Among the properties of the waters of the World Ocean, temperature and salinity are distinguished.
Water temperature The world's oceans change in the vertical direction (decreases with depth, since the sun's rays do not penetrate to great depths) and horizontally (the temperature of surface waters decreases from the equator to the poles from +25 ° C to - 2 ° C due to the difference in the amount of water received solar heat).
Surface water temperature. Ocean water is heated by the influx of solar heat onto its surface. The temperature of surface waters depends on the latitude of the place. In some areas of the ocean, this distribution is disrupted by the uneven distribution of land, ocean currents, constant winds, and water runoff from the continents. Temperature naturally changes with depth. Moreover, at first the temperature drops very quickly, and then quite slowly. The average annual temperature of the surface waters of the World Ocean is +17.5 °C. At a depth of 3-4 thousand m, it usually ranges from +2 to 0 °C.
Salinity of the water of the World Ocean.
Ocean water concentrates different salt: sodium chloride (gives water a salty taste) - 78% of the total amount of salts, magnesium chloride (gives water a bitter taste) - 11%, other substances. The salinity of sea water is calculated in ppm (the ratio of a certain amount of substance to 1000 weight units), denoted ‰. The salinity of the ocean varies, it varies from 32‰ to 38‰.
The degree of salinity depends on the amount of precipitation, evaporation, and desalination of rivers flowing into the sea. Salinity also changes with depth. To a depth of 1500 m, salinity decreases slightly compared to the surface. Deeper down, changes in water salinity are insignificant; it is 35‰ almost everywhere. The minimum salinity is 5‰ in the Baltic Sea, the maximum is up to 41‰ in the Red Sea.
Thus, water salinity depends : 1) on the ratio of precipitation and evaporation, which varies depending on the geographic latitude (since temperature and pressure change); Salinity may be lower where the amount of precipitation exceeds evaporation, where the influx of river water is large, where the ice is melting; 2) from depth.
Table “Properties of ocean waters”
The main feature of the water of oceans and seas is its salinity. In science, it is customary to measure salinity by the number of grams of salts contained in a kilogram of sea water. Since a kilogram is equal to a thousand grams, when we measure salinity in grams per kilogram, we essentially express it in thousandths - ppm. Therefore, salinity is said to be “expressed in ppm.” They agreed to denote salinity with a capital Latin letter S, and ppm - °/00.
The salinity of the surface water of the Black Sea is eighteen ppm. This means that one kilogram of Black Sea water contains eighteen grams of various salts.
The average salinity of the water in the World Ocean is thirty-five ppm (S=35°/00). In the surface water of the oceans and seas, quite significant deviations from this average value are observed. This depends on the fact that the amount of water evaporating from any part of the ocean surface and the amount of precipitation falling on the same surface during the same time are not the same at different latitudes. In the equatorial zone, a layer of precipitation about 2 m high falls per year, but less water evaporates; therefore, an excess of fresh water is obtained, which lowers the salinity of the surface water to about 34 °/00.
In the subtropical zone at latitudes between 30-35°, clear, dry weather prevails, there is little precipitation, and evaporation is very high. The predominance of evaporation over precipitation leads to the fact that the salinity of the surface water of the World Ocean in the subtropics is above average: in the Northern Hemisphere 38 °/00, and in the Southern Hemisphere - 37 °/00.
In temperate latitudes, precipitation is greater than in the subtropics, and evaporation is less; therefore, as you move north from the tropics in the Northern Hemisphere and south in the Southern Hemisphere, the salinity gradually approaches normal. In the polar zones, where evaporation is sharply reduced, the salinity of surface water is less than the average salinity of the World Ocean. It does not exceed 33-34 °/00 here
Thus, on the surface of the World Ocean there is a decreased salinity in the equatorial zone and an increased salinity to the north and south of it - in the subtropical zones. Towards the poles, salinity gradually decreases, becoming normal in temperate latitudes (S = 35 °/00). This pattern is somewhat violated by ocean currents. Cold currents carry low-salinity water from the polar zones to temperate latitudes, while currents coming from the subtropics carry saltier water to temperate latitudes.
In the coastal parts of the World Ocean, especially near the mouths of large rivers, such as the Amazon, Congo, Yenisei, Lena, Ob, the salinity of water on the surface decreases sharply.
All the differences in the salinity of ocean water that we talked about are observed only on the surface of the World Ocean. They can be seen in a layer of water several hundred meters thick. The salinity of the deep waters of the World Ocean is almost the same everywhere and is equal to 35 °/00.
How did the salts in it get into sea water? On their way, rivers dissolve the salts that make up the rocks, and then carry the salts into the oceans and seas.
Careful chemical analyzes have shown that seawater contains all the chemical elements common on land. It is interesting that the relationships between them in different parts of the World Ocean are the same, i.e. the chemical composition of the salts of the World Ocean is constant.
It turned out that salts dissolved in sea water are present in the following proportion (in%):
Chlorides (salts of hydrochloric acid). . . 88.7
Sulfates (salts of sulfuric acid). . . 10.8
Carbonates (salts of carbonic acid). . . 0.3
The rest of the salts………. 0.2
In all oceans these ratios are preserved. This once again shows the unity of the World Ocean and indicates that the water of the oceans mixes well.
In river water, unlike sea water, the majority is not of chlorides, but of carbonates. What happens to them in the ocean? They are used by living creatures living in seawater to build their shells and skeletons.
SEA WATER TEMPERATURE
It is known from physics that water has a very high heat capacity compared to air. To heat one cubic centimeter, or one gram, of water by 1°, you need to expend one calorie of heat. The same calorie can heat more than three thousand cubic centimeters of air by 1°.
Therefore, the surface temperature of the water in the World Ocean greatly influences the temperature of the air above it, and therefore the climate of those areas where this air penetrates thanks to the prevailing winds.
The highest water temperature on the surface of the World Ocean far from the coast is observed in the equatorial zone. The average annual temperature there reaches 28°. In shallow waters off the coast, the water warms up even more. It is interesting that during the year in the equatorial zone the temperature of ocean water remains almost unchanged. The highest temperature is usually no more than one degree above the average. The minimum temperature is also much lower than the average. This happens because in the equatorial zone the arrival of solar heat throughout the year is very uniform, since the length of the day all year round is approximately 12 hours, and the sun at noon is near the zenith.
From the equatorial zone and to the north and south, average annual water surface temperatures begin to decrease and in the subtropics reach 20°. In the subtropical zone, the sun rises almost to its zenith at noon in summer. At this time, the day is much longer than the night. In winter, the days are shorter and the sun does not rise as high at midday. Therefore, the difference in solar heat gain in summer and winter is significant. The highest and lowest water temperatures can differ from the annual average by up to 5°. For example, the average annual water temperature is 22°, the highest (maximum) is 27°, and the lowest (minimum) is 17°. Accordingly, the air temperature also changes.
From the subtropics towards the polar circles, the average annual temperature of surface water decreases rapidly and, finally, in winter it reaches the temperature at which ice forms,
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Salinity of sea water- this is the content in grams of all mineral substances dissolved in 1 kg of sea water, provided that bromine and iodine are replaced by an equivalent amount of chlorine, all carbon dioxide salts are converted into oxides, and all organic substances are burned at a temperature of 480 ° C. The salinity of water is expressed in g/kg, i.e. in thousandths - ppm and, as was said, is designated S‰ .
The salinity of sea water is close to the concept of mineralization ( M, mg/l). At salinity up to 20 ‰ S‰ ~M 10 -3 .
The salinity of sea water is determined by the chlorine content or by the electrical conductivity of the water, since sea water is an electrolyte: the more salts in the water, the greater its electrical conductivity, i.e., the lower the electrical resistance; By measuring the latter, you can use the tables to convert it into salinity. Measurements of the angle of refraction of light in water can be used, since this angle depends on salinity. Salinity can also be obtained by measuring the density of water. A complete chemical analysis is the most accurate, however, this method is too labor-intensive.
A very simple way to directly measure density with a hydrometer. The device allows you to easily determine the density of water, and then use tables to obtain salinity values. This method, however, is too crude. It gives a measurement error of up to 0.05‰ .
Previously, a method was used to determine salinity by chlorine concentration, or more precisely by chlorine content ( chlorinity is the total content in grams per 1 kg of sea water of halogens - chlorine, bromine, fluorine and iodine when converted to the equivalent chlorine content). This method allows you to determine salinity with an error of up to 0.01‰ . M. Knudsen obtained the formula back in 1902
S‰ = 0.030 + 1.805 Cl‰, (10.3)
where C1 is the chlorine content of the water. In 1967, by international agreement, instead of the Knudsen formula, a new formula was adopted, called “international”: S‰ = 1.80655 С1‰ . Due to the fact that the salt composition of marginal and inland seas is somewhat different from the average salt composition of ocean waters, there are special formulas of a similar structure for individual seas. So, for the waters of the Black Sea they use the formula S= 1.1856 + 1.7950 C1, Baltic - S= 0.115 + 1.805 C1, Azovsky – S= 0.21 + + 1.794 CI ( S and C1 - in ‰) . Using the same scheme, formulas were calculated for many lakes with salty and brackish water. So, for the waters of the Caspian Sea they use the formula S= 0.140 + 2.360 C1.
In connection with the transition in recent years to the electrometric method of measuring salinity, a new formulation of the concept of salinity through relative electrical conductivity was adopted R 15 at 15 °C and atmospheric pressure:
S= a 0 + A 1 R 15 + a 2 R 2 l5 + a 3 R 3 15 + A 4 R 4 15 + a 5 R 5 15 , (10.4)
Where R 15 = C sample /С 35 ‰, 15° - relative electrical conductivity of sea water at a temperature of 15 ° C and R atm , C 35 ‰, 15° - electrical conductivity of a sea water sample at a temperature of 15 ° C and a salinity of 35 ‰ . Instead of natural water in the denominator of the expression for R l5 to use a solution of potassium chloride KS1, the Practical Salinity Scale was introduced in 1978. With a mass fraction of KS1 = 32.4 10 -3, T = 15 °C and atmospheric pressure R l5 = 1, and the practical salinity is equal to 35.00‰, or 35 units of practical salinity.
Let's remember: How are the planet's waters divided by salinity? Why do travelers and sailors take fresh water on sea voyages?
Keywords:sea water, salinity, water temperature, ppm.
1. Water salinity. In all seas and oceans, water has a bitter-salty taste. It is impossible to drink such water. Therefore, sailors setting sail on ships take with them a supply of fresh water. Salt water can be desalinated in special installations that are available on sea vessels.
Mostly table salt, which we eat as food, is dissolved in sea water, but there are also other salts (Fig. 92).
* Magnesium salts give water a bitter taste. Aluminum, copper, silver, and gold were found in ocean water, but in very small quantities. For example, 2000 tons of water contains 1 g of gold.
Why are ocean waters salty? Some scientists believe that the primary ocean was fresh, because it was formed by river waters and rains that fell abundantly on the Earth millions of years ago. Rivers brought and continue to bring salt to the ocean. They accumulate and lead to salinity in ocean water.
Other scientists suggest that the ocean immediately became salty upon its formation, because it was replenished with salty waters from the bowels of the Earth. Future research may answer this question.
Rice. 92. The amount of substances dissolved in ocean water.
** The amount of salts dissolved in ocean water is enough to cover the surface of the land with a layer 240 m thick.
It is assumed that all naturally occurring substances are dissolved in seawater. Most of them are found in water in very small quantities: thousandths of a gram per ton of water. Other substances are contained in relatively large quantities - in grams per kilogram of sea water. They determine its salinity .
SALINITY sea water is the amount of salts dissolved in water.
Rice. 93. Salinity of surface waters of the World Ocean
Salinity is expressed in p r o m i l l y e, i.e. in thousandths of a number, and is denoted -°/oo. The average salinity of the waters of the World Ocean is 35°/oo. This means that every kilogram of sea water contains 35 grams of salts (Fig. 92). The salinity of fresh river or lake waters is less than 1°/oo.
The Atlantic Ocean has the most saline surface waters, the Arctic Ocean has the least saline (see Table 2 in Appendix 1).
The salinity of the oceans is not the same everywhere. In the open part of the oceans, salinity reaches its highest values in tropical latitudes (up to 37 - 38 °/oo), and in the polar regions the salinity of surface ocean waters decreases to 32 °/oo (Fig. 93).
The salinity of water in marginal seas usually differs little from the salinity of adjacent parts of the ocean. The water of inland seas differs from the water of the open part of the oceans in salinity: it increases in the seas of the hot zone with a dry climate. For example, the salinity of water in the Red Sea is almost 42°/oo. This is the saltiest sea in the World Ocean.
In the temperate seas, which receive a large amount of river water, salinity is below average, for example in the Black Sea - from 17°/oo to 22°/oo, in the Azov Sea - from 10°/oo to 12°/oo.
* The salinity of sea water depends on precipitation and evaporation, as well as currents, the influx of river water, the formation of ice and its melting. When seawater evaporates, salinity increases, and when precipitation falls, it decreases. Warm currents usually carry saltier water than cold ones. In the coastal strip, sea waters are desalinated by rivers. When seawater freezes, salinity increases; when seawater melts, on the contrary, it decreases.
The salinity of sea water varies from the equator to the poles, from the open part of the ocean to the shores, with increasing depth. Changes in salinity cover only the upper water column (down to a depth of 1500 - 2000 m). Deeper salinity remains constant and is approximately equal to the average ocean level.
2. Water temperature. The temperature of ocean water at the surface depends on the input of solar heat. Those parts of the World Ocean that are located in tropical latitudes have a temperature of + 28 0 C – +25 0 C, and in some seas, for example in the Red Sea, the temperature sometimes reaches +35 0 C. This is the warmest sea in the World Ocean. In the polar regions, the temperature drops to - 1.8 0 C (Fig. 94). At a temperature of 0 0 C, fresh water in rivers and lakes turns into ice. Sea water does not freeze. Its freezing is prevented by dissolved substances. And the higher the salinity of sea water, the lower its freezing point.
Fig.94. Temperature of surface waters of the World Ocean
With strong cooling, sea water, like fresh water, freezes. Sea ice forms. They constantly cover most of the Arctic Ocean, surround Antarctica, and appear in shallow seas at temperate latitudes in winter, where they melt in summer.
*Up to a depth of 200 m, the water temperature varies depending on the time of year: in summer the water is warmer, in winter it becomes colder. Below 200 m, the temperature changes due to the influx of warmer or colder waters by currents, and in the near-bottom layers it can increase due to the influx of hot water from faults in the oceanic crust. In one of these sources at the bottom of the Pacific Ocean, the temperature reaches 400 0 C.
The temperature of ocean waters also changes with depth. On average, for every 1,000 m of depth, the temperature drops by 2 0 C. At the bottom of deep-sea depressions the temperature is about 0 0 C.
1. What is called the salinity of sea water, how is it expressed? 2. What determines the salinity of sea water and how is it distributed in the World Ocean?
What explains this distribution?
3. How does the temperature of the waters of the World Ocean change with latitude and depth?
4*. Why does salinity in tropical areas reach the highest values for the open part of the ocean (up to 37 - 38°/oo), while in equatorial latitudes salinity is much lower?
Practical work. Determine salinity if 25 g of salts are dissolved in 1 liter of sea water.
2*. Calculate how much salt can be obtained from 1 ton of Red Sea water.
Competition of experts
. There is a sea on earth in which a person can stand on the surface of the water like a float (Fig. 95). What is the name of this sea and where is it located? Why does the water in this sea have such properties?
The Black Sea is shaped like an oval, elongated in the latitudinal direction. This basin is almost closed, separated by large land masses from other parts of the World Ocean (MO). In the northeast, the Crimean Peninsula deeply cuts into the water area; its northeastern peninsula separates the Black and Azov Seas. The pool is located in the southwestern part of the Eurasian continent. Along its surface, from northeast to southwest, a border is drawn between two parts of the world - Asia and Europe.
The lives of millions of people have long been connected with the waters of the Black and Mediterranean Seas; legends about giants and monsters were born here, and the greatest discoveries were made. Suffice it to remember that the straits and the surrounding peninsulas and islands are associated with the legends about Scylla and Kharbid, the voyage of the Argonauts led by Jason to Colchis for the Golden Fleece. Even in ancient times, Greek sailors and traders highly valued the fishing wealth of this water area and created prosperous colony cities on the shores, the remains of which can be seen on the Crimean peninsula. It is difficult to say what the salinity of the Black Sea was in ppm several thousand years ago. This indicator was introduced relatively recently, when a consistent and targeted study of hydrological features began.
The most important geographical features affecting sea salinity
The narrow Bosporus and Dardanelles straits connect the Black Sea basin successively with the Marmara and Aegean Seas, leading to the Mediterranean, which, in turn, communicates with the Atlantic Ocean through the Strait of Gibraltar. All of the listed parts of the MoD are navigable and are located in the eastern part of the Atlantic. Physiographical features that significantly or moderately affect the salinity of the Black Sea:
- location in the northern temperate and subtropical climate zones;
- a large catchment area that determines the flow of fresh water from rivers;
- weak connection with the Atlantic Ocean and Mediterranean Sea;
- average depth 1240 m, maximum - 2210 m;
- absence of large tidal waves and low tides.
River flow
Many European rivers flow from west to east and from north to south. The largest natural channel of the Old World is the river. The Danube flows through 10 countries and brings huge amounts of fresh water to the Black Sea. Other large and medium-sized rivers in this basin: Dnieper, Don, Kuban, Bug, Rioni, Dniester.
Fresh river water mixes little with deeper and denser layers, so a significant part of the fresh runoff evaporates from the sea surface. But its volume is so large that it increases the level of the Black Sea water by 5 m relative to the average levels of the Atlantic Ocean. The temperature and salinity of the Black Sea, on the contrary, are lower than in neighboring parts of the Mediterranean Sea. This feature led to the birth of a current directed to the southwest, towards the Bosphorus Strait.
Water mineralization
By studying the salinity of the water of the Black Sea and other parts of the Moscow Region, researchers measure not only the total content of dissolved substances in various layers and parts of the water area, but also determine the elemental composition. In addition to H 2 O molecules, sea water contains gaseous substances, mineral and organic compounds in the form of ions, molecules and other particles. The main components of salts in the Black Sea: carbonates, sulfates, nitrates and chlorides of calcium, magnesium, sodium, potassium. The presence of these solutes is related to the composition of the rocks on land and the seabed. The salinity of the Black Sea is affected by various compounds coming from surface and underground runoff and precipitation. Chemical interactions occur between substances, which also affects performance.
Water is enriched not only with salts from dissolved minerals and rocks, but also with organic matter. A significant part of the surface of the Northern Black Sea coast is composed of limestone, hence the high content of calcium, magnesium and sodium salts in the water. Basaltic rocks, when dissolved, increase the amount of silicon and iron. Substances contained in water increase its overall mineralization. It changes noticeably over the seasons, from the surface to the depths, from north to south, so reference books, textbooks and atlases may contain different indicators characterizing the salinity of the Black Sea. Most often, average values obtained based on long-term data are given.
What is salinity?
Almost the entire periodic table is present in sea water. But salinity is considered only the amount of dissolved substances in grams, which are obtained in solid form after evaporation of 1 kg of sea water. For convenience, this indicator is expressed as a percentage and ppm.
To facilitate calculations, the content of all halogens is equal to the equivalent amount of molecular chlorine. There are other features, for example, heating is accompanied by the removal of dissolved gaseous substances. When the sediment is heated, the organic matter decomposes.
Salinity of the Black Sea in percent
To characterize the studied indicator as a percentage, you need to remember what the content of the dissolved substance in 100 g of solution is called. This is the mass fraction, its percentage value can be found by dividing the mass of the solute by the mass of the solution and multiplying by 100%. Let’s say that when 1000 ml of water is evaporated, a precipitate is obtained whose mass is 17 g. The mass fraction (%) of dissolved substances is 1.7%.
Salinity of the Black Sea in ppm
Determining experimentally the mass of dissolved salts in terms of 1 kg of Black Sea water gives different indicators - from 8 to 22 g. To determine salinity in ppm, we take the value mentioned most often in the literature about the Black Sea - 17 g. Percentage is one hundredth of , and ppm is one thousandth part. Divide 17 g by 1000 g and multiply by 1000 (‰). Thus, we find that the average salinity of the Black Sea is 17‰ (ppm). For comparison, we present the average values for the World Ocean - 35‰. The salinity of the Red Sea is 42 ‰, the Kara Sea is 8 ‰. It turns out that the content of dissolved substances in the Black Sea water is almost 2.5 times lower than in the Red Sea.
A simple experiment to determine salinity
There is a way to find out on your own what mass of substances is contained in sea or fresh water. The experiment is simple and interesting, but to carry it out you will need heat-resistant dishes, a heater and a chemical balance. It is also necessary to take into account that the density of the saline solution is higher. Therefore, the mass of 1000 ml of sea water is greater than 1000 g. This means that without taking into account density, the calculations will be approximate.
To find out what the salinity of the Black Sea is, you will need 100-200 ml of sea water. The experience is as follows:
- Measure the volume and heat the selected liquid in an evaporation cup to a boil.
- When all the water has evaporated, a white residue will remain at the bottom of the dish.
- You need to collect the sediment on a piece of paper and weigh it on a scale.
- The resulting result is the total mass of all solutes in the sample.
How do mineralization and water temperature change?
The salinity of the Black Sea water in ancient times, as in subsequent centuries, was subject to fluctuations under the influence of climatic, meteorological factors, water regime in coastal regions and economic activities of the population. Water mineralization largely depends on the total flow of large and small rivers. During dry periods, the riverbeds become shallow, less fresh water flows into the sea, and the salt content increases.
The main patterns that have developed to date:
- the salinity of the surface layers of the Black Sea is 15-18‰, deep - 22.5-22.6‰;
- plumes of water of low salinity spread from the northwest along the coast to the south, from the southeast - along the coast of the Caucasus in a northerly direction;
- under the influence of river runoff, the salinity of the surface layer of the sea in the northwest can decrease to 10‰;
- salinity in the Bosphorus region increases with the rising water of the Sea of Marmara;
- The surface temperature in summer is 27-28 °C along the Black Sea coasts, in the central part of the water area - up to 22 °C;
- the maximum salinity of surface waters—18.3‰—is located in the east of the central part of the water area, south of Crimea.
- the maximum salinity at a depth of 100 m is located south of the Kerch Strait - over 20.6‰;
- from the surface to 150-200 m the temperature decreases and reaches about 9 °C;
- at a depth of 150 m there is practically no oxygen, hydrogen sulfide appears;
- In winter, the surface of the Black Sea cools greatly; in the northern part it can drop to sub-zero levels, but more often it remains at a level of 8-9 °C.
When freezing occurs, fluctuations in hydrological parameters are observed. Some areas of the water area are partially covered with ice; complete freeze-up rarely occurs. For example, chronicles have been preserved about how the Black Sea was covered with such strong ice in winter that traders could reach the Turkish coast on sleighs and on foot.
In general, the conditions of this water area are favorable for the development of flora and fauna. However, scientists have noticed that a decrease in salinity leads to a decrease in the biodiversity of the Black Sea. The fact is that the inhabitants of the World Ocean and its parts do not tolerate salinity below 20‰. For the population of Crimea, desalination of slightly salted sea water in the water area near the Sea of Azov is a solution to the problem of drinking and industrial water.