Discrimination Of The Absorption Properties Of Marine Particulates Using A Microphotometric Technique

A microphotometric technique is used to determine the contributions of phytoplankton cells and detrital materials to the bulk particulate absorption spectrum of a natural sample. The technique is based upon the direct determination of the absorption efficiency factor (Qa(X)), geometric cross-sectional area (G), and taxonomic information for many individual particles. Comparison of the mean values of Qa(X) with the total particulate absorption spectrum (ap (X )) permits the determination of the contributions of phytoplankton and detrital particles to the total particulate absorption. The reconstructed ap(X) spectra are well correlated with the sampled ap(X) (r>0.99; p<0.01) indicating that the primary absorbing materials are sampled in this analysis. The decomposition technique is applied to field data taken during a phytoplankton bloom in the Sargasso Sea (35°N, 70°W; April 1985). For this sample, the percentage of phytoplankton absorption contributing to the total varied from 40 to 90% with higher contributions for wavelengths which correspond to pigment absorption wavebands. This technique represents one of the first direct methods for separating the particulate absorption coefficient into phytoplankton and detrital components.

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