The spatial distribution of CO2 fluxes results from the superposition of several processes, including: (i) the properties of Atlantic water incoming though the Gibraltar strait and their spreading over the western Mediterranean by physical processes (advection and diffusion), which is the main driver of the above mentioned west-east gradient, (ii) a latitudinal gradient in temperature (and consequent CO2 solubility), with the eastern part of Mediterranean Sea also being the southern and warmer one, (iii) the role of terrestrial inputs of alkalinity from major rivers, clearly recognizable in the marginal subbasins, (iv) the effects of biological activities. A marked seasonal cycle – related mainly to the seasonal temperature cycle and to the biological activity – also is observed all over the basin, so that all subbasins become sources in summer time and sinks in winter time, as depicted – as selected examples – in Fig. 3 for the Alboran, Northewest, and Levantine sub-basins. The inter-annual variability intrinsic in the above- mentioned processes produces some year-to-year variability in space distribution of yearly CO2 fluxes, too. However its main features are preserved.