Surface-to-bottom total alkalinity, inorganic carbon and CTD data in coastal areas leeward of the Macaronesia archipelagos during POS533

Surface-to-bottom seawater sampling for total alkalinity (AT), total inorganic carbon (TIC) and dissolved oxygen determination were performed in archipelagic coastal waters of the Macaronesia region during the POS533 cruise (from February 28 to March 19, 2019) on board the RV Poseidon. The Macaronesia region show a high variability due to its location in a coupling area between the Canary Upwelling System along the Northwest African coast and the oligotrophic open-ocean waters of the Northeast Atlantic subtropical gyre and the influence of the island interaction with the Canary Current. Thus is a key zone in terms of CO2 distribution, natural and anthropogenic carbon inventory and air-sea exchange and requires the develop of regional-scale field studies. The water-column sampling was carried out in leeward coastal stations located in the archipelagos of Cape Verde, Canary and Madeira, as well as in the Cape Verde Ocean Observatory (CVOO) and the European Station for Time-Series in the Ocean of the Canary Islands (ESTOC). A bottle rosette sampler containing twelve 10 L Niskin bottles was used for depth water sampling. The obtained dataset includes temperature, salinity, AT, TIC and dissolved oxygen. The temperature and salinity were monitored by using a CTD placed in the rosette. The AT and TIC was determined on board from the depth water samples using a VINDTA 3C and following Mintrop et al., (2000). Samples were potentiometrically titrated with HCl for AT determination, while TIC was coulometrically determined. Both AT and TIC values were corrected using certified reference material (CRM) bottles (batch 177, provided by A. Dickson at Scripps Institution of Oceanography), giving values with an accuracy of ±1.5 and ±1.0 µmol kg-1, respectively. The dissolved oxygen was determined from the seawater samples collected in pre-calibrated glass wide neck bottles by using the WINKLER method, introduced by Winkler (1888) and optimized by Carpenter (1965) and Carrit and Carpenter (1966). A Metrohm 888 Titrando operated with the software Tiamo and an amperometric electrode to determine the end point was used for the titration (Culberson and Huang, 1987). These in-situ collected data improve the knowledge about the biogeochemistry in eastern boundary transitional areas and allows a better understanding of the role in the climate change of archipelagic waters, coastal regions and island/continental shelves. The provided datasets can be used in further biogeochemical studies in the Macaronesia region and in the entire Northeast Atlantic. The monitoring and data collection received fundings from the Atmosphere-Ocean-Islands-Biogeochemical interactions in the Macaronesian Archipelagos of Cabo Verde, the Canaries and Madeira project (AIMAC project) and the European Union's Horizon 2020 research and innovation program under grant agreement Nº 820989 (COMFORT project). In this case, the measurements complemented those done for iron study (Santana-Casiano and Quack, 2021).