Deep water currents are caused by denser, colder water sinking to the bottom of the ocean while warmer, shallow water rises towards the surface. This is known as thermohaline circulation, while the continuous movement of deep water currents in the world's oceans is called the Global Conveyor Belt.
Deep water currents are driven by density and comprise about 90 percent of the ocean's volume. Upswelling in these currents occurs when the cold water fills in the space left by the warm water rising to the surface. Deep water currents occur in the ocean at depths of greater than 1,312 feet; Currents that occur in the ocean at depths of less than 1,312 feet are known as surface currents.