Measurements of the carbonate system in the surface waters of the northeast Atlantic during summer 1991, following the main growth phase of a bloom of the coccolithophore Emiliania huxleyi are presented. We examine the perturbation of the carbonate system and assess the effect of calcification on the air-sea gradient of dissolved carbon dioxide in the surface ocean. An estimate of 1:1 organic to inorganic carbon uptake is calculated using the measurements of the surface carbonate parameters which is consistent with other estimates for E. huxleyi populations using radio-tracer methods. Using the changing ratio of dissolved carbon dioxide to nitrate concentration we demonstrate a relative increase in dissolved carbon dioxide due to calcification with evidence of this increase supported by estimates of the buffer factor and C:N assimilation ratios. Within the E. huxleyi bloom the effect of calcification on alkalinity appears to have reduced the air-sea gradient by ∼ 15 μatms (corrected to a constant temperature) using measurements from a 440 km section along the 20°W meridian. This reduction could prove to be significant in terms of the overall drawdown of carbon during the spring-summer season in this area.