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 byphytoplankton ( a � ). This parameter is important and necessaryfor comparing in situ bio-optical and satellite optical measurements. Such comparisons are needed for detecting primaryproductivityat a mesoscale level. At present, however, the parameters used in algorithms for predicting productivityare global averages. To avoid this bias, we measured the spatial-temporal variabilityof aas 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 m 2 (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 Bahia Vizcaino, with oceanographic conditions favorable for the growth of phytoplankton, showed lower values of the a �. The nano-microphytoplankton (45mm) community comprised of 26 diatom genera with mean abundance values of the 19.5 � 10 3 cells l � 1 . Nitzschia closterium, a pennate diatom, was almost uniform throughout the studyregion. Flow cy tometrymeasurements indicated that the picoplankton (o5mm) communityconsisted of two prokary otes, Prochlorococcus (mean 3.6 � 10 6 cells l � 1 ) and Synechococcus (mean 10.4 � 10 6 cells l � 1 ), and a mixture of picoeukaryotes (mean 6.5 � 10 6 cells l � 1 ). Analyses of Chl and carotenoid pigments determined byhigh-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 ARTICLE IN PRESS