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MOVEMENTS OF OCEAN WATER 111 Differences in water density affect vertical desilting the sediments and in removing mobility of ocean currents. Water with high polluted water from river estuaries. Tides are used to generate electrical power (in Canada, salinity is denser than water with low salinity France, Russia, and China). A 3 MW tidal and in the same way cold water is denser than power project at Durgaduani in Sunderbans warm water. Denser water tends to sink, while of West Bengal is under way. relativelylighterwatertendstorise.Cold-water ocean currents occur when the cold water at O CEAN C URRENTS the poles sinks and slowly moves towards the equator. Warm-water currents travel out from Ocean currents are like river flow in oceans. They represent a regular volume of water in a the equator along the surface, flowing towards definite path and direction. Ocean currents are the poles to replace the sinking cold water. influenced by two types of forces namely : Types of Ocean Currents (i) primary forces that initiate the movement of water; (ii) secondary forces that influence the The ocean currents may be classified based on currents to flow. their depth as surface currents and deep water The primary forces that influence the currents : (i) surface currents constitute about currents are: (i) heating by solar energy; 10 per cent of all the water in the ocean, these (ii) wind; (iii) gravity; (iv) coriolis force. Heawaters are the upper 400 m of the ocean; by solar energy causes the water to expand. (ii) deep water currents make up the other 90 That is why, near the equator the ocean water per centoftheoceanwater.Thesewatersmove is about 8 cm higher in level than in the middle around the ocean basins due to variations in latitudes. This causes a very slight gradient the density and gravity. Deep waters sink into and water tends to flow down the slope. Wind the deep ocean basins at high latitudes, where blowing on the surface of the ocean pushes the the temperatures are cold enough to cause the water to move. Friction between the wind and density to increase. the water surface affects the movement of the Ocean currents can also be classified water body in its course. Gravity tends to pull based on temperature : as cold currents and the water down the pile and create gradient warm currents: (i) cold currents bring cold variation. The Coriolis force intervenes and water into warm water areas. These currents causes the water to move to the right in the are usually found on the west coast of the northern hemisphere and to the left in the continents in the low and middle latitudes southernhemisphere.Theselargeaccumulations (true in both hemispheres) and on the east of water and the flow around them are called coast in the higher latitudes in the Northern Gyres. These produce large circular currents Hemisphere; (ii) warm currents bring warm in all the ocean basins. water into cold water areas and are usually observed on the east coast of continents in the Characteristics of Ocean Currents low and middle latitudes (true in both hemispheres). In the northern hemisphere Currents are referred to by their “drift”. they are found on the westcoastsofcontinents Usually, the currents are strongest near in high latitudes. the surface and may attain speeds over five knots. At depths, currents are Major Ocean Currents generally slow with speeds less than 0.5 Major ocean currents are greatly influenced by knots. We refer to the speed of a current as its “drift.” Drift is measured in terms thestressesexertedbytheprevailingwindsand of knots. The strength of a current refers coriolis force. The oceanic circulation pattern to the speed of the current. A fast current roughlycorrespondstotheearth’satmospheric is considered strong. A current is usually circulation pattern. The air circulation over the oceans in the middle latitudes is mainly strongest at the surface and decreases anticyclonic (more pronounced in the southern in strength (speed) with depth. Most hemisphere than in the northern hemisphere). currents have speeds less than or equal The oceanic circulation pattern also to 5 knots. correspondswiththesame.Athigherlatitudes, Reprint 2026-27