Project "Why is the sea salty?" Why is sea water salty?

Almost each of us, having carelessly opened our mouths while swimming in the sea and taken a sip of water, wondered, why is it salty? Of course, you can be like the ancient Greeks, who believe that the waters of the seas and oceans are the tears of Poseidon. But now they don’t believe in fairy tales, and a strictly scientific substantiation of the reasons for the appearance of salt in sea waters is required.

Theories of sea salinity

Researchers on this long-standing problem fall into two camps, proposing specific theories.

The salinity of the seas gradually increased

This was facilitated by the natural water cycle. Precipitation, acting on the rocks, washed out minerals from it, which ended up in river systems. And from the rivers, water saturated with salts was already flowing into the seas. The river flows themselves also contributed to the leaching of salts from soils and rocks.

Then the tireless Sun began to work. Under its hot influence, water evaporated, no longer containing salts. Distilled moisture also precipitated on the surface of the planet and continued its work of saturating the seas with salts.

The process continued for many millions of years, salt accumulated in sea waters, acquiring exactly the consistency that we now observe. Everything is simple and quite logical. However, there is some inconsistency in this theory.

For some reason Over the past half a billion years, the concentration of salts in sea waters has not changed. But rainfall and rivers are as active as ever. This discrepancy can be explained as follows. Salts delivered by rivers to the subsoil of the sea do not dissolve in them, but settle on the bottom surfaces. From them various rocks and rocky formations are formed.

Sea waters have been salty from the very beginning

During the formation of the earth's crust, powerful volcanic activity was observed. Thousands of volcanoes emitted gigantic amounts of all kinds of substances into the atmosphere, among which were:

• chlorine;
• bromine;
• fluorine.

Acid rains constantly fell on the earth's surface, contributing to the birth of seas.

Their oxidized waters interacted with rocks and pulled out from them:

• potassium;
• sodium;
• magnesium;
• calcium.

As a result, salts were obtained, with which the waters were saturated. But 500 million years ago this process ended.

More interesting versions of salt formation in the seas

The search for versions of the appearance of salty and fresh waters does not stop. At this time, two are the most interesting.

1. Our planet was formed exactly in this form - salty seas and fresh rivers. If it were not for the river currents, the rivers could also become salty, but fortunately, the seas cannot flow into them.
2. Animals contributed. For a long time, the waters were salty everywhere. But animals very actively consumed it from rivers and lakes in order to obtain the necessary chemical elements for the development of their organisms. Over many hundreds of millions of years, the rivers have lost all their sodium chloride reserves. But this version is more entertaining.

Features of sea water

For people, fresh water is familiar and its beneficial properties are obvious. But sea waters also have their own characteristics.

1. It is absolutely not suitable for drinking. The content of salts and other minerals in it is very high. They can only be removed from the body with more water. But if such water is desalinated, then it is quite drinkable.
2. In some countries, sea salt water is used for domestic needs. For example, in drainage sewer systems.
3. The benefits of sea water for treatment have long been known. It is used in the form of baths, rinses, and inhalations. This helps fight respiratory diseases and relieves muscle tension. Water with a high salt content also exhibits antibacterial properties.

The salinity of the waters of some known seas is as follows (at 0/00):

• Mediterranean – 39;
• Black – 18;
• Karskoe – 10;
• Barentsevo – 35;
• Red – 43;
• Caribbean - 35.

Such a disproportionate salt content in the waters of different seas is influenced by specific factors:

• drainage of rivers and streams flowing into them;
• precipitation water;
• transformation of sea ice;
• vital activity of all kinds of marine organisms;
• plant photosynthesis;
• bacteriological activity.

Now you know why the sea is salty!

It is known that oceans cover about 70 percent of the Earth's surface, and about 97 percent of all water on the planet is saline - that is, salt water. According to some estimates, salt in the ocean, evenly distributed over the surface of the globe, would form a layer more than 166 meters thick.

Sea water tastes bitterly salty, but where did all that salt come from? Everyone knows that the water in rain, rivers and even sea ice is fresh. Why are some of the Earth's waters salty and others not?

Causes of salinity of seas and oceans

There are two theories about why sea water is salty that give us the answer.

Theory #1

Rain that falls on the ground contains some carbon dioxide from the surrounding air. This causes rainwater to be slightly acidic due to carbon dioxide. Rain, falling on the ground, physically destroys the rock, and acids do the same chemically, and transport salts and minerals in a dissolved state in the form of ions. The ions in the runoff move into streams and rivers and then into the ocean. Many dissolved ions are used by organisms in the ocean. Others are not consumed and remain for long periods of time, their concentration increasing over time.

Two ions constantly present in seawater are chloride and sodium. They make up more than 90% of all dissolved ions, and the salt concentration (salinity) is about 35 parts per thousand.

As rainwater passes through the soil and percolates through rocks, it dissolves some minerals. This process is called leaching. This is the water we drink. And of course, we don’t feel the salt in it because the concentration is too low. Eventually this water, with a small load of dissolved minerals or salts, reaches river streams and flows into lakes and the ocean. But the annual addition of dissolved salts from rivers is only a small fraction of the total salt in the ocean. The dissolved salts carried by all the world's rivers would equal the amount of salt in the ocean in about 200-300 million years.

Rivers carry dissolved salts to the ocean. Water evaporates from the oceans to rain again to feed rivers, but the salts remain in the ocean. Due to the sheer volume of the oceans, it took hundreds of millions of years for salt levels to reach current levels.

It’s interesting to know: which ones exist on planet Earth?

Theory #2

Rivers are not the only source of dissolved salts. A few years ago, some features were discovered along the crest of oceanic ridges that changed the way we look at how the sea became salty. These features, known as hydrothermal vents, are places on the ocean floor where water seeping into ocean crust rocks gets hot, dissolves some minerals, and flows back into the ocean.

It comes with a large amount of dissolved minerals. Estimates of the amount of hydrothermal fluids now flowing from these vents indicate that the entire volume of ocean water could pass through the oceanic crust in about 10 million years. Thus, this process has a very important effect on salinity. However, the reactions between water and ocean basalt, the rock of the oceanic crust, are not one-way: some of the dissolved salts react with the rock and are removed from the water.

The final process that supplies the ocean with salt is submarine volcanism—the eruption of volcanoes underwater. This is similar to the previous process - reaction with hot rock dissolves some of the mineral components.

Why are the seas salty?

For the same reasons. Most seas are part of the world ocean with interconnected waters.

Why is the Black Sea salty? Although it is connected to the world ocean through straits, the Sea of ​​Marmara and the Mediterranean, ocean waters almost do not enter the waters of the Black Sea, since many large rivers flow into it, such as:

• Danube;
• Dnieper;
• Dniester and others.

Therefore, the level of the Black Sea is 2-3 meters higher than the ocean level, which prevents ocean water from penetrating into its waters. The salinity of this reservoir and other closed seas - such as the Caspian Sea, the Dead Sea - is rather explained by the first theory and the fact that once the boundaries of the oceans were different.

Will the oceans continue to become saltier? Most likely no. In fact, the sea had roughly the same salt content hundreds of millions (if not billions) of years ago. Dissolved salts are removed to form new minerals on the ocean floor, and hydrothermal processes create new salts.

Where water comes into contact with crustal rocks, either on land or in the ocean or oceanic crust, some of the minerals in the rock dissolve and are carried by the water to the ocean. The constant salt content does not change because new minerals are formed on the seabed at the same rate as the salt. Thus, the salt content of the sea is in a steady state.

Benefit for health

The salinity of sea water has been used by healers for centuries to treat various diseases.

From 1905 until the outbreak of World War I in 1914, biologist René Quinton conducted research to prove that seawater was chemically identical to blood. From these experiments, he developed specific techniques and established a viable protocol for therapy, which he called the "Sea Method". Many case histories indicate the effectiveness of its treatment.

Doctor Jean Jarricott (pediatrician) cured hundreds of children. Particularly good success was observed in children suffering from atrepsy and cholera. Back in 1924, he already practiced the oral use of sea water.

1. How to use it.
2. Application by injection and special effect on digestive problems.
3. Physical and chemical characteristics. Therapeutic definitions and principles of use.

Olivier Macé made huge strides in 1924 with the use of injections for difficult pregnancies and for prenatal applications.

In Senegal, Drs H. Loureu and G. Mbakob (1978) successfully treated one hundred children suffering from severe dehydration caused by diarrhea, vomiting and malnutrition using subcutaneous injections and oral administration of marine plasma.

André Passebecq and Jean-Marc Soulier made very detailed scientific observations of the effectiveness of seawater in various applications and advocated its use. Oral dosage as a mineral supplement does not seem to be very important, but regularity to normalize the body's pH, short- and medium-term therapy with a drinking solution invariably brings rapid results.

F. Paya (1997) reported the use of Quinton plasma to regulate the endocrine system in cases of secondary hyperdosteronism. It has also reported excellent success when administered orally in treating fatigue and maintaining performance in athletes. Paya has used either isotonic or hypertonic formulas with children and adults in cases of:

• dehydration;
• asthenia;
• loss of appetite.

The Germans have proven that consuming sea plasma is as effective as subcutaneous injections. In 70% of cases, patients suffering from psoriasis and neurodermatitis showed a significant improvement in their condition. In Canada, it is used as a food additive.

Children's questions sometimes baffle great sages. Anyone who has ever swum in the sea has most likely wondered: why is the sea salty and has such a specific taste? Science has never found a clear answer to this question, because there are several conflicting hypotheses explaining the salinity of the seas and oceans.

Are the rivers to blame?

It sounds absurd, but, nevertheless, this is the simplest and most common explanation. Over many kilometers of their path, rivers wash salty minerals from the soil and, when flowing into the sea, make it a little saltier. Then the process of the water cycle begins - pure fresh water evaporates very intensively from the vast surface of the sea, but minerals and salts remain.

All this has been happening for many millions of years, so is it any wonder that the sea has become like over-salted soup?

Opponents of this simple and logical theory argue that salts dissolved in sea water do not remain suspended, but rather precipitate over time and serve as the basis for the formation of rock layers and rocks. And the chemical composition of river and sea water itself is strikingly different - sea water has too few carbonates, but a lot of chlorides. River water, on the contrary, contains little table salt and a lot of soda and lime.

Proponents of the theory believe that such a difference in the content of various salts is explained by the fact that living organisms, which inhabit the depths of the sea in large numbers, used carbonates for nutrition and construction of the skeleton, leaving chlorides in the water. It is difficult, of course, to imagine that so many substances were eaten, because if all the salt were “pulled out” from the sea and scattered over the earth’s surface, the thickness of such a layer would be more than 100 meters.

If you believe this theory, then many centuries ago the seas were almost fresh, and the salinity of sea water was constantly increasing. This means that in the future our descendants will face very high salt levels in the water.

But are the seas getting saltier?

However, as research shows, the percentage of “salinity” has long remained unchanged and averages 30-40 grams of salt per liter of water. This means that the “extra” salt goes somewhere.

One of the versions, which was proposed back in the 18th century by Halley, says that the sea has always been salty, long before the first living organisms appeared on earth. Or the seas, by a lucky chance, formed on salt layers lying in the ground, eroded them over time and, having dissolved, became salty too.

The famous ocean explorer Zenkevich also believes that the water in the sea was originally salty due to the presence of substances in it that were released through a break in the earth's crust as a result of violent volcanic activity. Magma mixed with the water of the seas and oceans, and forever gave it a characteristic salty taste. According to scientists, this version is the most viable.

Scientists have not been able to finally come to one conclusion. The question of what mechanisms maintain the constancy of the chemical composition and constant pH level (by the way, its value of 7.4 corresponds to the acidity level in human blood) of the seas and oceans also remains open.

As you can see, nature is fraught with many mysteries, which cannot always be resolved. And simple questions often lead to complex and ambiguous answers.

Water is one of the most powerful solvents. It is capable of dissolving and destroying any rock on the surface of the earth. Streams of water, streams and drops gradually destroy granite and stones, and leaching of easily soluble components occurs from them. No strong rock can withstand the destructive effects of water. This is a long process, but inevitable. Salts that are washed out of rocks give sea water a bitter-salty taste.

But why is the water in the sea salty and the water in rivers fresh?

There are two hypotheses about this.

Hypothesis one

All impurities dissolved in water are carried by streams and rivers into the seas and oceans. River water is also salty, but it contains 70 times less salts than sea water. Water from the oceans evaporates and returns to the earth in the form of precipitation, and dissolved salts remain in the seas and oceans. The process of “supplying” salts to the seas by rivers has been going on for more than 2 billion years - time sufficient to “salt” the entire World Ocean.

Sea water contains almost all the elements that exist in nature. It contains magnesium, calcium, sulfur, bromine, iodine, fluorine, and small amounts of copper, nickel, tin, uranium, cobalt, silver and gold. Chemists have found about 60 elements in sea water. But most of all sea water contains sodium chloride, or table salt, which is why it is salty.

This hypothesis is supported by the fact that lakes that have no drainage are also salty.

Thus, it turns out that initially the water in the oceans was less salty than it is now.

But this hypothesis does not explain the differences in the chemical composition of sea and river water: chlorides (salts of hydrochloric acid) predominate in the sea, and carbonates (salts of carbonic acid) predominate in rivers.

Hypothesis two

According to this hypothesis, the water in the ocean was initially salty, and it was not the rivers that were to blame, but the volcanoes. Proponents of the second hypothesis believe that during the formation of the earth's crust, when volcanic activity was very high, volcanic gases containing vapors of chlorine, bromine and fluorine rained down as acid rain. Thus, the first seas on Earth were... acidic. By entering into a chemical reaction with hard rocks (basalt, granite), the acidic water of the oceans extracted alkaline elements from the rocks - magnesium, potassium, calcium, sodium. Salts were formed that neutralized sea water - it became less acidic.

As volcanic activity decreased, the atmosphere was cleared of volcanic gases. The composition of ocean water stabilized approximately 500 million years ago - it became salty.

But where do carbonates disappear from river water when they enter the World Ocean? They are used by living organisms - to build shells, skeletons, etc. But they avoid chlorides, which predominate in sea water.

Currently, scientists have agreed that both of these hypotheses have a right to exist, and do not refute, but complement each other.

Why is the water in the sea salty and not fresh? There are several theories about this. Some researchers claim that the salt remains from water from flowing rivers, others that it enters the water from rocks and stones, and others believe that the reason is volcanic emissions. In addition to salt, sea water contains many different substances and minerals.

Why is there salty water in the sea?

The seas are much larger than the rivers, but their composition remains virtually unchanged. If all the sea salt were spread on land, we would get a layer more than 150 meters thick, which is equal to the height of a 45-story building. Let's consider several theories why the sea is salty:

• The seas become salty from the water of the rivers flowing into them. There is nothing surprising. River water seems quite fresh, but it also contains salt. Its content is 70 times less than in the waters of the World Ocean. Flowing into the sea, rivers dilute their composition, but when river water evaporates, salt remains at the bottom of the seas. This process took place over billions of years, so the salt accumulated gradually.
• The second theory is why there is salty water in the sea. Salts that flow from rivers into the sea settle at the bottom. Over the course of many years, huge blocks of stone and rocks are formed from salts. Over time, sea currents wash away easily soluble substances and salts from them. Particles washed out of rocks and rocks make seawater salty and bitter.
• Another theory suggests that underwater volcanoes can release a lot of substances and salt into the environment. When the earth's crust was formed, volcanoes were extremely active and released acidic substances into the atmosphere. The acids formed rain and formed seas. At first they were acidic, but then the alkaline elements in the soil reacted with the acids and the result was salt. Thus, the water in the seas became salty.

Other researchers associate the salinity of sea waters with winds that bring salts into the water. With soils through which fresh liquid passes and becomes enriched with salts, and then flows into the ocean. Sea water can be saturated with salt by salt-forming minerals that make up the ocean floor, which get there from hydrothermal sources.

Why is the water in the seas constantly salty and this composition does not change? Sea water is diluted by rain and inflowing rivers, but this does not make it any less salty. The fact is that many of the elements that make up sea salt are absorbed by living organisms. Coral polyps, crustaceans and molluscs absorb calcium from salt, as they need it to build shells and skeletons. Diatom algae absorb silicon dioxide. Microorganisms and other bacteria consume dissolved organic matter. After organisms die or are consumed by other animals, the minerals and salts in their bodies return to the seafloor as remains or decay debris.

Sea water can be salty and varies depending on the time of year as well as climate. The highest salinity levels are found in the Red Sea and the Persian Gulf, as they are hot and evaporate intensely. In sea waters, which receive a lot of precipitation and a large volume of fresh water from large rivers, the salinity is much lower. The least salty seas and oceans are near polar ice, as they melt and dilute the sea with fresh water. But while the sea is covered with a crust of ice, the level of salt in the water rises. But in general, the salt levels in seawater remain constant.

The saltiest seas

The first place in salinity is occupied by the unique Red Sea. There are several reasons why this sea is so salty. Due to its location above the sea surface, there is low precipitation and much more water evaporates. Rivers do not flow into this sea; it is replenished thanks to precipitation and the waters of the Gulf of Aden, which also contain a lot of salt. The water in the Red Sea is constantly mixing. Evaporation occurs in the upper layer of water, and salts sink to the seabed. Therefore, the salt content increases significantly. Amazing hot springs were discovered in this reservoir; the temperature in them is maintained from 30 to 60 degrees. The composition of the water in these sources is unchanged.

Due to the absence of rivers flowing into the Red Sea, dirt and clay do not fall into the Red Sea, so the water here is clean and clear. The water temperature is 20-25 degrees all year round. Thanks to this, unique and rare species of marine animals live in the reservoir. Some consider the Dead Sea to be the saltiest. Indeed, its water contains a large amount of salt, which is why fish cannot live in it. But this body of water does not have access to the ocean, so it cannot be called a sea. It would be more correct to consider it a lake.