● Statement 1 is correct: Tides are also helpful in desilting the sediments and in removing polluted water from river estuaries.

● Tides are used to generate electrical power (in Canada, France, Russia, and China). A 3 MW tidal power project at Durgaduani in Sunderbans of West Bengal is under way.

● Statement 2 is correct: Since tides are caused by the earth-moon-sun positions which are known accurately, the tides can be predicted well in advance.

● This helps the navigators and fishermen plan their activities. Tidal flows are of great importance in navigation.

● Tidal heights are very important, especially harbours near rivers and within estuaries having shallow ‘bars’ at the entrance, which prevent ships and boats from entering into the harbour.

● During high tides when the water level rises, these ships navigate towards the port due to availability of abundant water.

The Agulhas Current is the western boundary current of the South-West Indian Ocean. It flows down the east coast of Africa. The source water at its northern end is derived from Mozambique channel eddies and the East Madagascar Current, but the greatest source of water is recirculation in the southwest Indian Ocean sub-gyre. Hence, pair 1 is correctly matched.

The Irminger Current is a north Atlantic ocean current setting westward off the southwest coast of Iceland. It is composed of relatively warm and saline waters from the eastern North Atlantic that are fed by the North Atlantic Drift. The Irminger Current is part of the North Atlantic subpolar gyre. Hence, pair 2 is incorrectly matched.

The Humboldt Current, also called the Peru Current, is a cold, low-salinity ocean current that flows north along the western coast of South America. Hence, pair 3 is correctly matched.

All of the above mentioned factors are responsible for generation of ocean currents.

● Ocean currents are influenced by two types of forces namely :

● (i) primary forces that initiate the movement of water;

● (ii) secondary forces that influence the currents to flow.

● The primary forces that influence the currents are:

â heating by solar energy;

â wind;

â gravity;

â coriolis force.

● Heating by solar energy causes the water to expand. That is why, near the equator the ocean water is about 8 cm higher in level than in the middle latitudes.

● This causes a very slight gradient and water tends to flow down the slope. Wind blowing on the surface of the ocean pushes the water to move.

● Friction between the wind and the water surface affects the movement of the water body in its course.

● Gravity tends to pull the water down the pile and create gradient variation. The Coriolis force intervenes and causes the water to move to the right in the northern hemisphere and to the left in the southern hemisphere.

Kuro Shio Current is a warm ocean current on the west side of the North Pacific Ocean. The warm waters of this current help to keep the Alaska coast ice free in winter.

Oya Siwo Current is a cold ocean current in the western North Pacific Ocean.

Peru Current (Humboldt Current) is a cold ocean current that flows north along the western coast of South America. The cold waters of the Peru Current are partly responsible for making the coast of northern Chile and western Peru with very scanty rainfall.

The Antarctic Circumpolar Current is an ocean current that flows clockwise from west to east around Antarctica. An alternative name for the ACC is the West Wind Drift.