I remember it was in the third grade, during a science lesson. The teacher told us that there are rivers on earth with fresh water, as well as seas and oceans with salt water. " Why is the water in the ocean salty?“- I asked and, oddly enough, Nadezhda Konstantinovna was confused. She simply did not know the answer to this seemingly simple childish question. And for the first time then I realized that teachers do not know everything in the world.
Ocean As I grew older, I tried to find the answer on my own using textbooks, the encyclopedia and the magazine “Around the World” (no one had thought about the Internet at that time). And I realized that I shouldn’t have blamed the teacher for incompetence: it turns out that science still doesn’t have an exact answer about reasons for the salinity of ocean water.
Why is the water in the ocean salty: hypotheses
Actually, the answer to the question is, why does the ocean water taste salty?, is obvious: because it contains a lot of salt. But I’ll try to figure out where it came from in such quantities. Here The main versions of the origin of salt in ocean water:
- volcanic;
- river;
- stone.
I'll tell you more about each of them.
The ocean water is salty due to volcanoes
Millions of years ago, when the earth's surface had not yet taken on its current shape, nand our planet had many active volcanoes , from which acidic substances were released into ocean water. Entering into various reactions, these acids turned into salts, which dissolved in the waters of the world's oceans.
Volcano in the ocean Here is the first answer to the question, p Why is there salty water in the seas and oceans?. Ocean water is salty because of the rivers that flow into it.
“How so? - you ask - the water in the rivers is fresh, which means it should dilute the ocean water, making it less salty! In fact, river water cannot be considered absolutely fresh: it contains salts, but in small quantities. Rivers take their water from streams that flow from underground freshwater reservoirs. Fresh rainwater is added to them. But on the way to the sea the river collects a large number of salts from sand and stones, with which its bed is covered. Flowing into the ocean, the river gives it this salt.
The river flows into the ocean Evaporation processes in the ocean are much more active than in rivers due to their enormous surface area. It turns out that fresh water evaporates, but salt remains. Ocean water is salty due to erosion of rocks
In fact, this version explains not the origin of ocean salt, but the stability of its concentration. The seas and oceans have enough a large line of shores that are constantly washed by waves. The waves leave on particles of water on coastal stones, which, evaporates and turns into salt crystals. Gradually, holes form in the stones and holes that are getting more and more salty. Over the years the rocks are destroyed and the salt returns to the ocean.
Stones on the coast For me personally, all these options for answering the question, p why ocean waters are salty, look controversial, but science has no others yet.
Ocean! This word sounds loud and menacing. This is one of a kind huge accumulation of water surrounding continents and islands. This is the boundless sea that washes the universe. But, I wonder what kind of water is in the ocean, what is its chemical composition?
Chemical composition of ocean water
Ordinary residents more often deal with fresh water, in which there are almost no foreign impurities. However, it also contains dissolved salts, although in small concentrations. What then can we say about the ocean? What is the water like in the ocean? Judging by its composition, the ocean can hardly be called water. It is very similar to strong salty brine. Each kilogram of it contains about 35 grams of various salts. Scientists have found that chemical compounds of all elements are dissolved in the ocean.
Salt in the ocean
The fact that there is salt water in the ocean is an undeniable fact. But in different parts of the World Ocean, the concentration of salt is different. The Atlantic is considered the saltiest of all oceans, although some scientists believe that the saltiest is - Indian Ocean. And the least salty is the water of the Gulf of Finland. Despite the fact that salinity differs in different parts of the World Ocean, the ratio of different salts in water is the same. This amazing constancy is explained by the mixing of water by waves and currents.
Is there an ocean with fresh water
Fresh water in the ocean? This is impossible! Although there are hypotheses in science, they are just assumptions. This desalination is explained by the influence powerful rivers flowing into the ocean and heavy precipitation in temperate latitudes. However, the rivers that flow towards the ocean do not contain pure fresh water. Rivers wash away rocks and, washing away salts, carry them into the ocean. And let's not forget about the water cycle. After evaporation, ocean water falls as rain or snow, collects in rivers and returns to the ocean. Thus, salinization of the ocean continues today.
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 there was sea water salty initially 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 most saline lakes: Bolshoye 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.
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 from 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.
Clutha River Delta in New Zealand.
Here Clutha is divided into two parts: Matau and Koau,
each of which flows into the Pacific 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 you decrease volcanic activity the atmosphere was cleared of volcanic gases. Compound ocean water stabilized about 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.
Have you ever thought about what you would do if you were on desert island in the open ocean? You would first want to find food, make fire, make shelter and find water. Water? That's right, and although you may be surrounded by an endless ocean, those of you who have been to a sea beach know that sea water is not suitable for drinking.
Why not? Because . But why is sea water salty and not suitable for drinking?
Ocean water is salty because it contains large amounts of dissolved minerals. These minerals are often called "salts". Depending on where you are in the world, seawater contains approximately 3.5% salts. The water around it has a high salinity, while the northern waters contain less salts.
At the bottom there is a huge amount of minerals that are destroyed and rise to the surface by natural ocean currents. As the movement of water and waves erodes the ocean floor, minerals dissolve in the water and the amount of salts increases. This is how the ocean constantly replenishes its salinity.
Oceans and seas also get some of their salt from streams, rivers and lakes. While this may seem counterintuitive since these bodies of water contain fresh water, you may be surprised to learn that all lakes, rivers and streams contain some amount of dissolved salts. However, the concentration of salts in these bodies of water is much less than in the oceans, so their water appears less salty than ocean water.
Salts cannot accumulate in most lakes because they have outlets such as rivers and streams. These outlets allow water to flow to the oceans, carrying minerals with the flow.
On the other hand, it is an example of a reservoir without an outlet. Minerals that flow into the Dead Sea cannot be released into the open ocean because there is no runoff. Because of this, the Dead Sea contains some of the saltiest water on Earth.
In fact, up to 35% of the salts are found in the waters of the Dead Sea! This is almost ten times more than the concentration of salt in the oceans. Salty water The Dead Sea is lethal to most living things, so you won't find any fish or sea creatures there. Only a few species of bacteria and algae can survive the harsh conditions of the Dead Sea. That's why it's called Dead!
While you certainly wouldn't want to drink the water from this sea, you can swim in it. Due to the high concentration of salt, the density of water in the Dead Sea is much greater than in fresh water. This allows the swimmer to stay well on the surface of the water. Diving into the Dead Sea is a bit like dropping a plastic lid into a bowl of water. The dense water makes it easy to swim, even without much effort. In fact, water makes swimmers so buoyant that it is very difficult for them to reach the bottom or swim underwater.
