Under most conditions nitrate uptake is light-dependent and may be characterized using the same uptake-irradiance response parameters as carbon. This suggests that the quantum yield of nitrate may be determined, which in turn allows for the determination of new production using existing quantum-based models of primary production. Balanced growth conditions are rare in upwelling phytoplankton assemblages, which makes it difficult to gauge new production from primary production. During the spring of 1995, a multi-investigator initiative was carried out to assess the role of biology in the air-sea exchange of carbon dioxide in coastal Central California. During the upwelling season this region is highly variable in space and time and provides the opportunity to study phytoplankton exhibiting a variety of physiological states and occurring in a variety of environmental milieus. Measured bio-optical parameters demonstrated no correlation to the corresponding environmental characteristics, and comparison of the calculated quantum yields demonstrated that phytoplankton carbon and nitrogen metabolic processes were not in a balanced state, as would be expected. Determination of new production rates using a simple bio-optical model was in good agreement with traditional estimates of new production using 15N incubations.