The biogeochemical properties of an extensive bloom (~250,000 km2) of the coccolithophore, EMiliania huxleyi, in the north east Atlantic Ocean were investigated in June 1991. Satellite (NOAA-AVHRR) imagery showed that the bloom was centered initially at 60¿--63 ¿N by 13¿--28 ¿W and lasted approximately 3 weeks. Spatial variations in satellite-measured reflectance were well correlated with surface measurements of the beam attenuation coefficient, levels of particulate inorganic carbon, and coccolith density. Rates of both photosynthesis and calcification were typically relatively low within the coccolithophore-rich waters, suggesting the population was in a late stage of development at the time of the field observations. Levels of dimethyl sulphide (DMS) in surface waters were high compared to average ocean values, with the greatest concentrations in localized areas characterized by relatively high rates of photosynthesis, calcification, and grazing by microzooplankton. The estimated spatially averaged flux of DMS to the atmosphere was 1122 nmol m-2 h-1, somewhat greater than that determined for the same region in June--July 1987. Coccolith production (1¿106 tonnes calcite-C) had a significant impact on the state of the CO2 system, causing relative increases of up to 50 &mgr;atm in surface pCO2 in association with alkalinity and water temperature changes. Gradients in pCO2 were as great as 100 &mgr;atm over horizontal distances of 20--40 km. The environmental implications of these findings are discussed in relation to the spatial and temporal distributions of E. huxleyi.