Ocean Currents
Nutrients Upwelling from the Deep Enrich Coastal Waters
Seawater moves around the globe modifying climates and sustaining fisheries.
Surface ocean currents
Wind moves surface water, and in the northern hemisphere the spinning of the earth deflects this movement so that we end up with currents that move in a clockwise circle in the Pacific and North Atlantic. In the Pacific this brings cool surface waters south along the West Coast of America, and in the North Atlantic warm waters are moved north along the East Coast and on to Western Europe.
- California Current - The California Current is first noticed off southern British Columbia, and is felt as far south as California. This means that the West Coast waters are cooler than those on the East Coast (at the same latitude).
- Gulf Stream - Warm coastal water flows north up the eastern seaboard and then swing over to keep Northern Europe relatively warm. In Europe the ‘Warm Medieval Period’ was followed by the ‘Little Ice Age’, and it is thought that this was caused by a reduction in the flow of water (the Gulf Stream is thought to have been weaker during the seventeenth and eighteenth centuries).
Deep Ocean Currents
Below the surface of the sea differences in water density drive the deep currents. They are relatively cold and pick up nutrients as they gather mineral material from the deep and the remains of organisms that drift down to them from the surface. Three thousand robots are wandering worldwide gathering data about these deep currents (Argo.net) and the information they record will vastly improve our understanding of the nature of these ‘underwater rivers’.
Upwelling
When the wind blows surface water away from the coast it is replaced by water which rises from the depths. This coastal upwelling brings nutrients to the surface where they fuel ‘blooms’ of phytoplankton, which in turn feed huge populations of animal plankton as well as fish, birds etc..
Unplanned Experiments!
On at least two occasions ships have lost cargo and oceanographers have benefited. In 1990 thousands of training shoes were washed overboard (May 27, 48°N, 161°W), and in 1992 this was followed by the accidental release of plastic bathtub toys (January 10, 44.7°N, 178.1°E). The bath toys floated and the trainers sank below the surface, so it was possible to gather information about both surface and sub-surface currents.
Oceanographers calculated where the floating toys ‘ought’ to be washed up, and on November 16 1992 (ten months later) they arrived on the Alaskan coast as predicted. Although this ‘experiment’ was not actually planned it proved to be an extremely good test for the accuracy of the mathematical models which are used to predict water movements. These models are used to predict the likely movement of oil-spills, so it is good to see that they work well. (It also shows that oceanographers do play with rubber ducks on occasions!)
Here is a list of important ocean currents, with links to further information.
Read an article about the effects of changing ocean currents on seabirds
Other articles by John Blatchford
