A BIOGEOCHEMICAL STUDY OF THE COCCOLITHOPHORE, EMILIANIA-HUXLEYI, IN THE NORTH-ATLANTIC

The biogeochemical properties of an extensive bloom (approximately 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-degrees-63 -degrees-N by 13-degrees-28-degrees-W and lasted approximately 3 weeks . Spatial variations in satellite-measured reflectance were well corre lated with surface measurements of the beam attenuation coefficient, l evels of particulate inorganic carbon, and coccolith density. Rates of both photosynthesis and calcification were typically relatively low w ithin the coccolithophore-rich waters, suggesting the population was i n a late stage of development at the time of the field observations. L evels 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, calci fication, and grazing by microzooplankton. The estimated spatially ave raged flux of DMS to the atmosphere was 1122 nmol m-2 h-1, somewhat gr eater than that determined for the same region in June-July 1987. Cocc olith production (1 x 10(6) tonnes calcite-C) had a significant impact on the state of the CO2 system, causing relative increases of up to 5 0 muatm in surface pCO2 in association with alkalinity and water tempe rature changes. Gradients in pCO2 were as great as 100 muatm over hori zontal distances of 20-40 km. The environmental implications of these findings are discussed in relation to the spatial and temporal distrib utions of E. huxleyi.