Effects in CO2 and light on the carbon acquisition of key diatom species in the Southern Ocean

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The ecology and biogeochemistry of the Southern Ocean is strongly dominated by key diatom species and the flagellate Phaeocystis. The mechanisms regulating the dominance of these species in the Southern Ocean ecosystem are poorly understood. According to the IPCC (scenario IS92a), surface water CO2 concentrations are expected to increase almost three-fold for the year 2100 relative to preindustrial values and to lower the pH (‘ocean acidification’) by 0.4 units. Rising temperatures will impact surface ocean stratification, which in turn will affect light climate and nutrient input from deeper layers. Climate models indicate that especially the Southern Ocean will be affected by these environmental changes. How will these changes shape phytoplankton community structure and possibly alter productivity? To answer this question the investigation of photosynthetic carbon acquisition has gained increasing importance in phytoplankton ecology. Studying the effects of CO2, light and iron on the carbon acquisition at the cellular and the ecosystem level will provide ecophysiological explanations for the spatial distribution of phytoplankton species in the present ocean and will further help predicting changes in future community structures. Moreover, the obtained results from this project will be incorporated in a cellular model and will be of particular relevance for improving parameterization of ecosystem models.