Ocean currents and climate. Advances of modern natural science
Sometimes they say that it would be more correct to call our planet not Earth, but Water, because land (“earth” as such) is only a quarter of its surface. The rest of the space belongs to the oceans that make up the world's oceans. It is in it, as scientists suggest, that life once originated... and to this day, the ocean largely determines life on land. And this is not only a matter of shipping, connecting cities and countries, fishing, which has fed many peoples from time immemorial, not only of a pleasant holiday on the sea coasts... The “breath” of the ocean is felt by earth's atmosphere– it is this that largely determines the climate.
The world's oceans are located in constant movement. The flows of water in it - a kind of “rivers in the ocean” - are called currents. They can be permanent and periodic, underwater and surface, cold and warm, steady (not changing over time) and steady (changing).
The reasons that give rise to sea currents are very diverse. There are tidal currents, especially strong near the coast, compensatory currents associated with the slope of the sea level, wind currents, and constant winds, changing direction depending on the season, generate the same currents - monsoon and trade winds. Currents are also caused by differences in atmospheric pressure above the ocean surface.
Constant currents have different directions. Some of them start at low latitudes and move to high ones - they carry warm waters, others - on the contrary, are cold currents. Since the main "battery" solar energy on our planet it is an ocean, then the weather on Earth largely depends on how sea currents “carry” and “distribute” heat to different land areas, and since the currents are constant, so does the climate.
Some permanent currents have even received proper names– for example, the Gulf Stream. This is a warm current from Florida to Scandinavia, the Barents Sea and the Arctic Ocean. The width of this current is from 70 to 90 km, and the depth extends almost to the bottom. This warm “river in the ocean” moves approximately 50 million cubic meters of water every second - that’s more than all the rivers on Earth combined! The world's most powerful ocean current carries warm waters from the Gulf of Mexico to the north, transferring up to 100 kcal/cm2 of heat - approximately as much as the world's oceans as a whole receive from the Sun. It is thanks to him that the port of Murmansk does not freeze in winter - despite the fact that it is located beyond the Arctic Circle. It also softens the climate European countries adjacent to Atlantic Ocean: North America has a harsher climate at the same latitude. However, this is also the merit of another movement - Labrador. By itself it is cold, but when it encounters the warm Gulf Stream, it deflects it, directing it towards Europe.
However, no less important role in the creation climatic conditions Cold currents also play. So, everyone knows that it’s hot in the tropics, but few people think that it could be even hotter there (maybe it would be impossible to live), if not for the cold Benguela Current off the southwestern coast of Africa and the same current Humboldt (aka Peruvian) off the west coast South America. It is they who have a “cooling” effect on the tropical region. At the same time, the influence Peruvian Current“dries out” the climate of South America, forming deserts.
Sea currents affect not only air temperature, but also movement air masses, sometimes even provoking hurricanes.
As you can see, ocean currents are a real weather “factory”. If they change, the climate as a whole will change. And these changes are happening right before our eyes. So, this is not the first year that the winter has been covered with snow. Western Europe, not accustomed to this state of affairs. Scientists explain this by the fact that the Gulf Stream is slowing down and cooling. This is due to the process of global cooling... yes, exactly cooling. None global warming no – but the cold snap is already approaching three centuries, and clear evidence of this is the cooling of the Gulf Stream. Is this somehow related to human activity? Head of the department rational environmental management and Ecology of the Faculty of Geography of Moscow State University, Academician A. Kapitsa believes that to assume this is sheer megalomania: a person cannot seriously damage nature. Global cooling associated with the displacement of magnetic poles, earth's axis and changes in solar activity.
Sea currents have a great influence on the climate. They transfer heat from one latitude to another and lead to climate cooling and warming. The coasts of continents, which are washed by cold currents, are colder than their interior parts, located at the same latitudes. The climate of the coasts washed by warm currents is warmer and milder than inside the mainland. Cold currents also increase the dryness of the climate. They cool the lower layers of air, and cold air, as you know, is denser and heavier and cannot rise, which is not conducive to the formation of clouds and precipitation. Warm currents warm the air and humidify it. As it rises, it becomes oversaturated, clouds form, and precipitation falls (Fig. 7).
Rice. 7.
An example of the different influence of warm and cold currents on climate is the climate east coast North America and the western coast of Europe between 550 and 700 northern latitude. The American coast is washed by the cold Labrador Current, the European coast by the warm North Atlantic Current. The first lies between annual temperatures of 0 and -10 0C, the second - +10 and 0 0C. The length of the frost-free period on the American coast is 60 days a year, on the European coast from 150 to 210 days. On the Labrador Peninsula there are treeless spaces (tundra), in Europe there are coniferous and mixed forests.
Relief and climate
Relief has a large and varied influence on climate. Mountain rises and ridges are mechanical obstacles to the path of air masses. In some cases, mountains are the border of areas with different climates, so they impede air exchange. Thus, the dry climate of central Asia is largely explained by the presence of large mountain systems on its outskirts.
The distribution of mountain slopes and ridges in relation to the oceans and sides of the horizon is the cause of the uneven distribution of precipitation. The windward slopes of the mountains receive more precipitation than the leeward ones, because the air, when rising along the slopes of the mountains, cools, becomes supersaturated and releases a lot of precipitation (Fig. 8). It is on the windward slopes of mountainous countries that the most humid regions of the Earth are located.
For example, the southern slopes of the Himalayas delay the summer monsoons and receive a lot of rainfall, so the flora and fauna there are rich and diverse. The northern slopes of the Himalayas are dry and deserted.
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Rice. 8.
Climatic conditions in the mountains depend on the absolute altitude. With altitude, the air temperature decreases, atmospheric pressure and humidity drop, the amount of precipitation increases up to a certain height and then decreases, the speed and direction of the wind and everything else change meteorological elements. This leads to the formation of high altitude climatic zones, the location and quantity of which is closely related to the geographical location, the height of the mountains, and the direction of the slopes. The climate in the mountains varies over relatively short distances and differs significantly from the climate of the neighboring plains.
Ocean currents create particularly sharp differences in the temperature regime of the sea surface and themselves influence the distribution of air temperature and atmospheric circulation. The persistence of ocean currents means that their influence on the atmosphere is of climatic significance. The ridge of isotherms on average temperature maps clearly shows warm influence The Gulf Stream on the climate of the eastern North Atlantic and Western Europe.
Cold ocean currents are also detected on average air temperature maps by corresponding disturbances in the isotherm configuration - cold tongues directed towards low latitudes.
Over areas of cold currents, the frequency of fogs increases, particularly in Newfoundland, where air can move from the warm waters of the Gulf Stream to the cold waters of the Labrador Current. Over cold waters in the trade wind zone, convection is eliminated and cloudiness sharply decreases. This, in turn, is a factor that supports the existence of so-called coastal deserts.
Influence of snow and vegetation cover on climate
Snow (ice) cover reduces heat loss from the soil and fluctuations in its temperature. The surface of the cover reflects solar radiation during the day and is cooled by radiation at night, so it reduces the temperature of the surface layer of air. In spring, it is spent on melting snow cover a large number of heat that is taken from the atmosphere. Thus, the air temperature above the melting snow cover remains close to zero. Temperature inversions are observed above the snow cover: in winter - associated with radiation cooling, in spring - with snow melting. Over the permanent snow cover of the polar regions, inversions or isotherms are observed even in summer. Melting snow cover enriches the soil with moisture and has great importance For climate regime warm season. A large albedo of snow cover leads to increased scattered radiation and an increase in total radiation and illumination.
Dense grass cover reduces the daily range of soil temperatures and lowers the average soil temperature. It also reduces the daily amplitude of air temperature. Forests have a more complex influence on climate, as they can increase the amount of precipitation above them due to the roughness of the underlying surface.
However, the influence of vegetation cover is mainly of microclimatic significance, which extends mainly to the surface air layers and to small areas.
General atmospheric circulation
The general circulation of the atmosphere is a system of large-scale air currents over the globe, that is, currents that are comparable in size to large parts of continents and oceans. From general circulation The atmosphere is distinguished by local circulations, such as splashes on the coasts of the seas, mountain-valley winds, glacial winds, etc. These local circulations at times in certain areas overlap with the general circulation of the atmosphere.
On daily synoptic maps weather, one can see how the general circulation currents are distributed at any given moment over large areas of the Earth or over the entire globe and how this distribution continuously changes. The variety of manifestations of the general circulation of the atmosphere especially depends on the fact that huge waves and vortices constantly appear in the atmosphere, which develop differently and move differently. This formation of atmospheric disturbances - cyclones and anticyclones - is the most characteristic feature of the general circulation of the atmosphere.
However, in the general circulation of the atmosphere, with all the variety of its continuous changes, one can notice some constant features that repeat annually. Such features are best detected by statistical averaging, in which daily circulation disturbances are more or less smoothed out.
The average pressure over each hemisphere decreases from the winter half of the year to the summer half of the year. From January to July it decreases over the northern hemisphere by several mb; in the southern hemisphere the opposite change occurs. But atmospheric pressure is equal to the weight of the air column, which means it is proportional to the mass of the air. This means that from the hemisphere in which it is currently summer, some mass of air flows into the hemisphere in which it is currently winter. This is how seasonal air exchange occurs between the hemispheres. During the year, 1013 tons of air are transferred from the northern hemisphere to the southern hemisphere and back.
We now turn to a more detailed consideration of the conditions of general circulation by zone.
16.11.2007 13:52
Current is the movement of water particles from one place in the ocean or sea to another.
Currents cover huge masses of ocean waters, spreading wide stripe on the surface of the ocean and capturing a layer of water of varying depth. On great depths and near the bottom there are slower movements of water particles, most often in the opposite direction compared to surface currents, which is part of the general water cycle of the World Ocean.
The main forces causing sea currents are determined by both hydrometeorological and astronomical factors.
The first should include:
1) density force or driving force of currents created by density differences due to uneven changes in temperature and salinity of sea water
2) the slope of sea level caused by excess or lack of water in a particular area, due to, for example, coastal runoff or wind surges and surges
3) sea level slope caused by changes in distribution atmospheric pressure, creating a decrease in sea level in areas of high atmospheric pressure and a rise in levels in areas of low pressure
4) wind friction on the surface of the sea waters and wind pressure on the rear surface of the waves.
The second ones include tidal forces of the Moon and the Sun, continuously changing due to periodic changes in the relative positions of the Sun, Earth and Moon and creating horizontal fluctuations of water masses or tidal currents.
Immediately after the occurrence of a flow caused by one or more of these forces, secondary forces arise that influence the flow. These forces are incapable of causing currents; they only modify the current that has already arisen.
These forces include:
1) the Coriolis force, which deflects any moving body to the right in the northern hemisphere, and to the left in the southern hemisphere from the direction of its movement, depending on the latitude of the place and the speed of movement of the particles
2) friction force, slowing down any movement
3) centrifugal force.
Sea currents are divided according to the following characteristics:
1. By origin, i.e. according to the factors that cause them - a) density (gradient) currents; b) drift and wind currents; c) waste or runoff currents; d) barogradient; e) tidal; f) compensatory currents, which are a consequence of the almost complete incompressibility of water (continuity), arise due to the need to compensate for the loss of water, for example, from the drive of water by the wind or its outflow due to the presence of other currents.
2. By region of origin.
3. By duration or stability: a) constant currents flowing from year to year in the same direction at a certain speed; b) temporary currents caused by transient causes and changing their direction and speed depending on the time of action and the magnitude of the generating force; c) periodic currents that change their direction and speed in accordance with the period and magnitude of tidal forces.
4. According to physical and chemical characteristics, for example, warm and cold. Moreover, the absolute value of temperature does not matter for the flow characteristics; the temperature of the waters of warm currents is higher than the temperature of the waters created by local conditions, the temperature of the waters of cold currents is lower.
Main currents in Pacific Ocean, influencing the climate of Primorye
Kuroshio (Kuro-Shio) The Kuroshio system is divided into three parts: a) Kuroshio proper, b) Kuroshio drift and c) North Pacific Current. Kuroshio proper is the name given to the area of warm current in the western part of the northern half of the Pacific Ocean between the island of Taiwan and 35°N, 142°E.
The beginning of Kuroshio is the branch of the North Trade Wind Current, running north along the eastern shores Philippine Islands . Near the island of Taiwan, Kuroshio has a width of about 185 km and a speed of 0.8-1.0 m/s. Then it deviates to the right and passes along the western shores of the Ryukyu island ridge, and the speed at times increases to 1.5-1.8 m/s. An increase in Kuroshio speeds usually occurs in summer with tailwinds of the summer southeast monsoon.
On the approaches to the southern tip of Kyushu Island, the current splits into two branches: the main branch passes through Van Diemen's Strait to the Pacific Ocean (Kuroshio proper), and the other branch goes to Korea Strait(Tsushima Current). Kuroshio itself, when approaching the southeastern tip of the island of Honshu - Cape Najima (35° N, 140° E) - turns to the east, being pushed away from the coast by the cold Kuril Current.
At a point with coordinates 35°N, 142°E. Two branches separate from Kuroshio: one goes south and the other goes northeast. This last branch reaches far to the north. Traces of the northeastern branch can be observed up to Commander Islands.
The Kuroshio drift is the section of warm current between 142 and 160°E, after which the North Pacific Current begins.
The most stable of all three components of the Kuroshio system is the Kuroshio current itself, although it is subject to large seasonal fluctuations; so in December, during greatest development With the winter monsoon blowing from the north or northwest, where Kuroshio is usually located, ships often note southward currents. This indicates a strong dependence of the flow on monsoon winds, possessing off the eastern coast of Asia great strength and consistency.
Kuroshio's influence on climate coastal countries East Asia such that the warming of waters in the Kuroshio region causes an exacerbation of the winter monsoon in winter.
. Kuril Current
The Kuril Current, sometimes called the Oya Sio, is a cold current. It originates in the Bering Sea and flows first south under the name Kamchatka Current along the eastern shores of Kamchatka, and then along the eastern shores of the Kuril ridge.
IN winter time through the straits Kuril ridge(especially through its southern straits) masses of cold water and sometimes ice enter the Pacific Ocean from the Sea of Okhotsk, which greatly increases Kuril Current. In winter, the speed of the Kuril Current fluctuates around 0.5-1.0 m/s, in summer it is slightly less - 0.25-0.35 m/s.
The cold Kuril Current flows first along the surface, penetrating south a little further than Cape Nojima - the southeastern tip of the island of Honshu. The width of the Kuril Current at Cape Nojima is about 55.5 km. Soon after passing the cape, the current drops under surface water ocean and continues for another 370 km in the form of an underwater current.
Main currents in the Sea of Japan
The Sea of Japan is located in the northwestern Pacific Ocean between the mainland coast of Asia, Japanese islands And Sakhalin Island V geographical coordinates 34°26"-51°41" N, 127°20"-142°15" E According to its physical and geographical position, it belongs to the marginal oceanic seas and is fenced off from adjacent basins by shallow barriers.
In the north and northeast, the Sea of Japan is connected to the Sea of Okhotsk by the Nevelskoy and La Perouse (Soya) straits, in the east - with Pacific Ocean, Sangar (Tsugaru) Strait, in the south - from East China Sea Korea (Tsushima) Strait. The smallest of them is the strait- Nevelskoy has maximum depth 10 m, a the deepest Sangarsky- about 200 m.
The greatest influence on the hydrological regime of the basin is exerted by subtropical waters entering through Korea Strait from the East China Sea. The movement of water in the Sea of Japan is formed as a result of the total effect of the global distribution of atmospheric pressure, wind field, heat and water flows. In the Pacific Ocean, isobaric surfaces tilt toward the Asian continent with a corresponding transfer of water. The Sea of Japan from the Pacific Ocean receives mainly the waters of the western branch of the warm Kuroshio, passing through the East China Sea and adding its waters.
Due to the shallowness of the straits, only surface water enters the Sea of Japan. Every year, from 55 to 60 thousand km3 of warm water enters the Sea of Japan through the Korean Irrigation. The stream of these waters in the form Tsushima Current changes throughout the year. It is most intense at the end of summer - beginning of autumn, when, under the influence of the southeast monsoon, the western branch of Kuroshio strengthens and water surges into East China Sea. During this period, the water inflow increases to 8 thousand km3 per month. At the end of winter, the influx of water into the Sea of Japan through the Korean Irrigation decreases to 1.5 thousand km3 per month. Due to the passage of the Tsushima Current off the western shores Japanese Islands, the sea level here is on average 20 cm higher than in the Pacific Ocean off the eastern coast of Japan. Therefore, already in the Sangar Strait, the first along the path of the waters of this current, there is an intense flow of water into the Pacific Ocean.
Approximately 62% of the waters of the Tsushima Current leave through this strait, as a result of which it then becomes greatly weakened. Another 24% of the volume of water coming from the Korea Strait flows through the La Perouse Strait, and already to the north its flow of warm water becomes extremely insignificant, but still an insignificant part of the water Tsushima Current penetrates into the summer Strait of Tartary. In it, due to the small cross-section of the Nevelskoy Strait most of these waters turn south. As the flow of water in the Tsushima Current moves north, water from other currents is included in it and jets are diverted from it. In particular, the jets that deviate to the west in front of the Tatar Strait merge with the waters leaving it, forming a stream flowing at low speed to the south. Primorsky Current.
South of Peter the Great Bay, this current divides into two branches: the coastal one continues to move south and, in part in separate jets, together with the return waters of the Tsushima Current in eddy gyres, exits into Korea Strait, and the eastern jet deviates to the east and connects with the Tsushima Current. The coastal branch is called the North Korean Current.
The entire listed system of currents forms a cyclonic circulation common to the entire sea, in which the eastern periphery consists of a warm current, and the western periphery consists of a cold one.
Temperature distribution and speed on the surface of the Sea of Japan are presented according to the electronic Atlas of oceanography of the Bering, Okhotsk and Japanese seas(TOI FEB RAS) for January, March, May, July, September, October.
Current speeds in the southern half of the sea are higher than in the northern half. Calculated by the dynamic method they are in the upper 25 meter layer Tsushima Current decrease from 70 cm/s to Korea Strait to approximately 29 cm/s at the latitude of the La Perouse Strait and become less than 10 cm/s at Tatar Strait. The speed of the cold current is significantly lower. It increases to the south from several centimeters per second in the north to 10 cm/s in the southern part of the sea.
In addition to constant currents, drift and wind currents are often observed, which cause surges and surges of water. There are cases when the total currents, composed mainly of constant, drift and tidal currents, are directed at right angles to the shore or away from the shore. In the first case, they are called pressing, in the second, squeezing. Their speed usually does not exceed 0.25 m/s.
Water exchange through the straits has a dominant influence on the hydrological regime of the southern and eastern half of the Sea of Japan. Flowing through Korea Strait subtropical waters of the Kuroshio branch warm throughout the year southern regions seas and waters adjacent to the coast of the Japanese islands up to the La Perouse Strait, as a result of which the waters of the eastern part of the sea are always warmer than the western.
Literature: 1. Doronin Yu. P. Regional oceanology. - L.: Gidrometeoizdat, 1986.
2. Istoshin I.V. Oceanology. - L.: Gidrometeoizdat, 1953.
3. Sea of Japan pilotage. Part 1, 2. - L.: Navy Cart Factory, 1972.
4. Atlas of oceanography of the Bering, Okhotsk and Japan seas (POI FEB RAS). - Vladivostok, 2002
Head of OGMM
Yushkina K.A.
Warm currents are the water heating pipes of the globe.
A. I. Voeikov
The world ocean, or the Earth's hydrosphere, unites almost all oceanic and sea waters having a single surface. It occupies almost three-quarters of the surface of the globe - 361 million km 2, while the land is only 149 million (Fig. 14).
The average depth is relatively small - 3.8 km. Such a thin hydrosphere can be likened to a 1 mm thick film on a globe with a diameter of 3 m. But it plays a huge role in organic life and climates of the Earth.
The ocean is the cradle of life. In the distant past, in warm and quiet sea lagoons, the first living cells, and then the simplest organisms, arose and developed. If the liquid film had evaporated, then on the dried-out Earth there would not have been a single corner for the modern highly developed organic world. And the thermal regime would be different - in January at the North Pole, instead of the current average temperature of -30°, it would become -80°.
Of all the natural surfaces of the Earth, the ocean surface is the best absorber solar radiation. But the same surface in a different state of aggregation (ice and snow) is the most perfect reflector. Although the temperature range of the ocean surface and the surface layer of the atmosphere is small, the water in this narrow range changes its state quite often and quickly. This variability has a dramatic effect on the climate.
The ocean is a huge distiller. It evaporates 448,000 km 3 of water annually, while the continents only 71,000. The warmer the ocean, the more moisture it evaporates. Moist air, covering the planet, reduces heat leakage into space, better irrigates the land and makes it easier for the farmer to grow abundant harvests. The ocean is a powerful thermoregulator of the planet. Thanks large mass water and its high heat capacity (3200 times greater than that of air) it accumulates in summer solar heat and spends it in winter to heat the atmosphere, leveling out interseasonal climate variability. In some cases, the ocean evens out interannual fluctuations. Continents are not capable of accumulating heat, so the continental climate, as a rule, increases with distance from the borders with the ocean.
The waters of the ocean are in continuous movement. They absorb solar heat more than land and are the main supplier of energy to global wind systems. Hurricanes and storm winds stir and move vigorously water masses. Thus, the current of the Western winds in the Southern Hemisphere annually carries about 6 million km 3 of water around the Earth, which is equal to two volumes Mediterranean Sea. The surface 100-200 meter layer is especially active. But the subsurface and even bottom layers of the ocean are in perpetual motion. Sea currents bring large masses heat and cold. A particle of water can do anything in the World Ocean. round the world travel, changing its state, heating up under the equator and turning into ice in the polar waters of both hemispheres.
Sea currents, together with air currents, equalize the temperature between polar and tropical latitudes and fully fulfill the role noted in the epigraph in the words of A.I. Voeikov.
In table Table 4 shows temperatures by latitude zones, calculated and observed. The difference is the result of heat exchange determined by circulation processes in the atmospheric and hydrosphere shells of the Earth. It is easy to see how strongly interlatitudinal heat exchange affects the Earth’s temperature field. If it were not for it, then in the equatorial zone the temperature would rise by 13°, and in latitudes from 60° north latitude to the pole the temperature would drop on average by 22°. At the latitudes of Moscow and Leningrad, the climate of the modern Central Arctic would dominate, i.e., completely unsuitable for the plant world.
A quantitative idea of the interlatitudinal heat transfer by sea and air circulation processes is given in Table. 5.
As can be seen from the table, the arrival of solar short-wave radiation quickly decreases from the equator to the pole, which is explained by the sphericity of the Earth. Losses through long-wave radiation, on the contrary, remain almost unchanged in all latitude zones, since the spherical surface of the Earth does not matter here. This results in a relative excess of heat in latitudes below 40° and a deficiency above this limit, which gives rise to the temperature contrasts given in Table. 4. B real conditions, as we have seen, excess and deficiency of heat are balanced due to interlatitudinal heat exchange carried out through water and air exchange mechanisms.
Of practical interest is the question: who plays the decisive role in transporting heat from the planetary boiler to the planetary refrigerator, i.e. from the equatorial and tropical latitudes to the polar ones? Sea or air advection?
IN different time the contribution of each of these advections is different. IN modern conditions and in colder times in the past, when the Arctic basin was largely all year round covered with drifting ice, sea advection is relatively small, but as Atlantic waters rush into the Arctic basin, its role increases. The current ratio of sea and air advection is defined differently by individual researchers: from 1:2 in favor of air exchange to 1:1.5 in favor of sea advection. We will not take air advection into account in our calculations, since its relative and absolute significance in acryogenic conditions naturally decreases. We will reserve the relatively small contribution of heat that air advection makes as a “safety margin”.
A.I. Voeikov, calling sea currents temperature regulators, believed that “ air currents They do not contribute to the equalization of temperatures between the equator and the pole to the same extent as sea currents, and in terms of their direct influence in this regard they cannot be equal to the latter. But their indirect influence is very great.”
P.P. Lazarev in 1927 built a model of oceanic and atmospheric circulation. This model showed that ocean currents passing through North Pole and bringing a large amount of heat to the polar region, they warm it. Paying tribute to the Soviet experimenter, the Englishman Brooks noted: “When the model reflected the modern distribution of land and sea, the currents that arose in the basin to the smallest detail turned out to be similar to the current currents... In models that reproduced the conditions of warm periods, ocean currents passed through the pole, while in models of cold periods, not a single current crossed the poles.”
Brooks rejected: self-sufficient role atmospheric circulation and believed that its possible changes are not capable of causing major climate changes on their own, without the involvement of other factors. “The role of atmospheric circulation,” he wrote, “should be considered as regulating, sometimes perhaps enhancing, but not generating major climate fluctuations.” If sea currents, according to the apt definition of A.I. Voeikov, serve as climate thermoregulators, then the same cannot be said about macrocirculations of the atmosphere. Of all the climate-forming factors, as noted by B.L. Dzerdzeevsky, they, despite their dynamism, are the least constant factor.
Analysis of bottom sediments in the Arctic basin also confirmed that it is sea currents, compared to air currents, that play a decisive role in climate formation. In cases where warm Atlantic waters penetrated weakly into the Arctic basin, temperatures in the polar latitudes fell. Low temperatures not only led to recovery ice cover basin, but also to the revival of ice sheets on the continents.
Giving great value directions of sea currents in climate formation, A.I. Voeikov wrote: “Don’t we have the right to say, having weighed the main conditions influencing the climate: without any change in the mass of current currents, without changes in the average air temperature on globe Temperatures in Greenland similar to those there in the Miocene period are again possible, and glaciers are again possible in Brazil. This requires only certain changes that direct the currents in a different way than now.” Many years later, Academician E.K. Fedorov pointed out the need for a thorough study of possible climate changes in connection with the deviation of some sea currents, believing that it should become one of the most important directions in our research.
Therefore, it will be useful to recall brief characteristics of modern ocean currents (Fig. 15).
The most powerful warm current in the World Ocean, which has a decisive impact on the climate of the Northern Hemisphere, is the system of North Atlantic currents under common name Gulf Stream. The system covers a vast area from the Gulf of Mexico to the shores of Spitsbergen and Kola Peninsula. Actually, the Gulf Stream is the area from the confluence of the Florida Current with the Antilles (30° north latitude) to the island of Newfoundland. At latitude 38°, the thickness reaches 82 million km 3 /sec, or 2585 thousand km 3 /year.
In the area of Nova Scotia and the southern edge of the Newfoundland Bank, the Gulf Stream comes into contact with the cold, desalinated waters of the Cabot Current, and then with the waters of the cold Labrador Current. The thickness of Labrador is approximately 4 million m 3 /sec. It, together with cold waters, carries sea ice and icebergs to the Big Bank area.
Ice of sea origin usually stays above the bank itself and, falling into the waters of the Gulf Stream, quickly melts. Icebergs have more long life. Once in the waters of the Gulf Stream, they drift to the northeast and even north again, and often make a long voyage throughout the North Atlantic. In exceptional cases, they are carried to the south, almost to 30° north latitude, and to the east almost to Gibraltar.
A significant part of the icebergs spread along the outskirts of the Big Bank, especially along the northern ones, where, running aground, they remain until they melt so much that their reduced draft allows them to continue their drift further.
In addition to sea ice and icebergs, in the area of Newfoundland, as well as off the coast of Labrador, there is also bottom ice, which floats to the surface as it forms and participates in the general drift of ice. Since the temperature difference between the Gulf Stream and Labrador is very large, the waters of the Gulf Stream are greatly cooled.
After passing the Great Newfoundland Bank, the Gulf Stream, called the North Atlantic Current, moves east from average speed 20-25 km/day and, as it moves towards the shores of Europe, it takes a north-eastern direction. Behind the banks of Newfoundland, it separates branch-sleeves that are lost in the whirlpools. At about 25° west longitude, a large branch of the Canary Current departs from its southern edge to the Iberian Peninsula.
When approaching the British Isles, a large branch separates from the North Atlantic Current on the left side - the Irminger Current, heading north towards Iceland; the main mass, crossing the Whyville-Thomson threshold, passes in the strait between the Shetland and Faroe Islands and enters the Norwegian Sea.
The line of Wyville-Thomson rapids, and then the Greenland-Iceland rapids, form a clear boundary between the Atlantic and Arctic oceans. At a depth of 1000 m south of the Faroe-Shetland Sill, which is less than 500 m deep, the water temperature is almost 8° higher than to the north. Salinity at the same depth on the southern side of the threshold is higher by 0.3 ppm. The explanation for this exceptional contrast lies in the deflection to the west of the deep layers of warm waters on south side, while on the northern side of the threshold the cold waters are deflected to the east. As a result, to the north of the threshold, the entire deep-water part of the Greenland and Norwegian seas is filled with very cold and dense water. This system of thresholds also demarcates areas dominated by Atlantic and Arctic waters on the surface.
The North Atlantic Current, bypassing the strait between the Faroe and Shetland Islands, called the Norwegian Warm Current, runs along the western coast of the Scandinavian Peninsula. In the area where the Arctic Circle intersects, a branch of an independent flow of warm waters departs from the left side of it, which has a stable direction to the north in all seasons of the year.
To the west of the North Cape, from the Norwegian Current on the right side, the North Cape Current departs east into the Barents Sea. East of the 35th meridian, although it breaks up into small jets, it plays a noticeable role in the term Barents Sea. Thus, the small Murmansk branch makes the Murmansk port open all year round for free floating ships of any type.
Due to the greater density, Atlantic waters in a significant part of the Barents Sea are submerged under light layers of local water. Part of the Atlantic waters penetrates the Kara Sea. At the same time, warm Atlantic water under a layer of local polar water also enters the Barents Sea from the north, from the Arctic basin along deep trenches to the west and east of Earth Franz Josef, where it ends up as a branch from the already deep Spitsbergen Current.
The left branch of the Norwegian Current, after the North Cape branch departs from it, goes north under the name of the Spitsbergen Current. Its main flow, upon entering the Spitsbergen-Greenland strait, loses part of its kinetic and thermal energy due to the fact that the strait reflects part of the water masses and due to lateral mixing with the waters of the oncoming cold East Greenland Current. The reflected water masses move first in the western and then in south direction, wedge into the cold jets of the East Greenland Current and, mixing with them, form circular currents in the region of the prime meridian and 74-78° northern latitude.
The Spitsbergen Current passes along the Western shores of Spitsbergen at a speed of about 6 km per day, with average temperature water 1.9° and salinity 35 ppm. North of Spitsbergen, due to the difference in densities, it sinks under the Arctic waters and continues its path in the Central Arctic in the form of a deep warm current. But this is not the only place where the warm waters of Svalbard are submerged under the cold Arctic ones. In the Greenland eastern shallow waters, high positive temperatures prevail everywhere at depths of more than 200 m. These warm waters can penetrate deep into bays and fiords. Of course, such deep penetration under the oncoming desalinated waters, quickly moving southward, carrying with them not only pack ice with deep draft, but also icebergs, cannot occur without big loss kinetic energy and warmth. The work of the North Pole-1 station has established a very active role of Atlantic waters in warming the upper cold layer. Even in winter, despite the low winter temperatures air, Atlantic waters, acting on the ice from below, weaken them all the time. This also applies to local ice, and to ice carried from the Central Arctic to the Greenland Sea.
The passage of Gulf Stream waters from the Strait of Florida to Thomson's Threshold takes 11 months, and from Thomson's Threshold to Spitsbergen about 13 months.
The Irminger Current, having separated as it approached northern shores British Isles from the North Atlantic Current, acquires a direction north towards Iceland. At approximately 63° north latitude the current bifurcates. Its right part goes into the Denmark Strait and with its warm waters washes not only the western shores of Iceland, but also the northern ones. In this area it comes into contact with the Icelandic branch of the East Greenland Current and, mixing with its waters, cools and moves to the southeast. The left, more powerful part of the Irminger, after branching, turns southwest and then south, under an oblique section it meets the flow of water and ice of the East Greenland Current. At the junction of the waters, the temperature at a distance of 20 to 36 km drops from 10 to 3°.
In the area of the southern tip of Greenland, the Irminger and East Greenland currents concentrically go around Cape Farwell and the entire southwestern part of the island and, under the name of the West Greenland Current, pass through Davis Strait to Baffin Bay.
The East Greenland Cold Current, which serves as the main route for water flow and ice removal from the Arctic Basin, originates on the continental shelf of Asia. With a gradual movement from the mainland to the north, the current in the Pole region bifurcates: one branch goes to the American sector of the Arctic, the other - towards the Greenland Sea. Off the northeastern coast of Greenland, the waters of a cold current flowing from the west along the northern coast of Greenland join the East Greenland Current. The width of the East Greenland Current at 75-76° north latitude is 175-220 km, the speed increases from two miles per day at a latitude of 80° to 8 miles at 75°, up to 9 miles at 70° and up to 16-18 miles at 65 -66° north latitude; The water temperature is below 0° everywhere. Having passed the Gulf of Denmark, it comes into contact with the warm Irminger, and with it it goes around Cape Farwell. In this area, sea ice and icebergs, falling into currents of warm water, quickly melt. Cape Farwell has a belt width floating ice in some months it reaches 250-300 km, but thanks to the warm waters of Irminger, north of Cape Desolation (62° north latitude), the ice never forms a closed cover here, and the width of its belt does not exceed several tens of kilometers.
The Labrador Current is a continuation of the cold Baffin Island Current, which originates at Smith Strait. It runs along the shores of the Labrador Peninsula and further south along eastern shore Newfoundland; its capacity is approximately 130,000 km 3 /year. It carries sea ice and icebergs and, as already noted, greatly cools the waters of the Gulf Stream. The waters of Labrador remain cold all year round, cooling the entire coastline it washes. Tundra vegetation in Newfoundland owes its existence to the cold waters of Labrador. It is noteworthy that at almost the same latitude, but on the other side of the Atlantic, in France, they grow the best varieties grapes
Looking at the current paths of the North Atlantic, we are convinced how right A.I. Voeikov was when he said that the direction of sea currents plays a huge role in climate formation. On the same meridian, the ice-free port of Murmansk is located far beyond the Arctic Circle, and the Azov ports, located 2,500 km to the south, freeze for several months every year. And finally, the North Atlantic Basin can be likened to a bathtub into which water flows through two taps. cold water(Labrador and East Greenland Currents) and after one - warm water Gulf Stream. By adjusting the taps, we can change the temperature of the Atlantic, and with it the climate of the surrounding continents. Recognition of the large role of sea currents in climate formation has determined, since the end of the last century, ways of regional improvements in the climate regime, changing the directions of warm and cold currents. Along with this, projects of large hydraulic engineering measures to regulate and transfer river flow were developed. Let us dwell on the main hydraulic engineering projects for the reclamation of natural conditions.