Notes-Class 9-Geography-Chapter-6-The Properties of Sea Water-Maharashtra Board

The Properties of Sea Water

Maharashtra Board-Class 9-Geography-Chapter-6

Notes

Topics to be Learn :

  • General characteristics of sea Water
  • Temperature of sea water
  • Salinity of sea water
  • Density of sea water

General characteristics of sea water :

  • Pacific Ocean is the largest water body on the earth.
  • The surface temperature of the seawater is not uniform everywhere.
  • Minerals from rocks and soil dissolve in water and get deposited in sea through rivers. This process is on for millions of years.
  • Evaporation took away only water but salt content remained in oceans. This made seas and oceans salty.
  • Land and water bodies vary in temperature.
  • Surface of the land gets heated fast and cools down rapidly. Water gets heated slowly and cools down slowly.
  • Temperature variation in heating up and cooling down of land is steep than that of water.
  • That is why, near equator average temperature of land is above 45°C while average temperature of ocean is about 25°C.
  • Near the poles the average temperature of land is -25°C while it is -2°C in case of water.

Temperature of sea water :

  • Temperature of sea water at surface and at depth is studied separately.

(i) Surface temperature of sea water :

(i) Surface temperature of sea water :

  • It is not uniform everywhere.
  • It changes with latitudes.
  • It decreases from equatorial areas towards the pole.
  • It is about 25°C near equator, about 16°C in mid latitude and 2°C near poles.
  • Location of the sea, ocean currents, cyclones, rainfall, sea waves, salinity, pollution, convectional moment of sea water, seasons, etc. factors influence the surface temperature of the sea.

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(ii) Temperature of seas as per the depth of water :

(ii) Temperature of seas as per the depth of water :

  • It decreases with increasing depth.
  • However, beyond a certain depth, temperature does not change much.
  • Temperature of the sea water changes rapidly with depth near equatorial areas. But such changes are moderate in mid latitude regions.
  • The difference in temperature with depth is lesser in polar region.
  • Most of the sun rays radiate back from surface of the sea and some of them penetrate to certain depth in water. The intensity of such sunrays decreases. Hence, after a certain depth, the temperature of the sea water remains same everywhere.
  • After 2000 m depth, the temperature of the sea water remains uniform at 4°C from the equatorial region to the polar areas.
  • Water at greater depth does not freeze.
  • The temperature of an open sea is always less than those of landlocked seas.

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Landlocked sea : Seas that are totally surrounded by land are called landlocked sea. Landlocked seas are not connected to any ocean.

Salinity of the sea water :

Salinity : The amount of salt in the water is gelled salinity of water.

  • Deposition of minerals and salts has made sea water salty.
  • Factors like temperature, evaporation, supply of fresh water, landlocked or open nature of sea decide salinity of sea water.
  • The buoyancy of sea water increases due to salinity. This is useful for water transportation as large and heavy ships easily float on such salty water.
  • Salt is obtained from the salt pans.
  • Salt is used in food as well as for making various chemicals and medicines.
  • Besides, salt is also used to preserve food for longer periods. It is also used in ice factories.

Distribution of salinity of sea water :

(i) Equatorial region:

  • Equatorial region between 5°N and 5°S, on one hand, has cloudy sky for longer periods and receive conventional rainfall every day.
  • Large rivers like Amazon and Congo also meet the sea in equatorial region and supply abundant freshwater. On the other hand, this region has higher temperature and more rate of evaporation. Therefore sea in these areas has a moderate to high salinity.

(ii) Tropical region :

  • Tropical region in general has a higher temperature and higher rate of evaporation and therefore, sea in tropical areas has a moderate salinity.

(iii) Mid latitudinal zones

  • Mid latitudinal zones between 25° and 35° in both the hemispheres has higher salinity.

(iv) Red Sea :

(iv) Red Sea :

  • Red Sea is an inlet part of an Indian Ocean which is located between the North East Africa and Arabian Peninsula.
  • The southern end of the sea is towards the Indian Ocean while the northern is as good as a landlocked sea.
  • There is a higher salinity in the Northern Red Sea while lower in the southern.
  • Salinity and temperature current of Indian Ocean largely influence and control the salinity and temperature of southern end.
  • High temperature and more evaporation have resulted in high salinity of the northern part of Red Sea.

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(v) Arabian Sea and Bay of Bengal :

(v) Arabian Sea and Bay of Bengal.

  • The temperature as well as the rate of evaporation of Arabian Sea is always high.  Narmada and Tapi are the only two major rivers of India meet Arabian Sea, which is less as compared to fresh water supply that the Bay of Bengal receive. As a result the salinity of Arabian Sea is as high as 36%.
  • All major rivers of India and Bangladesh namely Ganga, Mahanadi, Godavari, Krishna, Cauveri and Meghana empty in Bay of Bengal and provide abundant supply of fresh Water. As a result, the salinity of Bay of Bengal is less at 32%o, which is almost 4%o less than Arabian Sea.

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Know This :

With higher temperature and salinity, conditions to develop salt pans along the Arabian Sea are more conducive. Hence, the western coast of India along

Arabian Sea has more salt pans than the eastern coast of India along the Bay of Bengal.

(vi) Baltic Sea :

(vi) Baltic Sea :

  • It is located in temperate region and is a part of Northern Atlantic Ocean.
  • Baltic Sea is a landlocked sea and hence ocean currents of Atlantic Ocean do not make change in its properties.
  • Despite being a landlocked sea, less temperature, less evaporation and good supply of fresh water due to melting of ice caps resulted in less salinity of Baltic Sea.

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Other regions :

  • Temperate regions have less salinity.
  • Landlocked seas have more salinity than open seas.
  • The Dead Sea has a salinity of 332%.
Know This :

Dead Sea : The name of the sea itself gives an idea of the conditions there.

  • The sea is located at the border of Israel and Jordan.
  • This sea lies in mid latitude region and is surrounded by the deserts.
  • Dry climate, high temperature and less rainfall are salient features of this sea. The rate of evaporation is also very high.
  • All this has resulted in a very high salinity of sea which is 332%.
  • Saline pillars are developed due to very high salinity.
  • Normally the salinity of any sea is about 35%. Dead Sea salinity is 332%, which is almost 10 times more than the average. As a result, the density and buoyancy of the sea is also very high.
  • One can easily float in the sea.
  • In such a high salinity, no life survives except some unicellular organism.
  • The fish coming from the river Jordan also die as soon as they come here. Thus, this sea is named as the Dead Sea.

Density of sea water :

 Density of sea water :

  • Temperature and salinity of sea wider determine its density.
  • Temperature and density are inversely proportionate, i.e. if temperature is less then the density of sea water is more.
  • If salinity of the sea water is less then the density of sea water is also less.
  • However, despite less salinity, the density is more if the temperature of the sea water is less.
  • Effects of temperature and salinity on the density of the sea water is seen up to 500 m depth.
  • However, at the 1000 m depth, factors like temperature, salinity and density of sea water do not change.
  • The ocean currents are generated due to the difference in properties like temperature, salinity and density of sea water.
  • The distribution of temperature gets control due to ocean currents.
  • Regional climate of the earth also gets affected by the ocean currents.

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Useful links :

Main Page : - Maharashtra Board Class 9th Geography  - All chapters notes, solutions, videos, test, pdf.

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