Specific absorption coefficient and phytoplankton biomass in the southern region of the California Current

In recent years, experts of optical hydrology have shown great interest in the variability of the specific absorption coefficient of light by phytoplankton ( a ph * ). This parameter is important and necessary for comparing in situ bio-optical and satellite optical measurements. Such comparisons are needed for detecting primary productivity at a mesoscale level. At present, however, the parameters used in algorithms for predicting productivity are global averages. To avoid this bias, we measured the spatial–temporal variability of a ph * as part of the Jan-01 Investigaciones Mexicanas de la Corriente de California cruise along the southern California Current. We observed median values of 0.041 m2 (mg chlorophyll a (Chl a))−1 at 440 nm and 0.015 at 674 nm, with significant differences between inshore and offshore stations. In general, the stations located in the area of Bahía Vizcaíno, with oceanographic conditions favorable for the growth of phytoplankton, showed lower values of the a ph * . The nano-microphytoplankton (>5 μm) community comprised of 26 diatom genera with mean abundance values of the 19.5×103 cells l−1. Nitzschia closterium, a pennate diatom, was almost uniform throughout the study region. Flow cytometry measurements indicated that the picoplankton (<5 μm) community consisted of two prokaryotes, Prochlorococcus (mean 3.6×106 cells l−1) and Synechococcus (mean 10.4×106 cells l−1), and a mixture of picoeukaryotes (mean 6.5×106 cells l−1). Analyses of Chl and carotenoid pigments determined by high-performance liquid chromatographic confirmed the presence of the divinyl Chl a characteristic of Prochlorococcus. The nano-micro- and picoplankton were 82% and 18% of total phytoplankton biomass (μg C l−1), respectively. In general, we concluded that the phytoplankton community structure and biomass on this cruise showed conditions similar to oligotrophic systems.