Deep water currents
Topic: Movements of Ocean Water: Waves, Tides and Currents · NCERT: Class 11, Ch 13 "Movements of Ocean Water"
Meaning
Deep water currents are the slow movements of the 90% of ocean water that lies below the upper 400 m. Winds do not drive them. They move because of density (how heavy a given volume of water is) and gravity. At high latitudes, surface water becomes very cold and dense, so it sinks to the ocean floor. It then creeps slowly along the bottom towards the equator, and warmer surface water flows poleward to take its place. These currents carry heat, oxygen and nutrients through the deep ocean.
Example
In the Weddell Sea, off Antarctica, freezing sea ice leaves very salty, cold water behind. This water sinks to form Antarctic Bottom Water, the densest water in the ocean, which spreads along the floor into the Atlantic, Indian and Pacific Oceans.
Don't confuse with
- Surface currents: these are driven by wind, carry only about 10% of ocean water in the upper 400 m, and move much faster.
Related concepts
- Ocean current
- Forces driving ocean currents
- Ekman transport
- Gyre
- Surface currents
- Warm current
- Cold current