Aspects of dissolved inorganic carbon dynamics in the upwelling system off the Galician coast

In the present paper, we report data on the partial pressure of CO2 (pCO2) in surface seawater off the Galician coast, obtained during four cruises carried out in summer (upwelling conditions). Over the continental shelf, two processes that have opposite effects control pCO2 in surface waters: (a) the input from upwelling of deep cold water with high CO2 content that causes oversaturation of CO2 and (b) primary production that tends to decrease pCO2. In offshore waters, the distribution of pCO2 is mainly controlled by temperature change. In two distinct hydrographic coastal regions, the Rías Baixas area (RBA) and the Cape Finisterre area (CFA), the patterns of the distribution of pCO2 are complex but, in the Rías Baixas area, the averaged pCO2 values are systematically lower and temperature values higher. These differences between the two hydrographic regions are mainly related to the combination of outwelling from the Rías and the width of the continental shelf. In the Rías Baixas area, outwelling affects significantly the adjacent inner continental shelf but to a much lesser extent the outer continental shelf. In the Cape Finisterre area, the continental shelf is narrower and the ratio between the surface area of the shelf to the length of the shelf break is lower, inducing during an upwelling event, lower temperature and higher pCO2 values in surface waters than in the Rías Baixas area.