A fast method has been proposed [Antoine and Morel, this issue] to compute the oceanic primary production from the upper ocean chlorophyll‐like pigment concentration, as it can be routinely detected by a spaceborne ocean color sensor. This method is applied here to the monthly global maps of the photosynthetic pigments that were derived from the coastal zone color scanner (CZCS) data archive [Feldman et al., 1989]. The photosynthetically active radiation (PAR) field is computed from the astronomical constant and by using an atmospheric model, thereafter combined with averaged cloud information, derived from the International Satellite Cloud Climatology Project (ISCCP). The aim is to assess the seasonal evolution, as well as the spatial distribution of the photosynthetic carbon fixation within the world ocean and for a “climatological year”, to the extent that both the chlorophyll information and the cloud coverage statistics actually are averages obtained over several years. The computed global annual production actually ranges between 36.5 and 45.6 Gt C yr−1 according to the assumption which is made (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 needed 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 production estimates implies (1) new global data sets allowing a higher temporal resolution and a better coverage, (2) progress in the knowledge of physiological responses of phytoplankton and therefore refinements of the time and space dependent parameterizations of these responses.

[1] A climatology of Sea-viewing Wide Field-of-View Sensor (SeaWiFS) chlorophyll data over the Indian Ocean is used to examine the bloom variability patterns, identifying spatio-temporal contrasts in bloom appearance and intensity and relating them to the variability of the physical environment. The near-surface ocean dynamics is assessed using an ocean general circulation model (OGCM). It is found that over a large part of the basin, the seasonal cycle of phytoplankton is characterized by two consecutive blooms, one during the summer monsoon, and the other during the winter monsoon. Each bloom is described by means of two parameters, the timing of the bloom onset and the cumulated increase in chlorophyll during the bloom. This yields a regional image of the influence of the two monsoons on phytoplankton, with distinct regions emerging in summer and in winter. By comparing the bloom patterns with dynamical features derived from the OGCM (horizontal and vertical velocities and mixed-layer depth), it is shown that the regional structure of the blooms is intimately linked with the horizontal and vertical circulations forced by the monsoons. Moreover, this comparison permits the assessment of some of the physical mechanisms that drive the bloom patterns, and points out the regions where these mechanisms need to be further investigated. A new outcome of this study is that in many distinct areas, time shifts of 1-2 months are witnessed in the timing of the bloom onsets in adjoining regions. These time shifts are rationalized in terms of horizontal advection and Rossby wave propagation.

About 300 coastal zone color scanner (CZCS) scenes, gathered over the eastern Mediterranean basin mostly during the years 1979–1981, have been processed from level 1 by using improved pixel‐by‐pixel procedures for the atmospheric correction and pigment retrieval. The seasonal evolution of the upper ocean pigment concentration is described and analyzed within the whole basin and its subbasins. From the chlorophyll concentration in the top layer, and by using statistical relationships, the depth‐integrated pigment content is estimated and used in conjunction with a light‐photosynthesis model to estimate the carbon fixation. The model relies on a set of physiological parameters, selected after the validation of the light‐photosynthesis model and not on locally measured parameters. Additional information needed in the modeling are the photosynthetically available radiation (computed from astronomic and atmospheric parameters, combined with a cloud climatology), sea temperature and mixed‐layer depth (taken from Levitus (1982)). Actually, the model is used to generate look‐up tables in such a way that all possible situations (concerning available radiation, chlorophyll concentration, and temperature) are covered. The appropriate situation associated with any pixel is selected from these tables to generate primary production maps. Despite a relatively good spatial coverage, studying the interannual variability of the pigment distribution and primary production appeared to be impossible. Therefore 12 “climatological” monthly chlorophyll maps have been produced by merging the data corresponding to several years. The carbon fixation rates in each of the subbasins have been computed on a monthly basis, and annual mean values derived thereafter. The primary production values are compared with sparse field determinations. They are also compared with those previously derived for the Western basin, also by using CZCS data (Morel and André, 1991). When put together, these companion works provide a kind of record of the trophic status of the entire Mediterranean Sea in the early 1980s. Ocean color sensors to be launched next, like SeaWIFS, will allow the seasonal and interannual variabilities in the late 1990s to be addressed.

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A set of 114 coastal zone color scanner (CZCS) images of the western Mediterranean (mainly in the year 1981) have been processed and analyzed to describe the algal biomass evolution and estimate its potential carbon fixation. For that, the pigment concentration in the top layer, Csat, is used through empirical relationships to infer the depth‐integrated pigment content of the productive column, 〈C〉tot. A spectral light‐photosynthesis model driven by 〈C〉tot is operated with additional information, namely, about sea temperature and photosynthetically available radiation (computed from astronomical and atmospherical parameters then combined with a cloud climatology). This model also includes a standard set of physiological parameters which account for the light capture by algae and for the use of this radiant energy in photosynthesis. This model allows a climatology of ψ* the cross section for photosynthesis per unit of areal chlorophyll, to be produced and then convoluted with the biomass maps after they have been averaged and composited. On average and for the whole western Mediterranean, the pigment concentration in the upper layer is about 0.25 mg Chl m−3, leading to an areal mean concentration of 21 mg Chl m−2. The maximum (bloom) occurs in early May in all zones. Seasonal variations in algal biomass are much more marked in the northern part than in the southern part (apart from Alboran Sea); the south Tyrrhenian basin and the central part of the Algerian basin are steadily oligotrophic. The mean annual carbon fixation rate for the whole basin is about 94 g C m−2 yr−1, or 106 and 87, for the northern and southern basins when separately considered. The seasonality is expressed by a six‐fold change in the production rate (between February and May) within the northern zone, whereas only a two‐fold change occurs in the southern zone between the same months. These estimates, which compare well with previous episodic field data, considerably extend our knowledge of the temporal progression of productivity within the entire western Mediterranean and its various provinces.