Credit: © Chris Marsay

Anthropogenic combustion could be important in delivering biologically available iron to the ocean, finds a new study on the solubility of iron in aerosols over the Sargasso Sea. Iron availability regulates phytoplankton growth, which plays a significant role in sequestering carbon from the atmosphere.

Peter Sedwick of the Bermuda Institute of Ocean Sciences, Bermuda and his colleages1 collected aerosol iron samples during a series of cruises in the Sargasso Sea, taking in episodes of air transport from North America and North Africa, respectively. The African air, with a large contribution from the Sahara desert, was dusty and rich in iron aerosols, but less than 0.5% of the iron was soluble. In the North American samples there were much fewer iron aerosols in total, but the soluble fraction was almost 40 times larger. In addition, data collected on Bermuda earlier show high concentrations of human fuel combustion products in North American air relative to Saharan samples. The higher fraction of soluble iron in polluted air could be explained by the initial composition of the combustion aerosols, by chemical reactions of iron with other combustion products or by the relatively small size of anthropogenic aerosols.

The results suggest that fossil-fuel combustion could increase the deposition of biologically available iron into the oceans, potentially affecting ocean productivity and ocean carbon cycling.