Waves are up and down movements, caused by the action of winds on the water surfaces. Waves move in the direction of winds. When ocean levels rise and fall at regualr intervals during the course of the day. This is referred to as the tide. Tides are caused by the gravitational attraction between the moon and the Earth. The horizontal and vertical circulation of ocean waters creates currents. Major causes of ocean currents are wind, friction, gravity, and variations in water density in different parts of the oceans. These currents modify local climates. They distribute the heat energy form one latitude to another. Let us learn now about the circulation of ocean currents.
The Currents :
An ocean current can be defined as a horizontal movement of seawater at the ocean’s surface. Ocean currents are driven by the circulation of wind above surface waters. Frictional stress at the interface between the ocean and the wind causes the water to move in the direction of the wind. Large ocean currents are a response of the atmosphere and ocean currents are responsible for the flow of energy from the tropics to polar regions. In some cases, currents are transient features and affect only a small area. Other ocean currents are essentially permanent and extend over large horizontal distances.
On a global scale, large ocean currents are constrained by the continental masses found bordering the three oceanic basins. Continental borders cause these currents to develop an almost closed circular pattern called a gyre. Each ocean basin has a large gyre located at approximately 30°
North and South latitude in the subtropical regions. The currents in these gyres are driven by the atmospheric flow produced by the subtropical high pressure systems. Smaller gyres occur in the North Atlantic and
Pacific Oceans centered at 50° North. Currents in these systems are