Effect of Ocean Acidification on Iron Availability to Marine Phytoplankton

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Entry by Angelo Mao, AP 225, Fall 2010

Title: Effect of Ocean Acidification on Iron Availability to Marine Phytoplankton

Authors: Dalin Shi, Yan Xu, Brian M. Hopkinson, François M. M. Morel

Journal: Science

Volume: Vol 327

Pages: 676-679


Summary

Increased concentrations of carbon dioxide in the atmosphere lowers the ocean pH, which may have effects on phytoplankton species that form the basis of food chains in the ocean. The researchers determined that lower pH lowers iron uptake by phytoplankton. They determined that pH does not alter phytoplankton food uptake, and that it is the effect of acidification on the acid-base chemistry of release of iron from chelators that leads to lower iron uptake by phytoplankton species.

soft matter keywords: colloid, solubility, pH

Fe' concentration predicts uptake

Figure 1. Steady-state iron uptake in different species of phytoplankton. A, B, D, and E depict iron uptake as a function of total iron concentration at different pH. C and F depict iron uptake as a function of unchelated iron concentration, Fe'.

The researchers quantified uptake of iron in four different species of phytoplankton, "the coastal centric diatom Thalassiosira weissflogii, the open ocean–centric diatom Thalassiosira oceanica, the pennate diatom Phaeodactylum tricornutum, and the coccolithophore Emiliana huxley." Figure 1 shows an extreme case in which there is only one chelating agent at work, the tetracarboxylic acid EDTA. Although the uptake as a function of total iron concentration varied greatly with pH, the relations coalesced to one line when only unchelated iron was considered. The concentration of unchelated iron could be calculated by:

<math>Fe' = \sum_x [Fe(OH)_x^{(3-x)+}]</math>