To study how natural Southern Ocean phytoplankton communities acclimate to rapid fluctuations in irradiance levels that result from deep wind‐driven mixing of the upper water column, we measured their fluorescence properties (F v :F m , maximum quantum yield of photosystem II; and qN , non‐photochemical quenching) and pigment composition. Values of F v :F m were low (> 0.46) and qN was high ( v :F m and recovery was slow under...