Phytoplankton in deep convection : an experimental approach on the effect of temperature and short light conditions on growth and physiology

• Main Author: Walter, Bettina
• Other Authors: Beusekom, Justus van (Vertr.-Prof. Dr.)
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: Staats- und Universitätsbibliothek Hamburg Carl von Ossietzky 2013
• Subjects: Phytoplankton; Tiefendurchmischung; Lichtakklimatisierung; Temperature; deep convection; light acclimation; 500 Naturwissenschaften; 42.94 Meeresbiologie; ddc:500; North Atlantic
• Online Access: http://nbn-resolving.de/urn:nbn:de:gbv:18-69483; https://ediss.sub.uni-hamburg.de/handle/ediss/5574

The phytoplankton spring bloom of the North Atlantic is one of the largest biological events on earth. It strongly affects the biogeochemical cycle and the entire marine food web. Previous winter conditions strongly affect the timing and composition of the spring bloom Low light availability during deep convection was assumed to prevent phytoplankton growth in winter. However, noticeable chlorophyll a concentration were determined in a convective mixed layer and phytoplankton cells are transported via convection through the entire convective cell and thereby visit frequently the euphotic zone for short periods. These short periods of light availability may allow phytoplankton productivity in winter. Yet, very little is known about algae growth and physiology in a deep convection situation. In this thesis different laboratory experiments were carried out to test the growth of the diatom Thalassiosira weisflogii under different light and temperature conditions, simulating deep convection. Oxygen development, biochemical compounds and photosynthetic efficiency were measured to study surviving strategies and acclimation processes to low light availability. Furthermore, the effect of different over-wintering conditions (complete darkness and deep convection) on the onset of a spring bloom were addressed by comparing differences in surviving strategies and possible competition between two different phytoplankton species (Thalassiosira weisflogii and Rhodomonas sp.). T. weissflogii showed positive growth rates under two hours light per day at temperatures above 8°C. Under comparable experimental conditions positive net primary production was calculated from continuous oxygen measurements explaining these positive growth rates. The comparison of two different light intensities with the same daily light dose indicated much higher growth rates for the low light scenario under non-limiting temperature conditions. This strongly emphazises that compensation irradiance may not be the correct tool to describe the limit of ...