Modeling the inherent optical properties of the ocean based on the detailed composition of the planktonic community

We describe an approach to modeling the ocean's inherent optical properties (IOPs) that permits extensive analyses of IOPs as the detailed composition of suspended particulate matter is varied in a controlled manner. Example simulations of the IOP model, which includes 18 planktonic components cover ing a size range from submicrometer viruses and heterotrophic bacteria to m icroplanktonic species of 30-mum cell diameter, are discussed. Input data t o the model include the spectral optical cross sections on a per particle b asis and the particle-number concentration for each individual component. T his approach represents a significant departure from traditional IOP and bi o-optical models in which the composition of seawater is described in terms of a few components only or chlorophyll concentration alone. The simulatio ns illustrate how the separation and understanding of the effects of variou s types of particle present within a water body can be achieved. In an exam ple simulation representing an oligotrophic water body with a chlorophyll a concentration of 0.18 mg m(-3), the planktonic microorganisms altogether a re the dominant particulate component in the process of light absorption, b ut their relative contribution to light scattering is smaller than that of nonliving particles. A series of simulations of water bodies with the same chlorophyll a concentration but dominated by different phytoplankton specie s shows that composition of the planktonic community is an important source of optical variability in the ocean. (C) 2001 Optical Society of America.