Anita at the device for continuous carbon dioxide measurements

Currently the research vessel Maria S. Merian hosts 21 scientists from Germany, South Africa and Angola. We all want to learn more about the interplay of the Angolan Gyre and the northern border of the Namibian Upwelling System. During the upcoming 4 weeks we will study this highly interesting area in terms of biological, physical and also geochemical issues. I am a PhD student from the Leibniz Center of Tropical Marine Ecology in Bremen and I am interested in the relation of the atmospheric and the oceanic carbon dioxide (CO2) content. But why should that ratio be of interest?

Climate change and elevated atmospheric CO2 concentrations are big issues these days. Next to water vapor, CO2 is a strong atmospheric green house gas. And the interesting fact about CO2 is that it is the only atmospheric gas that not only dissolve in seawater but also reacts with seawater. Therefore the oceans contain much more CO2 than one would expect simply from the physical process of solution. In fact the oceans store 60 times more carbon than the atmosphere and 17 times more carbon than is stored in the terrestrial biosphere. The fascinating effect is that the oceans have a certain capacity to suppress the rise of the atmospheric CO2 level. During this expedition I want to find out how much CO2 is exchanged between the surface water and the overlying air. But why is this particular area so interesting in terms of CO2?

Upwelling is an upward transport of deeper water masses to the surface. This happens for example along the continental west coasts (also along the West African coast). There persistent southerly wind stress leads to an offshore Ekman transport of surface water which is subsequently replaced by deep water. This deep water is rich in nutrients and CO2. Both components fuel the growth of phytoplankton which is the basis of the marine food chain. This milieu favors a highly diverse and highly productive marine life. Coming back to the CO2, upwelling areas combine two processes. 1.) Near the coastline, were freshly upwelled water reaches the surface , a net CO2 degassing to the atmosphere takes place because the CO2 content of the deep water can be up to 3 times the atmospheric concentration. This region is normally a local CO2 source. 2.) More offshore a net CO2 uptake can often be measured e.g. because intense photosynthesis leads to CO2 depleted surface water, which leads to an uptake of atmospheric CO2. Those areas will most probably be local CO2 sinks.

In contrast to the open ocean, upwelling regions are highly variable in terms of its CO2 fluxes – not only on the local but also on the seasonal scale. But how big are those fluxes? And do they contribute significantly to the global carbon burial? A composite of all expeditions and measurements done so far, will provide an overview of the net CO2 fluxes of the Namibian Upwelling System and the Angolan Gyre.