Southern Ocean phytoplankton are major drivers of global carbon cycling accounting for 20% of the global annual primary production. Most of this production relies on large phytoplankton blooms of a few key diatom species and the flagellate Phaeocystis along the Antarctic continent, while pelagic phytoplankton contributes to a minor degree. The focus of the EcoTrace group is to elucidate the sensitivity of Southern Ocean phytoplankton to global change, in particular to ocean acidification. The availability of trace metals and light are considered key factors in controlling Southern Ocean phytoplankton productivity and community structure. Until now, only little information is available on how these environmental factors (trace metals, CO2, light) affect Southern Ocean phytoplankton. In particular research on interactive effects of these factors is still missing. The consequences will, however, most likely differ depending on the region, potentially altering the complex balance of biogeochemical cycles and climate feedback mechanisms.