Dear ESSD editorial team, dear authors,

Thank you for asking my opinion on this nice dataset contribution. I enjoyed reading about these detailed monitoring experiments which are highly useful to the sclerochronology community. Please find my minor comments below.

General comments

In their submission, the authors present and discuss a dataset containing oceanographic and geochemical measurements carried out in the Bay of Brest between January-March and October-December (depending on the parameter) during a monitoring experiment. The goal of this monitoring is to provide data on environmental variables that may influence the calcification and shell composition of marine mollusks (specifically the scallop pecten maximus). Mollusk shells are important archives of short-term (days to seasons) chemical and oceanographic variability in the shallow marine environment, and measurements in scallop shells that grew under known environmental conditions are instrumental in decoding these shell archives. In fact, several of the authors of this contribution have already demonstrated the value of these monitored growth experiments for developing scallop shells as archives for environmental change (e.g. (Chauvaud et al., 2011; Thébault et al., 2022; Fröhlich et al., 2022).

Reconstructions of primary productivity are among the most promising recent applications for these shell records, and recently developed productivity proxies show great potential to record this elusive but highly important component of the shallow marine environment. Therefore, this dataset will be of great value to the sclerochronology community, and this contribution is very timely given the renewed interest in mollusk shell geochemistry in the past years. The fact that the authors present it together with data from the scallop shells helps to show the utility of this monitoring data. In summary, I am glad to see this important work done and highly recommend publication of this data manuscript. My suggestions below will hopefully help the authors to slightly improve their manuscript, which already reads very well.

Specific comments

The monitoring and sampling strategies described by the authors are impressive. They collected a wide array of parameters in the Bay of Brest and deployed a stunning number (over 2500!) of P. maximus specimens in their study area. The material the consortium can obtain from these shells and which can be directly linked to in situ monitoring can feed academic studies for years to come.

The only downside of this dataset I can think of is that only one year of measurements is available. Based on the presented work, I am not sure if the authors aim to keep this monitoring in place for an extended period. If so, perhaps they can mention this in the text to show the reader that this dataset is a growing product. The downside of limiting the dataset to one year/season would be that many of the environmental variables in the region might show inter-annual variability, so the 2021 growth season may not be representative of the seasonal variability at the site. In addition, there will be differences in growth rate and perhaps in vital effects that affect the chemistry of mollusk shells between years and through their ontogenetic development. As it stands, the presented dataset cannot be used to test for this since all scallops included in the growth experiments are from the same cohort (age group) so have (approximately) the same age and are only followed for one year. These caveats make the conclusions drawn from the shell-environment comparison using the presented dataset limited in terms of their application to understand the growth and composition of “wild” scallop (and other mollusk) shells. That said, I understand that producing a dataset like this involves a lot of work, and even having this data for one growing season is a very important contribution to the field.

The authors describe the methodology of their monitoring in sufficient detail and, as far as I can judge, this sampling protocol is suitable for producing data of sufficient quality to make the comparison between environment and shell chemistry which is the main aim of the monitoring study. The authors did well to assemble a large consortium of researchers with the expertise to carry out these diverse types of measurements and bring together this multi-disciplinary dataset.

I find the differences in trace element concentrations between surface and bottom waters (lines 165-184) especially interesting since this difference is highly relevant for the interpretation of trace element records in mollusk shells, an active area of study.

In the section on geochemical analyses on the shells (lines 265-294) only Ba/Ca is discussed. To highlight the versatility of this method to produce multiple trace element (e.g. (Thébault et al., 2022)), I would highly recommend the authors to also briefly present additional trace element records to highlight the versatility of this dataset. I understand that Ba/Ca is probably the most relevant ratio for productivity work (the main aim of this contribution), but it would be highly interesting to the community to see the outcomes of trace elemental concentration measurements in the shells that show overlap with the list of trace elements that is measured in the water (see lines 165-184). To be clear: I am not suggesting the authors discuss every trace element ratio in as much detail as they do for Ba/Ca, but just to show a brief overview of the concentrations measured in the water and in the shells and their variability. Perhaps the authors can provide some boxplots summarizing this data.

Technical corrections

Line 207: “episodes” here should probably read “episode” (singular)

Line 267: “slabe” should read “slabs” I think

Kind regards,

Niels de Winter

References

Chauvaud, L., Thébault, J., Clavier, J., Lorrain, A., and Strand, Ø.: What’s Hiding Behind Ontogenetic δ13C Variations in Mollusk Shells? New Insights from the Great Scallop (Pecten maximus), Estuaries and Coasts, 34, 211–220, https://doi.org/10.1007/s12237-010-9267-4, 2011.

Fröhlich, L., Siebert, V., Walliser, E. O., Thébault, J., Jochum, K. P., Chauvaud, L., and Schöne, B. R.: Ba/Ca profiles in shells of Pecten maximus – A proxy for specific primary producers rather than bulk phytoplankton, Chemical Geology, 593, 120743, https://doi.org/10.1016/j.chemgeo.2022.120743, 2022.

Thébault, J., Jolivet, A., Waeles, M., Tabouret, H., Sabarot, S., Pécheyran, C., Leynaert, A., Jochum, K. P., Schöne, B. R., Fröhlich, L., Siebert, V., Amice, E., and Chauvaud, L.: Scallop shells as geochemical archives of phytoplankton-related ecological processes in a temperate coastal ecosystem, Limnology and Oceanography, 67, 187–202, https://doi.org/10.1002/lno.11985, 2022.

This article provides a description of the methods used to obtain a large and diverse body of information on water column and bivalve-shell chemistry, an overview of the information itself, and some analysis and interpretation of the data. The methods used are ‘state of the art’, and the data new and valuable. I was able to access the raw results at the website indicated. They appear to be complete and are fully usable, apart from the fact that I had to change the format of the ‘time’ column (A) to reveal the contents - twice in the case of the Sambat probe data in order to obtain both date and hour information. The presentation is very good, but I have made numerous suggestions for minor improvements to achieve a final polish. These suggestions (‘technical corrections’) are made in the annotated version of the text supplied alongside these comments. Although they are not differentiated by use of a different colour or typeface, the suggested changes should be readily distinguishable from ‘remarks’ in the annotated text. I have not checked the references in detail but I identified one omission from a title (indicated) and noted that generic and specific names were not italicised. The references do therefore need at least some attention.

I think it is permissible that only some of the results provided at the website have been analysed and discussed in the text (for instance, only Ba of the various elements measured in shells). However, it appears from lines 5/6 that more results were obtained during the monitoring exercise than are represented at the website. This would violate the ‘Completeness’ criterion:

• Completeness: a data set or collection must not be split intentionally, for example, to increase the possible number of publications. It should contain all data that can be reviewed without unnecessary increase of workload and can be reused in another context by a reader.

This could well be a misreading by me, but if so a different form of words would be useful to prevent the same by others.