The CISE-LOCEAN seawater isotopic database (1998–2021)

• Published in: Earth System Science Data
• Main Authors: G. Reverdin, C. Waelbroeck, C. Pierre, C. Akhoudas, G. Aloisi, M. Benetti, B. Bourlès, M. Danielsen, J. Demange, D. Diverrès, J.-C. Gascard, M.-N. Houssais, H. Le Goff, P. Lherminier, C. Lo Monaco, H. Mercier, N. Metzl, S. Morisset, A. Naamar, T. Reynaud, J.-B. Sallée, V. Thierry, S. E. Hartman, E. W. Mawji, S. Olafsdottir, T. Kanzow, A. Velo, A. Voelker, I. Yashayaev, F. A. Haumann, M. J. Leng, C. Arrowsmith, M. Meredith
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2022
• Subjects: envir; geo; Indian; North Atlantic
• Online Access: https://doi.org/10.5194/essd-14-2721-2022; https://essd.copernicus.org/articles/14/2721/2022/essd-14-2721-2022.pdf; https://doaj.org/article/5147ec4836a741c8b620e86841cdf3b6

The characteristics of the CISE-LOCEAN seawater isotope dataset (δ18O, δ2H, referred to as δD) are presented (https://doi.org/10.17882/71186; Waterisotopes-CISE-LOCEAN, 2021). This dataset covers the time period from 1998 to 2021 and currently includes close to 8000 data entries, all with δ18O, three-quarters of them also with δD, associated with a date stamp, space stamp, and usually a salinity measurement. Until 2010, samples were analyzed by isotopic ratio mass spectrometry and since then mostly by cavity ring-down spectroscopy (CRDS). Instrumental uncertainty in this dataset is usually as low as 0.03 ‰ for δ18O and 0.15 ‰ for δD. An additional uncertainty is related to the isotopic composition of the in-house standards that are used to convert data to the Vienna Standard Mean Ocean Water (VSMOW) scale. Different comparisons suggest that since 2010 the latter have remained within at most 0.03 ‰ for δ18O and 0.20 ‰ for δD. Therefore, combining the two uncertainties suggests a standard deviation of at most 0.05 ‰ for δ18O and 0.25 ‰ for δD. For some samples, we find that there has been evaporation during collection and storage, requiring adjustment of the isotopic data produced by CRDS, based on d-excess (δD − 8×δ18O). This adjustment adds an uncertainty in the respective data of roughly 0.05 ‰ for δ18O and 0.10 ‰ for δD. This issue of conservation of samples is certainly a strong source of quality loss for parts of the database, and “small” effects may have remained undetected. The internal consistency of the database can be tested for subsets of the dataset when time series can be obtained (such as in the southern Indian Ocean or North Atlantic subpolar gyre). These comparisons suggest that the overall uncertainty of the spatially (for a cruise) or temporally (over a year) averaged data is less than 0.03 ‰ for δ18O and 0.15 ‰ for δD. However, 18 comparisons with duplicate seawater data analyzed in other laboratories or with other datasets in the intermediate and deep ocean suggest a larger scatter. When ...