Phytoplankton, microscopic marine algae that photosynthesize, facilitate the sequestration of carbon dioxide from the atmosphere into the ocean, thus, contributing to the regulation of global climate. In the Southern Ocean, a high-nutrient low-chlorophyll region, phytoplankton production is limited by micronutrients including iron. The limiting role of light is also important, especially in the context of Southern Ocean phytoplankton adaptation to the low-iron conditions. The relative dominance of iron and light limitation on phytoplankton growth is important to understand how primary production, and the sequestration of carbon dioxide, will change in a future warming ocean. Thus, we conducted a series of incubation experiments during a research voyage off East Antarctica to investigate iron and light limitation in the austral summer. Our results show that, while light was the primary limiting factor of phytoplankton growth, iron addition became favourable for growth only under high light conditions. Our results support similar findings and provide a new insight from a different region of the Southern Ocean, at a later stage of the austral summer, and on smaller phytoplankton cells, improving our understanding of how phytoplankton production will change in the future.