Dependence of air temperature and freezing of sea water. Source: the scope of modernization of "Peter the Great" will be reduced

If you have noticed, then in the sea water freezes at temperatures well below zero degrees. Why it happens? It all depends on the concentration of salt in it. The more it is, the lower the freezing point. On average, a two ppm increase in water salinity lowers its freezing point by one tenth of a degree. So judge for yourself what the ambient temperature should be so that a thin layer of ice forms on the sea surface, with a water salinity of 35 ppm. It should be at least 2 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 ice formation here requires at least six degrees of frost. In order for the surface of the White Sea to be covered with ice, where the salinity of the water reaches 25 ppm, it is necessary for the temperature to drop to minus 1.4 degrees.

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

The freezing process of sea water has its own characteristics. Initially, primary ice crystals begin to form, which are incredibly similar to 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 dish, we get fresh water.

A porridge of ice needles, outwardly similar to a huge greasy spot, floats on the surface of the sea. Hence its original name - lard. With a further decrease in temperature, the fat 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 freezing fat and seizing droplets of sea water with needles. This is a rather chaotic process. That is why salt in the 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. With a slight frost, the rate of nilas formation is low, the needles capture little sea water, hence the salinity of the ice is low. In severe frost, the situation is exactly the opposite.

When sea ice melts, salt comes out of it first. As a result, it gradually becomes insipid.

The necessary conditions for water freezing are its cooling to the freezing point (supercooling), as well as the presence of crystallization nuclei in the water, which are embryos around which ice is growing. Crystallization nuclei can be dust particles, snow crystals or ice particles already existing in water.

Freezing of fresh and sea water

Plan

1. Freezing of sea and fresh water.

2. Classification of sea ice.

3. Geographic distribution of ice.

4. Navigational aids on ice.

With the cooling of the surface layer of fresh water, its density increases and water mixing occurs, which continues along the depth until the water density reaches its maximum value at a temperature of +4 ° C, throughout the entire depth of the basin. When the surface layer reaches a temperature of -0.13 ° C, ice begins to form.

For waters with salinity from 0 to 24.7 ‰, which are called brackish,the freezing process occurs in the same way as in fresh water, but at lower temperatures of the highest density and freezing of water, depending on its salinity. With a salinity equal to 24.7 ‰, the temperature of the highest density and the freezing point have the same value - 1.3 o C.

In seawater with a salinity greater than 24.7 ‰, the temperature of the highest density is lower than the freezing point, therefore, when the surface layer reaches the freezing point, the phenomenon of water mixing does not stop and the formation of ice crystals can occur not only in the surface, but also in the entire mixing layer. This phenomenon is observed when the mixing of waters occurs under the influence of wind, waves and currents. Ice formed in the water column or at the bottom is called deep and bottom, or anchor.Bottom ice, possessing a high lifting force, often carries stones, anchors and sunken objects to the surface.

The freezing process of brackish and sea waters also has a common property - salinization the remaining volume of water. This is due to the fact that after the water in the sea reaches the freezing point, pure fresh ice begins to emerge from it, as a result of which the salinity of the remaining volume of water increases. Therefore, further ice formation requires a new decrease in the temperature of the surface layer.

The formation of ice in the sea begins with the appearance of thin ice needles - crystals of pure ice. Crystals grow initially in a horizontal direction and then in a vertical direction. Salts dissolved in seawater and air bubbles are located in the spaces between the ice crystals. Thus, after formation, sea ice consists of crystals of pure ice, between which cells with salt brine and air bubbles are interspersed.

After the sea surface is covered with solid ice, its further growth occurs from below only due to water cooling. Average daily ice build-up ranges from 0.5 to 2 cm.

Properties of sea ice.One of the most important properties of sea ice is its salinity, which depends on the salinity of the water, the rate of ice formation, the state of the sea, the age of the ice and its thickness. The higher the rate of ice formation, the greater the salinity of the ice, since less saline solution has time to drain into the water. The older the ice, the more salt solution flows into the water, the lower its salinity. For perennial pack ice, it is only 1-2 ‰, while in the waters of Antarctica and the Arctic, the salinity of ice is 22-23 ‰, and in other basins, on average, 3-8 ‰.

The presence of brine inside sea ice affects other properties as well.

For example, the density of perennial sea ice, in which the salt cells, freed from the solution, are filled with air bubbles, have the lowest density. In general, the density of sea ice can be in the range of 0.85-0.94 g / cm 2. Consequently, the buoyancy of ice (elevation above the water) varies widely from 1/6 to 1/15.

With the onset of heat, due to thermal expansion, strong ice movements occur, which can cause damage to berths, port facilities, as well as vessels standing against the walls or drifting in the ice.

An important mechanical property of sea ice is hardness, elasticity and strength... Ice hardness is higher at lower temperatures. Sea ice is less durable than river ice, but it has greater elasticity and plasticity. For practical calculations of the possible load on ice and the passage of ice by ships, the bending strength at which the ice breaks is of great importance. The strongest is fresh or desalinated ice at low temperatures.

3.2. SEA ICE

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

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 the sea water S. It has been experimentally established that the freezing point of sea water can be determined (calculated) by the formula: t 3 \u003d -0.0545S. With 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 (a property of sea water) made it possible to divide the sea water into two groups according to the degree of salinity. Water with salinity 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, with a temperature of the highest density of 4 ° C. Water with a salinity of more than 24.7 ° / 00 is called sea.

The temperature at the highest density is below the freezing point. This leads to the occurrence of convective mixing, which retards the freezing of seawater. Freezing also slows down due to the 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 seawater with a salinity of 35 ° / 00 and a freezing point of -1.91 ° \u200b\u200bC? After the surface layer of water has cooled to the above temperature, its density will increase and the water will go down, and warmer water from the underlying layer will rise up. Stirring will continue until the temperature of the entire mass of water in the upper active layer drops to -1.91 ° \u200b\u200bC. Then, after some supercooling of the water below the freezing point, ice crystals (ice needles) begin to appear on the surface.

Ice needles are formed not only on the surface of the sea, but throughout the entire thickness of the mixed layer. Gradually, the ice needles freeze, forming ice spots on the sea surface that resemble a frozen fat... It differs little from water in color.

When snow falls on the sea surface, the ice formation process is accelerated, 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... Salo and snowflakes, under the influence of wind and waves, knock into pieces of white color, called sludge... With further compaction and freezing of the initial types of ice (ice needles, fat, sludge, snow), a thin, elastic crust of ice forms on the sea surface, easily sagging on the wave and, when compressed, forms jagged layers, called nilas... Nilas has a matte surface and a thickness of up to 10 cm, subdivided 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 sea surface is covered with a thin shiny crust called bottle... The flask is transparent, like glass, easily broken by wind or wave, its thickness is up to 5 cm.

On a light wave of ice fat, sludge or snowflake, as well as as a result of the flask and nilas breaking with a large swell, the so-called pancake ice... It is predominantly circular in shape from 30 cm to 3 m in diameter and up to about 10 cm in thickness, with raised edges due to the impact of ice floes against each other.

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

The upper surface of young ice in most cases is smooth or slightly wavy, the lower, on the contrary, is very uneven and in some cases (in the absence of currents) looks like a brush made of ice crystals. During the winter, the thickness of young ice gradually increases, its surface is covered with snow, and the color due to the brine flowing from it changes from gray to white. Young ice 10-15 cm thick is called gray, and 15-30 cm thick - gray-white... With a further increase in ice thickness, the ice becomes white. Sea ice, which lasted one winter and has a thickness of 30 cm to 2 m, is usually called white first-year icewhich is subdivided into thin (thickness from 30 to 70 cm), middle (from 70 to 120 cm) and fat (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 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, perennial ice, freshened and compacted by compressions, acquires a blue color. According to their mobility, sea ice is divided into stationary ice (fast ice) and drifting ice.

Drifting ice in shape (size) is subdivided into pancake ice, ice fields, fine ice (a piece of sea ice less than 20 m across), grated ice (broken ice less than 2 m across), endless (a large hummock or a group of hummocks, frozen together, up to 5 m above sea level), frost (pieces of ice frozen in the ice field), ice porridge (accumulation of drifting ice, consisting of fragments of other forms of ice not more than 2 m in diameter). In turn, ice fields, depending on the horizontal dimensions, are subdivided into:

Giant ice fields, more than 10 km across;

Vast ice fields, 2 to 10 km across;

Large ice fields, 500 to 2000 m across;

Fragments of ice fields, 100 to 500 m across;

Broken ice, 20 to 100 m across.

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

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

By its concentration, drifting ice is characterized as follows:

1. Compressed drifting ice. Drifting ice, the concentration of which is 10/10 (8/8), and no water is visible.

2. Frozen solid ice. Drifting ice, the concentration of which is 10/10 (8/8), and the ice floes were frozen together.

3. Very tight ice. Drifting ice with a concentration 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 ranges from 4/10 to 6/10 (from 3/8 to 6/8), with a large number of openings, 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 clear water space prevails over the ice.

7. Separate ice floes. Large area of \u200b\u200bwater containing sea ice less than 1/10 (1/8). In the complete absence of ice, this area should be called pure water.

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

Long-term observations of the wind drift of solid ice have shown that ice drift is in direct proportion to the wind that caused it, namely: the direction of ice drift deviates from the wind direction by about 30 ° in the northern hemisphere to the right, and in the southern hemisphere to the left, the drift speed is related with a wind speed of approximately 0.02 (r \u003d 0.02).

Table 5 shows the calculated values \u200b\u200bof the ice drift velocity depending on the wind speed.

Table 5

The drift of individual ice floes (small icebergs, their fragments and small ice fields) is different from the drift of solid ice. Its speed is higher, 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 deflection 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 vessels with a weak hull and for older vessels, the concentration limit is 5 points, for vessels of medium tonnage in good condition, -6 points. For ice-class ships, this limit can be increased to 7 points, and for icebreaking transport ships - up to 8-9 points. The indicated limits of the passability of drifting ice are taken out of practice for medium-heavy ice. When sailing in heavy perennial ice, these limits should be reduced by 1-2 points. With good visibility, sailing in ice concentration up to 3 points is possible for vessels of any class.

If it is necessary to travel through an area of \u200b\u200bthe sea covered with drifting ice, it must be borne in mind that it is easier and safer to enter the ice edge against the wind. It is dangerous to enter the ice with a tailwind or crosswind, as conditions of ice piling are created, which can lead to damage to the side of the vessel or its bilge part.

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Salts dissolved in sea water. Many different salts are dissolved in sea water, which give it a peculiar bitter-salty taste. The salty taste of sea water is mainly due to the sodium chloride (table salt) solution. Bitter taste depends on solutions of magnesium salts (MgCl 2 , MgSO 4 ). 1 thous. r(liter) of ocean water contains on average 27.2 r sodium chloride, 3.8 rmagnesium chloride, 1.7 r magnesium sulfate. Next are calcium sulfate (CaSO 4 ) 1,2 r,potassium sulfate (K 2 SO 4 ) 0,9 rand others, the content of which does not exceed 0.1 g.Thus, for 1 thousand. rocean water accounts for 35 r salts.

No matter how diluted sea water is with fresh waters, the percentage of salts that make up it remains strictly constant.

So:

In addition, up to 30 different substances are included in the composition of sea water, but their amount is so small that all of them together make up no more than 0.1%.

The water of the oceans and seas, as already mentioned, is in a continuous cycle. It evaporates, falls by atmospheric precipitation, passes long paths by ground and surface waters and returns to the ocean again. Passing these long paths, water dissolves many different substances and brings them to the oceans. Thus, the World Ocean is, as it were, a place of accumulation of those soluble substances that are constantly brought there by rivers and streams. However, if we compare the chemical composition of solutions contained in sea and fresh water, then we will notice a big difference.

In seawater, chloride salts prevail, while in river water, on the contrary, there are very few of them. River water contains a lot of carbonic salts (calcium carbonate), while seawater contains very few of them. The latter is explained by the fact that large quantities of calcium carbonate, silicon and other substances in the seas are consumed by animal and plant organisms to create all kinds of skeletal formations, shells, coral structures, etc. After the death of these organisms, their skeletons and shells fall to the bottom, forming there huge strata of deposits. In general, it should be noted that the ratio of salts in sea water is constantly regulated by the organic life of the sea.

Salinity. On 1 l (1 thous. d)blue water, as already mentioned, on average accounts for about 35 rsalts. In other words: for 1 thousand parts by weight of sea water there are 35 parts by weight of salts. The number 35 in this case means salinitysea \u200b\u200bwater, expressed in thousandths. Salinity is symbolically designated as follows: S\u003d 35 ° / oo, i.e. salinity (S) \u003d 35 ppm.

Ocean water taken away from the coast usually has salinity (S) \u003d 35 ° /oo... The water of the coastal parts, desalinated by rivers, has a salinity of 34-33 and even 32% o. In the zones of trade winds, where rains are rare, and evaporation is large, salinity rises to 36 and even 37% o.

In the Arctic Ocean, on the contrary, due to the low evaporation rate, the salinity on the surface drops to 34% o. Reduced salinity is also observed in the equatorial belt, where a lot of precipitation falls (Fig. 157).

At depths over 1000-1500 msalinity in all oceans 35% 0.

The situation is somewhat different with the seas. The marginal seas, connected to the oceans by a wide strait or a large number of straits, have a fairly high salinity. So, for example, in the Sea of \u200b\u200bJapan it is expressed in ЗЗ 0/00 in the Okhotsk Sea - 32 ° / oo. The inland seas, distant from the oceans, into which many large rivers flow, have low salinity. For example, the salinity of the Black Sea is 14-19 ° / O o, the Baltic Sea is 8-12% 0, and in the northern part of the Gulf of Bothnia it is even 3 ° / 00. On the contrary, the seas, surrounded by areas with a dry climate, have increased salinity. So, the Mediterranean Sea has a salinity of 38-39 ° / oo, and the Red Sea, surrounded by deserts, has a salinity of about 41% 0.

The study of salinity is of great importance both in science and in practical life. Accurate knowledge of salinity makes it possible to determine the currents and, in general, the movement of water masses in both horizontal and vertical directions. The salinity and specific gravity of sea waters are of great importance in defense. Submarine navigation, the depth and speed of submersion, mining of waters, torpedoing enemy ships, etc., require accurate knowledge of salinity and currents in one or another part of the sea.

Colour. Clear window glass seems to us to be completely transparent. But if you put two or three dozen clear transparent glasses in a stack, it turns out that the stack of glasses has become translucent and hardly transmits blue or slightly greenish light. This means that pure transparent glass is still not completely transparent and not colorless.

Approximately the same thing can be said about water. Pure distilled water appears colorless and crystal clear. However, this is only observed if the water layer is relatively thin. In a thicker layer, the water appears bluish. This bluish color is easy to spot in a white bathtub filled with clear, clear water.

To accurately determine the color of pure water, a glass tube of 5 mlength and, having filled it with distilled water, closed both ends of the tube with flat glasses. The tube was placed in a light-tight case. Placing one end of the tube in the window, we looked at the other end at the light. It turned out that pure distilled water has a wonderful delicate and pure blue color. This means that water absorbs red and yellow rays of the spectrum and transmits blue rays well.

Knowing that clear water is blue, we can easily understand why clean water of lakes, seas and oceans is predominantly blue. Any impurity to water changes color. So, for example, if you add the finest yellow or reddish powder to clean water, then the water acquires a greenish tint, etc. The latter is clearly visible at the sea near the coast after strong surfs: turbid water near the coast acquires a greenish color.

Salts dissolved in seawater do not affect the color of the water, due to which the water of the seas has a predominantly blue color. However, impurities of suspended silt particles immediately give the water one or another shade. So, for example, p. The Huang He (Yellow), flowing through the loess regions of China, paints the sea water yellowish (Yellow Sea). The admixture of silt particles brought by the rivers gives the water of the White Sea a greenish color, and the waters of the Baltic Sea a muddy green hue.

Transparency. Impurities of various substances not only change color, but also change the degree of transparency of the water. Everyone knows that turbid waters are the least transparent, and clean water is the most transparent. In science and in practical life (especially in defense), the study of the color and transparency of water is of great importance. To study the degree of transparency of water, a very simple device is used - the Secchi disc. It consists of a zinc disc having 30 cmin diameter, painted white. The disc, like a standard weighing pan, is suspended from a cord and slowly immersed in water. At the same time, they watch from above at what depth the white disk ceases to be visible. This depth determines the transparency of the pool water. So, for example, in the White Sea, the disc becomes invisible at a depth of 6-8 m,in Baltic 11 -13 m,in Black 28 m. The waters of the Mediterranean Sea are the most transparent - up to 50-60 m.The waters of the Pacific Ocean are also highly transparent (59 m)and especially the Sargasso Sea (66 m).

When determining transparency, color is usually also determined. The white disc changes color as you dive. In some basins, the disc becomes blue at some depth, in others green, etc.

To accurately designate the observed color, a scale is used, consisting of a number of tubes filled with solutions of various shades from blue to yellow.

The glow of the sea. At night, the glow of sea water is often observed. The latter does not come from the water itself, but from some organisms that live in seawater that are capable of emitting light. These organisms include: luminous bacteria, unicellular (especially night lights, which appear in large numbers at the end of summer), some jellyfish, etc.

Sea water temperature. Water is the most heat-intensive body on Earth. To heat up 1 cm 3water by 1 0, you need to spend as much heat as it takes to heat it 5 cm 3on the same 1 ° granite or 3134 cm 3air. This means that the heat capacity of water is five times greater than the heat capacity of granite and more than 3 thousand times more than the heat capacity of air.

The surface of the oceans and seas is more than 2/3 of the earth's surface. Consequently, more than 2/3 of the solar energy absorbed by the surface of the globe falls on the World Ocean. Part of this heat is spent on evaporation, part on heating the air over the sea, part, being reflected, is radiated into the heavenly space, and part goes to heating the water surface itself. As a result, according to rough estimates, of the total amount of solar heat falling on a unit of the surface of the water basin, 60% is spent on heating in the tropical zone, about 30% in the moderate and up to 10% in cold ones.

We have already noted the role of this heat in the life of the atmosphere and the life of continental waters. It was also said that the daily and annual fluctuations in the temperature of the water surface are completely different compared to

with land. Let us only recall that the daily amplitude of the ocean surface in the tropical zone is expressed in 0.5-1 °, in the temperate zone about 0 °, 4 and cold about 0 °, 1. As for the annual amplitude, it is also very small: in the hot zone 2-3 °, in the moderate zone from 5 to 10 ° and cold 1-2 °. Having noted these features in the heating of the water surface, we now turn to the temperatures of the oceans and seas.

Measurement of temperatures of seas and oceans. Measuring the temperature of the surface layers presents no difficulty. Take a bucket of water, put a thermometer in the bucket, which will show the temperature. As for the deeper layers of water, and especially the measurement of temperature at depths, here we have to use thermometers of a very special device, called depth thermometers(fig. 158).

A deep thermometer must first of all withstand the force of the enormous pressure that exists at depths. This is achieved, firstly, by enclosing the thermometer in a thick glass tube, and then in a copper sleeve so that the water touches the thick-walled glass tube of the thermometer only near the mercury ball. In addition, the depth thermometer must record the temperature that it noted at depth. The latter is achieved by the fact that at the right moment, according to a signal given from above, the thermometer quickly turns upside down. In this case, the column of mercury in the thermometer breaks, which makes it possible to record the reading of the thermometer.

Surface temperature of oceans and seas. Shipwhether that swim in various seas and oceans, daily, together with the determination of geographical coordinates, determine the temperature of the water on the surface of the sea. On the basis of such numerous observations, maps of the average monthly and annual temperatures of the surface of the World Ocean are compiled and the corresponding isotherms are plotted (Fig. 159). The isotherm maps show that the surface temperature of the oceans in the hot zone rises to the west, and in the temperate zone to the east. The latter depends, as we will see later, on the sea currents, which in the tropical zone are directed mainly to the west, and in the temperate zone deviate to the east.

Comparing the same average annual air temperatures over land and over the oceans, we see that in the hot zone the average annual temperature on land is slightly higher than over the sea. In temperate and cold zones, on the contrary, the temperature over the sea is much higher than over land. We have already noted this calming and warming influence of the sea.

Temperatures at depths. Direct measurements showed that daily fluctuations, although very negligible, can be seen to a depth of 25-30 m,annual up to 200-300 m,and in some cases even up to 350 m. Deeper than 300-350 mthe temperature remains constant at all seasons. In other words, at a depth of 300-350 mwe have a layer of constant temperature. However, with depth, the temperature continues to decrease gradually (for every 1,000 mdepths approximately 1-2 °), and at a depth of 3-4 thous. mit reaches 2 ° and even up to - 1 °. it

a gradual decrease in temperature with depth is explained by the fact that cold water, having a high density, sinks down, and warm water, being lighter, is concentrated in the upper layers. Unlike fresh water, seawater acquires the highest density not at 4 ° C, but at 2 ° and lower, which again depends on the degree of its salinity. The low temperature of the depths of all oceans is explained by the influence of the polar seas and oceans. There the water, cooling down to -1 and -2 °, sinks and slowly spreads along the bottom of all oceans. There is, however, a very slow, but constant movement of water in the bottom parts from the poles to the equator and in the upper parts from the equator to the poles (Fig. 160). The presence of such a movement makes it clear why the bottom temperatures of the southern parts of the oceans are lower than the same bottom temperatures of the northern parts of the oceans. The submarine threshold (Thomson's) in the Atlantic Ocean blocks the path to the bottom cold waters of the Arctic Ocean, due to which the bottom temperature in the North Atlantic Ocean is 3 °, 5 and 4 °, and beyond Thomson's threshold, in the Arctic Ocean, it immediately drops to -1 °, 2.

The absence of such rapids in the South Atlantic Ocean is counterproductive. There already from 50 ° S. sh. the bottom temperature is below 0 °.

The northern part of the Pacific Ocean is even more sharply separated from the Arctic Ocean, which leads to a decrease in temperatures to the south.

Freezing of sea water. The freezing process of sea water is much more complicated than fresh water. Fresh water under normal conditions freezes at 0 °, and sea water at lower temperatures. The freezing point of sea water depends primarily on the degree of its salinity, which can be clearly seen from the table below:

Fresh water has the highest density at 4 ° C. As for seawater, it reaches its greatest density at lower temperatures, again depending on the degree of salinity. For example:

The water of freshwater pools, when cooled from the surface, becomes heavier and sinks down, and lighter warm water rises in its place from the depths. This is a kind of movement (called convection)gradually captures more and more water layers. When, finally, the entire mass of water cools down to 4 ° C, i.e. reaches its maximum density, convection stops, because the water on the surface of the pool, cooling further, becomes lighter. Under these conditions, the surface layer further cools down very quickly and quickly freezes. In seawater, convection does not stop, because the density of water increases with decreasing temperature. In addition, when seawater freezes, ice crystals are formed from pure (fresh) water, and salt is released and increases the salinity of unfrozen water. With an increase in salinity, the freezing point and the temperature of the highest density, as can be seen from the tables above, decrease significantly. All this taken together greatly slows down the freezing process. Thus, freezing of seawater requires lower temperatures and longer periods of time. Abundant snowfall (desalting the surface of sea water) accelerates freezing. Excitement, on the other hand, slows down freezing.

When fresh water freezes, we distinguished three points: the formation of fat, the formation of pancake ice and, finally, the complete freezing of the entire surface. The freezing of the sea proceeds in approximately the same way. Crystals in seawater are formed larger and grow together in larger lumps and pieces of ice that almost completely cover the sea. The latter gives the sea a peculiar matte color. This initial period of freezing of the sea is known among sailors as ice lard.

Further, the ice floes increase in size, rub against each other and take the form of large floating plates of a more or less rounded shape. This peculiar, not yet continuous, mobile ice cover is called pancake ice.

If the weather is calm and the sea is not rough, then some "pancakes" freeze, resulting in a continuous ice cover, the thickness of which gradually increases. Excessive waves usually break the ice sheet into huge flat pieces of ice called ice fields.The ice fields under the influence of the winds approach each other, break open at the edges, piling up heaps and heaps of debris known as ice hummocks(fig. 161).

The height of hummocks above the surface of the ice field usually does not exceed 5 m,but in some cases it reaches 9 m.This underwater mass of ice is held back by a large accumulation of ice under the hummock. The thickness of the ice masses under the hummock usually exceeds the height of the hummock by two to three times, so that the total thickness of the hummock reaches 15-20 m.

The hummocky ice easily gets stuck in the shallows and forms accumulations of moving ice off the coast, known as coastal fast ice.The largest coastal fast ice reaches the eastern shores of Taimyr and especially near the New Siberian Islands and about. Wrangel (300-400 km width). The hummocks sitting separately on the shoals are called stamukhas.

The ice fields located within the Arctic Ocean do not have time to melt during the short and cool summer. In the following winter, the ice thickness increases. The result is thicker two-year-old ice. Ice thickening continues in the following years. As a result, thick and very hard ice up to 5 meters or more is formed. Large accumulations of moving perennial ice are known as polar pack.The polar pack occupies most of the surface of the Arctic Ocean.

We have already said that the ice fields of the Arctic Ocean cannot melt over the summer. If the warm waters of the Atlantic Ocean (the Gulf Stream) did not flow into the Arctic Ocean and the cold Greenland current did not carry the polar ice into the Atlantic Ocean, then the entire Arctic Ocean would turn into a continuous icy desert. It is very possible that the absence of a passage between the Atlantic and Arctic oceans was one of the

the main reasons for those ice ages that Eurasia and North America experienced in the Quaternary. The influence of currents on the freezing of the World Ocean is clearly visible on the attached climatic map.

Icebergs. Mainland Antarctica, about. Greenland and many other islands of the Arctic Ocean, as we already know, have thick layers of continental ice. Continental ice, sliding into the sea, gives rise to numerous floating mountains, or icebergs. According to rough estimates, more than 7 thousand icebergs annually enter the Baffin Sea from the western shores of Greenland.

The specific gravity of ice is about 0.9, while the specific gravity of sea water is slightly more than 1.0. Under these conditions, the ice mountains are submerged in water for 6 / 7 its volume. Thus, only 1/5 rises above the water - 1 / 7 part of the ice floe.

How large the floating ice mountains of Antarctica can be can be seen from the following examples. The continental ice of Antarctica is sliding down in huge masses, forming ice walls rising above sea level by 30-40 meters or more. The ice wall of the "Great Barrier" (Fig. 162), falling vertically into the sea, stretches for 750 km.It rises above the water by 30-40, and in some places by 70 m.The average ice thickness here is not less than 180-200 m.It is clear that the fragments of such a glacier can reach enormous sizes and have a table-like shape. In 1854, in the South Atlantic Ocean, a number of ships in their logs noted a meeting with an ice mountain, the length of which was more than 100 km,and the height above water is 90 m.Ice mountain 64 was encountered south of Australia in 1911. kmlength. Smaller ice mountains are much more common. For example, our expedition under the command of Bellingshausen in 1819 met up to 250 ice mountains off the coast of Antarctica. Sometimes ships have to go through the ice mountains for 400-500 km.

Icebergs are carried out by currents sometimes very far beyond the Arctic Circle. So floating ice mountains off the coast of North America go significantly south of about. Newfoundland and pose a great threat to ships. In the southern part of the ocean, icebergs go even further. In some cases, they reached 30 and even 25 ° S. sh., i.e., almost the limits of the tropical belt.

- A source-

Polovinkin, A.A. Fundamentals of General Geography / A.A. Polovinkin. - M .: State educational and pedagogical publishing house of the Ministry of education of the RSFSR, 1958. - 482 p.

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The table shows the thermophysical properties of a solution of calcium chloride CaCl 2, depending on the temperature and salt concentration: the specific heat of the solution, thermal conductivity, viscosity of aqueous solutions, their thermal diffusivity and Prandtl number. The concentration of CaCl 2 salt in solution is from 9.4 to 29.9%. The temperature at which the properties are given is determined by the salt content in the solution and ranges from -55 to 20 ° C.

Calcium chloride CaCl 2 may not freeze up to a temperature of minus 55 ° С... To achieve this effect, the salt concentration in the solution must be 29.9%, and its density will be 1286 kg / m 3.

With an increase in the concentration of salt in a solution, not only its density increases, but also such thermophysical properties as dynamic and kinematic viscosity of aqueous solutions, as well as the Prandtl number. For example, dynamic viscosity of CaCl 2 solution with a salt concentration of 9.4% at a temperature of 20 ° C is equal to 0.001236 Pa · s, and with an increase in the concentration of calcium chloride in the solution to 30%, its dynamic viscosity increases to 0.003511 Pa · s.

It should be noted that temperature has the strongest effect on the viscosity of aqueous solutions of this salt. When the calcium chloride solution is cooled from 20 to -55 ° C, its dynamic viscosity can increase by 18 times, and the kinematic viscosity by 25 times.

The following thermophysical properties of CaCl 2 solution:

• , kg / m 3;
• freezing temperature ° С;
• dynamic viscosity of aqueous solutions, Pa · s;
• prandtl number.

Density of calcium chloride CaCl 2 solution depending on temperature

The table shows the density values \u200b\u200bof a solution of calcium chloride CaCl 2 of various concentrations depending on the temperature.
The concentration of calcium chloride CaCl 2 in solution is from 15 to 30% at a temperature from -30 to 15 ° C. The density of an aqueous solution of calcium chloride increases with decreasing solution temperature and increasing salt concentration in it.

Thermal conductivity of CaCl 2 solution depending on temperature

The table shows the values \u200b\u200bof thermal conductivity of a solution of calcium chloride CaCl 2 of various concentrations at negative temperatures.
The concentration of CaCl 2 salt in solution is from 0.1 to 37.3% at a temperature from -20 to 0 ° C. As the salt concentration in the solution increases, its thermal conductivity decreases.

Heat capacity of CaCl 2 solution at 0 ° С

The table shows the values \u200b\u200bof the mass heat capacity of a solution of calcium chloride CaCl 2 of various concentrations at 0 ° C. The concentration of CaCl 2 salt in solution is from 0.1 to 37.3%. It should be noted that with an increase in the concentration of salt in the solution, its heat capacity decreases.

Freezing point of solutions of NaCl and CaCl 2 salts

The table shows the freezing point of solutions of sodium chloride NaCl and calcium CaCl 2, depending on the salt concentration. The salt concentration in the solution is from 0.1 to 37.3%. The freezing point of the brine is determined by the salt concentration in solution and for sodium chloride NaCl can reach a value of minus 21.2 ° C for a eutectic solution.

It should be noted that sodium chloride solution may not freeze up to minus 21.2 ° С, and the calcium chloride solution does not freeze at temperatures up to minus 55 ° С.

Density of NaCl solution depending on temperature

The table shows the density values \u200b\u200bof sodium chloride NaCl solution of various concentrations depending on temperature.
The concentration of NaCl salt in solution is from 10 to 25%. The density values \u200b\u200bof the solution are indicated at temperatures from -15 to 15 ° C.

Thermal conductivity of NaCl solution depending on temperature

The table gives the values \u200b\u200bof thermal conductivity of sodium chloride NaCl solution of various concentrations at negative temperatures.
The concentration of NaCl salt in solution is from 0.1 to 26.3% at temperatures from -15 to 0 ° C. According to the table, it can be seen that the thermal conductivity of an aqueous solution of sodium chloride decreases as the concentration of salt in the solution increases.

Specific heat capacity of NaCl solution at 0 ° С

The table shows the values \u200b\u200bof the mass specific heat of an aqueous solution of sodium chloride NaCl of various concentrations at 0 ° C. The concentration of NaCl salt in solution is from 0.1 to 26.3%. The table shows that with an increase in the concentration of salt in the solution, its heat capacity decreases.

Thermophysical properties of NaCl solution

The table shows the thermophysical properties of sodium chloride NaCl solution depending on temperature and salt concentration. The concentration of sodium chloride NaCl in solution is from 7 to 23.1%. It should be noted that when an aqueous solution of sodium chloride is cooled, its specific heat changes only slightly, the thermal conductivity decreases, and the viscosity of the solution increases.

The following thermophysical properties of NaCl solution:

• solution density, kg / m 3;
• freezing temperature ° С;
• specific (mass) heat capacity, kJ / (kg · deg);
• thermal conductivity coefficient, W / (m · deg);
• dynamic viscosity of the solution, Pa · s;
• kinematic viscosity of the solution, m 2 / s;
• thermal diffusivity, m 2 / s;
• prandtl number.

Density of solutions of sodium chloride NaCl and calcium CaCl 2 depending on concentration at 15 ° С

The table shows the density values \u200b\u200bof solutions of sodium chloride NaCl and calcium CaCl 2, depending on the concentration. The concentration of NaCl salt in solution is from 0.1 to 26.3% at a solution temperature of 15 ° C. The concentration of calcium chloride CaCl 2 in the solution is in the range from 0.1 to 37.3% at a temperature of 15 ° C. The density of sodium chloride and calcium chloride solutions increases with increasing salt content.

The coefficient of volumetric expansion of solutions of sodium chloride NaCl and calcium CaCl 2

The table shows the values \u200b\u200bof the average coefficient of volumetric expansion of aqueous solutions of sodium chloride NaCl and calcium CaCl 2, depending on concentration and temperature.
The volumetric expansion coefficient of the NaCl salt solution is indicated at a temperature of -20 to 20 ° C.
The volumetric expansion coefficient of the CaCl 2 chloride solution is presented at a temperature of -30 to 20 ° C.

Sources:

1. Danilova GN et al. Collection of problems on heat exchange processes in food and refrigeration industries. M .: Food industry, 1976. - 240 p.