Ocean thermohaline circulation mechanism. Illustration of the thermohaline circulation mechanism (red and blue arrows) driving large slow global currents in the world's oceans. These currents are driven by differences in temperature and salinity. Warm water on the surface of the ocean flows northwards, with evaporation making the water saltier along the way. At colder northern latitudes, the water becomes dense enough to sink to the sea floor where it travels south, re-emerging as it rises to the surface. Disruption of this thermohaline circulation could cause severe climate change. For this illustration without labels, see image C047/7670.