Summary of Abstract Submission

Abstract Submission No. IO50-04-0004PresentationPoster


R Barlow*1, R Brewin2

1 Bayworld Centre for Research & Education, South Africa
2 Plymouth Marine Laboratory, United Kingdom


A three-component model was used to compute fractional contributions of three phytoplankton size classes (micro-, nano-, and picophytoplankton) to the overall chlorophyll a concentration. Using HPLC data, model coefficients were fine-tuned for application to the southern African marine region. The refined model was applied to seasonal climatologies of MODIS Aqua chlorophyll a over the south-western Indian Ocean (SWIO) in summer and winter. During summer, high chlorophyll a was limited to shelf regions along the coasts of Southern Africa and Madagascar, while values less than 0.1 mg m-3 occurred over most the open ocean regions of the SWIO, between 0 and 40S. Between 40 and 45S, elevated values were associated with the Subtropical Convergence zone. During winter, chlorophyll a values up to 0.5 mg m-3 extended over a much larger area of the SWIO, with low values restricted to the Mozambique Channel and the subtropical gyre east of Madagascar. During both seasons, micro-phytoplankton comprised more than 50% of the total chlorophyll a in the shelf regions, and less than 10% in the open ocean, while the converse was true for pico-phytoplankton. During summer, nano-phytoplankton tended to dominate in small patches along the edges of continental shelves and in the Subtropical Convergence zone, while in winter, they were distributed over a larger area and contributed more to the total chlorophyll a. Characterizing spatial and temporal variations in phytoplankton size structure in this way will allow the evaluation of the influence of climate change and variability on ecosystems in the SWIO.