The in vivo specific absorption coefficient of phytoplankton a*ph (lambda) was measured along an equatorial transect in the Pacific Ocean during the JGOFS-cruise in Octobre 1994 in order to validate bio-optical models of primary production. The fiber filter technique was used on board, as well as spectrofluorometry for pigment determination and flow cytometry for cells counting. The a*ph (435-441 nm) walues strongly decreased from oligotrophic to mesotrophic waters (between 170°E and 153°W). This zonal variation reflected a change in phytoplankton composition, dominated by #Prochlorococcus$ in the oligotrophic zone and by picoeucaryotes in the mesotrophic one. Such variations in a*ph have to be taken into account for estimating primary production of the equatorial Pacific Ocean from ocean colour imagery. (Résumé d'auteur
