Metrological concepts applied to Total Alkalinity measurements in seawater: reference materials, inter-laboratory comparison and uncertainty budget

Capitaine, Gaëlle; Alliouane, Samir; Cariou, Thierry; Fin, Jonathan; Fisicaro, Paola; Wagener, Thibaut

doi:10.5194/os-22-75-2026

Articles | Volume 22, issue 1

https://doi.org/10.5194/os-22-75-2026

© Author(s) 2026. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/os-22-75-2026

© Author(s) 2026. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 22, issue 1

Research article

|

08 Jan 2026

Research article |

| 08 Jan 2026

Metrological concepts applied to Total Alkalinity measurements in seawater: reference materials, inter-laboratory comparison and uncertainty budget

Gaëlle Capitaine, Samir Alliouane, Thierry Cariou, Jonathan Fin, Paola Fisicaro, and Thibaut Wagener

Download

Final revised paper (published on 08 Jan 2026)
Preprint (discussion started on 08 Aug 2025)

Interactive discussion

Status: closed

RC1:
'Comment on egusphere-2025-3588', Anonymous Referee #1, 08 Oct 2025

The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2025/egusphere-2025-3588/egusphere-2025-3588-RC1-supplement.pdf

Citation: https://doi.org/10.5194/egusphere-2025-3588-RC1
- AC1: 'Reply on RC1', Gaëlle Capitaine, 07 Nov 2025
  
  Dear reviewer,
  We would like to greatly thank you for taking the time to review our manuscript, and giving us the opportunity to improve it thanks to your valuable comments and suggestions. We have carefully considered all your comments. You will find attached how we addressed them in the revised manuscript.
  Gaëlle Capitaine, on behalf of all co-authors
  
  Citation: https://doi.org/10.5194/egusphere-2025-3588-AC1
RC2:
'Comment on egusphere-2025-3588', Anonymous Referee #2, 11 Oct 2025

The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2025/egusphere-2025-3588/egusphere-2025-3588-RC2-supplement.pdf

Citation: https://doi.org/10.5194/egusphere-2025-3588-RC2
- AC2: 'Reply on RC2', Gaëlle Capitaine, 07 Nov 2025
  
  Dear reviewer,
  We would like to greatly thank you for taking the time to review our manuscript, and giving us the opportunity to improve it thanks to your valuable comments and suggestions. We have carefully considered all your comments. You will find below how we addressed them in the revised manuscript.
  Gaëlle Capitaine, on behalf of all co-authors
  
  Citation: https://doi.org/10.5194/egusphere-2025-3588-AC2

Peer review completion

AR – Author's response | RR – Referee report | ED – Editor decision | EF – Editorial file upload

AR by Gaëlle Capitaine on behalf of the Authors (07 Nov 2025) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (10 Nov 2025) by Mario Hoppema

RR by Anonymous Referee #2 (14 Nov 2025)

Suggestions for revision or reasons for rejection

The revised manuscript has been improved although I think the authors could do more to improve the presentation and clarity of the manuscript. There are still some typos and other errors which point to the need for the authors to carefully review their manuscript, as it is ultimately their responsibility to ensure the quality of the manuscript.

I think that the manuscript is mostly acceptable for publication pending minor corrections. I offer some comments below. I will leave it to the editor to decide if the authors have adequately addressed them.

Line 165: Instead of stating "using the materials and devices presented in Appendix B" and leaving the reader to search for this information in a supplementary section and losing their train of thought, it would be clearer to state, for example, "using the HCl standardized at SMU and a the Metrohm titration system as described in Appendix B."

Line 802: Metrohm is misspelled.

Line 567: "The precision of the method, 𝑠𝑅..." The authors did not address my previous comment here. They introduce a new notation 𝑠𝑅 that is not used in the other equations. (Equations 15 and 16 use sr for intra-laboratory standard deviation, which is different from sR.) The authors define sR as "precision...given by computation of sL and sr," but they don't describe exactly how sR is computed. Based on Table 5, it appears that sR is computed by summing sL and sr in quadrature (i.e., sR = sqrt(sL^2+sr^2) = 1.99 umol/kg as the authors report in the text).

Scientific notation: In various places in the manuscript, the authors have still left numeric values in E+XX notation rather than in scientific notation.

Fig 2 is a new addition in the revised manuscript. I would recommend including the results of Batch 1 on this graph so the stability of the two batches can be compared.

Expanded uncertainties and coverage factors: Although it is acceptable to report expanded uncertainties with a coverage factor of 2, it may not always represent a 95% level of confidence, depending on the effective degrees of freedom which was why I recommended the authors report this information. It can be included in the supplementary section. It may also be acceptable to state that the coverage factor of 2 corresponds approximately to a 95% level of confidence if this assumption is true for the authors' estimates.

Hide

RR by Anonymous Referee #1 (27 Nov 2025)

ED: Publish subject to minor revisions (review by editor) (10 Dec 2025) by Mario Hoppema

Dear Dr. Capitaine and co-authors,

Thank you for the revised submission of your manuscript. The two referees are generally satisified with the manucript and so am I. Your manuscript is almost ready for publication. They have given some final comments which I encourage you to take into account with the submission of the final manuscript files.
I have also listed some, mostly technical, comments which appear below.

Concentrations (or here called: amount contents) are given just in mol kg-1, i.e., without the addition sol, as per kg always refers to the solution. Please change at many places in the text

L22 … and interest of the reference materials ? I do not understand the term “interest” here. I think it can be deleted.
L24-25 What is k in k =2?

L39 I would write: (on the total scale)
L40 … all other variables (add: all)
L46 delete: being

L52 certified instead of characterized?
L59 a possible, instead of: an eventual

L60 “the compatibility of total alkalinity values” Compatibility of/against what?
L73 delete: of the work presented

L120 not clear what you mean with : by cycles
L120 dried (not: dry)
L122 delete: sol

L123 delete: known
L124 Change to: To fulfill these criteria …

L154 delete: sol
L157 delete: sol
L166 … was represented as a function of …

L167 Change to: With these data a linear regression was computed passing through the origin
L172 may instead of: can
L172 behavior (since you are using American English)

L205 was instead of: were
L215 It is not computed …

L218 analyzed
L231 delete: the following

L252 I suggest: This is approximately the precision reported to be achievable …
L259 … as a function of (instead of: in function of)

L261 associated with
L264 delete: for

L312-313 I suggest the following sentence to describe the meaning better: The close similarity of these values is evidence of the good reproducibility of the preparation of the batches.

L318 (caption Fig. 1) originating from (instead of: coming from)
L319 (caption Fig. 1) delete: Where, delete: one

L324 delete: established
L328 seem
L339 delete: before

L362 This (instead of: Which)
L395 “This is however tied to the stability of the RM achievable.” This is not clear. Can achievable be deleted?

L440 Scripps: Please be more specific and also add reference
L442 delete commas after material and after cruises

L517 possible (instead of: eventual)
L536 delete Each participants

L543 delete: developed: a stabilized natural seawater and an artificial solution
L550 delete: Where
L556 close (-d)

L601, 629 Eqs.
L625 possible (instead of: eventual)
L631 Please correct: Table 6Erreur ! Source du renvoi introuvable.

L652 delete: Where
L656 The same info was given in line 631. Please reduce doubling

With best wishes
Mario Hoppema
- editor

Hide

AR by Gaëlle Capitaine on behalf of the Authors (12 Dec 2025) Author's response Author's tracked changes Manuscript

ED: Publish as is (15 Dec 2025) by Mario Hoppema

AR by Gaëlle Capitaine on behalf of the Authors (18 Dec 2025) Manuscript

Short summary

Measuring total alkalinity in seawater is essential for understanding and monitoring the ocean carbonate system. To improve the reliability of these measurements, we developed reference materials and tested them in an inter-laboratory comparison. We also thoroughly quantified, for the first time, the uncertainty of the standard measurement method. These results, as well as the key metrological tools developed, support more accurate long-term monitoring of the ocean carbonate system.