European Carbonate system Time Series (November 2011 - April 2023) in the North East Atlantic, ESTOC site

The data includes carbonate system variables (pH, total dissolved inorganic carbon, total alkalinity and pCO2) measured in the water column of the European Station for time series in the Ocean, ESTOC, located at 29º10'N and 15º30'W in the northeast Atlantic Ocean, together with temperature and salinity. The period of ESTOC data started in February 1994 but the carbonate variables started on October 1995. Data for ESTOC until year 2010 were already included in PANGAEA (see related datasets).This new dataset includes all available water column measured carbonate variables from 2011 to April 2023 and new data for two visits before 2010, one in October 2007 and March 2008. A total of 626, 392 and 626 new samples are included, respectively, for total alkalinity (AT), pH in total scale (pHT) and total dissolved inorganic carbon (CT). Until 2011, sampling was done every two months. During 2012 and 2013, ship operations were stopped and re-started on February 2014, keeping since, seasonal visits to ESTOC. In 2016, a surface buoy with physical and biochemical sensors was included in ESTOC. Starting on February 2019, a General OceanicTM GO 8050 continuous underway pCO2 system with four calibration gasses together with sea surface temperature and salinity sensors (Curbelo-Hernández et al., 2021; doi:10.1016/j.scitotenv.2021.145804) was included in a volunteer observing ship (CanOA VOS line, ICOS-ERIC, https://meta.icos-cp.eu/labeling/ last visited 07/05/2023) passing close to ESTOC (25-30 km to the East). This pCO2 system has provided a total of 1502 data starting on February 2nd, 2019. For the pH in total scale, a potentiometric system was used during the first 2 years, calibrated again TRIS-artificial seawater buffers at 25ºC. After 1996, an automatic spectrophotometric pH system was developed using m-cresol purple with a precision of ± 0.0015 (n=15 for different batches of certified reference material, CRM) (González-Dávila et al., 2003). Samples for AT were potentiometrically titrated with HCl in a close cell to the carbonic acid endpoint until 2004, as described in detail in Mintrop et al. (2000; doi:10.7773/cm.v26i1.573). Since 2004, AT and CT were measured for the same 500 ml borosilicate glass bottle sample using a VINDTA 3C system (González-Dávila et al., 2010; doi:10.5194/bg-7-3067-2010) with coulometric determination. Sample accuracy for any of the three measured variables (pH ±0.0015; AT ±1.5 µmol kg-1, CT ± 1.0 µmol kg-1) has been maintained by routine analysis of seawater certified reference materials (CRMs; prepared and acquired to Andrew Dickson, UCSD). After 2019, the surface molar fraction of CO2 (xCO2) has been measured using a GO 8050 system described in detail in Curbelo-Hernández et al. (2021; Doi: 10.1016/j.scitotenv.2021.145804).