UPSC Geography Oceans and Continents / महासागरों और महाद्वीपों Short Notes - Hydrosphere

Hydrosphere

Oceans and Seas

• The Oceans comprise more than 70% of the earth's surface.
• The Seas receive almost 71% of all incoming solar energy due to its surface area.
• Oceans are the primary source of moisture in the atmosphere and much of the rain over the continents.
• Oceans are repository of a large number of useful metallic and non-metallic minerals such as petroleum, gas, salt, manganese, gold, diamonds, tin and Iron.
• Most characteristic feature of oceans and seas is their salinity.
• Salinity varies both horizontally and vertically and is maximum at tropics and decreases towards the equator and poles.

Continental shelves

• Continental shelf in the seaward extension of the continent from the shoreline to the continental edge.
• Continental shelves are rich in plankton, on which millions of fish thrive.
• The continental shelves are therefore the richest fishing grounds in the world, e.g. the Grand Banks of Newfound land, North Sea and Sunda Shelf.

Composition of Sea Water

• Average temperature of surface water of the oceans is 26.7°C and temperature gradually decreases from equator towards the poles.

Pacific Ocean Currents

Atlantic Ocean Currents

Indian Ocean Currents   

Ocean Ridge

• Pacific Ocean is the largest of all water bodies.
• Mariana, Tonga, Kuril, Philippine, Japan are the trench of Pacific ocean.
• Most striking feature of the Atlantic Ocean is the presence of mid-Atlantic Ridge. It extends from the north to the south paralleling the'S' shape of the ocean itself.
• Java or Sunda, Mauritius, Amirante trench are some of the important trench of the Indian Ocean.

Continental Slope: It is a steep slope, situated beyond continental shelf towards ocean and the slope generally varies between 2° to 5°. The average depth of water near continental slope varies between 200 m to 2000 m.

Deep Sea /Abyssal Plain: The extensive plain covering around 80% of the total area of ocean basin is known as Abyssal plain. The average depth varies between 3000 m to 6000 m. Some of the famous plains under this category are Alaska plain, Ameresian plain. Barracuda plain, Canary basin. Green land plain, etc.

Ocean Deep: The long, narrow I topographic depressions or trenches are called as Ocean deep. They generally run parallel to the coast. Ocean deeps are considered on the boundaries between two lithospheric plate. The challenger Deep in Mariana Trench is the greatest known deep in this world (10,994 meters/36070 feet).

Other major physical features Associated with Ocean and Sea.

Bay: Bay are the small water bodies separated from the large water bodies by an inward curved piece of land. The famous bays of the world are, Hudson Bay, Bay of pig, Chesapeake Bay, Bay of Bengal, etc.

Gulf: These are the large part of ocean or sea partially land locked and opens up through straits only. The world famous gulfs are Gulf of Mexico, the southern coast of United State and Cuba, Gulf of California, Gulf of Arizona.

Tides

• The periodic phenomenon of alternate rise and fall in the sea levels is known as Tide.
• It is produced due to gravitational interaction of the Earth, the Moon and the Sun.
• Spring tides: On the full moon and the new moon, tides are highest which are called Spring tides.
• Neap tides: A tide just after the first or third quarters of the moon when there is least difference between high and low water is called Neap tides.

Waves

• Waves are the oscillatory movements in water mainly produced by winds, manifested'by an alternate rise and fall in the entire sea surface.
• This movement may include event such as slippage of the sea floor along the earth quake fault, underwater volcanic explosion or under water landslides.