| Summary: | The main objectives of this work were to develop and apply a simple method of estimating the action spectrum and to explore, at different temporal and spatial scales, the variation in the action and absorption spectra, and the variation and predictability of the non-spectral photosynthesis parameters of phytoplankton in natural populations. These photosynthesis properties are central to the computation of primary production, given the underwater light field and biomass distribution. In the first part of the study, a simple method of estimating the photosynthetic action spectrum, using the shape of the absorption spectrum and the magnitude of the broad-band initial slope of the photosynthesis-irradiance curve, was developed and tested by comparing the estimated spectra with actual measurements of the action spectrum. The constructed and measured spectra were then applied in the computation of primary production at different stations across the North Atlantic. There was a good agreement in the production computed using the measured and constructed action spectra, confirming that the newly-developed method worked well. Therefore, the method could be applied in the field or in the laboratory. In the second part, the nature of variation in the spectrally-resolved and non-spectral photosynthesis parameters was explored. The data were collected in five large oceanic regions in the North Atlantic, known as biogeochemical provinces, during two different seasons, and at a single location in Bedford Basin (Nova Scotia) for twenty consecutive weeks. Some nine independent variables were tested for their ability to explain the variance in the photosynthesis parameters of phytoplankton. It was found that seasonal variation in photosynthesis parameters and the shapes of action and absorption spectra was larger than that between the provinces in a given season. Several independent variables, individually or in combination, were shown to explain a significant fraction of the variance in the photosynthesis parameters. At the time-series station in Bedford Basin, changes in hydrographic conditions were found to induce changes in species composition, which in turn had a significant effect on both the shapes and amplitudes of the corresponding action and absorption spectra. The results from this investigation should be useful for modelling primary production both at small and large scales. Thesis (Ph.D.)--Dalhousie University (Canada), 1997.
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