An Fe-Mn bottle addition experiment was conducted in the laboratory to investigate the importance of manganese (Mn) next to iron (Fe) for growth, photophysiological adaptation and trace metal requirements of a specific Southern Ocean phytoplankton: Phaeocystis antarctica. The depleted treatment (-FeMn) was a natural Antarctic sea water (sampled during PS112 in 2018) without any trace metals addition while the other three treatments were enriched with either FeCl3 alone (2.8 nM; -Mn treatment) or MnCl2 alone (2.8 nM; -Fe treatment) or both trace metals together (Control treatment). All treatments were done in triplicate 4L PC bottles. All incubation bottles were maintained at 100 μmol photons m-2 s-1 under a 16:8 (light:dark) hour cycle at 1 ̊C. After on average 10 days, samples for cell counts, photophysiology, particulate organic carbon, pigments, trace metals chemistry and trace metals intracelluar quotas were taken in order to detect how FeMn low supply effect this specie.