The concentration of carbon dioxide was measured during 18 cruises in the surface waters of the North Atlantic European Shelf (Galician Sea, Gulf of Biscay, Armorican Sea, Celtic Sea, English Channel, North Sea), covering all four seasons (9 out of 12 months) at interannual scale. This is the very first intensive field study of continental shelves, in terms of source/sink for atmospheric CO2, which allows to integrate fluxes on an annual basis and over a large surface area. Here we show that European continental shelves are a sink of 90--170 million tons of carbon per year, which is an additional appreciable fraction to the presently proposed flux for the open North Atlantic Ocean (~45%). The air-sea fluxes of CO2 we obtained are similar to those recently reported in the East China Sea, allowing us to conclude that the coastal ocean plays a considerable role in the global oceanic carbon cycle. ¿ 2001 American Geophysical Union