Lesson summary on the surrounding world on the topic "Arctic Ocean". Do we know everything about the properties of ice? How to explain complex physical processes to a child
Everyone knows that ice is frozen water, or rather, it is in a solid state of aggregation. But Why does ice not sink in water, but float on its surface?
Water is an unusual substance with rare, even anomalous properties. In nature, most substances expand when heated and contract when cooled. For example, mercury in a thermometer rises through a narrow tube and shows an increase in temperature. Because mercury freezes at -39ºC, it is not suitable for thermometers used in harsh temperature environments.
Water also expands when heated and contracts when cooled. However, in the cooling range from approximately +4 ºC to 0 ºC it expands. This is why water pipes can burst in winter if the water in them has frozen and large masses of ice have formed. The ice pressure on the pipe walls is enough to cause them to burst.
Water expansion
Since water expands when cooled, the density of ice (i.e. its solid form) is less than that of liquid water. In other words, a given volume of ice weighs less than the same volume of water. This is reflected by the formula m = ρV, where V is the volume of the body, m is the mass of the body, ρ is the density of the substance. There is an inversely proportional relationship between density and volume (V = m/ρ), i.e., with increasing volume (as water cools), the same mass will have a lower density. This property of water leads to the formation of ice on the surface of reservoirs - ponds and lakes.
Let's assume that the density of water is 1. Then the ice will have a density of 0.91. Thanks to this figure, we can find out the thickness of the ice floe that floats on the water. For example, if an ice floe has a height above water of 2 cm, then we can conclude that its underwater layer is 9 times thicker (i.e. 18 cm), and the thickness of the entire ice floe is 20 cm.
In the area of the North and South Poles of the Earth, water freezes and forms icebergs. Some of these floating ice mountains are enormous. The largest iceberg known to man is considered to be with a surface area of 31,000 square meters. kilometers, which was discovered in 1956 in the Pacific Ocean.
How does water in its solid state increase its volume? By changing its structure. Scientists have proven that ice has an openwork structure with cavities and voids, which, when melted, are filled with water molecules.
Experience shows that the freezing point of water decreases with increasing pressure by approximately one degree for every 130 atmospheres.
It is known that in the oceans at great depths the water temperature is below 0 ºС, and yet it does not freeze. This is explained by the pressure created by the upper layers of water. A layer of water one kilometer thick presses with a force of about 100 atmospheres.
Comparison of the densities of water and ice
Can the density of water be less than the density of ice and does this mean that he will drown in it? The answer to this question is affirmative, which is easy to prove with the following experiment.
Let's take from the freezer, where the temperature is -5 ºС, a piece of ice the size of a third of a glass or a little more. Let's put it in a bucket of water at a temperature of +20 ºС. What are we observing? The ice quickly sinks and sinks, gradually beginning to melt. This happens because water at a temperature of +20 ºС has a lower density compared to ice at a temperature of -5 ºС.
There are modifications of ice (at high temperatures and pressures), which, due to their greater density, will sink in water. We are talking about the so-called “heavy” ice - deuterium and tritium (saturated with heavy and superheavy hydrogen). Despite the presence of the same voids as in protium ice, it will sink in water. In contrast to “heavy” ice, protium ice is devoid of heavy hydrogen isotopes and contains 16 milligrams of calcium per liter of liquid. The process of its preparation involves purification from harmful impurities by 80%, due to which protium water is considered the most optimal for human life.
Meaning in nature
The fact that ice floats on the surface of bodies of water plays an important role in nature. If the water did not have this property and the ice sank to the bottom, this would lead to freezing of the entire reservoir and, as a result, the death of the living organisms inhabiting it.
When cold weather occurs, first at temperatures above +4 ºС, colder water from the surface of the reservoir sinks down, and warm (lighter) water rises. This process is called vertical circulation (mixing) of water. When it reaches +4 ºС throughout the entire reservoir, this process stops, since from the surface the water already at +3 ºС becomes lighter than that which is below. Water expands (its volume increases by approximately 10%) and its density decreases. As a consequence of the fact that the colder layer is on top, water freezes on the surface and an ice cover appears. Due to its crystalline structure, ice has poor thermal conductivity, meaning it retains heat. The ice layer acts as a kind of heat insulator. And the water under the ice retains its heat. Thanks to the thermal insulating properties of ice, the transfer of “cold” to the lower layers of water is sharply reduced. Therefore, at least a thin layer of water almost always remains at the bottom of a reservoir, which is extremely important for the life of its inhabitants.
Thus, +4 ºС - the temperature of maximum density of water - is the temperature of survival of living organisms in a reservoir.
Use in everyday life
Mentioned above was the possibility of water pipes bursting when water freezes. To avoid damage to the water supply system at low temperatures, there should be no interruptions in the supply of warm water that flows through the heating pipes. A vehicle is exposed to a similar danger if water is left in the radiator in cold weather.
Now let's talk about the pleasant side of the unique properties of water. Ice skating is great fun for children and adults. Have you ever wondered why ice is so slippery? For example, glass is also slippery, and also smoother and more attractive than ice. But skates don't glide on it. Only ice has such a specific delightful property.
The fact is that under the weight of our weight there is pressure on the thin blade of the skate, which, in turn, causes pressure on the ice and its melting. In this case, a thin film of water is formed, against which the steel blade of the skate slides.
Difference in freezing of wax and water
Experiments show that the surface of an ice cube forms a certain bulge. This is due to the fact that freezing in the middle occurs last. And expanding during the transition to a solid state, this bulge rises even more. This can be counteracted by the hardening of wax, which, on the contrary, forms a depression. This is explained by the fact that the wax contracts after turning into a solid state. Liquids that contract uniformly when frozen form a somewhat concave surface.
To freeze water, it is not enough to cool it to the freezing point of 0 ºC; this temperature must be maintained through constant cooling.
Water mixed with salt
Adding table salt to water lowers its freezing point. It is for this reason that roads are sprinkled with salt in winter. Salt water freezes at -8°C and below, so until the temperature drops to at least this point, freezing does not occur.
An ice-salt mixture is sometimes used as a “cooling mixture” for low-temperature experiments. When ice melts, it absorbs the latent heat required for the transformation from its surroundings, thereby cooling it. This absorbs so much heat that the temperature can drop below -15 °C.
Universal solvent
Pure water (molecular formula H 2 0) has no color, no taste, no smell. The water molecule consists of hydrogen and oxygen. When other substances (soluble and insoluble in water) get into the water, it becomes polluted, which is why there is no absolutely pure water in nature. All substances that occur in nature can be dissolved in water to varying degrees. This is determined by their unique properties - solubility in water. Therefore, water is considered a “universal solvent.”
Guarantor of stable air temperature
Water heats up slowly due to its high heat capacity, but, nevertheless, the cooling process occurs much more slowly. This makes it possible for the oceans and seas to accumulate heat in the summer. The release of heat occurs in winter, due to which there is no sharp change in air temperature on the territory of our planet throughout the year. Oceans and seas are the original and natural heat accumulator on the Earth.
Surface tension
Conclusion
The fact that ice does not sink, but floats on the surface, is explained by its lower density compared to water (the specific density of water is 1000 kg/m³, of ice - about 917 kg/m³). This thesis is true not only for ice, but also for any other physical body. For example, the density of a paper boat or an autumn leaf is much lower than the density of water, which ensures their buoyancy.
However, the property of water to have a lower density in the solid state is very rare in nature, an exception to the general rule. Only metal and cast iron (an alloy of the metal iron and the nonmetal carbon) have similar properties.
Young children very often ask interesting questions to adults, and they cannot always answer them right away. In order not to seem stupid to your child, we recommend that you familiarize yourself with a complete and detailed, well-founded answer regarding the buoyancy of ice. After all, it floats, not drowns. Why is this happening?
How to explain complex physical processes to a child?
The first thing that comes to mind is density. Yes, in fact, ice floats because it is less dense than . But how to explain to a child what density is? No one is obligated to tell him the school curriculum, but it’s quite possible to boil it all down to what it is. After all, in fact, the same volume of water and ice has different weights. If we study the problem in more detail, we can voice several other reasons besides density.
not only because its reduced density prevents it from sinking lower. The reason is also that small air bubbles are frozen in the ice. They also reduce the density, and therefore, in general, it turns out that the weight of the ice plate becomes even less. When ice expands, it does not take in more air, but all those bubbles that are already inside this layer remain there until the ice begins to melt or sublimate.
Conducting an experiment on the force of expansion of water
But how can you prove that ice is actually expanding? After all, water can also expand, so how can this be proven under artificial conditions? You can conduct an interesting and very simple experiment. To do this you will need a plastic or cardboard cup and water. The quantity does not have to be large; you do not need to fill the glass to the brim. Also, ideally you need a temperature of about -8 degrees or lower. If the temperature is too high, the experience will last unreasonably long.
So, water is poured inside, we need to wait for ice to form. Since we have chosen the optimal temperature at which a small volume of liquid will turn into ice within two to three hours, you can safely go home and wait. You need to wait until all the water turns into ice. After some time we look at the result. A cup that is deformed or torn by ice is guaranteed. At a lower temperature, the effects look more impressive, and the experiment itself takes less time.
Negative consequences
It turns out that a simple experiment confirms that ice blocks really expand when the temperature decreases, and the volume of water easily increases when freezing. As a rule, this feature causes a lot of problems for forgetful people: a bottle of champagne left on the balcony for a long time on New Year’s Eve breaks due to exposure to ice. Since the expansion force is very large, it cannot be influenced in any way. Well, as for the buoyancy of ice blocks, there is nothing to prove here. The most curious can easily carry out a similar experiment in spring or autumn on their own, trying to drown pieces of ice in a large puddle.
Almost a tenth of the earth's surface is permanently covered with ice. About 90 percent of this amount comes from the ice sheets of Antarctica and Greenland. The remaining 10 percent “belongs” to mountain glaciers. Interestingly, Antarctica's cover is 1.5 times greater than that of the United States, and there is 9 times more ice here than in the icy expanses of Greenland.
Residents of the northern regions use ice as drinking water. Interestingly, when seawater freezes, it contains minimal salt content. Therefore, melted ice can also be used by residents of the northern sea islands or polar regions, for example the Eskimos.
Naturally, in the northern regions, where there are no forests, ice also finds its second use - for the construction of houses. Externally, such a dwelling (they are called an igloo) resembles a hemispherical bowl turned upside down. It is made of large ice blocks. They enter the igloo through a small extension - a canopy. Ice has a fairly low thermal conductivity, and therefore the inside of the igloo quickly becomes warmer than the outside.
Arctic explorers, who were the first to see such ice huts, were surprised that with a frost of thirty degrees outside, the temperature inside the igloo was about zero. Igloos were common among the Eskimos of North America and Greenland.
Using such dwellings, the Eskimos could freely travel long distances across the ice while hunting. The experience of the Eskimos was adopted by scientists working at polar stations. Already at the first North Pole station, a radio station was installed in the ice house.
The study of ice is very important: fossil ice preserved in high-mountain glaciers and the depths of Antarctica constitute a kind of chronicle of distant eras. Their age is hundreds of thousands of years.
The fact is that the snow that falls on the surface of the glacier gradually turns into firn - loose, granular ice with a lot of air. Gradually, the firn becomes denser and forms ice, in which tiny bubbles remain. Scientists extract them by drilling into the glacier and study them in laboratories.
By analyzing the air of the distant past, scientists learn what the weather was like on Earth, where the winds blew from and what kind of dust they carried with them. It was from fossil ice that scientists learned that there were not one, but two great glaciations on Earth and that they occurred over the past 220 thousand years.
How does water turn into ice?
Let's see how water in a pond turns into ice. As the air cools, it cools the top layer of water. The upper cold layer of water becomes heavier than the warm lower layers, and it sinks down. This process continues until all the pond water has cooled to a temperature of about 4°C.
But the air temperature is dropping! When the upper layers of water cool to a temperature below 4° C, they remain on the surface. The fact is that water, cooled to a temperature below 4° C, essentially becomes lighter!
So, the upper layers of water are ready to freeze. When the temperature remains at or below the freezing point of 0°C, tiny crystals begin to form.
Each such crystal has six rays. When they combine, they form ice, and soon a crust of ice forms on the surface of the water. Sometimes the ice is transparent, sometimes it is not. Why? The fact is that when water droplets freeze, tiny air bubbles are released. They stick to the rays of ice crystals. The more ice crystals that form, the more air bubbles there are—that's opaque ice.
If the water underneath the ice moves, air bubbles gather together and clear ice forms.
Water, like some other substances, does not decrease its volume during the transition from liquid to solid state. When water freezes, it expands by one-ninth of its volume, meaning that when nine liters of water freeze, you get ten liters of solid ice! When car radiators and water pipes burst in winter, it is because the water freezes and expands in volume!
It is, as a rule, completely incomprehensible to the average person what these people do.
people there, “at the top of the Earth”, in conditions of extreme frosts, polar night,
on an ice floe that could break at any moment, and without the usual comfort
modern civilization. When I asked to talk about scientific
research on an ice floe to the deputy head of SP-36 for science, Vladimir
Churun, he thoughtfully said in response: “You know, I wouldn’t mind finding out either
about it!"
There are many ways to explore the Arctic. Automatic scientific complexes - meteorological and oceanographic stations, mass balance buoys, which are frozen into the ice and make it possible to determine the increase or change in the mass of the ice cover (by the way, such a buoy works on SP-37) - greatly facilitate data collection, but have their limitations. Of course, it would be tempting to sit in the office while data arrives via satellite communications from a system, for example, automatic hydrological stations - mooring or drifting buoys. But in a year, more than 50% of such (very expensive) buoys are usually lost - in this region, working conditions are quite difficult even for equipment specially designed for this due to the dynamics of ice fields (hummocking, compression).
Another way to obtain scientific data is through remote sensing of the Earth. Scientific satellites (unfortunately, not Russian ones) make it possible to obtain information about ice conditions in the visible, infrared, radar and microwave ranges. This data is mainly used for applied purposes: for guiding ships, for searching for suitable ice floes for drifting stations; at the drifting stations themselves, they help in the work - for example, at SP-36 they were used to locate a site suitable for constructing a runway. However, satellite information must be verified by comparing it with real observations - directly measured ice thickness, its age (it is not yet possible to directly measure this data from a satellite).
Scientific stations (already inhabited) can also be placed by freezing ships in ice (this method was tested by Fridtjof Nansen). From time to time, such projects are carried out; examples include the French yacht Tara or the American-Canadian SHEBA project involving a ship drifting in the Beaufort Sea. A similar project was considered for the nuclear icebreaker Arktika, but in the end it was abandoned for various reasons. However, frozen ships provide only a good base for the life of scientific personnel and energy supply for the scientific complex. To collect scientific data, people will still have to go to the ice to exclude outside influences. In addition, freezing ships is expensive (and distracts ships from their main work). 
“In my opinion, drifting ice is a natural load-bearing platform, the most optimal for both hosting a scientific complex and for people to live in,” says Vladimir Churun. “It allows you to drift for a long time and obtain pure scientific data without any outside influence. Of course, people on the ice floe are deprived of some comfort, but in the name of science we have to put up with this. Of course, obtaining scientific data must be carried out in a comprehensive manner, using all available means - drifting stations, air expeditions, satellite observation, automatic buoys, and scientific expedition vessels.” 
“The scientific program of SP-36 was quite extensive and successful,” Vladimir Churun explains to Popular Mechanics. “It included meteorological, aerological and hydrological observations, as well as studies of the properties of ice and snow cover. But research related to the ionosphere and the Earth’s magnetic field, which received considerable attention at drifting stations in Soviet times, has now been transferred to stationary polar stations on the mainland and on the islands.”
Air
The beginning of the station's work is not marked by the solemn moment of raising the Russian flag over the wardroom. Officially, the drifting station begins its work from the moment the first weather report is transmitted to the AARI, and from there to the global meteorological network. Since, as we know, “the Arctic is the kitchen of weather,” these data provide meteorologists with extremely valuable information. The study of baric (pressure, wind speed and direction at various altitudes) and temperature profiles of the atmosphere using probes up to an altitude of 30 km is used not only for weather prediction - this data can later be used for fundamental scientific purposes, such as refining models of atmospheric physics, and for applied ones - for example, supporting aircraft flights. Meteorologists and aerologists are responsible for all this data.
The work of a meteorologist may seem simple - it is taking meteorological data and sending it to Roshydromet. To do this, a set of sensors is located on a 10-meter weather mast that measures wind speed and direction, temperature and humidity, visibility and pressure. All information, including from remote sensors (snow and ice temperature, solar radiation intensity), flows to the weather station. Although data is taken from the station remotely, it is not always possible to carry out measurements without going to the weather site. “The cups of the anemometers and the radiation protection of the weather booth, where the temperature and humidity sensors are located, freeze over, they have to be cleared of frost (to access the top of the mast, the latter is made ‘breakable’), explains SP-36 meteorologist engineer Ilya Bobkov.- A During the melting season, the guy ropes have to be constantly reinforced to keep the mast stable. In addition, the station is not designed to operate in such severe frost conditions, below - 40°C, so we installed a heating device there - a regular 40-watt incandescent lamp. Of course, there are stations designed for such low temperatures, but they are less accurate.”
Above 10 m is the area of work for aerologists. “We study the upper layers of the atmosphere using aerological probes,” explains SP-36 leading aerological engineer Sergei Ovchinnikov. - The probe is a box weighing 140 g, it is attached to a balloon - a ball with a volume of about 1.5 m 3 filled with hydrogen, which is produced chemically in a high-pressure gas generator - from ferrosilicon powder, caustic soda and water. The probe has a built-in GPS receiver, a telemetry transmitter, as well as temperature, pressure and humidity sensors. Every two seconds, the probe transmits information along with its coordinates to a ground receiving station.” The coordinates of the probe make it possible to calculate its movement, wind speed and direction at various altitudes (altitude is determined by barometric method). The probe's electronics are powered by a water-filled battery, which is first kept in water for several minutes (life jackets with emergency beacons are equipped with similar power sources).
“The probes are launched every day at 0 and 12 o’clock GMT, if weather conditions permit; in strong winds, the probe simply “nails” to the ground. In less than a year, 640 releases took place, says Sergei Ovchinnikov. “The average ascent height was 28,770 m, the maximum was 32,400 m. The probe’s ascent speed was about 300 m per minute, so it reached its maximum height in about an hour and a half, the balloon as the lift swells, and then bursts, and the probe falls to the ground. True, it is almost impossible to find it, so the device is disposable, albeit expensive.”
Water
“The main emphasis in our work is on measuring current parameters, as well as temperature, electrical conductivity, and water density,” says SP-36 oceanologist Sergei Kuzmin. “In recent years, the fleet of instruments has been significantly updated, and now we can obtain results with high accuracy corresponding to world level. We now use profiling instruments that allow us to measure flow velocity using the transverse Doppler effect in several layers.
"We mainly studied Atlantic currents, the upper boundary of which is at a depth of 180-220 m, and the core - 270-400 m." In addition to studying currents, a daily study of the water column was provided using a probe that measured electrical conductivity and temperature; every six days, studies were carried out at a depth of up to 1000 m to “capture” the Atlantic waters, and once a week the probe was lowered to the entire maximum length of the cable - 3400 m to study the deep sea layers. “In some areas,” explains Sergei Kuzmin, “a geothermal effect can be observed in deep layers.”
The task of oceanologists on SP-36 also included collecting samples for subsequent analysis by hydrochemists. “Three times during the winter - in spring, summer and autumn - we took an ice core, which was then melted at room temperature, the resulting water was passed through a filter, and then frozen again,” says Sergei. - Both the filter and the ice were specially packaged for subsequent analysis. Snow samples and subglacial water were collected in the same way. Air samples were also taken using an aspirator, which pumped air through several filters that retained the smallest particles. Previously, in this way, it was possible, for example, to detect pollen of some plant species that flies to the polar regions from Canada and the Russian taiga.”
Why study currents? “By comparison with data accumulated over previous years, climate trends can be determined,” Sergei replies. “Such an analysis will make it possible to understand, for example, the behavior of ice in the Arctic Ocean, which is extremely important not only from a fundamental point of view, but also from a purely applied point of view, for example, when developing the natural resources of the Arctic.”
Snow
The program of special meteorological research included several sections. The structure of the snow and ice cover, its thermophysical and radiation properties were studied - that is, how it reflects and absorbs solar radiation. “The fact is that snow has a high reflectivity, and according to this characteristic, for example in satellite images, it very much resembles a cloud layer,” explains meteorologist Sergei Shutilin. - Especially in winter, when the temperature in both places is several tens of degrees below zero. I studied the thermophysical properties of snow depending on temperature, wind, cloudiness and solar radiation.” The penetration of solar radiation (of course, during the polar day) through snow and ice to various depths (including into water) was also measured. The morphology of snow and its thermophysical properties were also studied—temperature at various depths, density, porosity, and fractional composition of crystals in various layers. These data, together with radiation characteristics, will help clarify the description of snow and ice cover in models of various levels - both global and regional climate models.
During the polar day, measurements of ultraviolet radiation reaching the Earth's surface were carried out, and during the polar night, gas analyzers were used to study the concentrations of carbon dioxide, ground-level ozone and methane, emissions of which in the Arctic are apparently associated with geological processes. Using a special gas analyzer, it was also possible to obtain, according to Sergei Shutilin, unique data on the flow of carbon dioxide and water vapor through the surface of snow and ice: “Previously, there was a model according to which melt water from the coast fell into the ocean, the ocean became covered with ice, and under it anaerobic processes took place. And after the surface was freed from ice, a flow of carbon dioxide entered the atmosphere. We discovered that the flow goes in the opposite direction: when there is no ice, it goes into the ocean, and when there is ice, it goes into the atmosphere! However, this may also depend on the area - for example, measurements on SP-35, which drifted closer to the south and to the shelf seas in the eastern hemisphere, are consistent with the above hypothesis. So more research is needed." 
Ice is now receiving the closest attention, because it is a clear indicator of the processes taking place in the Arctic. Therefore, its study is extremely important. First of all, this is an assessment of the ice mass balance. It melts in the summer and grows in the winter, so regular measurements of its thickness using measuring rods at a designated site make it possible to estimate the rate of melting or growth of the ice floe, and these data can then be used to refine various models of multi-year ice formation. “At SP-36, the landfill occupied an area of 80x100 m, and from October to May 8,400 tons of ice grew on it,” says Vladimir Churun. “You can imagine how much ice has grown on the entire ice floe measuring 5x6 km!”
“We also took several cores of young and old ice, which will be studied at the AARI - chemical composition, mechanical properties, morphology,” says SP-36 ice researcher Nikita Kuznetsov. “This information can be used to refine various climate models, and also, for example, for engineering purposes, including for the construction of icebreakers.”
In addition, at SP-36, studies were carried out on the processes of the passage of various waves in sea ice: waves formed during collisions of ice floes, as well as those passing from the marine environment into ice. These data are recorded using highly sensitive seismometers and are subsequently used for applied models of ice interaction with solids. According to the leading engineer-ice researcher of SP-36, Leonid Panov, this makes it possible to evaluate the loads on various engineering structures - ships, drilling platforms, etc. - from the point of view of ice resistance: “Knowing the features of the interaction of ice with waves, it is possible to calculate the strength properties of ice , which means predicting exactly where it will break. Such methods will make it possible to remotely detect the passage of cracks and hummocking in dangerous areas, for example, near oil and gas pipelines.”
Not a resort
When I asked Vladimir how global climate change (namely, global warming) felt while working at the drifting station, he only smiled in response: “Of course, the area of ice and its thickness in the Arctic have decreased - this is a well-registered scientific fact. But at a drifting station, in the local space of the ice floe, global warming is not felt at all. In particular, during this wintering we recorded the minimum temperature in the last ten years (-47.3°C). The wind was not very strong - the maximum gusts were 19.4 m/s. But overall the winter from February to April was very cold. So, despite global warming, the Arctic has not become warmer, cozier, or more comfortable. It’s still just as cold here, the cold winds are still blowing, the ice is still the same all around. And there is no hope yet that Chukotka will soon become a resort.”
Dmitry Mamontov.
