~The Motion of the Ocean~
*Causes of Currents*
Ocean currents can be generated by wind, density differences in water masses caused by temperature and salinity variations, gravity, and events such as earthquakes. Currents are cohesive streams of seawater that circulate through the ocean.
What are gyres? Where do they occur?
A gyre in oceanography is any large system of rotating ocean currents, particularly those involved with large wind movements. Gyres are caused by the Coriolis effect; planetary vorticity along with horizontal and vertical friction, which determine the circulation patterns from the wind curl (torque).
Western/Eastern Ocean Boundary Currents
Global winds drag on the water’s surface, causing it to move and build up in the direction that the wind is blowing. And just as the Coriolis effect deflects winds to the right in the Northern Hemisphere and to the left in the Southern Hemisphere, it also results in the deflection of major surface ocean currents to the right in the Northern Hemisphere (in a clockwise spiral) and to the left in the Southern Hemisphere (in a counter-clockwise spiral). These major spirals of ocean-circling currents are called “gyres” and occur north and south of the equator.
Countercurrents, Upwelling, and Downwelling
Upwelling and downwelling describe mass movements of the ocean, which affect both surface and deep currents. These movements are essential in stirring the ocean, delivering oxygen to depth, distributing heat, and bringing nutrients to the surface. The Equatorial Counter Current is an eastward moving, wind-driven flowing 10-15m deep current found in the Atlantic, Indian, and Pacific Oceans. More often called the North Equatorial Countercurrent (NECC), this current flows west-to-east at about 3-10°N in the Atlantic and Pacific basins, between the North Equatorial Current (NEC) and the South Equatorial Current (SEC).
Heat Transport and Climate
The transfer of heat is normally from a high temperature object to a lower temperature object. Heat transfer changes the internal energy of both systems involved according to the First Law of Thermodynamics. The Earth’s climate is driven by a continuous flow of energy from the sun. Energy in the form of heat, from the sun, passes through the Earth’s atmosphere and warms the Earth’s surface. As the temperature increases, the Earth sends heat energy (infrared radiation) back into the atmosphere. Some of this heat is absorbed by gases in the atmosphere, such as carbon dioxide (CO2) , water vapour, methane, nitrous oxide, ozone and halocarbons.
El nino ENSO
El Niño is the warm phase of the El Niño Southern Oscillation (commonly called ENSO) and is associated with a band of warm ocean water that develops in the central and east-central equatorial Pacific (between approximately the International Date Line and 120°W), including off the Pacific coast of South America.
Deep Water Currents
An underwater current circles the globe with a force 16 times as strong as all the world's rivers combined [source: NOAA: "Ocean"]. This deep-water current is known as the global conveyor belt and is driven by density differences in the water. Water movements driven by differences in density are also known as thermohaline circulation because water density depends on its temperature (thermo) and salinity.
Studying Ocean Currents
As scientists struggle to understand how and why the earth's climate is changing, they are increasingly looking deep into the oceans, where oscillations in water temperature that travel on stately currents from one continent to another may cause weather trends to change from decade to decade.