Optical properties of diverse phytoplanktonic species: experimental results and theoretical interpretation

Abstract. The variability of the absorption (a*), attenuation (c*) and scattering (b*) coefficients per unit of chl a concentration has been investigated in the range 340-740 nm for nine species of phytoplankton from diverse classes. The experimental results are compared to the predictions of a previously presented model. Using the a*(\\) values, the size distribution of the suspension and the central value of the refractive index as input parameters, the model provides the spectral values of the efficiency factors for attenuation and scattering. This model, developed for spherical homogeneous cells, accounts for the large variations observed for c * and b*, whilst the package effect accounts for those of a*. For the studied species, the influence of the cell shape and of the internal structures on c * and b * does not appear crucial. From the theory/experiment comparison, a bulk refractive index can be deduced for each phytoplankter. This index is shown to be consistent with the water content and dry matter composition of the different algal classes as deduced from published data, and more surprisingly to covary with the intracellular chl a concentration of cells.