OCEANIC PRIMARY PRODUCTION .1. ADAPTATION OF A SPECTRAL LIGHT-PHOTOSYNTHESIS MODEL IN VIEW OF APPLICATION TO SATELLITE CHLOROPHYLL OBSERVATIONS

A global equation, designed to estimate the column-integrated oceanic primary production realized by a given phytoplankton biomass under var ious environmental conditions, is used to develop a practical method t o assess the primary production (P) from the chlorophyll concentration as provided by satellite imagery. This basic equation combines three terms, namely the photosynthetically available radiation impinging at the sea, surface, PAR(0+), the column-integrated chlorophyll content, < Chl >(tot), and the cross section for photosynthesis per unit of chl orophyll, Psi. Global monitoring of incident irradiance and near-surf ace algal biomass is now achievable from space, and thus the next step toward a monitoring of oceanic primary production would be to dispose in parallel of a ''climatological field'' of the Psi quantity. Actua lly, Psi depends on the two other terms of the equation (PAR(0+) and < Chl >(tot)), and in addition, on temperature (also detectable from s atellite). Therefore such a ''climatological field'' is variable and c omplex and it can be conveniently replaced by lookup tables allowing e asy interpolation. The entries are date, latitude, cloudiness, tempera ture, and remotely sensed chlorophyll concentration. This upper layer concentration is extended downward owing to previous results of a stat istical analysis of the chlorophyll vertical distribution; accordingly , two parallel tables, corresponding to well-mixed or stratified upper layers with uniform or non uniform chlorophyll vertical profiles, res pectively, are constructed. These tables are produced by systematicall y using a previously published spectral light-photosynthesis model. Fo r such extensive computations, the model necessarily relies on, and is operated with, a standard set of ecological and physiological paramet ers. Therefore sensitivity analyses have been carried out in view of a ssessing the impact on Psi, and on the resulting production of deviat ions in these parameters or parameterizations, vis-a-vis the standard values or formulations which were adopted when building the tables. Th e effects of the biomass vertical structure, of possible light and tem perature adaptation, and of the presence of degraded pigments are amon g the sensitivity studies which have been performed. The method as pro posed can accomodate any improvement and complexity in parameterizatio n to the extent that additional computation time is faced only when ge nerating the lookup tables, not when using them in conjunction with sa tellite data.