Ocean Currents and Tides

The earth’s oceans are really vast and majestic. They contain many beautiful plant and animal species. Two of the main forces of the oceans are ocean currents and ocean tides.

Ocean Currents

The horizontal and vertical circulation of ocean waters are known as currents. The main causes of ocean currents include variation in water density, gravity and wind friction. Surface ocean currents are primarily caused by the wind. Drift currents are surface currents produced primarily by the wind. Ocean currents can flow for thousands of kilometers and play a significant role in the climate of continents.

The winds that mainly affect the ocean currents are

• The Westerlies (40-50 degree latitudes) blow from west to east.
• The Trade Winds (20 degree latitudes) blow from east to west.

Both of these winds are a consequence of warm air from the tropics moving to the poles and the Coriolis effect (as water moves clockwise in the Northern Hemisphere and counter-clockwise in the Southern Hemisphere, because of the rotation of the Earth). Since continents block these enormous circular currents, smaller (though still huge) ocean current circles termed gyres are created. Differences in water density significantly affect vertical ocean currents (movement of surface ocean water to the bottom of the ocean and movement of deep ocean water to the surface). Variations in water density are caused by the temperature and variations in salinity (the amount of salt in water). Saltier water is denser than less salty water; cold water is denser than warm water. Less dense water tends to rise while denser water tends to sink. Cold-water currents are created as the cold water at the poles sinks and slowly moves toward the equator. Warm-water currents move from the equator along the surface, flowing toward the poles to replace the sinking cold water. As these currents mix the ocean's surface and deep waters, they help replenish the stock of oxygen in the water. Other causes of currents include ocean bottom topography tides, rain and runoff. Ocean topography includes mountains, slopes, ridges and valleys.

The seven major ocean currents are the Kuroshio Current, the Peru Current, the North and South Equatorial currents, East Wind Drift, the Gulf Stream and the Antarctic Circumpolar current. The Gulf Stream is one of the strongest existing currents. The Stream moves along through the Gulf of Mexico, past the east coast of the United States and on to Northern Europe. Without the warm Gulf Stream, England and other places in Europe would be equally cold as Canada. El Nino is a nature’s phenomenon in which an ocean current is reversed resulting in devastating climate changes from the west coast of South America all the way to Australia. Currents act as massive heat reservoirs and store heat during the summer and release it in the winter.

Ocean Tides

The Ocean surface rises and falls because of the motion of the earth and gravitational forces of the moon and sun. Other factors, which influence tides, include weather, winds, seafloor topography, local water depth and coastline configuration. The moon has the maximum effect on tides. The sun’s effect is about 40% of the moon. Tides originate in the ocean and move toward the coastlines. Tidal range is defined as the difference in height between the high tide and the low tide. The incoming tide along the coast is termed a flood current. The outgoing tide is termed an ebb current. The strongest flood and ebb currents generally take place before or near the time of the high and low tides. The weakest currents take place between the flood and ebb currents and are termed slack tides. Tidal flows must be taken into account for accurate navigation of the ocean. Tidal energy is known to be a clean, renewable source of energy. Even though tidal mills have been used since the Eleventh century, today only one sizable tidal power plant has been built, the 240 MW Rance Tidal Power Station in France.