show Abstracthide AbstractThe Southern Ocean harbours some of the most intense phytoplankton blooms on Earth. Changes in temperature and iron availability are expected to alter the intensity of these phytoplankton blooms, but little is known about how environmental change will influence community composition and downstream biogeochemical processes. We performed a bottle incubation bioassays on surface ocean microbial communities from McMurdo Sound in the Ross Sea, with and without iron addition, at -0.5 C, 3 C, and 6 C. We then examined nutrient uptake patterns as well as the growth and molecular responses of dominant primary producers to these conditions.