<i>p</i>CO₂ variability in the surface waters of the eastern Gulf of C&#225;diz (SW Iberian Peninsula)

Spatio-temporal variations in the partial pressure of CO₂ (pCO₂) were studied during eight oceanographic cruises conducted between March 2014 and February 2016 in surface waters of the eastern shelf of the Gulf of Cádiz (SW Iberian Peninsula) between the Guadalquivir river and Cape Trafalgar. pCO₂ presents a range of variation between 320.6 and 513.6 µatm with highest values during summer and autumn and lowest during spring and winter. For the whole study, pCO₂ shows a linear dependence with temperature, and spatially there is a general decrease from coastal to offshore stations associated with continental inputs and an increase in the zones deeper than 400 m related to the influence of the eastward branch of the Azores Current. The study area acts as a source of CO₂ to the atmosphere during summer and autumn and as a sink in spring and winter with a mean value for the study period of $-\mathrm{0.18}\pm \mathrm{1.32}$ mmol m⁻² d⁻¹. In the Guadalquivir and Sancti Petri transects, the CO₂ fluxes decrease towards offshore, whereas in the Trafalgar transect fluxes increase due to the presence of an upwelling. The annual uptake capacity of CO₂ in the Gulf of Cádiz is 4.1 Gg C yr⁻¹.