OCEANIC PRIMARY PRODUCTION .2. ESTIMATION AT GLOBAL-SCALE FROM SATELLITE (COASTAL ZONE COLOR SCANNER) CHLOROPHYLL

A fast method has been proposed [Antoine and Morel, this issue] to com pute the oceanic primary production from the upper ocean chlorophyll-l ike pigment concentration, as it can be routinely detected by a spaceb orne ocean color sensor. This method is applied here to the monthly gl obal maps of the photosynthetic pigments that were derived from the co astal zone color scanner (CZCS) data archive [Feldman et at., 1989]. T he photosynthetically active radiation (PAR) field is computed from th e astronomical constant and by using an atmospheric model, thereafter combined with averaged cloud information, derived from the Internation al Satellite Cloud Climatology Project (ISCCP). The aim is to assess t he seasonal evolution, as well as the spatial distribution of the phot osynthetic carbon fixation within the world ocean and for a ''climatol ogical year'', to the extent that both the chlorophyll information and the cloud coverage statistics actually are averages obtained over sev eral years. The computed global annual production actually ranges betw een 36.5 and 45.6 Gt C yr(-1) according to the assumption which is mad e (0.8 or 1) about the ratio of active-to-total pigments (recall that chlorophyll and pheopigments are not radiometrically resolved by CZCS) . The relative contributions to the global productivity of the various oceans and zonal belts are examined. By considering the hypotheses ne eded in such computations, the nature of the data used as inputs, and the results of the sensitivity studies, the global numbers have to be cautiously considered. Improving the reliability of the primary produc tion estimates implies (1) new global data sets allowing a higher temp oral resolution and a better coverage, (2) progress in the knowledge o f physiological responses of phytoplankton and therefore refinements o f the time and space dependent parameterizations of these responses.