Freezing point of sea water table. The freezing processes of fresh and sea water are different due to the difference in their chemical and physical properties. At what temperature can sea water freeze?

3 degrees Celsius, but the air temperature can be -20, and the water will not freeze, since in the ocean the water communicates with the warm seas... . Sea water is a solution 44 chemical elements, but salts play a primary role in it. Table salt gives water a salty taste, while magnesium salt gives it a bitter taste. Salinity is expressed in ppm (%o). This is a thousandth of a number. An average of 35 grams are dissolved in a liter of ocean water. various substances, which means the salinity will be 35%. The salinity of ocean waters is not the same everywhere. The following processes influence the value of salinity: water evaporation. During this process, salts and water do not evaporate; ice formation; precipitation that reduces salinity; river flow. The salinity of ocean waters near the continents is much less than in the center of the ocean, since river waters desalinate it; melting ice. Processes such as evaporation and ice formation contribute to an increase in salinity, while precipitation, river runoff, and ice melting reduce it. Main role Evaporation and precipitation play a role in changing salinity. Therefore, the salinity of the surface layers of the ocean, like temperature, depends on climatic conditions associated with latitude. The salinity of the Red Sea is 42%. This is explained by the fact that not a single river flows into this sea, very little precipitation falls here (tropics), and the evaporation of water from strong heating by the sun is very large. The water evaporates from the sea, but the salt remains. The salinity of the Baltic Sea is not higher than 1%. This is explained by the fact that this sea is located in a climate zone where there is less evaporation, but more precipitation falls. However, the overall picture can be disrupted by currents. This is especially noticeable in the example of the Gulf Stream - one of the most powerful currents in the ocean, the branches of which, penetrating far into the Arctic Ocean (salinity 10-11% o), carry water with a salinity of up to 35%0. The opposite phenomenon is observed off the coast North America, where, under the influence of a cold Arctic current, for example the Labrador Current, the salinity of water off the coast decreases. The salinity of the deep ocean is generally almost constant. Here, individual layers of water with different salinities can alternate in depth depending on their density.

Ocean water freezes at (-2 C)

Before giving the answer, let's find out how fresh water differs from salt water?

Salinity determined in ppm, so the saltiest body of water is the Dead Sea (300-350 ppm or 300-350 grams of salt in 1 liter of water).

Fresh water has a salinity of no more than 1 ppm.

There are a number of versions why the seas are salty. According to the main one during formation earth's crust There was high volcanic activity.

Volcanic gases contained bromine, chromium and fluorine, which in contact with water were transformed into acid. The acids then reacted with the solid rock of the ocean floor, resulting in the formation of salt.

After 500 million

At what temperature does sea water freeze?

years chemical composition Ocean water has stabilized, but a certain percentage of salt ended up in the ocean with river water.

With fresh water, everything is simpler; precipitation is responsible for freshness, and it fills fresh water bodies.

Endless cycle

Sort of perpetual motion machine- water cycle: rain washes away various contaminants, penetrates deep into the earth, breaks down minerals, then rainwater flows into rivers, which carry it into the seas.

At the junction of the river and the sea, the water is less salty. Then the sun heats the water of the world's oceans, it evaporates, and salt impurities settle. The liquid that has evaporated returns to the surface of the earth in the form of precipitation.

Precipitation also forms fresh glaciers, from where mountain rivers originate, gradually this fresh water will again reach the world's oceans and the cycle will repeat again.

Atlantic Ocean is the second largest in the world, about half of the large volume Pacific Ocean.

In the north it limits it in Greenland and Iceland, in the east - in Africa and Europe, in the west - in North and South America, and in the south - in Antarctica.

It is easy to see that the ocean flows off the coasts of almost all continents and has a distinctly oblong shape.

Characteristics of the Atlantic Ocean

The area of the Atlantic Ocean exceeds 91 million km2, which is very large.

Its depth is also impressive: a maximum of 8742 meters, with an average of about 3600 meters. Therefore, the size of the water is very high - 329.6 million km3. This is a quarter of the world's oceans.

Brief information:

- The lower part of the Atlantic Ocean is very rough and has many defects, depressions and small mountains. And from north to south through central part ocean floor, and passed through the Mid-Atlantic Ridge to separate the western and eastern ocean (almost identical).
sea ice

Earthquakes and underwater volcanic eruptions are observed in the area of the ridge.
— The sea, bays and straits occupy approximately 16% of the area of the Atlantic Ocean (14.7 million km2).
— There are relatively few islands in the ocean, about a thousand.
— Due to the large length of the reservoir, as well as the circulation of the atmosphere and ocean currents, the Atlantic Ocean includes all the climatic zones of the planet.
In general, the average outside temperature is 20 °C in summer, and in winter - from 0 to 10 °C. As the distance from the equator to the north increases, the temperature decreases markedly.
— Water salinity ranges from 34 ‰ (at the equator) to 39 ‰ (in the Mediterranean Sea). Although in areas where rivers flow into the ocean, this number can be halved.
— Floating ice on the surface of the ocean forms only in the northern and southern regions, since they are close to the fractures of the planet.
— The diversity of flora and fauna of the Atlantic Ocean is very large, but it boasts the number of living organisms.
Thanks to this, there are many people in the ocean. But this leads to a significant reduction in the number of representatives wildlife. Therefore, a catch limit was set and other similar restrictions were introduced.
— Minerals are mined in the Atlantic Ocean (oil, gas, iron ore, sulfur and many others).
This leads to gradual pollution of their waters.

— The Atlantic Ocean was named after the ancient Greek myth of Atlas, a powerful titan who had the firmament on his shoulders.
— Famous Bermuda Triangle is located in the Atlantic Ocean.
Many ships and planes have indeed disappeared in this area, but there is scientific evidence behind these incidents. However, no one knows for sure what actually happened.

At what temperature does sea water freeze?

The Arctic Ocean has become fresher

The Arctic Ocean has become fresher. Photo: Fotobank.ru/Getty Images

The Arctic Ocean absorbs quite a lot of fresh water.

Its sources are the great Siberian and North American rivers, sediments and glaciers. In addition, it receives slightly saline waters from the Pacific Ocean. Fresh water is lighter than salt water and therefore accumulates in the upper ocean layer. Benjamin Rabe and his team analyzed 5,000 salinity profiles at different depths. They used data from sensors on ships, drifting ice floes and submarines. Large quantity The data was collected as part of the International Polar Year 2007/2008.

When comparing the distribution of salinity in 2006-2008 with similar data from 1992-1999, scientists saw that the layer of desalinated water on the surface became thicker.

They estimated the increase at 20%, which is 8,400 cubic kilometers. The main reasons for the desalination of the Arctic Ocean are increased melting of glaciers, increased precipitation and increased river flow. The researchers confirmed these data using mathematical modeling.

Nadezhda Markina

infox.ru

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At what temperature does ocean water freeze? How does temperature depend on salinity?

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Answers
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and scanwords

Definitions from scanwords of the word ICEBERG

large ocean ice
"Fragment" of Antarctica
"Splinter" of Antarctica
"Titanic" ice
English "ice mountain"
floating ice for the Titanic
a mountain whose top is easier to reach than its bottom
drifting ice mountain
large body of ice floating in the sea
ice wanderer
the ice that sank the Titanic
ice mountain in the ocean
Fletcher's Ice Island
icy ocean traveler
the man from Pugacheva's song who doesn't like anyone
huge ice block in the sea
drifting body of water breaking off from a glacier
drifting ice mass broken off from a glacier with a deeply submerged underwater part
floating mountain of ice
floating ice mountain
floating ice mountain that has broken off from a coastal glacier
floating piece of Antarctica
destroyed the Titanic
obstacle for the Titanic
obstacle in the way of the Titanic
cause of the sinking of the Titanic
Cameron's Titanic Ice
titanic drowner
Titanic killer
cold in the ocean
cold friend of Alla Pugacheva
cause of the sinking of the Titanic
the largest of its kind was 350 km long, 40 km wide, and was discovered by the icebreaker Glacier in 1956
put together two Scandinavian words - "ice" and "mountain"
English "ice mountain"
Titanic killer
The sinking of the Titanic is associated with it
waterfowl ice for "Titatnik"
"shard" of Antarctica
obstacle for the Titanic
destroyed the Titanic
obstacle in the way of the Titanic
"titanic" ice
"fragment" of Antarctica

Sea water, unlike fresh water, does not have a specific freezing point, but it is always below 0°C. Freezing point sea water depends on its salinity: the higher the salinity, the lower the freezing point. Thus, at an average ocean salinity of 35%, water freezes at -1.9°C, and at a salinity of 40%, at -2.2°C. In the Black Sea, for example, where salinity is from 15 to 20%, ice appears when the water cools from -0.8 to -1.1 ° C.

When seawater cools to the freezing temperature corresponding to its salinity, the formation of ice crystals (freezing) begins. When freezing, the salts contained in sea water are not included in the composition of the resulting ice crystals, since the freezing temperature saline solution significantly lower (for example, the freezing point of steamed salt is -21°C). Therefore, most of the salts fall into the non-freezing subglacial water, and a certain amount freezes into the ice in the form of small drops of a strong salt solution, which significantly affects the physicochemical and mechanical properties sea ice. The lower the temperature at which water freezes, the more brine droplets remain in the sea ice and, therefore, the greater its salinity. Salts that fall into the surface layer during the freezing process of sea water increase its salinity, which lowers the freezing point.

The temperature of the highest relative density and the freezing point of sea water decrease with increasing salinity. At a salinity of 24.7%, both temperatures become the same: -1.33°C. Waters whose salinity is less than 24.7% are called brackish; their temperature of greatest density is above the freezing point. Therefore, the process of freezing of water with a salinity of less than 24.7% occurs in the same way as fresh water: first, the water reaches the temperature of the highest density at a given salinity, then the freezing point.

In water with a salinity of more than 24.7%, the temperature of the highest density is always below the freezing point, therefore, until the moment of freezing, the density of sea water increases with decreasing temperature, and the upper cooled layers of water (as heavier ones) sink down; Less dense and warmer waters rise to the surface, making ice formation more difficult. In this regard, in the seas and oceans the water freezes only after long autumn colds, when the entire water column, covered by vertical circulation (convection), is cooled to freezing temperature.

Fresh water has its greatest density at +4°C and begins to freeze at 0°C. In a freshwater pool, after cooling the water to +4°C, further cooling of its surface layer occurs very quickly. The water here becomes lighter than the underlying waters, which eliminates mixing and, therefore, the rise of warmer waters to the surface. water masses from the depths. Ice formed from fresh water is a homogeneous mass of ice crystals interspersed with air bubbles and various solid particles that were in the water.

If you noticed, water in the sea freezes at temperatures well below zero degrees. Why is this happening? It all depends on the concentration of salt in it. The higher it is, the lower the freezing temperature. On average, an increase in water salinity by two ppm lowers its freezing point by one tenth of a degree. So judge for yourself what the ambient temperature should be for a thin layer of ice to form on the surface of the sea, with a water salinity of 35 ppm. At a minimum, it should be two degrees below zero.

The same Azov Sea, with a water salinity of 12 ppm, freezes at a temperature of minus 0.6 degrees. At the same time, the adjacent Sivash remains unfrozen. The thing is that the salinity of its water is 100 ppm, which means that for ice to form here, at least six degrees of frost is necessary. In order for the surface of the White Sea, where the water salinity level reaches 25 ppm, to cover with ice, the temperature must drop to minus 1.4 degrees.

The most amazing thing is that in sea water cooled to minus one degree, snow does not melt. He just continues to swim in it until he turns into a piece of ice. But getting into the chilled fresh water, he immediately conceals it.

The process of freezing sea water has its own characteristics. First, primary ice crystals begin to form, which incredibly look like thin transparent needles. There is no salt in them. It is squeezed out of the crystals and remains in the water. If we collect such needles and melt them in some kind of container, we will get fresh water.

A mess of ice needles, looking like a huge greasy spot, floats on the surface of the sea. Hence its original name - lard. With a further decrease in temperature, the lard freezes, forming a smooth and transparent ice crust, which is called nilas. Unlike lard, nilas contains salt. It appears in it in the process of fat freezing and needles capturing droplets of sea water. This is a rather chaotic process. This is why salt in sea ice is distributed unevenly, usually in the form of individual inclusions.

Scientists have found that the amount of salt in sea ice depends on the ambient temperature at the time of its formation. When there is slight frost, the rate of formation of nilas is low, the needles capture little sea water, hence the salinity of the ice is low. In extreme cold, the situation is exactly the opposite.

When sea ice melts, the first thing that comes out is salt. As a result, it gradually becomes fresh.

At what temperature does water freeze? It would seem to be the simplest question that even a child can answer: the freezing point of water at normal atmospheric pressure of 760 mm Hg is zero degrees Celsius.

However, water (despite its extremely wide distribution on our planet) is the most mysterious and incompletely studied substance, so the answer to this question requires a detailed and reasoned conversation.

In Russia and Europe, temperature is measured on the Celsius scale, the highest value of which is 100 degrees.
The American scientist Fahrenheit developed his own scale with 180 divisions.
There is another unit of temperature measurement - the kelvin, named after the English physicist Thomson, who received the title of Lord Kelvin.

Conditions and types of water

Water on planet Earth can take three main states of aggregation: liquid, solid and gaseous, which can be transformed into different forms that simultaneously coexist with each other (icebergs in sea water, water vapor and ice crystals in clouds in the sky, glaciers and free-flowing rivers ).

Depending on the characteristics of origin, purpose and composition, water can be:

fresh;
mineral;
nautical;
drinking (we include tap water here);
rain;
thawed;
salty;
structured;
distilled;
deionized.

The presence of hydrogen isotopes makes water:

light;
heavy (deuterium);
superheavy (tritium).

We all know that water can be soft or hard: this indicator is determined by the content of magnesium and calcium cations.

Each of the types we have listed and states of aggregation water has its own freezing and melting points.

Freezing point of water

Why does water freeze? Ordinary water always contains some suspended particles of mineral or organic origin. These can be tiny particles of clay, sand or house dust.

When the temperature environment drops to certain values, these particles take on the role of centers around which ice crystals begin to form.

Air bubbles, as well as cracks and damage on the walls of the vessel containing water, can also become crystallization nuclei. The speed of the water crystallization process is largely determined by the number of these centers: the more of them, the faster the liquid freezes.

Under normal conditions (at normal atmospheric pressure), the temperature of the phase transition of water from liquid to solid is 0 degrees Celsius. It is at this temperature that water freezes outside.

Why does hot water freeze faster than cold water?

Hot water freezes faster than cold water - this phenomenon was noticed by Erasto Mpemba, a schoolboy from Tanganyika. His experiments with ice cream mixtures showed that the rate of freezing of heated masses was significantly higher than that of cold ones.

One of the reasons for this interesting phenomenon, called the “Mpemba paradox,” is the higher heat transfer of a hot liquid, as well as the presence of a larger number of crystallization nuclei in it compared to cold water.

Are the freezing point of water and altitude related?

When pressure changes, often associated with being at different altitudes, the freezing point of water begins to differ radically from the standard one characteristic of normal conditions.
Crystallization of water at altitude occurs at the following temperature values:

Paradoxically, at an altitude of 1000 m, water freezes at 2 degrees Celsius;
at an altitude of 2000 meters this occurs already at 4 degrees Celsius.

The highest freezing temperature of water in the mountains is observed at an altitude of over 5,000 thousand meters (for example, in the Fan Mountains or the Pamirs).

How does pressure affect the process of water crystallization?

Let's try to link the dynamics of changes in the freezing temperature of water with changes in pressure.

At a pressure of 2 atm, water will freeze at a temperature of -2 degrees.
At a pressure of 3 atm, the temperature of -4 degrees Celsius will begin to freeze water.

With increased pressure, the temperature at which the water crystallization process begins decreases, and the boiling point increases. At low pressure, a diametrically opposite picture is obtained.

That is why in high altitude conditions and a rarefied atmosphere it is very difficult to boil even eggs, since the water in the pot boils already at 80 degrees. It is clear that it is simply impossible to cook food at this temperature.

At high pressure, the process of melting the ice under the blades of the skates occurs even at very low temperatures, but it is thanks to it that the skates glide along the icy surface.

The freezing of the runners of heavily loaded sleds in the stories of Jack London is explained in a similar way. Heavy sleds putting pressure on the snow cause it to melt. The resulting water makes them easier to slide. But as soon as the sledges stop and stay in one place for a long time, the displaced water freezes and freezes the runners to the road.

Crystallization temperature of aqueous solutions

Being an excellent solvent, water easily reacts with various organic and inorganic substances, forming a mass of sometimes unexpected chemical compounds. Of course, each of them will freeze at different temperatures. Let's show this in a visual list.

The freezing point of a mixture of alcohol and water depends on the percentage of both components in it. The more water added to the solution, the closer to zero its freezing point. If there is more alcohol in the solution, the crystallization process will begin at values close to -114 degrees.
It is important to know that water-alcohol solutions do not have a fixed freezing point. Usually they talk about the temperature at the beginning of the crystallization process and the temperature of the final transition to the solid state.
Between the beginning of the formation of the first crystals and the complete solidification of the alcohol solution there is a temperature interval of 7 degrees. So, the freezing point of water with alcohol 40% concentration at initial stage is -22.5 degrees, and the final transition of the solution into the solid phase will occur at -29.5 degrees.

The freezing point of water with salt is closely related to the degree of its salinity: the more salt in the solution, the lower the position of the mercury column it will freeze.

To measure the salinity of water, a special unit is used - “ppm”. So, we have established that the freezing point of water decreases with increasing salt concentration. Let's explain this with an example:

The salinity level of ocean water is 35 ppm, while its average freezing point is 1.9 degrees. The salinity of the Black Sea waters is 18-20 ppm, so they freeze at a higher temperature with a range from -0.9 to -1.1 degrees Celsius.

The freezing point of water with sugar (for a solution whose molality is 0.8) is -1.6 degrees.
The freezing point of water with impurities largely depends on their quantity and the nature of the impurities included in the aqueous solution.
The freezing point of water with glycerin depends on the concentration of the solution. A solution containing 80 ml of glycerin will freeze at -20 degrees; when the glycerin content decreases to 60 ml, the crystallization process will begin at -34 degrees, and the start of freezing of a 20% solution is minus five degrees. As you can see, linear dependence in this case is absent. To freeze a 10% glycerin solution, a temperature of -2 degrees will be sufficient.
The freezing point of water with soda (meaning caustic alkali or caustic soda) presents an even more mysterious picture: a 44% caustic solution freezes at +7 degrees Celsius, and 80% at + 130.

Freezing of fresh water bodies

The process of ice formation in freshwater bodies occurs in a slightly different temperature regime.

The freezing point of water in a lake, just like the freezing point of water in a river, is zero degrees Celsius. Freezing of the cleanest rivers and streams begins not from the surface, but from the bottom, on which crystallization nuclei are present in the form of particles of bottom silt. At first, driftwood and aquatic plants are covered with a crust of ice. As soon as the bottom ice rises to the surface, the river instantly freezes through.
The frozen water on Lake Baikal can sometimes cool to sub-zero temperatures. This happens only in shallow water; the water temperature can be thousandths and sometimes hundredths of one degree below zero.
The temperature of Baikal water under the very crust of the ice cover, as a rule, does not exceed +0.2 degrees. In the lower layers it gradually increases to +3.2 at the bottom of the deepest basin.

Freezing point of distilled water

Does distilled water freeze? Let us remember that for water to freeze, it is necessary to have certain centers of crystallization in it, which can be air bubbles, suspended particles, as well as damage to the walls of the container in which it is located.

Distilled water, completely devoid of any impurities, does not have crystallization nuclei, and therefore its freezing begins at very low temperatures. The initial freezing point of distilled water is -42 degrees. Scientists managed to achieve supercooling of distilled water to -70 degrees.

Water that has been exposed to very low temperatures without crystallizing is called “supercooled.” You can place a bottle of distilled water in the freezer to achieve hypothermia, and then demonstrate a very impressive trick - watch the video:

By gently tapping a bottle taken out of the refrigerator or throwing a small piece of ice into it, you can show how instantly it turns into ice that looks like elongated crystals.

Distilled water: does this purified substance freeze under pressure or not? Such a process is possible only in specially created laboratory conditions.

Freezing point of salt water

The most amazing thing is that in sea water cooled to minus one degree, snow does not melt. He just continues to swim in it until he turns into a piece of ice. But when it gets into cooled fresh water, it immediately melts.

When sea ice melts, the first thing that comes out is salt. As a result, it gradually becomes fresh.

3.2. SEA ICE

All our seas, with rare exceptions, are covered with ice of varying thickness in winter. In this regard, navigation in one part of the sea becomes difficult during the cold half of the year, while in another it stops and can only be carried out with the help of icebreakers. Thus, freezing of the seas disrupts the normal operation of the fleet and ports. Therefore, for more qualified operation of the fleet, ports and offshore structures, certain knowledge is required physical properties sea ice.

Sea water, unlike fresh water, does not have a specific freezing point. The temperature at which ice crystals (ice needles) begin to form depends on the salinity of seawater S. It has been experimentally established that the freezing temperature of sea water can be determined (calculated) using the formula: t 3 = -0.0545S. At a salinity of 24.7%, the freezing point is equal to the temperature of the highest density of sea water (-1.33°C). This circumstance (property of sea water) made it possible to divide sea water into two groups according to the degree of salinity. Water with a salinity of less than 24.7% is called brackish and, when cooled, first reaches the temperature of the highest density and then freezes, i.e. behaves like fresh water, which has a temperature of highest density of 4° C. Water with a salinity of more than 24.7°/00 is called sea water.

The temperature at greatest density is below the freezing point. This leads to the occurrence of convective mixing, which delays the freezing of sea water. Freezing is also slowed down due to salinization of the surface layer of water, which is observed when ice appears, since when water freezes, only part of the salts dissolved in it remains in the ice, while a significant part of them remains in the water, increasing its salinity, and therefore, and the density of the surface layer of water, thereby lowering the freezing point. On average, the salinity of sea ice is four times less than the salinity of water.

How does ice form in sea water with a salinity of 35°/00 and a freezing point of -1.91° C? After the surface layer of water has cooled to the temperature indicated above, its density will increase and the water will sink down, and warmer water from the underlying layer will rise up. Mixing will continue until the temperature of the entire mass of water in the upper active layer drops to -1.91 ° C. Then, after some supercooling of the water below the freezing point, ice crystals (ice needles) begin to appear on the surface.

Ice needles form not only on the surface of the sea, but throughout the entire thickness of the mixed layer. Gradually, the ice needles freeze together, forming ice spots on the surface of the sea that resemble frozen water in appearance. salo. In color it is not much different from water.

When snow falls on the surface of the sea, the process of ice formation accelerates, since the surface layer is desalinated and cooled, in addition, ready-made crystallization nuclei (snowflakes) are introduced into the water. If the water temperature is below 0°C, then the snow does not melt, but forms a viscous mushy mass called snowy. Under the influence of wind and waves, lard and snow are knocked down into white pieces called sludge. With further compaction and freezing of the initial types of ice (ice needles, fat, slush, snow slush) a thin, elastic crust of ice is formed on the sea surface, easily bending in the wave and, when compressed, forming jagged layers called Nilas. Nilas has a matte surface and a thickness of up to 10 cm, and is divided into dark (up to 5 cm) and light (5-10 cm) nilas.

If the surface layer of the sea is highly desalinated, then with further cooling of the water and a calm state of the sea, as a result of direct freezing or from ice fat, the surface of the sea is covered with a thin shiny crust called bottle. The bottle is transparent, like glass, easily broken by wind or waves, its thickness is up to 5 cm.

On a light wave of ice fat, slush or snow, as well as as a result of the breaking of the bottle and nilas during a large swell, the so-called pancake ice. It has a predominantly round shape, ranging from 30 cm to 3 m in diameter and up to approximately 10 cm in thickness, with raised edges due to the impact of ice floes against one another.

In most cases, ice formation begins near the coast with the appearance of banks (their width is 100-200 m from the coast), which, gradually spreading into the sea, turn into fast ice Strands and fast ice refer to fixed ice, that is, ice that forms and remains stationary along the coast, where it is attached to a shore, an ice wall, or an ice barrier.

Top surface young ice in most cases, smooth or slightly wavy, the lower one, on the contrary, is very uneven and in some cases (in the absence of currents) looks like a brush of ice crystals. During the winter, the thickness of the young ice gradually increases, its surface is covered with snow, and the color, due to the flow of brine from it, changes from gray to white. Young ice 10-15 cm thick is called gray, and 15-30 cm thick - gray-white. With further increase in ice thickness, the ice becomes white. Sea ice that has lasted one winter and has a thickness of 30 cm to 2 m is usually called white. first-year ice, which is divided into thin(thickness from 30 to 70 cm), average(from 70 to 120 cm) and thick(more than 120 cm).

In areas of the World Ocean where the ice does not have time to melt over the summer and from the beginning of the next winter begins to grow again and by the end of the second winter its thickness increases and is already more than 2 m, it is called two-year-old ice . Ice that has existed for more than two years called perennial, its thickness is more than 3 m. It has a greenish-blue color, and with a large admixture of snow and air bubbles, it has a whitish color, glassy appearance. Over time, desalinated and compressed multi-year ice acquires a blue color. Based on their mobility, sea ice is divided into stationary ice (fast ice) and drifting ice.

Drifting ice is divided into: pancake ice, ice fields, crushed ice(a piece of sea ice less than 20 m across), grated ice(broken ice less than 2 m in diameter), not like that(a large hummock or a group of hummocks frozen together, up to 5 m high above sea level), frosty(pieces of ice frozen into an ice field), ice porridge(an accumulation of drifting ice consisting of fragments of other forms of ice no more than 2 m in diameter). In turn, ice fields, depending on their horizontal dimensions, are divided into:

Giant ice fields, more than 10 km across;

Extensive ice fields, from 2 to 10 km across;

Large ice fields, from 500 to 2000 m across;

Fragments of ice fields, from 100 to 500 m in diameter;

Coarse ice, from 20 to 100 m in diameter.

A very important characteristic for shipping is the concentration of drifting ice. The concentration is understood as the ratio of the area of the sea surface actually covered with ice to total area the sea surface on which drifting ice is located, expressed in tenths.

In the USSR, a 10-point ice concentration scale was adopted (1 point corresponds to 10% of the ice-covered area), in some foreign countries(Canada, USA) -8 points.

In terms of its concentration, drifting ice is characterized as follows:

1. Compressed drifting ice. Drifting ice with a concentration of 10/10 (8/8) and no water visible.

2. Frozen solid ice. Drifting ice with a concentration of 10/10 (8/8) and ice floes frozen together.

3. Very compact ice. Drifting ice, the concentration of which is greater than 9/10, but less than 10/10 (from 7/8 to 8/8).

4. Solid ice. Drifting ice, with a concentration of 7/10 to 8/10 (6/8 to 7/8), consisting of ice floes, most of which are in contact with each other.

5. Thin ice. Drifting ice, the concentration of which is from 4/10 to 6/10 (from 3/8 to 6/8), with a large number floods, ice floes usually do not touch one another.

6. Rare ice. Drifting ice in which the concentration is 1/10 to 3/10 (1/8 to 3/8) and an expanse of clear water dominates the ice.

7. Individual ice floes. A large area of water containing sea ice with a concentration of less than 1/10 (1/8). In the complete absence of ice, this area should be called clean water.

Drifting ice is in constant motion under the influence of wind and currents. Any change in wind over an area covered with drifting ice causes changes in the distribution of ice: the stronger and longer the wind action, the greater the change.

Long-term observations of the wind drift of compacted ice have shown that ice drift is directly dependent on the wind that caused it, namely: the direction of ice drift deviates from the wind direction by approximately 30° to the right in the northern hemisphere, and to the left in the southern hemisphere, the drift speed is related with a wind speed of a wind coefficient of approximately 0.02 (r = 0.02).

In table Figure 5 shows the calculated values of ice drift speed depending on wind speed.

Table 5

The drift of individual ice floes (small icebergs, their fragments and small ice fields) differs from the drift of consolidated ice. Its speed is greater, since the wind coefficient increases from 0.03 to 0.10.

The speed of movement of icebergs (in the North Atlantic) with fresh winds ranges from 0.1 to 0.7 knots. As for the angle of deviation of their movement from the direction of the wind, it is 30-40°.

The practice of ice navigation has shown that independent navigation of an ordinary sea vessel is possible when the concentration of drifting ice is 5-6 points. For large-tonnage ships with a weak hull and for old ships, the cohesion limit is 5 points, for medium-tonnage ships in good condition - 6 points. For ice-class ships this limit can be increased to 7 points, and for icebreaking transport ships - to 8-9 points. The indicated limits for the permeability of drifting ice are derived from practice for medium-heavy ice. When sailing in heavy multi-year ice, these limits should be reduced by 1-2 points. With good visibility, navigation in ice concentrations up to 3 points is possible for vessels of any class.

If you need to navigate through a sea area covered with drifting ice, you must keep in mind that it is easier and safer to enter the edge of the ice against the wind. Entering ice with a tailwind or crosswind is dangerous, as conditions are created to pile up on the ice, which can lead to damage to the side of the ship or its bilge part.

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