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Phytoplankton photosynthetic parameters (maximum light utilization coefficient, alpha*; maximum photosynthetic rate, P*m; maximum quantum yield, phi-max) off Baja California were estimated from samples collected at the 50% light level during winter, spring, summer, and autumn 1999. Chlorophyll concentration was also determined, and in situ experiments were conducted using the 14C method to determine primary production (PP) in the euphotic zone. The highest alpha* and phi-maxvalues were found during the spring survey, mainly at the coastal areas, associated with diatom and dinoflagellate abundances and high chlorophyll concentrations. However, high P*mvalues were measured during autumn in both inshore and offshore areas due to the presence of smaller phytoplankton cells. The average profiles of the photosynthetic parameters (alpha*(z) and P*m(z)) in the water column were estimated for 2 regions. These parameters were used to estimate PP with semi-analytical models. Modeled PP was contrasted with in situ PP to validate our calculated photosynthetic parameters in the euphotic zone. In general, modeled PP values were similar to in situ values (94 mg C·m–2·h–1), with a high correlation coefficient (r = 0.85). Modeled PP for coastal waters in the northern and central regions was 1.5-fold greater than in situ estimates during spring. In conclusion, when used with remotely sensed phytoplankton pigment and surface irradiance data, the average profiles of alpha* and P*m(z) could be a useful tool to calculate PP in our study area.
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