| Summary: | Thesis (MSc)--Stellenbosch University, 2018. ENGLISH ABSTRACT: The Southern Ocean is identified as a key component in the global carbon cycle due to a unique combination of physical circulation and biological processes. In light of a predicted changing climate, understanding in-situ environmental and biological processes becomes fundamentally important for improving biogeochemical models. Phytoplankton variability in the Indian and Atlantic Southern Ocean are assessed both spatially and temporally, in terms of the unique physical and chemical environments encountered in the major oceanic zones of the Southern Ocean. The approach identified the Polar Front as an important biogeochemical boundary in both summer and winter waters, separating silicic acid replete, diatom-dominated southern waters from northern waters associated with lower silicic acid concentrations and greater flagellate contribution. Summer waters along a 0 °E meridian (Atlantic Southern Ocean) were characterized by high chlorophyll-a (up to 0.56 μg/L) concentrations and bloom conditions at certain stations, which, in some instances were correlated to an influx of trace metals. Studying a suite of trace metal distributions proved to be an important additional variable in understanding phytoplankton variability, as certain metals seemed to be preferentially utilized, possibly driving underutilization of other metals, although it is unclear whether these events were mutually exclusive. Furthermore, it allowed for the association of certain trace metals to specific phytoplankton groups e.g. Zn, Mn distributions were positively correlated with diatoms. Our results indicate a complex relationship between the phytoplankton community and trace metal distribution, as it was unclear whether trace metal distributions drive the community composition or the community composition drives trace metal distributions. . Winter waters along a 30 °E meridian (Indian Southern Ocean) were characterized by deep mixed layers, limited irradiance and cold surface waters ...
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