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

(a) Slanting sunrays, melting snow- Low

(b) Cloudy sky, rainfall throughout the year-Medium

(c) Clear skies for the most part, perpendicular sunrays -High

(d) Less supply of freshwater, desert area around - High

(e) Low temperatures, ample supply of river water- Low

(f) Continental location, desert around, low rainfall- High

• The Baltic Sea is part of the Northern Atlantic Ocean and is located in a temperate region.
• Because the Baltic Sea is a landlocked sea, the Atlantic Ocean's ocean currents have no effect on its properties.
• Despite being a landlocked sea, the Baltic Sea has less salinity due to lower temperatures, less evaporation, and a plentiful supply of fresh water from melting ice caps.

• The Red Sea is an inlet of the Indian Ocean located between North East Africa and the Arabian Peninsula. It is a relatively narrow and long sea.
• The sea's southern end faces the Indian Ocean, while the northern end is as good as a landlocked sea.
• The Indian Ocean's salinity and temperature currents heavily influence and control the salinity and temperature of the southern end.
• On the northern side of the Red Sea, currents have little influence.
• Furthermore, this region is surrounded by the Sahara and the Arabian Desert.
• The northern part of the Red Sea has a high salinity due to high temperatures and increased evaporation.

• Salinity of the sea water is determined by the factors like temperature, supply of fresh water and landlocked or open nature of sea.
• Hence, the effect of latitudinal location is comparatively less significant factor on salinity of the sea.
• As a result the salinity of sea is not uniform even on the same latitude.
• E.g., the salinity of Indian Ocean and Atlantic Ocean is not same despite being on same latitude.

• Most of the sun rays radiate back from the surface of the sea, while some of them penetrate to certain depth in the water.
• As a result the intensity of sun rays decreases with increasing depth.
• Hence, with increasing depth, temperature of sea water decreases to certain limit.

• The Arabian Sea is located to the west of India. This sea is found in the tropics. The Arabian Sea is exposed to a clear sky and thus receives bright sunlight. The temperature and rate of evaporation in the Arabian Sea are always high. The Narmada and Tapi rivers are India's only two major rivers that meet the Arabian Sea, which is insignificant in comparison to the fresh water supply that the Bay of Bengal receives. As a result, the salinity of the Arabian Sea can reach 36%.
• In comparison, even though the Bay of Bengal is also located in tropical belt, it is surrounded by land on three sides. Sky over the Bay of Bengal is cloudy for most of the days in the year. Cyclones developing in this area also have its effect. Besides, all major rivers of India and Bangladesh namely Ganga, Mahanadi, Godavari, Krishna, Cauveri and Meghana (i.e. Brahmaputra + Ganga + Padma) 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.
• 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.

• Less rain falls in the mid-latitude belt between 25° and 35° latitude in both hemispheres.
• This region also has a lower proportion of fresh water supply from rivers.
• This belt also contains the world's major deserts, so the rate of evaporation is higher in the vicinity of these deserts.
• All of these factors contribute to the increasing salinity of sea water in the mid-latitude region.

Temperature differences with latitude from equator to pole, different rates of evaporation, river supply of fresh water, and open or landlocked nature of the sea are all factors that contribute to global salinity differences.

• The salinity of the sea near the Tropic of Cancer is approximately 36 high temperature.
• More salinity is caused by a high rate of evaporation and the landlocked nature of the seas, which obstructs the free movement of ocean currents.
• In comparison, the salinity of the sea around the Tropic of Capricorn is approximately 35.
• In the Southern Hemisphere, the proportion of land is lower.
• As a result, the salinity around the Tropic of Capricorn is controlled by ocean currents.

Latitudinal location of the sea, ocean currents, cyclones, rainfall, sea waves, salinity of the sea water, pollution, convectional movement of sea water and seasons affect the surface temperature of the sea water. Radiating sun rays from the surface of the sea and less intense sunrays penetrating only up to a certain depth also decide the temperature of sea water at a depth.

• The temperature of sea water with respect to depth is much greater than the temperature of sea water at the surface. With increasing depth, the temperature of the sea water drops. This temperature change, however, is not uniform throughout.
• The temperature of the sea water changes rapidly with depth at equatorial areas. Near equator, the surface temperature of the sea water is about 18°C. It reduces to 12°C at 500 m depth. It is about 8°C at 1000 m depth, 5°C at 1500 m depth and 4°C at 2000 m depth. Thus, the variation in the sea in the temperature of the sea water near surface to 2000 m depth is 18°C and 4°C respectively. This variation is about 14°C and 4°C around mid-latitudinal region.
• Near polar areas, however, the variation between surface temperature and temperature at depth is nil. Sea water temperature in this region is uniformly seen at 4°C.
• The majority of the sun's rays reflect back from the sea's surface, and some of them penetrate to a certain depth in the water. The strength of such sunrays weakens. As a result, after a certain depth, the temperature of the sea water remains constant throughout.

• Temperature, evaporation, fresh water supply, and whether the sea is landlocked or open determine the salinity of the sea water.
• The greater the temperature of the sea water, the greater the rate of evaporation, and thus the greater the salinity. For example, the salinity of sea water in the tropical region.
• Because of oblique sun rays, the temperature in temperate regions is lower, and thus the rate of evaporation is lower, resulting in less salinity.
• Fresh water supply from rivers meeting the sea, as in the Bay of Bengal, or melting ice caps, as in the Arctic Ocean, results in lower salinity.
• Ocean currents get obstructed in landlocked seas and hence salinity of the sea remains high in compared to open oceans.
• Mixing of water takes place easily in open seas and hence salinity remains controlled by ocean currents.

• The density of sea water increases as temperature rises. As a result, the density of cold sea water is greater than that of warm sea water.
• As a result, the density of sea water near the equator is lower than that of sea water in polar regions.
• At a certain depth, the temperature of sea water is uniform, and thus the density is also uniform.
• The density of sea water increases as the surface temperature decreases from the equator to the pole.
• Ocean currents are caused by the density difference.

• The rate of evaporation increases with increasing temperature. This further results in more salinity.
• Sea water in tropical belt therefore has more salinity. In contrast, the temperate is less in polar area and so the evaporation rate. As a result, the salinity is also less.
• Thus, as one moves from equatorial region to polar area, the temperature gradually decreases and so the salinity too.