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Abstract. Total alkalinity (AT) and dissolved inorganic carbon (CT) in the oceans are important properties to understand the ocean carbon cycle and its link with global change (ocean carbon sinks and sources, ocean acidification) and ultimately to find carbon-based solutions or mitigation procedures (marine carbon removal). We present an extended database (SNAPO-CO2; Metzl et al., 2024c) with 24 700 new additional data for the period 2002 to 2023. The full database now includes more than 67 000 AT and CT observations along with basic ancillary data (time and space location, depth, temperature, and salinity) in various oceanic regions obtained since 1993 mainly in the framework of French research projects. This includes both surface and water columns data acquired in open oceans, coastal zones, rivers, the Mediterranean Sea, and either from time series stations or punctual cruises. Most AT and CT data in this synthesis were measured from discrete samples using the same closed-cell potentiometric titration calibrated with certified reference material, with an overall accuracy of ±4 µmol kg−1 for both AT and CT. The same technique was used on board for underway measurements during cruises conducted in the southern Indian and Southern oceans. The AT and CT data from these cruises are also added to this synthesis. The data are provided in one dataset for the global ocean (https://doi.org/10.17882/102337, Metzl et al., 2024c) that offers a direct use for regional or global purposes, e.g., AT–salinity relationships, long-term CT estimates, constraint and validation of diagnostics CT and AT reconstructed fields, ocean carbon and coupled climate–carbon models simulations, and data derived from Biogeochemical Argo (BGC-Argo) floats. These data can also be used to calculate pH, fugacity of CO2 (fCO2), and other carbon system properties to derive ocean acidification rates or air–sea CO2 fluxes.
Metzl et al. (Fri,) studied this question.