An ocean current is any more or less permanent or continuous, directed movement of ocean water that flows in one of the Earth's oceans. The currents are generated from the forces acting upon the water like the earth's rotation, the wind, the temperature and salinity differences and the gravitation of the moon. The depth contours, the shoreline and other currents influence the current's direction and strength. Ocean currents can flow for thousands of kilometers. They are very important in determining the climates of the continents, especially those regions bordering on the ocean. Perhaps the most striking example is the Gulf Stream, which makes northwest Europe much more temperate than any other region at the same latitude. Deep ocean currents are driven by density and temperature gradients. Thermohaline circulation, also known as the ocean's conveyor belt, refers to the deep ocean density-driven ocean basin currents. These currents, which flow under the surface of the ocean and are thus hidden from immediate detection, are called submarine rivers.