What are the different types of water masses by latitude? Water masses of the world's oceans and frontal zones

The total mass of all waters of the World Ocean is divided by experts into two types - surface and deep. However, such a division is very conditional. A more detailed categorization includes the following several groups, distinguished based on territorial location.

Definition

First, let's define what water masses are. In geography, this designation refers to a fairly large volume of water that forms in one or another part of the ocean. Water masses differ from each other in a number of characteristics: salinity, temperature, as well as density and transparency. Differences are also expressed in the amount of oxygen and the presence of living organisms. We have given a definition of what water masses are. Now we need to look at their different types.

Water near the surface

Surface waters are those zones where their thermal and dynamic interaction with air occurs most actively. In accordance with the climatic characteristics inherent in certain zones, they are divided into separate categories: equatorial, tropical, subtropical, polar, subpolar. Schoolchildren who are collecting information to answer the question of what water masses are, also need to know about the depth of their occurrence. Otherwise, the answer in the geography lesson will be incomplete.

They reach a depth of 200-250 m. Their temperature often changes, since they are formed by water under the influence of precipitation. Waves, as well as horizontal ones, are formed in the thickness of surface water. This is where the largest number of fish and plankton are found. Between the surface and deep masses there is a layer of intermediate water masses. Their depth ranges from 500 to 1000 m. They are formed in areas of high salinity and high levels of evaporation.

Deep water masses

The lower limit of deep water can sometimes reach 5000 m. This type of water mass is most often found in tropical latitudes. They are formed under the influence of surface and intermediate waters. For those interested in what they are and what the characteristics of their various types are, it is also important to have an idea about the speed of currents in the ocean. Deep water masses move very slowly in the vertical direction, but their horizontal speed can be up to 28 km per hour. The next layer is bottom water masses. They are found at depths of over 5000 m. This type is characterized by a constant level of salinity, as well as a high level of density.

Equatorial water masses

“What are water masses and their types” is one of the compulsory topics of the general education school course. The student needs to know that waters can be classified into one group or another not only depending on their depth, but also on their territorial location. The first type mentioned in accordance with this classification is equatorial water masses. They are characterized by high temperature (reaches 28°C), low density, and low oxygen content. The salinity of such waters is low. There is a belt of low atmospheric pressure over the equatorial waters.

Tropical water masses

They are also quite well heated, and their temperature does not change by more than 4°C during different seasons. Ocean currents have a great influence on this type of water. Their salinity is higher, since in this climate zone there is a zone of high atmospheric pressure, and there is very little precipitation.

Moderate water masses

The salinity level of these waters is lower than that of others, because they are desalinated by precipitation, rivers, and icebergs. Seasonally, the temperature of water masses of this type can vary up to 10°C. However, the change of seasons occurs much later than on the mainland. Temperate waters vary depending on whether they are in the western or eastern regions of the ocean. The former, as a rule, are cold, and the latter are warmer due to warming by internal currents.

Polar water masses

Which water bodies are the coldest? Obviously, they are those located in the Arctic and off the coast of Antarctica. With the help of currents they can be carried to temperate and tropical areas. The main feature of polar water masses are floating blocks of ice and huge expanses of ice. Their salinity is extremely low. In the Southern Hemisphere, sea ice moves to temperate latitudes much more often than it does in the north.

Formation methods

Schoolchildren who are interested in what water masses are will also be interested in learning information about their formation. The main method of their formation is convection, or mixing. As a result of mixing, the water sinks to a considerable depth, where vertical stability is again achieved. This process can occur in several stages, and the depth of convective mixing can reach up to 3-4 km. The next method is subduction, or “diving.” With this method of forming masses, water sinks due to the combined action of wind and surface cooling.

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 nutrients 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 off the western coasts of the continents between tropical relatively cold waters and warm equatorial waters of inter-trade wind 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 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 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.

Surface water is a zone of active thermal and dynamic interaction

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. Having a lower temperature and, therefore, significant oxygen saturation, deep waters, rich in nutrients 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.

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.

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 off the western coasts of the continents between tropical relatively cold waters and warm equatorial waters of inter-trade wind 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.

1. The concept of water masses and biogeographical zoning

1.1 Types of water masses

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 waters goes south and southeast to 5-10° S. latitude.

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?10Î4 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.

1.2 Approaches and types of biogeographic classifications of water masses

Existing ideas about the water masses of the World Ocean, the areas and reasons for their formation, transport and transformation are extremely limited. At the same time, research into the entire diversity of water properties that occurs in real conditions is necessary not only to understand the structure and dynamics of water, but also to study the exchange of energy and substances, features of the development of the biosphere and other important aspects of the nature of the World Ocean.

Most intermediate, deep and bottom water masses are formed from surface ones. The subsidence of surface water occurs, as has already been said, mainly due to those vertical movements caused by horizontal circulation. Conditions are especially favorable for the formation of water masses in high latitudes, where the development of intense downward movements along the periphery of macrocirculation cyclonic systems is facilitated by higher water density and less significant vertical gradients than in the rest of the World Ocean. The boundaries of various types of water masses (surface, intermediate, deep and bottom) are the boundary layers separating structural zones. Similar water masses located within the same structural zone are separated by oceanic fronts. They are much easier to track near surface waters, where fronts are most pronounced. It is relatively easy to subdivide intermediate waters, which differ markedly in their properties from each other. It is more difficult to distinguish different types of deep and bottom waters given their homogeneity and still a rather weak idea of their movement. The use of new data (especially on the content of dissolved oxygen and phosphates in waters), which are good indirect indicators of water dynamics, made it possible to develop the previously developed general classification of water masses of the World Ocean. At the same time, the study of water masses conducted by A.D. was widely used in the Indian Ocean. Shcherbinin. The water masses of the Pacific and Arctic oceans have so far been less studied. Based on all available information, it was possible to clarify previously published schemes for the transfer of water masses in the meridional section of the oceans and construct maps of their distribution.

Surface water masses.Their properties and distribution limits are determined by zonal variability in the exchange of energy and substances and the circulation of surface waters. The following water masses are formed in the surface structural zone: 1) equatorial; 2) tropical, subdivided into north tropical and south tropical, their peculiar modification is the waters of the Arabian Sea and the Bay of Bengal; 3) subtropical, divided into northern and southern; 4) subpolar, consisting of subarctic and subantarctic; 5) polar, including Antarctic and Arctic. Equatorial surface water masses form within the equatorial anticyclonic system. Their boundaries are the equatorial and subequatorial fronts. They differ from other waters of low latitudes in having the highest temperature in the open ocean, minimal density, low salinity, oxygen and phosphate content, as well as a very complex system of currents, which, however, allows us to talk about the predominant transport of water from west to east by the Equatorial Countercurrent.

Tropical water masses are created in the tropical cyclonic macrocirculation system. Their boundaries are, on the one hand, tropical oceanic fronts, and on the other, the subequatorial front in the Northern Hemisphere, and the equatorial front in the Southern Hemisphere. In accordance with the prevailing rise of waters, the thickness of the layer they occupy is somewhat less than that of subtropical water masses, the temperature and oxygen content are lower, and the density and concentration of phosphates are slightly higher.

The waters of the northern Indian Ocean are noticeably different from other tropical water masses due to the peculiar moisture exchange with the atmosphere. In the Arabian Sea, due to the predominance of evaporation over precipitation, waters of high salinity up to 36.5 - 37.0‰ are created. In the Bay of Bengal, as a result of large river flows and the excess of precipitation over evaporation, the waters are highly desalinated; salinity from 34.0-34.5‰ in in the open part of the ocean gradually decreases towards the top of the Bay of Bengal to 32-31‰. Consequently, the waters of the northeastern part of the Indian Ocean are closer in their properties to the equatorial water mass, while in terms of their geographical location they are tropical.

Subtropical water masses are formed in subtropical anticyclonic systems. The boundaries of their distribution are tropical and subpolar oceanic fronts. Under conditions of prevailing downward movements, they receive the greatest development vertically. They are characterized by the maximum salinity for the open ocean, high temperature and minimum phosphate content.

Subantarctic waters, determining the natural conditions of the temperate zone of the southern part of the World Ocean, take an active part in the formation of intermediate waters as a result of downward movements in the zone of the subantarctic front.

In macrocirculation systems, due to vertical movements, intensive mixing of intermediate Antarctic waters with surface and deep waters occurs. In tropical cyclonic gyres, the transformation of water is so significant that it turned out to be advisable to distinguish here a special, eastern, type of intermediate Antarctic water mass.

2. Biogeographical zoning of the World Ocean

2.1 Faunal division of the littoral zone

Living conditions in the sea are determined by the vertical division of a given biocycle, as well as the presence or absence of a substrate for attachment and movement. Consequently, the conditions for the settlement of marine animals in the littoral, pelagic and abyssal zones are different. Because of this, it is impossible to create a unified scheme for zoogeographical zoning of the World Ocean, which is further aggravated by the very wide, often cosmopolitan distribution of most systematic groups of marine animals. That is why genera and species whose habitats have not been sufficiently studied are used as indicators of certain regions. In addition, different classes of marine animals give different distribution patterns. Taking into account all these arguments, the overwhelming majority of zoogeographers accept zoning schemes for marine fauna separately for the littoral and pelagic zones.

Faunal division of the littoral zone. The faunal division of the littoral zone is manifested very clearly, since individual areas of this biochore are quite strongly isolated both by land and climatic zones, and by wide stretches of the open sea.

There are the central Tropical region and the Boreal regions located to the north of it, and the Antiboreal regions to the south. Each of them has a different number of areas. The latter, in turn, are divided into subareas.

Tropical region. This region is characterized by the most favorable living conditions, which led to the formation here of the most complete harmoniously developed fauna, which did not know any breaks in evolution. The vast majority of classes of marine animals have their representatives in the region. The tropical zone, according to the nature of the fauna, is clearly divided into two regions: Indo-Pacific and Tropic-Atlantic.

Indo-Pacific region. This area covers the vast expanse of the Indian and Pacific Oceans between 40° N. w. and 40° S. sh., and only off the western coast of South America is its southern border sharply shifted to the north under the influence of cold currents. This also includes the Red Sea and the Persian Gulf, as well as countless straits between the islands.

Malay Archipelago and the Pacific Ocean. Favorable temperature conditions due to the large area of shallow waters and the stability of the environment over many geological periods have led to the development of an exceptionally rich fauna here.

Mammals are represented by dugongs (genus Halicore) from the sirenidae family, one species of which lives in the Red Sea, another in the Atlantic, and a third in the Pacific Ocean. These large animals (3-5 m in length) live in shallow bays, abundantly overgrown with algae, and occasionally enter the mouths of tropical rivers.

Of the seabirds associated with the coasts, small petrels and the giant albatross Diomedea exulans are typical of the Indo-Pacific region.

Sea snakes Hydrophiidae are represented by a large number (up to 50) characteristic species. All of them are poisonous, many have adaptations for swimming.

The fish of the marine fauna are extremely diverse. They are most often brightly colored, covered with multi-colored spots, stripes, etc. Of these, mention should be made of fused-jawed fish - diodon, tetradon and boxfish, parrot fish Scaridae, whose teeth form a continuous plate and are used for biting and crushing corals and algae, as well as surgeon fish armed with poisonous spines.

Coral reefs consisting of thickets of six-rayed (Madrepora, Fungia, etc.) and eight-rayed (Tubipora) corals reach enormous development in the sea. Coral reefs should be considered the most typical biocenosis of the Indo-Pacific littoral zone. Associated with them are numerous mollusks (Pteroceras and Strombus), distinguished by brightly painted and varied shells, giant tridacnids weighing up to 250 kg, as well as sea cucumbers, which serve as a commercial item (eaten in China and Japan under the name sea cucumber).

Among the marine annelids, we note the famous palolo. Masses of it rise to the surface of the ocean during the breeding season; eaten by Polynesians.

Local differences in the fauna of the Indo-Pacific region made it possible to distinguish the Indian-West Pacific, East Pacific, West Atlantic and East Atlantic subregions.

Tropico-Atlantic region. This region is much smaller in extent than the Indo-Pacific. It covers the littoral zone of the western and eastern (within the tropical Atlantic) coasts of America, the waters of the West Indies archipelago, as well as the western coast of Africa within the tropical zone.

The fauna of this area is much poorer than the previous one; only the West Indian seas with their coral reefs contain a rich and diverse fauna.

Sea animals here are represented by manatees (from the same sirenids), capable of going far into the rivers of tropical America and Africa. Pinnipeds include white-bellied seals, sea lions and the Galapagos fur seal. There are practically no sea snakes.

The fish fauna is diverse. It includes giant manta rays (up to 6 m in diameter) and large tarpon (up to 2 m in length), which are the object of sport fishing.

Coral reefs reach lush development only in the West Indies, but instead of Pacific madrepores, species of the genus Acropora, as well as hydroid corals Millepora, are common here. Crabs are extremely abundant and varied.

The littoral zone of the western coast of Africa has the poorest fauna, almost devoid of coral reefs and associated coral fish.

The region is divided into two subregions - Western Atlantic and Eastern Atlantic.

Boreal region. The region is located north of the Tropical Region and covers the northern parts of the Atlantic and Pacific Oceans. It is divided into three regions: Arctic, Boreo-Pacific and Boreo-Atlantic.

Arctic region. This area includes the northern coasts of America, Greenland, Asia and Europe, located outside the influence of warm currents (the northern coasts of Scandinavia and the Kola Peninsula, heated by the Gulf Stream, remain outside the area). The Okhotsk and Bering Seas also belong to the Arctic region in terms of temperature conditions and fauna composition. The latter corresponds to an ecological zone where the water temperature remains at 3-4 °C, and often lower. Ice cover remains here for most of the year; even in summer, ice floes float on the surface of the sea. The salinity of the Arctic Basin is relatively low due to the mass of fresh water brought by rivers. The fast ice characteristic of this area prevents the development of the littoral zone in shallow waters.

The fauna is poor and monotonous. The most typical mammals are walruses, hooded seals, the polar or bowhead whale, the narwhal (a dolphin with a hypertrophied left fang in the form of a straight horn) and the polar bear, whose main habitat is floating ice.

Birds are represented by gulls (primarily pink and polar gulls), as well as guillemots.

The fish fauna is poor: cod cod, navaga and polar flounder are common.

Invertebrates are more diverse and numerous. The small number of crab species is compensated by the abundance of amphipods, sea cockroaches and other crustaceans. Of the mollusks that are typical for Arctic waters, Yoldia arctica is typical, along with a lot of sea anemones and echinoderms. A peculiarity of Arctic waters is that starfish, urchins and brittle stars live here in shallow waters, which in other zones lead a deep-sea lifestyle. In a number of areas, the fauna of the littoral zone consists more than half of annelids sitting in calcareous tubes.

The uniformity of the fauna of a given region throughout its entire length makes it unnecessary to distinguish subregions within it.

Boreo-Pacific region. The region includes the coastal waters and shallow waters of the Sea of Japan and parts of the Pacific Ocean washing Kamchatka, Sakhalin and the northern Japanese Islands from the east, and in addition, the littoral zone of its eastern part - the coast of the Aleutian Islands, North America from the Alaska Peninsula to Northern California.

Ecological conditions in this area are determined by higher temperatures and their fluctuations depending on the time of year. There are several temperature zones: northern - 5-10°C (on the surface), middle - 10-15, southern - 15-20°C.

The Boreo-Pacific region is characterized by the sea otter, or sea otter, eared seals - fur seal, sea lion and sea lion; relatively recently, the Steller's sea cow Rhytina stelleri was found, completely destroyed by humans.

Typical fish are pollock, greenling and Pacific salmon - chum salmon, pink salmon, and chinook salmon.

Invertebrates of the littoral zone are diverse and abundant. They often reach very large sizes (for example, giant oysters, mussels, king crab).

Many species and genera of animals of the Boreo-Pacific region are similar to or identical to representatives of the Boreo-Atlantic region. This is the so-called amphiboreality phenomenon. This term denotes the type of distribution of organisms: they are found in the west and east of temperate latitudes, but are absent between them.

Thus, amphiboreality is one of the types of discontinuity in the ranges of marine animals. This type of gap is explained by the theory proposed by L.S. Berg (1920). According to this theory, the settlement of animals of boreal waters through the Arctic basin occurred both from the Pacific Ocean to the Atlantic, and vice versa, in eras when the climate was warmer than the modern one, and exit from the seas of the far north through the strait between Asia and America was carried out unhindered. Such conditions existed at the end of the Tertiary period, namely in the Pliocene. In the Quaternary period, a sharp cooling led to the disappearance of boreal species in high latitudes, zonation of the World Ocean was established and continuous habitats turned into broken ones, since the connection of inhabitants of temperate-warm waters through the polar basin became impossible.

The auks, the common seal, or seal Phoca vitulina, and many fish - smelt, sand lance, cod, and some flounders - have an amphiboreal distribution. It is also characteristic of a number of invertebrates - some mollusks, worms, echinoderms and crustaceans.

Boreo-Atlantic region. The area includes most of the Barents Sea, the Norwegian, North and Baltic Seas, the littoral zone of the east coast of Greenland, and finally the northeast Atlantic Ocean south to 36°N. The entire region is under the influence of the warm Gulf Stream, so its fauna is mixed, and along with the northern ones, it includes subtropical forms.

The harp seal is endemic. Seabirds - guillemots, razorbills, puffins - form giant nesting grounds (bird colonies). The most common fish are cod, among which is the endemic haddock. Flounder, catfish, scorpionfish, and gurnards are also numerous.

Among the various invertebrates, crayfish stand out - lobster, various crabs, hermit crabs; echinoderms - red starfish, beautiful brittle star “jellyfish head”; Of the bivalve mollusks, mussels and corsets are widespread. There are many corals, but they do not form reefs.

The Boreo-Atlantic region is usually divided into 4 subregions: Mediterranean-Atlantic, Sarmatian, Atlanto-Boreal and Baltic. The first three include the seas of the USSR - Barents, Black and Azov.

The Barents Sea is located at the junction of warm Atlantic and cold Arctic waters. In this regard, its fauna is mixed and rich. Thanks to the Gulf Stream, the Barents Sea has almost oceanic salinity and a favorable climate regime.

Its littoral population is diverse. Among the mollusks, edible mussels, large chitons, and scallops live here; from echinoderms - red starfish and urchin Echinus esculentus; from the coelenterates - numerous sea anemones and sessile jellyfish Lucernaria; Hydroids are also typical. Colossal aggregations are formed by the sea squirt Phallusia obliqua.

The Barents Sea is a high food sea. Fishing for numerous fish is widely developed here - cod, sea bass, halibut, and lumpfish. Non-commercial fish include spiny gobies, monkfish, etc.

The Baltic Sea, due to its shallow waters, limited connection with the North Sea, and also due to the rivers flowing into it, is highly desalinated. Its northern part freezes in winter. The fauna of the sea is poor and mixed in origin, since Arctic and even freshwater species join the Boreo-Atlantic ones.

The former include cod, herring, sprat and pipefish. Arctic species include the slingshot goby and the sea cockroach. Freshwater fish include pike perch, pike, grayling and vendace. It is interesting to note the almost complete absence of typical marine invertebrates here - echinoderms, crabs and cephalopods. Hydroids are represented by Cordylophora lacustris, marine mollusks - sea acorn Valanus improvisus, mussel and edible heart. Freshwater toothless moths, as well as pearl barley, are also found.

According to their fauna, the Black and Azov Seas belong to the Sarmatian subregion. These are typical inland bodies of water, since their connection with the Mediterranean Sea is only through the shallow Bosporus Strait. At depths below 180 m, the water in the Black Sea is poisoned with hydrogen sulfide and is devoid of organic life.

The fauna of the Black Sea is extremely poor. The littoral zone is inhabited by mollusks. The limpet Patella pontica, black mussel, scallops, heartfish and oyster are found here; small hydroids, sea anemones (from coelenterates) and sponges. The lancelet Amphioxus lanceolatus is endemic. Common fish include Labridae wrasses, Blennius blennies, scorpionfish, gobies, plumes, seahorses and even two species of stingrays. Dolphins stay off the coast - the panting dolphin and the bottlenose dolphin.

The mixedness of the fauna of the Black Sea is expressed by the presence of a certain number of Mediterranean species along with Black Sea-Caspian relics and species of freshwater origin. Mediterranean immigrants clearly predominate here, and the “mediterranization” of the Black Sea, as established by I.I. Puzanov, continues.

Antiboreal region. To the south of the Tropical region, similar to the Boreal region to the north, is the Antiboreal region. It includes the littoral of Antarctica and the subantarctic islands and archipelagos: South Shetland, Orkney, South Georgia and others, as well as the coastal waters of New Zealand, South America, southern Australia and Africa. It is along the Pacific coast of South America that, due to the cold southern current, the boundary of the Antiboreal region is advanced far to the north, to 6° S. w.

Based on the disconnection of the littoral areas of the region, two regions are distinguished in it: Antarctic and Antiboreal.

Antarctic region. The area includes the waters of three oceans washing the shores of Antarctica and nearby archipelagos. The conditions here are close to the Arctic, but even more severe. The boundary of floating ice runs approximately between 60-50° S. sh., sometimes slightly to the north.

The fauna of the region is characterized by the presence of a number of marine mammals: maned sea lion, southern seal, and true seals (leopard seal, Wedell seal, elephant seal). Unlike the fauna of the Boreal region, walruses are completely absent here. Among the birds of coastal waters, penguins should be mentioned first of all, living in huge colonies along the shores of all continents and archipelagos of the Antarctic region and feeding on fish and crustaceans. Especially famous are the emperor penguin Aptenodytes forsteri and the Adélie penguin Pygoscelis adeliae.

The Antarctic littoral is very unique due to the large number of endemic species and genera of animals. As is often observed in extreme conditions, relatively low species diversity corresponds to enormous population densities of individual species. Thus, the underwater rocks here are completely covered with accumulations of the sessile worm Cephalodiscus; in large numbers you can find sea urchins, stars and holothurians crawling along the bottom, as well as accumulations of sponges. Amphipod crustaceans are very diverse, and about 75% of them are endemic. In general, the Antarctic littoral, according to data from Soviet Antarctic expeditions, turned out to be much richer than could be expected, judging by the harsh temperature conditions.

Among both littoral and pelagic animals of the Antarctic region there are species that also live in the Arctic. This distribution is called bipolar. By bipolarity, as already noted, is meant a special type of disjunctive dispersal of animals, in which the ranges of similar or closely related species are located in polar or, more often, in moderately cold waters of the northern and southern hemispheres with a break in tropical and subtropical waters. When studying the deep-sea fauna of the World Ocean, it was discovered that organisms previously considered bipolar are characterized by a continuous distribution. Only within the tropical zone they are found at great depths, and in moderately cold waters - in the littoral zone. However, cases of true bipolarity are not that rare.

To explain the reasons that caused the bipolar spread, two hypotheses were proposed - relict and migration. According to the first, bipolar areas were once continuous and also covered the tropical zone, in which populations of certain species became extinct. The second hypothesis was formulated by Charles Darwin and developed by L.S. Berg. According to this hypothesis, bipolarity is the result of ice age events, when cooling affected not only Arctic and moderately cold waters, but also the tropics, which made it possible for northern forms to spread to the equator and further south. The end of the ice age and the new warming of the waters of the tropical zone forced many animals to move beyond its boundaries to the north and south or become extinct. In this way, gaps were formed. During their existence in isolation, the northern and southern populations managed to transform into independent subspecies or even close, but vicariating species.

Antiboreal region. The Antiboreal region proper covers the coasts of the southern continents located in the transition zone between the Antarctic region and the Tropical region. Its position is similar to that of the Boreo-Atlantic and Boreo-Pacific regions in the northern hemisphere.

The living conditions of animals in this region are much better compared to the conditions of other regions; its fauna is quite rich. In addition, it is constantly replenished by immigrants from the adjacent parts of the Tropical region.

The most typical and richest antiboreal fauna is the South Australian subregion. Marine animals here are represented by fur seals (genus Arctocephalus), elephant seals, crabeater seals and leopard seals; birds - several species of penguins from the genera Eudiptes (crested and little) and Pygoscelis (P. papua). Among invertebrates, endemic brachiopods (6 genera), worms Terebellidae and Arenicola, crabs of the genus Cancer, which are also found in the Boreo-Atlantic subregion of the northern hemisphere, should be mentioned.

The South American subregion is characterized by the fact that its littoral antiboreal fauna is distributed along the coast of South America far to the north. One species of fur seal, Arctocephalus australis, and the Humboldt penguin reach the Galapagos Islands. The movement of these and many other marine animals north along the eastern coast of the continent is facilitated by the Peruvian cold current and the rise of bottom waters to the surface. The mixing of water layers causes the development of a rich animal population. There are over 150 species of decapod crayfish alone, and half of them are endemic. Cases of bipolarity are also known in this subarea.

The South African subregion is small in area. It covers the Atlantic and Indian Ocean coasts of South Africa. In the Atlantic, its border reaches 17° south. w. (cold current!), and in the Indian Ocean only up to 24°.

The fauna of this subregion is characterized by the southern fur seal Arctocephalus pusillus, the penguin Spheniscus demersus, a mass of endemic mollusks, large crayfish - a special type of lobster Homarus capensis, numerous ascidians, etc.

2.2 Faunal division of the pelagic zone

The open parts of the World Ocean, where life occurs without connection with the substrate, are called pelagic zone. The upper pelagic zone (epipelagic) and the deep-sea zone (batypelagic) are distinguished. The epipelagic zone is divided according to the uniqueness of the fauna into Tropical, Boreal and Antiboreal regions, which, in turn, are divided into a number of regions.

Tropical region

The region is characterized by consistently high temperatures in the upper layers of water. The annual amplitudes of its fluctuations on average do not exceed 2 °C. The temperature of layers located deeper is much lower. In the waters of the region, there is a fairly significant species diversity of animals, but there are almost no huge concentrations of individuals of the same species. Many species of jellyfish, molluscs (pteropods and other pelagic forms), almost all appendiculars and salps are found only within the Tropical region.

Atlantic region. This area is distinguished by the following characteristic features of its fauna. Cetaceans are represented by Bryde's minke whale, and typical fish include mackerel, eels, flying fish, and sharks. Among the animals of the pleiston there is a brightly colored siphonophore - a strongly stinging physalia, or Portuguese man-of-war. A section of the tropical Atlantic called the Sargasso Sea is inhabited by a special community of pelagic animals. In addition to the neuston inhabitants already mentioned in the general description of the sea, the peculiar seahorses Hippocampus ramulosus and needlefish, the bizarre antennarius fish (Antennarius marmoratus), and many worms and mollusks find shelter on free-floating sargassum algae. It is noteworthy that the biocenosis of the Sargasso Sea is, in essence, a littoral community located in the pelagic zone.

Indo-Pacific region. The pelagic fauna of this area is characterized by the Indian minke whale Balaenoptera indica. However, there are other more widespread cetaceans here. Among the fish, the sailfish Istiophorus platypterus attracts attention, distinguished by its huge dorsal fin and the ability to reach speeds of up to 100-130 km/h; There is also a relative of the swordfish (Xiphias gladius) with a sword-shaped upper jaw, which is also found in the tropical waters of the Atlantic.

Boreal region

This region combines cold and moderately cold waters of the Northern Hemisphere. In the Far North, most of them are covered with ice in winter, and even in summer individual ice floes are visible everywhere. Salinity is relatively low due to the huge masses of fresh water brought by rivers. The fauna is poor and monotonous. To the south, to about 40° N. sh., there is a strip of waters where their temperature fluctuates greatly and the animal world is comparatively richer. The main area for commercial fish production is located here. The region's waters can be divided into 2 regions - Arctic and Euboreal.

Arctic region. The pelagic fauna of this area is poor, but very expressive. It includes cetaceans: the bowhead whale (Balaena mysticetus), the fin whale (Balaenoptera physalus) and the unicorn dolphin or narwhal (Monodon monocerus). Fish are represented by the polar shark (Somniosus microcephalus), capelin (Mallotus villosus), which feed on gulls, cod and even whales, and several forms of eastern herring (Clupea pallasi). Clion mollusks and calanus crustaceans, which reproduce in huge masses, constitute the usual food of toothless whales.

Euboreal region. The pelagic region covers the northern parts of the Atlantic and Pacific Oceans south of the Arctic region and north of the tropics. Temperature fluctuations in the waters of this area are quite significant, which distinguishes them from arctic and tropical waters. There are differences in the species composition of the fauna of the boreal parts of the Atlantic and Pacific oceans, but the number of common species is large (amphiboreality). The fauna of the Atlantic pelagic zone includes several species of whales (Biscay, humpback, bottlenose) and dolphins (pilot whale and bottlenose dolphin). Common pelagic fish include Atlantic herring Clupea harengus, mackerel, or mackerel, tuna Thynnus thunnus, which is not uncommon in other parts of the World Ocean, swordfish, cod, haddock, sea bass, sprat, and in the south - sardine and anchovy.

The giant shark Cetorhinus maximus is also found here, feeding on plankton, like baleen whales. Of the vertebrates of the pelagic zone, we note the jellyfish - cordate and cornerota. In addition to amphiboreal species, the pelagic zone of the boreal Pacific Ocean is inhabited by whales - Japanese and gray, as well as many fish - Far Eastern herring Clupea pallasi, sardines (Far Eastern Sardinops sagax and Californian S. s. coerulea species), Japanese mackerel (Scomber japonicus) are common. and king mackerel (Scomberomorus), from Far Eastern salmon - chum salmon, pink salmon, chinook salmon, sockeye salmon. Among invertebrates, Chrysaora and Suapea jellyfish, siphonophores, and salps are widespread.

Anti-boreal region

To the south of the Tropical region there is a belt of the World Ocean, which is distinguished as the Antiboreal region. Like its counterpart in the north, it is also characterized by harsh environmental conditions.

The pelagic zone of this region is inhabited by a single fauna, since there are no barriers between the waters of the oceans. Cetaceans are represented by the southern (Eubalaena australis) and dwarf (Caperea marginata) whales, humpback whales (Megaptera novaeangliae), sperm whales (Physeter catodon) and minke whales, which, like many other whales, migrate widely throughout all oceans. Among the fish, it is necessary to mention bipolar ones - anchovy, sardine of a special subspecies (Sardinops sagax neopilchardus), as well as notothenia, characteristic only of the anti-boreal fauna - Notothenia rossi, N. squamifrons, N. larseni, which are of great commercial importance.

As in the littoral zone, the Antiboreal and Antarctic regions can be distinguished here, but we will not consider them, since the faunal differences between them are small.

3. Classification of vertical structure related to the temperature of water masses and the content of living organisms in it

The aquatic environment is characterized by less heat inflow, since a significant part of it is reflected, and an equally significant part is spent on evaporation. Consistent with the dynamics of land temperatures, water temperatures exhibit smaller fluctuations in daily and seasonal temperatures. Moreover, reservoirs significantly equalize the temperature in the atmosphere of coastal areas. In the absence of an ice shell, the seas have a warming effect on the adjacent land areas in the cold season, and a cooling and moistening effect in the summer.

The range of water temperatures in the World Ocean is 38° (from -2 to +36 °C), in fresh water bodies - 26° (from -0.9 to +25 °C). With depth, the water temperature drops sharply. Up to 50 m there are daily temperature fluctuations, up to 400 - seasonal, deeper it becomes constant, dropping to +1-3 °C (in the Arctic it is close to 0 °C). Since the temperature regime in reservoirs is relatively stable, their inhabitants are characterized by stenothermism. Minor temperature fluctuations in one direction or another are accompanied by significant changes in aquatic ecosystems.

Examples: a “biological explosion” in the Volga delta due to a decrease in the level of the Caspian Sea - the proliferation of lotus thickets (Nelumba kaspium), in southern Primorye - the overgrowth of whitefly in oxbow rivers (Komarovka, Ilistaya, etc.) along the banks of which woody vegetation was cut down and burned.

Due to varying degrees of heating of the upper and lower layers throughout the year, ebbs and flows, currents, and storms, constant mixing of water layers occurs. The role of water mixing for aquatic inhabitants (aquatic organisms) is extremely important, since this equalizes the distribution of oxygen and nutrients within reservoirs, ensuring metabolic processes between organisms and the environment.

In stagnant reservoirs (lakes) of temperate latitudes, vertical mixing takes place in spring and autumn, and during these seasons the temperature throughout the reservoir becomes uniform, i.e. comes homothermy.In summer and winter, as a result of a sharp increase in heating or cooling of the upper layers, the mixing of water stops. This phenomenon is called temperature dichotomy, and the period of temporary stagnation is called stagnation (summer or winter). In summer, lighter warm layers remain on the surface, located above heavy cold ones (Fig. 3). In winter, on the contrary, there is warmer water in the bottom layer, since directly under the ice the temperature of surface waters is less than +4 °C and, due to the physicochemical properties of water, they become lighter than water with a temperature above +4 °C.

During periods of stagnation, three layers are clearly distinguished: the upper (epilimnion) with the sharpest seasonal fluctuations in water temperature, the middle (metalimnion or thermocline), in which a sharp jump in temperature occurs, and the bottom (hypolimnion), in which the temperature changes little throughout the year. During periods of stagnation, oxygen deficiency occurs in the water column - in the bottom part in summer, and in the upper part in winter, as a result of which fish kills often occur in winter.

Conclusion

Biogeographical zoning is the division of the biosphere into biogeographic regions that reflect its basic spatial structure. Biogeographical zoning is a section of biogeography that summarizes its achievements in the form of schemes of general biogeographic division. Biogeographical zoning division considers the biota as a whole as a set of floras and faunas and their biocenotic territorial complexes (biomes).

The main option (basic) of universal biogeographical zoning is the natural state of the biosphere without taking into account modern anthropogenic disturbances (deforestation, plowing, catching and extermination of animals, accidental and intentional introduction of foreign species, etc.). Biogeographical zoning is developed taking into account the general physical and geographical patterns of distribution of biotas and their regional, historically developed isolated complexes.

This course work examined the methodology of biogeographic zoning of the World Ocean, as well as the stages of biogeographic research. Summing up the results of the work performed, we can conclude that the set goals and objectives were achieved:

Methods for researching the World Ocean were studied in detail.

The zoning of the World Ocean is considered in detail.

The exploration of the World Ocean has been studied in stages.

Bibliography

1.Abdurakhmanov G.M., Lopatin I.K., Ismailov Sh.I. Fundamentals of zoology and zoogeography: A textbook for students. higher ped. textbook establishments. - M.: Publishing center "Academy", 2001. - 496 p.

2.Belyaev G.M., Bottom fauna of the greatest depths (ultra-abyssal) of the world ocean, M., 1966

.Darlington F., Zoogeography, trans. from English, M., 1966

.Kusakin O.G., To the fauna of Isopoda and Tanaidacea of shelf zones of Antarctic and subantarctic waters, ibid., vol. 3, M. - L., 1967 [v. 4 (12)]

.Lopatin I.K. Zoogeography. - Mn.: Higher School, 1989

.Pacific Ocean, vol. 7, book. 1-2, M., 1967-69. Ekman S., Zoogeography of the sea, L., 1953.

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Large volumes of water are called water masses, and their regular spatial combination is called the hydrological structure of a reservoir. The main indicators of water masses in reservoirs, which make it possible to distinguish one water mass from another, are such characteristics as density, temperature, electrical conductivity, turbidity, water transparency and other physical indicators; water mineralization, content of individual ions, gas content in water and other chemical indicators; content of phyto- and zooplankton and other biological indicators. The main property of any water mass in a reservoir is its genetic homogeneity.

According to their genesis, two types of water masses are distinguished: primary and main.

Per primary water masses lakes are formed in their catchment areas and enter reservoirs in the form of river runoff. The properties of these water masses depend on the natural characteristics of the catchment areas and change seasonally depending on the phases of the hydrological regime of the rivers. The main feature of the primary water masses of the flood phase is low mineralization, increased water turbidity, and a fairly high content of dissolved oxygen. The temperature of the primary water mass during the heating period is usually higher, and during the cooling period, lower than in the reservoir.

Main water masses are formed in the reservoirs themselves; their characteristics reflect the features of the hydrological, hydrochemical and hydrobiological regimes of water bodies. Some of the properties of the main water masses are inherited from the primary water masses, some are acquired as a result of intra-reservoir processes, as well as under the influence of the exchange of matter and energy between the reservoir, the atmosphere and bottom soils. Although the main water masses change their properties throughout the year, they generally remain more inert than the primary water masses. (The surface water mass is the upper most heated layer of water (epilimnion); the deep water mass is usually the thickest and relatively homogeneous layer of colder water (hypolimnion); the intermediate water mass corresponds to the temperature jump layer (metalimnion); the bottom water mass is a narrow layer of water at the bottom, characterized by increased mineralization and specific aquatic organisms.)

The influence of lakes on the natural environment is manifested primarily through river flow.

A distinction is made between the general constant impact of lakes on the water cycle in river basins and the regulatory impact on the intra-annual regime of rivers. The main influence of land wastewater bodies on the continental part of the water cycle (as well as salts, sediments, heat, etc.) is the slowdown of water, salt - and heat exchange in the hydrographic network. Lakes (like reservoirs) are accumulations of water that increase the capacity of the hydrographic network. The lower intensity of water exchange in river systems, including lakes (and reservoirs), has a number of serious consequences: accumulation of salts, organic matter, sediment, heat and other components of river flow (in the broad sense of the term) in reservoirs. Rivers flowing from large lakes, as a rule, carry less salts and sediments (Selenga River - Lake Baikal). In addition, waste lakes (like reservoirs) redistribute river flow over time, exerting a regulatory effect on it and leveling it throughout the year. Land reservoirs have a noticeable impact on local climatic conditions, reducing the continental climate and increasing the duration of spring and autumn, on inland moisture circulation (slightly), contributing to increased precipitation, the appearance of fogs, etc. Reservoirs also influence the groundwater level, generally increasing it , on the soil-vegetation cover and fauna of adjacent territories, increasing the diversity of species composition, abundance, biomass, etc.

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, is of great importance. 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. Intermediate water masses are formed under conditions of increased evaporation and constant increase. 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. Formed 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 water: they give it heat and moisture, absorb carbon dioxide from it, and release oxygen.

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 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 atmospheric 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. This is where the warm, salty water of the North Atlantic Current mixes with the cold, fresher water of the 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

There are no conditions for the formation of such a water mass in the Pacific Ocean.

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.

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 there is a high level of 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 levels of 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 of average 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.

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 extends into temperate latitudes much further than in the Northern Hemisphere. The salinity of polar water masses is low, since floating ice has a strong desalination effect.

There are no clear boundaries between different types of water masses that differ in origin, 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.

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