| Summary: | Thesis (MSc)--Stellenbosch University, 2024. ENGLISH ABSTRACT: Marine phytoplankton communities vary in functional groups prevalence across the Southern Ocean. The variability of phytoplankton groups, some drivers of important biogeochemical processes, is intricately linked to their adaptation to specific environmental conditions. Community group composition will thus vary as the surface water environment does. In the southern Ocean, different latitudes (ocean zones), longitudes (ocean sectors), and times of year (seasons) support distinct community profiles. In characterising the relationships that exist between specific phytoplankton groups and major environmental drivers, we can contribute to the baseline understanding of the Southern Ocean ecosystem, with implications for the biogeochemical processes its phytoplankton support and the trophic food web these primary producers underpin. Phytoplankton community structure was determined by chemotaxonomic pigment reconstruction (CHEMTAX) for historically under-surveyed austral spring and winter voyages to the Indian and Atlantic Ocean sectors of the Southern Ocean. Complimented by ship-board environmental monitoring of the physical sea surface environment (temperature, salinity, and light) and macronutrient parameters (nitrate, phosphate, silicate), the relationships between phytoplankton groups and major environmental drivers were explored using Canonical Correlation Analysis (CCA). From this analysis we determined group-environment associations that promote similar community structures three broad zonal regions: northernmost temperate, transitional sub-Antarctic, and southernmost polar. Phytoplankton communities across these regions appear to become increasingly dominated by fewer groups placing greater importance on key functional groups further south. Some group-environments associations appear independent of ocean zone, sector, or season, emphasizing the coupling between major groups components of Southern Ocean phytoplankton communities and their ...
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