Ocean circulation

define ocean circulation

The large-scale movement of seawater in the Earth’s oceans and also plays an important role in distributing heat around the planet. 

Surface currents are driven by major wind belts, e.g. trade winds, westerlies and polar easterlies.  These major wind belts transfer energy to the ocean surface, causing the water to move. 

Gyres

Gyres are large patterns of circulation, which can be found in each major ocean basin.

For example:

• The Gulf Stream is a part of the larger North Atlantic Subtropical Gyre, where the warm water from the Caribbean sea flows along the eastern coast of the USA, and then heads north-eastward into the North Atlantic Ocean. 

• The surface current has high wind speeds, e.g. 2-4 knots. The Gulf stream can enhance rainfall on the east coast of the USA and has a warming effect on the climate of north-western europe

What drives deep currents?

Deep currents (or thermohaline circulation/global conveyor belt) are driven by differences in temperature and salinity. 

Deep current: cold and dense water

Cold and dense water

Sinks and flows along the ocean floor

In the North Atlantic, surface water cools and becomes denser, sinking to form North Atlantic Deep Water (NADW). This deep water flows southward along the Ocean floor.

Deep current: warm and less dense water

Warmer, less dense water

Rises towards the surface

In the Southern Ocean deep water rises to the surface, eventually forming Antarctic Intermediate Water (AAIW). This water then flows northward.

What is the relationship between temperature and pressure?

If air pressure decreases, the temperature decreases. It also explains why air gets colder at higher altitudes, where pressure is lower.

Low and high pressure

Due to global atmospheric and ocean circulations, a pattern of pressure builds up. The distribution of this varies with seasons. The Siberian high is a semi-permanent high pressure system, which tends to dominate northern Asia; it plays a vital role in the development of Asian winter monsoon as the pressure differences between the Siberian high and the lower pressure systems drives the flow of cold air from the continent towards the oceans. 

What is Contentiality?

Contentiality is the degree to which the climate of a region is influenced by its distance from the moderating effects of large bodies of water (like oceans and large lakes).  Main effects are greater temperature range between seasons, lower precipitation, drier air and delayed seasons.