The properties and dynamics of ocean waters, the exchange of energy and substances both in the World Ocean and between the oceanosphere and atmosphere strongly depend on the processes that determine the nature of our entire planet. At the same time, the World Ocean itself has an extremely strong influence on planetary processes, that is, on those processes that are associated with the formation and change in the nature of the entire globe.
The main ocean fronts almost coincide in position with atmospheric fronts. The significance of the main fronts is that they delimit the warm and highly saline sphere of the World Ocean from the cold and low-salinity one. Through the main fronts within the ocean column, properties are exchanged between low and high latitudes and the final phase of this exchange is completed. In addition to hydrological fronts, ocean climatic fronts are distinguished, which is especially important, since ocean climatic fronts, having a planetary scale, emphasize the general picture of the zonal distribution of oceanological characteristics and the structure of the dynamic water circulation system on the surface of the World Ocean. They also serve as the basis for climate zoning. Currently, within the oceanosphere there is a fairly wide variety of fronts and frontal zones. They can be considered as boundaries of waters with different temperatures and salinity, currents, etc. The combination in space of water masses and boundaries between them (fronts) forms the horizontal hydrological structure of waters individual areas and the Ocean as a whole. According to the law geographical zoning The following most important types in the horizontal structure of waters are distinguished: equatorial, tropical, subtropical, subarctic (subpolar) and subantarctic, arctic (polar) and Antarctic. Each horizontal structural zone has, accordingly, its own vertical structure, for example, equatorial surface structural zone, equatorial intermediate, equatorial deep, equatorial bottom and vice versa; in each vertical structural layer, horizontal structural zones can be distinguished. In addition, within each horizontal structure, more subdivisions are distinguished, for example, the Peru-Chilean or Californian structure, etc., which ultimately determines the diversity of the waters of the World Ocean. The boundaries of separation of vertical structural zones are boundary layers, and the most important types of waters of horizontal structure are ocean fronts.
· Vertical structure of ocean waters
In each structure, water masses of the same vertical location in different geographical regions have different properties. Naturally, the water column near the Aleutian Islands, or off the coast of Antarctica, or at the equator differs in all its physical, chemical and biological characteristics. However, water masses of the same type are connected by their common origin, similar conditions of transformation and distribution, and seasonal and long-term variability.
Surface water masses are most susceptible to the hydrothermodynamic influence of the entire complex of atmospheric conditions, particularly the annual variation of air temperature, precipitation, winds, and humidity. When transported by currents from areas of formation to other areas, surface waters are relatively quickly transformed and acquire new qualities.
Intermediate waters are formed mainly in zones of climatically stationary hydrological fronts or in seas of the Mediterranean type in the subtropical and tropical zones. In the first case, they are formed as desalinated and relatively cold, and in the second - as warm and salty. Sometimes an additional structural unit is identified - subsurface intermediate waters, located at a relatively shallow depth below the surface ones. They form in areas of intense evaporation from the surface (salty waters) or in areas of strong winter cooling in the subarctic and arctic regions of the oceans (cold intermediate layer).
The main feature of intermediate waters in comparison with surface waters is their almost complete independence from atmospheric influence along the entire path of distribution, although their properties at the source of formation differ in winter and summer. Their formation apparently occurs by convective means on the surface and in subsurface layers, as well as due to dynamic subsidence in zones of fronts and current convergences. Intermediate waters spread mainly along isopycnal surfaces. Tongues of increased or decreased salinity, found on meridional sections, cross the main zonal jets of oceanic circulation. The movement of intermediate water nuclei in the direction of the tongues still does not have a satisfactory explanation. It is possible that it is carried out by lateral (horizontal) mixing. In any case, the geostrophic circulation in the core of intermediate waters repeats the main features of the subtropical circulation cycle and does not differ in extreme meridional components.
Deep and bottom water masses are formed at the lower boundary of intermediate waters by mixing and transforming them. But the main centers of origin of these waters are considered to be the shelf and continental slope of Antarctica, as well as the Arctic and subpolar regions of the Atlantic Ocean. Thus, they are associated with thermal convection in the polar zones. Since convection processes have a pronounced annual course, the intensity of formation and cyclicality in time and space of the properties of these waters should have seasonal variability. But these processes have hardly been studied.
The listed community of water masses that make up the vertical structure of the ocean gave grounds for introducing a generalized concept of structural zones. The exchange of properties and mixing of waters in the horizontal direction occur at the boundaries of the main macro-scale elements of water circulation, along which hydrological fronts pass. Thus, the water areas of water masses are directly connected with the main water cycles.
Based on analysis large quantity Based on averaged T, S-curves, 9 types of structures (from north to south) were identified throughout the Pacific Ocean: subarctic, subtropical, tropical and eastern tropical northern, equatorial, tropical and subtropical southern, subantarctic, antarctic. The northern subarctic and both subtropical structures have eastern varieties, due to the specific regime of the eastern part of the ocean off the coast of America. The northern eastern tropical structure also gravitates toward the coasts of California and southern Mexico. The boundaries between the main types of structures are elongated in the latitudinal direction, with the exception of the eastern varieties, in which the western boundaries have a meridional orientation.
The boundaries between the types of structures in the northern part of the ocean are consistent with the boundaries of the types of stratification of the vertical profiles of temperature and salinity, although the source materials and the methods for their preparation are different. Moreover, a combination of vertical T- and S-profile types define structures and their boundaries in much more detail.
The subarctic structure of waters has a vertically monotonous increase in salinity and a more complex change in temperature. At depths of 100 - 200 m in the cold subsurface layer, the largest salinity gradients are observed throughout the vertical. A warm intermediate layer (200 - 1000 m) is observed when salinity gradients weaken. The surface layer (up to 50 - 75 m) is subject to sharp seasonal changes in both properties.
Between 40 and 45° N. w. there is a transition zone between the subarctic and subtropical structures. Moving east from 165° - 160° W. etc., it directly passes into the eastern varieties of subarctic, subtropical and tropical structures. On the surface of the ocean, at depths of 200 m and partly at 800 m, throughout this entire zone there are waters with similar properties that belong to the subtropical water mass.
The subtropical structure is divided into layers containing corresponding water masses of varying salinity. The subsurface layer of high salinity (60 - 300 m) is characterized by increased vertical temperature gradients. This leads to the preservation of stable vertical stratification of waters by density. Below 1000 - 1200 m there are deep waters, and below 3000 m there are bottom waters.
Tropical waters have significantly higher surface temperatures. The subsurface high-salinity layer is thinner but has higher salinity.
In the intermediate layer, the reduced salinity is expressed sharply due to the distance from the source of formation on the subarctic front.
The equatorial structure is characterized by a surface desalinated layer (up to 50 - 100 m) with a high temperature in the west and a significant decrease in it in the east. Salinity also decreases in the same direction, forming an eastern equatorial-tropical water mass off the coast of Central America. The subsurface layer of increased salinity occupies an average thickness of 50 to 125 m, and in terms of salinity values it is slightly lower than in the tropical structures of both hemispheres. The intermediate water here is of southern, subantarctic origin. Along the long path, it is intensively eroded, and its salinity is relatively high - 34.5 - 34.6%. In the north of the equatorial structure, two layers of low salinity are observed.
The structure of waters in the southern hemisphere has four types. Directly adjacent to the equator is a tropical structure that extends south to 30° S. w. in the west and up to 20° south. w. in the east of the ocean. It has the highest salinity on the surface and in the subsurface layer (up to 36.5°/oo), as well as the maximum temperature for the southern part. The subsurface layer of high salinity extends to a depth of 50 to 300 m. Intermediate waters deepen to 1200 - 1400 m with a salinity in the core of up to 34.3 - 34.5%o. Particularly low salinity is observed in the east of the tropical structure. Deep and bottom waters have a temperature of 1 - 2°C and a salinity of 34.6 - 34.7°/oo.
The southern subtropical structure differs from the northern one in its greater salinity at all depths. This structure also contains a subsurface salinity layer, but it often extends to the ocean surface. Thus, a particularly deep, sometimes up to 300 - 350 m, surface, almost uniform layer of increased salinity is formed - up to 35.6 - 35.7 °/oo. Intermediate water of low salinity is located at the greatest depth (up to 1600 - 1800 m) with a salinity of up to 34.2 - 34.3% o.
In the subantarctic structure, salinity on the surface decreases to 34.1 - 34.2%o, and temperature - to 10 - 11°C. In the core of the layer of high salinity it is 34.3 - 34.7%o at depths of 100 - 200 m, in the core of intermediate water of low salinity it decreases to 34.3%o, and in deep and bottom waters it is the same as in overall in the Pacific Ocean, - 34.6 - 34.7°/oo.
In the Antarctic structure, salinity monotonically increases towards the bottom from 33.8 - 33.9%o to maximum values in the deep and bottom waters of the Pacific Ocean: 34.7 - 34.8°/oo. In temperature stratification, a cold subsurface and a warm intermediate layer again appear. The first of them is located at depths of 125 - 350 m with temperatures in summer up to 1.5°, and the second - from 350 to 1200 - 1300 m with temperatures up to 2.5°. Deep waters here have the highest lower limit - up to 2300 m.
Reasons that disturb the balance: Currents Ebbs and flows Changes in atmospheric pressure Wind Coastline Water runoff from land
The world ocean is a system of communicating vessels. But their level is not always and not the same everywhere: at one latitude it is higher near the western shores; on one meridian rises from south to north
Circulation systems Horizontal and vertical transfer of water masses occurs in the form of a system of vortices. Cyclonic vortices - a mass of water moves counterclockwise and rises. Anticyclonic eddies - a mass of water moves clockwise and descends. Both movements are generated by frontal disturbances of the atmospheric hydrosphere.
Convergence and divergence Convergence is the convergence of water masses. Ocean levels are rising. The pressure and density of water increases and it sinks. Divergence is the divergence of water masses. The sea level is falling. Deep water rises. http://www. youtube. com/watch? v=dce. MYk. G 2 j. Kw
Vertical stratification Upper sphere (200 -300 m) A) upper layer (several micrometers) B) wind effect layer (10 -40 m) C) temperature jump layer (50 -100 m) D) seasonal circulation penetration layer and temperature variability Ocean currents capture only the water masses of the upper sphere.
Deep sphere Does not reach the bottom at 1000 m.
The body of water outside the land is called the world's oceans. The waters of the World Ocean occupy about 70.8% of the surface area of our planet (361 million km 2) and play an extremely important role in the development of the geographical envelope.
The world's oceans contain 96.5% of the waters of the hydrosphere. The volume of its waters is 1,336 million km 3 . The average depth is 3711 m, the maximum is 11022 m. The prevailing depths are from 3000 to 6000 m. They account for 78.9% of the area.
Water surface temperatures range from 0°C and below in polar latitudes to +32°C in the tropics (Red Sea). Towards the bottom layers it decreases to +1°C and below. The average salinity is about 35 ‰, the maximum is 42 ‰ (Red Sea).
The world's oceans are divided into oceans, seas, bays, and straits.
Borders oceans Not always and not everywhere they take place along the shores of continents; they are often carried out very conditionally. Each ocean has a set of qualities unique to it. Each of them is characterized by its own system of currents, a system of ebbs and flows, a specific distribution of salinity, its own temperature and ice regime, its own circulation with air currents, its own depth patterns and dominant bottom sediments. There are the Pacific (Great), Atlantic, Indian and Arctic oceans. Sometimes the Southern Ocean is also isolated.
Sea - a significant area of the ocean, more or less isolated from it by land or underwater rises and distinguished by its natural conditions(depth, bottom topography, temperature, salinity, waves, currents, tides, organic life).
Depending on the nature of the contact between continents and oceans seas are divided into the following three types:
1.Mediterranean seas: located between two continents or located in fault zones of the earth’s crust; they are characterized by a strongly rugged coastline, a sharp change in depth, seismicity and volcanism (Sargasso Sea, Red Sea, Mediterranean Sea, Marmara Sea, etc.).
2. Inland seas: they protrude deeply into the land, located inside continents, between islands or continents or within an archipelago, significantly separated from the ocean, characterized by shallow depths (White Sea, Baltic Sea, Hudson Sea, etc.).
3. Marginal seas: located along the edges of continents and big islands, on continental shallows and slopes. They are wide open towards the ocean (Norwegian Sea, Kara Sea, Sea of Okhotsk, Sea of Japan, Yellow Sea, etc.).
Geographical location The sea is largely determined by its hydrological regime. Inland seas are weakly connected to the ocean, so the salinity of their water, currents and tides differ markedly from those of the ocean. The regime of the marginal seas is essentially oceanic. Most of the seas are located off the northern continents, especially off the coast of Eurasia.
Bay - a part of the ocean or sea that extends into the land, but has free water exchange with the rest of the water area, slightly different from it in terms of natural features and regime. The difference between the sea and the bay is not always perceptible. In principle, the bay is smaller than the sea; Every sea forms bays, but the opposite does not happen. Historically, in the Old World, small water areas, for example, the Azov and Marble seas, are called seas, and in America and Australia, where the names were given by European discoverers, even large seas are called bays - Hudson, Mexican. Sometimes identical water areas are called one sea, the other a bay (Arabian Sea, Bay of Bengal).
Depending on the origin, structure of the coast, shape and size, bays are called bays, fjords, estuaries, lagoons:
Bays (harbours)– small bays, protected from waves and winds by capes protruding into the sea. They are convenient for mooring ships (Novorossiysk, Sevastopol - Black Sea, Golden Horn - Sea of Japan, etc.).
Fjords– narrow, deep, long bays with protruding, steep, rocky shores and a trough-shaped profile, often separated from the sea by underwater rapids. The length of some can reach over 200 km, depth - over 1000 m. Their origin is associated with faults and erosional activity of Quaternary glaciers (the coast of Norway, Greenland, Chile).
Estuaries– shallow bays that protrude deeply into the land with spits and bays. They form in widened river mouths when coastal land subsides (Dnieper and Dniester estuaries in the Black Sea).
Lagoons– shallow bays with salty or brackish water stretched along the coast, separated from the sea by spits, or connected to the sea by a narrow strait (well developed on the Gulf Coast).
Lips- small bays into which large rivers usually flow. Here the water is highly desalinated, its color differs sharply from the water in the adjacent area of the sea and has yellowish and brownish shades (Penzhinskaya Bay).
Straits - relatively narrow expanses of water that connect separate parts of the World Ocean and separate land areas. According to the nature of water exchange they are divided into: flow-through– currents are directed along the entire cross section in one direction; exchange– waters move in opposite directions. In them, water exchange can occur vertically (Bosporus) or horizontally (La Perouse, Davisov).
Structure The structure of the world's oceans is called the vertical stratification of waters, horizontal (geographical) zonality, the nature of water masses and oceanic fronts.
In a vertical section, the water column breaks up into large layers, similar to the layers of the atmosphere. The following four spheres (layers) are distinguished:
Upper sphere is formed by direct exchange of energy and matter with the troposphere. It covers a layer of 200–300 m thickness. This upper sphere is characterized by intense mixing, light penetration and significant temperature fluctuations.
Intermediate Sphere extends to depths of 1500–2000 m; its waters are formed from surface waters as they sink. At the same time, they are cooled and compacted, and then mixed in horizontal directions, mainly with a zonal component. They are distinguished in polar regions by increased temperature, in temperate latitudes and tropical regions by low or high salinity. Horizontal transfers of water masses predominate.
Deep Sphere does not reach the bottom by about 1000 m. This sphere is characterized by a certain homogeneity. Its thickness is about 2000 m and it concentrates more than 50% of all the water in the World Ocean.
Bottom sphere occupies the lowest layer of the ocean and extends to a distance of approximately 1000 m from the bottom. The waters of this sphere are formed in cold zones, in the Arctic and Antarctic, and move over vast areas along deep basins and trenches, and are characterized by the lowest temperatures and the highest density. They perceive heat from the bowels of the Earth and interact with the ocean floor. Therefore, as they move, they transform significantly.
A water mass is a relatively large volume of water that forms in a certain area of the World Ocean and has almost constant physical (temperature, light), chemical (gases) and biological (plankton) properties for a long time. One mass is separated from another by an ocean front.
The following types of water masses are distinguished:
1. Equatorial water masses are characterized by the highest temperature in the open ocean, low salinity (up to 34–32 ‰), minimal density, and high content of oxygen and phosphates.
2. Tropical and subtropical water masses are created in areas of tropical atmospheric anticyclones and are characterized by high salinity (up to 37 ‰ and more) and high transparency, poverty of nutrient salts and plankton. Ecologically, they are oceanic deserts.
3. Temperate water masses are located in temperate latitudes and are characterized by great variability in properties both by geographic latitude and by season. Temperate water masses are characterized by intense exchange of heat and moisture with the atmosphere.
4. The polar water masses of the Arctic and Antarctic are characterized by the lowest temperature, highest density, and high oxygen content. Antarctic waters intensively sink into the bottom sphere and supply it with oxygen.
The waters of the World Ocean are in continuous movement and stirring. Unrest– oscillatory movements of water, currents– progressive. The main cause of disturbances (waves) on the surface is wind at a speed of more than 1 m/s. The excitement caused by the wind fades with depth. Below 200 m, even strong waves are no longer noticeable. At a wind speed of approximately 0.25 m/s, ripple When the wind increases, the water experiences not only friction, but also air blows. The waves grow in height and length, increasing the oscillation period and speed. The ripples turn into gravitational waves. The size of the waves depends on wind speed and acceleration. Maximum height in temperate latitudes (up to 20 - 30 meters). The least waves are in the equatorial belt, the frequency of calms is 20 - 33%.
As a result of underwater earthquakes and volcanic eruptions, seismic waves arise - tsunami. The length of these waves is 200 - 300 meters, the speed is 700 - 800 km/h. Seiches (standing waves) arise as a result of sudden changes in pressure above the water surface. Amplitude 1 – 1.5 meters. Characteristic of closed seas and bays.
Sea currents- These are horizontal movements of water in the form of wide streams. Surface currents are caused by wind, while deep currents are caused by different densities of water. Warm currents (Gulf Stream, North Atlantic) are directed from lower latitudes towards wider latitudes, cold currents (Labrodor, Peruvian) - vice versa. In tropical latitudes off the western coasts of continents, trade winds drive warm water and carry it westward. In its place rises from the depths cold water. 5 cold currents are formed: Canary, California, Peruvian, Western Australian and Benguela. In the southern hemisphere, cold currents of the Western Winds flow into them. Warm waters are formed by moving parallel to the trade wind currents: North and South. In the Indian Ocean in the northern hemisphere there is a monsoon season. On the eastern coasts of the continents they are divided into parts, deviate to the north and south and run along the continents: at 40 - 50º north latitude. under the influence of western winds, the currents deviate to the east and form warm currents.
Tidal movements Ocean waters arise under the influence of the gravitational forces of the Moon and the Sun. The highest tides occur in the Bay of Fundy (18 m). There are semidiurnal, diurnal and mixed tides.
Also, the dynamics of waters are characterized by vertical mixing: in zones of convergence - subsidence of water, in zones of divergence - upwelling.
The bottom of the oceans and seas is covered with sedimentary deposits called marine sediments , soils and silts. Based on their mechanical composition, bottom sediments are classified into: coarse sedimentary rocks or psephites(blocks, boulders, pebbles, gravel), sandy rocks or psammits(coarse, medium, fine sands), silty rocks or silts(0.1 – 0.01 mm) and clayey rocks or pellites.
According to the material composition among bottom sediments distinguish between weakly calcareous (lime content 10–30%), calcareous (30–50%), highly calcareous (more than 50%), weakly siliceous (silicon content 10–30%), siliceous (30–50%) and highly siliceous (more than 50%) sediments. According to their genesis, terrigenous, biogenic, volcanogenic, polygenic and authigenic deposits are distinguished.
Terrigenous precipitation is brought from land by rivers, wind, glaciers, surf, tides in the form of products of rock destruction. Near the shore they are represented by boulders, then by pebbles, sands, and finally by silts and clays. They cover approximately 25% of the bottom of the World Ocean and lie mainly on the shelf and continental slope. A special type of terrigenous sediments are iceberg deposits, which are characterized by a low content of lime, organic carbon, poor sorting and a varied granulometric composition. They are formed from sedimentary material that falls to the ocean floor when icebergs melt. They are most typical for the Antarctic waters of the World Ocean. Terrigenous deposits of the Arctic Ocean are also distinguished, formed from sedimentary material brought by rivers, icebergs, river ice. Turbidites, the sediments of turbidity flows, also have a mostly terrigenous composition. They are typical of the continental slope and continental foot.
Biogenic sediments are formed directly in the oceans and seas as a result of the death of various marine organisms, mainly planktonic, and the precipitation of their insoluble remains. Based on their material composition, biogenic deposits are divided into siliceous and calcareous.
Siliceous sediments consist of the remains of diatoms, radiolarians and flint sponges. Diatom sediments are widespread in the southern parts of the Pacific, Indian and Atlantic oceans in the form of a continuous belt around Antarctica; in the northern part of the Pacific Ocean, in the Bering and Okhotsk seas, but here they contain a high admixture of terrigenous material. Individual spots of diatomaceous oozes were found at great depths (more than 5000 m) in the tropical zones of the Pacific Ocean. Diatom-radiolarian deposits are most common in the tropical latitudes of the Pacific and Indian oceans; siliceous-sponge deposits are found on the shelf of Antarctica and the Sea of Okhotsk.
Lime deposits, like siliceous ones, are divided into a number of types. The most widely developed are foraminiferal-coccolithic and foraminiferal oozes, distributed mainly in the tropical and subtropical parts of the oceans, especially in the Atlantic. Typical foraminiferal silt contains up to 99% lime. A significant part of such silts consists of shells of planktonic foraminifera, as well as coccolithophores - shells of planktonic calcareous algae. With a significant admixture of shells of planktonic pteropod mollusks in the bottom sediments, pteropod-foraminiferal deposits are formed. Large areas of them are found in the equatorial Atlantic, as well as in the Mediterranean, Caribbean Seas, in the Bahamas, in the western Pacific and other areas of the World Ocean.
Coral-algal deposits occupy the equatorial and tropical shallow waters of the western Pacific Ocean, cover the bottom of the northern Indian Ocean, the Red and Caribbean Seas, and shell carbonate deposits occupy the coastal zones of the seas of temperate and subtropical zones.
Pyroclastic, or volcanogenic, sediments are formed as a result of the entry of products of volcanic eruptions into the World Ocean. Usually these are tuffs or tuff breccias, less often - unconsolidated sands, silts, and less often sediments of deep, highly saline and high-temperature underwater sources. Thus, at their outlets in the Red Sea, highly ferrous sediments with a high content of lead and other non-ferrous metals are formed.
TO polygenic sediments There is one type of bottom sediments - deep-sea red clay - a sediment of pelitic composition of brown or brown-red color. This color is due to the high content of iron and manganese oxides. Deep-sea red clays are common in abyssal basins of the oceans at depths of more than 4500 m. They occupy the most significant areas in the Pacific Ocean.
Authigenic or chemogenic sediments are formed as a result of chemical or biochemical precipitation of certain salts from sea water. These include oolitic deposits, glauconitic sands and silts, and ferromanganese nodules.
Oolites- tiny balls of lime, found in the warm waters of the Caspian and Aral seas, the Persian Gulf, and in the area of the Bahamas.
Glauconite sands and silts– sediments of various compositions with a noticeable admixture of glauconite. They are most widespread on the shelf and continental slope off the Atlantic coast of the USA, Portugal, Argentina, on the underwater edge of Africa, off the southern coast of Australia and in some other areas.
Ferromanganese nodules– condensations of iron and manganese hydroxides with an admixture of other compounds, primarily cobalt, copper, and nickel. They occur as inclusions in deep-sea red clays and in places, especially in the Pacific Ocean, form large accumulations.
More than a third of the total area of the World Ocean bottom is occupied by deep-sea red clay, and foraminiferal sediments have approximately the same area of distribution. The rate of sediment accumulation is determined by the thickness of the layer of sediment deposited on the bottom over 1000 years (in some areas 0.1–0.3 mm per thousand years, in river mouths, transition zones and trenches - hundreds of millimeters per thousand years).
The distribution of bottom sediments in the World Ocean clearly reveals the law of latitudinal geographic zoning. Thus, in tropical and temperate zones, the ocean floor to a depth of 4500–5000 m is covered with biogenic calcareous deposits, and deeper - with red clays. The subpolar belts are occupied by siliceous biogenic material, and the polar belts are occupied by iceberg deposits. Vertical zoning is expressed in the replacement of carbonate sediments at great depths with red clays.
The structure of the World Ocean is its structure - vertical stratification of waters, horizontal (geographical) zonality, the nature of water masses and ocean fronts.
Vertical stratification of the World Ocean
In a vertical section, the water column breaks up into large layers, similar to the layers of the atmosphere. They are also called spheres. The following four spheres (layers) are distinguished:
The upper sphere is formed by the direct exchange of energy and matter with the troposphere in the form of microcirculation systems. It covers a layer of 200-300 m thickness. This upper sphere is characterized by intense mixing, light penetration and significant temperature fluctuations.
The upper sphere is divided into the following partial layers:
- a) the topmost layer several tens of centimeters thick;
- b) wind exposure layer 10-40 cm deep; he participates in excitement, reacts to the weather;
- c) a layer of temperature jump, in which it drops sharply from the upper heated layer to the lower layer, not affected by the disturbance and not heated;
- d) a layer of penetration of seasonal circulation and temperature variability.
Ocean currents usually capture water masses only in the upper sphere.
The intermediate sphere extends to depths of 1,500 - 2,000 m; its waters are formed from surface waters as they sink. At the same time, they are cooled and compacted, and then mixed in horizontal directions, mainly with a zonal component. Horizontal transfers of water masses predominate.
The deep sphere does not reach the bottom by about 1,000 m. This sphere is characterized by a certain homogeneity. Its thickness is about 2,000 m and it concentrates more than 50% of all the water in the World Ocean.
The bottom sphere occupies the lowest layer of the ocean and extends to a distance of approximately 1,000 m from the bottom. The waters of this sphere are formed in cold zones, in the Arctic and Antarctic, and move over vast areas along deep basins and trenches. They perceive heat from the bowels of the Earth and interact with the ocean floor. Therefore, as they move, they transform significantly.
9.10 Water masses and ocean fronts of the upper sphere of the ocean
A water mass is a relatively large volume of water that forms in a certain area of the World Ocean and has almost constant physical (temperature, light), chemical (gases) and biological (plankton) properties for a long time. The water mass moves as a single unit. One mass is separated from another by an ocean front.
The following types of water masses are distinguished:
- 1. Equatorial water masses are limited by the equatorial and subequatorial fronts. They are characterized by the highest temperature in the open ocean, low salinity (up to 34-32‰), minimum density, high content of oxygen and phosphates.
- 2. Tropical and subtropical water masses are created in areas of tropical atmospheric anticyclones and are limited from the temperate zones by the tropical northern and tropical southern fronts, and subtropical ones by the northern temperate and northern southern fronts. They are characterized by high salinity (up to 37‰ and more) and high transparency, poverty of nutrient salts and plankton. Ecologically, tropical water masses are oceanic deserts.
- 3. Temperate water masses are located in temperate latitudes and are limited from the poles by the Arctic and Antarctic fronts. They are characterized by great variability in properties both by geographical latitude and by season. Temperate water masses are characterized by intense exchange of heat and moisture with the atmosphere.
- 4. The polar water masses of the Arctic and Antarctic are characterized by the lowest temperature, highest density, and high oxygen content. Antarctic waters intensively sink into the bottom sphere and supply it with oxygen.
Ocean water is a solution that contains all chemical elements. The mineralization of water is called its salinity . It is measured in thousandths, in ppm, and is designated ‰. The average salinity of the World Ocean is 34.7 ‰ (rounded to 35 ‰). One ton of ocean water contains 35 kg of salts, and their total amount is so great that if all the salts were extracted and evenly distributed over the surface of the continents, a layer 135 m thick would form.
Ocean water can be considered as a liquid multi-element ore. Table salt, potassium salts, magnesium, bromine and many other elements and compounds are extracted from it.
Water mineralization is an indispensable condition for the emergence of life in the ocean. It is sea waters that are optimal for most forms of living organisms.
The question of what the salinity of water was at the dawn of life, and in what kind of water organic matter arose, is resolved relatively unambiguously. Water, released from the mantle, captured and transported the mobile components of the magma, and primarily salts. Therefore, the primary oceans were quite mineralized. On the other hand, only pure water is decomposed and removed by photosynthesis. Consequently, the salinity of the oceans is steadily increasing. Data from historical geology indicate that Archean reservoirs were brackish, that is, their salinity was about 10-25 ‰.
52. Penetration of light into water. Transparency and color of sea water
The penetration of light into water depends on its transparency. Transparency is expressed by the number of meters, that is, the depth at which a white disk with a diameter of 30 cm is still visible. The greatest transparency (67 m) was observed in 1971 in the central part of the Pacific Ocean. The transparency of the Sargasso Sea is close to it - 62 m (along a disk with a diameter of 30 cm). Other water areas with clean and transparent water are also located in the tropics and subtropics: in the Mediterranean Sea - 60 m, in the Indian Ocean - 50 m. The high transparency of tropical water areas is explained by the peculiarities of water circulation in them. In seas where the amount of suspended particles increases, transparency decreases. In the North Sea it is 23 m, in the Baltic Sea – 13 m, in the White Sea – 9 m, in the Azov Sea – 3 m.
Water transparency is of high ecological, biological and geographical importance: phytoplankton vegetation is possible only to depths to which sunlight penetrates. Photosynthesis requires a relatively large amount of light, so plants disappear from depths of 100-150 m, rarely 200 m. The lower limit of photosynthesis in the Mediterranean Sea is at a depth of 150 m, in the North Sea - 45 m, in the Baltic Sea - only 20 m.
53. Structure of the World Ocean
The structure of the World Ocean is its structure - vertical stratification of waters, horizontal (geographical) zonality, the nature of water masses and ocean fronts.
Vertical stratification of the World Ocean. In a vertical section, the water column breaks up into large layers, similar to the layers of the atmosphere. They are also called spheres. The following four spheres (layers) are distinguished:
Upper sphere is formed by direct exchange of energy and matter with the troposphere in the form of microcirculation systems. It covers a layer of 200-300 m thickness. This upper sphere is characterized by intense mixing, light penetration and significant temperature fluctuations.
Upper sphere breaks down into the following particular layers:
a) the topmost layer several tens of centimeters thick;
b) wind exposure layer 10-40 cm deep; he participates in excitement, reacts to the weather;
c) a layer of temperature jump, in which it drops sharply from the upper heated layer to the lower layer, not affected by the disturbance and not heated;
d) a layer of penetration of seasonal circulation and temperature variability.
Ocean currents usually capture water masses only in the upper sphere.
Intermediate Sphere extends to depths of 1,500 – 2,000 m; its waters are formed from surface waters as they sink. At the same time, they are cooled and compacted, and then mixed in horizontal directions, mainly with a zonal component. Horizontal transfers of water masses predominate.
Deep Sphere does not reach the bottom by about 1,000 m. This sphere is characterized by a certain homogeneity. Its thickness is about 2,000 m and it concentrates more than 50% of all the water in the World Ocean.
Bottom sphere occupies the lowest layer of the ocean and extends to a distance of approximately 1,000 m from the bottom. The waters of this sphere are formed in cold zones, in the Arctic and Antarctic, and move over vast areas along deep basins and trenches. They perceive heat from the bowels of the Earth and interact with the ocean floor. Therefore, as they move, they transform significantly.
Water masses and ocean fronts of the upper sphere of the ocean. A water mass is a relatively large volume of water that forms in a certain area of the World Ocean and has almost constant physical (temperature, light), chemical (gases) and biological (plankton) properties for a long time. The water mass moves as a single unit. One mass is separated from another by an ocean front.
The following types of water masses are distinguished:
1. Equatorial water masses limited by the equatorial and subequatorial fronts. They are characterized by the highest temperature in the open ocean, low salinity (up to 34-32 ‰), minimal density, and a high content of oxygen and phosphates.
2. Tropical and subtropical water masses are created in areas of tropical atmospheric anticyclones and are limited from the temperate zones by the tropical northern and tropical southern fronts, and subtropical ones by the northern temperate and northern southern fronts. They are characterized by high salinity (up to 37 ‰ and more), high transparency, and poverty of nutrient salts and plankton. Ecologically, tropical water masses are oceanic deserts.
3. Moderate water masses are located in temperate latitudes and are limited from the poles by the Arctic and Antarctic fronts. They are characterized by great variability in properties both by geographical latitude and by season. Temperate water masses are characterized by intense exchange of heat and moisture with the atmosphere.
4. Polar water masses The Arctic and Antarctic are characterized by the lowest temperature, highest density, and high oxygen content. Antarctic waters intensively sink into the bottom sphere and supply it with oxygen.
Ocean currents. In accordance with the zonal distribution of solar energy over the surface of the planet, similar and genetically related circulation systems are created both in the ocean and in the atmosphere. The old idea that ocean currents are caused solely by winds is not supported by the latest scientific research. The movement of both water and air masses is determined by the zonality common to the atmosphere and hydrosphere: uneven heating and cooling of the Earth's surface. This causes upward currents and a loss of mass in some areas, and downward currents and an increase in mass (air or water) in others. Thus, a movement impulse is born. Transfer of masses - their adaptation to the field of gravity, the desire for uniform distribution.
Most macrocirculatory systems last all year. Only in the northern part of the Indian Ocean do currents change following the monsoons.
In total, there are 10 large circulation systems on Earth:
1) North Atlantic (Azores) system;
2) North Pacific (Hawaiian) system;
3) South Atlantic system;
4) South Pacific system;
5) South Indian system;
6) Equatorial system;
7) Atlantic (Icelandic) system;
8) Pacific (Aleutian) system;
9) Indian monsoon system;
10) Antarctic and Arctic system.
The main circulation systems coincide with the centers of action of the atmosphere. This commonality is genetic in nature.
The surface current deviates from the wind direction by an angle of up to 45 0 to the right in the Northern Hemisphere and to the left in Southern Hemisphere. Thus, trade wind currents go from east to west, while trade winds blow from the northeast in the Northern Hemisphere and from the southeast in the Southern Hemisphere. The top layer can follow the wind. However, each underlying layer continues to deviate to the right (left) from the direction of movement of the overlying layer. At the same time, the flow speed decreases. At a certain depth, the current takes the opposite direction, which practically means it stops. Numerous measurements have shown that the currents end at depths of no more than 300 m.
In the geographic shell as a system of a higher level than the oceanosphere, ocean currents are not only water flows, but also bands of air mass transfer, directions of exchange of matter and energy, and migration paths of animals and plants.
Tropical anticyclonic ocean current systems are the largest. They extend from one coast of the ocean to the other for 6-7 thousand km in the Atlantic Ocean and 14-15 thousand km in the Pacific Ocean, and along the meridian from the equator to 40° latitude, for 4-5 thousand km. Steady and powerful currents, especially in the Northern Hemisphere, are mostly closed.
As in tropical atmospheric anticyclones, the movement water is coming clockwise in the Northern and counterclockwise in the Southern Hemisphere. From the eastern shores of the oceans (western shores of the continent), surface water relates to the equator, in its place it rises from the depths (divergence) and compensatory cold water comes from the temperate latitudes. This is how cold currents are formed:
Canary Cold Current;
California cold current;
Peruvian cold current;
Benguela Cold Current;
Western Australian cold current, etc.
The current speed is relatively low and amounts to about 10 cm/sec.
Jets of compensatory currents flow into the Northern and Southern Trade Wind (Equatorial) warm currents. The speed of these currents is quite high: 25-50 cm/sec on the tropical periphery and up to 150-200 cm/sec near the equator.
Approaching the shores of continents, trade wind currents naturally deviate. Large waste streams are formed:
Brazilian Current;
Guiana Current;
Antillean Current;
East Australian Current;
Madagascar Current, etc.
The speed of these currents is about 75-100 cm/sec.
Due to the deflecting effect of the Earth's rotation, the center of the anticyclonic current system is shifted to the west relative to the center of the atmospheric anticyclone. Therefore, the transport of water masses to temperate latitudes is concentrated in narrow strips off the western shores of the oceans.
Guiana and Antilles currents wash the Antilles and most of the water enters the Gulf of Mexico. The Gulf Stream flow begins from here. Its initial section in the Strait of Florida is called Florida Current, the depth of which is about 700 m, width - 75 km, thickness - 25 million m 3 /sec. The water temperature here reaches 26 0 C. Having reached the middle latitudes, the water masses partially return to the same system off the western coasts of the continents, and are partially involved in the cyclonic systems of the temperate zone.
The equatorial system is represented by the Equatorial Countercurrent. Equatorial countercurrent is formed as a compensation between the Trade Wind currents.
Cyclonic systems of temperate latitudes are different in the Northern and Southern Hemispheres and depend on the location of the continents. Northern cyclonic systems – Icelandic and Aleutian– are very extensive: from west to east they stretch for 5-6 thousand km and from north to south about 2 thousand km. The circulation system in the North Atlantic begins with the warm North Atlantic Current. It often retains the name of the initial Gulf Stream. However, the Gulf Stream itself, as a drainage current, continues no further than the New Foundland Bank. Starting from 40 0 N water masses are drawn into the circulation of temperate latitudes and, under the influence of westerly transport and Coriolis force, are directed from the shores of America to Europe. Thanks to active water exchange with the Arctic Ocean, the North Atlantic Current penetrates into the polar latitudes, where cyclonic activity forms several gyres and currents Irminger, Norwegian, Spitsbergen, North Cape.
Gulf Stream in a narrow sense, it is the discharge current from the Gulf of Mexico to 40 0 N; in a broad sense, it is a system of currents in the North Atlantic and the western part of the Arctic Ocean.
The second gyre is located off the northeastern coast of America and includes currents East Greenland and Labrador. They carry the bulk of Arctic waters and ice into the Atlantic Ocean.
The circulation of the North Pacific Ocean is similar to the North Atlantic, but differs from it in less water exchange with the Arctic Ocean. Katabatic current Kuroshio goes into North Pacific, going to Northwestern America. Very often this current system is called Kuroshio.
A relatively small (36 thousand km 3) mass of ocean water penetrates into the Arctic Ocean. The cold Aleutian, Kamchatka and Oyashio currents are formed from the cold waters of the Pacific Ocean without connection with the Arctic Ocean.
Circumpolar Antarctic system The Southern Ocean, according to the oceanicity of the Southern Hemisphere, is represented by one current Western winds. This is the most powerful current in the World Ocean. It covers the Earth with a continuous ring in a belt from 35-40 to 50-60 0 S latitude. Its width is about 2,000 km, thickness 185-215 km3/sec, speed 25-30 cm/sec. To a large extent, this current determines the independence of the Southern Ocean.
The circumpolar current of the Western winds is not closed: branches extend from it, flowing into Peruvian, Benguela, West Australian currents, and from the south, from Antarctica, coastal Antarctic currents flow into it - from the Weddell and Ross seas.
The Arctic system occupies a special place in the circulation of the World Ocean waters due to the configuration of the Arctic Ocean. Genetically, it corresponds to the Arctic pressure maximum and the trough of the Icelandic minimum. The main current here is Western Arctic. It moves water and ice from east to west throughout the Arctic Ocean to the Nansen Strait (between Spitsbergen and Greenland). Then it continues East Greenland and Labrador. In the east, in the Chukchi Sea, it is separated from the Western Arctic Current Polar Current, going through the pole to Greenland and further into the Nansen Strait.
The circulation of the waters of the World Ocean is dissymmetrical relative to the equator. The dissymmetry of currents has not yet received a proper scientific explanation. The reason for this is probably that meridional transport dominates north of the equator, and zonal transport in the Southern Hemisphere. This is also explained by the position and shape of the continents.
In inland seas, water circulation is always individual.
54. Land waters. Types of land waters
Atmospheric precipitation, after it falls on the surface of continents and islands, is divided into four unequal and variable parts: one evaporates and is transported further into the continent by atmospheric runoff; the second seeps into the soil and into the ground and lingers for some time in the form of soil and underground water, flowing into rivers and seas in the form of groundwater runoff; the third in streams and rivers flows into the seas and oceans, forming surface runoff; the fourth turns into mountain or continental glaciers, which melt and flow into the ocean. Accordingly, there are four types of water accumulation on land: groundwater, rivers, lakes and glaciers.
55. Water flow from land. Quantities characterizing runoff. Runoff factors
The flow of rain and melt water in small streams down the slopes is called planar or slope drain. Jets of slope runoff collect in streams and rivers, forming channel, or linear, called river , drain . Groundwater flows into rivers in the form ground or underground drain.
Full river flow R formed from superficial S and underground U : R = S + U . (see Table 1). Total river flow is 38,800 km 3 , surface runoff is 26,900 km 3 , underground runoff is 11,900 km 3 , glacial runoff (2500-3000 km 3) and groundwater flow directly into the seas along the coastline of 2000-4000 km 3.
Table 1 – Water balance land without polar ice caps
Surface runoff depends on the weather. It is unstable, temporary, poorly nourishes the soil, and often needs regulation (ponds, reservoirs).
Ground drain occurs in soils. In the wet season, the soil receives excess water on the surface and in rivers, and in the dry months groundwater fed by rivers. They ensure constant water flow in rivers and normal soil water regime.
The total volume and ratio of surface and underground runoff varies by zone and region. In some parts of the continents there are many rivers and they are full-flowing, the density of the river network is large, in others the river network is sparse, the rivers have low water or dry up altogether.
The density of the river network and the high water content of rivers is a function of the flow or water balance of the territory. Runoff is generally determined by the physical and geographical conditions of the area, on which the hydrological and geographical method of studying land waters is based.
Quantities characterizing runoff. Land runoff is measured by the following quantities: runoff layer, runoff module, runoff coefficient, and runoff volume.
The drainage is most clearly expressed layer , which is measured in mm. For example, on the Kola Peninsula the runoff layer is 382 mm.
Drain module – the amount of water in liters flowing from 1 km 2 per second. For example, in the Neva basin the runoff module is 9, on the Kola Peninsula – 8, and in the Lower Volga region – 1 l/km 2 x s.
Runoff coefficient – shows what proportion (%) of atmospheric precipitation flows into rivers (the rest evaporates). For example, on the Kola Peninsula K = 60%, in Kalmykia only 2%. For all land, the average long-term runoff coefficient (K) is 35%. In other words, 35% of the annual precipitation flows into the seas and oceans.
Volume of flowing water measured in cubic kilometers. On the Kola Peninsula, precipitation brings 92.6 km 3 of water per year, and 55.2 km 3 flows down.
Runoff depends on climate, the nature of the soil cover, topography, vegetation, weathering, the presence of lakes and other factors.
Dependence of runoff on climate. The role of climate in the hydrological regime of land is enormous: the more precipitation and less evaporation, the greater the runoff, and vice versa. When humidification is greater than 100%, runoff follows the amount of precipitation regardless of the amount of evaporation. When humidification is less than 100%, the runoff decreases following evaporation.
However, the role of climate should not be overestimated to the detriment of the influence of other factors. If we recognize climatic factors as decisive and the rest as insignificant, then we will lose the opportunity to regulate runoff.
Dependence of runoff on soil cover. Soil and ground absorb and accumulate (accumulate) moisture. The soil cover transforms atmospheric precipitation into an element of the water regime and serves as a medium in which river flow is formed. If the infiltration properties and water permeability of soils are low, then little water gets into them, and more is spent on evaporation and surface runoff. Well-cultivated soil in a meter layer can store up to 200 mm of precipitation, and then slowly release it to plants and rivers.
Dependence of runoff on relief. It is necessary to distinguish between the meaning of macro-, meso- and microrelief for runoff.
Already from minor elevations the flow is greater than from the adjacent plains. Thus, on the Valdai Upland the runoff module is 12, and on the neighboring plains it is only 6 m/km 2 /s. Even greater runoff in the mountains. On the northern slope of the Caucasus it reaches 50, and in the western Transcaucasia - 75 l/km 2 /s. If there is no flow on the desert plains of Central Asia, then in the Pamir-Alai and Tien Shan it reaches 25 and 50 l/km 2 /s. In general, the hydrological regime and water balance of mountainous countries is different from that of plains.
In the plains, the effect of meso- and microrelief on runoff is manifested. They redistribute the runoff and influence its rate. In flat areas of the plains, the flow is slow, the soils are saturated with moisture, and waterlogging is possible. On slopes, planar flow turns into linear. There are ravines and river valleys. They, in turn, accelerate runoff and drain the area.
Valleys and other depressions in the relief in which water accumulates supply the soil with water. This is especially significant in areas of insufficient moisture, where soils are not soaked and groundwater is formed only when fed by river valleys.
Effect of vegetation on runoff. Plants increase evaporation (transpiration) and thereby dry out the area. At the same time, they reduce soil heating and reduce evaporation from it by 50-70%. Forest litter has high moisture capacity and increased water permeability. It increases the infiltration of precipitation into the soil and thereby regulates runoff. Vegetation promotes the accumulation of snow and slows down its melting, so more water seeps into the ground than from the surface. On the other hand, some of the rain is retained by the leaves and evaporates before reaching the soil. Vegetation cover counteracts erosion, slows down runoff and transfers it from surface to underground. Vegetation maintains air humidity and thereby enhances intra-continental moisture circulation and increases precipitation. It affects moisture circulation by changing the soil and its water-receiving properties.
The influence of vegetation varies in different zones. V.V. Dokuchaev (1892) believed that steppe forests are reliable and faithful regulators of the water regime of the steppe zone. In the taiga zone, forests drain the area through greater evaporation than in fields. In the steppes, forest belts contribute to the accumulation of moisture by retaining snow and reducing runoff and evaporation from the soil.
The influence on the runoff of swamps in zones of excessive and insufficient moisture is different. In the forest zone they are flow regulators. In forest-steppe and steppes, their influence is negative; they absorb surface and groundwater and evaporate them into the atmosphere.
Weathering crust and runoff. Sand and pebble deposits accumulate water. They often filter streams from distant places, for example, in deserts from the mountains. On massively crystalline rocks, all surface water drains away; On the shields, groundwater circulates only in cracks.
The importance of lakes for regulating runoff. One of the most powerful flow regulators are large flowing lakes. Large lake-river systems, like the Neva or St. Lawrence, have a very regulated flow and this significantly differs from all other river systems.
Complex of physical and geographical factors of runoff. All of the above factors act together, influencing one another in the integral system of the geographical envelope, determining gross moisture content of the territory . This is the name given to that part of atmospheric precipitation that, minus the rapidly flowing surface runoff, seeps into the soil and accumulates in the soil cover and soil, and then is slowly consumed. It is obvious that it is gross moisture that has the greatest biological (plant growth) and agricultural (farming) significance. This is the most essential part of water balance.