Circulation in the oceans helps transport the solar energy that falls at the equator towards the poles. Like the atmosphere, uneven heating drives this flow of energy poleward. Unlike the atmosphere, the oceans are warmed from the top-down rather than from the bottom up, so heat-driven convection is not enough to cause ocean circulation. For density-driven circulation to mix the oceans at a large enough scale to matter, changes in both temperature and salinity are required.
