Large-scale climate signals of a European oxygen isotope network from tree rings

Balting, Daniel F.; Ionita, Monica; Wegmann, Martin; Helle, Gerhard; Schleser, Gerhard H.; Rimbu, Norel; Freund, Mandy B.; Heinrich, Ingo; Caldarescu, Diana; Lohmann, Gerrit

doi:https://doi.org/10.5194/cp-17-1005-2021

Articles | Volume 17, issue 3

https://doi.org/10.5194/cp-17-1005-2021

© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/cp-17-1005-2021

© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 17, issue 3

Research article

|

07 May 2021

Research article |

| 07 May 2021

Large-scale climate signals of a European oxygen isotope network from tree rings

Daniel F. Balting, Monica Ionita, Martin Wegmann, Gerhard Helle, Gerhard H. Schleser, Norel Rimbu, Mandy B. Freund, Ingo Heinrich, Diana Caldarescu, and Gerrit Lohmann

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Final revised paper (published on 07 May 2021)
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Preprint (discussion started on 30 Mar 2020)
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Interactive discussion

Status: closed

AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment

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RC1: 'Review of Balting et al. ‘Large scale climate signals of a European oxygen isotope network from tree-rings - predominantly caused by ENSO teleconnections?’', Anonymous Referee #1, 05 Aug 2020
- AC1: 'Reply to Reviewer 1', Daniel Balting, 22 Sep 2020
RC2: 'Review of Large scale climate signals of a European oxygen isotope network from tree-rings - predominantly caused by ENSO teleconnections?', Anonymous Referee #2, 18 Aug 2020
- AC2: 'Reply to Reviewer 2', Daniel Balting, 22 Sep 2020

Peer-review completion

AR: Author's response | RR: Referee report | ED: Editor decision

ED: Reconsider after major revisions (12 Oct 2020) by Julie Loisel

AR by Daniel Balting on behalf of the Authors (04 Dec 2020) Author's response Manuscript

ED: Referee Nomination & Report Request started (22 Dec 2020) by Julie Loisel

RR by Anonymous Referee #2 (26 Jan 2021)

Suggestions for revision or reasons for rejection

Review 2:

The authors improved the manuscript but still some issues remain:

1. EOF Analysis: Please check e.g. https://atmos.washington.edu/~dennis/552_Notes_4.pdf or other publications, text books etc: The empirical orthogonal function (EOF) analysis decomposes a data set in terms of orthogonal basis functions which are determined from the data. The term EOF analysis is also interchangeable with the geographically weighted PCA (principal component analysis). From reading the answer to reviewer 1 I get the impression that the lead author does not fully understand what the EOF (PCA) analysis is. May there are some typos in the formula presented.

2. A clear discussion of the former major comment 2 is missing in the manuscript: The authors need to say that a signal recorded by the trees can originate from different source regions during different seasons and that this can have strong implications in the interpretation of the proxies used. To make a simple example. You have a yearly value of delta18O and we just look at one year. The Value is obtained be a mixture of seasonal signals. In Europe the winter circulation and summer circulation deviate dramatically. So you can think of a multitude of combinations between a certain winter circulation (e.g. strong NAO leading to moisture transport from the Atlantic) and a predominant southwesterly flow leading to transport from the Mediterranean. So, your proxy is mixing both signals and I doubt that it is possible with one proxy to say something about this specific circulation of that at least the authors need to discuss the problems related with delta18O from trees.

3. The authors still not mention the problem related to pooling versus not pooling trees to measure delta18O. Please discuss this issue when introducing the data and also in the discussion section, see Hangartner et al. 2012 Methods to merge overlapping tree-ring isotope series to generate multi-centennial chronologies.

4. I disagree with the answers made to mayor comment 3. In winter you find as leading mode diploe structures over Europe. Furthermore, the authors state “The ENSO anomalies (either El Niño or La Niña) develop in winter and it needs 3-6 months to see a signal in the European climate. This lagged relationship is typical for many ENSO related teleconnections. This long transition from the tropical Pacific to central North Atlantic affects in turn the large-scale atmospheric circulation and as a consequence the climate over Europe, especially in spring and summer.”. Again an effect on the large scale atmospheric circulation is not necessary as with an unchanged atmospheric circulation over the Atlantic the warming induced by ENSO you change the delta18O at the source region and then transport it to Europe. So I suggest that the authors shall be more careful in the interpretation of the data. They only show statistical relations ships (not causal ones) and sometimes they are rather weak.

5. The 20CR reanalysis is not described. It remains unclear what they use (ensemble mean or individual member, I guess it is the ensemble mean) I strongly recommend to use the individual ensemble members in this analysis so that the authors can assess the uncertainty of their results related to the uncertainty of the reanalysis product.

6. How does Figure 7 look like for PC2? In section 4.5, you interpret it as a pure summer signal, so the question is if they confirm it with a similar analysis.

7. Extremes: It is just a wording issue but I think the 33% of the data are not an adequate definition to be extreme. (see also my previous comment).

8. Specific comments:
Around L60: please discuss in 1-2 sentences the nonlinearty of the ENSO response presented in the existing literature.
L104: If you only use the 12 times series in your analysis – will you get similar results for the period 1850 to 1998 when using all data sets? If yes this would be good if not, e.g., the correlation is as weak as for the period 1600-1850 then the “non-stationarity” of the ENSO signal over time is just due the fact that you include more data after 1850.
L110,L114: The wording “we want to” is weird.
L121 and elsewhere: The authors mix using different tense - here, they suddenly sue simple perfect. Please correct the entire manuscript.
L204. Please remove “Discussion” as this is now a separate section.
Section 3.4 I think this is more a evaluation of the data so should be mentioned earlier. (Just a suggestion)
L314: You did not show droughts, so just write dry conditions.
Section 4.1 Discuss Hangartner et al 2012 here.
L340 is influencing –> influences
L357: is getting -> gets
L361 Please say how the teleconnection have changed in the publications Rimbu and Felis
L384: “However as discussion above” reads bad.
Fig 4,5,6: exchange column and row.

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RR by Anonymous Referee #3 (18 Feb 2021)

ED: Publish subject to minor revisions (review by editor) (05 Mar 2021) by Julie Loisel

AR by Daniel Balting on behalf of the Authors (18 Mar 2021) Author's response Author's tracked changes Manuscript

ED: Publish as is (23 Mar 2021) by Julie Loisel

AR by Daniel Balting on behalf of the Authors (24 Mar 2021)

Short summary

To extend climate information back in time, we investigate the climate sensitivity of a δ¹⁸O network from tree rings, consisting of 26 European sites and covering the last 400 years. Our results suggest that the δ¹⁸O variability is associated with large-scale anomaly patterns that resemble those observed for the El Niño–Southern Oscillation. We conclude that the investigation of large-scale climate signals far beyond instrumental records can be done with a δ¹⁸O network derived from tree rings.