The Southern Ocean (SO) is an important sink for anthropogenic carbon dioxide (CO2). Climate change will cause changes in various environmental parameters, which in turn can affect growth and productivity of SO phytoplankton. Due to global warming, sea surface temperatures will increase and lead to a more stratified and shallower mixed layer resulting potentially in higher light availability and enhanced primary production of iron-limited phytoplankton. On the other hand, ocean acidification may reduce the bioavailability of iron to phytoplankton. To examine the influence of iron availability in combination with current and future higher CO2 concentrations under low and high irradiance on SO phytoplankton physiology, bottle manipulation experiments with a natural phytoplankton assemblage from the Drake Passage were conducted. Ocean acidification led to lowered abundances of Pseudo-nitzschia species at both irradiances. While higher irradiance stimulated daily particulate organic carbon production, this stimulating effect, however, was reduced under high pCO2, but only under iron-limitation. Moreover, the ratio of biogenic silicate to particulate organic carbon remained unchanged by high pCO2 for both iron treatments under high light, but declined under low light. Gaining more insight on the complex interplay of multiple environmental factors is valuable to predict future responses of SO phytoplankton to climate change.