MODELING THE SEASONAL COURSE OF THE UPPER OCEAN PCO(2) .1. DEVELOPMENT OF A ONE-DIMENSIONAL MODEL

A one-dimensional model is developed to simulate the seasonal course o f the mixed-layer CO2 partial pressure (pCO(2)) at a given oceanic sit e. This rather detailed numerical tool is particularly designed to qua ntify the relative role of physical and biological processes in the mo dulation of the pCO(2). It accounts for (i) the variations in the phys ical environment, i.e., mixed-layer depth, temperature and eddy diffus ivity, in response to the external forcing, (ii) the photosynthetic ca rbon fixation, (iii) the fate of the organic carbon produced through p hotosynthesis, either locally recycled or exported down to deep waters , and which is parameterised by using the temporal variations of the c hlorophyll content combined with a f-ratio, (iv) the chemistry of CO2 in seawater, allowing the pCO(2) inside the mixed layer to be computed from the total inorganic carbon (Sigma CO2) and total alkalinity (TA) contents. The carbon fluxes resulting from air-sea exchange, upward t ransport, and net primary production are thus simultaneously assessed. The model is purposely developed under the constraint of using (almos t exclusively) remotely-sensed data, namely those about chlorophyll, w ind, temperature, and incident irradiance; nevertheless, an a priori k nowledge of the oceanic zone under consideration and corresponding var iables is required when initializing the model. If the photosynthetic carbon uptake is explicitely accounted for, the model, however, cannot predict the algal biomass evolution. On the contrary, it is driven by this evolution and the chlorophyll concentration, as delectable from space, is the main input into the carbon-based biological compartment of the code.