Ocean and Seawater - Class VII

The Dead Sea is one of the world's saltiest bodies of water, with a salinity significantly higher than that of the open ocean.

The average surface temperature of the world's oceans generally ranges from about 2 degrees Celsius to 29 degrees Celsius. This range accounts for the variation from polar waters to tropical regions.

Over millions of years of rain, rivers and streams have washed over rocks containing the compound Sodium Chloride and carried it into the seas and oceans.

Salinity is the saltiness or dissolved salt content in a body of water. Salinity is an important factor in determining many aspects of the chemistry of natural waters and of biological processes within it, and is a thermodynamic state variable that, along with temperature and pressure, governs physical characteristics like the density and heat capacity of the water.

Factors affecting salinity in surface layers of ocean include:

1. The salinity of water in the surface layer of oceans depends mainly on evaporation and precipitation.
2. Surface salinity is greatly influenced in coastal regions by the fresh water flow from rivers, and in polar regions by the processes of freezing and thawing of ice.
3. Wind, also influences salinity of an area by transferring water to other areas.
4. The ocean currents contribute to the salinity variations.
5. Salinity, temperature and density of water are interrelated. Hence, any change in the temperature or density influences the salinity of an area.

Although many factors combine to influence weather, the four main ones are solar radiation, the amount of which changes with Earth's tilt, orbital distance from the sun and latitude, temperature, air pressure and the abundance of water.

After 2000m, the temperature of the seawater is uniform everywhere. It
is around $4^0C$ according to depth. And therefore, the water of greater
depths does not freeze.

Temperate is one of the major property of seawater. It always varies from region to region. The surface temperature of the sea water decreases from the equatorial area towards the poles. Some factors which effects the temperature of sea water are:-

• Cyclone
• Rainfall
• Salinity
• ocean currents
• pollution

After 2000m, the temperature of the seawater is uniform everywhere. It is around $4 ^oC$ according to depth. And therefore, the water of greater depths does not freeze.

Temperate is one of the major property of seawater. It always varies from region to region. The surface temperature of the sea water decreases from the equatorial area towards the poles.

In seas where the supply of freshwater exceeds the rate of evaporation, salinity is low. Near the estuaries generally the salinity is low because ample amount of fresh water enters the sea or ocean.

Because of the sun's heat, evaporation happens at a faster rate. Evaporated water turns into water vapour and reduces in quantity. But amount of salt remains the same in the remaining water and therefore the salinity of the water increases.

The uneven distribution of temperature on earth, uneven supply of freshwater, etc. affects the salinity of seawater. If temperature is high, evaporation will be high and it will result in high salinity. Again if evaporation is high but supply of fresh water exceeds evaporation than salinity will be low. So in many ways the salinity of sea water is effected.

Salinity is the amount of salt dissolved in a body of water. Salinity is an important factor in determining many aspects of the natural waters and of biological process within it, and is a thermodynamic state variable that, along with temperature and pressure, governs physical characteristics like the density and heat capacity of the water.

Temperature and salinity are the two properties of sea water that control the density of the sea water. If temperature reduces, density of water increases.

In tropical zone, temperature is generally higher than the other parts and so the rate of evaporation is also higher, therefore, salinity is higher.

In seas where the rate of evaporation is high than the supply of freshwater, salinity is high. It happens because due to evaporation water turns into water vapour and reduces in quantity, but the amount of salt remains the same.

In the polar areas, temperature is very low and hence evaporation is also very less in polar areas, so salinity is low.

Salinity is not affected much in seas where both the supply of freshwater and evaporation of water is low. Because in both the reasons salinity almost remains the same.