Global Biogeochem. Cycles 22, GB1023 (2008)

Credit: PLANKTOS

Seeding the ocean surface with iron could hold promise for storing carbon dioxide in the deep sea, suggests new research. The findings contrast with results from earlier studies that have questioned the validity of this geoengineering solution to climate change.

Stéphanie Jacquet at Vrije Universiteit Brussel, Belgium, and colleagues investigated the export of organic carbon to the deep sea during an artificial iron-induced phytoplankton bloom in the Southern Ocean in 2004. During the experiment, Jacquet's team measured particulate barium concentrations in the water column, which acted as an indicator of whether carbon was sinking or undergoing remineralization, the process by which marine organisms oxidize organic carbon to carbon dioxide. Only 12–14 percent of organic carbon was remineralized in the upper 1,000 metres of the water column, a smaller fraction than for comparable areas with natural algal blooms. The remaining organic matter sank, sometimes rapidly as large particles, into the deeper ocean.

The results suggest that fertilizing the ocean with iron could have potential for mitigating climate change. The researchers urge caution, however, in extrapolating the results to the entire Southern Ocean, as the study site was an eddy, which may have influenced the transport of carbon to the deep sea.