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Why is the sea salty?

“Why is the sea salty?” - one of children's favorite summer questions. In our new column “Why” we will regularly answer the most interesting questions of preschoolers and schoolchildren in clear and simple language, as well as hold exclusive competitions!

Why is the sea salty? Why does a hedgehog need needles? Why did they add “-s” to many words in the last century? Why do cats purr and what do they do? Is it possible to create a time machine according to the laws of physics? As a parent or teacher of primary and secondary schools, you will hear these questions more than once. We will be happy to answer them.

Why is the sea salty?

The answer to this question must begin with an explanation of where the water in the sea and ocean comes from. In rivers we find springs and springs - underground springs, but where does the water, and salty one, come from in the sea?

The reserves of both the Black Sea and the Atlantic Ocean are replenished with fresh water from rivers and precipitation in the form of snow or rain. Both consist of fresh water (in fact, also salty, just in a very small concentration). But unlike rivers, water from oceans and seas does not flow anywhere, but only evaporates when exposed to the sun’s rays. When evaporation occurs, the salts remain.

Another factor in the salinity of the sea is the movement of the rivers themselves flowing into it. On the way to the seas and oceans, river flows wash the salts that make up the stone out of the rocks and bring them with them to the sea, albeit in small quantities.

It turns out that the sea has become salty? Was it fresh before that? No, that's not true. The main reason, which modern scientists agree with, is the process of formation of the sea itself, which was just as salty millions of years ago. The fault for this is not the rivers, which did not exist then, but the volcanoes that covered our planet.

The water of the primary ocean was formed from volcanic gases, the composition of which is approximately the following: 75% of water accounts for 15% carbon dioxide and about 10% of various chemical compounds. These compounds include methane, ammonia, sulfur, chlorine and bromine, as well as various gases. So when the products of the eruption fell to the ground in the form of acid rain, they reacted with the bottom of the future sea, and as a result we got a salty solution.

How much salt is there in the sea?

About 35 are dissolved in one liter of sea water grams of salt.

How much water is there in the sea?

If we take the average depth of the world's oceans to be 3703 meters, and take the average surface area to be 361.3 million square kilometers, we get 1.338 billion km 3

Which seas are the freshest and saltiest?

Let's start with another record holder - the largest sea. The absolute champion in this category is the Sargasso Sea, which is located inside the Atlantic Ocean. Its area reaches 8.5 million square kilometers.

But the freshest sea is in Russia, and this sea is the Baltic. Compared to the waters of the Atlantic, its sunshine is 5 times lower. Why? About 250 rivers flow into the Baltic Sea, which “desalinize” the waters.

What about the saltiest sea?

The record holder for the percentage of salts is the Red Sea. Its salinity is about 41 grams per liter of water! This phenomenal content explains the unique properties of the sea: it is very easy to float in it, and being in it itself is quite beneficial for health.

Why is the Red Sea so salty? The point is the fumes, which we wrote about at the very beginning. Water evaporates from this sea at a tremendous speed due to high temperature and low humidity, so that rains simply do not have time to “desalinate” it, moreover, very little of it falls.

Question - competition

Using the data above, calculate how much TOTAL salt is dissolved in ALL the seawater on our planet?

Send your answers in private messages to our communities at

Why is the water in the ocean salty and the water in rivers fresh? The answer to this question is ambiguous. There are different points of view that reveal the essence of the problem. According to scientists, it all comes down to the ability of water to destroy rock and leach easily soluble components from it, which end up in the ocean. This process occurs continuously. Salts saturate sea water, giving it a bitter-salty taste.

Everything seems to be clear, but at the same time, there are two diametrically opposed opinions on this issue. The first comes down to the fact that all the salts dissolved in the water are carried by rivers into the ocean, saturating the sea water. There are 70 times less salts in river water, so it is impossible to determine their presence in it without special tests. It seems to us that the river water is fresh. In fact, this is not entirely true. Seawater is constantly saturated with salts. This is also facilitated by the process of evaporation, as a result of which the amount of salts constantly increases. This process is endless and lasts about two billion years. This is enough time to make the water salty.

The composition of sea water is quite complex. It contains almost the entire periodic table. But most of all, it contains sodium chloride, which makes it salty. By the way, in closed lakes the water is also salty, which confirms the correctness of this hypothesis.

Everything seems to be correct, but there is one thing! Sea water contains salts of hydrochloric acid, and river water contains carbonic acid. That is why scientists have put forward an alternative hypothesis. They believe that sea water was originally salty, and rivers have nothing to do with it. This is all due to volcanic activity, the peak of which occurred at the time of formation of the earth’s crust. Volcanoes released huge amounts of steam saturated with acids into the atmosphere, which condensed and fell to the ground in the form of acid rain. The sediments saturated the seawater with acid, which reacted with the hard basaltic rocks. As a result, huge amounts of alkali were released, including sodium, potassium and calcium. The resulting salt neutralized the acid in seawater.

Over time, volcanic activity decreased, the atmosphere was cleared of vapors, and less and less acid rain fell. About 500 million years ago, the composition of sea water stabilized and became what we know it today. But the carbonates that enter the ocean with river water serve as an ideal building material for marine organisms. They build coral islands, shells, and their skeletons from it.

Which hypothesis to choose is a purely personal matter. In our opinion, they both have a right to exist.

Would you say that rivers wash it out of the soil into the waters of the World Ocean? Nothing of the kind. Not much water flows into the World Ocean from rivers. Free fresh water on Earth is less than 1%. Even less enters the seas and oceans, so influent waters can neither “desalinize” nor “salinize” the ocean.

Why is the water in the world's oceans salty?

Actually, sea water contains more than just salt. If you extract all the gold dissolved there from the World Ocean, you can cover the entire Earth with a gold layer one and a half meters thick!

In addition, sea water contains iron, magnesium, calcium, iodine, sulfur... How did all this get there?

Just over four billion years ago, literally the entire surface of the planet was strewn with numerous active volcanoes. Trillions of tons of molten lava poured onto the surface, and volcanic gases were released into the atmosphere in huge quantities.

Volcanic gases contain a lot of carbon dioxide, sulfur oxide, sulfuric and hydrochloric acids, methane and many other substances from the bowels of the Earth. Therefore, the atmosphere of our planet was opaque, hot and poisonous.

However, time passed, and the primary atmosphere began to cool. When it cooled to +100 degrees, the water vapor turned into droplets of water, which began to fall to the surface. The first rain fell on planet Earth - and what rain!

Firstly, this rain poured without stopping for hundreds of millions of years. Secondly, it was warm, even hot, and very cloudy. Thirdly, the drops of this rain contained an incredible amount of burning acids - sulfuric and hydrochloric. There's no way you'll be able to have fun running and jumping in such rain in shorts - you need a spacesuit!

Puddles of water began to form on the surface of the Earth, which gradually grew, turning first into large puddles, then into lakes, then into seas, then into oceans... At some point, our planet was completely covered by one huge ocean, with almost there was no sushi! Only tiny volcanic islands. It would be more correct to call such a planet not Earth, but Water - all of it was one vast (but not very deep) ocean.

What was the water of this primordial ocean like?

Lake Kawah on the island of Java

On the island of Java, Indonesia, there is an active volcano called Ijen. Inside its crater there is the most amazing Lake Kawah, the waters of which are in some ways very similar to the ancient lakes and seas of the Earth. Don’t even try to lie on the local beach, much less swim in this lake! Its shores, instead of sand, are thickly strewn with sulfur, and the water burns the skin like fire - if it gets into your eyes, you can go completely blind!

The water of Lake Kawah is a very strong mixture of sulfuric and hydrochloric acid. Almost as caustic and aggressive as the acid inside a car battery, only natural. Imagine - if you lower an iron nail into such water, it will hiss, gas bubbles will come from it, and after some time the nail will completely dissolve in this water, like a lump of sugar in a glass of hot tea! If we decide to sail on this lake on a boat made of metal, in a few hours the hull of the boat will be corroded by acid, and it will drown along with its passengers! Why is this happening?

The fact is that this is one of the main properties of acid - when it “meets” metals, it immediately enters into a violent chemical reaction with them. In this reaction, a metal and an acid produce hydrogen gas and a substance that chemists call... salt!

For example, in our experiment with a nail in the water of Lake Kawah, hydrochloric acid reacts with the iron from which the nail is made. The result is hydrogen (remember the fizzing bubbles?) and a salt called ferric chloride. In exactly the same way, in the waters of the ancient ocean of the Earth, hydrochloric acid reacted with destroyed rocks, including the metal sodium - and sodium chloride was obtained, that is, the kitchen salt familiar to us all...

As a result, the ocean water gradually turned from cloudy, hot and acidic into clear, salty and not at all dangerous to humans - swimming in sea water is not only not harmful, but even very good for health!

This transformation was completed a long time ago - scientists say that already two billion years ago the chemical composition of the World Ocean was practically no different from what it is today.

So the leaching of minerals from the soil does not particularly affect the salinity of the waters of the World Ocean...

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The phenomena of the world around us raise a lot of questions among the curious. For example, when you find yourself on the shore of an endless body of water, you begin to think: what kind of water in the ocean is fresh or salty? How can we explain the chemical composition of ocean water and is it safe to drink?

Since ancient times, the composition of water in the seas and oceans has surprised people. In Germany, there are legends that claim that at the bottom of every sea there is a magical salt mill, and in Hungary - that this is all because of the tears of an unfortunate girl grieving under the water.

Finding out whether the water in the ocean is salty is actually as easy as shelling pears - just look at the materials of modern research. Indeed, sea and ocean water is very salty, and sometimes the concentration of salts is excessively high: one glass of “drink” from the Dead Sea is enough to prevent you from regaining consciousness at all.

The saltiest bodies of water in the world are:

• Atlantic Ocean: southern part (salt concentration is 37.9 ppm) and northern part (37.6);
• Pacific Ocean: southern part (36.9) and northern (35.9);
• Entire Indian Ocean (36.4 ppm).

Why is the ocean water salty?

Oddly enough, even modern scientists have not found a clear answer to such a simple question - why is the water in the ocean salty? Some researchers believe that this is due to volcanic activity, while others believe that salt comes into the oceans through rivers and seas.

About the amount of salt and fresh water on earth.

Two theories

The first group of scientists claims that a very long time ago, when the earth’s crust was just being formed, volcanoes on Earth were extremely active. Their eruptions led to the occurrence of acid rain - but the World Ocean itself consisted of acids. As a result, various complex substances “collided” with each other, and as a result of the reaction, ocean waters became safe for life, which had yet to arise. But only very salty ones.

As for the “earth” theory, it says that salts are contained in all reservoirs of the world. And this is true - fresh water is not devoid of salts, there are just very few of them. Flowing into the oceans, rivers and seas bring with them salts washed out of the soil. They, in turn, remain in place - and where else can they go? Yes, during the natural cycle, water evaporates from the surface of the oceans, but the salts are too heavy to follow it.

As you can see for yourself, these theories are quite logical. Or maybe both groups of researchers are right at once, and the salts first appeared thanks to volcanoes, and numerous currents brought even more of them?

Can a fresh ocean arise?

What determines the salinity of water in the ocean? Many factors play a role here, including underwater currents, the presence of glaciers, the intensity of their melting, the activity of evaporation, etc. In addition, in the depths, under the very bottom of the ocean, there are deposits of the purest fresh water.

But even if we imagine that a crystal clear body of water will appear on Earth, it is obvious that fresh water in the ocean would not linger for long. After all, no one doubts that rivers constantly add salts washed out of the soil into ocean waters - scientists are skeptical only that this could cause the appearance of vast salty reservoirs as such.

Is it possible to drink sea water

So, we figured out why the water in the seas and oceans is salty, and found out that drinking it is not recommended. But why does this limitation exist?

In fact, ocean water is contraindicated for humans due to the structural features of the body. The kidneys are responsible for removing salts and other “heavy” substances from food, which may simply not be able to cope with the excess load. And a liter of sea water contains more than 30 grams of salt! That is why unfortunate people who are shipwrecked and manage to escape in boats often die of thirst in the middle of the water.

Why is the sea salty: Video

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.