Deep ocean currents are caused by density differences in the water, which are typically due to variations in salinity and temperature. Deep ocean currents are those found below 1,312 feet (400 meters). They are also known as thermohaline circulation and make up approximately 90 percent of the ocean.
The density differences that cause deep ocean currents occurs when warm water comes into contact with cold water. The warm water has less salt and is less dense than the cold water. Therefore, it rises to the surface while the colder, saltier water sinks to the bottom. This causes upwelling, where the cold water must rise to fill the space left by the warm water as it is rising to the surface. The cold water leaves a void when it rises, which the warm water must fill in a process known as downwelling. This rising and falling creates the deep water current. The current moves water through the ocean in a submarine river, known as the Global Conveyor Belt
Deep ocean currents affect the world's weather. For example, the Gulf Stream is a warm current that moves from the Gulf of Mexico to Europe. The warm water of this current keeps water at the surface warm, which in turn keeps Europe warmer than other regions at the same latitude. A cold current is the Humboldt Current, which is located near Peru and Chile and keeps the Chilean coast cool.