Determining the impact of non-algal materials on water-leaving solar stimulated fluorescence signals in coastal waters

Solar stimulated fluorescence (SSF) signals have been identified as a diagnostic identifier for phytoplankton populations and efforts are underway to relate these signals to algal physiology. However, in coastal waters one must also take into account the effect of algal and non-algal materials on the underwater light field as this could have an impact on fluorescence excitation and propagation to the sea surface. In this study we examine the impact of varying loads of mineral particles and colored dissolved organic materials (CDOM) on water-leaving SSF signals using Hydrolight radiative transfer simulations. We assess the impact of algal and non-algal absorption and scattering on the production and propagation of SSF signals using realistic ranges of material concentrations and specific inherent optical properties (IOPs) derived from in situ data. We show that SSF signals in coastal waters are profoundly dependent on underwater light climates that are, in turn, strongly influenced by non-algal materials.