Class 9 MAHARASHTRA STATE TEXTBOOK BUREAU Solutions Social Studies Chapter 6 - The Properties of Sea Water
The Properties of Sea Water Exercise 56
Solution 1(a)
Low
Solution 1(b)
Low
Solution 1(c)
High
Solution 1(d)
High
Solution 1(e)
Low
Solution 1(f)
High
Solution 2(a)
The Baltic Sea lies in the temperate region. In such regions, the sunrays are slanting and therefore, the temperatures are lower. Many rivers drain into the Baltic Sea. Hence, the supply of fresh water is more.
Therefore, despite being landlocked, due to low rate of evaporation and adequate supply of fresh water, the salinity of the Baltic Sea is low.
Solution 2(b)
The Red Sea is one of the saltiest bodies of water in the world, due to the high evaporation rate. The northern part of the Red Sea is more saline than the southern part because it mainly has the Gulf of Suez water which lies to the west of the Sinai Peninsula. The water from the Gulf of Suez is known to have a salinity of about 40 parts per thousand because of high evaporation and the resultant high density.
Solution 2(c)
Oceans located at the same latitude do not have same salinity because latitude does not affect the salinity of the ocean. In Oceans where rate of evaporation is more than the supply of fresh water, the salinity is higher. Oceans where a lot of rivers drains and have a low evaporation rate, the salinity is high. The salinity of the oceans depends on factors like rate of evaporation and supply of fresh water.
Solution 2(d)
The rays of the sun are not able to penetrate deep into sea water. This is the reason that temperature decreases up to 2000m. After the depth of 2000m, the seawater is around 40C everywhere from the equatorial to Polar Regions. The temperature does not fall below 40C. Thus, the seawater at a greater depth does not freeze.
Solution 2(e)
- The Arabian Sea lies lying to the west and Bay of Bengal lies to the east of India.
- Many large peninsular rivers drain their waters in the Bay of Bengal and on the contrary, only small seasonal coastal rivers drain in the Arabian Sea.
- Hence, the salinity of the eastern coast is 34%, while it is 35% in the Arabian Sea.
- Thus, there are more salt-pans on the Western coast of India than its Eastern coast.
Solution 2(f)
- Mid-latitudinal zones lies between 25° to 35° north and south of the equator.
- In this zone, the rainfall is less and the supply of fresh water from rivers is also low.
- This region experiences high-temperature conditions which are marked by the presence of hot deserts of the world. These high-temperature conditions lead to a high rate of evaporation.
- Thus, the salinity of the seas is higher in mid-latitudinal zones.
Solution 3(a)
The uneven distribution of temperature on earth and uneven supply of freshwater affects the salinity of seawater.
- The rate of evaporation and the supply of freshwater greatly affect the salinity of the oceans or the seas.
- Because of sun's heat, evaporation happens at a faster rate. Water evaporates leaving the salt behind. In seas where evaporation is high, the salinity is high. For example, in the tropical zone, temperature is higher. Rate of evaporation is also higher and therefore, the salinity is higher. For example, many large peninsular rivers drain their waters in the Bay of Bengal and on the contrary, only small seasonal coastal rivers drain in the Arabian Sea.
- Hence, the salinity of the eastern coast is less than the western coast.
- Salinity of a sea is not affected if the supply of freshwater and evaporation of water is low.
Solution 3(b)
The uneven distribution of temperature on earth, uneven supply of freshwater, etc. affects the salinity of seawater. In tropical zone, temperature is higher and the rate of evaporation is also higher, therefore, salinity is higher.
Solution 3(c)
- The surface temperature of sea water is not the same everywhere. This is dependent on various factors.
- The surface temperature of sea water decreases from equatorial regions towards the Poles.
- Besides the latitudinal location, rainfall, cyclones, sea waves, salinity, convectional currents and pollution also affect the surface temperature of oceans.
- In regions where the cold ocean currents flow, the surface ocean temperature is low. It is high in those regions where warm ocean currents flow.
Solution 3(d)
- The rays of the sun are not able to penetrate deep into sea water. This is the reason that temperature decreases up to 2000m.
- After the depth of 2000m, the seawater is around 40C everywhere from the equatorial to Polar Regions.
- The temperature does not fall below 40C. Thus, the seawater at a greater depth does not freeze.
- The surface temperature of the sea changes rapidly with depth at the equatorial regions. In Polar Regions the difference in temperature is less.
Solution 3(e)
The rate of evaporation and the supply of freshwater greatly affect the salinity of the oceans or the seas.
- Because of sun's heat, evaporation happens at a faster rate. Water evaporates leaving the salt behind. In seas where evaporation is high, the salinity is high.
- In those seas where the supply of freshwater exceeds the rate of evaporation, salinity is low.
- Salinity of a sea is not affected if the supply of freshwater and evaporation of water is low.
Solution 4(a)
Reduction in temperature increases the density of sea water. Sea water gets denser as temperature goes down. So, the cold water is denser than the warm water. Increasing salinity also increases the density of sea water.
Solution 4(b)
The presence of salt in water increases its density. Thus, the sea water which is saline is denser than the sea that is less saline.
