The sensitivity of atmospheric CO2 concentrations to input of iron to the oceans

There have been several recent advances in our understanding of the geochemistry of iron and its effect on the marine biota. In this contribution, we highlight two such advances, namely results of the Ironex experiments in the equatorial Pacific and the recent publication of the first global data set for iron concentrations in the oceans. These have profound consequences for our understanding of the factors that set the pre-anthropogenic concentration of carbon dioxide in the atmosphere, and how these may have changed between glacial and interglacial time. Some of these consequences we are able to quantify and explore, but others open new questions for which we have as yet no answers.