Properties of ocean water and zonal features. Chemical properties of ocean waters

Salinity. Ocean water consists by weight of 96.5% pure water and less than 4% dissolved salts, gases and suspended insoluble particles. The presence of relatively small amounts of different substances gives it significant differences from other natural waters.
In total, 44 chemical elements were found in a dissolved state in the ocean water. It is assumed that all substances found in nature are dissolved in it, but due to negligible quantities they cannot be detected. There are main components of the salinity of ocean water (Cl, Na, Mg, Ca, K, etc.) and minor ones, contained in negligible quantities (among them gold, silver, copper, phosphorus, iodine, etc.).
A remarkable feature of Ocean water is the constancy of its salt composition. The reason for this may be the continuous mixing of the waters of the World Ocean. However, this explanation cannot be considered exhaustive.
The total amount of salts contained in the water of the World Ocean is 48 * 10 x 15 tons. This amount of salts is enough to cover the entire surface of the Earth with a layer of 45 m, and the surface of the land with a layer of 153 m.
With a very low silver content (0.3 mg per m3), the total amount of it in the ocean water is 20,000 times greater than the amount of silver mined by people over the entire historical period. Gold is contained in ocean water in the amount of 0.006 mg per 1 m3, while its total amount reaches 10 billion tons.
In terms of salt composition, ocean water differs significantly from river water (Table 19).

Ocean water contains the most (27 g per 1 liter of water) common table salt (NaCl), which is why Ocean water tastes salty; magnesium salts (MgCl2, MgSO4) give it a bitter taste.
Significant differences in the ratio of salts in the water of the Ocean and in the water of rivers cannot but seem surprising, since rivers continuously carry salts into the Ocean.
It is assumed that the salt composition of the ocean waters released from the earth's interior is associated with their origin. Ocean waters emerged with their original salinity. Subsequently, a certain salt composition was balanced. The amount of salts carried out by rivers is to some extent balanced by their consumption. The consumption of salts is influenced by the formation of iron-manganese nodules, the removal of salts by the wind and, of course, the activity of organisms that extract salts (primarily calcium salts) from the ocean water to build skeletons and shells. The skeletons and shells of dead organisms partially dissolve in water, and partially form bottom sediments and, thus, fall out of the cycle of matter.
Plants and animals living in the Ocean absorb and concentrate in their bodies various substances found in the water, including those that humans have not yet been able to detect. Calcium and silicon are absorbed especially vigorously. Algae sequester billions of tons of carbon and release billions of tons of oxygen each year. Water passes through the gills of fish during respiration; many animals, filtering food, pass large amounts of water through the gastrointestinal tract; all animals swallow water with food. Ocean water one way or another passes through the body of animals and plants, and this ultimately determines its modern salt composition.
Ocean waters have an average salinity of 35‰ (35 g of salts per 1 liter of water). Changes in salinity are caused by changes in the flow of salts or fresh water.
Salts enter the Ocean along with water flowing from land, are brought and carried away during water exchange with neighboring areas of the Ocean, are released or consumed as a result of various processes occurring in the water. The constant flow of salts into the Ocean from land should have caused a gradual increase in the salinity of its waters. If this does happen, it happens so slowly that it remains undetected to this day.
The main reason for differences in ocean water salinity is a change in the balance of fresh water. Precipitation on the surface of the Ocean, runoff from land, and melting ice cause a decrease in salinity; evaporation and ice formation, on the contrary, increase it. The influx of water from land significantly affects the salinity near the coast and especially near the confluence of rivers.
Since salinity on the surface of the Ocean in its open part depends mainly on the ratio of precipitation and evaporation (i.e., on climatic conditions), its distribution reveals latitudinal zoning. This is clearly visible on the map isohaline- lines connecting points with the same salinity. In equatorial latitudes, the surface layers of water are somewhat desalinated (34-35‰) due to the fact that precipitation exceeds evaporation. In subtropical and tropical latitudes, the salinity of the surface layers is increased and reaches a maximum for the surface of the open Ocean (36-37‰. This is explained by the fact that the water consumption for evaporation is not covered by precipitation. The ocean loses moisture, but salts remain. To the north and south of the tropical latitudes, the salinity of ocean waters gradually decreases to 33-32‰, which is determined by a decrease in evaporation and an increase in precipitation. The decrease in salinity on the surface of the Ocean is facilitated by melting floating ice. The latitudinal zonality in the distribution of salinity on the surface of the Ocean is disrupted by currents. Warm currents increase salinity, cold ones, on the contrary , lower it.
The average salinity at the surface of the oceans varies. The Atlantic Ocean has the highest average salinity (35.4 ‰), the lowest - the Arctic Ocean (32 ‰). The increased salinity of the Atlantic Ocean is explained by the influence of the continents and its comparative narrowness. In the Arctic Ocean, Siberian rivers have a desalination effect (off the coast of Asia, salinity drops to 20‰).
Since changes in salinity are associated mainly with the inflow-outflow balance of water, they are well expressed only in the surface layers that directly receive (precipitation) and release water (evaporation), as well as in the mixing layer. Mixing covers a water column up to 1500 m thick. Deeper, the salinity of the waters of the World Ocean remains unchanged (34.7-34.9‰). The nature of the change in salinity depends on the conditions that determine salinity at the surface. There are four types of vertical changes in salinity in the Ocean: I - equatorial, II - subtropical, III - moderate and IV - polar,
I. In equatorial latitudes, where the water on the surface is desalinated, salinity gradually increases, reaching a maximum at a depth of 100 m, where saltier waters come to the equator from the tropical part of the Ocean. Below 100 m, salinity decreases, and starting from a depth of 1000-1500 m it becomes almost constant. II. In subtropical latitudes, salinity quickly decreases to a depth of 1000 m; deeper it is constant. III. In temperate latitudes, salinity varies little with depth. IV. In polar latitudes, salinity on the surface of the Ocean is the lowest; with depth it first increases rapidly, and then, from about a depth of 200 m, remains almost unchanged.
The salinity of water on the surface of the seas can differ greatly from the salinity of water in the open part of the Ocean. It is also determined primarily by the balance of fresh water, which means it depends on climatic conditions. The sea is influenced by the land it washes to a much greater extent than the ocean. The deeper the sea extends into the land, the less connected it is with the Ocean, the more its salinity differs from the average ocean salinity.
Seas in polar and temperate latitudes have a positive water balance, and therefore the salinity on their surface is reduced, especially at the confluence of rivers. Seas in subtropical and tropical latitudes, surrounded by land with a small number of rivers, have high salinity. The high salinity of the Red Sea (up to 42‰) is explained by its position among the land, in a dry and hot climate. Precipitation on the sea surface is only 100 mm per year, there is no runoff from land, and evaporation reaches 3000 mm per year. Water exchange with the Ocean occurs through the narrow Bab-el-Mandeb Strait.
The increased salinity of the Mediterranean Sea (up to 39‰) is the result of the fact that runoff from land and precipitation do not compensate for evaporation, and water exchange with the Ocean is difficult. In the Black Sea (18‰), on the contrary, evaporation is almost compensated by runoff (annual runoff layer 80 cm), and precipitation makes the water balance positive. The lack of free water exchange with the Sea of ​​Marmara contributes to the preservation of the low salinity of the Black Sea.
In the North Sea, which is influenced, on the one hand, by the Ocean, and on the other, by the highly desalinated Baltic Sea, salinity increases from southeast to northwest from 31 to 35‰. All the margins of the sea, closely connected with the Ocean, have a salinity close to the salinity of the adjacent part of the Ocean. In the coastal parts of the seas that receive rivers, the water is highly desalinated and often has a salinity of only a few ppm.
The change in salinity with depth in the seas depends on the salinity on the surface and the associated water exchange with the Ocean (or with the neighboring sea).
If the salinity of the sea is less than the salinity of the Ocean (the neighboring sea) at the strait connecting them, denser ocean water penetrates through the strait into the sea and sinks, filling its depths. In this case, the salinity in the sea increases with depth. If the sea is saltier than the neighboring part of the Ocean (sea), the water in the strait moves along the bottom towards the Ocean, along the surface - towards the sea. The surface layers acquire the salinity and temperature characteristic of the sea in the given physiographic conditions. The salinity of bottom waters corresponds to the salinity on the surface during the period of lowest temperatures.
Various cases of changes in salinity with depth are clearly visible in the Mediterranean, Marmara and Black seas. The Mediterranean Sea is saltier than the Atlantic Ocean. In the Strait of Gibraltar (depth 360 m) there is a deep current from the sea to the ocean. Mediterranean water drops from the threshold, creating an area of ​​increased salinity at some depth in the Ocean near the threshold. Ocean water flows across the surface of the strait into the sea. The salinity of water at the bottom of the Mediterranean Sea throughout its entire length is 38.6‰, while on the surface it varies from 39.6‰ in the eastern part to 37‰ in the western part. Accordingly, in the eastern part salinity decreases with depth, and in the western part it increases.
The Sea of ​​Marmara is located between two seas, the more saline Mediterranean and the less saline Black Sea. Salty Mediterranean water, penetrating through the Dardanelles, fills the depths of the sea, and therefore the salinity at the bottom is 38‰. The Black Sea water, moving along the surface, comes to the Sea of ​​Marmara through the Bosphorus and desalinizes the water of the surface layers to 25‰.
The Black Sea is highly desalinated. Therefore, water of Mediterranean origin penetrates from the Marmara Sea to the Black Sea along the bottom of the Bosphorus and, sinking, fills its depths. The salinity of water in the Black Sea increases with depth from 17-16 to 22.3‰.
The water of the World Ocean contains colossal amounts of valuable chemical raw materials, the use of which is still very limited. About 5 million tons of table salt are extracted from the waters of the oceans and seas annually, including more than 3 million tons in the countries of Southeast Asia. Potassium and magnesium salts are extracted from sea water. Bromide gas is obtained as a by-product during the extraction of table salt and magnesium.
To extract chemical elements contained in very small quantities from water, you can use the amazing ability of many ocean inhabitants to absorb and concentrate certain elements in their bodies, for example, the concentration of iodine in a number of algae is thousands and hundreds of thousands of times higher than its concentration in ocean water. Mollusks absorb copper, aspidia - zinc, radiolarians - strontium, jellyfish - zinc, tin, lead. Fucus and kelp contain a lot of aluminum, and sulfur bacteria contain sulfur. By selecting certain organisms and enhancing their ability to concentrate elements, it will be possible to create artificial mineral deposits.
Modern chemistry has produced ion exchange resins (exchange resins) that have the property of absorbing various substances from solution and retaining them on their surface. A pinch of ion exchanger can desalinate a bucket of salt water and extract salts from it. The use of ion exchangers will make the wealth of ocean salts more accessible for people to use.
Gases in Ocean water. Gases are dissolved in ocean water. These are mainly oxygen, nitrogen, carbon dioxide, as well as hydrogen sulfide, ammonia, and methane. Water dissolves the gases of the atmosphere in contact with it; gases are released during chemical and biological processes, brought by land waters, and enter the ocean water during underwater eruptions. Redistribution of gases in water occurs when it is stirred. Due to the high dissolving ability of water, the ocean has a great influence on the chemical composition of the atmosphere.
Nitrogen is present everywhere in the Ocean, and its content remains almost unchanged, since it combines poorly and is little consumed. Some infiltrating bacteria convert it into nitrates and ammonia.
Oxygen enters the Ocean from the atmosphere and is released during photosynthesis. It is consumed in the process of respiration, for the oxidation of various substances, and is released into the atmosphere. The solubility of oxygen in water is determined by its temperature and salinity. When the surface of the Ocean heats up (spring, summer), water releases oxygen to the atmosphere, and when it cools (autumn, winter), it absorbs it from the atmosphere. Ocean water has less oxygen than fresh water.
Since the intensity of photosynthesis processes depends on the degree of illumination of water by sunlight, the amount of oxygen in water fluctuates throughout the day, decreasing with depth. Below 200 m there is very little light, there is no vegetation and the oxygen content in the water drops, but then, at greater depths (>1800 m), as a result of the circulation of ocean waters, it increases again.
The oxygen content in the surface layers of water (100-300 m) increases from the equator to the poles: at a latitude of 0° - 5 cm3/l, at a latitude of 50° - 8 cm3/l. Water from warm currents is poorer in oxygen than water from cold currents.
The presence of oxygen in ocean water is a necessary condition for the development of life in it.
Carbon dioxide, unlike oxygen and nitrogen, is found in ocean water mainly in a bound state - in the form of carbon dioxide compounds (carbonates and bicarbonates). It enters water from the atmosphere, is released during the respiration of organisms and during the decomposition of organic matter, and comes from the earth's crust during underwater eruptions. Like oxygen, carbon dioxide dissolves better in cold water. When the temperature rises, water releases carbon dioxide to the atmosphere; when the temperature decreases, it absorbs it. A significant portion of atmospheric carbon dioxide dissolves in ocean water. Carbon dioxide reserves in the Ocean are 45-50 cm3 per 1 liter of water. A sufficient amount of it is a prerequisite for the life of organisms.
In sea water, the amount and distribution of gases can be significantly different than in ocean water. In seas whose depths are not supplied with oxygen, hydrogen sulfide accumulates. This occurs as a result of the activity of bacteria that use sulfate oxygen to oxidize nutrients under anaerobic conditions. Normal organic life does not develop in a hydrogen sulfide environment.
An example of a sea whose depths are contaminated with hydrogen sulfide is the Black Sea. The increase in water density with depth ensures the balance of the water mass in the Black Sea. Complete mixing of water does not occur in it, oxygen gradually disappears with depth, the content of hydrogen sulfide increases, reaching 6.5 cm3 per 1 liter of water at the bottom.
Inorganic and organic compounds containing elements necessary for organisms are called nutrient.
The distribution of nutrients and energy (solar radiation) in the Ocean determines the distribution and productivity of living matter.
Ocean water density with increasing salinity it always increases, since the content of substances having a greater specific gravity than water increases. An increase in density on the ocean surface is facilitated by cooling, evaporation and ice formation. As the density of water increases, convection occurs. When heated, as well as when salt water mixes with precipitation water and melt water, its density decreases.
On the surface of the Ocean there is a change in density ranging from 0.996 to 1.083. In the open ocean, density, as a rule, is determined by temperature and therefore increases from the equator to the poles. With depth, the density of water in the Ocean increases.
Pressure. For every square centimeter of the ocean's surface, the atmosphere presses with a force of approximately 1 kg (one atmosphere). The same pressure on the same area is exerted by a column of water with a height of only 10.06 m. Thus, we can assume that for every 10 m of depth, the pressure increases by 1 atmosphere. If we take into account that water contracts and becomes denser with depth, it turns out that the pressure at a depth of 10,000 m is equal to 1119 atmospheres. All processes occurring at great depths occur under strong pressure, but this does not prevent the development of life in the depths of the Ocean.
Ocean water transparency. The radiant energy of the Sun, penetrating into the water column, is dissipated and absorbed. The transparency of the water depends on the degree of its dispersion and absorption. Since the amount of impurities contained in water is not the same everywhere and changes over time, transparency also does not remain constant (Table 20). The least transparency is observed off the coast in shallow water, especially after storms. Water transparency decreases significantly during the period of massive plankton development. The decrease in transparency is caused by the melting of ice (ice always contains impurities, in addition, the mass of air bubbles contained in the ice passes into water). It has been noticed that water transparency increases in places where deep water rises to the surface.

Currently, transparency measurements at different depths are made using a universal hydrophotometer.
The color of the water of oceans and seas. The thickness of the pure water of the Ocean (sea), as a result of the collective absorption and scattering of light, has a blue or blue color. This color of water is called the “color of the sea desert.” The presence of plankton and inorganic suspended matter affects the color of the water, etc. it takes on a greenish tint. Large amounts of impurities make the water yellowish-green; near river mouths it can even be brownish.
To determine the color of Ocean water, they use the sea color scale (Forel-Uhle scale), which includes 21 test tubes with liquid of different colors - from blue to brown.
In equatorial and tropical latitudes, the dominant color of ocean water is dark blue and even blue. For example, the Bay of Bengal, the Arabian Sea, the southern part of the China Sea, and the Red Sea have such water. Blue water in the Mediterranean Sea, the water of the Black Sea is close to it in color. In temperate latitudes, in many places the water is greenish (especially near the coast); it becomes noticeably greener in areas where the ice melts. In polar latitudes, greenish color predominates.

Salinity is the most important feature of ocean water. This solution contains almost all chemical elements known on Earth. The total amount of salts is 50-10 16 tons. They can cover the ocean bottom with a layer of 60 m, the entire Earth - 45 m, land - 153 m. The ratio of salts in ocean water remains constant, this is ensured by the high dynamics of ocean waters. The composition is dominated by NaCl (77.8%), MgCl (10.9%), etc.

The average salinity of ocean water is 35 0/00. Deviation from the average salinity in one direction or another is caused by changes in the incoming and outgoing balance of fresh water. Thus, precipitation, water from glaciers, and runoff from land reduce salinity; Evaporation increases salinity.

There are both zonal and regional features in the distribution of salinity in the ocean. Zonal features are associated with climatic conditions (distribution of precipitation and evaporation). In the equatorial zone, the waters are slightly saline (O>E), in tropical and subtropical latitudes (E>O) the maximum salinity for surface ocean waters is 36-37 0 / 00, to the north and south of this zone the salinity decreases. Melting ice contributes to a decrease in salinity in high latitudes.

The latitudinal zonality in the distribution of salinity on the ocean surface is disrupted by currents. Warm ones increase salinity, cold ones decrease them. The average salinity of the oceans at the surface varies. The Atlantic Ocean has the highest salinity - 35.4 0/00, the lowest is the Arctic Ocean - 32 0/00 (the desalinating role of Siberian waters is great). Changes in salinity are associated mainly with surface layers that directly receive fresh water and are determined by the depth of mixing. All changes in salinity occur in the upper layers to depths of 1500 m; deeper salinity does not change.

Water temperature of the World Ocean.

Changes in the course of heat balance elements determine the course of water temperature. Daily amplitudes of water temperature fluctuations on the ocean surface do not exceed on average 0.5 0 C. The largest daily amplitude is in low latitudes (up to 1 0 C), the smallest in high latitudes (up to 0 0 C). Daily temperature fluctuations in the ocean play a subordinate role.

The annual amplitudes of temperature fluctuations on the ocean surface are greater than the daily ones. Annual temperature fluctuations are small at low (1 0) and high (2 0) latitudes. In the first case, a large amount is evenly distributed throughout the year, in the second, during the short summer the water does not have time to heat up much. The largest annual amplitudes (from 10 0 to 17 0) are observed in temperate latitudes. The highest average annual water temperatures (27-28 0) are observed in equatorial and tropical latitudes, to the north and south of them the temperature drops to 0 0 C and lower in polar latitudes. The thermal equator is located approximately at 5 0 C north latitude. Ocean currents disrupt the zonal temperature distribution. Currents that transport heat towards the poles (for example, the Gulf Stream) are identified as positive temperature anomalies. Therefore, in tropical latitudes, under the influence of currents, the water temperature on the eastern shores is higher than on the western shores, and in temperate latitudes, on the contrary, on the western shores it is higher than on the eastern shores. In the southern, more seaward hemisphere, the zonality in the distribution of water temperatures is almost unchanged. The highest temperature on the ocean surface (+32 0 C) was observed in August in the Pacific Ocean, the lowest in February in the Arctic Ocean (-1.7 0 C). On average per year, the ocean surface in the southern hemisphere is colder than in the northern hemisphere (influence of Antarctica). The average annual temperature on the ocean surface is +17.4 0 C, which is higher than the annual air temperature of +14 0. The warmest is the Indian Ocean - about +20 0 C. The heat of solar radiation, which heats the upper layer of water, is extremely slowly transferred to the underlying layers. Heat redistribution in the ocean water occurs due to convection and mixing by waves and currents. Hence, the temperature decreases with depth. At a depth of somewhere around 100-200 m, the temperature drops sharply. A layer of sharp drop in water temperature with depth is called a thermocline.

Thermocline in the ocean from the equator to 50-60 0 s. and S. exists constantly at depths from 100 to 700 m. In the Arctic Ocean, the water temperature drops to a depth of 50-100 m, and then increases, reaching a maximum at a depth of 200-600 m. This increase in temperature is caused by the penetration of warm waters from temperate latitudes, more salty, than the upper layers of water.

Ice in the ocean appears at high latitudes when the water temperature drops below freezing point. The freezing point depends on its salinity. The higher the salinity, the lower the freezing point. Ice has a lower density than fresh ice. Salt ice is less durable than fresh ice, but more plastic and viscous. It does not break in swell (weak waves). It takes on a greenish tint, in contrast to the blue color of fresh ice. Ice in the ocean can be either stationary or floating. Fixed ice is a continuous sheet of ice associated with land or shoals. Usually this is fast ice. Floating ice (drifting) is not connected to the shore and moves under the influence of wind and currents.

1.1 Distribution of water and land on the globe.

The total surface of the earth is 510 million sq. km.

The land area is 149 million sq. km. (29%)

Occupied by water - 310 million sq. km. (71%)

In the Northern and Southern Hemispheres, the ratio of land surface and water is not the same:

In the Southern Hemisphere, water accounts for 81%

In the Northern Hemisphere, water accounts for 61%

The continents are more or less separated from each other, while the waters of the ocean form a continuous body of water on the surface of the globe, which is called the World Ocean. According to physical and geographical features, the latter is divided into separate oceans, seas, bays, bays and straits.

Ocean - the largest part of the World Ocean, bounded on different sides by unconnected continents.

Since the 30s of the twentieth century, a division into 4 oceans has been accepted: Quiet, Indian, Atlantic, Arctic (formerly Southern Arctic).

The continents that divide the World Ocean define the natural boundaries between the oceans. In the high southern latitudes there are no such boundaries and they are accepted here conditionally: between the Pacific and Atlantic along the meridian of Cape Horn (6804 ‘W), from the island of Tierra del Fuego to Antarctica; between the Atlantic and Indian - from Cape Agulhas along the meridian 20E. ; between Indian and Pacific - from Cape South-East to the island. Tasmania along the meridian 14655’.

The areas of the oceans as a percentage of the total area of ​​the World Ocean are;

Quiet - 50%

Atlantic - 25.8%

Indian - 20.8%

Arctic - 3.6%

In each of the oceans, seas are distinguished and represent more or less isolated and fairly extensive areas of the ocean, which have their own hydrological regime, connecting under the influence of local conditions and difficult water exchange with adjacent areas of the ocean.

The seas, according to the degree of their isolation from the ocean and physical and geographical conditions, are divided into three main groups:

1.inland seas

A. middle seas

b. semi-closed

2. marginal seas

3. interisland seas

Mediterranean Seas surrounded on all sides by land and connected to the ocean by one or more straits. They are characterized by maximum isolation of natural conditions, closed circulation of surface waters and the greatest independence in the distribution of salinity and temperature.

These seas include: Mediterranean, Black, White Seas.

Semi-enclosed seas partially limited by continents and separated from the ocean by peninsulas or a chain of islands, rapids in the straits between which complicate water exchange, but it is still carried out much more freely than in the Mediterranean seas.

Example: the Bering, Okhotsk, and Japanese seas, which are separated from the Pacific Ocean by the Aleutian, Kuril, and Japanese islands.

Rim Seas are more or less open parts of the ocean, separated from the ocean by peninsulas or islands.

Water exchange between seas of this type and the ocean is practically free. The formation of the current system and the distribution of salinity and temperature are equally influenced by both the continent and the ocean. The marginal seas include: the Arctic seas, except for the White Sea.

Interisland seas - these are parts of the ocean surrounded by a ring of islands, the rapids in the straits between which prevent any free exchange of water. As a result of the influence of the ocean, the natural conditions of these seas are similar to the natural conditions of the ocean. There is some independence in the nature of the currents and the distribution of temperature and salinity on the surface and at the depths of these seas. Seas of this type include the seas of the East Indian archipelago: Sulu, Celeba, Benda, Java, etc.

The smaller divisions of the ocean are bays, bays and straits. The difference between a bay and a bay is quite arbitrary.

Bay called the part of the sea that juts into the land and is sufficiently open to the influence of adjacent waters. The largest bays: Biscay, Guinea, Bengal, Alaska, Hudson, Anadyr, etc.

Bay called a small bay with the mouth of the bay itself, limited by islands or peninsulas, which somewhat complicate the water exchange between the bay and the adjacent body of water. Example Sevastopol, Zolotoy Rog, Tsemeskaya, etc.

In the north, the bays that protrude deeply into the land where rivers usually flow are called lips; at the bottom of the lips there are traces of river sediments, the water is highly desalinated.

The largest bays: Obskaya, Dvinskaya, Onega, etc. Winding, low, deeply protruding bays into the mainland, formed due to glacial erosion, are called fiords .

Liman called the mouth of a river valley, or ravine, flooded by the sea, as a result of a slight subsidence of the land. Lagoon called: a) a shallow body of water, separated from the sea as a result of sediment deposition in the form of a coastal bar and connected to the sea by a narrow strait; b) an area of ​​sea between the mainland and a coral reef or atoll.

Strait called a relatively narrow part of the World Ocean, connecting two bodies of water with fairly independent natural conditions.

1.2. Chemical composition and salinity of sea water

Sea water differs from fresh water in taste, specific gravity, transparency, color, and more aggressive effects. Due to the strong polarity and large dipole moment of the molecules, water has a high dissociating ability. Therefore, various salts are dissolved in ionic dispersed form, and sea water is essentially a weak, fully ionized solution with an alkaline reaction, which is determined by the excess of the sum of cation equivalents by an average of 2.38 mg-equiv/l (alkaline solution). Weight reduced to vacuum The amount expressed 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 into oxides, and organic matter is burned, is usually called the salinity of sea water. Salinity is indicated by the symbol S. A unit of salinity is taken to be 1 g of salts dissolved in 1000 g of sea water and called ppm , denoted by %0. The average amount of minerals dissolved in 1 kg of sea water is 35 g and, therefore, the average salinity of the world's oceans is S = 35%0.

Theoretically, sea water contains all known chemical elements, but their weight content is different. There are two groups of elements contained in sea water.

1 group. Major ions of ocean water.

Ions and molecules	Per 1 kg of water (S = 35%0)
Chloride Cl
Sulfated SO4
Hydrocarbonate HCO3
Bromide B2
Fluoride F
Boric acid H2 BO3
Sum of anions:
Sodium Na
Magnesium Mg
Calcium Ca
Strontium Sr
Sum of cations
Sum of ions

Group 2 - Microelements whose total content does not exceed 3 mg/kg.

Certain elements are present in seawater in vanishingly small quantities. Example: silver - 310 -7 g, gold - 510 -7 g. The main elements are found in salt compounds in sea water, the main ones being NaCl and MgCl, constituting 88.7% by weight of all solids dissolved in sea water ; sulfates MgSO4, CaSO4, K2SO4 making up 10.8% and carbonate CaCO3 making up 0.3%. As a result of the analysis of sea water samples, it was found that the content of dissolved minerals can vary widely (from 2 to 30 g/kg), but their percentage ratio can be assumed to be constant with sufficient accuracy for practical purposes. This pattern is called constancy of the salt composition of sea water .

Based on this pattern, it turned out to be possible to associate the salinity of sea water with the content of chlorine (as the element contained in the largest amount in sea water)

S = 0.030 + 1.805 Cl.

River water contains on average 60.1% carbonates and 5.2% chlorides. However, despite the fact that every year 1.6910 9 tons of carbonates (HCO3) enter the World Ocean with the water of rivers, the flow of which is 3.610 4 , their total content in the ocean remains practically unchanged. The reasons are:

Intensive consumption by marine organizations to build limestone formations.

Precipitation due to poor solubility.

It should be noted that it is almost impossible to detect changes in salt content because the total mass of water in the ocean is 5610 15 tons and the supply of salts turns out to be practically negligible. For example, it will take 210 5 years to change the content of chloride ions by 0.02%0.

Salinity on the surface of the ocean in its open parts depends on the relationship between the amount of precipitation and the amount of evaporation, and the fluctuation in salinity for these reasons is 0.2%0. The greater the difference in temperature between water and air, the wind speed and its duration, the greater the amount of evaporation. This leads to an increase in water salinity. Precipitation reduces surface salinity.

In the polar regions, salinity changes with melting and ice formation and fluctuations here are approximately 0.7%0.

The change in salinity across latitudes is approximately the same for all oceans. Salinity increases from the poles to the tropics, reaching 20-25°C. and Yu. or and decreases again at the equator. Distribution by latitude in the Atlantic Ocean of salinity, precipitation, evaporation, density, and water temperature. (Figure 1).

A uniform change in the salinity surface is obtained due to the presence of oceanic and coastal currents, as well as as a result of the removal of fresh water by large rivers.

The less the sea is connected to the ocean, the more different the salinity of the seas is from the salinity of the ocean.

Salinity of the seas:

Mediterranean 37-38%0 in the west

38-39%0 in the east

Red Sea 37%0 in the south

41%0 in the north

Persian Gulf 40%0 in the north

37-38%0in the east

In depth, fluctuations in salinity occur only at a depth of 1500 m. Below this horizon, salinity does not change significantly. The distribution of salinity in depth is affected by horizontal movements and vertical circulation of water masses. To map the distribution of salinity on the surface of the ocean or on any other horizon, salinity lines are drawn - isohalines .

1.3. Gases in sea water

In contact with the atmosphere, sea water absorbs gases contained in it from the air: oxygen, nitrogen, carbon dioxide.

The amount of dissolved gases in seawater is determined by the partial pressure and solubility of the gases, which depends on the chemical nature of the gases and decreases with increasing temperature.

Table of solubility of gases in fresh water at a partial pressure of 760 mmHg.

	Gas solubility (ml/l)
	Oxygen			Carbon dioxide	Hydrogen sulfide

The solubility of oxygen and nitrogen that do not react with seawater also depends on salinity and decreases with its increase. The content of soluble gases in seawater is estimated in absolute units (ml/l) or as a percentage of the saturated amount, i.e. on the amount of gases that can dissolve in water at a given temperature and salinity, normal humidity and pressure of 760 mmHg. Oxygen and nitrogen, due to the better solubility of oxygen in sea water, are in a 1:2 ratio. The oxygen content fluctuates in time and space from significant supersaturation (up to 350% then in shallow water as a result of photosynthesis, to its complete disappearance when consumed by the respiration of organisms and oxidation and in the absence of vertical circulation.

Since the solubility of oxygen largely depends on temperature, in the cold season oxygen is absorbed by sea water, and with increasing temperature, excess oxygen passes into the atmosphere.

Carbon dioxide is contained in the air in an amount of 0.03% and therefore its content in water should be achieved at 0.5 ml/l. However, unlike oxygen and nitrogen, carbon dioxide not only dissolves in water, but also partially enters into compounds with bases (since water has a slightly alkaline reaction). As a result, the total content of free and bound carbon dioxide can reach 50 ml/l. Carbon dioxide is consumed during photosynthesis and for the construction of calcareous formations by organisms. A small part of carbon dioxide (1%) combines with water to form carbonic acid

CO2 + H2O  H2CO3.

Oxygen dissociates releasing bicarbonate and carbonate ions, as well as hydrogen ions

H2CO3  H + HCO3

H2CO3  H + CO3

A normal solution of hydrogen ions contains 1 g
in 1 liter of water. Experiments have established that at a H ion concentration of 110 -7 g/l, water is neutral. It is convenient to express the concentration of hydrogen ions by an exponent with the opposite sign and denote pH.

For neutral water pH = 7

If hydrogen ions predominate pH< 7 (кислая реакция).

If hydroxyl ions predominate pH > 7 (alkaline reaction).

It has been established that with a decrease in the content of free carbon dioxide, the pH increases. In the open ocean, water has a slightly alkaline reaction or pH = 7.8 - 8.8.

1.4. Temperature and thermal properties of sea water

The ocean surface is heated directly and by diffuse solar radiation.

In the absence of continents, the temperature on the surface of the ocean would depend only on the latitude of the place. In fact, with the exception of the southern part of the World Ocean, the map is completely different due to the dismemberment of the ocean, the influence of oceanic plants and vertical circulation.

Average gas temperatures on the surface of the oceans:

Atlantic - 16.9 С

Indian - 17.0 С

Quiet 19.1 С

Global - 17.4С

Average air temperature 14.3 С

The highest is in the Persian Gulf (35.6 С). The lowest is in the Arctic Ocean (-2 С). Temperature decreases with depth to horizons of 3000 - 500 m very quickly, then to 1200 - 1500 m much more slowly, and from 1500 m to the bottom either very slowly or does not change at all. (Figure 2)

Fig.2. Temperature changes with depth at different latitudes.

Daily temperature fluctuations quickly decrease with depth and die out at a horizon of 30-50 m. The maximum temperature at depth occurs 5-6 hours later than at the surface. The depth of penetration of gas temperature fluctuations depends on environmental conditions, but usually does not exceed 300 - 500 m. The specific heat capacity is very high:

1 Cal/g * deg = 4186.8 J/kg * deg.

Substance	Heat capacity Cal/G*deg
Fresh water
Sea water
Liquid ammonia

When 1 cubic cm of water is cooled by 1°C, an amount of heat is released sufficient to heat about 3000 cubic meters per 1 m. cm air.

The thermal conductivity of sea water is determined by the coefficient of molecular thermal conductivity, which varies depending on temperature, salinity, pressure within the range (1.3 - 1.4) 10 -3 Cal / cm  degsec.

Heat transfer in this way occurs extremely slowly. In real conditions, there is always turbulent fluid movement, and heat transfer in the ocean is always determined by the coefficient of turbulent thermal conductivity.

1.5. Density, specific gravity and compressibility of sea water

The density of sea water is the ratio of a unit weight of a volume of water at the temperature at the time of observation to the weight of a unit volume of distilled water at a temperature of 4  C ( ).

It is known from physics that density is defined as mass enclosed in units of volume (g/cm ; kg/m ).

Since the density and specific gravity of distilled water at 4 °C is taken = 1, then the numerical density ( ) and physical density are equal.

In oceanography, density is not measured but calculated through specific gravity, with 2 forms of specific gravity used for intermediate calculations:

The following concepts are derived:

Conditional density

Conditional specific gravity at 17.5  WITH

Conditional specific gravity at 0  C (standard conventional weight of sea water)

The world ocean - the totality of the oceans and individual seas of the Earth - occupies about 71% of the entire earth's surface.

It owns 98% of the entire hydrosphere, which is 1338 million km 3. The world's oceans are one. It is studied by a complex science - oceanology, a section of which is ocean chemistry. Ocean chemistry is the science of the properties, structure and interactions of substances found in the water column, bottom sediments and the surface layer of the atmosphere. Considering the interaction of the ocean with border regions, ocean chemistry in a broad sense should be classified as the science of geochemistry (chemistry of the Earth).

The main directions in research in ocean chemistry are the study of the physicochemical nature of sea water, the chemical foundations of primary biological productivity, chemical exchange at the interfaces of the atmosphere - ocean, ocean - bottom, sea bottom sediments, the cycle of individual elements and organic matter.

The practical significance of the science of ocean chemistry is determined by the fact that the degree of development and use of land resources is so great that there is a danger of their rapid depletion. Knowledge of ocean chemistry is necessary for the rational use of the World Ocean and its protection from pollution.

Origin and evolution of ocean water composition. According to modern views, the Earth was formed from cold cosmic matter about 4.6 billion years ago. During gravitational compression and due to the decay of radioactive isotopes, its interior was heated.

However, scientists' calculations show that the Earth was not completely melted. Heat removal could take place according to the following mechanism. In the melt zone, the more refractory substances fall first to the bottom of the zone, while the more easily melting substances float up and become overheated and melt the roof. The melt zone thus rises to the lithosphere.

The release of water from the solid matter of chondrite meteorites, the composition of which is considered to be closest to the Earth's mantle, was experimentally proven by A.P. Vinogradov using the so-called zone melting. When meteorites were heated, low-melting silicates saturated with volatile substances melted. Consequently, a melt arrived on the Earth’s surface, after cooling which formed the earth’s crust, hydrosphere (primary ocean) and atmosphere. This theory is confirmed by the identity of the composition of the gases of active volcanoes with the primary atmosphere.

The question may arise: was the mass of the mantle, which contains only 0.5% water, sufficient to form the World Ocean? Calculations show that the mass of water contained in the mantle is 10 times greater than the mass of the World Ocean.

The temperature at the Earth's surface with a thin primary atmosphere, according to calculations, is estimated at + 15 ° C, therefore, a hydrosphere constantly existed on Earth, which left a certain imprint on the evolution of the earth's crust and atmosphere.

Every year, a layer of water exceeding the volume of seven Black Seas evaporates from the surface of the World Ocean. It would seem that the sea level should decrease accordingly. However, all the evaporated water is compensated by tens of thousands of large and small rivers and precipitation.

The reserves of the seas are also replenished by water seeping from the land through coastal and bottom rocks - underground runoff.

Until now, it has not been possible to accurately determine the amount of underground flow. Employees of the Institute of Water Problems of the USSR Academy of Sciences have done a great job of summarizing world experience in assessing underground flow.

According to geographical, geological, natural and other characteristics, the entire coastal part of the land, including continents and large islands, was divided into almost 500 sections. Using mathematical modeling based on data from long-term geological observations, the amount of runoff from each of the continents was calculated.

There are three stages of formation of the salt mass of the ocean. At the first stage, the waters of the primary ocean had an acidic reaction, since chlorine, bromine and fluorine were released in the form of strong acids: HCl, HBr and HF. Acids reacted with ultrabasic and basic rocks and alkaline, alkaline earth, and other elements passed into water. Thus, all seawater anions are products of mantle degassing, and cations are products of the destruction of crustal rocks.

The general salinity of ocean waters was probably close to modern ones, but the ratios of the main components underwent significant changes. The main anions were carbonate and bicarbonate, not chloride. There was no sulfate ion in the waters of the primary ocean, which serves as evidence of the absence of oxygen in the ocean and atmosphere.

The second stage of the formation of the chemical composition of the ocean is associated with the emergence of life on Earth. The first ancient reliable remains of the vital activity of organisms were found in shales, whose age is 3.1-3.4 billion years.

The release of free oxygen during photosynthesis led to changes in the composition of the atmosphere and ocean. The atmosphere became nitrogen-oxygen. Carbon compounds were oxidized to carbon dioxide, which was almost entirely extracted through photosynthesis. Sulfur and hydrogen sulfide oxidized, and sulfate ions began to accumulate in the ocean. The main forms of nitrogen in seawater are molecular nitrogen and nitrate, rather than ammonia. Iron went from divalent to trivalent and lost its geochemical mobility. The mobility of calcium and magnesium has increased.

After the establishment of a stable composition of the atmosphere, the last stage of the formation of the salt composition of the World Ocean began. The modern composition of ocean waters was established 1.5-0.5 billion years ago.

Composition of sea water. The world's oceans cover 71% of the surface of our planet, which is crucial for the life of the entire globe due to the exceptional properties of water in general and ocean waters in particular.

Water does not occur in nature as a pure substance. In a strict scientific sense, we are always dealing with a complex solution of substances in water. Water is the most amazing and mysterious substance. Many physicochemical properties of water are anomalous: its boiling point, based on the properties and position of oxygen and hydrogen in the periodic table of D.I. Mendeleev, turns out to be 180 ° C higher, the freezing point should be minus 100 ° below zero. The values ​​of surface tension, thermal conductivity and dielectric constant of water are the highest. The highest density of water is at +4° C. The solid phase (ice) is lighter than the liquid phase is also an anomaly. Scientists still cannot explain some exceptional properties of water, for example, water does not form scale after exposure to a magnetic field.

Sea water is a 3.5% solution of salts, with a small amount of dissolved gases and organic compounds. What are the minerals dissolved in ocean water, the so-called “sea salt”? Theoretically, all chemical elements should be present in seawater in a dissolved or suspended state.

The chemical composition of sea water, according to O. A. Alekin, is divided into five groups:

1. Basic, or main, ions. These eleven elements make up 99.98% by weight of all salts dissolved in ocean water.

Main ions of sea water

All other elements are found in sea water in very small quantities (their total content does not exceed 0.02%).

2. Biogenic elements (C, H, N, P, Si, Fe, Mn) that make up organisms.

3. Gases dissolved in seawater: oxygen, nitrogen, carbon dioxide, argon, hydrogen sulfide, hydrocarbons and inert gases.

4. A group of elements with a concentration of less than 1·10 6 (microelements).

5. Organic substances.

The vast majority of sea salt is chlorides, not carbonates. This is the main difference between sea water and river water, in which carbon dioxide salts predominate. In the ocean, carbon dioxide salts cannot accumulate above a certain limit and are precipitated in the form of calcium carbonate.

Constancy of the composition of sea water. At the end of the 19th century. Scottish chemist W. Dittmar found that the relative content of basic salts is constant for the entire ocean. The constancy of the salt composition of sea water is the most important regularity in the chemistry of the ocean. The concentration of dissolved salts, or salinity, can vary significantly, for example from 10 g/kg in the Baltic Sea to 130 g/kg in the lagoons of the Gulf of Mexico.

The value of salinity was taken to be the weight of the dry residue contained in 1 kg of sea water, when carbonates are converted into oxides, bromides and iodides are replaced by an equivalent amount of chlorine and organic matter is burned at 480 ° C. Salinity is designated by the symbol S. The unit of measurement is g/kg or ‰ (ppm). However, in practice, this method is not used due to its complexity, and salinity is calculated from chlorine content, electrical conductivity or refractive index.

Currently, the recommended ratio between salinity and chlorinity is: S‰= 1.80655‰ Cl. Salinity is an important chemical and physical characteristic of seawater. By determining only salinity, it is possible to calculate the concentration of any major ion in seawater. The solubility of gases depends on salinity and temperature. Based on salinity and temperature, density is calculated, the distribution of which determines the movement of water masses.

The distribution of salinity in the surface layer of the ocean (excluding seas) is zonal. The lowest salinity values ​​are observed in the polar regions, which is due to melting ice, and for the Arctic Ocean - also by continental runoff, and in the narrow equatorial zone, which is explained by a positive fresh balance (atmospheric precipitation prevails over evaporation). The highest salinity is observed in subtropical zones around 20° north and south latitude.

The heterogeneity of the salinity field of the World Ocean is the result of physical processes associated with the native balance. Evaporation and precipitation are of greatest importance. Every year, 447,000 km 3 evaporates from the ocean surface and 411,000 km 3 of atmospheric precipitation falls. River flow is an important factor in coastal areas.

The zonal distribution of salinity is disrupted by currents. The Gulf Stream system carries water with salinity up to 35‰ into the Norwegian Sea and the Arctic. The East Greenland and Labrador Currents significantly reduce salinity, transporting water desalinated by melting ice and precipitation.

Among the local features of the ocean salinity field, it should be noted that the desalinating influence of large rivers such as the Amazon and Congo is well expressed near the coast. The Amazon River, the largest in its flow (10% of the world's river flow falls on its share), has a salt composition of about 40 mg/l, which is almost 1000 times less than the average salinity of sea water.

The distribution of salinity in the seas is characterized by significant fluctuations due to the influence of river runoff and climatic conditions. For example, in the Caspian Sea the salinity in the middle part is about 13%o, and in the Kara-Bogaz-Gol Bay the salinity reaches 300%.

The change in salinity along the vertical ocean is much more complex than on the surface and is associated with the distribution of water layers depending on density.

Nutrients. Of particular interest is the World Ocean as a habitat for life. It was here, according to many scientists, that life originated, which in the long process of evolution gave rise to a colossal variety of forms. Over 300,000 species of living organisms live in the ocean: from microscopic algae to the largest animals on the planet - 160-ton blue whales.

The diversity of life on Earth is amazing, although it is based on one type of chemical process - photosynthesis, which creates organic substances from inorganic substances in plants.

Most of the flora of the ocean are microscopic phytoplankton organisms (aquatic plants attached to the bottom occupy a very small part), which are basically the primary products of the sea. The volume of annual phytoplankton production in the World Ocean is estimated at 500 billion tons. On the basis of primary production, all other marine organisms develop - bacteria, zooplankton, fish, sea animals. Of practical importance for humanity are the products provided by free-swimming animals (fish, cephalopods, mammals). It is estimated at only 200 million tons, including inedible species and reproduction reserves.

For the development of phytoplankton, in addition to the energy of sunlight, inorganic components are necessary. Organisms contain up to 60 chemical elements; however, 90-95% of the mass of organisms consists of six elements: carbon, oxygen, hydrogen, nitrogen, phosphorus and silicon.

Compounds of carbon, nitrogen, phosphorus, silicon, which are necessary for the life of organisms, are called nutrients.

The consumption of nutrients in the upper producing layers of the ocean by phytoplankton and their removal from these layers with the remains of organisms falling down leads to depletion of the layers. As for carbon compounds, the reserves of this element in the form of CO 2 in the sea, atmosphere and bottom sediments are so large that changes in its concentration due to plant development seem insignificant. But nitrogen, phosphorus and silicon may not be enough with intensive development of phytoplankton.

The study of the chemistry of carbon, nitrogen, phosphorus and silicon is of great importance not only for marine chemistry, but also for biology. Carbon is found in the ocean in the form of inorganic (carbon dioxide CO 2, carbonic acid, bicarbonate HCO 3 - and carbonate CO 3 2) and organic compounds.

Carbon dioxide plays an important role in the carbon cycle. This carbon compound has special physical and chemical properties and is found in nature in a variety of forms and large quantities.

The hydrosphere, with its biochemical and geochemical processes, has a huge impact on the dynamics of CO 2 and the content of carbon dioxide in the atmosphere. Changes in the concentration of CO 2 in the atmosphere affect the heat balance of the earth's surface, the chemical properties of water, geological phenomena and climate.

The carbonate system regulates the pH of seawater, which affects the processes of dissolution and precipitation of chemical compounds and creates favorable conditions for the existence of organisms in the ocean.

In the surface layers of the ocean, CO 2 is absorbed during plant photosynthesis. This loss is compensated by the dissolution of carbon dioxide from the atmosphere.

At great depths, where photosynthesis stops due to lack of light, CO 2 is formed due to the decomposition of organic matter as a result of decay. In the upper 500-meter layer, on average, up to 87% of primary production is oxidized. 0.1% of organic matter enters the bottom sediments, of which only 0.0001 part goes to the formation of oil.

An increase in CO 2 concentration with depth causes an increase in the solubility of calcium carbonate, so the calcareous skeletons of organisms that settle to the bottom are partially or completely dissolved.

Carbon dioxide reserves in the ocean are maintained by supply from the atmosphere, respiration of aquatic organisms, decomposition of organic residues, dissolution of calcareous rocks of the bottom and shores, supply from underwater volcanic eruptions and from continental runoff.

The decrease in carbon dioxide is caused by its release into the atmosphere, consumption by phytoplankton during photosynthesis, and precipitation as calcium carbonate on the ocean floor.

According to O. A. Alekin, the entire amount of hydrocarbonates (1.7 billion tons), calcium (0.494 billion tons) and partially magnesium (0.36 billion tons) deposited in the ocean annually.

Nitrogen. The chemistry of nitrogen in the sea, along with the chemistry of carbon, is the most complex. The main forms of nitrogen in the ocean are: ammonia, nitrite, nitrate, organic and free nitrogen. The exchange of nitrogen between its compounds and living organisms determines its content.

Inorganic forms of nitrogen are absorbed during photosynthesis by phytoplankton, which, in turn, serves as the basis for the nutrition of zooplankton. Nitrogen regeneration occurs during the decomposition of organic matter.

Ammonia nitrogen appears at the first stage of decomposition of organic matter in the upper productive zone. Large concentrations of ammonium ion are not observed due to further oxidation to nitrites or consumption by phytoplankton.

Nitrite ions, like ammonia, are found in seawater in small concentrations and, under the influence of bacteria in the presence of oxygen, are oxidized into nitrate ions. In the absence of oxygen (in the zone of minimum oxygen), nitrates are reduced by organic matter to nitrites.

Nitrate nitrogen is the main form of nitrogen in the sea (65% of fixed nitrogen is contained in this form) and represents the main source of nitrogen nutrition for organisms and the final product of mineralization of organic matter. Below the photosynthetic zone, the nitrate concentration increases rapidly, reaching a maximum at 400-1000 m.

Nitrogen in the form of various compounds enters the ocean with continental runoff and precipitation. The approximate content of “bound” nitrogen (organic, nitrate and ammonia), according to our calculations, can be taken to be about 0.6 in river runoff, and 0.3 mg/l in precipitation. Considering the World Ocean as a first approximation as an environment in dynamic chemical equilibrium, it is obvious that nitrogen from atmospheric precipitation + nitrogen from continental runoff compensate for the process of denitrification (the process of converting nitrogen compounds into free nitrogen) in the ocean. The amount of nitrogen that ends up in bottom sediments is small. The process of nitrogen fixation, since the process is endothermic and has limited development, can be neglected when calculating the nitrogen balance. In this case, denitrification leads to an annual loss of about 0.3 g of nitrogen under 1 m 2 of the surface of the World Ocean.

Phosphorus is also one of the main biogenic elements. Most of the phosphorus (about 90%) is in the form of soluble inorganic compounds, organic phosphorus makes up 5-7% and suspended solid phosphorus - 3-5%. The main source of phosphorus in the ocean is continental runoff. River waters contain phosphorus in inorganic and organic forms and in the form of suspended matter of inorganic origin. Another source of phosphorus is the aeolian removal of terrigenous material, volcanic activity and exchange with the bottom.

Inorganic phosphorus, like forms of inorganic nitrogen, is absorbed by plants and converted into organic compounds. Organic phosphorus, under the influence of bacteria or enzymes, is converted back into inorganic form. The phosphorus cycle scheme is similar to the nitrogen cycle, but has two differences: compared to nitrogen, phosphorus is released from organic matter more quickly, and phosphorus exchanges with bottom sediments.

The distribution of inorganic phosphorus in the ocean is determined by the processes of its consumption by phytoplankton and regeneration, as well as by dynamic reasons. In surface waters, the concentration of phosphorus is lower than in deep waters. With depth, the concentration of phosphorus increases, reaching maximum values ​​in the range of 500-1200 m. Seasonal changes in phosphates in the surface layer are similar to changes in nitrates. In spring and summer in high and temperate latitudes, the rapid development of phytoplankton can lead to the complete disappearance of nutrient salts in the photosynthesis zone. For most of the year, there are no nutrients in the surface layers of the equatorial and tropical zones. Only in areas of rising deep waters are high concentrations of nitrogen and phosphorus compounds observed.

Silicon is part of the skeletons of various marine organisms. Although silicon is one of the common elements in the earth's crust, its concentration in seawater is low. The main form of silicon in the ocean is dissolved inorganic (95%), suspended inorganic form is about 1%, the rest is organic.

The distribution of silicon in the ocean is similar in general terms to the distribution of nitrogen and phosphorus. The smallest amount of silicon is found in the surface layers, where it is used by phytoplankton, although its concentration (unlike nitrogen and phosphorus) never reaches zero. With depth, its concentration increases due to the dissolution of skeletal parts, reaching a maximum at the bottom. The maximum silicon content is located deeper than the maximum phosphorus and nitrogen, since the regeneration of phosphorus and nitrogen from the soft tissues of organisms is faster than the dissolution of skeletons and shells, some of which reach the bottom. Diatomaceous oozes occupy up to 10% of the ocean floor area. This loss of silicon from the general cycle is compensated by river runoff and aeolian (wind transport).

Dissolved gases. Gases enter the ocean as a result of exchange with the atmosphere, during volcanic underwater activity and as a result of chemical and biological processes occurring in seawater.

The ratio of oxygen to nitrogen in seawater is approximately 1:2, while in the atmosphere it is 1:4, i.e. the relative oxygen content in seawater is increased.

Oxygen in sea water is a mobile and active element. The presence of oxygen in water is necessary for the existence of most organisms.

The oxygen concentration in the ocean fluctuates up to 10 ml/l. The main sources of oxygen in seawater are: exchange with the atmosphere and its release as a result of the process of photosynthesis. Absorption of oxygen from the atmosphere can only occur at concentrations below equilibrium, which depends on temperature and salinity.

Processes that reduce the concentration of oxygen in the ocean include the release of oxygen into the atmosphere and the consumption of chemical, biochemical and biological processes.

Based on the oxygen concentration, the ocean water column can be divided into four zones: surface, intermediate, deep and bottom.

The surface zone, in turn, can be divided into the upper layer, the layer of greatest photosynthesis and the lower layer. The upper layer (0-10 m), due to exchange with the atmosphere, is almost always saturated with oxygen (100% saturation at a given temperature and salinity). The layer of the greatest photosynthesis is characterized by oxygen supersaturation (up to 120-130%). The lower boundary of this layer is determined by the depth at which the amount of oxygen produced by phytoplankton is equal to the amount of oxygen consumed. The lower layer is located from the compensation point to the intermediate zone and is characterized by a drop in oxygen concentration.

The intermediate zone (the oxygen minimum layer) changes its position in different parts of the ocean from 100-300 to 1400-1600 m. In this zone there is a sharp drop in temperature and oxygen content to 0.5 ml/l.

The deep zone occupies the main part of the ocean and is characterized by a fairly high oxygen content - up to 5 ml/l. If the ocean waters did not mix, then a further decrease in oxygen concentration would be expected. In the deep zone of the ocean, there is a movement of water masses of Arctic and Antarctic origin, which at low temperatures were saturated with oxygen, which causes the enrichment of the zone. Even in the deep-sea depressions (more than 8 km) of Tonga, Kermadec and Mariana, the oxygen content is quite high - about 4 ml/l.

The bottom zone occupies a small part of the ocean and is characterized by low oxygen content.

Seasonal changes in oxygen are observed only in the surface zone in the middle and high latitudes. In winter, oxygen concentration increases due to increased solubility of gases with decreasing temperature, despite a decrease in photosynthesis. In summer there is a decrease in oxygen levels, but sometimes there are outbreaks of algae blooms that create an oxygen glut in the surface zone.

Among the gases dissolved in seawater, nitrogen has the highest concentration. However, due to chemical inertness, nitrogen almost does not participate in the processes occurring in the ocean.

Hydrogen sulfide. Hydrogen sulfide appears in seawater only in the absence of oxygen. The formation of hydrogen sulfide during the biochemical reduction of sulfates occurs with the participation of anaerobic bacteria. Another source of hydrogen sulfide is the decomposition of organic matter.

Temporary formation of hydrogen sulfide was noted in the Indian and Atlantic oceans, in the deep fjords of Norway. Hydrogen sulfide is constantly contained in the Black Sea at depths of more than 150-200 m due to the lack of exchange of deep waters through the shallow Bosphorus Strait and weak vertical circulation of water in the Black Sea itself. The concentration of hydrogen sulfide in it reaches 7 ml/l.

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Theoretically, there are no substances insoluble in water, so sea water contains almost all the elements of the periodic table. True, some elements are found in such small quantities that their presence is detected only in marine organisms that collect these elements from the sea water around them. These are, for example, cobalt, nickel and tin, found in the blood of sea cucumbers, lobsters, oysters and other animals. The presence of some other elements is proven only by their presence in marine sediments.

The average amount of solids dissolved in the waters of the World Ocean is about 3.5% by weight. Sea water contains the most chlorine - 1.9%. sodium - 1.06%. magnesium - 0.13%, sulfur - 0.088%, calcium - 0.040%, potassium - 0.038%, bromine - 0.0065%, carbon - 0.003%. The content of other elements, including biogenic and microelements, is negligible, less than 0.3%. Precious metals have been discovered in the ocean waters, but their concentration is insignificant, and given the overall large amount in the ocean (gold - 55 * 105 tons, silver - 137 * 106 tons), their extraction is unprofitable. The main feature that distinguishes the waters of the World Ocean from the waters of land is their high salinity. The number of grams of substances dissolved in 1 liter of water is called salinity. Sea water is a solution of 44 chemical elements, but salts play a primary role in it. Table salt gives the water a salty taste, while magnesium salt gives it a bitter taste. Salinity is expressed in ppm (%o). This is a thousandth of a number. An average of 35 grams of various substances are dissolved in a liter of ocean water, which means the salinity will be 35%.

The salinity of water in the World Ocean is not the same everywhere. In the open part it varies within 33-37°/oo and depends on climatic conditions (differences in evaporation and amount of precipitation). Therefore, its distribution clearly shows the features of latitudinal zoning, which makes it possible to map this characteristic (isohaline maps). In some areas, latitudinal zoning is disrupted by the influence of salt transport by currents. The average salinity at the surface of the oceans varies. The Atlantic Ocean has the highest average salinity - 35.3°/0o, the Arctic Ocean has the lowest - 32%o (in the estuary areas up to 20°/oo).

Gases in ocean water. Water absorbs (dissolves) gases with which it comes into contact. Therefore, ocean water contains all atmospheric gases, as well as gases brought by river waters, released during chemical and biological processes, and during underwater eruptions. The total amount of gases dissolved in water is small, but they play a decisive role in the development of all organic life in the seas and oceans.

Carbon dioxide, unlike oxygen and nitrogen, is found in ocean water mainly in a bound form, in the form of carbon dioxide compounds - carbonates and bicarbonates. Carbon dioxide reserves in the ocean are maintained by the respiration of organisms and the dissolution of calcareous rocks of the bottom and shores, as well as modern organogenic deposits (skeletons, shells, etc.). Significant amounts of carbon dioxide enter the ocean during underwater volcanic eruptions. Like oxygen, carbon dioxide dissolves faster in cold water. When the temperature rises, water releases carbon dioxide to the atmosphere, and when it decreases, it absorbs it, so in the tropics water releases carbon dioxide into the atmosphere; in polar latitudes, on the contrary, carbon dioxide from the atmosphere enters the water.