The effect of iron on carbon dioxide in the oceans

Approximately 40% of the CO₂ added to the atmosphere is thought to be taken up by the oceans. This uptake of CO₂ can be due to the solubility of the gas in cold sinking waters (the solubility pump) or the biological conversion to organic carbon that sinks to deep waters and is converted back to CO₂ (the biological pump). For the biological pump to work the phytoplankton growing in the surface waters need nutrients. In some parts of the ocean, however, the surface waters have high concentrations of nutrients and low concentrations of chlorophyll or phytoplankton. It has been postulated that plants do not grow in these waters due to a lack of iron (the Iron Hypothesis). Recently there have been two open ocean experiments (Ironex I and II) that have been made to test this hypothesis. This was done by adding large amounts of iron-enriched seawater to surface waters. The waters were then sampled for a number of days to examine the changes in the biological and chemical properties of the iron-enriched patch. The results of these experiments are reviewed in this paper.