Deep ocean currents are primarily caused by differences in water density, which are controlled by variations in temperature and salinity-a process known as thermohaline circulation. Cold, salty water is denser than warm, less salty water, so in polar regions where seawater gets very cold and saltier (due to sea ice formation leaving salt behind), the denser water sinks and drives deep ocean currents
. This sinking of dense water pulls surface water down, creating a global conveyor belt that moves water masses through the deep ocean, transporting heat, nutrients, and dissolved gases around the globe. The thermohaline circulation is a crucial component of the Earth's climate system and ocean circulation
. While surface currents are mostly driven by wind, deep ocean currents flow thousands of meters below the surface and are driven by these density differences. Additionally, the energy that sustains this circulation ultimately comes from turbulent mixing powered by winds and tides, which help mix heat downward and maintain the circulation
. In summary, the movement of deep ocean currents is caused by:
- Differences in water density due to temperature (cold water is denser) and salinity (saltier water is denser)
- Sinking of cold, salty water in polar regions
- The resulting thermohaline circulation or "ocean conveyor belt" that drives deep water flow globally
- Energy input from wind and tidal mixing that sustains this circulation
