The ocean plays a central role in determining the climate of the earth. The oceanic circulation largely controls the temporal evolution of cli mate changes resulting from human activities such as the increase of greenhouse gases in the atmosphere, and also affects the magnitude and regional distribution of those changes. On interannual and longer time scales the ocean is, through its interaction with the atmosphere, a source of important natural climate variations which we are only now beginning to recognise but whose cause has yet to be properly determined. Chem ical and biological processes...