Seasonal model of primary production estimated by natural fluorescence in a coastal region of Gulf of California, Mexico

Abstract

The goal of this research was to study the main factors that control the primary productivity (PP) and integrated primary productivity (PPI) during a seasonal cycle in La Paz bay. We carried out eight cruises between June 2000 and June 2001. At each cruise were recorded the vertical profiling of temperature, light and chlorophyll fluorescence using natural fluorescence equipment (PNF-300) and also were taken discrete samples to determinate nitrate concentration at 6 depths in the euphotic zone (Ze). Using the PNF-300 data set we estimated the PP and PPI. The vertical temperature distribution was stratified between June to September, mixed between November and February. During March and May was considered as a stabilization period. Nitrate concentration 0-70 m were 0.34 to 19.08 µM-NO3. The 3 µM-NO3 isolines variation were useful to characterize the stratification and mixed water conditions in the water column. The PP vertical profiles ranged between 0.01 mg C m-3 h-1 in deepest euphotic zone and 20.57 mg C m-3 h-1 near to the surface. It was confirmed the existence of two seasons in the primary production cycle: high productivity from March to August and low productivity from September to February. Each season mode depends of the light penetration factors and the water column stratification. A lineal model based in the critical depth as a important parameter to explain the seasonal variability of the phytoplankton primary productivity variation.