Estimation of new primary production in the Benguela upwelling area, using ENVISAT satellite data and a model dependent on the phytoplankton community size structure

The spatial and temporal variations of oceanic new primary production have a crucial importance for the study of biogeochemical fluxes in the ocean; however, they have been poorly documented. In this paper, we propose a revision of the shift-up'' new production model developed for upwelling areas by Dugdale et al. (1989), and later adapted by Kudela and Dugdale (1996), using ocean color and sea surface temperature satellite data as inputs. The major improvement of the model is that the estimation of nitrogen uptake rates takes into account the phytoplankton community size structure, estimated for each pixel using the method of Uitz et al. (2006). Appropriate physiological parameters are then used for each size class. This revised model has been applied to Medium-Resolution Imaging Spectrometer and Advanced Along Track Scanning Radiometer data acquired over the year 2003, using the Benguela upwelling area as a test site. The combination of the new production model with a total production model allows the seasonal variations of new and total productions (including the respective contributions of the three size classes) to be estimated and compared. Even though microphytoplankton are generally considered to be responsible for new production, our results show that the contribution of small cells should not be overlooked in the upwelling-affected areas.