Review of paper titled “A worldwide meta-analysis (1977–2020) of sediment core dating using fallout radionuclides including ¹³⁷Cs and ²¹⁰Pbxs” by Foucher et al.

General comment: reject

Comments:

  Based on the compilation of 573 articles published between 1977 and 2020, reporting the collection of 1351 individual dating sediment cores, this review documents the occurrence of three main sources of ¹³⁷Cs that are the most widely detected in sediment cores (the thermonuclear bomb testing peak in 1963, the Chernobyl accident in 1986, the Fukushima accident in 2011), as well as 24 additional local releases of ¹³⁷Cs. The correct attribution of these sources may improve the chronology of surface sediment. Furthermore, this review also highlights the low proportion in the Southern Hemisphere, compared to what has been published for the Northern Hemisphere, and outlines the necessity to use additional tools (e.g., ²⁴⁰Pu/²³⁹Pu isotopic ratios) to provide an unambiguous distinction between potential sources and avoid any dating errors.

While this worldwide meta-analysis of ¹³⁷Cs will be of interest to those studying of dating surface sediment cores in Environmental and Earth sciences, this review represents fairly superficial and does not present significantly new ideas. Two major flaws, to be illustrated further below, exist in the current version: 1. More articles using ¹³⁷Cs for dating surface sediment cores should be included in this review. 2. The potential influence of Chernobyl accident, Chinese Nuclear Tests and Fukushima accident is highly overestimated. For these and other reasons, listed below, I do not recommend publication in the prestigious journal of Earth System Science Data. I provide my comments below:

1. As this manuscript is classified as Review Article, the current content does not justify its publication in Earth System Science Data. Although the search words of “¹³⁷Cs” and “sediment core” were used in Web of Science (WOS) and a total of 573 articles (or 910 publications) were found, a large number of studies for paleoclimate which was established the chronology based on ¹³⁷Cs, have not been included in this review. For example, Lake Sugan (Wu et al., 2010, EST, doi: 10.1021/es9029649), Lake Bosten (Liao et al., 2014, EST, doi: 10.1021/es405364m), Lake Sayram (Lan et al., 2019, Science China, doi:10.1007/s11430-018-9240-x), … in northwestern China (as cited by Lan et al., 2020, QSR, doi: 10.1016/j.quascirev.2020.106413). Well, I believe this review is also not a comprehensive study in other regions. So, this review manuscript is not sufficient for the worldwide meta-analysis of ¹³⁷Cs and I suggest the search word of this study in WOS includes the paleoclimate or paleoenvironment as well as late Holocene.
2. The potential influence of Chernobyl accident, Chinese Nuclear Tests (CNT) and Fukushima accident is highly overestimated in this manuscript. Based on the potential influence of radioactivity transport from the Chernobyl accident and Chinese Nuclear Tests, and the comparison with deposition records of 26 European lake sediments and 5 Alpine ice cores, Lan et al (2020, QSR, doi: 10.1016/j.quascirev.2020.106413) propose that the ¹³⁷Cs fallout maximum of lake sediments in NW China and central Asia is primarily attributable to the global atmospheric thermonuclear weapon tests in 1963-1964 and that there is no unambiguous evidence to confirm the Chernobyl- and CNT-derived ¹³⁷Cs local-fallout subpeaks. The evidence of references at Line 315-327, which is associated with Chernobyl- and CNT-derived ¹³⁷Cs, is insufficient. Accordingly, ¹³⁷Cs of lake sediments in southern and eastern China should also cannot record the Chernobyl- and CNT-derived ¹³⁷Cs local-fallout subpeaks. As suggested by authors, ²⁴⁰Pu/²³⁹Pu ratios should be a good candidate to achieve this type of discrimination. Frankly, Wu et al (2010, EST, doi: 10.1021/es9029649) and Liao et al (2014, EST, doi: 10.1021/es405364m) have conducted the ²⁴⁰Pu/²³⁹Pu ratios in lake sediments of northern China and have a similar idea with Lan et al (2020, QSR, doi: 10.1016/j.quascirev.2020.106413).

 Furthermore, as suggested by authors, the attribution of ¹³⁷Cs peaks to Chernobyl and Fukushima in Mexico and Ghana should be taken with great caution in view of the observations made in this manuscript (Fig. 4c).

Specific comments/suggestions:

1. Line 2: ²¹⁰Pb_xs in Title should change to ²¹⁰Pb.
2. Line 20-21: the others information need not shown in Abstract.
3. Line 49-50: this sentence should be cited more representative references.
4. Line 110-111: should explain how to corrected to 1 Jan 2020.
5. Line 193-196: Fig. 4 does not show the average activity.
6. Line 203: as suggested as aforementioned, the Chernobyl sign in China is incorrect.
7. Line 246-248: check this sentence.
8. Line 280: the ²⁴⁰Pu/²³⁹Pu ratio is much better than Plutonium.
9. Line 316-327: rewrite this paragraph. Yunnan Province is located in southwestern China not southeastern China.

As replied by the authors, if the revised manuscript will fully discuss the reasons for the discrepancies of the different original ¹³⁷Cs and will contain other relevance to this topic, the reviewer recommends to a major revision for this manuscript.

The authors present a manuscript titled "A worldwide meta-analysis (1977-2020) of sediment core dating using fallout radionuclides including 137Cs and 210Pbxs". The aim of the manuscipt is to do a review to sediment core dating by using radionuclides. The authors have also uploaded a comprehensive data set to open source platform. I think the work is of interest and is of use to scientific community. The English used in this manuscript is at good level and the narrative proceeds in logical manor. I think is ready for publication after minor revision.

Here are some comments in more detail

- Generally, try to use past tense in the manuscript instead of present tense

- The Chinese nuclear weaposn test are referred here as "local releases". I find this term controversial since the Chinese tests were detected in aerosols in the other side of the world and Cs-137 originating from the Chinese test have been detected in Scandinavia which is practically on the other side of the globe.

- The authors used one database and two search words in their data aquisition. I am bit doubtful that this provided the best result although the result consisted of 573 articles, Especially some studies utilizing Pb-210 as the main nuclide may have been missed.

- Section 3.3. I am bit concerned if this section actually deals with excess or unsupported fraction of the Pb-210 ? It is not clearly mentioned how the supported and unsupported fractions were distinquished ? In section 3.4. the isotopes needed to determine the supported fraction. namely Ra-226 and it's daughters, are observed in very rare cases.

- Section 4.1.  what is menat by post-accidental fallout ? Isn't all the fallout post-accidental ie, deposited after the accident

line 364: which isotopic evidences you are referring to ?

line 369: A similar findings was made...

line 400: reusable format ? what does this mean ?

line 413: "complementary tracers" what tracers are you referring to ? Please provide and example.