Seawater Carbonate System Variables in the Surface Waters of Two Time-Series in the NW Mediterranean Sea with Monthly Sampling: L'Estartit Oceanographic Station (EOS; 22/01/2010 to 23/08/2019) and the Blanes Bay Microbial Observatory (BBMO; 22/12/2009 to 02/08/2022) [Dataset]

Abstract

The database provides discrete measurements of seawater carbonate system variables (pH and total alkalinity) and ancillary variables (dissolved inorganic nutrients, temperature, salinity, and pressure) in surface seawater collected at two time-series stations, EOS and BBMO, conducted over 2009–2022. The database compiles all the information, measurements, and analysis performed (including date, location, and equipment used). All chemical analyses were assigned a quality indicator. At the two time-series stations, monthly sampling of surface seawater was performed. BBMO temperature and salinity were measured with a SAIV-A/S-SD204 CTD, while at EOS temperature was measured with reversible thermometers and salinity was measured with two CTDs, a SAIV-A/S-SD204 CTD and a CTD75M. For consistency between BBMO and EOS datasets, the salinity record obtained with the SAIV-A/S-SD204 CTD is considered in this study. When salinity values from the SAIV-A/S-SD204 CTD were missing, salinity values from CTD75M were used. The salinity records obtained with the two CTDs were quality controlled and calibrated to obtain a consistent dataset. Discrete seawater samples for pH, TA, and dissolved inorganic nutrients were taken monthly from a depth of 0.5 m both stations (with a Niskin bottle at EOS and in 10 L polyethylene carboys at BBMO). The biogeochemical variables shown in the database are pH reported on the total hydrogen ion scale at 25 °C (PH_TOT), total alkalinity (ALKALI), and dissolved inorganic nutrients (phosphate, PHSPHT, Silicate, SILCAT, and Nitrate, NITRAT). PH_TOT data were obtained by the spectrophotometric method with m-cresol purple using a Cary 100 UV-vis spectrophotometer containing a 25 °C-thermostated cells holder following Clayton and Byrne (1993). Triplicate samples were taken. At EOS, three cylindrical optical glass cells with a 10 cm path-length were filled directly from the Niskin bottle right after reaching land, ready to be analyzed in the next 3–4 hrs. At BBMO, a 150 mL glass bottle was filled leaving no headspace, and three 10 cm path-length cylindrical optical glass cells were filled from it once in the ICM laboratory (< 2h after sampling). For ALKALI measurements, two samples per site were taken in 500 mL borosilicate glass bottles were filled, rinsed three times, and carefully filled from the bottom with a tube. Samples for ALKALI were poisoned with 300 µL mercuric chloride (HgCl2) saturated solution to halt biological activity (Dickson et al., 2007), right after reaching land for EOS samples and at the ICM laboratory for BBMO samples. Bottles were then stored in the dark at room temperature until they were measured in the laboratory, within days up to one month. Each ALKALI sample was measured by duplicate. ALKALI was analyzed by potentiometric titration, determined by double endpoint titration (Mintrop et al., 2000; Pérez and Fraga, 1987), and calibrated with reference materials (Prof. A. Dickson, Scripps Institution of Oceanography (USA); Batches #93, #104, #136, and #179). Samples for dissolved inorganic nutrients were stored frozen at -20 °C in sterile falcon tubes until analysis. These tubes were filled directly from the Niskin bottle upon reaching land in EOS and from a bottle at the ICM laboratory in the case of BBMO samples. Dissolved inorganic nutrients were determined by standard continuous flow analysis with colorimetric detection (Hansen and Grassof, 1983) using a Bran + Luebbe autoanalyser