Masses of water that continuously move through the oceans are called currents. They are so strong that no continental river can compare with them.

What types of currents are there?

Until a few years ago, only currents moving on the surface of the seas were known. They are called superficial. They flow at depths of up to 300 meters. We now know that deep currents occur in deeper areas.

How do surface currents occur?

Surface currents are caused by constantly blowing winds - trade winds - and reach speeds of 30 to 60 kilometers per day. These include equatorial currents (directed to the west), off the eastern coasts of continents (directed towards the poles) and others.

What are trade winds?

Trade winds are air currents (winds) that are stable throughout the year in the tropical latitudes of the oceans. In the Northern Hemisphere, these winds are directed from the northeast, in the Southern Hemisphere - from the southeast. Due to the rotation of the Earth, they always deviate to the west. The winds that blow in the Northern Hemisphere are called northeast trade winds, and in the Southern Hemisphere they are called southeast trade winds. Sailing ships use these winds to arrive at their destination faster.

What are equatorial currents?

Trade winds blow constantly and so strongly that they divide the ocean waters on both sides of the equator into two powerful westerly currents, which are called equatorial currents. On their way they find themselves on the eastern coasts of parts of the world, so these currents change direction to the north and south. Then they fall into other wind systems and break up into small currents.

How do deep currents arise?

Deep currents, unlike surface ones, are caused not by winds, but by other forces. They depend on the density of the water: cold and salty water is denser than warm and less salty, and therefore sinks lower to the seabed. Deep currents occur because cooled, salty water in northern latitudes sinks and continues to move above the seafloor. A new, warm surface current begins its movement from the south. The cold deep current carries water towards the equator, where it warms up again and rises. Thus, a cycle is formed. Deep currents move slowly, so sometimes years pass before they rise to the surface.

What is worth knowing about the equator?

The equator is an imaginary line that passes through the center of the Earth perpendicular to the axis of its rotation, that is, it is equally distant from both poles and divides our planet into two hemispheres - the Northern and Southern. The length of this line is about 40,075 kilometers. The equator is located at zero degree latitude.

Why does the salt content of seawater change?

The salt content of seawater increases when the water evaporates or freezes. The North Atlantic Ocean has a lot of ice, so the water there is saltier and colder than at the equator, especially in winter. However, the salinity of warm water increases with evaporation, as salt remains in it. Salt content decreases when, for example, ice melts in the North Atlantic and fresh water flows into the sea.

What are the effects of deep currents?

Deep currents carry cold water from polar regions to warm tropical countries, where water masses mix. Rising cold water affects the coastal climate: rain falls directly on the cold water. The air arrives on the warm continent almost dry, so the rains stop and deserts appear on the coastal shores. This is how the Namib Desert on the South African coast came into being.

What is the difference between cold and warm currents?

Depending on the temperature, sea currents are divided into warm and cold. The first ones appear near the equator. They carry warm waters through cold waters located near the poles and heat the air. Counter sea currents flowing from the polar regions towards the equator transport cold waters through the surrounding warm ones, and as a result the air cools. Sea currents are like a huge air conditioner that distributes cold and warm air around the globe.

What are burs?

Bores are tidal waves that can be observed in those places where rivers flow into the seas - that is, at the mouths. They arise when so many waves running towards the shore accumulate in a shallow and wide funnel-shaped mouth that they all suddenly flow into the river. In the Amazon, one of the South American rivers, the surf became so raging that a five-meter wall of water advanced more than a hundred kilometers inland. Bors also appear in the Seine (France), the Ganges delta (India) and on the coast of China.

Alexander von Humboldt (1769-1859)

German naturalist and scientist Alexander von Humboldt traveled extensively throughout Latin America. In 1812, he discovered that a cold deep current moves from the polar regions to the equator and cools the air there. In his honor, the current that carries water along the coast of Chile and Peru was named the Humboldt Current.

Where on the planet are the largest warm sea currents?

The largest warm sea currents include the Gulf Stream (Atlantic Ocean), Brazil (Atlantic Ocean), Kuroshio (Pacific Ocean), Caribbean (Atlantic Ocean), North and South Equatorial Currents (Atlantic, Pacific and Indian Oceans), and the Antilles (Atlantic Ocean). ocean).

Where are the largest cold sea currents?

The largest cold sea currents are the Humboldt (Pacific Ocean), Canary (Atlantic Ocean), Oyashio or Kuril (Pacific Ocean), East Greenland (Atlantic Ocean), Labrador (Atlantic Ocean) and California (Pacific Ocean).

How do sea currents affect climate?

Warm sea currents, first of all, affect the air masses surrounding them and, depending on the geographical location of the continent, warm the air. Thus, thanks to the Gulf Stream in the Atlantic Ocean, the temperature in Europe is 5 degrees higher than it could be. Cold currents that move from the polar regions to the equator, on the contrary, lead to a decrease in air temperature.

What are the effects of changes in sea currents?

Ocean currents can be affected by sudden events such as volcanic eruptions or changes associated with El Niño. El Niño is a warm water current that can displace cold currents near the coasts of Peru and Ecuador in the Pacific Ocean. Although El Niño's influence is limited to certain areas, its effects affect the climate of remote regions. It causes heavy rainfall along the coasts of South America and eastern Africa, resulting in devastating floods, storms and landslides. In contrast, the tropical rainforests around the Amazon experience a dry climate that reaches Australia, Indonesia and South Africa, contributing to droughts and the spread of forest fires. Near the Peruvian coast, El Niño leads to mass die-offs of fish and corals as plankton, which live primarily in cold water, suffer as it warms.

How far can sea currents carry objects out to sea?

Sea currents can carry objects that fall into the water over vast distances. For example, wine bottles can be found in the sea, which 30 years ago were thrown from ships in the ocean between South America and Antarctica and carried thousands of kilometers away. Currents carried them across the Pacific and Indian oceans!

What is worth knowing about the Gulf Stream?

The Gulf Stream Current is one of the most powerful and famous sea currents that arises in the Gulf of Mexico and carries warm waters to the Spitsbergen archipelago. Thanks to the warm waters of the Gulf Stream, Northern Europe enjoys a mild climate, although it should be much colder here since it is located as far north as Alaska, where it is freezing cold.

What are sea currents - video

They play a big role in shaping the climate on planet Earth, and are also largely responsible for the diversity of flora and fauna. Today we will get acquainted with the types of currents, the reasons for their occurrence, and consider examples.

It's no secret that our planet is washed by four oceans: the Pacific, Atlantic, Indian and Arctic. Naturally, the water in them cannot be stagnant, as this would long ago lead to an environmental disaster. Thanks to the fact that it constantly circulates, we can live fully on Earth. Below is a map of ocean currents; it clearly shows all the movements of water flows.

What is an ocean current?

The current of the World Ocean is nothing more than the continuous or periodic movement of large masses of water. Looking ahead, let’s say right away that there are many of them. They differ in temperature, direction, depth penetration and other criteria. Ocean currents are often compared to rivers. But the movement of river flows occurs only downward under the influence of gravity. But the circulation of water in the ocean occurs due to many different reasons. For example, wind, uneven density of water masses, temperature differences, the influence of the Moon and the Sun, changes in pressure in the atmosphere.

Causes

I would like to start my story with the reasons that give rise to the natural circulation of water. Even now there is practically no accurate information. This can be explained quite simply: the ocean system does not have clear boundaries and is in constant motion. Now the currents that are closer to the surface have been studied in more depth. Today, one thing is known for sure: the factors influencing water circulation can be both chemical and physical.

So, let's look at the main reasons for the occurrence of ocean currents. The first thing I want to highlight is the impact of air masses, that is, wind. It is thanks to him that surface and shallow currents function. Of course, wind has nothing to do with water circulation at great depths. The second factor is also important: the impact of outer space. In this case, currents arise due to the rotation of the planet. And finally, the third main factor that explains the causes of ocean currents is different densities of water. All streams of the World Ocean differ in temperature, salinity and other indicators.

Directional factor

Depending on the direction, ocean water circulation flows are divided into zonal and meridional. The first ones move west or east. Meridional currents go south and north.

There are also other types that are caused by such ocean currents called tidal currents. They are most powerful in shallow waters in the coastal zone, at river mouths.

Currents that do not change strength and direction are called stable, or established. These include the Northern Trade Wind and Southern Trade Wind. If the movement of a water flow changes from time to time, then it is called unstable, or unsteady. This group is represented by surface currents.

Surface currents

The most noticeable of all are surface currents, which are formed due to the influence of wind. Under the influence of the trade winds that constantly blow in the tropics, huge flows of water are formed in the equator region. They form the Northern and Southern Equatorial (trade wind) currents. A small part of these turns back and forms a countercurrent. The main flows are diverted to the north or south when colliding with continents.

Warm and cold currents

The types of ocean currents play a critical role in the distribution of climate zones on Earth. Warm streams are usually called water streams that carry water with temperatures above zero. Their movement is characterized by a direction from the equator to high latitudes. These are the Alaska Current, the Gulf Stream, Kuroshio, El Niño, etc.

Cold currents transport water in the opposite direction compared to warm ones. Where a current with a positive temperature occurs on their path, an upward movement of water occurs. The largest are considered to be Californian, Peruvian, etc.

The division of currents into warm and cold is conditional. These definitions reflect the ratio of the water temperature in the surface layers to the ambient temperature. For example, if the flow is colder than the rest of the water mass, then such a flow can be called cold. If on the contrary, then it is considered

Ocean currents determine many things on our planet. By constantly mixing the water in the World Ocean, they create conditions favorable for the life of its inhabitants. And our lives directly depend on this.

Geography lesson V 7th grade e

Topic: “Ocean Currents”

Target: reveal the reasons for the circular movement of surface waters, give an idea of ​​the general pattern of surface currents in the World Ocean.

Tasks:

To form an idea of ​​ocean currents, the reason for their occurrence, types of currents and their use.

identify general patterns of ocean currents

Continue training in working with contour maps, identifying patterns, reading atlas maps.

To cultivate an aesthetic perception of geographical objects

Equipment: textbook, atlas, map of the oceans, physical map of the hemispheres, presentation, geographic simulator, test, portraits of travelers (H. Columbus, T. Heyerdahl).

Main content: ocean currents. Reasons for the formation of ocean currents. Types of ocean currents. The main surface currents of the World Ocean. The importance of ocean currents.

Lesson type: combined.

DURING THE CLASSES

Organizing time

Good morning, guys! Take a seat and check that you are ready for the lesson and that everything is in place. Today we have not just a lesson - today we have a holiday, because guests came to us - geography teachers from all over our region. We were expecting guests, and today, putting aside all preparatory worries, let's plunge into the world of the wonderful science of geography.

Checking homework.

In the last lesson, we studied the topic...climatic zones and regions of the earth. Let's remember what we talked about in the last and previous lessons.

1. Go to the board to complete an individual task

Draw a diagram of atmospheric circulation using colored crayons (Task card, blue, red and green chalk)

2.An individual test of our geographic simulator on questions will be completed on a laptop

3. Let’s remember what a climate zone is?

Climate zone –

What are the different climate zones? (main and transitional)

What prefix do we use to denote the transitional climate zone (Sub)

How many main belts? (7)

Name the main climatic zones (equatorial, tropical, temperate, Arctic, Antarctic)

Show the main climate zones on the map...

How many transition belts? (6)

Name the transitional climate zones (2 subequatorial, 2 subtropical, subarctic, subantarctic)

Show the transition zones on the map...

What is the difference between main and transition belts.

Do all zones have climatic regions (no)

In which climate zone there are no climatic regions

Name and show them on the map of the temperate zone region of Eurasia (temperate continental, continental, sharply continental, monsoon)

4. Let’s listen to what you wrote in your home mini-essay “I would like to live in the ...... belt, because .....

Let's see how you coped with the task... test completed

Updating knowledge

You and I remembered what we studied and it’s time for us to turn to new material, but it will not be entirely new for us. In the 6th grade we already became acquainted with the peculiarities of the nature of the Earth.

And today we will move from atmospheric processes to water ones.

What is the name of the water layer of the Earth? (hydrosphere)

And the symbol of our lesson will be this picture . It depicts the famous Norwegian traveler Thor Heyerdahl. (photo)

In 1947, he and 5 like-minded people built a raft of 9 balsa wood logs and named it Kon-Tiki. In 101 days the brave navigator crossed over Pacific Ocean.

And in 1969, he undertook a new dangerous expedition to prove the possibility of African peoples crossing the Atlantic Ocean.

He and six of his followers built a boat from papyrus and named it "Ra". Their first trip was unsuccessful. The next year they went out to the ocean again on a papyrus boat and this time reached their goal in 57 days.

Let's look at the map: Thor Heyerdahl sailed by boat from the port of Safi (32 0 With. w. and 9 0 h. d.) to the island of Barbados (13 0 With. w. and 59 0 h. d.). Follow its route on a map of the oceans. What helped the traveler along the way?

A good way to travel is to travel with the help of ocean currents. And in order to use it, you need to get acquainted with the currents

The topic of our lesson, you guessed it– ocean currents

Let's open our notebooks and write down the date and topic of our lesson.

What do you guys think, what questions do we face in this topic?

What are ocean currents?

What types of currents are there?

How are they formed?

How do people use ocean currents?

To get answers to the questions that interest us, we need to turn to our main source of knowledge. What is this? Textbook. Let's open the textbook page and find and read what an ocean current is.

Ocean current -

People have known about ocean currents for a long time. A historical background was prepared for us by...

(MESSAGE ABOUT THE HISTORY OF THE DISCOVERY OF OCEAN CURRENTS)

What causes the formation of ocean currents in the World Ocean?

VIDEO

What reason leads to the formation of currents (due to the influence of constant winds). What constant winds do we know? (Task at the board)But there are several other reasons that affect the direction of currents:

1. Constant winds.2. Outlines of continents.

3. Bottom topography
4 . The rotation of the Earth around its axis.

Let's turn to another reliable source of geographic information - a map. How are ocean currents shown on a map? (arrows)

The North Atlantic Current off the coast of Scandinavia has a temperature of +10 0 S. What kind of current is this?( Warm)

And the Peruvian Current off the coast of South America has a temperature of +19 0 S, what is it? (Cold).

What's the contradiction? (+10 0 C - warm, + 19 0 C – cold)What is the question?

Which currents are called cold and which are called warm?

Let's work and fill out the table you have on your desk

Let's write it down

Current name

Color on the map

Current water temperature

Ocean surface temperature

Temperature comparison

Current type

North Atlantic

red

warm

Peruvian

blue

cold

Conclusion: A current is cold if its temperature is several degrees lower than the temperature of the surrounding ocean water….

Read the page in the textbook and compare whether we made the right conclusion?

- Warm current - This is a current whose water temperature is several degrees higher than the temperature of the surrounding water.

- Cold current - This is a current whose temperature is several degrees lower than the surrounding water.

Find on the map and mark the following currents: Gulf Stream, Canary, Peruvian, Labrador, West Wind Current, Kuroshio.

Which ones are warm? Cold? What pattern did you notice in the arrangement of these currents? ( Warm currents move from the equator, cold currents move from the poles, close, and flow counterclockwise.)

Look carefully at the map. What conclusions can be drawn by analyzing current patterns in the northern and southern hemispheres?

The direction of currents clockwise and counterclockwise is influenced by the rotation of the Earth around its axis. North of the equator, currents bend to the right, south of the equator, to the left. This phenomenon is called the Coriolis effect, named after the French mathematician Gaspard de Coriolis who described it. This is a law of physics and you will study it in high school. In the northern hemisphere, currents travel clockwise, while in the southern hemisphere they travel counterclockwise.

Fizminutka

Let us take a break from our research and warm up. What phenomena can be found in the ocean? Waves, storm, hurricane, tsunami... Let's try to depict these phenomena... wave... higher... the storm begins... A hurricane... during a sea earthquake a tsunami is formed... quieter, quieter.... We moor to the shore... that is, at the desk. Let's warm up... Let's continue.

– Are all currents driven by wind?

If the flow of water encounters an obstacle (land or rising bottom relief), it divides, bending around the obstacle from different sides. The flow also, if it encounters an obstacle, is most often divided into twosewage currents

– When the West Wind Current, which is a wind current, collides, one drain current is formed, and the West Wind Current continues to move on. But there are cases when the wind current ceases to exist as a result of a collision with the mainland, and instead of it two waste currents are formed. Find examples on the map.(California and Alaska, East Australian and Inter-trade, Kuroshio and Inter-trade.)

Draw the two waste streams on the contour maps with thicker arrows.

From what current is ... flow formed?
- Find the current of the Western Winds on the ocean map. Which oceans does it cross?

(VIDEO ABOUT THE CURRENT OF WESTERN WINDS)

Poem about the Current of the West Winds

Antarctica past Australia, America and Africa
Past all possible islands...
Everyone is sailing, my boats are sailing
Along the course of the Western winds.
I'll draw it on a worn map
This amazing route
In the blue of the vast expanse
Everyone is sailing, the boats are sailing.

Speaking about ocean currents, it seems to me that it will be very useful to know the peculiarities of the current of our native sea.

What sea am I talking about? (Black)

Which ocean basin does it belong to (Atlantic)

Help us learn about the currents of the Black Sea...

Black Sea Currents

The main current of the Black Sea is the Main Black Sea Current. It is directed counterclockwise and forms two noticeable rings (“Knipovich glasses”, this name is associated with the Russian hydrologist Nikolai Knipovich, who described this current). The current is very changeable. In the coastal waters of the Black Sea, vortices of the opposite direction are formed - anticyclonic currents.

Who likes to swim in the sea in summer? Why?

Water procedures are very useful, but know that the sea is fraught with danger... Please….

Secrets of the Black Sea

When swimming in the Black Sea, you should be aware of the existence of a local Black Sea current - “ draft». In the world, such a phenomenon is called RIP.

Most often, this current forms during a storm near sandy shores. The water flowing onto the shore does not return evenly, but in streams along the channels formed in the sandy bottom.

Getting caught in the jet's current is dangerous: it can be carried out to the open sea. To get out of the tug, you need to swim not straight to the shore, but at an angle to reduce the resistance of receding water.

V. Stage of consolidation of knowledge

We have practically dealt with the material. Let's remember what we wanted to know...

Have we received answers... But we don’t know everything. You can supplement your knowledge by completing your homework, which we will write down in your diary.VI. Homework

1. Study &20., describe one of the currents according to the plan p.572.Creativeexerciseprepare a report on the currentEl Niño

Screening test

1.What has the greatest influence on the formation of currents in the ocean

A) constant winds

B) earthquakes

B) the gravity of the moon

2. What types of currents are there?

A) warm

B) cold

B) warm and cold

3. What currents begin at the equator

A) warm

B) cold

B) warm and cold

4. What are the influences of ocean currents?

A) on climate formation

B) on the formation of the ocean floor topography

B) on the rotation of the Earth

5.Name the largest cold current

A) Gulf Stream

B) Current of the Western winds

B) Peruvian Current

VII. Summing up results lesson A

Did you like the lesson?

What made an impression?

What did you like most?

I liked your work in class and I want to evaluate it

History of the discovery of surface currents

The first mentions of the existence of sea currents are found among ancient Greek scientists; Aristotle in his writings talks about currents in the Kerch, Bosporus and Dardanelles straits. And the Carthaginians had some idea about the Sargasso Sea.

It is known that in the Middle Ages the Norwegians discovered a sea route from northern Europe, first to Iceland, and then to Greenland and North America. On these voyages the Normans became familiar with sea currents. This is clear from the names they gave to noticeable places they encountered along the way, such as: Fr. Currents, Currents Bay, Currents Cape.

The Arabs sailed extensively in the Indian Ocean and established sea links with China, Mesopotamia and Egypt. They were familiar with monsoon currents.

The Portuguese, while moving south along the coast of Africa, became acquainted with the Guinea and Bengal Currents, and Vasco da Gama at the end of the 15th century, during his first voyage to India, noticed the Mozambique Current.

First observations of ocean currents

The first detailed observation of currents in the open ocean was made by Christopher Columbus during his first voyage to America, on September 13, 1492 in the region of 27° N. w. and 40° W. d. He noticed from the deviation of the lot, lowered deep into the water, that the ship was being carried by the current to the SW. Columbus's subsequent voyages introduced him even more to the North Equatorial Current and gave him the opportunity to suggest that the waters of the ocean along the equator move “together with the vault of heaven” to the west. On his fourth voyage (1502-1504), Columbus discovered a current running along the coast of Honduras.

The movement of water in the oceans is just beginning to be studied, even very little is known about surface currents, and deep and bottom currents have not yet been studied at all. Meanwhile, there is no doubt that the surface and deep-sea movement of water in the oceans forms one complex system, which, even in its part coinciding with the ocean surface, has not been sufficiently studied. It is not surprising because this most complex oceanographic phenomenon, no less complex than similar movements in the ocean of air, does not yet have a coherent theory that covers all the reasons that determine the movement of water in the ocean.

The reasons that can excite the movement of water in the ocean and create an observable system of ocean currents can be divided into three groups. The reasons are of a cosmic nature, density differences and winds.

According to the modern view, cosmic causes, the rotation of the Earth and the tides, cannot excite anything similar to the currents observed in the surface layers, and therefore these causes are not considered here.

The second group of causes that excite currents are all those conditions that produce density differences in sea water, namely the uneven distribution of temperature and salinity.

The third reason for the emergence of surface (and therefore, partly underwater) currents is wind.

Water density difference

Density differences were widely recognized as the most important cause of ocean currents, a view that gained currency especially after the oceanographic studies of the Challenger expedition.

At this time, first Carpenter and then Moya suggested that the difference in densities is one of the main causes of currents. Recently, Scandinavian scientists: Nansen, Bjerknes, Sandström, Petterson, have again renewed interest in the phenomenon of density differences as the cause of currents.

The difference in densities in sea water is the result of the simultaneous action of many causes that always exist in nature and therefore continuously change the densities of sea water particles in different places.

Every change in water temperature is accompanied by a change in its density, and the lower the temperature, the greater the density. Evaporation and freezing also increase density, while precipitation decreases it. Since the salinity on the surface depends on evaporation, precipitation and melting of ice - phenomena that occur continuously - the salinity on the surface is constantly changing, and with it the density.

A map of the annual average density distribution shows that this element is unevenly distributed over the ocean surface, and a cross-section of the Atlantic Ocean along the meridian confirms that densities are unevenly distributed in the oceans and at depths. Lines of equal densities (isopycnals) descend towards the tropical belt into the depths of the ocean, and with distance from the equator they come to the surface.

All this indicates that if no other causes exciting currents in the ocean existed, but only an uneven distribution of densities, then the waters of the ocean would certainly begin to move; However, the system of currents that arose in this way, both in character and in speed, would be completely different from what is now observed, because other no less important reasons that also excite the currents would be absent.

For example, in the trade wind stripes a layer of water several meters thick evaporates, and about 2 m of this evaporated water falls in the calm equatorial strip. From here, desalinated water (with the existing current system) is carried eastward by the Equatorial Countercurrent. The remaining mass of water vapor is transported by the anti-trade wind to temperate zones, where it falls out. Thus, there is a constant loss of water in the tropics, which must be replaced by an influx from temperate latitudes. However, this reason alone is not able to create the system of currents observed in the oceans.

In the same way, ice in the subpolar and polar latitudes partly desalinates the water, makes it lighter, and partly cools it, increases its density and forces it to sink down, thus causing the cooling of the deep layers of the ocean, and therefore gives impetus to the movement of surface waters from temperate latitudes to polar. However, this reason alone cannot create the entire existing complex system of currents.

Thus, there is no doubt that the density difference, constantly maintained by many reasons throughout the entire mass of waters of the World Ocean, should contribute to the formation of water movement, both on the surface and at depths.

The Norwegian scientist V. Bjerknes outlined his views on the reasons that can initiate motion in any medium, no matter liquid or gas. These reasons lie solely in the heterogeneity of the environment itself, which is always observed in nature. Bjerknes's ideas are remarkable precisely because he analyzes movement in cases taken from nature, and not in some ideal environment, completely homogeneous, as is usually done.

Since Bjerknes takes a non-homogeneous medium, the basis of his reasoning should be a detailed study of the distribution of densities in the medium under consideration. Knowledge of the density distribution gives an idea of ​​the internal structure of the medium, and the latter allows one to judge the nature of the particle movements occurring in it.

The essence of Bjerknes' idea of ​​calculating current velocities based on density distributions. Let us assume that in any mass of water the temperature and salinity are distributed completely evenly, then the density will be the same everywhere, and, consequently, the selected mass of water will be homogeneous. Under such conditions, at the same depths, the pressures will be the same and will depend only on the number of layers located above each layer (to a first approximation, with every 10 m of depth, the pressure increases by one atmosphere).

If in such a homogeneous medium we draw surfaces of equal pressure, or, as they are otherwise called, isobaric, then they will coincide with level surfaces.

If we now make a vertical section of this mass of water, then on it the isobaric surfaces will be depicted as a system of parallel and horizontal lines.

If in a selected mass of water temperature and salinity are distributed unevenly, then the density of water at the same depths, independent of these conditions, will be different.

Instead of density, Bjerknes uses inverse quantities - specific volumes - and through places in the liquid where the latter are identical, he draws surfaces that, on a taken vertical section, are depicted by curves, which he called isosteres.

Thus, on a vertical section you will get two systems of lines, some will be straight, parallel to the isobar horizon, and others - isosteres - will intersect them at different angles. The more the equilibrium in the liquid is disturbed, i.e., the further it is from homogeneity, the more the density, and therefore the specific volumes, will be more different at the same depths. Therefore, where the liquid is more homogeneous, isosteres will be close to isobars; Where at close distances along the horizontal surface of the isobars there are significant differences in the homogeneity of the structure of the liquid, there the isosteres will rise or fall steeply.

Wind influence

The connection between wind and surface currents is so simple and easily noticeable that among sailors the wind has long been recognized as an important cause of currents.

The first person to point out in science the wind as the main cause of currents was W. Franklin in his discussions about the causes of the Gulf Stream (1770). Then A. Humboldt (1816), expounding his view on the causes of currents, pointed to the wind as their first cause. The primary importance of wind as a cause of currents was thus long recognized by many, but it received strong support from the mathematical treatment of the issue by Zoeppritz (1878).

Zoeppritz examined the question of the gradual transfer of motion from the surface layer of water set in motion by the wind to the next, from the last to the one lying underneath, etc. Zoeppritz showed that in the case of an infinitely long time of action of the driving force of the wind, the movement will be transmitted, in depth in such a way that the velocities in the layers will decrease in proportion to the depths, regardless of the magnitude of internal friction. If the forces act for a limited time, and the entire system of moving particles has not reached a stationary state, then the velocities at different depths will depend on the magnitude of friction. For his hypothesis, Zoeppritz borrowed the coefficient of friction from experiments on the flow of liquids, including sea water, and inserted it into his formulas.

An objection was made to this theory, pointing out that the amount of motion existing in the trade winds is much less than the corresponding value in the equatorial current. However, here we must take into account the duration and continuity of the trade winds; It is obvious that the wind in this case, after the flow reaches a steady state, only needs to make up for the loss of movement from internal friction, and therefore the wind, in the aggregate, over a long period of time can impart to the water the amount of movement that is observed in it and produce the existing flow.

Another more important objection indicates that the value of friction accepted in theory does not correspond at all to the actual value, because when one layer of water moves over another, whirlpools must certainly form, which absorb enormous amounts of energy. Consequently, the calculation of the magnitude and nature of the propagation of velocity with depth was constructed incorrectly.

Finally, the most important shortcoming of Zoeppritz's theory was recently noticed by Nansen, namely, it completely missed the influence of the deviation resulting from the rotation of the Earth on its axis.

Zoeppritz's theory (which dominated for about 30 years) drew attention to the important features of the wind (drift) hypothesis of currents, and its main merit is that it was the first to express the influence of wind numerically, and, as always happens in such cases, the shortcomings of the hypothesis served as a source for further study, the result of which was a new, more advanced wind theory, owned by the Swedish scientist V. Ekman, which took into account the evasive force from the rotation of the Earth on its axis.

If we assume the ocean to be vast and of infinite depth, and the wind above it to act continuously for such a long time that a stationary state has been established in the water set in motion, then under these conditions the following conclusions are obtained.

First of all, it is necessary to point out that the surface layer of water is set in motion by the wind due to two reasons: firstly, friction, and secondly, pressure on the windward sides of the waves, because as a result of the wind, not only currents arise, but also waves. Both of these reasons can be collectively called tangential friction.

According to Ekman's wind (drift) theory, motion from the surface layer is transmitted downward from layer to layer, decreasing exponentially. In this case, the direction of the surface current deviates from the direction of the wind producing it by 45° for all latitudes equally.

The influence of the deflecting force from the rotation of the Earth on the axis is reflected not only in the deviation of the current on the surface from the wind by 45°, but also in a further continuous rotation of the direction of the flow when transmitting movement in depth from layer to layer. Thus, with the transfer of the current from the surface to depth, not only does the speed decrease rapidly (in geometric progression), but also the direction of the current constantly turns to the right in the northern hemisphere, and to the left in the southern hemisphere.

At the mouths of rivers flowing into the seas, the same phenomena are observed. River water, being lighter than sea water, even when mixed with sea water, forms a lighter layer that has a certain movement from the shore. The mass of such a surface current is also greater than the mass of river water alone (according to the fair remark of Admiral S. O. Makarov), due to the mixing of river water with sea water. The current formed in this way sucks the colder water into the sea or ocean from the lower layers and causes a decrease in temperature in the surface layers at such depths where, at some distance from the confluence of the river, the temperature is much higher. This phenomenon was observed by Ekman near Gothenburg in the Kattegat.

Exactly the same influence of the river flow on the rise of more salty and dense deep water into layers closer to the surface was observed by S. O. Makarov both on the Kronstadt roadsteads and in the harbors of the port precisely after prolonged eastern winds, increasing the speed of the flow of surface fresh water from the river. Neva and, as a result, reducing the thickness of the surface layer.

Effect of atmospheric pressure

In the seas, a similar influence of atmospheric pressure on their various parts has a significant effect on the currents in the straits connecting them with the oceans or other seas. For example, the Gulf Stream, at its beginning in the Strait of Florida, happens to have greater speed in northern, i.e., opposite, winds and less in southern, favorable winds. This discrepancy is explained by the influence of atmospheric pressure; When northerly winds blow over the Gulf Stream in the Straits of Florida, then there is weak atmospheric pressure over the Gulf of Mexico, causing the level in the Gulf to rise, the slope towards the Straits of Florida increases, and this in turn accelerates the flow of water from the Gulf through the Strait of Florida to the north. Southern winds occur in the Strait of Florida if there is high pressure over the Gulf of Mexico, which is why then the level in the Gulf decreases and the level slope in the Strait of Florida becomes smaller, and therefore the speed of the current decreases, despite tailwinds.

Review of all the above causes of currents

The above reasons that stimulate the movement of water in the ocean come down to three conditions: the influence of differences in atmospheric pressure, the influence of differences in the density of sea water and the influence of wind. The influence of the Earth's rotation on the axis and the influence of the coasts can only modify the nature of existing currents, but the latter two circumstances themselves cannot excite any movements of water.

The influence of atmospheric pressure differences cannot excite any significant currents. The following two reasons remain: differences in the density of sea water and wind.

Density differences in the ocean always exist, and therefore they always tend to set water particles in motion. In this case, density differences act not only in the horizontal direction, but also in the vertical direction, exciting convection currents.

The wind, according to modern views, not only causes the emergence of surface currents, but also causes the origin of currents at different depths to the very bottom. Thus, the importance of wind as a causative agent of currents has recently expanded and become more universal.

The material that oceanography has on the distribution of densities in different places and at different depths in the oceans is still very small and not accurate enough; but based on it, it is already possible to make an attempt to determine numerically (using the Bjerknes method) those current speeds that a density difference can excite in the surface layers of the oceans.

Based on a meridional section through the North Equatorial Current of the Atlantic Ocean, it was determined that existing between 10 and 20° N. w. the difference in density could produce a current of 5-6 nautical miles in 24 hours. Meanwhile, the average daily speed of the Equatorial Current observed in this place is about 15-17 nautical miles. If we calculate the speed of the same Equatorial Current, corresponding only to the influence of the wind (taking the NE trade wind speed to 6.5 m per second), we get a daily current speed of 11 nautical miles. Adding this value to the 5-6 nautical miles of daily speed due to the difference in density, we obtain the observed 16-17 nautical miles per day.

The above example shows that the wind, apparently, turns out to be a more important cause of the excitation of currents on the surface of the ocean than the difference in densities.

A similar example for the Baltic Sea is even more convincing; it shows that even where at short distances the density differences are very large, the influence of the wind is still of greater importance for the occurrence of currents (see p. 273, currents of the Baltic Sea).

Finally, the very existence of changes in monsoon currents, as well as some movement and change in the currents of the tropical strip in all oceans in winter and summer of the same hemisphere, show once again the great importance of winds for the existing system of currents. The movement of the meteorological equator with the seasons, of course, affects the distribution of water temperature (see the chapter on temperature), and therefore the distribution of water density, but these changes are very small; changes in the wind system caused by the movement of the meteorological equator are very significant.

Thus, of these three causes of currents, it must be admitted that the wind is one of the most important. Many circumstances indicate this; There is no doubt that if the wind did not exist, then the current systems that arose in the oceans would be very significantly different from the existing ones.

Here it would be appropriate to point out that in the ocean there are many currents with waters of completely different densities running side by side, and despite the fact that there is no exchange of water between them.

Finally, all currents move along a bed formed by ocean waters, which always have completely different physical properties than the waters of the currents themselves; however, even under these conditions, the currents continue to exist and move without immediately mixing their waters with neighboring ones. Of course, such mixing of their waters occurs, but it occurs very slowly and is largely determined by the formation of whirlpools when one layer of water moves over another.

This I know

2. What are the reasons for the formation of currents?

The main reason for the formation of currents is wind. In addition, the movement of water is affected by the difference in its temperature, density, and salinity.

3. What is the role of ocean currents?

Ocean currents influence climate formation. Currents redistribute heat on Earth. Planktonic organisms move through currents.

4. Name the types of ocean currents and give examples of them?

Currents of origin are wind (Western Wind Current), tidal, or density.

Temperature currents can be warm (Gulf Stream) or cold (Benguela).

Stability currents can be permanent (Peruvian) or seasonal (currents of the northern part of the Indian Ocean, El Nino)

5. Match current – ​​warm (cold):

1) current of the Western winds

2) Gulf Stream

3) Peruvian

4) Californian

5) Kuroshio

6) Benguela

A) warm

B) cold

I can do this

6. Give examples of the interaction between the ocean and the atmosphere.

Currents redistribute heat and influence air temperature and precipitation formation. Sometimes the interaction of currents and the atmosphere leads to the formation of unfavorable and dangerous weather phenomena.

7. Characterize the flow of the Western winds according to plan:

1. Geographical location

The current bends between 400 and 500 S. Earth.

2. Type of flow

A) according to the properties of water (cold, warm)

The current is cold.

B) by origin

The current of the Western Winds is wind-driven in origin. It is caused by the westerly transfer of winds in temperate latitudes.

C) by stability (permanent, seasonal)

The flow is constant.

D) by location in the water column (surface, deep, bottom)

The current is superficial.

8. In ancient times, not knowing the real reasons for the formation of currents in the Ocean, sailors believed that Neptune - the Roman god of the seas - could drag a ship into the ocean depths. Using information from popular science and fiction literature, the Internet, collect materials about ships whose disappearance is associated with currents. Present the materials in the form of drawings, essays, reports.

Secrets of the Bermuda Triangle

The Bermuda Triangle or Atlantis is a place where people disappear, ships and planes disappear, navigation instruments fail, and almost no one ever finds the crashed. This hostile, mystical, ominous country for humans instills such great horror in the hearts of people that they often simply refuse to talk about it.

Few people knew about the existence of such a mysterious and amazing phenomenon called the Bermuda Triangle a hundred years ago. This mystery of the Bermuda Triangle began to actively occupy people's minds and force them to put forward various hypotheses and theories in the 70s. last century, when Charles Berlitz published a book in which he extremely interestingly and fascinatingly described the stories of the most mysterious and mystical disappearances in this region. After this, journalists picked up the story, developed the theme, and the history of the Bermuda Triangle began. Everyone began to worry about the secrets of the Bermuda Triangle and the place where the Bermuda Triangle or the missing Atlantis is located.

This wonderful place or the lost Atlantis is located in the Atlantic Ocean off the coast of North America - between Puerto Rico, Miami and Bermuda. It is located in two climatic zones at once: the upper part, the larger part in the subtropics, the lower part in the tropics. If these points are connected to each other by three lines, the map will show a large triangular figure, the total area of ​​which is about 4 million square kilometers. This triangle is quite arbitrary, since ships also disappear outside its borders - and if you mark on the map all the coordinates of disappearances, flying and floating vehicles, you will most likely get a rhombus.

For knowledgeable people, the fact that ships often crash here does not cause much surprise: this region is not easy to navigate - there are many shallows, a huge number of fast water and air currents, cyclones often form and hurricanes rage.

Water currents. Gulf Stream.

Almost the entire western part of the Bermuda Triangle is crossed by the Gulf Stream, so the air temperature here is usually 10°C higher than in the rest of the territory of this mysterious anomaly. Because of this, in places where atmospheric fronts of different temperatures collide, you can often see fog, which often amazes the minds of overly impressionable travelers. The Gulf Stream itself is a very fast current, the speed of which often reaches ten kilometers per hour (it should be noted that many modern transoceanic ships move not much faster - from 13 to 30 km/h). An extremely fast flow of water can easily slow down or increase the movement of a ship (here it all depends on which direction it is sailing). It is not surprising that in earlier times ships of weaker power easily went off course and were carried completely in the wrong direction, as a result of which they crashed and disappeared forever in the oceanic abyss.

In addition to the Gulf Stream, strong but irregular currents constantly appear in the Bermuda Triangle area, the appearance or direction of which is almost never predictable. They are formed mainly under the influence of tidal waves in shallow water and their speed is as high as that of the Gulf Stream - and is about 10 km/h. As a result of their occurrence, whirlpools often form, causing trouble for small ships with weak engines. It is not surprising that if in former times a sailing ship got here, it would not be easy for it to get out of the whirlwind, and under particularly unfavorable circumstances, one might even say impossible.

In the east of the Bermuda Triangle is the Sargasso Sea - a sea without shores, surrounded on all sides instead of land by strong currents of the Atlantic Ocean - the Gulf Stream, North Atlantic, North Passat and Canary.

Outwardly, it seems that its waters are motionless, the currents are weak and inconspicuous, while the water here is constantly moving, since water flows, pouring into it from all sides, rotate the sea water clockwise. Another remarkable thing about the Sargasso Sea is the huge amount of algae in it (contrary to popular belief, there are also areas with completely clear water here). When in former times ships drifted here for some reason, they became entangled in dense sea plants and, falling into a whirlpool, albeit slowly, they were no longer able to get out.