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

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In the present paper, we report data on the partial pressure of CO 2 ( pCO 2) 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 pCO 2 in surface waters: (a) the input from upwelling of deep cold water with high CO 2 content that causes oversaturation of CO 2 and (b) primary production that tends to decrease pCO 2. In offshore waters, the distribution of pCO 2 is mainly controlled by temperature change. In two distinct hydrographic coastal regions, the Rı́as Baixas area (RBA) and the Cape Finisterre area (CFA), the patterns of the distribution of pCO 2 are complex but, in the Rı́as Baixas area, the averaged pCO 2 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 Rı́as and the width of the continental shelf. In the Rı́as 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 pCO 2 values in surface waters than in the Rı́as Baixas area.