Phosphorus, Sulphur, Iron, Oxygen and Climate

This chapter describes the important nutrient cycles of phosphorus, sulphur, iron and oxygen. The pre-industrial phosphorus cycle is described, as is its current perturbation through human use. Phosphorus is a non-renewable resource, so it is expected to run out soon. At the geological timescale, the importance of weathering is shown using the example of the rise of the Himalayas and its interaction with the carbon cycle. The iron cycle is also important, as iron is carried far by dust and is thought to have played a major role in glacial–interglacial transitions. The sulphur cycle is also tightly related to oxygen, as analysis of the geological record shows. Recent developments in measuring oxygen variations in the atmosphere and in ice cores have shown that, at the 0.5 million-year timescale, the geological thermostat appears to work and that current levels are declining as a result of fossil fuel burning.