| Sumario: | From June 25 to July 10 of 1986 temperature, salinity, dissolved oxygen, nutrients, chlorophyll a and primary productivity were determined daily at one station off Punta Banda, Baja California. Hydrographic variables suggested that coastal upwelling events were present at the beginning and at the end of the period studied, with a relaxation period in the middle and weak upwelling before July 10. During strong upwelling events surface values of temperature, salinity, dissolved oxygen and phosphate were: 13 to 14ºC, 33.65 to 33.70‰, 4.0 to 5.0 ml/l and between 0.95 to 1.25 µM, respectively. We found low chlorophyll a and primary productivity values as a result of unadapted phytoplankton as well as strong mixing of water in the area. Higher chlorophyll a and primary productivity values were measured at the beginning of the relaxation period; with 4.8 mg.m–3 of chlorophyll a and 3.6 mgCm–3.h–1 of primary production. The phytoplankton size fraction <8 µm was dominant in biomass and prirnary productivity, except during strong upwelling events when the phytoplankton size fraction >8 µm contributed more to biomass and primary production.
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