SignificanceAtmospheric dust supply of micronutrients to the Southern Ocean is an important regulator of phytoplankton productivity, impacting the global carbon cycle. Understanding how phytoplankton respond to changes in dust supply has become increasingly important, with supply predicted to alter with future climate change. We show that Patagonian dusts, which differ in characteristics by source region, can supply different amounts of the essential micronutrients iron and manganese to the Southern Ocean and subsequently drive different responses in the resident phytoplankton. Changes in dust supply, including shifts in source regions, could therefore be an important factor controlling phytoplankton productivity in the past and future Southern Ocean.