| dc.description | When phytoplankton are bathed in the natural radiance field of the ocean, some of the chlorophyll molecules emit red light in a phenomenon known as sun-induced chlorophyll fluorescence (SICF). In this thesis, I approach the study of SICF from several perspectives. For field studies deploying floating spectroradiometers, an inversion model of reflectance in the fluorescence band is developed and applied. The model is used in two optical regimes: in coastal waters of Nova Scotia, where chromophoric dissolved organic matter absorption was sufficiently high to prevent the retrieval of phytoplankton biomass using standard ocean color algorithms; and in the Bering Sea, where phytoplankton biomass dominated the optical signal. In the first example, the retrieval of phytoplankton biomass was possible using the fluorescence signal corrected for changes in the quantum yield of fluorescence with irradiance. In the second application, the accurate retrieval of phytoplankton absorption from ocean color allowed the quantum yield of fluorescence to be estimated. For global observations of fluorescence from space (i.e., provided by the MODIS spectroradiometer on the Aqua and Terra satellites), I created and applied two algorithms for retrieving the quantum yield of fluorescence or phytoplankton biomass. A comparison with the MODIS chlorophyll data product showed that 86% of the retrievals using the new fluorescence algorithm were within a factor of two of the standard ocean color algorithm. The new algorithm for the quantum yield will be an improvement in regions where the 412 nm band is poorly retrieved, but will perform similarly to the previous algorithm in other regions. Lastly, in a theoretical study I developed a mechanistic model of phytoplankton fluorescence at the level of the chloroplast. This approach reconciles fluorescence emission with photosynthesis and heat dissipation in phytoplankton on timescales varying from seconds to days. The model includes photochemical and non-photochemical quenching, damage and repair of photosystem II (PSII), acclimation of the antenna size of PSII, the ratio of photoprotective to photosynthetic pigments, and nutrient limitation. The results of this thesis should allow better retrieval and interpretation of the physiological and taxonomic information contained in sun-induced fluorescence. | en_US |
