Ocean Currents

• The oceans are layered, with less-dense water at the surface and more dense water at depth. The density is determined by temperature (warmer = less dense) and salinity (fresher = less dense).
• The ocean currents, the movement of the ocean in the surface layer, are driven mostly by the wind.
• In certain areas surface water becomes sufficiently cold and salty to become very dense and sink to significant depths. This water then circulates around the world in a very large, slow current system called the thermohaline circulation because it is caused by temperature and salinity (haline) variations.
• Ocean currents circulate all over the globe

The main current in the Southern Ocean is the Antarctic Circumpolar Current - The big ACC! (Circumpolar means it is continuous around a polar region) It flows from west to east, all the way around Antarctica. The ACC is huge! It is the biggest current in the world and can move up to 150 billion litres per second of water. It can reach speeds in narrow channels of up to 1 metre per second.

This is the same as 150 times the water contained in all the rivers in the world, or the water contained in 75,000 Olympic swimming pools going past every second!

The volume of water that is transported by the ACC is so large, not because it flows fast, but because of the depth. It has a depth of up to 4000m and extends from just south of New Zealand to most of the way to Antarctica.

The Southern Ocean has some of the highest winds on Earth, and these winds move the currents. Friction between the sea water and the bottom of the ocean cause the movement of the water or current to slow down. It is the balance between these two forces that stop the currents from getting faster and faster