A MODEL FOR PARTITIONING PARTICULATE ABSORPTION INTO PHYTOPLANKTONIC AND DETRITAL COMPONENTS

A model for partitioning total particulate absorption, measured on gla ss fiber filters, into phytoplanktonic and detrital components is deve loped. The model reconstructs absorption spectra for living phytoplank ton using total particulate absorption at the red absorption maxima fo r chlorophylls a and b, concentrations of chlorophyll a and pheopigmen t, and mean normalized absorption spectra for laboratory-grown algal c ultures. The model was developed in stages for two types of phytoplank ton assemblages. Section A of the model applies to waters dominated by eukaryotic algae and is based on absorption spectra for chromophytic (phytoplankton containing chlorophyll c) and chlorophytic (containing chlorophyll b) species. Section B of the model. allowing more variabil ity in spectral shape, was developed for algal communities with more d iverse pigmentation. All spectra are processed through Section A. with an internal evaluation determining whether processing continues throu gh Section B. Detrital spectra, generated as the difference between to tal particulate and modelled phytoplanktonic spectra, included pheopig ment absorption and had high blue absorption. Blind tests on samples o f known composition predicted absorption within 8-10% at 436 nm and 1- 13% when averaged from 400 to 700 nm, which is within the expected acc uracy of the glass fiber filter method. No true measure of phytoplankt on absorption in field samples is available for testing the model, but results from methanol-extractions were used for comparison despite in clusion of pheopigment absorption as ''phytoplankton''. For samples co llected from coastal waters of Washington State, the Sargasso Sea and coastal waters of Norway, modelled absorption (averaged over 400-700 n m) ranged from 25% lower to 0.5% higher than the methanol-extraction r esults; pheopigment absorption inappropriately included in the phytopl ankton component accounts for the higher phytoplanktonic absorption es timated by the methanol technique. Successful application of the model to samples from widespread locations, of different absorption magnitu des, and with varied spectral shapes indicate that the model can be us ed in diverse environments.