Spatial distribution of chlorophyll α and primary productivity in relation to winter physical structure in the Gulf of California

The spatial distribution of chlorophyll α and productivity of phytoplankton and their relation with stratification was studied during winter of 1990 in the Gulf of California. According to the stratification parameter of the water column (Ф) we can distinguish three different zones during winter: one with strong turbulence (5<Ф<10 J m−3) close to the islands; the second zone with moderate turbulence (15<Φ<30 J m−3) in the central Gulf, and the third with high stratification (40<Ф<60 J m−3) in the southern Gulf. The lowest stratification was registered in the area near to Angel de la Guarda and Tiburon Islands, associated with low surface temperature (14–15°C), high surface chlorophyll a concentration (2.0–4.0 mg m 3) and low primary productivity (1.0–2.5 mgC m−3 h −1). Higher integrated values of chlorophyll a and primary productivity were measured in the central-southern area, related to moderate turbulence or stratification. Spring tides and wind stress appeared to be the principal physical factors for the high productivity in the central Gulf during winter. Moderate turbulence in the central-southern Gulf allows phytoplankton growth, however high turbulence in the area close to the large islands result in low primary productivity values.