Applications of chlorophyll a fluorescence in bio-optical models of phytoplankton biomass and productivity

Chlorophyll a fluorescence is a function of both phytoplankton biomass and physiology. Fluorescence measured by in-water, aircraft, and future satellite instruments can provide estimates of phytoplankton absorption coefficients in diverse aquatic environments. A two-component model was developed to isolate mathematically the solar-induced fluorescence signal within the upwelling irradiance spectrum. One component separates irradiance resulting from fluorescence from the total using a linear approximation. A second component corrects for attenuation using coefficients that incorporate the angular distributions of excitation and emission irradiances. Results compare favorably with models rigorously derived for surface application; this model also can be used in sub-surface waters.; Model-derived phytoplankton absorption coefficients were highly correlated with measured values. Variation was attributed to differing species composition and physiology. For remote-sensing of surface phytoplankton absorption, a single equation using red to green reflectance ratios could be applied to a wide range of biomass concentrations. In areas where colored dissolved organic material is not correlated with phytoplankton pigment, a red fluorescence-based algorithm decreases the need for local calibration.; Variations in fluorescence due to physiology were examined using independent measurements of photosynthetic absorption coefficients and the fluorescence model. Responses of fluorescence efficiency and carbon quantum yield to irradiance conform to mechanistic photobiology model predictions. This result indicates that mechanistic models can be incorporated into to bio-optical models of primary productivity.; Chlorophyll a fluorescence excitation was evaluated as a method to quantify the photosynthetic component of the phytoplankton absorption coefficient. The photosynthetic component increased as a function of decreasing irradiance for cultures and for field samples collected from stratified regions of the water column. The inverse correlation indicates that this parameter integrates physiological responses to irradiance and has the potential to provide estimates of mixed layer dynamics.; The use of chlorophyll a fluorescence in bio-optical models will increase spatial and temporal coverage of primary production estimates that are essential to understanding carbon cycling in the marine environment.