Water mass. Water masses of the oceans and frontal zones What are the water masses

The entire mass of the waters of the World Ocean is conditionally divided into surface and deep. Surface waters - a layer 200–300 m thick - are very heterogeneous in terms of natural properties; they can be called oceanic troposphere. The rest of the water ocean Stratosphere, constituting the main mass of waters, is more homogeneous.

Surface waters - a zone of active thermal and dynamic interaction

ocean and atmosphere. In accordance with zonal climatic changes, they are subdivided into various water masses, primarily according to 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.

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

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

Tropical water masses(5– 35° N sh. and 0–30°S sh.) are distributed along the equatorial peripheries of subtropical baric maxima; they form trade winds. The temperature in summer reaches +26...+28°C, in winter it drops to +18...+20°C, and it differs near the western and eastern coasts due to currents and coastal stationary upwellings and downwellings. Upwelling(English, upwelling- floating) - the upward movement of water from a depth of 50–100 m, generated by offshore winds near the western coasts of the continents in a band of 10–30 km. Possessing a low temperature and, in connection with this, a significant saturation with oxygen, deep waters, rich in biogenic and mineral substances, entering the surface illuminated zone, increase the productivity of the water mass. Downwellings- descending flows near the eastern coasts of the continents due to the surge of water; they bring heat and oxygen down. The temperature jump layer is expressed throughout the year, salinity is 35–35.5‰, oxygen content is 2–4 g/m 3 .

Subtropical water masses have the most characteristic and stable properties in the "core" - circular water areas, limited by large rings of currents. The temperature during the year varies from 28 to 15°C, there is a layer of temperature jump. Salinity 36–37‰, oxygen content 4–5 g/m 3 . In the center of the cycles, the waters sink. In warm currents, subtropical water masses penetrate into temperate latitudes up to 50 ° N. sh. and 40–45°S sh. These transformed subtropical water masses here occupy almost the entire water area of the Atlantic, Pacific and Indian oceans. Cooling, subtropical waters give off 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. For them, a variety of characteristics is typical both for the seasons of the year and for the hemispheres. The 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/m 3 , so the waters are rich in life forms. These water masses occupy the north of the Atlantic and the Pacific Ocean, penetrating in cold currents along the eastern coasts of the continents into temperate latitudes. In the southern hemisphere, they form a continuous zone south of all continents. In general, this is the western circulation of air and water masses, a strip of storms.

Polar water masses in the Arctic and around Antarctica, they have a low temperature: in summer about 0 ° C, in winter -1.5 ... -1.7 ° C. Brackish sea and fresh continental ice and their fragments are constant here. There is no temperature jump layer. Salinity 32–33‰. The maximum amount of oxygen dissolved in cold waters is 5–7 g/m 3 . On the border with subpolar waters, dense cold waters sink, especially in winter.

Each water mass has its own source of formation. When water masses with different properties meet, they form ocean fronts, or convergence zones (lat. converge- I'm going). They usually form at the junction of warm and cold surface currents and are characterized by the sinking 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 near the eastern coasts of the continents at 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 velocities, seasonal temperature fluctuations, wind wave sizes, amount of fog, cloudiness, etc.) reach extreme values. To the east, due to the mixing of waters, frontal contrasts are blurred. It is in these zones that frontal cyclones of extratropical latitudes originate. Two frontal zones also exist on both sides of the thermal equator near the western coasts of the continents between relatively cold tropical waters and warm equatorial waters of the trade wind countercurrents. They are also distinguished by high values of hydrometeorological characteristics, high dynamic and biological activity, and intense interaction between the ocean and the atmosphere. These are 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: near the western coasts of the continents of temperate latitudes and above the thermal equator near the eastern coasts of the continents. Such zones are rich in phyto- and zooplankton, are distinguished 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 water subsidence predominates. Their properties are somewhat different depending on the latitude of distribution. The total transport of these waters is directed from high latitudes to the equator.

Deep and especially near-bottom waters (the thickness of the layer of the latter is 1000–1500 m above the bottom) are distinguished by high uniformity (low temperatures, richness of oxygen) and slow speed of movement in the meridional direction from the polar latitudes to the equator. Especially widespread are Antarctic waters, "sliding" from the continental slope of Antarctica. They not only occupy the entire southern hemisphere, but also reach 10–12°N. sh. in the Pacific Ocean, up to 40 ° N. sh. in the Atlantic and to the Arabian Sea in the 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 gives the atmosphere the bulk of the heat, converting the radiant energy of the sun into heat. The ocean is a huge distiller, supplying the land with fresh water through the atmosphere. The heat entering the atmosphere from the oceans causes different atmospheric pressures. The difference in pressure creates wind. 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.

water masses

the volume of water, commensurate with the area and depth of the reservoir and having a relative uniformity of physico-chemical characteristics that are formed in specific physiographic conditions. The main factors that form V. m. are the heat and water balances of a given region and, consequently, the main indicators of V. m. are temperature and salinity. Often, in the analysis of W. m., indicators of the content of oxygen and other hydrochemical elements in it are also taken into account, which make it possible to trace the spread of W. m. from the region of its formation and transformation. The characteristics of the windmill do not remain constant; they are subject to seasonal and long-term fluctuations within certain limits and change in space. As they spread from the region of their formation, water waves are transformed under the influence of changes in the conditions of heat and water balances and mix with the surrounding waters. Primary and secondary water waves are distinguished. Primary water waves are those whose distinguishing features are formed under the direct influence of the atmosphere and are characterized by the greatest limits of change in a certain volume of water. To the secondary - V. m., which are formed as a result of mixing of primary V. m. and are distinguished by the greatest uniformity of their features. In the vertical structure of the World Ocean, water waves are distinguished: surface (primary) - up to a depth of 150-200 m; subsurface (primary and secondary) - at a depth of 150-200 m up to 400-500 m; intermediate (primary and secondary) - at a depth of 400-500 m up to 1000-1500 m, deep (secondary) - at a depth of 1000-1500 m up to 2500-3000 m; bottom (secondary) - below 3000 m. The boundaries between the V. m. are the zones of the fronts of the World Ocean, the separation zone, and the transformation zone, which can be traced along the increasing horizontal and vertical gradients of the main indicators of V. m.

Each of the oceans has its own characteristic waters. For example, in the Atlantic Ocean there are different types of waters: the Gulf Stream, the northern tropical, the southern tropical, and other surface waters, the northern subtropical, the southern subtropical, and other subsurface waters. m., North Atlantic, South Atlantic, and other intermediate V. m., Mediterranean deep V. m., etc.; in the Pacific Ocean, the northern tropical, northern central subtropical, southern tropical, and other surface seas, the northern subtropical, southern subtropical, and other subsurface seas, the northern Pacific, southern Pacific, and other intermediate seas. , Pacific deep V. m., etc.

The method of T, S-curves, and the isopycnal method is used in the study of water levels, which make it possible to establish the uniformity of temperature, salinity, and other indicators on the curve of their vertical distribution.

Lit.: Agerov VK, On the main water masses in the hydrosphere, M. - Sverdlovsk, 1944; Zubov N. N., Dynamic Oceanology, M. - L., 1947; Muromtsev A. M., Main features of the hydrology of the Pacific Ocean, L., 1958; his, Basic features of the hydrology of the Indian Ocean, L., 1959; Dobrovolsky A.D., On the determination of water masses, "Oceanology", 1961, vol. 1, c. one; Basic Features of the Hydrology of the Atlantic Ocean, ed. A. M. Muromtseva. Moscow, 1963. Defant A., Dynamische Ozeanographie, B., 1929; Sverdrup H. U., Jonson M. W., Fleming R. H., The oceans, Englewood Cliffs, 1959.

A. M. Muromtsev.

Great Soviet Encyclopedia. - M.: Soviet Encyclopedia. 1969-1978 .

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The water masses of the World Ocean can be divided into types characterized by certain properties or a certain ratio of various characteristics. The name of each Water mass reflects the area of formation (source) and the ways of its movement. For example, Antarctic bottom water is formed in various areas around the Antarctic continent and is found near the bottom in large areas of the ocean. Water masses are formed either as a result of thermohaline changes due to the interaction of the sea and the atmosphere, or as a result of the mixing of two or more waters. After formation, the Water mass shifts to a horizon determined by its density, depending on the vertical distribution of the density of the surrounding water, and, gradually mixing or interacting with the atmosphere (if the Water mass spreads near the surface or on horizons close to the surface), loses its characteristic feature (or traits), which she acquired in the area of formation.

The main water masses of the World Ocean are formed as a result of thermohaline changes. Such Water masses have an extremum in one or more characteristics. The layer in which this extremum is observed (the depth of the layer is determined by the density of water) is called the middle layer. This layer can be found in the study of the vertical distribution of the typical properties of V. m.

The largest part of the surface and subsurface water masses are the central water masses, which are found in temperate latitudes in both hemispheres. They are characterized by high salinity and rather high temperatures and can be subdivided into such subtypes as the western and eastern central water masses. It is these water masses that are the source of the middle layer with a low salinity maximum (subtropical countercurrent), which is formed as a result of subsidence of surface waters in subtropical convergence zones (35-40° N and S) in most tropical regions of the ocean. Between the central water masses of the northern and southern hemispheres is equatorial water. This water mass is well developed in the Pacific and Indian Oceans, but it is absent in the Atlantic Ocean.

In the direction towards the poles, the central water masses are cooling, which is associated with the melting of ice and the temperature contrast between water and the atmosphere. Between the polar surface water masses and deep waters there are waters of the intermediate zone—subarctic and subantarctic surface waters. At the junction of the water masses of the intermediate zone, the waters sink along the convergence zone. This zone, or polar front, can be considered as the area of formation of intermediate water masses of the World Ocean. They are cold, have low salinity and separate the upper warm water sphere from the lower cold one. In the Atlantic Ocean, the most common intermediate water mass is the Antarctic intermediate water, which forms within the southern polar front; it can be traced by the "kernel method" up to 20°N. sh. To the north of this latitude there is a middle layer with a weakly pronounced salinity minimum.

Subarctic intermediate water occurs at more northerly latitudes, but is much less pronounced and does not spread as widely as Antarctic intermediate water.

Due to the shallowness of the Bering Strait, circulation between the Arctic Ocean and the North Pacific is limited; therefore, the subarctic intermediate water in the Pacific Ocean has a small distribution. However, off the coast of Russia, the water sinks and the formation of an intermediate water mass, very similar to the subarctic one; since this water mass is of Nearctic origin, it is called the North Pacific Intermediate Water.

Deep and bottom waters are formed in the polar regions, most actively around the Antarctic continent and in the regions adjacent to South Greenland. The influence of the Arctic Basin on the deep-water circulation of the World Ocean is insignificant due to the separation of the depths of the Arctic Basin by underwater ridges - rapids. It is assumed that the source of most of the deep and bottom waters is the Atlantic sector of the Southern Ocean (the Weddell Sea). Strong deep-sea circulation leads to the fact that the influence of the Atlantic Ocean is felt in most areas of the World Ocean. The Pacific Ocean does not have large sources of deep water and therefore the flow below 2000 m is probably weak. The Indian Ocean has a complex deep water system that depends more on the mixing of many other Water masses than on the formation of Water mass types as a result of thermohaline changes.

The formation of water masses occurs in accordance with the geophysical conditions of individual regions of the World Ocean. In the process of genesis, significant volumes of water acquire a set of characteristic physicochemical and biological properties, which remains practically unchanged within 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 due to geographic latitude. Precipitation and evaporation play the main role in changing the salinity of waters. The 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 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 layer thickness is 200–250 meters.

Intermediate water masses located at a depth of 500-1000 meters. They form in tropical latitudes, where there is a high level of salinity and evaporation.

Formation of deep masses caused by the 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 very low temperatures, constant salinity 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 density and salinity, high temperature (up to +28 degrees), low oxygen content.

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

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

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

What are water masses?

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

In the zones of divergence, there is a divergence of water masses, accompanied by the rise of water from the depths.

physical and geographical conditions. The main factors shaping water masses, are the heat and water balances of the given area and, consequently, the main indicators water masses- temperature and salinity. Often in analysis water masses indicators of the content of oxygen and other hydrochemical elements in it are also taken into account, which make it possible to trace the distribution water masses from the region of its formation and transformation. Characteristics water masses do not remain constant, they are subject to seasonal and long-term fluctuations within certain limits and change in space. As it spreads from the area of formation water masses are transformed under the influence of changes in the conditions of thermal and water balances and are mixed with surrounding waters. Distinguish between primary and secondary water masses to primary water masses include those whose distinctive features are formed under the direct influence of the atmosphere and are characterized by the greatest limits of change in a certain volume of water. To the secondary water masses formed as a result of mixing of primary water masses and characterized by the greatest homogeneity of their characteristics. In the vertical structure of the World Ocean, there are water masses: surface (primary) - up to a depth of 150-200 m; subsurface (primary and secondary) - at a depth of 150-200 m up to 400-500 m; intermediate (primary and secondary) - at a depth of 400-500 m up to 1000-1500 m, deep (secondary) - at a depth of 1000-1500 m up to 2500-3000 m; bottom (secondary) - below 3000 m. borders between water masses are zones of fronts of the World Ocean, zones of separation and zones of transformation, which can be traced along the increasing horizontal and vertical gradients of the main indicators water masses

Each of the oceans has its own characteristic water masses For example, in the Atlantic Ocean there are: water masses Gulf Stream, Northern Tropical, Southern Tropical, etc. Surface water masses water masses, North Atlantic, South Atlantic and other intermediate water masses, Mediterranean deep water masses and etc.; in the Pacific Ocean - Northern tropical, Northern central subtropical, Southern tropical and other surface water masses, Northern subtropical, Southern subtropical and other subsurface water masses, North Pacific, South Pacific and other intermediate water masses, Pacific deep water masses and etc.

When studying water masses the T, -kp method and the isopycnal method are used, which make it possible to establish the uniformity of temperature, salinity, and other indicators on the curve of their vertical distribution.