Salinity of sea water and its definition. Why is the sea salty? The salinity of the world's oceans depends on

The main feature of the water of the 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, then, by measuring the salinity in grams per kilogram, we, in essence, express it in thousandths - ppm. Therefore, they say that salinity is "expressed in ppm". Salinity was denoted by the 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 waters of the World Ocean is thirty-five ppm (S=35°/00). In the surface water of the oceans and seas, rather significant deviations from this average value are observed. This depends on the fact that the amount of water evaporating from any part of the surface of the ocean, and the amount of precipitation falling in the same time on the same surface, is not the same at different latitudes. In the equatorial zone, a layer of precipitation about 2 m high falls during the 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, with little precipitation and very high evaporation. 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 - 37 ° / 00.

In temperate latitudes, the amount of precipitation is greater than in the subtropics, and evaporation is less; therefore, with distance from the tropics to the north in the Northern Hemisphere and to the south in the Southern Hemisphere, the salinity gradually approaches normal. In the subpolar 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 here 33-34 ° / 00

Thus, on the surface of the World Ocean, there is a lower salinity in the equatorial zone and an increased one - to the north and south of it - in the subtropical zones. Toward the poles, salinity gradually decreases, becoming normal in temperate latitudes (S=35 °/00). This pattern is somewhat violated by ocean currents. Cold currents carry water of low salinity from the subpolar zones to temperate latitudes, and currents coming from the subtropics carry more saline water to temperate latitudes.

In the coastal parts of the World Ocean, especially near the mouths of large rivers, such as, for example, the Amazon, Congo, Yenisei, Lena, and Ob, the salinity of the water on the surface drops sharply.

All the differences in the salinity of ocean water, which we talked about, are observed only on the surface of the oceans. 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 sea water get into it? 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 sea water contains all the chemical elements common on land. It is interesting that the ratios 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 the salts dissolved in sea water are in it 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

Other 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, most of all are not chlorides, but carbonates. What happens to them in the ocean? They are used by living creatures living in sea water 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. It takes one calorie of heat to heat one cubic centimeter, or one gram, of water by 1°. The same calorie can heat more than three thousand cubic centimeters of air by 1 °.

Therefore, the temperature of the surface of the water in the World Ocean strongly affects the temperature of the air above it, and, consequently, the climate of those areas where this air penetrates due to the prevailing winds.

The highest water temperature on the surface of the World Ocean away from the coast is observed in the equatorial zone. The average annual temperature there reaches 28 °. Near the coast in shallow water, the water warms up even more. Interestingly, during the year in the equatorial zone, the temperature of ocean water almost does not change. The highest temperature is usually no more than one degree above the average. The minimum temperature is just as low as the average. This happens because in the equatorial zone the arrival of solar heat during 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, the average annual temperatures of the surface of the water begin to decrease and in the subtropics reach 20 °. In the subtropical zone, the sun rises almost to the 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 noon. Therefore, the difference in the arrival of solar heat 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 surface water temperature drops rapidly and finally, in winter, reaches the temperature at which ice forms,

) or PSU units (Practical Salinity Units) of the practical salinity scale (Practical Salinity Scale).

Salinity in ppm is the amount of solids in grams dissolved in 1 kg of sea water, provided that all halogens are replaced by an equivalent amount of chlorine, all carbonates are converted to oxides, organic matter is burned.

In 1978, the practical salinity scale (Practical Salinity Scale 1978, PSS-78) was introduced and approved by all international oceanographic organizations, in which salinity measurement is based on electrical conductivity (conductometry), and not on water evaporation. In the 1970s, oceanographic CTD probes became widely used in marine research, and since then, water salinity has been measured mainly by electrical methods. To verify the operation of electrical conductivity cells that are immersed in water, laboratory salt meters are used. In turn, standard sea water is used to check salt meters. Standard sea water, recommended by the international organization IAPSO for calibration of salt meters, is produced in the UK by Ocean Scientific International Limited (OSIL) from natural sea water. If all measurement standards are followed, salinity measurement accuracy up to 0.001 PSU can be obtained.

The PSS-78 gives numerical results that are close to measurements of mass fractions, and differences are noticeable either when measurements with an accuracy better than 0.01 PSU are needed, or when the salt composition does not correspond to the standard composition of ocean water.

• Atlantic Ocean - 35.4 ‰ The highest salinity of surface waters in the open ocean is observed in the subtropical zone (up to 37.25 ‰), and the maximum is in the Mediterranean Sea: 39 ‰. In the equatorial zone, where the maximum amount of precipitation is noted, salinity decreases to 34 ‰. A sharp desalination of water occurs in the estuarine areas (for example, at the mouth of La Plata - 18-19 ‰).
• Indian Ocean - 34.8 ‰. The maximum salinity of surface waters is observed in the Persian Gulf and the Red Sea, where it reaches 40-41 ‰. High salinity (more than 36 ‰) is also observed in the southern tropical zone, especially in the eastern regions, and in the northern hemisphere also in the Arabian Sea. In the neighboring Bay of Bengal, due to the desalination effect of the Ganges runoff from the Brahmaputra and the Irrawaddy, the salinity is reduced to 30-34 ‰. The seasonal difference in salinity is significant only in the Antarctic and equatorial zones. In winter, desalinated waters from the northeastern part of the ocean are carried by the monsoon current, forming a tongue of low salinity along 5°N. sh. In summer, this language disappears.
• Pacific Ocean - 34.5 ‰. Tropical zones have the maximum salinity (up to a maximum of 35.5-35.6 ‰), where intensive evaporation is combined with a relatively small amount of precipitation. To the east, under the influence of cold currents, salinity decreases. A large amount of precipitation also lowers salinity, especially at the equator and in the western circulation zones of temperate and subpolar latitudes.
• Northern Arctic ocean - 32 ‰. There are several layers of water masses in the Arctic Ocean. The surface layer has a low temperature (below 0 °C) and low salinity. The latter is explained by the freshening effect of river runoff, melt water and very weak evaporation. Below, a subsurface layer stands out, colder (up to −1.8 °C) and more salty (up to 34.3 ‰), formed by mixing surface waters with the underlying intermediate water layer. The intermediate water layer is Atlantic water coming from the Greenland Sea with a positive temperature and high salinity (more than 37 ‰), spreading to a depth of 750-800 m. Deeper lies the deep water layer, which also forms in the Greenland Sea in winter, slowly creeping in a single stream from the strait between Greenland and Svalbard. The temperature of deep waters is about -0.9 ° C, salinity is close to 35 ‰. .

The salinity of ocean waters varies depending on the geographical latitude, from the open part of the ocean to the coast. In the surface waters of the oceans, it is lowered in the equatorial region, in polar latitudes.

Salinity is the amount of dissolved solid mineral substances (salts), expressed in grams, in 1 kg of sea water. A thousandth of a whole is called ppm and is indicated by the sign% o. For example, if the salinity of ocean water is 35% o, then this means that 1 kg (1000 g) of this water contains 35% o (ppm) of dissolved substances.

Salinity is one of the main characteristics of sea water; its value expresses the degree of concentration of all substances dissolved in water (mainly salts).

The salinity value in a particular area of ​​the World Ocean depends on a number of factors: on the inflow of fresh water and the amount of precipitation, the intensity of water evaporation, the formation and melting of ice, and water mixing processes.

Evaporation increases the salinity of seawater as the salts remain in solution. As sea ice melts, salinity decreases because sea ice tends to have less salinity than
salinity of the surrounding waters.

During the formation of sea ice, salinity increases due to the fact that only part of the salts passes into the ice.

What is the salinity of the waters of the World Ocean and its geographical distribution?

Salinity in different places, both on the surface and at the depths of the oceans and seas, is not the same. The average salinity of the waters of the World Ocean is 35% o.

In the open parts of the oceans, salinity changes little (from 32 to 37.9% o), in the seas it is much more - from 2 (in the Gulf of Finland of the Baltic Sea) to 42% o (in the Red Sea).

The general pattern of changes in salinity across latitudes under the influence of atmospheric precipitation and evaporation is characteristic of all oceans: salinity increases in the direction from the poles to the tropics, reaches a maximum value of about 20-25 ° north and south latitudes and decreases again in the equatorial zone.

The uniform change in salinity in the surface layers is disturbed by the influence of oceanic and coastal currents and enrichment fresh waters of large rivers. The highest salinity of the World Ocean (S = 37.9% o, not counting some seas, west of the Azores.

The salinity of the seas is the more different from the salinity of the ocean, the less the seas communicate with it; it also depends on their geographical location, in particular on climatic conditions. The salinity of the seas is greater than the oceans: Mediterranean - in the west 37-38% 0, in the east - 38-39% 0;

The salinity of the Red Sea is 37% o in the south, and up to 42% o in the north, in the Persian Gulf in the north the salinity is 40% o, in the eastern part - from 37 to 38% o.

Salinity: in the Sea of ​​Azov in the middle part from 10 to 12% o, and off the coast - 9.5% o.

Salinity of water in the Black Sea, in the middle part - from 10 to 12% o, and in the northwestern - 17% o, with increasing depth of the sea, the salinity of the water increases to 22% o;

in the Baltic Sea with east winds - 10%o, with western and south-western winds - from 10 to 22%o; in the Gulf of Finland near the island of Kotlin - 2% 0; in the White Sea on the border with the Barents 34-34.5% o, in the Gorla - 27-30% o, and in the middle part - from 24 to 27% o.

In the Caspian Sea, salinity is 12.8% o and in
In the Aral Sea, the average salinity is 10.3% o.

The salinity of the Russian Arctic and Far Eastern seas in areas remote from the coast is 29-30% o.

With increasing depth, salinity changes only up to 1500 m, below this horizon and to the bottom - slightly and ranges from 34 to 35% o.

In the polar regions, when ice melts, salinity increases with depth, and when ice forms, the salinity of sea water decreases.

In temperate latitudes, the salinity of sea water changes little with depth, in the subtropical zone it rapidly decreases to a depth of 1000 m, in the tropical zone it increases to a depth of 100 m, then decreases to a depth of 500 m, after which it slightly increases to a depth of 1500 m, and below remains unchanged.

What is the salinity and density of sea water?

As the temperature drops, the density of salty sea water increases, that is, the sea is saltier in winter than in summer! During the autumn and winter cooling, the water on the sea surface becomes denser, heavier.
With further cooling, surface sea water, being denser and heavier, "sinks" and mixes with warmer and lighter deep water.

This feature of salty sea water contributes to the mitigation of the Earth's climate. When cooling 1 cu. see sea water at 19C 3134 cu. see the air is heated by 1 °C.

The salinity of sea water increases the vertical circulation in the oceans and seas. The air receives much more heat (thermal energy) from the salty waters of the World Ocean than it would receive if the ocean waters were fresh.

The intensity of freezing of sea water and the development of ice phenomena in the seas and oceans depend on salinity.

The horizontal and vertical distribution of seawater density contributes to the horizontal and vertical circulation of water.

Knowing the vertical distribution of the density of sea water, it is possible to determine the direction and speed of currents, as well as the stability of a particular water mass: if the mass is unstable, then denser water lies above less dense water, and the waters will mix (vertical circulation).

The density of sea water is of great importance for the inhabitants of the ocean. It determines the stability of the composition of waters, which affects the distribution of organic and inorganic matter in the ocean.

The density of water affects the draft of ships. When moving from ocean water to fresh water and vice versa, their draft can change up to 0.3 m. Therefore, for the correct loading of ships in
ports and ensure the safety of navigation, it is necessary to know the value of salinity and density in the port of loading and at the passage to the sea to the port of destination and take them into account correctly.

Seventy percent of the surface of our planet is covered with water - most of it is in the oceans. The waters of the World Ocean are heterogeneous in composition and have a bitter-salty taste. Not every parent can answer the child's question: "Why does sea water taste so good?" What determines the amount of salt? There are different points of view on this matter.

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What determines the salinity of water

At different times of the year in different parts of the hydrosphere, salinity is not the same. Several factors influence its change:

• ice formation;
• evaporation;
• precipitation;
• currents;
• river flow;
• melting ice.

While the water from the surface of the ocean evaporates, the salt does not erode and remains. Her concentration is increasing. The freezing process has a similar effect. Glaciers contain the largest supply of fresh water on the planet. The salinity of the oceans during their formation increases.

The opposite effect is characterized by the melting of glaciers, in which the salt content decreases. Salt also comes from rivers flowing into the ocean and precipitation. The closer to the bottom, the less salinity. Cold currents reduce salinity, warm currents increase it.

Location

According to experts, The concentration of salt in the seas depends on their location. Closer to the northern regions, the concentration increases, to the south it decreases. However, the concentration of salt in the oceans is always greater than in the seas, and location does not have any effect on this. This fact is not explained.

Salinity is due to the presence of magnesium and sodium. One of the options for explaining the different concentrations is the presence of certain land areas enriched in deposits of such components. However, such an explanation is not very plausible, if we take into account the sea currents. Thanks to them, over time, the salt level should stabilize throughout the volume.

World Ocean

The salinity of the ocean depends on the geographical latitude, the proximity of rivers, the climatic features of objects etc. Its average value according to the measurement is 35 ppm.

Near the Antarctic and the Arctic in cold areas, the concentration is less, but in winter, during the formation of ice, the amount of salt increases. Therefore, the water in the Arctic Ocean is the least salty, and in the Indian Ocean, the concentration of salt is the highest.

In the Atlantic and Pacific oceans, the concentration of salt is approximately the same, which decreases in the equatorial zone and, conversely, increases in tropical and subtropical regions. Some cold and warm currents balance each other. For example, the salty Labrador Current and the unsalted Gulf Stream.

Interesting to know: How many exist on Earth?

Why are the oceans salty

There are different points of view that reveal the essence of the presence of salt in the ocean. Scientists believe that the reason is the ability of water masses to destroy the rock, leaching easily soluble elements from it. This process is ongoing. Salt saturates the seas and gives a bitter taste.

However, there are diametrically opposed opinions on this issue:

Volcanic activity decreased over time, and the atmosphere cleared of vapor. Acid rain fell less and less, and about 500 years ago, the composition of the ocean water surface stabilized and became what we know it today. Carbonates, which enter the ocean with river water, are an excellent building material for marine organisms.

Our planet is covered by water by 70%, of which more than 96% is occupied by oceans. This means that most of the water on Earth is salty. What is the salinity of water? How is it determined and what does it depend on? Can this water be used on the farm? Let's try to answer these questions.

What is the salinity of water?

Most of the water on the planet has salinity. It is commonly referred to as seawater and is found in the oceans, seas, and some lakes. The rest is fresh, its amount on Earth is less than 4%. Before you understand what the salinity of water is, you need to understand what salt is.

Salts are complex substances that consist of cations (positively charged ions) of metals and anions (negatively charged ions) of acidic bases. Lomonosov defined them as "fragile bodies that can dissolve in water." Many substances are dissolved in sea water. It contains sulfates, nitrates, phosphates, sodium, magnesium, rubidium, potassium cations, etc. Together, these substances are defined as salts.

So what is the salinity of water? This is the content of dissolved substances in it. It is measured in thousandths - ppm, which are indicated by a special symbol -% o. Ppm is the number of grams in one kilogram of water.

What determines the salinity of water?

In different parts of the hydrosphere and even at different times of the year, the salinity of the water is not the same. It changes under the influence of several factors:

• evaporation;
• ice formation;
• precipitation;
• melting ice;
• river flow;
• currents.

When water evaporates from the surface of the oceans, the salts remain and do not erode. As a result, their concentration increases. Freezing has a similar effect. Glaciers contain the largest supply of fresh water on the planet. During their formation, the salinity of the waters of the World Ocean increases.

The melting of glaciers is characterized by the opposite effect, reducing the salt content. In addition to them, the source of fresh water is precipitation and rivers flowing into the ocean. The salt level also depends on the depth and nature of the currents.

Their highest concentration is on the surface. The closer to the bottom, the less salinity. affect the salt content in a positive direction, cold, on the contrary, reduce it.

Salinity of the oceans

What is the salinity of sea water? We already know that it is far from the same in different parts of the planet. Its indicators depend on geographic latitudes, climatic features of the area, proximity to river objects, etc.

The average salinity of the waters of the World Ocean is 35 ppm. Cold regions near the Arctic and Antarctic are characterized by a lower concentration of substances. Although in winter, when ice forms, the amount of salt increases.

For the same reason, the least saline ocean is the Arctic Ocean (32% o). The Indian Ocean is the highest. It covers the area of ​​the Red Sea and the Persian Gulf, as well as the southern tropical zone, where the salinity is up to 36 ppm.

The Pacific and Atlantic oceans have approximately equal concentrations of substances. Their salinity decreases in the equatorial zone and increases in subtropical and tropical regions. Some are warm and balance each other out. For example, the non-salty Gulf Stream and the salty Labrador in the Atlantic Ocean.

Salinity of lakes and seas

Most of the lakes on the planet are fresh, as they are fed mainly by precipitation. This does not mean that there are no salts in them at all, just that their content is extremely small. If the amount of dissolved substances exceeds one ppm, then the lake is considered salty or mineral. The Caspian Sea has a record value (13% o). The largest fresh lake is Baikal.

Salt concentration depends on how the water leaves the lake. Fresh water bodies are flowing, while more saline ones are closed and subject to evaporation. The determining factor is also the rocks on which the lakes formed. So, in the area of ​​the Canadian Shield, rocks are poorly soluble in water, and therefore the reservoirs there are “clean”.

The seas are connected to the oceans through straits. Their salinity is somewhat different and affects the average ocean waters. Thus, the concentration of substances in the Mediterranean Sea is 39% o and is reflected in the Atlantic. The Red Sea, with an indicator of 41% o, greatly raises the average. The most salty is the Dead Sea, in which the concentration of substances ranges from 300 to 350% o.

Properties and significance of sea water

Not suitable for economic activity. It is not suitable for drinking, as well as watering plants. However, many organisms have long adapted to life in it. Moreover, they are very sensitive to changes in its salinity. Based on this, organisms are divided into freshwater and marine.

So, many animals and plants that live in the oceans cannot live in the fresh water of rivers and lakes. Edible mussels, crabs, jellyfish, dolphins, whales, sharks and other animals are exclusively marine.

People use fresh water for drinking. Salt is used for medicinal purposes. In small quantities, water with sea salt is used to restore the body. The therapeutic effect is produced by bathing and taking baths in sea water.