This study will examine the sources of variability of light absorption by "detrital" particles on bio-optical properties in both eutrophic and oligotrophic waters. In a number of bio-optical studies "detrital" particulate material has been observed to cause a pronounced increase in absorption from the blue into the near- ultraviolet. This study seeks to better define the nature of the dominant blue- to uv-absorbing particulate chromophores in waters with different optical characteristics, and to identify the types of particle (detrital and living organisms) with which such chromophores are associated. These objectives will be addressed in combined laboratory and field investigations. The study will utilize analytical approaches which consider the question of detrital absorption at several levels: characterization of individual particle types (by epifluorescence microscopy coupled to an image analyzer); analyses of chromophore composition; measurements of particulate spectral absorption (total and "partitioned"); and, in the field, optical profiling. Laboratory studies will focus on the potential contribution of living organisms (particularly heterotrophic bacteria and protozoans) to "detrital" absorption, the chromophore composition of biogenic detritus produced by microzooplankton, the relative importance of different biological chromophore types, and the stability of chromophores in detrital particles. Field work (within the South Atlantic Bight) will extend the results of the laboratory study to compare turbid inshore coastal waters with oligotrophic waters beyond the shelf break. The role of geopolymers versus biogenic chromophores in detrital absorption will be assessed. The results of this study will be relevant to several disciplines, including bio-optical oceanography and marine photochemistry.
