Adaptation mechanisms of Antarctic phytoplankton to persistent iron limitation
Low iron concentrations limit growth of Antarctic phytoplankton throughout the year. Results from the European Iron Fertilization Experiment (EIFEX) showed that large, chain forming diatoms were the main beneficiaries of iron fertilization. However, it was demonstrated for the first time that small diatoms benefited from increased iron availability as well. Laboratory experiments showed that light limitation of Southern Ocean diatoms may be less common than hitherto suggested. Further, iron and silicate co-limitation in Chaetoceros dichaeta resulted in distinct frustule malformation that would likely decrease grazing protection of this species in the field. Decreases in the elemental Si : C, Si : N, and Si : P ratios of diatoms under high iron concentrations were caused by different mechanisms instead of solely by the assumed decreased silicification. Additionally, it was demonstrated for the first time that Southern Ocean diatoms are able to use volcanic ash as an iron source and increase chlorophyll concentrations and photosynthetic efficiency significantly.