Ocean Currents
Ocean currents are distinctive movements of the ocean’s surface water. Driven by forces such as tides, wind and gravity, currents keep our oceans in constant motion. Ocean currents can flow for thousands of kilometres and they are very important in determining the climates of the continents, especially those regions bordering the ocean.
Countless currents have been named, but the seven major ones are the Antarctic Circumpolar Current (or West Wind Drift), East Wind Drift, the North and South Equatorial Currents, the Peru Current, the Kuroshio Current and the Gulf Stream. These currents flow in large rotating loops called gyres. In the northern hemisphere, gyres spin in a clockwise direction, and in the southern hemisphere, gyres spin in an anti-clockwise direction. This is because of the Earth’s spinning rotation and is called the Coriolis Effect.
In the Atlantic Ocean there are equatorial currents which flow east to west (because of the effects of the Trade Winds). The North Equatorial Current flows north from the Equator to the Gulf of Mexico. Here it turns because of the shape of the land and the Earth’s rotation. It then flows northwards towards the UK.
It is because of the North Atlantic current that we in the UK have milder winters than other places at the same latitude as the warm current warms our seas and the wind that approaches from the south-west.
This current then moves north towards the North Pole. Here, because of the cooling effect of the ice sheets, the water cools sinks and makes its way, as a colder current (the Labrador Current) south towards the Equator. This makes the coastline it passes (Canada and Greenland) colder than it would be without the effect of the current.
There is a relatively new school of thought that claims global warming may actually result in the UK being colder than it is now (instead of hotter) because the warm current is being stopped as the ice caps are melting. If the ice caps melt, there will no longer be the cooling and sinking of the water at the poles. Without this part of the circle, the other part (the warm current) would cease to exist. Only time will tell!
There are also similar movements in the Southern Atlantic and Pacific Ocean. The Pacific Currents reverse through the year due to the changes in the monsoon wind direction.
In terms of fishing, where there are warmer currents certain types of fish that live in the warmer seas will be found further north than they would without the current and vice versa.
Without currents, the Earth's temperatures would change dramatically as they perform a job that benefits the entire planet as they act as enormous heat reservoirs and store heat in the summer and release it during the winter. Currents are the mass transport system that moves large amounts of heat, plus suspended solids and dissolved chemicals between high and low latitudes, effectively moderating the world’s climate.
Knowledge of surface ocean currents is essential in reducing costs of shipping, since they reduce fuel costs. In the sail-ship era knowledge was even more essential. A good example of this is the Agulhas current, which long prevented Portuguese sailors from reaching India. Even today, shipping companies employ surface currents to their benefit.