Primary productivity, calcification and new production

Mike Lucas (UCT/NOC), Anastasia Charalampopoulou (NOC) and Marlene Jahnke (University of Konstanz)

 Climate change due to CO2 emissions is having an effect on ocean chemistry; in particular they are becoming more acidic. This is likely to have an effect on the ocean’s carbonate system and could also have a major effect on the physiology of marine organisms. Calcifying organisms, such as sea urchins, pteropods and a particular group of important phytoplankton called coccolithophores are especially affected, as an acid environment can dissolve their shells and affect their ability to calcify. We are working with coccolithophores because they comprise a great proportion of biogenic calcification (50-80%). Moreover, calcite is considered to be an important ballast material for organic carbon transport from the surface to the deep ocean and therefore plays an important role in the global carbon cycle.
On this cruise we will make simultaneous in-situ measurements of the carbonate chemistry, coccolithophores abundance/morphology/biodiversity and calcification rates to investigate how natural populations of coccolithophores respond to changes in the carbonate system and especially to the declining calcite saturation state which is particularly significant in high latitudes.
Another part of our work concerns the role of iron in the world oceans. Iron is an essential micro-nutrient for phytoplankton that is required for the photosynthetic machinery in the cells and it is also required for nitrogen metabolism. One group on board the ship is undertaking incubations of phytoplankton in iron enriched seawater to determine if the region south of Iceland is iron limited. As part of this, we will be making measurements of nitrate uptake as a function of iron concentration to determine whether phytoplankton in this region are indeed iron limited. If so, this will have implications for the effectiveness of the biological carbon pump to add to the information we get from the calcification experiments.