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...

Four large, open‐ocean diatoms from the Southern Ocean ( Actinocyclus sp., Thalassiosira sp., Fragilariopsis kerguelensis , and Corethron pennatum ) were grown in natural (low iron) Southern ocean seawater with increasing Fe concentrations. With increasing dissolved iron (Fe diss ) concentrations, the growth rates increased three‐ to sixfold. The species with the smallest cells had the highest growth rates. The half‐saturation...

In analogy to the Fe hypothesis, the Zn hypothesis states that Zn may limit primary production in some regions of the world oceans and therefore influence the global carbon cycle. The proposed mechanism is via carbon limitation due to a lack of the cofactor Zn in carbonic anhydrase. In the current conceptual model for the use of inorganic carbon by E. huxleyi , carbonic anhydrase in the chloroplast generates CO 2 from HCO 3 −...

Zinc and cobalt are essential trace metals for phytoplankton growth and can substitute for each other metabolically in some eukaryotic algal species, especially in some marine diatoms and coccolithophorids. In the present study, it is reported that in the marine diatom Chaetoceros calcitrans , Co cannot replace Zn: in contrast, Co substitution of Zn was found in Emiliania huxleyi . It is concluded that Co can substitute for Zn...

Blooms of large diatoms dominate the CO 2 drawdown and silicon cycle of the Southern Ocean in both the past and present. The growth of these Antarctic diatoms is limited by availability of iron (and light). Here we report the first assessment of growth rates in relation to iron availability of two truly oceanic Antarctic diatom species, the large, chain‐forming diatom Chaetoceros dichaeta and the small, unicellular diatom C. b...