| Summary: | Thesis (PhD)--Stellenbosch University, 2023. ENGLISH ABSTRACT: Marine phytoplankton in the Southern Ocean are essential for the Antarctic food web and help regulate the global ocean biogeochemistry, thereby mediating the warming effect of carbon dioxide (CO2). Yet, spatially and temporally, phytoplankton distribution and their controlling factors are still poorly studied in the Southern Ocean. Owing to low sampling resolution, features such as frontal and island regions have been less sampled. Moreover, the dynamics of trace metals which serve as essential micronutrients has been the least studied in the Southern Ocean. Most studies focussed on iron (Fe) and total chlorophyll-a, few on extended suites of metals and phytoplankton groups. There are still uncertainties how the trace metals Fe, copper (Cu), zinc (Zn), nickel (Ni), cobalt (Co), manganese (Mn), and cadmium (Cd), will affect phytoplankton abundance and community composition, especially in the understudied Southern Ocean during winter. In this thesis Southern Ocean phytoplankton dynamics and the complex interplay with various parameters were elucidated. Through three research papers, phytoplankton distribution was studied utilizing multi-parameter datasets, collected during two research cruises to the Southern Ocean one during summer in the Atlantic sector (0 - 8°E) and another during winter in the Indian sector (30°E). Summer phytoplankton distribution were characterised in the Atlantic Southern Ocean at high resolution across the major zones, within fronts, in sea ice influenced zones (e.g., polynya) and close to Subantarctic islands using a suite of HPLC phytoplankton pigments. Cyanobacteria dominated the Subtropical zone; haptophytes the Subantarctic and Polar Frontal zones while diatoms and haptophytes dominated the Antarctic zone south of the Polar Front. Additionally, distinct communities were observed in frontal, sea ice and near-island regions. For example, phytoplankton abundance in fronts were up to 10-fold higher than in the major zones ...
|
|---|