Department of Earth Sciences

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Browsing Department of Earth Sciences by Subject "Acclimation"

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    CHEMTAX determination of Southern Ocean phytoplankton distribution and adaption: An observational and experimental study assessing the co-limitation of Light, Iron and other Trace Metals on phytoplankton productivity and community composition.
    (Stellenbosch : Stellenbosch University, 2018-12) Viljoen, Johannes Jacobus; Fietz, Susanne; Stellenbosch University. Faculty of Science. Dept. of Earth Sciences.
    ENGLISH ABSTRACT: This multi-manuscript study reports an elucidated understanding of the consequences key environmental changes has on phytoplankton community structure, productivity and their acclimation abilities for the Atlantic Sector of the Southern Ocean. All three manuscripts are based on data gathered on board the RV SA Agulhas II on a north-south transect along the Good Hope monitoring between Cape Town and the Antarctic Fimbul ice shelf (0° longitude). This transect crossed multiple oceanic fronts and zones from which a multi-parameter in-situ observational study of the links between trace metals and phytoplankton dynamics could be carried out. In addition, two stations were used to conduct bulk-community bottle incubation experiments to assess the response of phytoplankton in growth, photophysiology and community structure to iron and light variability in the Polar Frontal Zone and Antarctic waters. The results from the incubation studies revealed that the response of phytoplankton to changes in iron and light availability are very region-specific. In the Polar Frontal Zone irradiance is limiting significant phytoplankton growth and in the Antarctic Zone, iron addition resulted in growth stimulation even at low light levels. By combining data from the surface and the un-amended incubation bottles sampled from the respective depth of fluorescence maximum an assessment of how representative the surface and chla-max communities are of their region and, considering logistical constraints, if we can only use one to understand phytoplankton dynamics. Due to additional changes in irradiance and availability of iron with vertical depth, which is region specific, the acclimation of phytoplankton, which affects their photochemical efficiency (Fv/Fm) and productivity, can vary with depth which is exemplified by regional differences in water column structure and dynamics. The possibility of sampling a niche community when only one depth is sampled, which could lead to results of a very depth-specific acclimated phytoplankton community and not that of a regional representative one, was also investigated. The multi-parameter in-situ observational study that includes parallel trace metal and phytoplankton community structure data showed that there are certain changes in phytoplankton community structure that can only be explained by the addition of a suite of trace metals as additional variables. This led to the observation that when these essential micronutrients are incorporated into studies, the timing of phytoplankton sampling relative to the time of an event like the release of trace metals from hydrothermal vents or melting ice can be very important. For the Atlantic Southern Ocean, it can be shown that the present and future state of phytoplankton dynamics greatly depends on key environmental changes such as irradiance, varying degrees of iron-light co-limitation and the proven strong influence of trace metal availability. Keywords: pigments; acclimation; multi-parameter; incubation; GEOTRACES