Previously, before the invention of radio, a bottle sealed with sealing wax was thrown from a ship that was crashing, where they put a note indicating the place of the disaster. The sailors hoped that maybe the bottle would be seen from another ship and they would be rescued. Many of these bottles in those days were caught off the coast of the Scandinavian Peninsula, although, judging by the notes, they were thrown thousands of kilometers from the place of discovery, somewhere in the central part of the Atlantic Ocean.
When scientists began to compare the map, where the arrows indicate the direction of the winds over the oceans, with the map, where the ocean currents are indicated, it turned out that these directions almost coincided. Thus, in our time, one can easily explain why bottles thrown in the central part of the Atlantic Ocean were found off the coast of the Scandinavian Peninsula.
- Ocean currents are formed mainly under the influence of constant winds. That is, the wind drives the water and makes it move in a certain direction.
- tides are also one of the causes of sea currents.
- In connection with different water density in different parts of water basins, water can also move long distances.
Here, on both sides of the Equator, constant winds blow from Africa to America. Under the influence of these winds, water flows along the Equator, part of it enters Gulf of Mexico, from where it rushes in a powerful stream into the Atlantic Ocean and further - to the shores of Europe. Off the coast of America, this current is called the Gulf Stream. The waters of the Gulf Stream flow at a speed of up to 10 km per hour. The width of the water flow is from 75 to 120 km, and the depth is 700 m. It is estimated that all rivers the globe, taken together, carry less water than the Gulf Stream. In the northern part Atlantic Ocean it is called the North Atlantic. This current is warm, since it is born in the warmest part of the Atlantic Ocean.
cold currents
The cold Labrador Current passes from the Arctic Ocean past Greenland to the Labrador Peninsula. The water of this current is much colder than the surrounding water.
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Oceanic, or sea, currents are the forward movement of water masses in the oceans and seas, caused by various forces. Although the most significant cause of the currents is the wind, they can also form due to the unequal salinity of individual parts of the ocean or sea, the difference in water levels, and the uneven heating of different parts of the water areas. In the ocean there are eddies created by bottom irregularities, their size often reaches 100-300 km in diameter, they capture layers of water hundreds of meters thick. If the factors causing the currents are constant, then a constant current is formed, and if they are episodic, then a short-term, random current is formed. According to the prevailing direction, the currents are divided into meridional, carrying their waters to the north or south, and zonal, spreading latitudinally. Currents in which the water temperature is higher than the average temperature for the same latitudes are called warm, lower - cold, and currents having the same temperature as the surrounding waters are called neutral. Monsoon currents change their direction from season to season, depending on how the coastal monsoon winds blow. Countercurrents move towards neighboring, more powerful and extended currents in the ocean. The direction of currents in the World Ocean is influenced by the deflecting force caused by the rotation of the Earth, the Coriolis force. In the Northern Hemisphere, it deflects currents to the right, and in the Southern Hemisphere, to the left. The speed of currents on average does not exceed 10 m/s, and they extend to a depth of no more than 300 m. In the World Ocean, there are constantly thousands of large and small currents that go around the continents and merge into five giant rings. The system of currents of the World Ocean is called circulation and is connected, first of all, with the general circulation of the atmosphere. Ocean currents redistribute solar heat absorbed by masses of water. Warm water, heated by the sun's rays at the equator, they carry to high latitudes, and cold water from the polar regions, due to currents, gets to the south. Warm currents increase air temperature, while cold currents, on the contrary, decrease it. Territories washed by warm currents have a warm and humid climate, and those near which cold currents pass are cold and dry. The most powerful current of the World Ocean is the cold current of the West Winds, also called the Antarctic circumpolar (from Latin cirkum - around). The reason for its formation are strong and stable westerly winds blowing from west to east over the vast expanses of the Southern Hemisphere from temperate latitudes to the coast of Antarctica. This current covers a zone with a width of 2500 km, extends to a depth of more than 1 km and carries up to 200 million tons of water every second. There are no large land masses on the path of the Western Winds, and it connects in its circular flow the waters of three oceans - the Pacific, Atlantic and Indian. The Gulf Stream is one of the largest warm currents northern hemisphere. It passes through the Gulf of Mexico (eng. Gulf Stream - the Gulf) and carries the warm tropical waters of the Atlantic Ocean to high latitudes. This giant stream of warm water largely determines the climate of Europe, making it soft and warm. Every second, the Gulf Stream carries 75 million tons of water (for comparison: the Amazon, the most full-flowing river in the world, is 220 thousand tons of water). At a depth of about 1 km under the Gulf Stream, a countercurrent is observed.
Variety of currents. Currents in the seas and oceans are just as important a form of water movement as waves.
Flow is the movement of water in a horizontal direction.
Currents carry huge masses of water over long distances. Their length can reach several thousand kilometers, width - tens and even hundreds of kilometers, thickness - several kilometers.
One of the largest currents is the Gulf Stream (Fig. 129). It carries more water than all the rivers of our planet combined.
Rice. 129. Main sea currents
How are warm and cold surface currents marked on a map? Find the largest warm and cold currents in the figure.
Rice. 130. Variety of ocean currents
Ocean currents differ in temperature, depth, duration of existence (Fig. 130).
A warm current is one whose temperature is higher than the temperature of the surrounding water. Cold - the temperature of which is lower than the temperature of the surrounding water. If we compare the water temperature of the currents themselves, then the water of the cold current in the tropics can be warmer than the water of the warm current in high latitudes.
Causes of currents. The main cause of surface currents is wind. touching water surface, it carries water with it. Under the influence of stable westerly winds, the most powerful westerly current in the World Ocean arises, forming a ring around Antarctica.
The direction of the currents is also influenced by the position of the continents and the outlines of their coasts. The land becomes a barrier, forcing the current to turn and head along the coasts.
In the depths of the seas and oceans, currents form due to differences in water density. More dense waters move towards less dense ones, creating powerful water streams. Information about underwater currents is important for fishing and submarine traffic.
The meaning of currents. Ocean currents affect the climate and nature of the Earth. They redistribute heat and cold between latitudes. Warm currents bring heat from tropical to temperate and arctic latitudes. Cold currents return cold water to the equator. At the same time, the currents strongly influence the climate of the coastal territories of the continents.
Think about how warm and cold ocean currents affect the nature of the coasts.
Thanks to currents in the oceans and seas, not only heat is redistributed, but also dissolved nutrients and gases. Living organisms get more opportunities for development. With the help of currents, plants and animals move and populate new territories. Currents can help or hinder navigation, so sailors and fishermen must consider their direction and speed.
Questions and tasks
- What is flow?
- What is considered a warm current? which one is cold?
- Name the main reasons for the formation of currents.
- What is the significance of currents for the climate of the Earth, plants and animals of the ocean?
How does the temperature change surface water in the oceans?
The temperature of the surface waters of the oceans decreases in the direction from the equator to the poles.
What determines the density of the oceans?
The density of the waters of the oceans depends on temperature and salinity.
Find the largest warm and cold currents in the figure.
Think about how warm and cold ocean currents affect the nature of the coasts.
Warm and cold currents affect the climate and nature of the coasts. Thus, warm currents increase the air temperature by and increase the amount of precipitation. Cold currents lower temperatures and reduce rainfall.
Questions and tasks
1. What is a current?
Flow is the movement of water in a horizontal direction.
A warm current has a water temperature several degrees higher than the surrounding ocean water. Cold current - Vice versa. Warm currents usually move from warmer latitudes to colder latitudes, and cold currents, vice versa.
3. What are the main reasons for the formation of currents.
The main cause of surface currents is wind. Touching the water surface, it entails water. In the depths of the seas and oceans, currents form due to differences in water density.
4. Find and point to physical map world's largest ocean currents, listed in the text of the paragraph.
Warm currents - South and North trade winds, Monsoon, Gulf Stream, North Atlantic, Brazilian.
Cold currents - the course of the Western winds, Peruvian, Labrador.
5. Using figure 154, trace the possible paths of a corked bottle that was thrown from a ship off the western coast. South America.
A corked bottle thrown into the water off the western coast of Young America will enter the Peruvian current and head north towards the equator. At the equator, the bottle will fall into the South trade wind current. It will carry the bottle to the shores of Australia or New Guinea.
6. What is the significance of currents for the climate of the Earth, plants and animals of the ocean?
Ocean currents affect the climate and nature of the Earth. They redistribute heat and cold between latitudes. Warm currents bring heat from tropical to temperate and arctic latitudes. Cold currents return cold water to the equator. The North Atlantic Current is the main reason for the mildness of the climate Northern Europe. Due to the currents in the oceans and seas, not only heat is redistributed, but also dissolved nutrients and gases. Living organisms get more opportunities for development. With the help of currents, plants and animals move and populate new territories.
Which moves with a certain cyclicity and frequency. Differs in a constancy of physical and chemical properties and a specific geographical location. It can be cold or warm, depending on belonging to the hemispheres. Each such flow is characterized by increased density and pressure. The flow rate of water masses is measured in sverdrupa, in a broader sense - in units of volume.
Varieties of currents
First of all, cyclically directed water flows are characterized by such features as stability, speed, depth and width, Chemical properties, influencing forces, etc. Based on the international classification, there are three categories of flows:
1. Gradient. Occur when exposed to isobaric layers of water. A gradient ocean current is a flow characterized by horizontal movements of the isopotential surfaces of the water area. According to their initial features, they are divided into density, baric, stock, compensation and seiche. As a result of the runoff flow, precipitation and ice melting are formed.
2. Wind. Determined by the slope of the sea level, the strength of the air flow and fluctuations in mass density. A subspecies is drifting. This is a flow of water caused purely by the action of the wind. Only the surface of the pool is exposed to oscillations.
3. Tidal. They appear most strongly in shallow water, in estuaries and near the coast.
A separate type of flow is inertial. It is caused by the action of several forces at once. According to the variability of movement, constant, periodic, monsoon and trade wind flows are distinguished. The last two are determined by direction and speed seasonally.
Causes of ocean currents
At the moment, the circulation of waters in the world's waters is only beginning to be studied in detail. By and large, specific information is known only about surface and shallow currents. The main snag is that the oceanographic system has no clear boundaries and is in constant motion. It is a complex network of flows due to various physical and chemical factors.
Nevertheless, the following causes of ocean currents are known today:
1. Cosmic impact. This is the most interesting and at the same time difficult to learn process. In this case, the flow is determined by the rotation of the Earth, the impact on the atmosphere and hydrological system of the planet of cosmic bodies, etc. A striking example is the tides.
2. Wind exposure. The circulation of water depends on the strength and direction of air masses. In rare cases, we can talk about deep currents.
3. Density difference. Streams are formed due to uneven distribution of salinity and temperature of water masses.
atmospheric effect
In the world's waters, this kind of influence is caused by the pressure of heterogeneous masses. Coupled with cosmic anomalies, water flows in the oceans and smaller basins change not only their direction, but also their power. This is especially noticeable in the seas and straits. A prime example is the Gulf Stream. At the beginning of his journey, he is characterized by increased speed.
During the Gulf Stream, it is accelerated simultaneously by opposite and fair winds. This phenomenon forms a cyclic pressure on the layers of the pool, accelerating the flow. From here in a certain period of time there is a significant outflow and inflow a large number water. The lower the atmospheric pressure, the higher the tide.
When the water level drops, the slope Strait of Florida becomes smaller. Because of this, the flow rate is significantly reduced. Thus, it can be concluded that increased pressure reduces the force of the flow.
wind impact
The connection between the flows of air and water is so strong and at the same time simple that it is hard not to notice even with the naked eye. Since ancient times, navigators have been able to calculate the appropriate ocean current. This became possible thanks to the work of the scientist W. Franklin on the Gulf Stream, dating back to the 18th century. A few decades later, A. Humboldt indicated precisely the wind in the list of the main extraneous forces affecting the water masses.
From a mathematical point of view, the theory was substantiated by the physicist Zeppritz in 1878. He proved that in the World Ocean there is a constant transfer of the surface layer of water to deeper levels. In this case, the wind becomes the main influencing force on the movement. The current velocity in this case decreases in proportion to the depth. The determining condition for the constant circulation of waters is an infinitely long time of action of the wind. The only exceptions are the trade winds of air, which cause the movement of water masses in the equatorial strip of the World Ocean seasonally.
Density difference
The impact of this factor on water circulation is the most important cause of currents in the World Ocean. Large-scale studies of the theory were carried out by the international expedition Challenger. Subsequently, the work of scientists was confirmed by Scandinavian physicists.
The heterogeneity of the densities of water masses is the result of several factors at once. They have always existed in nature, representing a continuous hydrological system of the planet. Any deviation in water temperature entails a change in its density. In this case, it is always observed back proportional dependence. The higher the temperature, the lower the density.
Also, the state of aggregation of water affects the difference in physical indicators. Freezing or evaporation increases density, precipitation decreases it. Affects the strength of the current and salinity of water masses. It depends on the melting of ice, precipitation and the level of evaporation. In terms of density, the World Ocean is quite uneven. This applies to both surface and deep layers of the water area.
Currents of the Pacific Ocean
The general scheme of flows is determined by the circulation of the atmosphere. Thus, the east trade wind contributes to the formation of the North Current. It crosses the waters from the Philippine Islands to the coast Central America. It has two branches that feed the Indonesian Basin and the Equatorial Ocean Current Pacific Ocean.
The largest currents in the water area are the Kuroshio, Alaska and California currents. The first two are warm. The third stream is the cold ocean current of the Pacific Ocean. The basin of the Southern Hemisphere is formed by the Australian and Tradewind currents. A little to the east of the center of the water area, the Equatorial countercurrent is observed. Off the coast of South America, there is a branch of the cold Peruvian current.
During the summer, the El Niño ocean current operates near the equator. It pushes back the cold masses of water of the Peruvian Stream, forming a favorable climate.
Indian Ocean and its currents
The northern part of the basin is characterized by a seasonal change of warm and cold flows. This constant dynamics is caused by the action of the monsoon circulation.
In winter, the Southwest Current dominates, which originates in the Bay of Bengal. A little further south is Western. It's an ocean current indian ocean crosses the water area from the coast of Africa to the Nicobar Islands.
In summer, the east monsoon contributes to a significant change in surface waters. The equatorial countercurrent shifts to a depth and noticeably loses its strength. As a result, its place is occupied by powerful warm Somali and Madagascar currents.
Arctic ocean circulation
The main reason for the development of the undercurrent in this part of the World Ocean is a powerful influx of water masses from the Atlantic. The fact is that the centuries-old ice cover does not allow the atmosphere and cosmic bodies to influence the internal circulation.
The most important course of the Arctic Ocean is the North Atlantic. It drives huge volumes of warm masses, preventing the water temperature from dropping to critical levels.
The Transarctic current is responsible for the direction of ice drift. Other major streams include the Yamal, Svalbard, North Cape and Norwegian currents, as well as a branch of the Gulf Stream.
currents of the atlantic basin
The salinity of the ocean is extremely high. The zonality of water circulation is the weakest among other basins.
Here the main ocean current is the Gulf Stream. Thanks to him, the average water temperature is kept at around +17 degrees. This warm ocean warms both hemispheres.
Also the most important streams of the basin are the Canary, Brazilian, Benguela and Tradewind currents.