Satellite and ship studies of coccolithophore production along a continental shelf edge

Abstract

Each year since the Coastal Zone Color Scanner (CZCS)¹ was launched on the Nimbus 7 satellite in November 1978, extensive patches of water giving strong reflectance of visible light have been observed during the early summer along the outer margin of the north-west European continental shelf between 45 and 60° N (refs 2, 3). Various hypotheses including coccolithophores, phytoplankton with external calcified plates or coccoliths, were suggested to explain a comparable feature on Landsat images for July 1977⁴. To test these, we report here observations made from French and UK research vessels in 1982, using unprocessed CZCS images supplied by the University of Dundee and Centre de Météorologie Spatiale in Lannion to locate suitable sampling areas immediately before and during the cruise, and atmospherically corrected data from the European Space Agency for subsequent analysis and calibration of the reflectance signals. The high reflectance was found to be caused by a surface bloom of the widespread coccolithophore, Emiliania huxleyi (Lohm.) Hay et Mohler, which also produced abundant detached coccoliths. This finding is of relevance to recent work both on the ecology of coccolithophores⁵, including their importance in the sedimentation of biogenic carbon^6,7 and lipids⁸ and in palaeoclimatic studies⁹, and on the development of reliable remote sensing techniques for the estimation of chlorophyll in oceanic waters¹⁰.