Carbon system parameters in the surface water of the saltpans of the Bay of Cádiz

[Description of methods used for collection/generation of data] The database provides discrete measurements of carbon system parameters in water samples collected at 13 stations during 5 campaigns conducted over 2020–2021. Geographic coordinates of sampling stations are provided. Some physical data (i.e. pressure, temperature and salinity) are also included. During the campaigns, temperature, salinity, conductivity, dissolved oxygen and pH were obtained with an EXO TM 2 multiparametric probe sonde. Surface seawater was subsequently collected for biogeochemical analysis. The biogeochemical variables shown in the database are pH in SWS and NBS scale (pH_SWS and pH_NBS), total alkalinity (AT), and inorganic nutrients (nitrite, nitrate, ammonium, silicate and phosphate), Dissolved Organic Carbon (DOC), Suspended Solid Matter (SSM), and chlorophyll a (Chla). · pH_NBS data were obtained by the EXO TM 2 multiparametric probe sonde and pH_SWS was measured with a Metrohm pH meter (model 780) at SWS scale that was calibrated according to DelValls & Dickson, (1998). · Samples for AT analysis were collected in 500-ml borosilicate bottles, and poisoned with 200 μl of HgCl2-saturated aqueous solution and stored until measurement in the laboratory. AT was measured by potential titration according to Mintrop et al. (2000) with a Titroprocessor (model Metrohm 794 for 2020 and model Metrothm 888 for 2021). · Water samples (5 mL, two replicates) for inorganic nutrients determination were taken, filtered immediately (Whatman GF/F, 0.7 μm) and stored frozen for later analyses in the shore-based laboratory. Nutrients concentrations were measured with a continuous flow auto-analyzer using standard colorimetric techniques (Hansen & Koroleff 1999). · Water samples for DOC and total dissolved nitrogen (TDN) determination were taken, filtered immediately (Whatman GF/F, 0.7 μm) and 100 μl of orthophosphoric acid (3:1) was added. Stored in fridge for later analyses in the laboratory. DOC and TDN concentrations were obtained by catalytic oxidation at high temperature (720°C) and chemiluminescence, respectively, applying the protocol described by Alvarez-Salgado & Miller, (1998). · SSM and the organic (particulate organic matter (POM) and inorganic (particulate inorganic matter (PIM)) fractions were determined by the loss on ignition method, filtering the water through pre-weighed Whatman 0.7 μm GF/F glass fibre filters pre-combusted at 450°C, with subsequent filter desiccation for 48 h and finally combustion. · Chla concentration was obtained by filtering water through Whatman 0.7 μm GF/F glass fibre filters that were maintained frozen and in the dark until analysis. The extract was measured by fluorometry following the method of Welschmeyer (1994).