peer reviewed ; In the present paper we report partial pressure of CO2 (pCO2) data obtained off the Belgian coast during 24 cruises. The temporal and spatial resolution of this data set allows us to discuss satisfactorily seasonal and inter-annual variability of pCO2 in the study area. The dynamics of pCO2 are described using two approaches: fixed reference stations and area survey cruises. The air-water fluxes of CO2 in the Scheldt estuarine plume and in the outerplume region are estimated quantitatively, showing that these areas correspond respectively to a net annual source and sink of atmospheric CO2. The annually integrated air-water fluxes for the Scheldt estuarine plume range between +1.1 and +1.9 mol m−2 year−1 as a function of the formulation of the exchange coefficient of CO2. The annual net emission of CO2 from the estuarine plume to the atmosphere is estimated to be between +2.3 to +4.0 Gmol year−1 which represents 17 to 29% of the estimate reported in the literature for the Scheldt inner estuary.