Chlorophyll profiles and the water column structure in the Gulf of California

Abstract

Remote sensors provide information on the photosynthetic pigment concentration for the upper 22% of the euphotic zone. To model primary production in the water column from satellite-derived photosynthetic pigments, estimates of the vertical distribution of pigment concentration are required. A Gaussian distribution function is used to represent the pigment vertical profile with four parameters. We used 268 chlorophyll concentration profiles from 1973 through 1993, to estimate these parameters. Cluster analysis of surface temperature was used to define the cool season as the period end of November–end of June, and the rest of the year is considered the warm season. Cluster analysis of surface temperature and chlorophyll data grouped the stations into four regions for the cool season and into two regions for the warm season. Regression models were developed for each region and season to estimate the depth of the deep chlorophyll maximum as a function of the mixed layer depth or an index of stratification. We were not able to generate useful regression models to predict the other three Gaussian parameters. Thus, their representative means were calculated for each region and season. Assuming a homogeneous biomass profile resulted in underestimation of integrated primary production by as much as 60% with respect to the values derived from the non-homogeneous profiles.