Investigation of the Optical Backscattering to Scattering ratio of Marine Particles in Relation to their Biogeochemical Composition in the Eastern English Channel and Southern North Sea

The variability of the backscattering to scattering ratio of marine particles, bbp/bp, is examined from in situ measurements performed during spring and earlier summer 2004 in the eastern English Channel and southern North Sea, as part of the French National Program of Coastal Environment (PNEC). This area is characterized by a quasi permanent background of terrigenous material from direct inputs, or resuspension effects, and by relatively intense spring phytoplankton blooms (mainly diatoms and the prymnesiophyte Phaeocystis globosa). The bbp/bp surface values range between 0.0024 and 0.0417, with a mean value of 0.0138 ± 0.0083. In order to interpret such a great variability, simultaneous water samples were collected for the biogeochemical characterization of the bulk suspended particle population. We show that the bbp/bp variability is closely related to the composition of the particulate assemblage expressed by Chl, the POC/SPM and POC/Chl ratios, where Chl, POC, and SPM are the concentrations of chlorophyll a, particulate organic carbon and suspended particulate matter, respectively. The expected decrease of bbp/bp from mineral to phytoplankton dominated waters is confirmed from biogeochemical measurements, for the first time. Our results also suggest that the relative proportion between living and non living organic material has a strong (and sometimes the greatest) impact on the backscattering to scattering ratio.JRC.H.3-Global environement monitorin