Physicochemical properties of ocean waters. Basic physical and chemical properties of ocean (sea) water. The world's oceans and its parts

Salinity of ocean, sea and river water

Gas composition of ocean water

Heat capacity of ocean waters

Ocean temperature

Density of water

The ability of water to self-purify

Table 1. Salt content in sea and river water (in% of the total mass of salts)

Change in water volume with temperature change

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)
Ions and molecules
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)

Temperature regime of MO waters. The temperature regime of MO waters is determined by the thermal balance. The ocean receives heat from total solar radiation. from moisture condensation on the water surface, ice formation and chemical and biological processes that occur with the release of heat; the ocean receives heat brought by precipitation and river waters; the temperature of the deep-sea layers is affected by the warmth of the Earth (this is evidenced by high temperatures up to 260 0 C in the depressions of the Red Sea - the water here is a hot brine with a salinity of 270 0 / 00). Heat is lost due to effective radiation of the water surface, water evaporation, ice melting, turbulent exchange with the atmosphere, heating of cold water in rivers and currents. The incoming solar radiation and heat consumption for evaporation are of decisive importance in the heat balance.

The average annual temperature of the Moscow Region is 17.4 0 C, the highest average annual water temperature was noted for the Pacific Ocean (19.1 0 C), the lowest - for the Arctic Ocean (0.75 0 C). The distribution of heat in the ocean water occurs due to convection and mixing as a result of waves and currents. The water temperature decreases with depth. At a certain depth in the water column, a sharp decrease in temperature is observed; here a layer of temperature jump stands out - thermocline Based on changes in water temperature with depth, several types of temperature distribution are distinguished.

IN equatorial type the water temperature quickly decreases from 26.65 0 C on the surface to 10.74 0 C at a depth of 300 m. The thermocline is observed at a depth of 200-300 m. Further, to a depth of 1000 m, the water temperature decreases slowly, and deeper remains almost constant.

IN tropical type the water temperature drops sharply from 26.06 0 C to 13.60 0 C at a depth of 300 m, then the water temperature changes more smoothly.

IN subtropical type the water temperature decreases from 20.3 0 C at the surface to 13.1 0 C at a depth of 300 m. In the subpolar type, the temperature decreases from 8.22 0 C at the surface to 5.20 0 C at a depth of 150 m. The polar type is characterized by a decrease water temperature to a depth of 100 m, then the temperature begins to rise to 1.8 0 C at a depth of 400 m. Due to the influx of warm Atlantic waters. At a depth of 1000 m, the water temperature is 1.55 0 C. In the layer from the surface to a depth of 1000 m, a zonal change in temperature and salinity of water is observed; deeper water characteristics remain almost constant.

Physicochemical properties of MO waters. Back at the beginning of the 19th century. It was noticed that the amount of salts dissolved in ocean waters can vary greatly, but the salt composition and the ratio of various salts in the ocean waters are the same. This pattern is formulated as a property of constancy of the salt composition of sea waters. Per 1 kg of sea water there are 19.35 g of chlorine, 2.70 g of sulfates, 0.14 g of bicarbonates, 10.76 g of sodium, 1.30 g of magnesium, 0.41 g of calcium. The quantitative ratio between the main salts in MO water remains constant. Total salinity is determined by the amount of chlorine in water (the formula was obtained by M. Knudsen in 1902):

S = 0.030 + 1.805 Cl

The waters of the oceans and seas belong to the chloride class and the sodium group, in this they differ sharply from river waters. Just eight ions account for more than 99.9% of the total mass of salts in seawater. The remaining 0.1% accounts for all other elements of the D.I. table. Mendeleev.

The distribution of salinity in water masses is zonal and depends on the ratio of precipitation, influx of river water and evaporation. In addition, the salinity of water is influenced by water circulation, the activity of organisms and other reasons. At the equator, there is a reduced salinity of water (34-33 0/00), due to a sharp increase in precipitation, the flow of full-flowing equatorial rivers and slightly reduced evaporation due to high humidity. In tropical latitudes, the highest water salinity is observed (up to 36.5 0/00), associated with high evaporation and small amounts of precipitation at baric pressure maxima. In temperate and polar latitudes, water salinity is reduced (33-33.5 0/00), which is explained by an increase in precipitation, river runoff and melting sea ice.

The latitudinal distribution of salinity is disrupted by currents, rivers and ice. Warm ocean currents transport saltier waters towards high latitudes, while cold currents transport less salty waters towards low latitudes. Rivers desalinate the estuarine areas of oceans and seas. The influence of the Amazon rivers is very great (the desalination influence of the Amazon is felt at a distance of 1000 km from the mouth), Congo, Niger, etc. Ice has a seasonal effect on the salinity of waters: in winter, when ice forms, the salinity of water increases, in summer, when ice melts, it decreases.

The salinity of the deep waters of the Moscow Region is uniform and generally amounts to 34.7-35.0 0 / 00. The salinity of bottom waters is more varied and depends on volcanic activity on the ocean floor, the release of hydrothermal waters, and the decomposition of organisms. The nature of changes in the salinity of ocean waters with depth is different at different latitudes. There are five main types of changes in salinity with depth.

IN equatorial latitudes salinity gradually increases with depth and reaches its maximum value at a depth of 100 m. At this depth, saltier and denser waters of the tropical latitudes of the oceans approach the equator. To a depth of 1000 m, salinity very slowly increases to 34.62 0/00, deeper salinity remains virtually unchanged.

IN tropical latitudes salinity increases slightly to a depth of 100 m, then gradually decreases to a depth of 800 m. At this depth, the lowest salinity is observed in tropical latitudes (34.58 0 / 00). Obviously, less salty but colder waters of high latitudes spread here. From a depth of 800 m it increases slightly.

IN subtropical latitudes salinity quickly decreases to a depth of 1000 m (34.48 0/00), then becomes almost constant. At a depth of 3000 m it is 34.71 0 / 00.

IN subpolar latitudes salinity slowly increases with depth from 33.94 to 34.71 0/00, in polar latitudes Salinity increases more significantly with depth - from 33.48 to 34.70 0 / 00.

The salinity of the seas is very different from the salinity of the sea. The salinity of water in the Baltic (10-12 0/00), Black (16-18 0/00), Azov (10-12 0/00), White (24-30 0/00) seas is due to the desalinating influence of river waters and atmospheric precipitation . The salinity of water in the Red Sea (40-42 0/00) is explained by low precipitation and high evaporation.

The average salinity of the Atlantic Ocean waters is 35.4; Quiet – 34.9; Indian - 34.8; Arctic Ocean – 29-32 0/00.

Density– the ratio of the mass of a substance to its volume (kg/m3). The density of water depends on the salt content, temperature and depth at which the water is located. As the salinity of water increases, the density increases. The density of water increases with decreasing temperature, with increasing evaporation (as the salinity of water increases), and with the formation of ice. Density increases with depth, although very slightly due to the low compressibility coefficient of water.

The density of water varies zonally from the equator to the poles. At the equator, the water density is low - 1022-1023, which is due to low salinity and high water temperatures. Toward tropical latitudes, the density of water increases to 1024-1025 due to an increase in water salinity due to increased evaporation. In temperate latitudes, the density of water is average, in polar latitudes it increases to 1026-1027 due to a decrease in temperature.

The ability of water to dissolve gases depends on temperature, salinity and hydrostatic pressure. The higher the temperature and salinity of the water, the less gases can dissolve in it.

Various gases are dissolved in ocean water: oxygen, carbon dioxide, ammonia, hydrogen sulfide, etc. Gases enter the water from the atmosphere due to river runoff, biological processes, and underwater volcanic eruptions. Oxygen is of greatest importance for life in the ocean. It is involved in planetary gas exchange between the ocean and atmosphere. 5 x 10 10 tons of oxygen are produced annually in the active layer of the ocean. Oxygen comes from the atmosphere and is released during photosynthesis of aquatic plants, spent on respiration and oxidation.

Carbon dioxide is found in water mainly in a bound state, in the form of carbon dioxide compounds. It is released during the respiration of organisms, during the decomposition of organic matter, and is used for the construction of skeletons by corals.

Nitrogen is always present in ocean water, but its content relative to other gases is less than in the atmosphere. In some seas, hydrogen sulfide can accumulate in the depths; this occurs due to the activity of bacteria in an oxygen-free environment. Hydrogen sulfide pollution has been noted in the Black Sea; its content has reached 6.5 cm 3 /l; organisms do not live in such an environment.

Water clarity depends on the scattering and absorption of solar radiation, on the amount of mineral particles and plankton. The highest transparency is observed in the open ocean at tropical latitudes and is equal to 60 m. Water transparency decreases in shallow water near river mouths. Water transparency decreases especially sharply after a storm (up to 1 m in shallow water). The least transparency is observed in the ocean during the period of active plankton reproduction. The depth of penetration of sunlight into the ocean and, consequently, the distribution of photosynthetic plants depends on the transparency of the water. Organisms that can absorb solar energy live at depths of up to 100 m.

The thickness of clear water has a blue or dark blue color, a large amount of plankton leads to the appearance of a greenish tint, and near rivers the water may be brown.

ocean water– a universal homogeneous ionized solution, which contains all chemical elements. The solution contains solid minerals (salts) and gases, as well as suspensions of organic and inorganic origin.

Salinity of sea water. By weight, dissolved salts make up only 3.5%, but they give the water a bitter-salty taste and other properties. The composition of sea water and the content of different groups of salts in it are visible from Table 8. Sea water in composition differs sharply from river water, because chlorides predominate in it. It is interesting to note that the composition of salts in blood plasma is close to the composition of salts in seawater, in which, as many scientists believe, life originated.

Ta blitz 8

(in% of the total mass of salts) (according to L.K. Davydov and others)

Salinity– amount of salts in grams in 1 kg of sea water. The average salinity of the Ocean is 35% 0. Of the 35 grams of salts, seawater contains the most table salt (about 27 g), which is why it is salty. Magnesium salts give it a bitter taste. Lines on a map connecting points with the same salinity are called isohalines.

Ocean water was formed from hot salty solutions of the earth's interior and gases, so salinity her original one. The composition of sea water resembles that of juvenile waters, i.e., waters and gases released from magma during volcanic eruptions and first entering the water cycle on Earth. Gases released from modern volcanoes consist mainly of water vapor (about 75%), carbon dioxide (up to 20%), chlorine (7%), methane (3%), sulfur and other components.

The initial composition of seawater salts and its salinity were somewhat different. The changes it underwent during the evolution of the Earth were caused primarily by the emergence of life, especially the mechanism of photosynthesis and the associated oxygen production. Some changes were apparently introduced by river waters, which at first leached rocks on land and delivered easily soluble salts to the Ocean, and later mainly carbonates. However, living organisms, especially animals, consumed huge amounts of first silicon and then calcium to form their internal skeletons and shells. After dying, they sank to the bottom and dropped out of the mineral cycle, without increasing the carbonate content in sea water.

In the history of the development of the World Ocean, there were periods when salinity fluctuated towards decrease or increase. This happened both as a result of geological reasons, because tectonic activation of the subsoil and volcanism influenced the activity of magma degassing, and due to climate changes. During harsh ice ages, when large masses of fresh water were preserved on land in the form of glaciers, salinity increased. During warming during interglacial periods, when melted glacial waters entered the Ocean, it decreased. During arid epochs, salinity increased, and during humid epochs it decreased.

The distribution of surface water salinity to approximately a depth of 200 m shows zoning, which is associated with the balance (inflow and consumption) of fresh water, and above all with the amount of precipitation and evaporation. River waters and icebergs reduce the salinity of sea water.

In equatorial and subequatorial latitudes, where more precipitation falls than water is spent on evaporation (K moistening >1), and river flow is high, salinity is slightly less than 35% 0 . In tropical and subtropical latitudes, due to a negative fresh balance (little precipitation and high evaporation), the salinity is 37%. In temperate latitudes, salinity is close to 35%. In the subpolar and polar latitudes, salinity is the lowest - about 32% o, since the amount of precipitation exceeds evaporation, river flow is high, especially in Siberian rivers, and there are many icebergs, mainly around Antarctica and Greenland.

Rice. 82. Types of vertical distribution of salinity (according to L.K. Davydov and others)

The zonal pattern of salinity is disrupted by sea currents and the influx of river waters. For example, in the temperate latitudes of the northern hemisphere, salinity is greater on the western coasts of the continents, where subtropical waters of high salinity brought by warm currents arrive, and less on the eastern coasts of the continents, where cold currents bring less saline subpolar waters.

Of the oceans, the Atlantic Ocean has the highest salinity. This is explained, firstly, by its comparative narrowness in low latitudes, combined with its proximity to Africa with its deserts, from where a hot, dry wind unhindered blows onto the ocean, increasing the evaporation of sea water. Secondly, in temperate latitudes, the westerly wind carries Atlantic air far into the interior of Eurasia, where a significant part of the precipitation falls from it, not completely returning to the Atlantic Ocean. The salinity of the Pacific Ocean is less, since it, on the contrary, is wide in the equatorial belt, where the salinity of the water is low, and in the temperate latitudes the Cordillera and the Andes retain heavy precipitation on the windward western slopes of the mountains, and they again enter the Pacific Ocean, desalinizing it.

The lowest water salinity in the Arctic Ocean, especially off the Asian coast, near the mouths of Siberian rivers, is less than 10%. However, in subpolar latitudes, there is a seasonal change in water salinity: in autumn - winter, when sea ice forms and river flow decreases, salinity increases, in spring - summer, when sea ice melts and river flow increases, it decreases. Around Greenland and Antarctica in summer, salinity also becomes lower due to melting icebergs and the thawing of the marginal parts of ice sheets and shelves.

The maximum salinity of water is observed in tropical inland seas and bays surrounded by deserts, for example in the Red Sea - 42% 0, in the Persian Gulf - 39% 0.

Despite the different salinity of sea water in different areas of the Ocean, the percentage of salts dissolved in it remains unchanged. It is ensured by the mobility of water, its continuous horizontal and vertical mixing, which together leads to the general circulation of the waters of the World Ocean.

The vertical change in water salinity in the oceans varies. Five zonal types of vertical distribution of salinity are outlined: I – polar, II – subpolar, III – moderate, IV – tropical and V – equatorial. They are presented in the form of graphs in Figure 82.

The distribution of salinity in depth in the seas is very different depending on the balance of fresh moisture, the intensity of vertical mixing and water exchange with neighboring water areas.

Annual fluctuations in salinity in the open parts of the Ocean are insignificant and in the surface layers do not exceed 1%o, and from a depth of 1500 - 2000 m, salinity is practically unchanged throughout the year. In coastal marginal seas and bays, seasonal fluctuations in water salinity are more significant. In the seas of the Arctic Ocean at the end of spring, salinity decreases due to the influx of river waters, and in water areas with a monsoon climate in summer - also due to the abundance of precipitation. In polar and subpolar latitudes, seasonal changes in the salinity of surface waters are largely due to the freezing of water in the fall and the melting of sea ice in the spring, as well as the melting of glaciers and icebergs during the polar day, which will be discussed later.

The salinity of water affects many of its physical properties: temperature, density, electrical conductivity, speed of sound, speed of ice formation, etc.

It is interesting to note that in the seas near karst coasts at the bottom there are often powerful underwater (submarine) sources of fresh water rising to the surface in the form of fountains. Such “fresh windows” among salt water are known off the coast of Yugoslavia in the Adriatic Sea, off the coast of Abkhazia in the Black Sea, off the coast of France, Florida and other places. This water is used by sailors for household needs.

Gas composition of the oceans. In sea water, in addition to salts, the gases nitrogen, oxygen, carbon dioxide, hydrogen sulfide, etc. are dissolved. And although the content of gases in water is extremely insignificant and varies noticeably in space and time, they are sufficient for the development of organic life and biogeochemical processes.

Oxygen in seawater more than in the atmosphere, especially in the upper layer (35% at 0 °C). Its main source is phytoplankton, which is called the “lungs of the planet.” Below 200 m, the oxygen content decreases, but from 1500 m it increases again, even at equatorial latitudes, due to the flow of water from the polar regions, where oxygen saturation reaches 70–90%. Oxygen is consumed by release into the atmosphere when there is an excess of it in the surface layers (especially during the day), for the respiration of marine organisms and for the oxidation of various substances. Nitrogen less in seawater than in the atmosphere. The free nitrogen content is related to the breakdown of organic matter. Nitrogen dissolved in water is absorbed by special bacteria and converted into nitrogen compounds, which are of great importance for the life of plants and animals. A certain amount of free and bound carbon dioxide, which enters the water from the air during the respiration of marine organisms, during the decomposition of organic substances, and also during volcanic eruptions. It is important for biological processes because it is the only source of carbon that plants need to build organic matter. Hydrogen sulfide is formed in deep stagnant basins in the lower parts of water columns during the decomposition of organic matter and as a result of the activity of microorganisms (for example, in the Black Sea). Since hydrogen sulfide is a highly toxic substance, it sharply reduces the biological productivity of water.

Since the solubility of gases is more intense at low temperatures, the waters of high latitudes contain more of them, including the most important gas for life - oxygen. Surface waters there are even oversaturated with oxygen and the biological productivity of waters is higher than in low latitudes, although the species diversity of animals and plants is poorer. During the cold season, the Ocean absorbs gases from the atmosphere; during the warm season, it releases them.

Density– an important physical property of sea water. Sea water is denser than fresh water. The higher the salinity and lower the temperature of the water, the greater its density. The density of surface waters increases from the equator to the tropics due to an increase in salinity and from temperate latitudes to the polar circles as a result of a decrease in temperature, and in winter also due to an increase in salinity. This leads to intense subsidence of polar waters during the cold season, which lasts 8–9 months. In the bottom layers, polar waters move towards the equator, as a result of which the deep waters of the World Ocean are generally cold (2 - 4°C), but enriched with oxygen.

Color and transparency depend on the reflection, absorption and scattering of sunlight, as well as on substances of organic and mineral origin suspended in water. Blue color is characteristic of water in the open part of the Ocean, where there are no suspended matter. Along the coasts, where there is a lot of suspended matter brought by rivers and temporary watercourses from the land, as well as due to the agitation of coastal soil during waves, the color of the water is greenish, yellow, brown, etc. When there is an abundance of plankton, the color of the water is bluish-green.

For visual observations of the color of sea water, a color scale is used, consisting of 21 test tubes with colored solutions - from blue to brown. The color of water cannot be identified with the color of the sea surface. It depends on weather conditions, especially cloudiness, as well as wind and waves.

Transparency is better in the open part of the Ocean, for example in the Sargasso Sea - 67 m, worse - near the coasts, where there is a lot of suspended matter. Transparency decreases during the period of mass development of plankton.

Glow of the sea (bioluminescence) – This is the glow in sea water of living organisms containing phosphorus and emitting “living” light. First of all, the simplest lower organisms (nocturnal flies, etc.), some bacteria, jellyfish, worms, and fish in all layers of water glow. Therefore, the dark depths of the Ocean are not completely devoid of light. The glow intensified

It occurs during rough seas, so ships at night are accompanied by real illumination. There is no consensus among biologists about the purpose of the glow. It is believed that it serves either to scare away predators, or to search for food, or to attract individuals of the opposite sex in the dark. The cold glow of sea fish allows fishing vessels to find their schools.

Sound conductivity – acoustic properties of sea water. The propagation of sound in sea water depends on temperature, salinity, pressure, gas and suspended matter content. On average, the speed of sound in the World Ocean ranges from 1400–1550 m/s. With increasing temperature, salinity and pressure it increases, and with decreasing temperature it decreases. Layers with different sound conductivities have been discovered in the oceans: sound-diffusing layer and a layer with sound superconductivity - underwater

"sound channel". Accumulations of zooplankton and, accordingly, fish are confined to the sound-scattering layer. It experiences diurnal migrations: it rises at night and descends during the day. It is used by submariners as it dampens noise from submarine engines, and by fishing vessels to detect schools of fish. The “sound channel” began to be used for short-term forecasting of tsunami waves, in the practice of underwater navigation for ultra-long-distance transmission of acoustic signals.

Electrical conductivity sea water is high. It is directly proportional to salinity and temperature.

Natural radioactivity sea waters are small, but many plants and animals are capable of concentrating radioactive isotopes. Therefore, the catch of fish and other seafood is currently undergoing special testing for radioactivity.

Water is the simplest chemical compound of hydrogen and oxygen, but ocean water is a universal, homogeneous ionized solution, which contains 75 chemical elements. These are solid minerals (salts), gases, as well as suspensions of organic and inorganic origin.

Vola has many different physical and chemical properties. First of all, they depend on the table of contents and the ambient temperature. Let's give a brief description of some of them.

Water is a solvent. Since water is a solvent, we can judge that all waters are gas-salt solutions of different chemical compositions and different concentrations.

Salinity of sea water(Table 1). The concentration of substances dissolved in water is characterized by salinity, which is measured in ppm (%o), i.e. grams of a substance per 1 kg of water.

Basic connections	Sea water	river water
Chlorides (NaCI, MgCb)
Sulfates (MgS0 4, CaS0 4, K 2 S0 4)
Carbonates (CaSOd)
Compounds of nitrogen, phosphorus, silicon, organic and other substances

Lines on a map connecting points with the same salinity are called isohalines.

Fresh water salinity(see Table 1) is on average 0.146%o, and sea - on average 35 %O. Salts dissolved in water give it a bitter-salty taste.

About 27 of the 35 grams is sodium chloride (table salt), so the water is salty. Magnesium salts give it a bitter taste.

Since the water in the oceans was formed from hot salty solutions of the earth's interior and gases, its salinity was original. There is reason to believe that in the first stages of the formation of the ocean, its waters differed little in salt composition from river waters. Differences emerged and began to intensify after the transformation of rocks as a result of their weathering, as well as the development of the biosphere. The modern salt composition of the ocean, as shown by fossil remains, developed no later than the Proterozoic.

In addition to chlorides, sulfites and carbonates, almost all chemical elements known on Earth, including noble metals, were found in sea water. However, the content of most elements in sea water is negligible; for example, only 0.008 mg of gold per cubic meter of water was detected, and the presence of tin and cobalt is indicated by their presence in the blood of marine animals and in bottom sediments.

Salinity of ocean waters— the value is not constant (Fig. 1). It depends on climate (the ratio of precipitation and evaporation from the ocean surface), the formation or melting of ice, sea currents, and near continents - on the influx of fresh river water.

Rice. 1. Dependence of water salinity on latitude

In the open ocean, salinity ranges from 32-38%; in the marginal and Mediterranean seas its fluctuations are much greater.

The salinity of waters down to a depth of 200 m is especially strongly influenced by the amount of precipitation and evaporation. Based on this, we can say that the salinity of sea water is subject to the law of zonation.

In equatorial and subequatorial regions, salinity is 34%c, because the amount of precipitation is greater than the water spent on evaporation. In tropical and subtropical latitudes - 37 since there is little precipitation and evaporation is high. In temperate latitudes - 35% o. The lowest salinity of sea water is observed in the subpolar and polar regions - only 32, since the amount of precipitation exceeds evaporation.

Sea currents, river runoff and icebergs disrupt the zonal pattern of salinity. For example, in the temperate latitudes of the Northern Hemisphere, water salinity is greater near the western shores of the continents, where currents bring saltier subtropical waters, and less salinity is near the eastern shores, where cold currents bring less salty water.

Seasonal changes in water salinity occur in subpolar latitudes: in the fall, due to the formation of ice and a decrease in the strength of river flow, the salinity increases, and in the spring and summer, due to the melting of ice and an increase in river flow, the salinity decreases. Around Greenland and Antarctica, salinity decreases during the summer as a result of the melting of nearby icebergs and glaciers.

The saltiest of all oceans is the Atlantic Ocean, the waters of the Arctic Ocean have the lowest salinity (especially off the Asian coast, near the mouths of Siberian rivers - less than 10%).

Among parts of the ocean - seas and bays - the maximum salinity is observed in areas limited by deserts, for example, in the Red Sea - 42%c, in the Persian Gulf - 39%c.

The salinity of water determines its density, electrical conductivity, ice formation and many other properties.

In addition to various salts, various gases are dissolved in the waters of the World Ocean: nitrogen, oxygen, carbon dioxide, hydrogen sulfide, etc. As in the atmosphere, oxygen and nitrogen predominate in ocean waters, but in slightly different proportions (for example, the total amount of free oxygen in the ocean 7480 billion tons, which is 158 times less than in the atmosphere). Despite the fact that gases occupy relatively little space in water, this is enough to influence organic life and various biological processes.

The amount of gases is determined by the temperature and salinity of the water: the higher the temperature and salinity, the lower the solubility of gases and the lower their content in water.

So, for example, at 25 °C up to 4.9 cm/l of oxygen and 9.1 cm3/l of nitrogen can dissolve in water, at 5 °C - 7.1 and 12.7 cm3/l, respectively. Two important consequences follow from this: 1) the oxygen content in the surface waters of the ocean is much higher in temperate and especially polar latitudes than in low (subtropical and tropical) latitudes, which affects the development of organic life - the richness of the former and the relative poverty of the latter waters; 2) at the same latitudes, the oxygen content in ocean waters is higher in winter than in summer.

Daily changes in the gas composition of water associated with temperature fluctuations are small.

The presence of oxygen in ocean water promotes the development of organic life in it and the oxidation of organic and mineral products. The main source of oxygen in ocean water is phytoplankton, called the “lungs of the planet.” Oxygen is mainly spent on the respiration of plants and animals in the upper layers of sea waters and on the oxidation of various substances. In the depth range of 600-2000 m there is a layer oxygen minimum. A small amount of oxygen here is combined with a high content of carbon dioxide. The reason is the decomposition in this layer of water of the bulk of the organic matter coming from above and the intensive dissolution of biogenic carbonate. Both processes require free oxygen.

The amount of nitrogen in seawater is much less than in the atmosphere. This gas is mainly released into water from the air by the breakdown of organic matter, but is also produced by the respiration of marine organisms and their decomposition.

In the water column, in deep stagnant basins, as a result of the vital activity of organisms, hydrogen sulfide is formed, which is toxic and inhibits the biological productivity of waters.

Water is one of the most heat-intensive bodies in nature. The heat capacity of just a ten meter layer of the ocean is four times greater than the heat capacity of the entire atmosphere, and a 1 cm layer of water absorbs 94% of the solar heat arriving at its surface (Fig. 2). Due to this circumstance, the ocean slowly warms up and slowly releases heat. Due to their high heat capacity, all water bodies are powerful heat accumulators. As the water cools, it gradually releases its heat into the atmosphere. Therefore, the World Ocean performs the function thermostat of our planet.

Rice. 2. Dependence of heat capacity on temperature

Ice and especially snow have the lowest thermal conductivity. As a result, ice protects the water on the surface of the reservoir from hypothermia, and snow protects the soil and winter crops from freezing.

Heat of vaporization water - 597 cal/g, and heat of fusion - 79.4 cal/g - these properties are very important for living organisms.

An indicator of the thermal state of the ocean is temperature.

Average ocean temperature- 4 °C.

Despite the fact that the surface layer of the ocean serves as the Earth's thermoregulator, in turn, the temperature of sea waters depends on the thermal balance (heat inflow and outflow). Heat inflow consists of , and heat consumption consists of the costs of water evaporation and turbulent heat exchange with the atmosphere. Despite the fact that the proportion of heat spent on turbulent heat exchange is not large, its significance is enormous. It is with its help that planetary heat redistribution occurs through the atmosphere.

At the surface, ocean temperatures range from -2°C (freezing point) to 29°C in the open ocean (35.6°C in the Persian Gulf). The average annual temperature of the surface waters of the World Ocean is 17.4°C, and in the Northern Hemisphere it is approximately 3°C higher than in the Southern Hemisphere. The highest temperature of surface ocean waters in the Northern Hemisphere is in August, and the lowest in February. In the Southern Hemisphere the opposite is true.

Since it has thermal relationships with the atmosphere, the temperature of surface waters, like the air temperature, depends on the latitude of the area, i.e., it is subject to the law of zonation (Table 2). Zoning is expressed in a gradual decrease in water temperature from the equator to the poles.

In tropical and temperate latitudes, water temperature mainly depends on sea currents. Thus, thanks to warm currents in tropical latitudes, temperatures in the western oceans are 5-7 °C higher than in the east. However, in the Northern Hemisphere, due to warm currents in the eastern oceans, temperatures are positive all year round, and in the west, due to cold currents, the water freezes in winter. In high latitudes, the temperature during the polar day is about 0 °C, and during the polar night under the ice - about -1.5 (-1.7) °C. Here the water temperature is mainly influenced by ice phenomena. In the fall, heat is released, softening the temperature of the air and water, and in the spring, heat is spent on melting.

Table 2. Average annual temperatures of ocean surface waters

Average annual temperature, "C		Average annual temperature, °C
North hemisphere	Southern Hemisphere	North hemisphere	Southern Hemisphere

The coldest of all oceans- Northern Arctic, and the warmest— The Pacific Ocean, since its main area is located in equatorial-tropical latitudes (average annual water surface temperature -19.1 ° C).

An important influence on the temperature of ocean water is exerted by the climate of the surrounding areas, as well as the time of year, since solar heat, which heats the upper layer of the World Ocean, depends on this. The highest water temperature in the Northern Hemisphere is observed in August, the lowest in February, and vice versa in the Southern Hemisphere. Daily fluctuations in sea water temperature at all latitudes are about 1 °C; the largest annual temperature fluctuations are observed in subtropical latitudes - 8-10 °C.

The temperature of ocean water also changes with depth. It decreases and already at a depth of 1000 m almost everywhere (on average) below 5.0 °C. At a depth of 2000 m, the water temperature levels out, decreasing to 2.0-3.0 ° C, and in polar latitudes - to tenths of a degree above zero, after which it either decreases very slowly or even increases slightly. For example, in the rift zones of the ocean, where at great depths there are powerful outlets of underground hot water under high pressure, with temperatures up to 250-300 ° C. In general, there are two main layers of water vertically in the World Ocean: warm superficial And powerful cold, extending to the bottom. Between them there is a transition temperature jump layer, or main thermal clip, within it there is a sharp drop in temperature.

This picture of the vertical distribution of water temperature in the ocean is disrupted at high latitudes, where at a depth of 300-800 m a layer of warmer and saltier water coming from temperate latitudes can be traced (Table 3).

Table 3. Average ocean water temperatures, °C

A sharp increase in the volume of water when freezing- This is a peculiar property of water. With a sharp drop in temperature and its transition through the zero mark, a sharp increase in the volume of ice occurs. As the volume increases, the ice becomes lighter and floats to the surface, becoming less dense. Ice protects deep layers of water from freezing, as it is a poor conductor of heat. The volume of ice increases by more than 10% compared to the initial volume of water. When heated, the opposite process of expansion occurs—compression.

Temperature and salinity are the main factors that determine the density of water.

For sea water, the lower the temperature and higher the salinity, the greater the density of the water (Fig. 3). Thus, at a salinity of 35%o and a temperature of 0 °C, the density of sea water is 1.02813 g/cm 3 (the mass of each cubic meter of such sea water is 28.13 kg more than the corresponding volume of distilled water). The temperature of sea water with the highest density is not +4 °C, like fresh water, but negative (-2.47 °C at a salinity of 30% and -3.52 °C at a salinity of 35%o

Rice. 3. Relationship between the density of sea ox and its salinity and temperature

Due to the increase in salinity, the density of water increases from the equator to the tropics, and as a result of a decrease in temperature, from temperate latitudes to the Arctic Circle. In winter, polar waters descend and move in the bottom layers towards the equator, so the deep waters of the World Ocean are generally cold, but enriched with oxygen.

The dependence of water density on pressure was revealed (Fig. 4).

Rice. 4. Dependence of seawater density (L"=35%o) on pressure at different temperatures

Equatorial

This is an important property of water. During the process of evaporation, water passes through the soil, which, in turn, is a natural filter. However, if the pollution limit is violated, the self-cleaning process is disrupted.

Color and transparency depend on the reflection, absorption and scattering of sunlight, as well as on the presence of suspended particles of organic and mineral origin. In the open part, the color of the ocean is blue; near the coast, where there is a lot of suspended matter, it is greenish, yellow, and brown.

In the open part of the ocean, water transparency is higher than near the coast. In the Sargasso Sea, water transparency is up to 67 m. During the period of plankton development, transparency decreases.

In the seas such a phenomenon as glow of the sea (bioluminescence). Glow in sea water living organisms containing phosphorus, primarily such as protozoa (nightlight, etc.), bacteria, jellyfish, worms, fish. Presumably the glow serves to scare away predators, to search for food, or to attract individuals of the opposite sex in the dark. The glow helps fishing vessels locate schools of fish in seawater.

Sound conductivity - acoustic properties of water. Found in the oceans sound-diffusing my And underwater "sound channel" possessing sound superconductivity. The sound-dissipating layer rises at night and falls during the day. It is used by submariners to dampen noise from submarine engines, and by fishing vessels to detect schools of fish. "Sound
signal" is used for short-term forecast of tsunami waves, in underwater navigation for ultra-long-distance transmission of acoustic signals.

Electrical conductivity sea water is high, it is directly proportional to salinity and temperature.

Natural radioactivity sea waters are small. But many animals and plants have the ability to concentrate radioactive isotopes, so seafood catches are tested for radioactivity.

Mobility- a characteristic property of liquid water. Under the influence of gravity, under the influence of wind, attraction by the Moon and the Sun and other factors, water moves. As it moves, the water is mixed, which allows waters of different salinity, chemical composition and temperature to be evenly distributed.

IN tropical type the water temperature drops sharply from 26.06 0 C to 13.60 0 C at a depth of 300 m, then the water temperature changes more smoothly.

Physicochemical properties of MO waters. Back at the beginning of the 19th century. It was noticed that the amount of salts dissolved in ocean waters can vary greatly, but the salt composition and the ratio of various salts in the ocean waters are the same. This pattern is formulated as a property of constancy of the salt composition of sea waters. Per 1 kg of sea water there are 19.35 g of chlorine, 2.70 g of sulfates, 0.14 g of bicarbonates, 10.76 g of sodium, 1.30 g of magnesium, 0.41 g of calcium. The quantitative ratio between the main salts in MO water remains constant. Total salinity determined by the amount of chlorine in water (the formula was obtained by M. Knudsen in 1902):

S = 0.030 + 1.805 Cl

IN subtropical latitudes salinity quickly decreases to a depth of 1000 m (34.48 0/00), then becomes almost constant. At a depth of 3000 m it is 34.71 0 / 00.

IN subpolar latitudes salinity slowly increases with depth from 33.94 to 34.71 0/00, in polar latitudes Salinity increases more significantly with depth - from 33.48 to 34.70 0 / 00.

The average salinity of the Atlantic Ocean waters is 35.4; Quiet – 34.9; Indian - 34.8; Arctic Ocean – 29-32 0/00.

The ability of water to dissolve gases depends on temperature, salinity and hydrostatic pressure. The higher the temperature and salinity of the water, the less gases can dissolve in it.

The thickness of clear water has a blue or dark blue color, a large amount of plankton leads to the appearance of a greenish tint, and near rivers the water may be brown.