Variabilty of the primary productivity and photosythetic pigments in a swelling zone in the South region of the California Current

Abstract

Processes and physical-chemical conditions of the water column off Bahía Magdalena, BCS wereanalyzed during an annual cycle (2008-2009), to determine their influence on the seasonal variability of primary production (14C) and selected phytoplankton groups characterized by their photosynthetic pigments. Local wind data, coastal upwelling index, temperature and salinity (CTD) and inorganic dissolved nutrients (NO2¯+NO3¯, PO 4-3 y SiO3-2) were also analyzed. The temperature distribution in the water column showed three hydrographic stages during the study (stratification, transition and mixing). Integrated values of the photosynthetic pigments varied in a similar way as temperature, with lower concentrations during the stratification stage and higher during the mixing stage. Nutrients and primary productivity (PP) showed two defined seasonal conditions, withlow values from September to February, and high values from March to June. These two stages were observed respectively during low (<66 m3 s-1 100 m shoreline) and high (>125 m3 s-1 100 m shoreline) intensity according to the coastal upwelling index. We conclude that coastal upwelling is the process modulating the PP level (r= 0.74, p<0.05) off Bahía Magdalena, influencing nutrient availability in the euphotic zone. The presence and concentration of photosynthetic pigments showed a modulated variability in the three hydrographical stages, with minimal concentrations during the stratification and transition, and a maximum at the mixing stage due to the presence of coastal upwelling (vertical mixing).