Introduction :

Hydrosphere :

The main constituents of the hydrosphere :

• All of the earth's water bodies are a part of the hydrosphere. All oceans, seas, rivers and their tributaries, lakes, reservoirs, and groundwater are included in this.
• Oceans constitute 97.7% of all the world's water.

 Salts in water :

• In drinking water, the proportion of salts is quite low.
• Water from oceans and seas has a greater amount of salt. Hence, it tastes salty.

Causes of the rise in the levels of minerals and salts in ocean water :

• The oceans are home to a variety of living species, from tiny planktons to enormous whales. When they die, their remains end up in the sea.
• Remains of aquatic life, trees, and bushes flowing with the river water, etc. gets decomposed in oceans releasing various minerals and salts in the ocean water.
• Volcanic eruptions taking place in oceans results in adding of different minerals, ashes, salts and gases to the ocean water.
• Due to continuous evaporation of ocean water, the proportion of salt increases.

Salinity of ocean water :

• Salinity of ocean water is expressed in terms of mils. (particles per thousand : %o)
• The average salinity of oceanic water is 35 %o.
• The Dead Sea is known to have the maximum salinity. Its salinity is 332 %o.

Salt pans and salt and other minerals :

• Salt as a substance is obtained by constructing salt pans in the coastal areas.
• Salt is an item in our diet.
• Like salt, many other minerals like phosphates, sulphates, iodine, etc. are also obtained from the sea.

Fish and other marine animals :

• We get fish from seas, rivers and lakes. The proportion of fish in seas is much greater than of those in rivers and lakes.
• Catching marine animals is a large scale activity the world over. It is one of the ancient occupations of human beings.
• Marine animals are used for preparing various food items, producing fertilizers, pharmaceuticals, etc. and for research.
• The life of people from countries/islands like Seychelles, Mauritius, Maldives, etc. largely depends on the sea.

Oceans and Climate :

• We can observe that the nearness to the sea and continentality is the main reason leading to differences in the temperature range of different places.
• The places that are far away from the oceans have a greater temperature range.
• In the regions close to the oceans, because of the heating of sea water, water vapour gets mixed in the air. This water vapour holds the heat in the air and the air remains humid. Therefore, regions close to the oceans have an equal climate.
• In the regions far away from the oceans, the amount of water vapour is extremely less. As its effect, the air remains dry. Therefore, regions fax away from the oceans have an extreme climate.

Pressure Belts and Winds :

• The equatorial region receives perpendicular sunrays. As a result, this region gets more heat. On the other hand, polar regions receive extremely slanted sunrays_ As a result, these regions get less heat.
• This differential heating creates imbalance in the temperature of air in different parts. This in turn leads to formation of belts of high and low pressure on the earth
• Winds blow due to pressure differences in these belts. These winds are called Planetary winds.

Ocean currents :

• Planetary Winds move the oceanic water in the form of currents. Ocean currents are of the following two types : (1) Warm ocean currents and (2) Cold ocean currents.
• Warm ocean currents move from the equatorial region to the polar regions and cold ocean currents move from the polar regions to the equatorial region. This leads to redistribution of heat on the earth.
• Cold ocean currents flowing from the polar regions to the equatorial zones reduce the temperatures of the coasts in the equatorial region.
• The warm ocean currents flowing from the equatorial region to the polar regions increases the temperatures of the coasts in the polar region.

Water cycle :

• The oceans have vast expanse. Therefore, huge amount of vapour is created.
• From this vapour, the earth gets rainfall. Thus, oceans are the source of rains.
• The rainwater flows through streams and rivers and finally flows back into the oceans.
• It means the beginning and end of the water cycle takes place in the oceans.
• The water cycle indicates that the movement of water between earth’s surface and earth’s atmosphere is continuous in nature.

Ocean and resources :

Man gets the following resources from the oceans :

• Minerals like iron, lead, cobalt, sodium, manganese, chromium, zinc, etc.
• Precious items like pearls and corals and ornamental items like shells.
• Mineral oil and natural gas.
• Food items like prawns, clams, crabs, starfish, mackerel, pomfret, Indian shark
• Indian salmon, etc. and medical plants.

Oceanic Transport :

• Oceans have provided us the most economic option of transportation.
• Waterways are used extensively for international trade.
• Countries like Spain, Norway, and Japan have become more significant in maritime transportation.
• By waterways, bulky materials like coal, crude oil, raw materials, metallic materials, food grains, etc. can be transported with ease.
• Water transport carried out along ocean currents, accelerates the speed of ships and also saves fuel to a considerable extent.

Issues related to oceans :

• Water covers roughly 70.8% of the earth's surface. Man engages in numerous activities in order to satisfy his needs.
• These cause the generation of vast quantities of various waste types. These waste products contribute to pollution.
• Oceanic water pollution is a significant and dangerous problem that has emerged recently.

Causes of an increase in pollution of oceanic water :

• Oil spills, exploitative fishing, releasing the waste produced in the coastal cities into the seas, sewage released by industries and cities, etc. factors have caused an increase in pollution of oceanic water. ‘
• As a result, many aquatic animals are under the threat of being extinct.