Von Jasmin Heiden, Florian Koch et al.
We are 12 biologists and chemists on board R.V. Polarstern from several research institutes (Alfred Wegener Institute, Universities of Geneva, Bremen and Oldenburg and the ETH Zürich) that constitute the working group ProIron. Our mission on board is to examine impacts of different trace metal and climate change on microalgal community structure and productivity in the Drake Passage and the West Antarctic Peninsula. More specifically we investigate the effects of trace metal limitation (iron, zinc, cobalt, manganese, vitamin B12) on micoalgal communities and the recycling of those trace metals. We do this in conjunction with changing climatic factors such as light availability and carbon dioxide concentrations.
Microalgea are tinny microorganisms that do a great job by fixing atmospheric CO2 via photosynthesis (a process referred to as primary productivity) being able to modulate the carbon cycle and Earth’s climate. The reason we are interested in Southern Ocean (SO) microalgae is that they contribute >20 % to global marine productivity and hence have a major impact on the global carbon cycle. In addition large areas of the SO have high macronutrient availability (nitrate, phosphate, silicate), while the standing stock of phytoplankton is low, they are, in fact oceanic desserts. These areas are called HNLC areas (High Nutrients Low Chlorophyll). How can this be? There are enough macro nutrients and light, the factors necessary to sustain plant growth so how come the water is so devoid of plankton? This paradox can be attributed to the fact that some other element necessary for growth must be lacking. In the late 1980s John Martin discovered that it is iron.
Iron is essential for several cellular processes including being an integral part of proteins involved in the photosynthetsis and microalgal limitation by iron has been demonstrated many time across the Southern Ocean. However we still do not quite understand the parameters controlling as well the global implications that iron limitation exerts. Therefore our work is designed to investigate the link between iron chemistry and its ability to support microalgal community using two approaches: (i) incubation experiments where we modulate iron chemistry and study the response of the microalgal communities, (ii) isolation of the key players influencing iron chemistry in-situ, including microalgae themselves but also bacteria, viruses and organic compounds. We will bring those back to our home laboratory to explore their influence on iron biogeochemistry. But what about the effect of other potentially growth limiting trace elements such as zinc, cobalt, manganese and vitamin B12, which are also required for microalgal growth. Very little is known about these so called co-limitions with iron in the SO.
Our research questions for his expedition, were: Is iron the only limiting factor? Could other trace metals also limit growth, and if so how does this impact the microalgae and what are the consequences when several metals are co-limiting growth? In order to answer these questions we are conducting seven experiments on board to investigate the effects of trace metal limitation (iron, zinc, cobalt, manganese, vitamin B12) on micoalgal communities and the recycling of those trace metals. We also look at the impact of light availability and carbon dioxide concentrations.
As mentioned before we also look at other environmental factors shaping micoalgal community composition. Due to the ongoing increase of atmospheric carbon dioxide concentrations in the atmosphere from burning of fossil fuel this carbon dioxide the world’s oceans are absorbing an ever increasing amount of CO2, where it reacts with the seawater and results in a lowering the pH a phenomenon known as ‘ocean acidification. This can impact microalgal growth as they require carbon dioxide during photosynthesis in order to form particulate organic matter. It is not clear whether microalgae may benefit from the rise in carbon dioxide availability and how this interacts with iron limitation. We therefore want to see how microalgae react to a combination of these two influencing environmental factors.
best wishes, the ProIron group