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Water masses and their properties. Water masses of the world's oceans Surface water masses

Characteristics of water masses

Water masses are classified not only depending on depth, but also by origin. Regarding this they are:

  • equatorial,
  • tropical,
  • moderate,
  • polar.

Equatorial water masses They are formed near the equator, so they are well heated by the Sun. The water temperature is +27, +28 degrees and varies by seasons only by 2 degrees. Heavy rainfall and rivers flowing into the ocean greatly desalinate the water, so the salinity of equatorial waters is lower compared to tropical latitudes.

The water masses of tropical latitudes are also well heated by the Sun, but their temperature is lower and is +20, +25 degrees, and by season it changes by 4 degrees. Currents have a great influence on water temperature. Warm currents coming from the equator are characteristic of the western parts of the ocean, so the water here will be warmer. Cold currents come to the eastern part of the ocean and reduce the water temperature.

In tropical latitudes, downward air currents dominate, resulting in high Atmosphere pressure with little precipitation. There are few rivers here and their desalination effect is insignificant, so the salinity of water in this area is high.

To the north are temperate latitudes, where the formation of moderate water masses occurs. The seasonal distribution of temperatures is clearly visible here, and the difference is 10 degrees. Winter temperatures range from 0 to 10 degrees, and in summer the change occurs from 10 to 20 degrees.

The salinity of temperate water masses is lower than tropical ones, because atmospheric precipitation, rivers flowing into the ocean and icebergs entering these latitudes have a great desalination effect.

The western and eastern parts of the oceans within temperate latitudes also have temperature differences. The western parts of the oceans will be cold, and the eastern parts will be warmed by warm currents.

In the Arctic region and off the coast of Antarctica, polar water masses are formed, which, with the help of currents, are carried to temperate latitudes, sometimes reaching tropical latitudes. A feature of polar water masses is the presence of floating ice, which has a strong desalination effect. Therefore, the salinity of polar water masses is low.

Note 1

There are no clear boundaries between water masses of different origins; there are only transition zones, which are more clearly expressed in those places where warm and cold currents come into contact.

Water masses depending on criteria

Depending on the criteria, different amounts of water masses are allocated.

The Antarctic bottom water mass is the largest in volume in the World Ocean, occupying the bottom layer around the continent. It extends north in the Atlantic Ocean to the 40th parallel north latitude. The meridional section of this water mass shows lower temperature and salinity compared to the waters above. The main place of its formation is the Weddell Sea and the shelf around Antarctica, where conditions favorable for this have formed. The salinity of the Antarctic bottom water mass is 34.6 ppm, and the temperature is -0.4 degrees. From the place of its formation, it slowly moves into the Atlantic, participating in the horizontal circulation of ocean waters;

The second largest volume in the World Ocean is the deep and bottom North Atlantic water mass. Its formation occurs in the winter between Greenland and Iceland. Here the warm and salty water of the North Atlantic Current mixes with cold and more fresh water East Greenland Current. The temperature of this water mass in the area of ​​formation varies with depth from 2.8 to 3.3 degrees, and the salinity also changes from 34.90 to 34.96 ppm. The North Atlantic deep and bottom water mass from the formation area spreads south to a depth of 2000-4000 m on top of the Antarctic bottom water. It is prevented from moving in a northerly direction by the rising ocean floor;

Figure 1. North Atlantic water mass. Author24 - online exchange of student work

Note 2

To form such a water mass in Pacific Ocean no conditions.

Surface water is the Antarctic intermediate water mass, which in the convergence zone spreads northward to a depth of 1000-1500 m. In the Atlantic Ocean region it is noticeable up to 15 degrees north latitude. Its salinity here is minimal and equal to 33.8 ppm, the temperature is reduced to 2.2 degrees;

Stationary subtropical maximums of atmospheric pressure are characterized by the formation of central water masses. Their feature is maximum salinity. Intense convection develops on their peripheries during periods of cooling, as a result of which the central masses increase their thickness in the Pacific Ocean to 200-300 m, and in the Sargasso Sea of ​​the Atlantic Ocean their thickness increases to 900 m;

In the area of ​​the equator, equatorial water masses of 3 oceans are formed - the Pacific, Indian and Atlantic. Due to the fact that a lot of precipitation falls in the equatorial region, these water masses are highly desalinated compared to the central water masses. The equatorial water mass is less pronounced in the Atlantic Ocean because water is transferred from the Southern to the Northern Hemisphere here;

In the formation of deep waters of the Atlantic Ocean, the Mediterranean water mass plays a rather noticeable role, the temperature of which is 13.0-13.6 degrees, and the salinity is 38.4-38.7 ppm. This water mass has a high density, due to which, having flowed through the Strait of Gibraltar, it sinks to a depth of 1000 m and spreads like a fan over the vast expanse of the North Atlantic;

  • In the northwestern part of the Indian Ocean, a similar role is played by the Red Sea water mass with a temperature of 23 degrees and a salinity of 40 ppm.

Other types of water masses

The formation of the Antarctic circumpolar water mass involves North Atlantic deep and bottom water rising near Antarctica, to which a certain amount of Antarctic intermediate and bottom water is mixed.

The mixture that is formed rises as an independent water mass into the upper layer of the ocean. It occupies a place between the Antarctic coastal waters and the Antarctic convergence.

Antarctic circumpolar water in the circular transport of water forms a ring that encircles Antarctica.

The upper layer of Antarctic circumpolar water is characterized by divergence of zonal transport, which causes the rise of North Atlantic deep and bottom water in the Antarctic region.

Between the Antarctic convergence and the southern boundary of the central water masses lies the subantarctic water mass. It forms a closed ring in which it moves from west to east. This water mass is the result of the mixing of central water masses with Antarctic intermediate water at their southern peripheries.

In the Northern Hemisphere, over a large expanse of the Pacific Ocean, north of the 40th parallel, there is a subarctic water mass. It was formed by the processes of cooling and desalination of water in the Bering and Okhotsk seas, as well as in the adjacent part of the ocean.

In the Atlantic, this type of water is formed in small quantities.

Four water masses are present in the Arctic Ocean, and the entire water column has a negative temperature, with only a thin layer of water with a positive temperature.

The active layer of the ocean with desalinated waters and negative temperatures drops to a depth of 200-250 m - this is the surface water mass. In winter, this layer is completely covered by convection, and the temperature drops almost to the freezing point - about -1.7 degrees.

In summer the temperature is just above freezing. The salinity on the surface of this water mass is 31.3-31.5 ppm.

A unique phenomenon in the World Ocean is the warm Atlantic layer, formed from the warm West Spitsbergen Current. In order for this water mass, due to its high density, to sink under the surface layer of the Arctic Ocean with its salinity up to 34.75 ppm, it is enough for the water to cool to 3-4 degrees.

Then it spreads throughout the ocean at a depth of 200-500 m, and even near the Bering Strait it retains high salinity and a positive temperature of +0.4 degrees.

Deep and bottom water masses are formed in the Greenland Sea.

Note 3

Thus, the water masses that form in certain areas of the World Ocean well reflect the vertical and horizontal zoning, which is the main geographical pattern of the nature of the planet.

Water masses- these are large volumes of water formed in certain parts of the ocean and differing from each other in temperature, salinity, density, transparency, amount of oxygen and other properties. In contrast, in them great importance It has. Depending on the depth there are:

Surface water masses. They are formed under the influence of atmospheric processes and the influx of fresh water from the mainland to a depth of 200-250 m. Here, salinity often changes, and their horizontal transport in the form of ocean currents is much stronger than deep transport. Surface waters contain the highest levels of plankton and fish;

Intermediate water masses. They have a lower limit of 500-1000 m. In tropical latitudes, intermediate water masses are formed under conditions of increased evaporation and constant rise. This explains the fact that intermediate waters occur between 20° and 60° in the Northern and Southern Hemispheres;

Deep water masses. They are formed as a result of mixing surface and intermediate, polar and tropical water masses. Their lower limit is 1200-5000 m. Vertically, these water masses move extremely slowly, and horizontally they move at a speed of 0.2-0.8 cm/s (28 m/h);

Bottom water masses. They occupy a zone below 5000 m and have constant salinity, very high density, and their horizontal movement is slower than vertical.

Depending on their origin, the following types of water masses are distinguished:

Tropical. They form in tropical latitudes. The water temperature here is 20-25°. The temperature of tropical water masses is greatly influenced by ocean currents. The western parts of the oceans are warmer, where warm currents (see) come from the equator. The eastern parts of the oceans are colder because cold currents come here. Seasonally, the temperature of tropical water masses varies by 4°. The salinity of these water masses is much greater than that of the equatorial ones, since as a result of downward air currents little precipitation is established and falls here;

water masses. In the temperate latitudes of the Northern Hemisphere, the western parts of the oceans are cold, where cold currents pass. The eastern regions of the oceans are warmed by warm currents. Even in the winter months, the water temperature in them ranges from 10°C to 0°C. In summer it varies from 10°C to 20°C. Thus, the temperature of temperate water masses varies by 10°C between seasons. They are already characterized by the change of seasons. But it comes later than on land, and is not so pronounced. The salinity of temperate water masses is lower than that of tropical ones, since the desalination effect is exerted not only by rivers and precipitation that fall here, but also by those entering these latitudes;

Polar water masses. They form in and off the coast. These water masses can be carried by currents to temperate and even tropical latitudes. In the polar regions of both hemispheres, water cools to -2°C, but still remains liquid. Further decrease leads to the formation of ice. Polar water masses are characterized by an abundance of floating ice, as well as ice that forms huge ice expanses. The ice lasts all year and is in constant drift. In the Southern Hemisphere, in areas of polar water masses, they extend into temperate latitudes much further than in the Northern Hemisphere. The salinity of polar water masses is low, since ice has a strong desalination effect. There are no clear boundaries between the listed water masses, but there are transition zones - zones of mutual influence of neighboring water masses. They are most clearly expressed in places where warm and cold currents meet. Each water mass is more or less homogeneous in its properties, but in transition zones these characteristics can change dramatically.

Water masses actively interact with it: they give it heat and moisture, absorb carbon dioxide from it, and release oxygen.

WATER MASS, a volume of water commensurate with the area and depth of a reservoir, possessing relative homogeneity of physical, chemical and biological characteristics, formed in specific physical and geographical conditions (usually on the surface of the ocean, sea), different from the surrounding water column. The characteristics of water masses acquired in certain areas of the oceans and seas are preserved outside the area of ​​formation. Adjacent water masses are separated from each other by front zones of the World Ocean, division zones and transformation zones, which can be traced along increasing horizontal and vertical gradients of the main indicators of water masses. The main factors in the formation of water masses are the thermal and water balances of a given area, respectively, the main indicators of water masses are temperature, salinity and density, which depends on them. The most important geographical patterns - horizontal and vertical zoning - manifest themselves in the ocean in the form of a specific structure of waters, consisting of a set of water masses.

In the vertical structure of the World Ocean, water masses are distinguished: surface - to a depth of 150-200 m; subsurface - up to 400-500 m; intermediate - up to 1000-1500 m, deep - up to 2500-3500 m; bottom - below 3500 m. Each of the oceans has characteristic water masses; surface water masses are named in accordance with the climate zone where they were formed (for example, subarctic Pacific, tropical Pacific, and so on). For the underlying structural zones of oceans and seas, the name of the water masses corresponds to their geographical area (Mediterranean intermediate water mass, North Atlantic deep, deep Black Sea, Antarctic bottom, etc.). The density of water and the characteristics of atmospheric circulation determine the depth to which the water mass sinks in the area of ​​its formation. Often, when analyzing a water mass, indicators of the content of dissolved oxygen and other elements in it, the concentration of a number of isotopes are also taken into account, which make it possible to trace the distribution of the water mass from the area of ​​its formation, the degree of mixing with surrounding waters, and the time spent outside of contact with the atmosphere.

The characteristics of water masses do not remain constant; they are subject to seasonal (in the upper layer) and long-term fluctuations within certain limits, and change in space. As they move from the area of ​​formation, water masses are transformed under the influence of changed heat and water balances, peculiarities of atmospheric and ocean circulation, and mix with surrounding waters. As a result, a distinction is made between primary water masses (formed under the direct influence of the atmosphere, with the greatest fluctuations in characteristics) and secondary water masses (formed by mixing primary ones, characterized by the greatest uniformity of characteristics). Within the water mass, a core is distinguished - a layer with the least transformed characteristics, preserving the distinctive features inherent in a particular water mass - minimums or maximums of salinity and temperature, the content of a number of chemical substances.

When studying water masses, the method of temperature-salinity curves (T, S-curves), the kernel method (study of the transformation of temperature or salinity extremes inherent in a water mass), the isopycnal method (analysis of characteristics on surfaces of equal density), and statistical T, S-analysis are used. The circulation of water masses plays an important role in the energy and water balance of the Earth’s climate system, redistributing thermal energy and desalinated (or salted) waters between latitudes and different oceans.

Lit.: Sverdrup N. U., Johnson M. W., Fleming R. N. The oceans. N. Y., 1942; Zubov N.N. Dynamic oceanology. M.; L., 1947; Dobrovolsky A.D. On the determination of water masses // Oceanology. 1961. T. 1. Issue. 1; Stepanov V. N. Oceanosphere. M., 1983; Mamaev O.I. Thermohaline analysis of the waters of the World Ocean. L., 1987; aka. Physical oceanography: Favorites. works. M., 2000; Mikhailov V.N., Dobrovolsky A.D., Dobrolyubov S.A. Hydrology. M., 2005.

Under the influence of certain geophysical factors. The water mass is characterized by a constant and continuous distribution of physicochemical and biological properties over a long period of time. All components of the water mass form a single complex that can change or move as one. Unlike air masses, vertical zonality plays a rather important role for masses.

Main characteristics of water masses:

  • water temperature,
  • content of biogenic salts (phosphates, silicates, nitrates),
  • content of dissolved gases (oxygen, carbon dioxide).

The characteristics of water masses do not remain unchanged all the time; they fluctuate within certain limits with seasons and over many years. There are no clear boundaries between water masses; instead, there are transitional zones of mutual influence. This can be most clearly observed at the boundary of warm and cold sea currents.

The main factors in the formation of water masses are the heat and water balances of the region.

Water masses interact quite actively with the atmosphere. They give it heat and moisture, biogenic and mechanical oxygen, and absorb from it carbon dioxide.

Classification

There are primary and secondary water masses. The first include those whose characteristics are formed under the influence of the earth’s atmosphere. They are characterized by the greatest amplitude of changes in their properties in a certain volume of the water column. Secondary water masses include those that are formed under the influence of mixing of primary ones. They are characterized by the greatest homogeneity.

Based on depth and physical-geographical properties, the following types of water masses are distinguished:

  • superficial:
    • surface (primary) - to depths of 150-200 m,
    • subsurface (primary and secondary) - from 150-200 m to 400-500 m;
  • intermediate (primary and secondary) - the middle layer of ocean waters about 1000 m thick, at depths from 400-500 m to 1000-1500 m, the temperature of which is only a few degrees above the freezing point of water; a permanent boundary between surface and deep waters, which prevents their mixing;
  • deep (secondary) - at depths from 1000-1500 m to 2500-3000 m;
  • bottom (secondary) - deeper than 3 km.

Spreading

Types of surface water masses

Equatorial

Throughout the year, the equatorial waters are strongly heated by the sun, which is at its zenith. Layer thickness - 150-300 g. Horizontal movement speed ranges from 60-70 to 120-130 cm/sec. Vertical mixing occurs at a speed of 10 -2 10 -3 cm/sec. The water temperature is 27°...+28°С, seasonal variability is small 2°C. The average salinity is from 33-34 to 34-35 ‰, lower than in tropical latitudes, because numerous rivers and heavy daily rainfalls have a rather strong effect, desalinating the upper layer of water. Conditional density 22.0-23.0. Oxygen content 3.0-4.0 ml/l; phosphates - 0.5-1.0 µg-at/l.

Tropical

Layer thickness - 300-400 g. Horizontal movement speed ranges from 10-20 to 50-70 cm/sec. Vertical mixing occurs at a speed of 10 -3 cm/sec. The water temperature ranges from 18-20 to 25-27°C. Average salinity is 34.5-35.5 ‰. Conditional density 24.0-26.0. Oxygen content 2.0-4.0 ml/l; phosphates - 1.0-2.0 µg-at/l.

Subtropical

Layer thickness - 400-500 g. Horizontal movement speed ranges from 20-30 to 80-100 cm/sec. Vertical mixing occurs at a speed of 10 -3 cm/sec. The water temperature ranges from 15-20 to 25-28°C. Average salinity is from 35-36 to 36-37 ‰. Conditional density from 23.0-24.0 to 25.0-26.0. Oxygen content 4.0-5.0 ml/l; phosphates -

Subpolar

Layer thickness - 300-400 g. Horizontal movement speed ranges from 10-20 to 30-50 cm/sec. Vertical mixing occurs at a speed of 10 -4 cm/sec. The water temperature ranges from 15-20 to 5-10°C. Average salinity is 34-35 ‰. Conditional density 25.0-27.0. Oxygen content 4.0-6.0 ml/l; phosphates - 0.5-1.5 mcg-at/l.

Literature

  1. (English) Emery, W. J. and J. Meincke. 1986 Global water masses: summary and review. Oceanologica Acta, 9:-391.
  2. (Russian) Agenorov V.K. About the main water masses in the hydrosphere, M. - Sverdlovsk, 1944.
  3. (Russian) Zubov N. N. Dynamic oceanology. M. - L., 1947.
  4. (Russian) Muromtsev A. M. Main features of the hydrology of the Pacific Ocean, L., 1958.
  5. (Russian) Muromtsev A. M. Main features of the hydrology of the Indian Ocean, Leningrad, 1959.
  6. (Russian) Dobrovolsky A.D. On the determination of water masses // Oceanology, 1961, vol. 1, issue 1.
  7. (German) Defant A., Dynamische Ozeanographie, B., 1929.
  8. (English) Sverdrup N. U., Jonson M. W., Fleming R. N., The oceans, Englewood Cliffs, 1959.

The entire mass of waters of the World Ocean is conventionally divided into surface and deep. Surface water – a layer 200–300 m thick – is very heterogeneous in its natural properties; they can be called oceanic troposphere. The remaining waters are oceanic stratosphere, component of the main body of water, more homogeneous.

Surface water is a zone of active thermal and dynamic interaction

ocean and atmosphere. In accordance with zonal climate changes, they are divided into different water masses, primarily according to their thermohaline properties. Water masses- these are relatively large volumes of water that form in certain zones (foci) of the ocean and have stable physicochemical and biological properties for a long time.

Highlight five types water masses: equatorial, tropical, subtropical, subpolar and polar.

Equatorial water masses(0-5° N) form inter-trade wind countercurrents. They have constantly high temperatures (26-28 °C), a clearly defined temperature jump layer at a depth of 20-50 m, low density and salinity - 34 - 34.5‰, low oxygen content - 3-4 g/m3, small saturation with life forms. The rise of water masses predominates. In the atmosphere above them there is a belt of low pressure and calm conditions.

Tropical water masses(5– 35° N. w. and 0–30° S. w.) are distributed along the equatorial peripheries of subtropical pressure maxima; they form trade wind currents. The temperature in summer reaches +26...+28°C, in winter it drops to +18...+20°C, and it differs on the western and eastern coasts due to currents and coastal stationary upwellings and downwellings. Upwelling(English, upwelling– ascent) is the upward movement of water from a depth of 50–100 m, generated by driving winds off the western coasts of continents in a zone of 10–30 km. Possessing a low temperature and, therefore, significant oxygen saturation, deep waters, rich in biogenic and minerals, entering the surface illuminated zone, increase the productivity of the water mass. Downwellings– downward flows off the eastern coasts of the continents due to the surge of water; they carry heat and oxygen down. The temperature jump layer is expressed all year round, salinity is 35–35.5‰, oxygen content is 2–4 g/m3.

Subtropical water masses have the most characteristic and stable properties in the “core” - circular water areas limited by large rings of currents. The temperature throughout the year varies from 28 to 15°C, there is a layer of temperature jump. Salinity 36–37‰, oxygen content 4–5 g/m3. At the center of the gyres, waters descend. In warm currents, subtropical water masses penetrate into temperate latitudes up to 50° N. w. and 40–45° S. w. These transformed subtropical water masses occupy almost the entire water area of ​​the Atlantic, Pacific and Indian oceans. Cooling, subtropical waters release a huge amount of heat to the atmosphere, especially in winter, playing a very significant role in planetary heat exchange between latitudes. The boundaries of subtropical and tropical waters are very arbitrary, so some oceanologists combine them into one type of tropical waters.

Subpolar– subarctic (50–70° N) and subantarctic (45–60° S) water masses. They are characterized by a variety of characteristics both by season and by hemisphere. Temperature in summer is 12–15°C, in winter 5–7°C, decreasing towards the poles. There is practically no sea ice, but there are icebergs. The temperature jump layer is expressed only in summer. Salinity decreases from 35 to 33‰ towards the poles. The oxygen content is 4 – 6 g/m3, so the waters are rich in life forms. These water masses occupy the northern Atlantic and Pacific Oceans, penetrating in cold currents along the eastern shores of the continents into temperate latitudes. In the southern hemisphere they form a continuous zone south of all continents. In general, this is a western circulation of air and water masses, a strip of storms.

Polar water masses in the Arctic and around Antarctica they have low temperatures: in summer about 0°C, in winter –1.5...–1.7°C. Brackish sea and fresh continental ice and their fragments are permanent here. There is no temperature jump layer. Salinity 32–33‰. The maximum amount of oxygen dissolved in cold waters is 5–7 g/m3. At the border with subpolar waters, a sinking of dense cold waters is observed, especially in winter.

Each water mass has its own source of formation. When water masses with different properties meet, oceanological fronts, or convergence zones (lat. converge- I agree). They usually form at the junction of warm and cold surface currents and are characterized by the subsidence of water masses. There are several frontal zones in the World Ocean, but there are four main ones, two each in the northern and southern hemispheres. In temperate latitudes, they are expressed along the eastern coasts of continents on the boundaries of the subpolar cyclonic and subtropical anticyclonic gyres with their respectively cold and warm currents: near Newfoundland, Hokkaido, the Falkland Islands and New Zealand. In these frontal zones, hydrothermal characteristics (temperature, salinity, density, current speed, seasonal temperature fluctuations, the size of wind waves, the amount of fog, cloudiness, etc.) reach extreme values. To the east, due to mixing of waters, the frontal contrasts are blurred. It is in these zones that frontal cyclones of extratropical latitudes originate. Two frontal zones exist on both sides of the thermal equator at western shores continents between tropical relatively cold waters and warm equatorial waters of inter-trade countercurrents. They are also distinguished by high values ​​of hydrometeorological characteristics, great dynamic and biological activity, and intense interaction between the ocean and the atmosphere. These are the areas where tropical cyclones originate.

Is in the ocean and divergence zones (lat. diuergento– I deviate) – zones of divergence of surface currents and rise of deep waters: off the western coasts of continents at temperate latitudes and above the thermal equator off the eastern coasts of continents. Such zones are rich in phyto- and zooplankton, are characterized by increased biological productivity and are areas of effective fishing.

The oceanic stratosphere is divided by depth into three layers, differing in temperature, illumination and other properties: intermediate, deep and bottom waters. Intermediate waters are located at depths from 300–500 to 1000–1200 m. Their thickness is maximum in polar latitudes and in the central parts of anticyclonic gyres, where subsidence of waters predominates. Their properties are somewhat different depending on the breadth of their distribution. The general transport of these waters is directed from high latitudes to the equator.

Deep and especially bottom waters (the thickness of the layer of the latter is 1000–1500 m above the bottom) are distinguished by great homogeneity (low temperatures, rich oxygen) and a slow speed of movement in the meridional direction from the polar latitudes to the equator. Antarctic waters, “sliding” from the continental slope of Antarctica, are especially widespread. They not only occupy the entire southern hemisphere, but also reach 10–12° N. w. in the Pacific Ocean, up to 40° N. w. in the Atlantic and to the Arabian Sea in Indian Ocean.

From the characteristics of water masses, especially surface ones, and currents, the interaction between the ocean and the atmosphere is clearly visible. The ocean provides the atmosphere with the bulk of its heat by converting the sun's radiant energy into heat. The ocean is a huge distiller that supplies the land with fresh water through the atmosphere. Heat entering the atmosphere from the oceans causes different atmospheric pressures. Due to the difference in pressure, wind arises. It causes excitement and currents that transfer heat to high latitudes or cold to low latitudes, etc. The processes of interaction between the two shells of the Earth - the atmosphere and the oceanosphere - are complex and diverse.

As a result of dynamic processes occurring in the column of oceanic waters, a more or less mobile stratification of waters is established in it. This stratification leads to the separation of so-called water masses. Water masses are waters characterized by their inherent conservative properties. Moreover, water masses acquire these properties in certain areas and retain them throughout the entire space of their distribution.

According to V.N. Stepanov (1974), distinguish: surface, intermediate, deep and bottom water masses. The main types of water masses can, in turn, be divided into varieties.

Surface water masses are characterized by the fact that they are formed through direct interaction with the atmosphere. As a result of interaction with the atmosphere, these water masses are most susceptible to: mixing by waves, changes in the properties of ocean water (temperature, salinity and other properties).

The thickness of the surface masses is on average 200-250 m. They are also distinguished by the maximum intensity of transport - on average about 15-20 cm/s in the horizontal direction and 10 10-4 - 2 10-4 cm/s in the vertical direction. They are divided into equatorial (E), tropical (ST and YT), subarctic (SbAr), subantarctic (SbAn), Antarctic (An) and Arctic (Ap).

Intermediate water masses are distinguished in polar regions with elevated temperatures, in temperate and tropical regions - with low or high salinity. Their upper boundary is the boundary with surface water masses. The lower boundary lies at a depth of 1000 to 2000 m. Intermediate water masses are divided into subantarctic (PSbAn), subarctic (PSbAr), North Atlantic (PSAt), North Indian Ocean (PSI), Antarctic (PAn) and Arctic (PAR) masses.

The main part of the intermediate subpolar water masses is formed due to the subsidence of surface waters in the subpolar convergence zones. The transport of these water masses is directed from the subpolar regions to the equator. In the Atlantic Ocean, subantarctic intermediate water masses pass beyond the equator and are distributed to approximately 20° N latitude, in the Pacific Ocean - to the equator, in the Indian Ocean - to approximately 10° S latitude. Subarctic intermediate waters in the Pacific Ocean also reach the equator. In the Atlantic Ocean they quickly sink and get lost.

In the northern part of the Atlantic and Indian Oceans, intermediate masses have a different origin. They form on the surface in areas of high evaporation. As a result, excessively salty waters are formed. Due to its high density, these salty waters experience a slow sinking. To these are added dense salty waters from the Mediterranean Sea (in the North Atlantic) and from the Red Sea and the Persian and Oman Gulfs (in the Indian Ocean). In the Atlantic Ocean, intermediate waters spread under the surface layer to the north and south from the latitude of the Strait of Gibraltar. They spread between 20 and 60° N latitude. In the Indian Ocean, the distribution of these water is flowing to the south and southeast to 5-10° S.

The circulation pattern of intermediate waters was revealed by V.A. Burkov and R.P. Bulatov. It is characterized by an almost complete attenuation of wind circulations in the tropical and equatorial zones and a slight shift of subtropical gyres towards the poles. In this regard, intermediate waters from polar fronts spread to tropical and subpolar regions. The same circulation system includes subsurface equatorial countercurrents such as the Lomonosov Current.

Deep water masses are formed mainly at high latitudes. Their formation is associated with the mixing of surface and intermediate water masses. They usually form on shelves. Cooling and accordingly acquiring greater density, these masses gradually slide down the continental slope and spread towards the equator. The lower boundary of deep waters is located at a depth of about 4000 m. The intensity of circulation of deep waters was studied by V.A. Burkov, R.P. Bulatov and A.D. Shcherbinin. It weakens with depth. The main role in the horizontal movement of these water masses is played by: southern anticyclonic gyres; circumpolar deep current in the Southern Hemisphere, which ensures the exchange of deep water between the oceans. The horizontal movement speeds are approximately 0.2-0.8 cm/s, and the vertical ones are 1 10-4 to 7 10O4 cm/s.

Deep water masses are divided into: circumpolar deep water mass of the Southern Hemisphere (CHW), North Atlantic (NSAt), North Pacific (GST), North Indian Ocean (NIO) and Arctic (GAr). Deep North Atlantic waters are characterized by high salinity (up to 34.95%) and temperature (up to 3°) and a slightly increased speed of movement. Their formation involves: waters of high latitudes, cooled on the polar shelves and submerged when mixing surface and intermediate waters, heavy salty waters of the Mediterranean, rather salty waters of the Gulf Stream. Their subsidence increases as they move to higher latitudes, where they experience gradual cooling.

Circumpolar deep waters are formed exclusively due to the cooling of waters in the Antarctic regions of the World Ocean. The northern deep masses of the Indian and Pacific oceans are of local origin. In the Indian Ocean due to the runoff of salty waters from the Red Sea and the Persian Gulf. In the Pacific Ocean, mainly due to the cooling of waters on the Bering Sea shelf.

Bottom water masses are characterized by the lowest temperatures and the highest density. They occupy the rest of the ocean deeper than 4000 m. These water masses are characterized by very slow horizontal movement, mainly in the meridional direction. Bottom water masses are distinguished by slightly larger vertical displacements compared to deep water masses. These values ​​are due to the influx of geothermal heat from the ocean floor. These water masses are formed due to the subsidence of overlying water masses. Among bottom water masses, the Antarctic bottom water (BWW) is the most widespread. These waters are clearly visible by their lowest temperatures and relatively high oxygen content. The center of their formation is the Antarctic regions of the World Ocean and especially the Antarctic shelf. In addition, the North Atlantic and North Pacific bottom water masses (PrSAt and PrST) are distinguished.

Bottom water masses are also in a state of circulation. They are characterized predominantly by meridional transport in a northerly direction. In addition, in the northwestern part of the Atlantic there is a clearly defined southward current, fed by the cold waters of the Norwegian-Greenland basin. The speed of movement of near-bottom masses increases slightly as they approach the bottom.

Just like air space, water space is heterogeneous in its zonal structure. We will talk about what is called water mass in this article. We will identify their main types, and also determine the key hydrothermal characteristics of oceanic waters.

What is the water mass of the World Ocean called?

Oceanic water masses are relatively large layers of oceanic waters that have certain properties (depth, temperature, density, transparency, amount of salts contained, etc.) characteristic of a given type of body of water. The formation of the properties of a certain type of water masses occurs over a long period of time, which makes them relatively constant and the water masses are perceived as a single whole.

Main characteristics of marine water masses

Oceanic water masses in the process of interaction with the atmosphere acquire various characteristics, differing depending on the degree of impact, as well as on the source of formation.


Main zones of water masses of the World Ocean

The complex characteristics of water masses are formed under the influence of not only territorial characteristics in combination with climatic conditions, but also due to the mixing of different water flows. The upper layers of ocean waters are more susceptible to mixing and influence of the atmosphere than the deeper layers of water in the same geographic region. In connection with this factor, the water masses of the World Ocean are divided into two large sections:


Types of waters of the oceanic troposphere

The oceanic troposphere is formed under the influence of a combination of dynamic factors: climate, precipitation, and the tide of continental waters. Due to this surface water have frequent fluctuations in temperature and salinity levels. The movement of water masses from one latitude to another forms the formation of warm and

The greatest saturation of life forms in the form of fish and plankton is observed. Types of water masses in the oceanic troposphere are usually divided according to geographic latitudes with a pronounced climatic factor. Let's name the main ones:

  • Equatorial.
  • Tropical.
  • Subtropical.
  • Subpolar.
  • Polar.

Characteristics of equatorial water masses

The territorial zonality of equatorial water masses covers a geographical band from 0 to 5 northern latitude. The equatorial climate is characterized by almost uniformly high temperatures throughout the entire calendar year, therefore the water masses of this region are sufficiently warmed up, reaching a temperature of 26-28.

Due to heavy precipitation and the influx of fresh river water from the mainland, equatorial oceanic waters have a small percentage of salinity (up to 34.5‰) and the lowest conditional density (22-23). The saturation of the region's aquatic environment with oxygen also has the lowest rate (3-4 ml/l) due to the high average annual temperature.

Characteristics of tropical water masses

The zone of tropical water masses occupies two bands: 5-35 in the northern hemisphere (north tropical waters) and up to 30 in the southern hemisphere (south tropical waters). They are formed under the influence of climate characteristics and air masses - trade winds.

The summer temperature maximum corresponds to the equatorial latitude, but in winter this figure drops to 18-20 above zero. The zone is characterized by the presence of ascending water flows from a depth of 50-100 meters near the western coastal continental lines and downward flows near the eastern shores of the continent.

Tropical types of water masses have a higher salinity index (35-35.5‰) and conditional density (24-26) than that of the equatorial zone. The oxygen saturation of tropical water flows remains approximately at the same level as that of the equatorial strip, but the saturation with phosphates is higher: 1-2 µg-at/l versus 0.5-1 µg-at/l in equatorial waters.

Subtropical water masses

The temperature during the year in the subtropical water zone can drop to 15. In tropical latitudes, water desalination occurs to a lesser extent than in other climatic zones, since there is little precipitation here, while intense evaporation occurs.

Here the water salinity can reach up to 38‰. Subtropical water masses of the ocean, when cooled in the winter, give off a lot of heat, thereby making a significant contribution to the heat exchange process of the planet.

The boundaries of the subtropical zone reach approximately 45 southern hemispheres and 50 northern latitudes. There is an increase in the saturation of waters with oxygen, and therefore with life forms.

Characteristics of subpolar water masses

As you move away from the equator, the temperature of the water streams decreases and varies depending on the time of year. So, in the territory of subpolar water masses (50-70 N and 45-60 S), in winter the water temperature drops to 5-7, and in summer it rises to 12-15 about S.

Water salinity tends to decrease from subtropical water masses towards the poles. This happens due to the melting of icebergs - sources of fresh water.

Characteristics and features of polar water masses

The localization of polar oceanic masses is the circumcontinental polar northern and southern spaces, thus, oceanologists highlight the presence of Arctic and Antarctic water masses. The distinctive features of polar waters are, of course, the lowest temperature indicators: in summer the average is 0, and in winter 1.5-1.8 below zero, which also affects the density - here it is the highest.

In addition to temperature, low salinity (32-33‰) is also noted due to the melting of continental fresh glaciers. The waters of polar latitudes are very rich in oxygen and phosphates, which has a beneficial effect on the diversity of the organic world.

Types and properties of water masses in the oceanic stratosphere

Oceanologists conventionally divide the oceanic stratosphere into three types:

  1. Intermediate waters cover water columns at depths from 300-500 m to 1000 m, and sometimes 2000 m. Compared with the other two types of water masses in the stratosphere, the intermediate layer is the most illuminated, warm and more rich in oxygen and phosphates, and therefore the underwater world is richer in plankton and various types fish Under the influence of the proximity to water flows of the troposphere, in which rapidly flowing water mass predominates, the hydrothermal characteristics and flow speed of water flows in the intermediate layer are very dynamic. The general tendency for the movement of intermediate waters is observed in the direction from high latitudes to the equator. The thickness of the intermediate layer of the oceanic stratosphere is not the same everywhere; a wider layer is observed near the polar zones.
  2. Deep waters have a distribution area starting from a depth of 1000-1200 m, and reaching 5 km below sea level and are characterized by more constant hydrothermal data. The horizontal flow of water flows in this layer is much less than intermediate waters and amounts to 0.2-0.8 cm/s.
  3. The bottom layer of water is the least studied by oceanologists due to its inaccessibility, because it is located at a depth of more than 5 km from the surface of the water. The main features of the bottom layer are an almost constant level of salinity and high density.

Water masses are large volumes of water that form in certain parts of the ocean and differ from each other in temperature, salinity, density, transparency, amount of oxygen contained and many other properties. Unlike air masses, vertical zonation is of great importance in them. Depending on the depth, the following types of water masses are distinguished:

Surface water masses. They are located to a depth of 200-250 m. Here the water temperature and salinity often change, since these water masses are formed under the influence of precipitation and the influx of fresh continental waters. Waves and horizontal ocean currents form in surface water masses. This type of water mass contains the highest content of plankton and fish.

Intermediate water masses. They are located to a depth of 500-1000 m. Basically, this type of mass is found in the tropical latitudes of both hemispheres and is formed under conditions of increased evaporation and a constant increase in salinity. Deep water masses. Their lower limit can reach up to 5000 m. Their formation is associated with the mixing of surface and intermediate water masses, polar and tropical masses. They move vertically very slowly, but horizontally at a speed of 28 m/hour.

Bottom water masses. They are located in the World Ocean below 5000 m, have constant salinity and very high density.

Water masses can be classified not only depending on depth, but also by origin. In this case, the following types of water masses are distinguished:

Equatorial water masses. They are well warmed by the sun, their temperature varies by season by no more than 2° and is 27 - 28°C. They are desalinated by heavy precipitation and rivers flowing into the ocean at these latitudes, so the salinity of these waters is lower than in tropical latitudes.

Tropical water masses. They are also well warmed by the sun, but the water temperature here is lower than in equatorial latitudes and amounts to 20-25°C. Seasonally, the temperature of waters in tropical latitudes varies by 4°. The temperature of the waters of this type of water mass is greatly influenced by ocean currents: the western parts of the oceans, where warm currents from the equator arrive, are warmer than the eastern parts, since cold currents arrive there. The salinity of these waters is much higher than that of the equatorial ones, since here, as a result of downward air currents, high pressure is established and little precipitation falls. Rivers also do not have a desalination effect, since there are very few of them in these latitudes.

Moderate water masses. By season, the water temperature of these latitudes differs by 10°: in winter the water temperature ranges from 0° to 10°C, and in summer it varies from 10° to 20°C. These waters are already characterized by a change of seasons, but it occurs later than on land and is not so pronounced. The salinity of these waters is lower than that of tropical waters, since the desalination effect is exerted by precipitation, rivers flowing into these waters, and icebergs entering these latitudes. Temperate water masses are also characterized by temperature differences between the western and eastern parts of the ocean: the western parts of the oceans, where cold currents pass, are cold, and the eastern regions are warmed by warm currents.

Polar water masses. They form in the Arctic and off the coast of Antarctica and can be carried by currents to temperate and even tropical latitudes. Polar water masses are characterized by an abundance of floating ice, as well as ice that forms huge ice expanses. In the Southern Hemisphere in areas of polar water masses sea ​​ice they extend into temperate latitudes much further than in the North. The salinity of polar water masses is low, since floating ice has a strong desalination effect.

Between different types water masses differing in origin do not have clear boundaries, but there are transition zones. They are most clearly expressed in places where warm and cold currents meet. Water masses actively interact with the atmosphere: they give it moisture and heat and absorb carbon dioxide from it and release oxygen. The most characteristic properties of water masses are salinity and temperature.

The formation of water masses occurs in accordance with the geophysical conditions of individual areas of the World Ocean. During the process of genesis, significant volumes of water acquire a set of characteristic physicochemical and biological properties, which remains practically unchanged throughout the entire space of their distribution.

Properties

The main properties of water masses include salinity and temperature. Both of these indicators depend on climatic factors determined by geographic latitude. The main role in changing the salinity of waters is played by precipitation and evaporation. Temperature is influenced by the climate of the surrounding areas and ocean currents.

Types

In the structure of the World Ocean, the following types of water masses are distinguished: bottom, deep, intermediate and surface.

Surface masses are formed under the influence of precipitation and fresh continental waters. This explains the constant changes in temperature and salinity. Waves and horizontal ocean currents also arise here. The thickness of the layer is 200–250 meters.

Intermediate water masses located at a depth of 500–1000 meters. They are formed in tropical latitudes, where it is observed high level salinity and evaporation.

Formation of deep masses caused by mixing of surface and intermediate water masses. This type of water is found in tropical latitudes. Their horizontal speed can be up to 28 km per hour. The temperature at depths of more than 1000 meters is approximately +2–3 degrees.

Bottom water masses characterized by very low temperatures, constant salinity levels and high density. This type of water occupies that part of the ocean that is deeper than 3000 meters.

Kinds

Depending on the territorial location, there are such types of water masses as equatorial, tropical, subtropical, temperate and polar.

Equatorial water masses are characterized by: low level density and salinity, high temperature (up to +28 degrees), low oxygen content.

Tropical water masses are in the zone of influence of ocean currents. The salinity of such masses is higher, since evaporation here prevails over precipitation.

Moderate masses are desalinated by rivers, precipitation and icebergs. These latitudes are characterized by seasonal changes in water temperatures, and the average annual temperature gradually decreases towards the poles from 10 to zero degrees.

The salinity level in the polar layers is quite low, since floating ice has a strong desalinating effect. At a temperature of about -2 degrees, sea ​​water medium salinity freezes (the higher the salinity, the lower the freezing point).

What are water masses?

Answering the question of what water masses are, it makes sense to talk about the processes occurring in the transition zones between them. When the masses meet, the waters mix, while the denser ones sink to depth. Such areas are called convergence zones.

In divergence zones, water masses diverge, accompanied by the rise of water from the depths.