In many regions of the Southern Ocean, surface concentrations of the trace metal iron are very low. Iron is an essential nutrient, required for numerous metabolic pathways in phytoplankton cells. Atmospheric dust is an important source for iron input into the ocean. An insufficient supply of iron can lead to reduced growth and alterations in the photophysiology. Therefore, iron is a key factor in controlling Antarctic phytoplankton productivity and species composition. However, in experiments looking at the effects of iron on phytoplankton physiology, iron is commonly added as iron chloride and not in the form of dust. This PhD project will focus on the effects of inorganic iron in comparison to iron-containing dust as iron sources in combination with current and future elevated CO2 concentrations on Southern Ocean phytoplankton ecology and physiology. Rising CO2 concentrations in the atmosphere will reduce the pH of the world’s oceans. Ocean acidification will affect Southern Ocean phytoplankton by potentially altering the availability of iron. In order to study the impact of different climate change scenarios on Southern Ocean phytoplankton, laboratory experiments with selected species as well as shipboard experiments with natural phytoplankton assemblages during an expedition to the Southern Ocean will be conducted.