Atlantic Ocean Circulation (Gulf Stream)
Large-scale circulation in the ocean that transforms low-density upper ocean waters to higher-density intermediate and deep waters and returns those waters back to the upper ocean. The Atlantic Ocean Circulation is driven by high surface water densities and mechanical forces such as wind or tides. It is sometimes less precisely referred to as the Gulf Stream.
The Atlantic Ocean Circulation is part of a global thermohaline circulation - a giant conveyor belt that carries water around the world's oceans. This circulation, or movement, is primarily driven by changes in water density. In the oceans when water is cold it contains a greater volume of salt, and is therefore denser (or heavier). As water warms it expands and therefore contains less salt in comparison to the same volume of cooler water; this makes warmer water less dense than cooler. In simple terms the circulation is caused by a tension between the formation of cooler deep water masses in the polar regions and warmer water in the tropics, near the equator. Because the cooler water in the polar regions has a greater density than the warmer water it tends to sink and follow deep circulation patterns. This means that the sea level in cooler regions is slightly lower than the tropical regions. In turn this creates a slow but large flow of water in the upper ocean which flows into the cooler regions and so the process continues, hence the term overturning. Other process, such as winds and tides, also contribute to the thermohaline circulation.
The thermohaline circulation plays an important role in the Earth's climate system, for example by regulating the temperature in polar regions and so affecting the amount of sea ice. The thermohaline circulation partially drives the Atlantic Ocean Circulation, which is sometimes incorrectly known as the Gulf Stream. There has been some concern that climate change could trigger the MOC to shut down which in turn could lead to a cooling in north-west Europe.
Find out more
- IPCC Fourth Assessment Report, Working Group 1 report The Physical Science Basis , Chapter 5
- Briefing Note on the Gulf Stream on the UKCIP website