Ocean color observations and modeling for an optically complex site: Santa Barbara Channel, California, USA

An extensive bio‐optical data set from the Santa Barbara Channel (SBC), California, is used to assess the in‐water constituents responsible for ocean color variability in this optically complex coastal site and to develop locally optimized ocean color models. The Santa Barbara Channel is a productive region of the California Current System. Chlorophyll concentrations are highly variable (range from 0.06 to 19.8 mg m −3 ) and are higher than the typical open ocean conditions (mean of 2.2 mg m −3 and standard deviation of 2.4 mg m −3 ). Thus chlorophyll pigments are a prime driver of reflectance variability in the SBC. Reflectance is also influenced by colored dissolved organic matter and suspended sediments which only weakly covary with chlorophyll. Detrital particulates are responsible for only a small (ca. 10%) portion of nonwater absorption, whereas phytoplankton and colored dissolved organic matter contribute approximately equally to the total nonwater absorption coefficient at 440 nm. Remote‐sensing reflectance spectra show the expected relationships with in situ determinations of absorption and backscattering where reflectance variability is absorption‐driven in the blue and backscattering‐driven in the green. The performance of existing empirical and semianalytical ocean color algorithms is shown to be satisfactory, although clearly not excellent. The optical complexity of the SBC suggests that regionally specific semianalytical models should be developed to best account for the independently varying optical constituents. Importantly, an optimization of a semianalytical model using the present data set does not result in substantial improvements in performance. Analyses of the causes and the implications of this conundrum are discussed.