Sea surface carbon dioxide off the Iberian Peninsula (North Eastern Atlantic Ocean)

The variability in carbon dioxide in the eastern North Atlantic Ocean was analysed during three seasons with differing hydrographical and meteorological conditions that corresponded to upwelling and downwelling. No correlation between surface pCO2 and chlorophyll was found in spring, although a significant correlation was found in autumn when strong downwelling was observed. The convergence that developed over the slope during strong downwelling, produced different regimes of water column stability on the shelf and created areas of high and low pCO2. A positive correlation (r2=0.50; n=33) between surface pCO2 and chlorophyll occurred during the upwelling season. High pCO2 is found when the greatest concentration of chlorophyll exists. The uptake of carbon by photosynthetic activity masked the increase in dissolved inorganic carbon concentration at the surface due to the upwelling event. Without this biological input, the increase in pCO2 during the upwelling would be even higher. Air–sea fluxes of CO2 were calculated for the three studied seasons. The average CO2 flux from the atmosphere to the ocean (0.47 mmol m−2 d−1) in the eastern margin of North Atlantic was slightly lower than those given in previous studies in the North Atlantic ocean because of the influence of upwelling.