Potential tephra site “b” (Storsjom) is misspelt and slightly misplaced on the map. It should be “Storsjön” and as it only has a c. 250 varves long floating chronology (Labuhn et al. 2018) it might not qualify as a “robust varve chronology” with "high potential for cryptotephra investigations "? In addition, Storsjön was covered by the Scandinavian ice sheet during all of the four eruptions shown in Fig. 4 (e.g. Hughes et al. 2016; Stroeven et al. 2016).
Fig. 4, p.9:

Comment: The known distribution of the Vedde ash is vastly underestimated as it is also found across Arctic Russia and into the Polar Ural Mountains (Haflidasson et al. 2019) and on Svalbard (Farnsworth et al. 2022).

Refs:

Bakke, J., Dahl, S. O., Paasche, Ø., Løvlie, R., & Nesje, A. (2005). Glacier fluctuations, equilibrium-line altitudes and palaeoclimate in Lyngen, northern Norway, during the Lateglacial and Holocene. The Holocene, 15(4), 518–540. https://doi.org/10.1191/0959683605hl815rp
Farnsworth, W. R., Ingólfsson, Ó., Mannerfelt, E. S., Kalliokoski, M. H., Guðmundsdóttir, E. R., Retelle, M., Allaart, L., Brynjólfsson, S., Furze, M. F. A., Hancock, H. J., Kjær, K. H., Pieńkowski, A. J., & Schomacker, A. (2022). Vedde Ash constrains Younger Dryas glacier re-advance and rapid glacio-isostatic rebound on Svalbard. Quaternary Science Advances, 5(June 2021), 100041. https://doi.org/10.1016/j.qsa.2021.100041
Haflidason, H., Regnéll, C., Pyne‐O’Donnell, S., & Svendsen, J. I. (2019). Extending the known distribution of the Vedde Ash into Siberia: occurrence in lake sediments from the Timan Ridge and the Ural Mountains, northern Russia. Boreas, 48(2), 444–451. https://doi.org/10.1111/bor.12354
Hughes, A. L. C., Gyllencreutz, R., Lohne, Ø. S., Mangerud, J., & Svendsen, J. I. (2016). The last Eurasian ice sheets – a chronological database and time‐slice reconstruction, DATED‐1. Boreas, 45(1), 1–45. https://doi.org/10.1111/bor.12142
Labuhn, I., Hammarlund, D., Chapron, E., Czymzik, M., Dumoulin, J.-P., Nilsson, A., Régnier, E., Robygd, J., & von Grafenstein, U. (2018). Holocene Hydroclimate Variability in Central Scandinavia Inferred from Flood Layers in Contourite Drift Deposits in Lake Storsjön. Quaternary, 1(1), 2. https://doi.org/10.3390/quat1010002
Stroeven, A. P., Hättestrand, C., Kleman, J., Heyman, J., Fabel, D., Fredin, O., Goodfellow, B. W., Harbor, J. M., Jansen, J. D., Olsen, L., Caffee, M. W., Fink, D., Lundqvist, J., Rosqvist, G. C., Strömberg, B., & Jansson, K. N. (2016). Deglaciation of Fennoscandia. Quaternary Science Reviews, 147, 91–121. https://doi.org/10.1016/j.quascirev.2015.09.016
Sinceraly,

Carl Regnéll

Citation: https://doi.org/10.5194/essd-2023-154-CC1
- AC1: 'Reply on CC1', Anna Beckett, 15 Sep 2023
  
  We would like to thank Carl Regnéll for the constructive feedback. We copied all comments in to the document attached, numbered them in order of appearance (CC1-1 to CC1-4) and provided a response accordingly. We hope to have addressed all concerns and improved the manuscript according to the suggestions.
  
  Citation: https://doi.org/10.5194/essd-2023-154-AC1
RC1:
'Comment on essd-2023-154', Anonymous Referee #1, 17 Jul 2023

General comments:
The manuscript “Tephra data from…” by Beckett et al., 2023 aims at assembling a dataset of tephra layers found in (varved) European lake records during the time interval 25 ka BP to 8 ka BP. This is a valuable approach, as tephra layers can be excellent isochronous marker horizons within sedimentary records, which can be utilized to improve chronologies and to enable inter-site paleoenvironmental comparisons. Since record specific tephra datasets are most commonly published in individual publications, combining published results in a database can foster data accessibility and reusability.
In the present form, it is not clear if this contribution reports on a novel modification/extension of the existing database VARDA or if the presented results are a summary of a VARDA database query. Comparing the structure of VARDA presented in Ramisch et al., 2020 with the actual database website and with the information given about data collection within the manuscripts, some fields (geochemistry) may have been added. However in the manuscripts it is also stated, that this is beyond the scope of this paper. Therefore, I strongly suggest to stress clearly, what is a new or has been modified and what is just a summary of a database query.
It is stated that the project focuses on varved records, but for the integrity of a robust tephra-dataset it is extremely important to consider also data of non-varved records. Important information about the age and glass geochemical composition, which are needed for correct correlations and precise chronologies, may come from such non-varved records and thus would be not considered otherwise. The authors already have partially identified this issue, including data from Lake Ohrid/Prespa, although their non-varved character is not consequently reported (see also community comment, as this seems to be the case for other records). However, the approach stills appears incomplete. As the manuscript is reported to be the initial phase, setting the basis for an overarching project, this needs to be considered in depth for the overall long-term project aim to construct global frameworks.
With regard to the compiled dataset of tephra layers, there is no discussion about the quality of the data collected (quality of geochemical analyses, ages). Even if the authors state that the best age of a tephra/eruption may be a subjective feature, the general quality of available ages could be addressed, as in the end for the application of tephrochronology a single age is needed to unify and align chronologies and their records (and it was done in Figure 4).
Specific comments:
Title: Consider rephrasing as with the focus set to European volcanism and varved lakes, the dataset collection rather reports on a regional than a global tephra framework. Also, there is no discussion about existing ages, so that chronologies were not improved yet.
Abstract:
Consider rephrasing with regard to point out if this contribution represents modification or a query of the VARDA database.
Please check the given numbers about records and tephra layers. Not all 19 records represent varved records, further Figure 3 shows more than 49 tephra layers…
Introduction:
Figure 1 is not crucially needed with respect to the dataset compiled.
Methods:
It appears that only records registered within VARDA were considered, which may be insufficient to present a full list of (varved) records. Using only data given in VARDA strongly depends on data quality, maintenance and update of this database. This is not discussed within the manuscript. For example, for the Lake Ohrid tephra data the latest results 2019-2023 are not included in VARDA (and were potentially also missed by the google scholar search). Therefore, to provide a reasonable and critical review of existing data to compile a dataset about tephra layers of the LGIT, there should be not only one database considered, but also additional non-database listed references included to ensure completeness and quality of the presented data.
I would suggest rephrasing of the data collection paragraph in order to point out, how VARDA was modified (see general comment).
For the new data fields, there are some fields listed in the supplementary data (such as data_availability, datset, lake, geochemistry_availability), which are not given in the tables of the manuscript. There are also only major element data fields (Table 1), whereas also trace element data is given in the attached dataset. For Table 2: What about adding a field for importing uncalibrated radiocarbon ages in order to simplify recalibration of radiocarbon ages using the same IntCal curve. Please consider adding the information based on which calibration curve the age was calibrated.
Further, for the tables presented I would consider avoiding colour coding of mandatory and optional fields in order to make figures accessible to readers with colour-blindness.
Results:
Referring to the community comment, I also welcome the provided original references of the compiled individual datasets. Please check if your list of references (p.6) is complete and includes latest references (and the consequences for Figure 3).
Based on the tephra correlations presented in Figure 3, eight of them are reported within the focussed time-interval. Consider if it is applicable to report on the different geochemical results of these eight (everywhere the same composition, variations?) and about their potential ages, findings may also be picked up in the implications section.
Figure 3: Is it necessary to report tephra layers well beyond this interval? Otherwise, I would suggest highlighting the focussed time-interval.
Implications:
I like the idea of comparing the known distribution of an ash cloud with the location of available records to identify potential new targets for (crypto)-tephra investigations. Please specify how the list of (7) new locations was compiled. Maybe it is worthwhile to consider a function for VARDA to report also non-successful cryptotephra investigations, which did not yield any (crypto-)tephra findings. Also these (negative) findings may help to improve knowledge about ash distribution, but also avoid unnecessary investigations by others.

Citation: https://doi.org/10.5194/essd-2023-154-RC1
- AC2: 'Reply on RC1', Anna Beckett, 15 Sep 2023
  
  We are very grateful to Reviewer #2 for the constructive and thorough review that has helped us to improve the manuscript. We copied all comments into the attached document, numbered them in order of appearance (RC1-1 to RC1-15) and provided a response accordingly.
  
  Citation: https://doi.org/10.5194/essd-2023-154-AC2
RC2:
'Comment on essd-2023-154', Christine Lane, 25 Jul 2023

Beckett et al. report on the addition of information about the occurrence and geochemical compositions of tephra layers within European varve sequences reported in the Varve Database (VARDA). Tephra layers offer the potential to connect varve chronologies at single moments in time with the potential to compare and transfer differential and absolute dating information between sites and increase overall dating precision by replication. The authors state the aim to incorporate information from tephra in varves globally over the coming 5 years, as well as increase the window of time for which data is included. The reasoning for the addition of tephra information is well presented in the manuscript, although as VARDA already includes relevant palaeo proxy datasets for many sites, it is unclear why this particular “proxy” requires a stand-alone publication. The addition of the “event” layer bar in the GICC05 panel of the VARDA home page is a useful tool for quick reference however, and perhaps as the database grows it will be able to provide a useful online reconnaissance tool for project design and field site selection.
Whilst this paper addresses the inclusion of tephra data, I found myself browsing VARDA more generally and found myself confused by the inclusion of many non-varved lakes (I’ll just note some of the ones I am familiar with as I have worked on them: Lake Victoria, Lake Tanganyika, Lake Bled). I felt a clearer description of the VARDA database itself was probably needed to make sense of the datasets entered to date.
My comments here are organised under the headings indicated by the ESSD Review guidelines, followed by some minor editorial notes.
1. Significance
This particular compilation of tephra layers reported in varve sequences in Europe is unique in that draws together commonalities in the records and could be a great time-saver in looking up sites and articles. Highlighting the value of tephra layers to varve researchers is also beneficial. Additional value could be achieved by including specific and relevant search tools, such as those from the RESET database (Bronk Ramsey et al., 2015) that are used within the article to show the connectivity between records using tephra layers and maps (e.g. KDE) of the sites where tephra layers have been reported. The RESET database is problematic as it is no longer maintained, but in terms of a tephra data repository it is more complete and contains critical data missing from the VARDA database as presented (see comments under Data Quality). The VARDA team might be better to find a means to connect VARDA with that database, rather than starting again to record all of the published tephra layers in Europe within a new repository.
One note that caught my attention was a sentence in the conclusions about the opportunity to explore machine learning approaches to tephra compositional analyses. As there is no mention of this in the body of the paper, it needs further exploration and justification. If there are additional novel tools being created that could really add to the uniqueness and usefulness of the growing compilation.
2. Data Quality
Data in VARDA is easily searched and clearly presented and downloadable. I applaud the inclusion of EPMA analytical conditions but I cannot understand the exclusion of secondary standard data, which is critical to evaluating whether one can compare to another tephra dataset or not. The authors referred more than once in the manuscript (e.g. within Table 2 that sets out mandatory and optional criteria for metadata) to the inclusion of “Standards used for analytical calibration, e.g. Lipari Obsidian”. Two types of standards are used in EPMA work and there seems to be confusion here. Primary standards are usually a suite of minerals or oxides with known elemental compositions, which are used to calibrate the instrument. The publication of primary standard data is not conventional, as what matters is that the data is accurate, not which minerals were used for which elements. Secondary standards are materials of known composition that are analysed before, during and after a run of analyses on an unknown sample, in order to demonstrate the accuracy and precision of the calibration. These are usually matrix-matched to the material being analysed, so the Lipari Obsidian, for example, is a commonly used secondary standard for the analysis of volcanic glass. The tephrochronology community has long called for the inclusion of secondary standard analyses alongside ALL tephra compositional datasets, so that the data may be trusted to make comparisons between tephra datasets generated at different times and on different instruments (e.g. Hunt and Hill., 1996; Kuehn et al., 2011; Wallace et al., 2022). At present, I couldn’t find any secondary standard data within the VARDA database, which means that if I were to use it to trace tephra layers, I would immediately have to open the original article and extract the data from there, rather than from VARDA. Those less conscientious might unintentionally propagate poor data and miscorrelations. I strongly recommend that the database authors amend the database to include either i. a clear statement that *only* data with secondary standards within 2 standard deviations of published assays are included in the database (a lot of work for data stewards), or, ii. secondary standard analyses for all tephra datasets, alongside a link to published assays.
In addition, reviewing the criteria for recording tephra geochemical data, I would recommend that data type (e.g. single grain, whole rock) and material (e.g. glass shards, mineral, pumice) are added as essential criteria. This is also essential metadata for ensuring like is being compared with like and whilst most data will be single-grain glass shard analyses, it should not be a given.
3. Presentation
The article and the database are clearly presented and easily accessible. No issues here at all.
4. Minor editorial notes
Title: I would focus here on European and LGIT tephra data in varve records as the potential and value of a global inventory isn’t obvious from the article and data at this stage.
Abstract: There is inconsistent use of capitalisation and hyphenation in “last Glacial-Interglacial transition” between the paper title and the abstract that needs correcting one way or the other.
Introduction, Line 39: the term “well defined” needs explaining.
Methods, Line 73 and 98/99: References to standards used for calibration, rather than secondary standards, needs correcting.
Figure 2 and 3: Bled, Ohrid and Prespa (at least) are not varved and their inclusion needs an explanation. If non-varved lakes are included, then what do we get from VARDA that is unique? There are asterisks noting that Ohrid and Prespa are non-varved in Fig 3, but not Bled. Other sites I am less familiar with.
Results, lines 126 and 133: The Mediterranean does not describe a volcanic region and it would be better to define to at least Italian and Hellenic Arc, if not specific volcanic fields.
Line 151: I would replace “tephra plume” with “tephra fallout area” to avoid any indication that the sites studied faithfuly capture the plume dispersal of an eruption. This is especially pertinent given that within the screen shot of Askja-S sites, Iceland (therefore the volcano) is not included in the shaded envelope.

References used:
Ramsey, Christopher Bronk, Rupert A. Housley, Christine S. Lane, Victoria C. Smith, and A. Mark Pollard. "The RESET tephra database and associated analytical tools." Quaternary Science Reviews 118 (2015): 33-47.
Hunt, John B., and Peter G. Hill. "An inter-laboratory comparison of the electron probe microanalysis of glass geochemistry." Quaternary International 34 (1996): 229-241.
Kuehn, Stephen C., Duane G. Froese, Phil AR Shane, and INTAV Intercomparison Participants. "The INTAV intercomparison of electron-beam microanalysis of glass by tephrochronology laboratories: results and recommendations." Quaternary International 246, no. 1-2 (2011): 19-47.
Wallace, Kristi L., Marcus I. Bursik, Stephen Kuehn, Andrei V. Kurbatov, Peter Abbott, Costanza Bonadonna, Katharine Cashman et al. "Community established best practice recommendations for tephra studies—from collection through analysis." Scientific data 9, no. 1 (2022): 447.

Citation: https://doi.org/10.5194/essd-2023-154-RC2
- AC3: 'Reply on RC2', Anna Beckett, 15 Sep 2023
  
  We appreciate the clear and constructive review by Christine Lane. Many points have been incorporated in our revised version of the manuscript or will be taken on board for future iterations of the dataset (see responses to individual comments attached). We copied all comments into the document attached, numbered them in order of appearance (RC2-1 to RC2-12) and provided a response accordingly.
  
  Citation: https://doi.org/10.5194/essd-2023-154-AC3
CC2:
'Comment on essd-2023-154', Stefan Wastegård, 03 Aug 2023

Dear Authors,
I have a few comments in addition to the other comments, which I all agree to.
I am not familiar with the VARDA database, but I question your decision to include Aspevatnet (not varved) and L. Storsjön (not Storsjom) as potential varve sites for the LGIT. Storsjön was under the Fennoscandian Ice Sheet during most of the LGIT and it would be better to mention south Sweden as a potential area for tephras in glacial varves, as in MacLeod et al (2014) and Devine (2020, PhD thesis).
Tephra distribution maps should be updated (see also comment by Carl Regnell). I don't fully understand how Kernel maps are constructed, but e.g. Laacher See Tephra has not been found in Latvia, and Vedde Ash and Askja-S not in FInland (not so far, anyway). I think that the maps are misleading and should inlcude all known sites, not only sites in the RESET database.
Some older references are missing, e.g. Merkt et al. (1993; Boreas) who found Saksunarvatn in four sites in north Germany, of which at least one sequence was varved. This paper could also be cited as an example of improved techniques for cryptotephra extraction along with Blockley et al. (2005) and Walsh et al. (2021). The manuscript has a focus on European deposits, which is understandable, but I think that you should cite the "classic" varve/tephra paper by Stihler et al. (1992; Geology) in the introduction.
Small comment: Zillen should be Zillén consistently

Citation: https://doi.org/10.5194/essd-2023-154-CC2
- AC4: 'Reply on CC2', Anna Beckett, 15 Sep 2023
  
  Our thanks extend to Stefan Wastegård for the constructive feedback. All comments were addressed in the document attached where we have numbered them in order of appearance (CC2-1 to CC2-4). We hope to have addressed all concerns and improved the manuscript according to the suggestions.
  
  Citation: https://doi.org/10.5194/essd-2023-154-AC4
AC5: 'Comment on essd-2023-154', Anna Beckett, 15 Sep 2023

We thank the reviewers for their comments, and those who provided community comments too. We will respond to all comments individually but there are some general points mentioned in multiple comments that we would like to address, here labelled as General Responses 1 to 3 (GR-1 - GR-3).
GR-1: There is some confusion as to the purpose of this work; this work is an addition to the Varved Sediments Database (VARDA) as opposed to a data compilation exercise using the database. This was not made clear within the text and in the revised manuscript we now explicitly state that this data is a new addition to VARDA (Lines 15, 18, 60, 74).
GR-2: The Kernel Density Estimate plots are not meant to be a comprehensive overview of all known findings of the tephra layers, instead they are intended for use as a statistical and schematic diagram to highlight the future potential to better synchronise varve chronologies using tephra layers. We hope that further clarification in the caption of Figure 4 addresses this issue.
GR-3: The inclusion of tephra data into VARDA is not intended to be used as a new database for tephrochronologists; we aim that the inclusion of tephra data enables varve chronologists to better synchronise varve chronologies to an absolute timescale using tephra as an isochronous marker horizon.

On behalf of all authors,
Anna Beckett

Citation: https://doi.org/10.5194/essd-2023-154-AC5

Anna Beckett et al.

Data sets

Major Element and Trace Element Compositions of Tephra Layers Found in European Varved Lake Records Anna Beckett, Cecile Blanchet, Alexander Brauser, Rebecca Kearney, Celia Martin-Puertas, Ian Matthews, Konstantin Mittelbach, Adrian Palmer, Arne Ramisch, Achim Brauer https://doi.org/10.5880/fidgeo.2023.015

Anna Beckett et al.

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Short summary

This paper focuses on volcanic ash (Tephra) in European annually laminated (varve) lake records spanning the period 25 ka BP to 8 ka BP. Tephra enables the synchronisation of these lake records to absolute timescales. The data incorporates geochemical data from 49 individual known tephra layers across 19 varve lake records. We highlight the potential for synchronising multiple records using just one tephra layer across continental scales whilst supporting reproducibility through accessible data.


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