We study the salinity of the seas: why the water in the sea is salty. Why is the water in the seas and oceans salty? What does the salinity of water depend on?

Anyone who was on the beach could see that the water in the sea tasted salty. But where does salt come from if fresh water enters the ocean through rains, rivers, etc.? Why is the sea salty and has it always been like this - time to figure it out!

How is water salinity determined?

Salinity refers to the salt content in water. Most often, salinity is measured in " ppm » (‰). Permille is one thousandth of a number. Let's give an example: a water salinity of 27 ‰ will mean that one liter of water (this is approximately 1000 grams) contains 27 grams of salt.

Water with an average salinity of 0.146 ‰ is considered fresh.

Average The salinity of the World Ocean is 35 ‰. What makes water salty is sodium chloride, also known as table salt. Among other salts, its share in sea water is the highest.

The saltiest sea is the Red Sea. Its salinity is 41‰.

Where does salt come from in the seas and oceans?

Scientists still disagree about whether seawater was originally salty or acquired such properties over time. Depending on the versions, different sources of the appearance of salts in the World Ocean are considered.

Rains and rivers

Fresh water always has a small amount of salts, and rainwater is no exception. It always contains traces of dissolved substances that were captured during its passage through the atmosphere. Getting into the soil, rainwater washes away a small amount of salts and eventually carries them to lakes and seas. From the surface of the latter, water intensively evaporates, falls again in the form of rain and brings new minerals from the land. The sea is salty because all the salts remain in it.

The same principle applies to rivers. Each of them is not completely fresh, but contains small amounts of salts captured on land.

Confirmation of the theory - salt lakes

Proof that salt comes through rivers are the saltiest lakes: the Great Salt Lake and the Dead Sea. Both are about 10 times saltier than seawater. Why are these lakes salty?, while most of the world's lakes are not?

Lakes are usually temporary storage areas for water. Rivers and streams bring water to lakes, and other rivers carry it away from these lakes. That is, water comes in from one end and leaves from the other.

The Great Salt Lake, the Dead Sea and other salt lakes have no outlets. All the water that flows into these lakes leaves only through evaporation. When water evaporates, dissolved salts remain in bodies of water. Thus, some lakes are salty because:

• the rivers carried salt to them;
• the water in the lakes evaporated;
• the salt remained.

Over many years, salt in the lake water has accumulated to its current level.

Interesting fact: The density of salt water in the Dead Sea is so high that it practically pushes a person out, preventing him from sinking.

The same process made the seas salty. Rivers carry dissolved salts to the ocean. Water evaporates from the oceans to fall again as rain and replenish rivers, but the salts remain in the ocean.

Hydrothermal processes

Rivers and rain are not the only source of dissolved salts. Not long ago, they were discovered on the ocean floor hydrothermal vents. They represent places where seawater has seeped into the rocks of the Earth's crust, become hotter, and is now flowing back into the ocean. Along with it comes a large amount of dissolved minerals.

Submarine volcanism

Another source of salts in the oceans is underwater volcanism - volcanic eruption underwater. It is similar to the previous process in that seawater reacts with hot volcanic products and dissolves some of the mineral components.

Will the seas be saltier?

Most likely no. In fact, the sea has had roughly the same salt content for hundreds of millions, if not billions of years. The salt content has reached a steady state. The fact is that part of the salts goes to the formation of mineral rocks at the bottom - this compensates for the influx of new salts.

Summary

There is no mystery in the answer to the question: “Why is the sea salty?” Salt is deposited by rain and rivers, hydrothermal and volcanic processes on the ocean floor.

Having visited the beach for the first time, the child asks his parents: why is the water in the sea salty? This simple question baffles adults. After all, everyone knows that a bitter aftertaste will definitely remain on the lips and the whole body. Why is the sea salty? We begin to reason: fresh rivers flow into this part of the World Ocean. So it can't taste that bad! But you can’t go against the facts: the water is not fresh. Let's figure out at what stage the initial composition of H2O changes.

Why is the salinity increased?

There are several theories about this. Some scientists believe that salt remains from the evaporated water of flowing rivers, others - that it is washed out of rocks and stones, others associate this compositional feature with the action of volcanoes... Let's begin to consider each version in order:

The reservoir becomes salty from the water of the rivers that flow into it. Strange pattern? Not at all! Although river moisture is considered fresh, it still contains salt. Its content is very small: seventy times less than in the vast depths of the World Ocean. Therefore, flowing into a large body of water, rivers desalinate its composition. But the river water gradually evaporates, but the salt remains. The volumes of impurities in the river are small, but over billions of years a lot of them accumulate in sea water.

Salts flowing from rivers into the sea settle on its bottom. From them, huge blocks of stone and rocks are formed on the ocean floor over thousands of years. Year after year, the current destroys any stones, leaching easily soluble constituent substances from them. Including salt. Of course, this process is long, but inevitable. Particles washed out of rocks and rocks give the ocean an unpleasant, bitter taste.

Underwater volcanoes release many substances into the environment, including salts. During the formation of the earth's crust, volcanic activity was very high. They released acidic substances into the atmosphere. Frequent acid rain formed seas. Accordingly, at first the water in the constituent parts of the ocean was acidic. But the alkaline elements of the soil - potassium, magnesium, calcium, etc. - reacted with acids and formed salts. Thus, water in various places of the ocean acquired the characteristics that are now familiar.

Other assumptions known today are related

• with the winds bringing salt into the water;
• with soils, passing through which fresh liquid is enriched with salts and enters the ocean;
• with salt-forming minerals located under the ocean floor and supplied through hydrothermal vents.

It is probably correct to combine all the hypotheses in order to understand the ongoing process. Nature gradually built all its ecosystems, closely intertwining things that were incompatible at first glance.

Where is the highest concentration of salt?

Sea water is the liquid that is most abundant on earth. It’s not for nothing that many people associate vacations primarily with the beach and coastal waves. Surprisingly, the mineral composition of the liquid in different bodies of water never coincides. There are many reasons for this. For example, salinity depends on the intensity of fresh water evaporation, the number of rivers, types of inhabitants and other factors. Which sea is the saltiest?

The answer is given by statistics: the Red Sea is rightfully called the saltiest. One liter of its water contains 41 grams of salts. If we compare with other reservoirs, then in a liter of liquid from the Black there are 18 grams of various salts, in the Baltic this figure is even lower - 5 grams. The chemical composition of Mediterranean is 39 grams, which is still lower than the above characteristics of Red. In ocean water - 34 grams.

Reasons for the unique feature of the Red Sea:

On average, about 100 mm of precipitation falls above the surface per year. This is very little, considering that about 2000 mm of water evaporates per year.

No rivers flow into this reservoir; it is replenished only by precipitation and waters from the Gulf of Aden. And its water is also salty.

The reason is also the intensive mixing of water. In winter and summer, the layers of liquid change. Evaporation occurs in the upper layer of water. The remaining salts fall down. Therefore, the salinity of water in this part of the water expanse increases significantly.

The Dead Sea is sometimes called the saltiest. Its waters contain 340 grams of salt per liter of water. That’s why it’s dead: the fish die in it. But some features of this body of water do not allow it to be considered a sea: it does not have access to the ocean. Therefore, it is more correct to call this body of water a lake.

As you know, sea water is a solution of various salts, giving it a characteristic bitter-salty taste.


At the same time, rivers that flow into seas and oceans consist only of fresh water, the concentration of dissolved salts in which is significantly lower than in sea water. But how can this be, why do sea and river water contain such different amounts of dissolved substances? Let's find out what scientists think about this.

Version No. 1 – salt accumulated gradually

Rain or melt water is an almost pure distillate: it contains a minimal amount of substances collected during the fall in the atmosphere to the surface of the earth.

Absorbing into the soil and collecting in streams and then in rivers, water dissolves minerals, which are then carried with river water into the ocean. Evaporation from the surface of the ocean, which occurs much more intensely than on land, again raises clean, distilled water into the atmosphere, and salts remain in the ocean.

This process continues for billions of years, during which the concentration of salts in sea water has increased tenfold. This hypothesis is supported by the existence of salt lakes on the land surface that have never been in contact with the waters of the World Ocean. As a rule, these are closed reservoirs into which water only flows in the form of streams, but does not flow out.


True, this theory does not explain the difference between the composition of salts in sea and river water. Fresh water also contains various salts, but these are, as a rule, carbonates - carbonic acid salts, which are formed as a result of the breakdown of organic residues - fallen leaves, etc.

Sea water contains up to 80 different chemical elements and their compounds, but the predominant substance in it is sodium chloride, or ordinary table salt, which gives a characteristic salty taste. Where does table salt come from in the sea if it is not washed off the land? This question is answered by the second version proposed by scientists.

Version No. 2 – salt was in the water initially

Billions of years ago, when our planet was still very young, violent volcanic activity took place in its crust. Eruptions large and small were a daily occurrence.

A large amount of volcanic gases, which contained chlorine, bromine and fluorine in free form, were released into the atmosphere and waters of the World Ocean. The atoms of these elements reacted with water vapor and formed acid molecules, so in the initial period of its existence, sea water was not salty, but acidic.

These acids, having high chemical activity, reacted with metals contained in volcanic rocks - sodium, magnesium, potassium, etc. The compounds formed as a result of the reaction were the salts that gave the water its today’s “sea” taste.

The acids were almost completely neutralized, and the modern composition of sea water stabilized about 500 million years ago - a fact proven by studying the rocks of the sea and ocean floor.

How did it all really happen?

Most likely, both processes described above are to blame for the fact that sea water has become salty. The water of the World Ocean actually received its initial level of salts due to the active volcanic activity of the earth’s crust.

Today's salt levels are maintained by the leaching of minerals by rivers, as well as by the activities of numerous living organisms that use dissolved substances to build their cells.

Interesting fact: although sea water is completely undrinkable, the concentration of salt in it corresponds to the salt content in human blood plasma.

Daily bathing in sea water strengthens the body and helps fight many different diseases of the skin, respiratory tract, nervous system, etc.

From time to time we come across some questions related to our planet that have not yet been answered. For example, the presence of salt in ocean water. How did she get there?

The scientific basis for the appearance of salt water in the sea was laid by the work of Edmund Halley in 1715. He suggested that salt and other minerals were washed out of the soil and carried to the sea by rivers. Having reached the ocean, the salts remained and gradually concentrated. Halley noted that most lakes that do not have a water connection with the oceans have salt water.

Halley's theory is partly correct. In addition, it should be mentioned that sodium compounds were washed out from the bottom of the oceans in the early stages of their formation. The presence of another salt element, chlorine, is explained by its release (in the form of hydrochloric acid) from the bowels of the Earth during volcanic eruptions. Sodium and chlorine ions gradually became the main components of the salt composition of sea water.

But we don't know if this can explain the presence of SUCH a huge amount of salt in the oceans. If all the oceans were dried up, the remaining salt could be used to build a wall 230 km high and almost 2 km thick. Such a wall could circle the entire globe along the equator.

Or another comparison. The salt of all the dried up oceans is 15 times larger in volume than the entire European continent!

The regular salt we use every day is obtained from seawater, salt springs, or from mining rock salt deposits. Sea water contains 3-3.5% salt. Inland seas, such as the Mediterranean Sea, Red Sea, contain more salt than open seas. The Dead Sea, occupying only 728 square meters. km., contains approximately 10,523,000,000 tons of salt. There is so much salt in it that it is almost impossible to drown in such water, since the density of the water has increased due to the salts.

On average, a liter of sea water contains about 30 g of salt. Rock salt deposits in various parts of the earth were formed many millions of years ago as a result of the evaporation of sea water. To form rock salt, nine-tenths of the volume of sea water must evaporate; It is believed that inland seas were located on the site of modern deposits of this salt. They evaporated faster than new sea water came in - so rock salt deposits appeared.

The main amount of table salt is obtained from rock salt. Usually, mines are laid to salt deposits. Clean water is pumped through the pipes, which dissolves the salt. Through the second pipe this solution rises to the surface.

In Hong Kong, seawater is widely used in toilet flush systems. More than 90% of them use sea water for flushing in order to save fresh water. The practice began in the 1960s and 1970s, when extracting fresh water supplies became difficult for residents of the former British colony.

Sea water can be drunk in small quantities for 5-7 days without harm to health.

Did you know that sailors lost in sea waters most often died of thirst? This is a paradox - after all, the ship is surrounded by thousands of tons of life-giving moisture! The fact is that the chemical composition of sea water is not suitable for our body, so it cannot be drunk. In addition, it has a specific taste - due to the salts dissolved in it. The question arises: how did they get there and why is the water in the sea salty?

Ocean waters contain almost all elements of the periodic table. Most of all - hydrogen and oxygen, which are combined into water molecules. There are also impurities containing:

• calcium;
• magnesium;
• bromine;
• sulfur;
• fluorine.

But the main mineral part is made up of chlorine and sodium ions, that is, ordinary salt, which gives the water a salty taste. It remains to be seen who salted the water in the seas.

How sea water was formed

Scientists still have not found an answer to the question of why sea water is salty and river water is not. There are two hypotheses for the formation of sea water. The main difference between them is the way they look at the beginning of this process. Some believe that the ocean became salty quite recently, while others are sure that this happened in the early stages of the planet’s existence.

River infusions

The waters of rivers and lakes are also salty. But we don’t feel this, since the sodium chloride content in them is 70 times less than in the sea. According to the “river” hypothesis of the origin of sea water, dissolved impurities enter the ocean with the flow of rivers. The water in the sea gradually evaporates, but the minerals remain, so their concentration is constantly increasing. The process of ocean salinization, according to this group of scientists, has been going on for several billion years, resulting in water becoming more and more salty.

However, studies conducted over many years show that the salt content in the world's oceans does not change for a long time, and substances entering it with river water can only maintain this value at the same level. In addition, this hypothesis does not explain the different composition of river and sea water: rivers have a lot of carbonates, while chlorides predominate in the sea.

Consequence of volcanic activity

Proponents of the second hypothesis believe that sea water was salty already when life on Earth did not yet exist. And the reason for this is volcanoes. During the formation of the earth's crust, many magma emissions occurred. Volcanic gases contained compounds of bromine, fluorine and chlorine, which fell as part of acid rain. As a result, an acidic ocean appeared on the planet.

The ocean's acids began to react with the alkaline elements of the hard rocks of the earth, giving rise to more stable compounds - salts. Thus, table salt, which is familiar to us, was formed as a result of the interaction of perchloric acid from the ocean and sodium ions from frozen volcanic rocks.

Gradually, the sea water became less acidic and acquired a salty taste. Proponents of this theory believe that the ocean acquired its modern properties 500 million years ago, when the Earth’s surface was cleared of volcanic gases and the composition of the water stabilized.

Then how to explain the disappearance of carbonates that come with the river flow? This is the “work of the hands” of marine inhabitants. They learned to use these minerals to build skeletons and shells, which are necessary for the protection and mechanical support of the body.

In which sea is it impossible to drown?

The salts that make up water can change its properties, including density. The higher it is, the more difficult it is to immerse a solid body in liquid, so it is easier to swim in sea water. From this point of view, many are interested in which sea has the saltiest water.

The Dead Sea, which is actually a lake and is fed by the waters of the Jordan River, has the highest concentration of sodium chloride. It is located between Israel and Jordan and is very attractive to tourists who want to relax and improve their health. Most of all, people like to swim there, since the high density of the water prevents drowning.

The saltiest water in the world has a salinity index of 33.7%, which is almost 9 times higher than that in the world's oceans. This sea was called dead due to the absence of its usual inhabitants - algae and fauna. But many types of microscopic organisms live in it - fungi, omycetes and bacteria.

Why is the sea salty: Video

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