Hydrosphere

The part of the earth's surface is covered by water is called hydrosphere. Large divisions of salt water are called oceans and portion of them more or less enclosed by land are known as seas.

          Nearly 71 percent of the earth's surface is covered by water. The volume of water in the hydrosphere is about 1250 million cubic kilometers and the volume of all lands above sea level is only 69.4 million cubic kilometers i.e. 1/18th of the total volume of water in the world. If all the ups and downs of the lithosphere are leveled up, the water of hydrosphere will submerge the entire globe up to a depth of 3650 meters.

          The Pacific Ocean: It is the biggest and deepest ocean. It covers more than one third of the surface of the earth. It is bounded by North and South America on the east and Asia and Australia on the west. The area of this ocean is 16,43,00,000 sq. km.

          Atlantic Ocean: It is also biggest ocean of the world. It is bounded by Europe and Africa on the east and North and South America on the west. It is the saltiest ocean of the world. The area of this ocean is 8,20,00,000 sq. km.

          The Indian Ocean: It is mostly lies on the Southern Hemisphere. It is bounded by Asia on the north, East Indies on the east and Australia and Africa on the west. The area of this ocean is 7,30, 00,000 sq. km.

          90% of the total area of hydrosphere is covered by these three oceans.
Movements of the Ocean Water:
·        Ocean Current
·        Tides
·        Waves

Ocean Current
          Regular movements of the surface waters of the oceans in particular direction are called ocean currents. They are the actual movement of water like a river, so they are called oceanic rivers of cold or warm water flowing in the ocean.

Two Types of Ocean Currents
1.     Warm or surface current
2.     Cold or under current

Causes of the Ocean Current Formation
1.     Permanent winds or Prevailing wind
2.     Variation in Temperature
3.     Variation in Salinity
4.     The Rotation of the earth
5.     The Direction of Land masses

1. Prevailing Winds: Generally it is said that prevailing winds are the chief cause of the currents in the ocean. The wind drifts the surface layers of the ocean water and gives birth to the current. The Trades and the Westerly give rise to the chief current of the world.

2. Variation in Temperature: it is also believed that ocean currents are caused by the difference of temperature of polar and equatorial water. Warm water is lighter than cold water. Hence, the warm water near the equator expands and flows towards the poles, and cold water of the Polar Regions flows towards the equator along the bottom of the ocean. Thus, a cycle of currents is produced.

3. Variation in salinity: Saline water is denser and heavier than fresh water. Fresh water flows on the surface of the oceans or seas, while the salty water being denser and heavier sinks below. Where two seas with different salinities connected together, a current flows the less saline sea to the more saline sea. The currents flow between Atlantic Ocean and Mediterranean Sea caused by the variation of salinity of the ocean water.

4. The Rotation of earth: The rotation of the earth brings about change in the direction of currents. Because of this reason, the currents in the Northern Hemisphere are deflected to their right and those in the Southern Hemisphere are deflected to their left.

5. The Direction of Land masses: The direction of land masses affects the direction of currents. For example, the south equatorial current is parted by the Cape san Roque and instead of keeping its westerly direction; it is deflected partly to the left and partly to the right.