| Summary: | Ships of opportunity have been used to investigate ocean–atmosphere CO 2 fluxes in the English Channel and Southern Bight of the North Sea. Continuous underway measurements of the fugacity of seawater carbon dioxide ( f CO 2 sw ), chlorophyll, temperature and salinity have been performed along 26 transects during the spring and autumn periods. The spatial f CO 2 sw distribution along the Channel and Southern Bight is modulated by the photosynthetic activity, temperature changes and water mixing between inputs from the North Atlantic Ocean and riverine discharges. The seasonal variability of f CO 2 sw is assessed and discussed in terms of the biology and temperature effects, these having similar impacts. The variation of f CO 2 sw shows similar interannual patterns, with lower values in spring. The annual average of air–sea CO 2 fluxes places the English Channel as neutral area of CO 2 uptake. The spring and autumn data allow differentiating between distal and proximal continental areas. The Southern Bight shows a tendency towards net CO 2 uptake on the distal continental shelf, whereas the Scheldt and Thames Plumes show a CO 2 source behaviour on the proximal continental shelves.
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