Q1. Tick the correct box according to the salinity of the ocean water ✔
Ans.
Q2. Give reasons.
(a) Salinity is low in the land-locked Baltic Sea.
Ans.
(1) The Baltic Sea lies in the temperate region. (2) The fresh water from the surrounding land gets run off and the salt density is also low. (3) Hence, despite a landlocked sea due to less temperature, less evaporation, good supply of fresh water salinity is low in the land-locked Baltic Sea
(b) There is higher salinity in the northern Red Sea while lower in the southern.
Ans. (1) Red Sea is one of the saltiest bodies of water in the world, owing to high evaporation. (2) The salinity is 35‰ in the southern part because of the effect of the Gulf of Aden. (3) It reaches 41‰ in the northern part, owing mainly to the Gulf of Suez and the high evaporation as well as very little precipitation. (4) Hence there is higher salinity in the northern Red Sea while lower in the southern.
(c) Oceans located at the same latitude do not have same salinity.
Ans. (1) The salinity of the oceans depends on factors like temperature, rate of evaporation and supply of freshwater. (ii) Oceans where rate of evaporation is more than the supply of freshwater, the salinity is higher. (iii) Oceans where supply of freshwater exceeds the rate of evaporation, salinity is low.
(d) With increasing depth, the temperature of sea water decreases to a certain limit.
Ans. (1) While most of the sunrays radiate back from the surface of the sea, some of them penetrate to certain depths in the water. (2) As a result, the intensity of sunrays decreases with the increasing depth. (3) The temperature decreases up to 2000m depth. After 2000m, the temperature of the seawater is uniform everywhere. (4) Hence, With increasing depth, the temperature of sea water decreases to a certain limit.
(e) There are more salt-pans on the Western coast of India than its eastern coast.
Ans. (1) Sea is deeper in western coast than sea on eastern coast. (2) Most of the rivers drain their waters in the Bay of Bengal but, only small seasonal coastal rivers drain in the Arabian Sea. (3) Hence, the salinity of the eastern coast is less than 34 ‰, while it is as high as 36‰ in the Arabian Sea. (4) Thus, there are more salt-pans on the Western coast of India than its Eastern coast.
(f) Salinity increases in the mid-latitudinal zones.
Ans. (1) In mid-latitudinal zones (25° to 35° N and S), rainfall is less and the supply of freshwater from rivers is also low. (2) This zone has the hot deserts of the world. (3) Thus, the salinity of the seas is found to be higher here.
Q3. Answer the following questions.
(a) What are the factors affecting the salinity of the sea water?
Ans.
Following factors affects the salinity of the sea water:
(1) Difference in rate of evaporation.
(2) Difference in temperature.
(3) Supply of fresh water.
(b) Explain the distribution of salinity around the Tropic of Cancer and tropic of Capricorn.
Ans. (1) The salinity of sea around Tropic of Cancer is about 36‰. This is due to high temperature, high rate of evaporation and landlocked nature of seas. (2) However, the salinity of sea around Tropic of Capricorn is about 35‰. The proportion of land is less in Southern hemisphere around Tropic of Capricorn as a result ocean currents control the salinity of around Tropic of Capricorn.
(c) What are the factors affecting the temperature of the sea water?
Ans.
Following factors affects the temperature of the sea water :
(1)Cyclones,
(2) Rainfall,
(3) Sea waves,
(4) Ocean currents,
(5) Salinity,
(6) Convectional currents,
(7) Seasons,
(8) Radiating sun rays from the surface of the sea, etc.
(d) Explain the changes occurring in the temperature of sea water according to the depth.
Ans. (1) While most of the sunrays radiate back from the surface of the sea, some of them penetrate to certain depths in the water. (2) As a result, the intensity of sunrays decreases with increasing depth. (3) Temperature decreases up to 2000m depth. After 2000m, the temperature of the seawater is uniform everywhere. (4) It is around 4 0C everywhere from the equatorial regions to the polar areas. (5) Temperature reduces only up to 4 0C according to depth. And therefore, the water at greater depths does not freeze. (6) The temperature of the seawater changes rapidly with depth at the equatorial areas. (7) The difference in temperature is lesser in polar areas.
(e) Name the factors affecting salinity.
Ans. (1) Because of 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 water increases. (2) In seas where the rate of evaporation is high than the supply of freshwater, salinity is high. (3) In seas where the supply of freshwater exceeds the rate of evaporation, salinity is low. (4) Salinity is not affected much in seas where both the supply of freshwater and evaporation of water is low.
Q4. Explain how temperature affects the following.
(a) the density of sea water
Ans. (1) If temperature reduces, density of water increases. (2) Hence, cold water is denser than hot water. (3) Temperature has a greater effect on the density of water than salinity does. (4) A parcel of water with higher salinity can actually float on top of water with lower salinity, if the parcel with higher salinity is quite a bit warmer than the lower salinity parcel.
(b) the salinity of sea water
Ans. (1) The rate of evaporation increases with increasing temperature. This further results in more salinity. (2) Sea water in tropical belt therefore has more salinity. (3) In contrast the temperature is less in polar area and so the evaporation rate. As a result, the salinity is also less.