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

Gilles Reverdin 1 Claire Waelbroeck 1 Catherine Pierre 2 Camille Akhoudas 1 Giovanni Aloisi 3 Marion Benetti 4 Bernard Bourlès 5 Magnus Danielsen 6 Jérôme Demange 2 Denis Diverrès 5 Jean-Claude Gascard 4 Marie-Noëlle Houssais 7 Hervé Le Goff 8 Pascale Lherminier 9 Claire Lo Monaco 2 Herlé Mercier 9 Nicolas Metzl 2 Simon Morisset 10 Aïcha Naamar 2 Thierry Reynaud 9 Jean-Baptiste Sallée 1 Virginie Thierry 9 Susan E. Hartman 11 Edward W. Mawji 11 Solveig Olafsdottir 6 Torsten Kanzow 12 Anton Velo 13 Antje Voelker 14, 15 Igor Yashayaev 16 F. Alexander Haumann 17 Melanie J. Leng 18 Carol Arrowsmith 18 Michael Meredith 19 
1 PROTEO - Processus et interactions de fine échelle océanique
LOCEAN - Laboratoire d'Océanographie et du Climat : Expérimentations et Approches Numériques
2 CYBIOM - Cycles biogéochimiques marins : processus et perturbations
LOCEAN - Laboratoire d'Océanographie et du Climat : Expérimentations et Approches Numériques
7 VOG - Variabilité de l'Océan et de la Glace de mer
LOCEAN - Laboratoire d'Océanographie et du Climat : Expérimentations et Approches Numériques
8 DITM - Développement Instrumental et Techniques Marines
LOCEAN - Laboratoire d'Océanographie et du Climat : Expérimentations et Approches Numériques
17 AOS Program - Atmospheric and Oceanic Sciences Program [Princeton]
GFDL - NOAA Geophysical Fluid Dynamics Laboratory, Princeton University
Abstract : 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 averaging the 18 comparisons done for δ18O, we find a difference of 0.082 ‰ with a standard error of 0.016 ‰. Such an average difference is expected due to the adjustments applied at LOCEAN to saline water data produced either by CRDS or isotope ratio mass spectrometry (IRMS), but the scatter found suggests that care is needed when merging datasets from different laboratories. Examples of time series in the surface North Atlantic subpolar gyre illustrate the temporal changes in water isotope composition that can be detected with a carefully validated dataset.

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Submitted on : Friday, August 5, 2022 - 2:08:58 PM
Last modification on : Tuesday, August 9, 2022 - 3:28:45 AM

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Gilles Reverdin, Claire Waelbroeck, Catherine Pierre, Camille Akhoudas, Giovanni Aloisi, et al.. The CISE-LOCEAN seawater isotopic database (1998-2021). Earth System Science Data, Copernicus Publications, 2022, 14, pp.2721-2735. ⟨10.5194/essd-14-2721-2022⟩. ⟨insu-03746451⟩

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