Modeling in situ phytoplankton absorption from total absorption spectra in productive inland marine waters

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Abstract
Dissolved and suspended materials in the ocean modify the in‐water light field by absorbing and scattering photons. Direct measurement of inherent optical properties of individual optical constituents is difficult since the constituents themselves cannot all be separated. A model was developed to resolve in situ phytoplankton absorption from a measured in situ total absorption spectrum which includes water, dissolved organics, particulate detritus, and phytoplankton. The model was tested on a set of absorption spectra obtained from the productive waters around the San Juan Islands, Washington. Results indicate that the model can predict the spectral shape of phytoplankton absorption (r2 > 0.9) and total photon absorption by phytoplankton with <27% error. Total photon absorption can be used to estimate phytoplankton absorption of light energy for improved primary production predictions, given submarine light field measurements or model calculations. Although developed for high chlorophyll waters, the model parameters are easily modified for various Case 1 optical domains.