A Compartmental Analysis of the Kinetics of Iron Uptake by Two Antarctic Diatoms

In the so-called ‘High-Nutrient Low-Chlorophyll’ (HNLC) regions there are high amounts of basic nutrients (such as carbon, nitrate, phosphate and silicate), but low phytoplankton productivity. Studies have shown that iron (Fe) is a limiting nutrient and the research in this work has looked at the kinetics of iron speciation and its uptake mechanisms by two Antarctic diatoms. The influence of different types of light regimes was also studied. The presented data indicated that for the PMMA bottles used in our experiments, the affinity for the wall is of similar magnitude to the iron capacity and affinity for naturally occurring ligands in seawater. This makes that iron wall sorption should be seriously considered in small volume experiments, both in assessments of shorter-term dynamics and in end-point observations in equilibrium conditions. Furthermore the effect of two strong Fe-binding organic ligands, phytic acid (PA) and desferrioxamine B (DFOB) was investigated. On short time scales (<36 h) organic complexation of Fe and the influence of the dark-light cycle overruled the impacts of UV light on the directional flow rates of Fe speciation.