Iron Uptake By Plankton Decreases As Oceans Acidify

Ocean acidification resulting from increased carbon dioxide levels might decrease the bioavailability of iron for marine phytoplankton, according to a report by Princeton University’s Dalin Shi, François M. M. Morel, and coworkers (Science, DOI: 10.1126/science.1183517). In laboratory studies, the team tested the effect of pH on iron uptake by four species of phytoplankton in the presence of different classes of metal chelators. They found that iron uptake decreased as the pH decreased in the presence of the chelators ethylenediaminetetraacetic acid and desferriferrioxamine B. In contrast, iron uptake didn’t change with pH in the presence of the catechol azotochelin. In analyses using Atlantic Ocean surface water, Shi and coworkers found modest decreases in iron uptake of about 10% by a model diatom when they decreased the pH of seawater from 8.4 to 7.8. Biogeochemist Constant M. G. van den Berg of England’s University of Liverpool finds the results surprising. “We did not know that iron uptake would be less at lower pH, as the calculated concentration of bioavailable inorganic iron actually increases slightly with decreasing pH,” van den Berg says. “This is indeed very important.”