Light scattering and chlorophyll concentration in case 1 waters: A reexamination

An analysis is presented based on a large dataset (N = 2,787) made up of recent measurements of the beam attenuation coefficient at 660 nm and of the chlorophyll concentration by using the SeaTech transmissometer and the high-pressure liquid chromatography technique, respectively. This analysis, restricted to case 1 waters, aims at reassessing a previous nonlinear relationship established between the particle scattering coefficient, b(p) (very close to the particle attenuation coefficient, c(p)), and the chlorophyll concentration, [Chl]. As a first result, nonlinearity is fully confirmed over the whole range of oceanic chlorophyll concentration (about 3 orders of magnitude). Despite more accurate measurements, the scatter in this relationship remains large and is actually comparable to that observed within the old dataset. Rather than establishing a single relationship between c(p) (or b(p)) and [Chl] for the entire upper water column, the deep layer and the near-surface layer (important for remote-sensing application) have been studied separately. This separation has led to two distinct expressions. A more appropriate parameterization is thus proposed when dealing specifically with, and modeling, the near-surface layer. As a consequence, a modified criterion is also suggested with a view to identifying turbid case 2 waters.