Canary Islands coastal carbon dioxide data

Introduction We present here high-resolution datasets which span six years (February 2019 - February 2025) and are based on daily-weekly physicochemical observations of surface waters in the Canary Islands (subtropical Northeast Atlantic). Data were collected by Surface Ocean Observing Platforms (SOOPs) operating in underway mode aboard two Volunteer Observing Ship (VOS): the cargo vessel Jona Sophie (formerly RENATE P) operated by Nisa Marítima (dataset name: JonaSophie_Canary_Feb2019_Feb2025.csv), and the ferry Benchijigua Express operated by Fred Olsen Express (dataset name: FredOlsen_Canary_Feb2019_Feb2025.csv). These VOS lines are designed and maintained by the QUIMA research group at IOCAG-ULPGC and are integrated within the CanOA and CARBOCAN observational networks in the Canary Islands (for further details, see Curbelo-Hernández et al., 2021a, 2021b, 2025 and Sánchez-Mendoza et al., 2026). Additionally, we provide data derived from monthly discrete observations in the coastal sampling sites of Abades (Tenerife southeast; TNF-SE) and El Pajar (Gran Canaria south; GC-S) between May 2023 and April 2024 (dataset name: Samplings_Canary_May2023_April2025.csv). Dataset content JonaSophie_Canary_Feb2019_Feb2025.csv and FredOlsen_Canary_Feb2019_Feb2025.csv include the following variables: · “Date” (dd/mm/yyyy) · “Time” (hh:mm:ss) · “Latitude” · “Longitude” · “sst”: Sea surface temperature measured with a SBE38 thermometer at the main seawater intake of the vessel, with an instrumental error of ±0.01ºC. · “sss”: Sea surface salinity measured with a SBE45 thermosalinograph just before the water supply to the equilibrator, with an instrumental error of ±0.005. · “fCO2sw”: fugacity of CO2 in the sea surface (units: µatm) derived from Co2 molar fraction measurements (xCO2; ppm). · “fCO2atm”: fugacity of CO2 in low atmosphere (units: µatm) derived from Co2 molar fraction measurements (xCO2; ppm). The dataset contains some gaps, including a year-long gap from September 2021 to 2022 due to vessel maintenance and shorter gaps due to technical issues, which were addressed during routine maintenance. Some technical issues in 2020 were delayed due to COVID-19 constraints. Samplings_Canary_May2023_April2025.csv include the following variables: · “station”: Sampling sites (ABADES/PAJAR) · “Date” (dd/mm/yyyy) · “Time” (hh:mm:ss) · “Latitude” · “Longitude” · “sst”: Sea surface temperature measured with a multiparametric sensor. · “sss”: Sea surface salinity measured with a multiparametric sensor. · “AT”: Total Alkalinity (µmol kg-1)* · “CT”: Total Inorganic carbon (µmol kg-1)* *AT and CT were determined from discreate seawater samples using a VINDTA 3C and following Mintrop et al., 2000. AT was analyzed via potentiometric titration with HCl, following the carbonic acid endpoint method (Millero et al., 1993; Dickson and Goyet, 1994), while CT was determined through coulometric titration (Johnson et al., 1993). The VINDTA 3C was calibrated using Certified Reference Material (CRMs) by A. Dickson, ensuring an accuracy of ±1.5 μmol kg-1 for AT and ±1.0 μmol kg-1 for CT. References Curbelo-Hernández, D., González-Dávila, M., González, A. G., González-Santana, D., and Santana-Casiano, J. M. (2021ª). CO2 fluxes in the Northeast Atlantic Ocean based on measurements from a surface ocean observation platform, Sci. Total Environ., 775, 145804, https://doi.org/10.1016/j.scitotenv.2021.145804. Curbelo-Hernández, D., Santana-Casiano, J. M., González, A. G., and González-Dávila, M. (2021b). Air-Sea CO2 Exchange in the Strait of Gibraltar, Front. Mar. Sci., 8, 1701, https://doi.org/10.3389/FMARS.2021.745304. Curbelo-Hernández, D., González-Santana, D., González, A. G., Santana-Casiano, J. M., and González-Dávila, M. 2025. Spatiotemporal variations in surface marine carbonate system properties across the western Mediterranean Sea using volunteer observing ship data. Biogeosciences, 22(13), 3329-3356. https://doi.org/10.5194/bg-22-3329-2025. Sánchez-Mendoza, I., González-Dávila, M., González-Santana, D. et al. (2026). Modelling seawater pCO2 and pH in the Canary Islands region based on satellite measurements and machine learning techniques. Ocean Science, 22(1), 609-628. https://doi.org/10.5194/os-22-609-2026. Data ownership and contact These datasets were generated and curated by the QUIMA-IOCAG research group (University of Las Palmas de Gran Canaria, Spain). For data usage beyond the scope of this repository, clarification of methodologies, or potential scientific collaborations, users are encouraged to contact the dataset authors. Acknowledgement This research was supported by the Canary Islands Government and the Loro Parque Foundation through the CanBIO project, CanOA subproject (2019–2024), and CARBOCAN agreement (Consejería de Transición Ecológica y Energía, Gobierno de Canarias). This work also received funding from the PLANCLIMAC2 project (1/MAC/2/2.4/0006) under the Interreg VI Madeira–Azores–Canarias (MAC) 2021–2027 Territorial Cooperation Programme, co-funded by the European Regional Development Fund (ERDF). The SOOP CanOA-VOS line is part of the Spanish contribution to the Integrated Carbon Observation System (ICOS-ERIC Class 1 Ocean Station). The participation of David Curbelo-Hernández was funded by PhD grant no. PIFULPGC-2020-2 ARTHUM-2. We thank the owner of the Jona Sophie, Reederei Stefan Patjens GmbH & Co. KG, as well as NISA-Marítima, the captains, and crew members for their support during this collaboration. We also thank the Fred Olsen Express shipping company and its captains and crews for their assistance with all operations. Special thanks are extended to the technician Adrián Castro-Álamo for biweekly equipment maintenance and discrete sampling aboard the vessels.