In order to quantitatively investigate the role of phytoplanktonic blooms inthe open ocean on sea surface temperature (SST) prediction, the mixed layer model of Gaspar (1985, 1988) is coupled to a primary production model adapted from Agoumi (1985), allowing an interactive prediction of the upper ocean turbidity, over two seasonal cycles at Ocean Weather Station (OWS) R (Romeo). (In this paper we use ''turbidity'' for total optical content, thus including mineral and phytoplanktonic content.) The validity of Gaspar's model, originally tested at OWS P (Papa), is first demonstrated for OWS R in its only thermodynamic version. Agoumi's (1985) model, developed for multiyear simulations over the English Channel, is then adapted to the case of the open ocean upper layers. It is shown how turbulent mixing is an important factor regulating primary production and nutrient fluxes, in order to obtain spring and autumn phytoplanktonic blooms and winter decay. Finally, it is shown how the typical spring and autumn errors in SST prediction from the mixed-layer model can be changed in sign in the thermodynamic-biological-optical coupled version of the model. These results confirm that the phytoplanktonic seasonal cycle has a significant impact on sea surface temperature simulation. It is therefore resonable to consider taking this factor into account in future upper ocean simulation experiments, and some recommendations are suggested for further studies.