Relationship between community structure and the bio-optical properties of marine phytoplankton

In the marine environment it is often observed that changes in the absorptive and photosynthetic properties of marine phytoplankton are accompanied by changes in temperature. Since temperature is accessible to remote sensing, it is a possible proxy for the absorptive properties of phytoplankton, but its utility in this regard is relatively untested. Although temperature has been incorporated into several primary production models that use ocean colour data, such models have limited success in predicting primary production on regional scales. In this study, I assess the value of temperature as an indicator of the photosynthetic and absorptive properties of marine phytoplankton and consider how it might be applied to refine algorithms for retrieval of algal biomass and primary production from remotely-sensed data on ocean colour.; In the first part of the study, the use of temperature as a predictor of the absorptive characteristics of phytoplankton is assessed for a broad range of oceanic regimes. Using temperature as an independent variable, nearly half of the variance in the specific absorption coefficient of phytoplankton ($a*f$(λ)) at wavelengths (λ) 676 and 443 nm is explained. Using HPLC pigment and flow cytometric data, I demonstrate that our results are consistent with the view that the size structure and the taxonomic composition of phytoplanktonic communities are regulated by physical processes, for which temperature is often a suitable proxy.; In the second part, variability in the absorptive and photosynthetic properties of marine phytoplankton is examined in two regions: the Scotian Shelf and Bedford Basin. At both study sites, a strong correlation was found between phytoplankton size structure (indexed by the chlorophyll-a specific absorption coefficient at 676 nm) and primary productivity (indexed by the parameters of the photosynthesis-irradiance (P-E) response curve). The P-E parameter $PBm$ was also strongly correlated with temperature. The results also show, however, that using temperature as a surrogate for $PBm$ and $a*f$(λ) in global algorithms of primary production will require a greater understanding of the underlying processes driving the relationships between temperature, phytoplankton community structure and light-saturated photosynthesis.