COMPOSITION AND DISTRIBUTION OF PHYTOPLANKTON IN THE EASTERN MEDITERRANEAN SEA DURING WINTER TIME <B>COMPOSITION AND DISTRIBUTION OF PHYTOPLANKTON IN THE EASTERN MEDITERRANEAN SEA DURING WINTER TIME</B> <HR><P> Vidussi, F., Claustre, H. & Marty, J.-C.<BR> Laboratoire de Physique et Chimie Marines, Université P. et M. Curie, Paris VI, CNRS-INSU, B.P. 08, F-06230 Villefranche-sur-mer, France</B><P><P> The winter composition and distribution of phytoplankton was investigated in the Eastern Mediterranean basin, as part of an intensive sampling program [67 stations visited during the Meteor 31/1 cruise (30 Dec. 1994 - 5 Feb. 1995)]. Diagnostic pigment concentrations (chlorophylls and carotenoids), as analysed by HPLC, were used as biomarkers of the specific phytoplankton biomass. The complete data set, which corresponds to about 700 discrete samples, will be presented and analysed in detail during the MTP-workshop. Here, as an example, we present the phytoplankton pigment signature of one station (Station 74) near Cyprus eddy, an anticyclonic eddy south of Cyprus in the Levantin basin. The integrated concentration (0 to 200 m) in total chlorophyll a (chlorophyll a plus divinyl-chlorophyll a) was very low (11.4 mg m<SUP>-</SUP><SUP>2</SUP>). Nanoflagellates (prymnesiophytes and chrysophytes) were the dominant phytoplankton and autotrophic prokaryotes (cyanobacteria and prochlorophytes) were the second most abundant. This characteristic attests the very oligotrophic nature of this area, which is confirmed by the low value (0.08) of the Fp ratio, a proxy of the f-ratio (new production : total production). The total chlorophyll a concentration ranged between 0.074 and 0.118 microgram(s) l<SUP>-</SUP><SUP>1</SUP> in the upper 100 m and drastically decreased to undetectable values at 200 m. Vertical profiles of zeaxanthin (cyanobacteria and prochlorophytes) and divinyl-chlorophyll a (prochlorophytes) show typical vertical segregation in phytoplankton distribution : while cyanobacteria were present at the surface lightened layers, prochlorophytes dominated at the level of the chlorophyll maximum. For a flow cytometry analysis of the phytoplankton distribution during the same Meteor 31/1 cruise, please refer to the abstract by Martin and Denis (1996, this volume).<B><P><P> Acknowledgements</B><P><P> This work is a contribution to GEODYME sub-project and we are grateful to Prof. Dr. Wolfgang Roether for the opportunity to participate at the METEOR 31/1 cruise.<P><P>