Surface ocean temperature of Ocean (in 0 o C)

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1 Chapter No 7: Properties of ocean water The physical properties of sea water include heat and temperature (thermal condition) density, color, odour etc. Heat present in ocean water is vital significance as it determines environment. A) Distribution of Temperature of sea water: The distribution of temperature of ocean water is studied in two ways. 1) Horizontal Distribution (Temperature surface water) 2) Vertical Distribution (From Surface water to the bottom) Since the ocean has three dimensional shape the depth of oceans, besides latitudes is also taken into account in the study of temperature distribution. The following factors affect the distribution of temperature ocean water Latitudes: The temperature of ocean water on average the temperature of surface water of the ocean is 26.7 o c (80 o f) and the temperature gradually decreases from equator towards the poles. The rate of decrease of temperature with increasing latitude is generally 0.5 o F per latitude. The average temperate recorded at 40 o Latitude 14 o C (57 o F) and 0 o c (32 o F) near the poles. The ocean in the northern hemisphere recorded relatively higher average temperate than in the southern hemisphere.the decreases of temperature with increasing latitude in the northern Atlantic ocean the temperature is very low because of warmer ocean current The average temperature between 50 o to70 o N Latitude is recorded a 5 o C(41 o F). Surface ocean temperature of Ocean (in 0 o C) latitude Hemisphere Hemisphere Hemisphere Prof. Shaziya Nausheen, Department of Geography, M.G.V s Arts, Commerce and Science College,

2 latitude Hemisphere Hemisphere Hemisphere Latitude Pacific Atlantic Indian Southern Hemisphere Southern Hemisphere Southern Hemisphere Density: Density refers to the amount of mass per unit volume of substance.it is usually measured in gram (amount of mass) per cubic centimeter of volume and is expressed g/cm 3.The density of pure water is 1.00 g/cm 3 of pure water is taken as standard for the measured of density of other substances since the sea water carries a few dissolved substances such as salt in it, its density is slightly higher than that of pure water. In fact the average density of sea water is g/ cm 3 ( g/cm 3 ) which is 2 to3 % higher than the density of pure water ( 1.00 g/ cm 3 ) of 4 C temperature.the density of sea water gradually increases with decreasing temperature and highest density is recorded at the temperature of -1.3 o C. B) Salinity Meaning: Salinity of the ocean water simply means the presence of dissolve salts in the sea water.the chemical oceanography define salinity in more technical term while general oceanography and geographers describe salinity of sea water in simple ways. Definition: Salinity is the degree of saltiness of the ocean and seas expressed as the number of parts per thousand of salt dissolved in 1000 parts of water or it is number of unit of all contained in number units.the average salinity of the ocean water is 35 gram per 1000 grams of ocean 2 Prof. Shaziya Nausheen, Department of Geography, M.G.V s Arts, Commerce and Science College,

3 water. It is expressed as 35%o.It means in 1000 gram of ocean water there are35 gram of all kind of salt. Sodium chloride is the main maker of ocean water salinity other constituents include the role of magnesium, chloride.magneisum sulphete, calcium sulphete, potassium sulphate, calcium carbonate and magnesium bromide. Ocean Salt concentration Salt Concentration Percentage Sodium chloride ( NaCl)) Magnesium chloride (MgCl2) Magnesium sulphate (MgSO4) Calcium sulphate (CaSO4) Potassium sulphate (K2SO4) Calcium carbonate (CaCO3) Magnesium Bromide (MgBr2) Total 35.00%o 100.% Sources of ocean salinity: Basically the most significant sources of sea water salinity is the chemical weathering of continental rocks and transport of weathered material by the rivers to the oceans but there are also few minor sources. Thus ocean salinity is derived from the following sources. 1) Various kind of salt derived from the earth crust are dissolved in rain water and the river carry them to the ocean in solution. 2) Marine organism like coral, polyps, mollusus, oysters etc. extract carbonate of lime from the sea water to form the shells or skeleton. 3) Sea weeds and other marine plants consumers certain amount of carbonate extracted from sea water. 4) Glaciers, wind, waves there little bit in adding to dissolve substance in the ocean. 3 Prof. Shaziya Nausheen, Department of Geography, M.G.V s Arts, Commerce and Science College,

4 5) Submarine volcanic eruption. Causes of Salinity: Major cause of ocean water salinity lie its supply of river water of Calcium Carbonate: Is more several marine organisms like coral poolys, oysters, form iniferal species like Globally ermine, pteropodes utilization calcium carbonate for the building of their body shelts or Skelton.Hence proportion of calcium carbonate declines and that of sodium chloride relatively increase.so that sea water becomes saltine of brackish.thus river water has chloride percentage only 2 and sea water bears 75% of chloride. Salt: Salt are also added to sea water due mainly by erosional phenomena of the crust forms of volcanic ash,born,iodin,sulphur and chlorine are thus added into the oceans and the process of salination is assisted. Open Ocean: Open ocean water surface exposed to high amount solar energy cause evaporation of sea water. The water gets evaporated but salts are left behind those promote saltiness. Horizontal Distribution of Sea water salinity: Horizontal Distribution of surface Sea water salinity at world level is studied in relation to latitude but regional distribution of sea water salinity in term of individual oceans and sea is in different oceans seas and lakes. 4 Prof. Shaziya Nausheen, Department of Geography, M.G.V s Arts, Commerce and Science College,

5 Latitudinal Distribution of surface salinity. Hemisphere Latitude Zone Salinity Southern Hemisphere Controlling Factors of Salinity: These are the following. 1) Evaporation: Evaporation is the prime control of salinity at any place and time. Okada the Japanese scientist. Inferred that the influence of evaporation on salinity distribution of seas. Oceans and lakes is substantial control. Evaporation leads to vaporization of water on one hand and leaving of salts behind on the other hand. W.Sschmid and wust enumerated the amount of evaporation by field observations. The total process depends upon degree of temperature and dryness are lack of humidity. Hence areas of high solar radiation with clear sunlight and long daytime period causes intensive evaporation of sea water. As a result the salinity of the water body increases. Strong winds and clear sky conditions promote the effect of evaporation. Winds carry the vapour elsewhere so that ample room for production of new vapour is crated. Clear sky increases the moisture holding capacity of the air. Naturally speed and amount of evaporation. In ocean water salinity becomes to increases the boiling point and slightly deceases the vapour tension. Therefore the ratio between the temperature and the humidity gradient of air at a short distance from the sea surface varies with one portion of the sea to other. 5 Prof. Shaziya Nausheen, Department of Geography, M.G.V s Arts, Commerce and Science College,

6 2) Supply of Fresh water by rivers: Rivers meeting the seas oceans and lakes supply fresh water so that areas of such supply bear lower salinity. Absence of river, streams and non-perennial character shows higher amount of salinity. Hence near the salinity is found comparatively low. The average salinity of Arabian Sea is 38%o and that of Bay of Bengal is 30%o.It is about 20%o in Bay of Bengal near the mouth of Ganga due to supply of Fresh water. During period of maximum surface run-off salinity is found low naturally due to constant supply of fresh water. See the following examples: i) Gulf of Bothnia_Many rivers _Salinity 5%o ii) Black Sea_ Receiving water from Danube, Dnelper_ Salinity 18%o iii) Mediterranean _Lack of fresh water supply _ Salinity 40%o 3) Mixing of water: Big seas or oceans generally have lower salinity as compared to small sea or Island seas. When there is mixing of water between the large and small sea naturally salinity of the small seas is affected. It is found lower in contact and mixing of water of great oceans. For Example in the Gibraltar area where Mediterranean water mixes with Atlantic Ocean the Salinity is comparatively lower than rest of the Mediterranean. 4) Atmospheric pressure and wind direction: Differences in atmospheric pressure guiding the wind influence salinity though slight but positively. Atmospheric pressure on Baltic Sea for this compensation the high salinity water passes from North Sea to Baltic Sea and thus salinity of Baltic Sea slightly increases. Along the Californian coast the northeast trade winds drive. Warm saline water away from the coast and colder less saline water swells up from the bottom small seas do get affected by advance of strong winds so that mixing of surface water occurs so that there is decline or increase in salinity. Strong prevailing winds in respective areas of oceans may drive off the warm and saline water particularly in lower mid-latitudes and higher mid- latitudes so that changes in salinity results. 5) Periodic variations of salinity: The difference between precipitation and evaporation brings about periodic variation in salinity with the cycle of seasons. Well known scientist in the field, Bohnecke found out that there are periodic variations in salinity and North Atlantic Ocean following. I) March 70% (Highest salinity) II) November 36.59% (lowest salinity) 6 Prof. Shaziya Nausheen, Department of Geography, M.G.V s Arts, Commerce and Science College,

7 Highest salinity is found at the end of June and lowest in Decmber.Generally, Salinity is high during spring and lower in fall. Diurnal variation do affect salinity but difference are too small. 6) Movement of sea water: Movement of sea water like tidal currents, drift or ocean currents and vertical movement in some parts of the sea bring about mixing of the surface water with unlike water from neighboring or far distant parts of the ocean. i) Tidal water: Surging of forward and backward movement. ii) Drifts: Movement of warmer and cold currents. iii) Vertical movement: Bring upward downward mixing of saline water of heterogeneous property. 7) Precipitation: Amount of precipitation is responsible to supply of fresh water.hence more the precipitation more chances for dilution of salinity and less of it causes higher salinity. According to wust that precipitation evaporation index is quite important to determine the degree and variation of salinity of any part of the sea or ocean.thus deviation from normal value of salinity is directly proportional to the difference between evaporation and precipitation of concerned area. C) Land locked sea: These seas which is surrounded by land on all sides is known as landlocked sea. Locking by land on all side does not permit easy mixing of water.as a result salinity of the landlocked seas is found higher than open sea. These are the Examples. 1) Mediterranean sea: Mediterranean is largest landlocked sea of the world. This sea narrow strait of Gibraltar that connects it with open stretch of Atlantic Ocean. Since the strait is much narrow there is no easy mixing of water with the open sea. Secondly there is high mound at the depth of 3000 m.in the passage of strait that interrupts the possible mixing of water. Hence the salinity is higher than Atlantic. 7 Prof. Shaziya Nausheen, Department of Geography, M.G.V s Arts, Commerce and Science College,

8 2) Red Sea: It is another example of landlocked sea having high salinity than open sea (Indian Ocean). Red sea is bounded by great and deserts like Sahara and Arabian (Thar ) desert so that climate is arid hot due to high temperatures.southern portion bears 36.5%o salinity while northern portion (Suez) bears 41%o salinity. To the south it is connected to open part of Indian Ocean hence some scope for mixing to water reduces salinity ad %o 3) North Sea: Its salinity is 31 to 35 %o.as it lies higher latitudes of colder climate. Evaporation is thus less.rivers from British Isles.Norway,Sweden,Finland join the sea,melting snow in summer supply ample fresh water. 4) Baltic Sea: Baltic Sea records lowest salinity 2 to 7 %o as it lies in high latitudes of cold climate region. 5) Black Sea: Black sea is bound by mild climate condition, Don Rivers supply fresh water. Hence the salinity is low.it is 18 to 18.5 %o only the area /size of the sea is small. In Azure Sea it s less than black sea. Dead Sea (Fully Land locked): As the name indicate.dead sea does not allow any living organism to survive due to highest salinity of any sea/ocean in the world. Its salinity is 240 %o reasons of highest salinity are as following I) Location in hot tropical belt ii) Landlocked sea iii) Bound by hot deserts iv) High temperature all-round the year v) Intensive rate of evaporation vi) Clear sky condition most of the year round vii) Meagre rainfall /precipitation viii) Poor supply of fresh ix) Water from few non perennial stream and Jordan River. c) Salinity of lakes: Lakes are relatively smaller in area than seas. The lakes which receive river on one side and give room for river sources on either side have less salinity.because such lakes have inlets and outlet for salts present in water.on the contrary the lakes which enjoy meeting of rivers only there is room for concentration of salt and salinity increases. Best example of such kind is salt lake in United States of America. Lakes in the desert and semi-arid tracks of the world bear high salinity again due to arid condition in favors of high evaporation rates and lack of supply of fresh water. In Utah 8 Prof. Shaziya Nausheen, Department of Geography, M.G.V s Arts, Commerce and Science College,

9 Province of united states of America, the Great Salt Lake possesses salinity around 220%o while in van lake of Asia Minor in Turkey the salinity is 230%o Salinity of lakes In India: Dr. Notisingh.a.O Hume and Dr.Godbole studied salinity of Indian lakes and found that saline lakes are shown majority in Rajastan. saccording to.dr. Goud bole strong dry saline winds across runn of Kutch promote salinity of Rajasthan Lake. It is estimated that about 1, 30,000 tons of sodium chloride is carried by these saline winds. Salt water lakes are found in arid or desert region lack of outlet and intense evaporation leads to salinity of such lakes. Lakes Eyre in Australian great desert is classic example.it is heading towards disappearance now-a-days. Absence of outlet equal to supply and evaporation water. Highly saline lakes in India are Udiwana, sambar and panchbhadra.there are salt lakes so far known through field observation of the experts. These lakes are the seats of salt production from these salt lakes. Significance of salinity: The ocean salinity has significance effect on physical property of sea water and other aspect of the oceans as follows. 1) The freezing and boiling points are greatly affected and controlled by addition or substation of salt in sea water. The saline water freezes slowly in comparison to fresh water. It is known to all that pure water. It is known to all that pure water freeze at the temperature of 0 o C freezing point. If the salinity of sea water becomes 35%o then it would freeze the temperature of 1.91oC.On the other hand the boiling point of saline water is higher than fresh water. 2) Salinity and density of sea water are positively correlated i.e. the salinity of sea water increase its density because solutes of in water have greater atomic weight than molecules of fresh drowned in the sea water with very high salinity. 3) Evaporation is controlled by salinity of the oceans. In fact, solutes in water; lowers the rate of evaporation in the ocean. Thus more saline water is less evaporated than saline water. It may be mentioned that evaporation also controls salinity of sea water.more evaporation reduces the volume of sea water and hence the concentration off alt increase 4) Spatial variation in sea water salinity becomes potent factor in the origin of ocean currents 5) The ocean salinity affects the Marin organism and plant community. 9 Prof. Shaziya Nausheen, Department of Geography, M.G.V s Arts, Commerce and Science College,