| Summary: | Thesis (PhD)--Stellenbosch University, 2020. ENGLISH ABSTRACT: Bioactive trace metals, including copper (Cu), zinc (Zn), nickel (Ni) and cadmium (Cd), are essential micronutrients to marine phytoplankton and their availability in the surface ocean has been shown to influence phytoplankton community composition and abundance. Through photosynthesis, phytoplankton are the primary drivers of the marine carbon cycle therefore constraining trace metal – phytoplankton dynamics, as well as other biogeochemical processes controlling trace metal distributions, is critical to understanding the greater carbon cycle. Owing to logistical constraints, less attention has been directed toward trace metal cycling on a seasonal basis. This is particularly important in the high latitude ocean regions where large seasonal fluctuations in environmental conditions e.g. light, wind and temperature, are likely to impact trace metal distributions directly or indirectly. To this end, this study focuses on the data scarce Southern Ocean and investigates the distribution and biogeochemical cycling of Cu, Zn, Ni and Cd in summer and in winter, two seasons with contrasting environmental conditions for phytoplankton growth. This framework provided a unique opportunity to characterise the Southern Ocean winter reset period and to assess the role of deep winter mixing as a potential in-situ physical trace metal supply mechanism to aid surface productivity. In order to address these questions, research cruises were conducted in summer and winter in the Atlantic sector of the Southern Ocean (0 - 8°E) while a third cruise took place in winter in the Indian Sector of the Southern Ocean (30°E). In the Atlantic sector, first winter measurements of dissolved (0.2 µm filtered seawater) Cu (dCu), Zn (dZn) and Ni (dNi) were compared with corresponding summer measurements from the same locations. Differences in trace metal distributions were most evident in the surface mixed layer where winter concentrations were consistently greater compared to summer. ...
|
|---|