Types of sea ice. sea ice
Introduction
The most important characteristic feature of the seas of polar and temperate latitudes is the presence of more or less stable ice cover. The practical development of areas significantly depends on the extent to which this constantly operating natural factor has been studied.
It is clear that a sufficiently complete account of the ice cover when solving oceanological, technical and other problems is impossible without a detailed study of the physical properties and dynamics of sea ice.
A large amount of data from field observations and experiments, theoretical research, as well as the introduction of computer technology currently contribute to an in-depth study of sea ice.
A large number of works by various authors are devoted to the study of individual particular problems of this problem. A number of monographs have been published where the physics of the ice cover is discussed in great detail. However, in most of these works, sea ice is studied either from the standpoint of solid state physics (V.V. Lavrov, P.A. Shuisky, etc.) or from the point of view of engineering applications (I.S. Peschansky).
In this course work, ice is considered as a physical object, the existence and properties of which are determined by the processes of interaction between the ocean and the atmosphere. The formation and melting of ice, changes in its thickness and strength depend on the properties of ice as a solid. At the same time, the distribution of ice, its drift, the bearing capacity of the ice cover and a number of other characteristics appear only in conditions of its interaction with the water and air environments.
Without leaving aside the physical and technical aspects of the problem as a whole, I see my main task in the fullest possible disclosure of the properties of the sea ice cover as one of the hydrological elements of the freezing seas.
The purpose of the courseworkThe work is to consider ice phenomena in the seas and oceans.
To achieve the goal, the following were set tasks:
.Description of ice phenomena and their types
.Studying the concept of ice regime
.Studying the properties and structure of sea ice
.Analysis of sea ice classifications
The course work consists of an introduction, 3 chapters, a conclusion, a list of references and an appendix. The total volume of work is 29 pages. The text is illustrated with tables, figures and diagrams.
1. Ice phenomena
Ice phenomena - elements of the ice regime of seas and oceans, characteristics of the state of water bodies in terms of ice regime, phases of occurrence, development and disappearance of various types of ice. Usually, ice phenomena also include ice formations, which are forms of the existence of ice in water bodies. Depending on the context, sometimes it is still advisable to separate the concepts of ice phenomena and ice formations. For example, ice formations - slush, ice cover, ice floes and ice fields; ice phenomena, respectively - slush, freeze-up, ice drift.
Ice phenomena and ice formations are divided into 3 groups:
period of autumn ice phenomena;
freezing;
spring ice phenomena.
1.1 . Ice phenomena and ice formations during the freezing period
Types of ice phenomena:
Zaberegi are strips of ice frozen to the shore when the main part of the water body is not frozen. There are three types of shorelines: primary, formed by freezing water off the coast; alluvial, resulting from ice and slush freezing to the shore during ice drift or ice drift; residual, which remain off the coast when the ice cover is destroyed. On large lakes these ice formations are called fast ice.
Fat - surface primary ice formations, consisting of needle-shaped and plate-shaped, loosely interconnected ice crystals, in appearance resembling spots of frozen fat (hence the name) and turning into thin ice films as they grow. It is formed in the surface supercooled (i.e., having a temperature below 0°C) layer of water. It is observed with the onset of negative air temperatures.
Inland ice - ice crystals or their accumulations in the form of a spongy, opaque mass in the water column or at the bottom; floating inland ice on the surface of the water looks like snow-white lumps of various shapes.
Suga - accumulations of inland ice (Fig. 1). Autumn ice drift is the movement of ice floes and ice fields in the ocean and seas.
Rice. 1 Shuga (Photo by M.P. Protskaya)
Sludge movement is the movement of sludge on the surface or inside a water stream. Sometimes, over time, individual lumps freeze together, forming sludge fields, as a result of which it is difficult to distinguish a sludge drift from an ice drift.
Snezhura is a snow cover on water, formed when heavy snow falls on the surface of water close to the freezing point. It quickly becomes saturated with water and forms a mushy viscous mass. When frozen, it forms slush. (Fig. 2)
Rice. 2 Snezhura (Photo by Yu.P. Zamoshsky)
Pancake ice is floating round ice floes with a diameter of 0.5 to 3 m, with a roll of crushed ice along the edges. It is formed when fat, sludge and small ice floes freeze.
Broken ice is floating ice floes of irregular shape. There are coarse (from 20 to 100 m) and small broken (ice floes measuring from 2 to 20 m) ice and pieces of ice (from 0.5 to 2 m).
Ice porridge is a mixture of crushed ice, sometimes with slush and snow slush. It accumulates at the edge of the ice or shores in a dense layer of several meters.
Ice fields are ice floes larger than 100 m in size. There are small ice fields with the largest size from 100 to 500 m and large ice fields - more than 500 m.
Ice shafts are ice formations in the form of ridges composed of slush and broken ice. They are formed during the autumn ice drift along the coast. The height of the shafts reaches 1 m; the river flows as if on icy banks.
An ice bridge is a short section of ice cover formed in places where banks meet or as a result of stopping and freezing of floating ice and slush.
Iceberg is a large free-floating piece of ice in the ocean and sea (Fig. 3) As a rule, it breaks off from ice shelves. Since the density of ice is 920 kg/m³ and the density of sea water is about 1025 kg/m³, about 90% of the iceberg's volume is under water.
The shape of an iceberg depends on its origin:
· Icebergs from outlet glaciers are table-shaped with a slightly convex upper surface, which is dissected by various types of irregularities and cracks. Characteristic of the Southern Ocean.
· Icebergs from cover glaciers are distinguished by the fact that their upper surface is practically never flat. It is slightly inclined, like a pitched roof. Their sizes, compared to other types of icebergs in the Southern Ocean, are the smallest.
· Icebergs of ice shelves, as a rule, have significant horizontal dimensions (tens and even hundreds of kilometers). Their average height is 35-50 m. They have a flat horizontal surface, almost strictly vertical and smooth side walls
Rice. 3 View of an iceberg underwater (#"justify"> Ice phenomena and ice formations during the freeze-up period
Ice cover - ice in the form of a continuous, motionless cover on the surface of water bodies.
Hummocks are piles of ice floes on the ice cover, formed as a result of movement and compression of the ice cover (Fig. 4)
Rice. 4 Ridge of hummocks (Photo by Sergei Lyakhovts).
Polynya is a space with an open water surface in the ice cover.
Cracks are breaks in the ice cover that form under the influence of fluctuations in air temperature and water level, movements and other reasons. There are surface dry cracks and through cracks filled with water.
Ice dam is an ice formation that occurs as a result of water reaching the surface of the ice and its freezing due to the restriction of the water section by the growing ice cover and freezing of the riverbed in shallow places. In some cases, it is formed when groundwater flows from the slopes of the banks onto the surface of the ice cover.
Slush path is part of the ice cover formed from frozen slush in the form of a longitudinal strip between the banks. The ice on a sludge path is usually hummocky.
Settled dried ice is a section of ice cover near the shore or in shallow water that has settled to the bottom as the water level decreases.
Snowflake is water on ice formed as a result of melting snow during prolonged thaws.
Layered ice - two-layer and multi-layer ice floes formed when ice floes move on top of each other. Multilayer ice floes reach a thickness of 2-3 m or more.
Ice phenomena and ice formations during the break-up period
Edges are strips of open water along the shores, formed before breaking up as a result of melting ice, rising water levels, and also due to an increased influx of groundwater.
Water on ice - accumulations of standing water on ice, formed from melting snow or due to water protruding from under the ice cover. Ice raised - floating and separation of ice cover from the shores without breaking when the water level rises; if the ice was lifted without detachment from the banks, the ice swelled. Ice movement is small movements of the ice cover in certain sections of the river, occurring under the influence of currents, wind, and rising levels. There can be one or several movements.
Naslud is ice formed when melt water freezes on the ice cover after a thaw (the similar-sounding term nasluz means a completely different formation - low-transparent water-snow ice formed from snow on a transparent layer of lake ice). A clearing is a space of open water in the ice cover, formed as a result of ice movement.
Ice piles are a pile of ice floes, often in the form of shafts on the banks and in the floodplain of a river, formed during the spring ice drift. They reach especially large sizes in areas of former ice jams. Residual banks are strips of stationary ice left near the coast in the spring when the ice cover collapses.
2.Phases of the ice regime of the seas and oceans
ice ocean cover
Phases of the ice regime are a set of naturally repeating processes of the emergence, development and destruction of ice formations on water bodies. The following main types of ice regime are distinguished:
) ice formations and ice phenomena are absent. This type is typical for tropical latitudes;
) ice phenomena are observed, but there is no freeze-up (mainly mountainous areas of the subtropical zone);
) unstable ice cover is observed (temperate climate on the western coasts of the continents);
) Every year in winter, stable freeze-up of varying durations is observed (subarctic and temperate zones);
) freeze-up throughout the year (occurs only near lakes of the Arctic zone and high-mountain climates close to it). For type 4, which occupies the vast majority of Russian territory, three main phases of the ice regime are distinguished:
freezing;
freezing;
autopsy.
Freezing is a phase of the ice regime, characterized by the formation of ice cover on watercourses and reservoirs. The freezing period begins with the appearance of ice and ends with the formation of freeze-up. There are processes of ice formation (the appearance of floating ice) and the formation of a continuous ice cover. Ice formation occurs when water crystallizes at any point in the water column and at the bottom, and the formation of a continuous ice cover occurs both due to the freezing of water on the surface and due to the freezing of floating masses of ice, banks and ice brought by currents or drift. Based on the nature of ice cover formation, two types are distinguished: static and dynamic. The static type of freezing is typical for shallow and small lakes, reservoirs, ponds, sections of small rivers and slow-flowing canals. In the surface layer, ice crystals form in the form of thin transparent needles, clusters of which create matte spots (grease), and banks are formed near the shore in shallow water, gradually growing from the shore to the deep-water part. Under calm freezing conditions, they have a smooth surface and a small initial thickness. Their further spread and freezing of floating ice formations on them leads to the establishment of a continuous ice cover. The dynamic type of freezing is characterized by intense mixing; cooling of water occurs throughout the entire depth of the mixed layer, which contributes to the supercooling of the entire thickness and the drift of crystallization nuclei to the depth. The resulting inland ice may exceed the amount of ice formed on the surface. Accumulations of bottom ice form at the bottom. The freezing of ice formations and ice fragments floating on the surface increases the amount of ice material and ultimately leads to the formation of a continuous ice cover.
Freeze-up is a phase of the ice regime characterized by the presence of a stationary ice cover, a period during which a stationary ice cover is observed. During the first days of freeze-up, when the ice is still thin and the heat flow from water into the air significantly exceeds the heat flow from the water column to the surface, ice growth occurs relatively quickly. Subsequently, as the thickness of the ice increases and the layer of snow on the ice grows, the process slows down. When equilibrium is established between the heat flow through the snow-ice cover and its influx to the lower surface of the ice, the growth of ice thickness from below stops. In the second half of winter, a significant increase in ice can be observed due to the freezing of water-saturated snow, when, as a result of the ice bending under the weight of the snow mass, water comes to the surface through cracks. At the beginning of spring, the ice begins to melt from below due to reduced heat loss to the atmosphere. After the ice cover is freed from snow, intensive melting of the ice from above begins.
Breakup is a phase of the ice regime characterized by the destruction of the ice cover. The beginning of the destruction of the ice cover occurs under the influence of thermal factors - the melting of ice from below due to a decrease in heat loss to the atmosphere. After the ice cover is freed from snow, intensive melting of the ice from above begins. Mechanical factors either complement the processes of thermal destruction of ice, or are the main reason for the opening of watercourses and reservoirs. Mechanical factors include the movement of water under the ice, which creates a constant force applied to the lower edge of the ice and directed downstream, as well as the spring rise in level, which creates an upward force, tearing off the ice near the coast, creating a deflection of the ice cover. The destruction of ice intensifies with the formation of open water spaces - the action of the wind is added to the work of the wind, the destruction of ice floes during drift, etc.
[(#"justify">)]
. sea ice
Properties of sea ice
The most important properties of sea ice are porosity and salinity, which determine its density (from 0.85 to 0.94 g/cm³). Due to the low density of ice, ice floes rise above the water surface by 1/7 - 1/10 of their thickness. Melting of sea ice begins at temperatures above -2.3°C. Compared to freshwater, it is more difficult to break into pieces and is more elastic.
1. Salinity
The salinity of sea ice depends on the salinity of the water, the rate of ice formation, the intensity of water mixing and its age. On average, the salinity of ice is 4 times lower than the salinity of the water that formed it, ranging from 0 to 15 ppm (on average 3-8 ppm).
Sea water, the salinity of which is below 24.695 ppm (so-called brackish water), when cooled, first reaches the highest density, like fresh water, and with further cooling and without stirring it quickly reaches its freezing point.
If the salinity of the water is above 24.695 ppm (salt water), it cools to the freezing point with a constant increase in density with continuous mixing (exchange between the upper cold and lower warmer layers of water), which does not create conditions for rapid cooling and freezing of water, that is, when Under the same weather conditions, salty ocean water freezes later than brackish water.
2. Density
Sea ice is a complex physical body consisting of fresh ice crystals, brine, air bubbles and various impurities. The ratio of the components depends on the conditions of ice formation and subsequent ice processes and affects the average density of ice. Thus, the presence of air bubbles (porosity) significantly reduces the density of ice. Ice salinity has less of an effect on density than porosity. With an ice salinity of 2 ppm and zero porosity, the ice density is 922 kilograms per cubic meter, and with a porosity of 6 percent it decreases to 867. At the same time, with zero porosity, an increase in salinity from 2 to 6 ppm leads to an increase in ice density only from 922 to 928 kilograms per cubic meter.
Thermophysical properties
The average thermal conductivity of sea ice is about five times higher than that of water and eight times higher than that of snow, and is about 2.1 W/m degrees, but may decrease towards the lower and upper surfaces of the ice due to increased salinity and increase in the number of pores.
The heat capacity of sea ice approaches that of fresh ice as the temperature of the ice decreases as the brine freezes. With increasing salinity, and therefore increasing brine mass, the heat capacity of sea ice increasingly depends on the heat of phase transformations, that is, temperature changes. The effective heat capacity of ice increases with increasing salinity and temperature.
The heat of fusion (and crystallization) of sea ice ranges from 150 to 397 kJ/kg, depending on temperature and salinity (with increasing temperature or salinity, the heat of fusion decreases).
Optical properties
Pure ice is transparent to light rays. Inclusions (air bubbles, salt brine, dust) scatter the rays, significantly reducing the transparency of the ice.
The color of sea ice in large massifs varies from white to brown.
White ice is formed from snow and has many air bubbles or brine cells.
Young sea ice, which has a granular structure and contains significant amounts of air and brine, is often green in color.
Perennial hummocky ice from which impurities have been squeezed out, and young ice that has frozen under calm conditions, often have a blue or blue color. Glacier ice and icebergs are also blue. In blue ice, the needle-like structure of the crystals is clearly visible.
Brown or yellowish ice is of river or coastal origin and contains admixtures of clay or humic acids.
The initial types of ice (ice lard, slush) have a dark gray color, sometimes with a steel tint. As the thickness of the ice increases, its color becomes lighter, gradually turning white. When melting, thin pieces of ice turn gray again.
If the ice contains a large amount of mineral or organic impurities (plankton, aeolian suspensions, bacteria), its color can change to red, pink, yellow, even black.
Due to the property of ice to retain long-wave radiation, it is capable of creating a greenhouse effect, which leads to heating of the water underneath it.
Mechanical properties
The mechanical properties of ice mean its ability to resist deformation.
Typical types of ice deformation: tension, compression, shear, bending. There are three stages of ice deformation: elastic, elastic-plastic, and destruction stage. Taking into account the mechanical properties of ice is important when determining the optimal course of icebreakers, as well as when placing cargo and polar stations on ice floes, and when calculating the strength of a ship’s hull (Ivanov, 1976), (Nazarov, 1938)
Sea ice structure
When the sea surface cools to freezing point temperature, a large number of disks or plates of pure ice, called slush, appear in the upper layer of water (a few centimeters thick) . mm,and the shape can be extremely varied - from squares (or almost squares) to hexagonal formations. The optical axis of such a plate is always perpendicular to the plane of its surface. These elemental ice crystals float on the surface of the water, forming what is called ice grease, which gives the surface of the sea a somewhat oily appearance. In calm water, the plates float in a horizontal position and are With- the axes are directed vertically. Wind and waves cause the plates to collide, turn over and take different positions as a result; Gradually freezing, they form a permanent ice cover, in which individual crystals are randomly oriented. In the first stage of formation, young ice is surprisingly flexible; under the influence of waves coming from the open sea or caused by a moving ship, it bends without breaking, and the amplitude of vibrations of the ice surface can reach several centimeters.
Subsequently, if the temperature does not increase, individual plates play the role of seed crystals. The mechanism of this process has not yet been fully studied. As can be seen from Fig. 4, ice consists of individual crystals, each of which has purely individual properties, for example, the degree of transmission of polarized light (the same for the entire given crystal, “but different from others). In some cases, a structural cell of ice is called a grain rather than a separate crystal, since it is clear that it has a complex substructure and consists of many parallel plates. The relationship between this substructure and the primary sludge mentioned above is quite obvious. There is no doubt that some of the grain is formed from frozen sludge plates, which are then preserved as separate layers of crystal. However, apparently, there is some other process, since in some cases crystals begin to grow on the lower surface of a fairly thick ice cover, and they also have a plate-like structure. Whatever the mechanism of crystal formation, all of them - both in sea ice and in freshwater - consist of a large number of plates, exactly parallel to each other. The optical axis of the crystal is located perpendicular to these plates.
Interesting results are obtained from studying the distribution of crystals according to the orientation of their optical axes depending on the depth of their occurrence in the ice thickness. Orientation can be characterized by two angles - polar, which is the angle between c-axisboth vertical and azimuthal, i.e. an angle measured from some arbitrary direction, for example from the north-south line. The magnitudes of azimuthal angles usually do not obey any law; rare exceptions to this rule may be caused by unusual tidal phenomena. Polar angles exhibit a certain pattern. As mentioned above, the orientation of crystals near the ice surface is quite variable, since it depends on the influence of wind during ice formation. But as you go deeper into the ice, the polar angles increase, and at a depth of about 20 cmThe optical axes of almost all crystals are oriented horizontally. A laboratory study of the freezing of distilled water (Perey and Pounder, 1958), provided that it was cooled from only one direction and the water was in a calm state, gave the results shown in Table. Horizontal sections were taken from the ice surface and from depths 5 and 13 cm.Each section was examined using a universal polariscope. At the same time, the ratio of areas (in percentage) occupied by crystals with the same - within 10-degree intervals - orientation of the optical axes was determined.
Orientation of crystals in ice sheet (Pounder, 1967)
Depth, cm% area occupied by crystals with polar angles within 0 - 10 degrees 10 - 20 degrees 70 - 80 degrees 80 - 90 degrees 0 5 1368 12 137 3 26 18 145 26 43
A similar situation is observed in natural sea ice that has reached a certain “age”. Exceptions occur in cases where, during the growth of the ice cover, movements occur that cause compression and fracture of the ice. Thus, the bulk of sea ice that has existed for a year or more consists of crystals, the optical axes of which are directed horizontally and oriented chaotically in azimuth. The length (vertical height) of such crystals reaches 1 mand more, with a diameter from 1 to 5 cm.The reasons for the predominance of crystals with horizontal optical axes in ice help to understand Fig. 4. Since an ice crystal has one main axis of symmetry, it can grow primarily in two directions. Ice molecules attach to the crystal lattice either in planes (of the crystal) perpendicular to c-axisand called basal planes , or in the direction of the c-axis, which in turn leads to an increase in the area of the basal planes. Based on the laws of thermodynamics, we can come to the conclusion that the first type of crystal growth should be more intense than the second, which is confirmed by experiments.
Rice. 5 The predominance of growth of crystals with inclined optical axes, causing the gradual disappearance of a crystal with a vertical With-axis. (Pounder, 1967)
Ice-water interface
Studying the undersurface of growing sea ice helps understand how water freezes. Lower 1-2 cm Ice strata consist of plates of pure (fresh) ice with layers of brine between them. The plates that make up part of a separate crystal are parallel to each other and are usually located vertically. This is the so-called skeletal (or frame) layer. The mechanical strength of this layer is usually extremely low. With further freezing, the plates thicken somewhat, ice bridges appear between them and solid ice gradually forms, in which the brine is contained in the form of drops or cells between the plates. A decrease in ice temperature leads to a decrease in the size of the cells filled with brine, which take the form of long vertical cylinders of almost microscopic dimensions in cross section. Such cells can be found in Fig. 4 in the form of rows of black dots located along the lines between the plates. A certain number of brine cells are also present at the boundaries between the crystals, but the bulk of the brine is contained inside individual grains. In Fig. Table 5 shows the results of a statistical study of the thickness of the plates in a sample of annual sea ice. It can be seen that the plates have a uniform thickness, on average in the range of 0.5-0.6 mm.The diameter of the nests containing brine is usually about 0.05 mm.
Rice. 6 Statistical distribution of blade thickness in first-year sea ice. (Pounder, 1967)
Sufficient data on the length of such nests is still not available; it is only known that it fluctuates within much wider limits than the diameter. Approximately we can assume that the length of the nests is about 3 cm.
Thus, we see that in most cases sea ice consists of macroscopic crystals with a complex internal structure - it contains plates of pure ice and a large number of cells containing brine. In addition, ice usually contains many small spherical air bubbles formed from air dissolved in water, released during the freezing process. The portion of sea ice volume occupied by liquid brine is an extremely important parameter called brine content v (Fig. 6). It can be calculated by knowing the salinity, temperature and density of sea ice. Based on the knowledge of the phase relationships of salt solutions contained in sea water at low temperatures, (Assur, 1958) calculated v for those values of salinity and ice temperature that are found on the globe. The results obtained by Assur do not take into account the presence of air bubbles in the ice, but the effect of the latter on the value of v can be determined experimentally by comparing the density of a sample of sea ice with the density of freshwater ice at the same temperature. (Pounder, 1967)
Rice. 7 Migration of brine along a temperature gradient (Pounder, 1967)
Types of sea ice
Sea ice is divided into three types based on its location and mobility:
floating (drifting) ice;
pack multi-year ice (pack)
Fast ice is a type of fixed ice in the seas and oceans and their bays along the coast.
Rice. 8 (Snow-covered fast ice and drifting ice on the Baltic Sea)
Dynamically, sea ice is divided into mobile (drifting) and stationary. Fixed ice includes fast ice and stamukha.
Fast ice is a sheet of ice attached to a shore or shoal that extends from a few meters to hundreds of kilometers from the shore when the water freezes. Fast ice experiences only vertical vibrations when the water level changes. It can be formed both at its location when a sea wave freezes, and as a result of freezing. This species can break up and thus become drift ice. In high-latitude areas, fast ice can exist for several years and reach a thickness of 10-20 m. To combat fast ice, icebreakers are used on sea routes.
Floating ice is not connected to the shore and drifts under the influence of wind and current. These include the initial stages of ice (fat, snow slush, slush, pancake ice), its later forms (nilas, young fish, one-year, two-year and multi-year ice), ice in the form of fields, their fragments or individual ice floes, as well as icebergs, their debris and ice islands.
Depending on the size of the ice floes, floating ice is divided into the following forms:
§ ice fields are the largest formations of drifting ice in terms of area, which are divided by size into giant (over 10 km in diameter), extensive (2-10 km), large (0.5-2 km) and fragments of fields - ice floes measuring 100 - 500 m;
§ coarse ice - ice floes measuring 20-100 m;
§ small broken ice - ice floes measuring 2-20 m;
§ grated ice - ice floes measuring 0.5-2 m;
§ frost - pieces of ice of various ages frozen in an ice field;
§ hummocks - individual piles of fragments of ice floes (hillocks) on the ice cover, formed as a result of strong collision or compression of ice;
§ nesyak - a large hummock or a group of hummocks frozen together, representing a separate ice floe with relatively small horizontal and large vertical dimensions; draft up to 20-25 m and height above sea level up to 5 m.
Pack ice is long-term polar sea ice that has survived more than 2 annual cycles of growth and melting. Typically observed as vast ice fields in the Arctic Basin, as well as fast ice along the northern shores of Greenland, in the northern straits of the Canadian Arctic Archipelago and in the Antarctic. Hummocks on park ice fields are usually smoothed out by repeated melting, making their surface predominantly hilly. In the Arctic, park ice covers an area of 60 to 90% of the ice cover. Thick park ice is impassable for ships.
Pack ice is understood as free-floating ice masses that have slid into the water and become detached from glaciers on land, as well as drifting ice floes that are subsequently captured by coastal ice. Sea ice has the following property: even when formed, it is less salinous than sea water. As its “life” continues, it gets closer and closer to a fresh state and finally becomes fit for consumption.
Rice. 9 Pack ice
Conclusion
ice ocean cover
The study and analysis of the data allowed us to draw the following conclusions:
.Ice phenomena also include ice formations, which are forms of the existence of ice in water bodies.
.The phases of the ice regime correspond to characteristic periods of the ice regime - autumn ice phenomena, freeze-up, spring ice phenomena.
.Sea ice is a complex formation, heterogeneous in its thermophysical properties, formed under the influence of a whole complex of external factors.
.The most important properties of sea ice are porosity and salinity, which determine its density (from 0.85 to 0.94 g/cm³).
.The structure of sea ice consists of a large number of disks or plates of pure ice called Suga.The thickness of these ice floes is very small, the average size is approximately 2.5 cm * 0.5 mm,and the shape can be extremely varied - from squares (or almost squares) to hexagonal formations.
.Ice in the oceans and seas is usually classified according to a number of
characteristics, the main ones of which are genetic, dynamic, age and morphological.
Bibliography
1.Barton V., Cabrera N., Frank F. Growth of crystals and the equilibrium structure of their surfaces // In: Elementary processes of crystal growth. Per. from English M.: Foreign publishing house. lit., 1959. S. 11 - 168.
2. Burke A.K. Sea ice. L.: Glavsevmorputi, 1940. 94 p.
Doronin Yu.P., Kheisin D.E., Sea ice. L.: Gidrometeoizdat, 1975. 318 p.
Zhukov L.A. General oceanology. L.: Gidrometeoizdat, 1976. 376 p.
Zubov N.N. Sea waters and ice. L., Gidrometeoizdat, 1938. 451 p.
Nazarov V.S. To the study of the properties of sea ice // Proceedings of the AARI 1938, vol. 110, pp. 101-108.
Pounder E.F. Physics of ice. M.: "PEACE". Per. from English Shinkar G.G., 1967, p. 30 - 39.
Saveliev B.A. Structure, composition and properties of ice cover in marine and fresh water bodies. Ed. Moscow State University, 1963. 541 p.
Kheisin D.E. Ice cover dynamics. L., Gidrometeoizdat, 1967. 215 p.
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Sea ice is ice formed in the sea (ocean) when water freezes. Since sea water is salty, freezing of water with a salinity equal to the average salinity of the World Ocean occurs at a temperature of about?1.8°C.
The most important properties of sea ice are porosity and salinity, which determine its density (from 0.85 to 0.94 g/cm³). Due to the low density of ice, ice floes rise above the surface of the water by 1/7 - 1/10 of their thickness. Melting of sea ice begins at temperatures above ?2.3 °C. Compared to freshwater, it is more difficult to break into pieces and is more elastic.
The salinity of sea ice depends on the salinity of the water, the rate of ice formation, the intensity of water mixing and its age. On average, the salinity of ice is 4 times lower than the salinity of the water that formed it, ranging from 0 to 15 ‰ (on average 3-8 ‰).
Sea ice is a complex physical body consisting of fresh ice crystals, brine, air bubbles and various impurities. The ratio of the components depends on the conditions of ice formation and subsequent ice processes and affects the average density of ice. Thus, the presence of air bubbles (porosity) significantly reduces the density of ice. Ice salinity has less of an effect on density than porosity. With an ice salinity of 2 ‰ and zero porosity, the ice density is 922 kg/m³, and with a porosity of 6% it decreases to 867. At the same time, with zero porosity, an increase in salinity from 2 to 6 ‰ leads to an increase in ice density only from 922 to 928 kg /mi.
Based on the degree of mobility, sea ice is divided into stationary and drifting. The main form of fixed ice is fast ice, which can be formed by natural freezing of water or as a result of drifting ice of any age category freezing to the shore. Fixed ice also includes stamukhas - hummocky formations sitting on the ground in shallow water or near the shore. All other types of sea ice are classified as drifting ice, which moves under the influence of wind and currents. As a result of the heterogeneity of wind and current fields, differences in the thickness and structure of ice fields and complex interaction with the shores, the drift of ice fields, ice floes and pieces of ice occurs unevenly. This leads to their collisions, deformations and fractures.
Based on their concentration, drifting ice is divided into individual ice floes, sparse ice, compact ice, very compact ice and continuous ice. The movement of compacted ice is accompanied by deformations, including movements and shifts of ice fields and ice floes relative to each other, rotation of the ice floes, and the formation of hummocks, cracks, and cracks. As a result of movements and deformation, ice is redistributed on the sea surface, its concentration changes, and the structure and morphology of the ice cover changes.
After the ice has consolidated to 9-10 points, if the forces that caused it continue to act, compression begins, during which layering and hummocking of the ice occurs. The process of hummocking consists of breaking the ice cover, followed by tilting the fragments up to a vertical position, crushing the edges of the ice floes, pushing the ice floes over one another, and piling up ice ridges and ridges. With the relative movement of ice fields, long straight ridges of hummocks of finely crushed ice are formed. Ridges of hummocks of strike-slip origin are characteristic of areas where significant differences in drift velocities are observed. At the boundary of fast ice with moving ice, depending on the direction of drift, cracks or gaps may appear, or shear ridges of hummocks or compression hummocks may form. At shallow sea depths and intense hummock formation, the bases of hummocks can reach the ground. Such hummocks plow furrows at the bottom.
Depending on the reasons causing the forward movement of ice, several types of drift are distinguished. Wind drift occurs under the influence of wind. This drift continues for some time even after the wind stops, since the drifting ice involves the upper layers of water in its movement. The speed of wind drift of sea ice is close to 1:50 wind speed. The direction of drift usually does not coincide with the direction of the wind. In the Arctic seas, under the influence of Coriolis forces, the direction of drift deviates to the right of the wind direction at an angle of 28°, and in the Antarctic seas - in the opposite direction. In many seas, for example, the White, Barents, Bering, Okhotsk and others, tidal ice drift, caused by currents at high and low tides, plays an important role.
The direction of drift is greatly influenced by the proximity of the coastline, the presence of islands and shoals, and bottom topography. As a result of the simultaneous influence of many factors, ice drift is often uneven; individual ice masses and accumulations can drift in different directions and at different speeds. The boundaries between them are called drift divides, which are characterized by the presence of strips of grated ice and hummock belts.
According to the stages of ice development, several so-called initial types of ice are distinguished (in order of time of formation):
ice needles,
ice lard,
intra-water (including bottom or anchor), formed at a certain depth and objects located in the water under conditions of turbulent mixing of water. Further types of ice in time of formation are nilas ice:
nilas, formed on a calm sea surface from fat and snow (dark nilas up to 5 cm thick, light nilas up to 10 cm thick) - a thin elastic crust of ice that easily bends on water or swell and forms jagged layers when compressed;
flasks formed in desalinated water in a calm sea (mainly in bays, near river mouths) - a fragile shiny crust of ice that easily breaks under the influence of waves and wind;
pancake ice formed during weak waves from icy fat, snow or slush, or as a result of a break as a result of waves of a flask, nilas or so-called young ice. They are round-shaped ice plates from 30 cm to 3 m in diameter and 10 - 15 cm thick with raised edges due to rubbing and impacts of ice floes. The further stage of development of ice formation is young ice, which is divided into gray (10 - 15 cm thick) and gray-white (15 - 30 cm thick) ice. Sea ice that develops from young ice and is no more than one winter old is called first-year ice. This first-year ice can be:
thin first-year ice - white ice 30 - 70 cm thick,
average thickness - 70 - 120 cm,
thick first-year ice - more than 120 cm thick. If sea ice has melted for at least one year, it is classified as old ice. Old ice is divided into:
residual first-year ice - ice that has not melted in summer and is again in the freezing stage,
two-year-old - lasting more than one year (thickness reaches 2 m),
multi-year - old ice 3 m thick or more, which has survived melting for at least two years. The surface of such ice is covered with numerous irregularities and mounds formed as a result of repeated melting. The lower surface of perennial ice is also highly uneven and varied in shape.
Distribution of sea ice.
The area of sea ice varies seasonally from 9 to 18 million km² in the Northern Hemisphere and from 5 to 20 million km² in the Southern Hemisphere. Maximum development of ice cover in the Northern Hemisphere is observed in February-March, and in Antarctica - in September-October. In general, sea ice on the globe, taking into account seasonal variations, covers 26.3 million km² with an average cover thickness of about 1.5 m. Sea ice forms in all seas of the Arctic Ocean. In winter, they also form in the Bering, Okhotsk, Azov, Aral and White Seas, in the Finnish, Bothnian and Riga Gulfs of the Baltic Sea, in the northern parts of the Japanese and Caspian Seas and at times on the northwestern coast of the Black Sea.
In the Arctic, there are six gradations of first-year and multi-year ice, differing in thickness and time of their existence. One-year ice is called thin when its thickness is 30-70 cm, medium thickness - from 70 to 120 cm and thick - more than 120 cm. Two-year ice has a thickness of 180-280 cm, three- and four-year ice - 240-280 cm. The thickness of multi-year ice reaches 280 -360 cm. During the period of maximum development of ice cover in the Arctic Ocean, multi-year ice covers 28% of the total area, two-year ice - 25%, first-year and young ice - 47%.
In the Southern Hemisphere, ice cover develops from April to September concentrically around Antarctica. Multi-year ice is practically non-existent there, and two-year ice covers less than 25% of the area of maximum ice development.
Glacial record
Snow falling on a glacier lies in a layer on its surface, and winter deposits are very different in structure from summer ones. Every year, a new layer of snow buries last year’s layer, and so on for tens and hundreds of thousands of years. The glacier grows, the ancient layers become deeper and deeper, and the entire ice mass is divided into annual layers, similar to the annual rings of trees. This is how the glacial record is written, but in order to read it, you must at least learn to determine the age of each glacial layer.
In the upper part of the glacier, which was formed “very recently” - over the last few thousand years - the age of the layer is determined without much difficulty. To do this, simply count the annual layers, consisting of winter and summer deposits. As the depth increases, this becomes increasingly difficult because the ice flows slowly. Therefore, when determining the age of ancient layers, special calculations are used that take this movement into account.
Glaciers record much more detailed information about past eras than tree rings. They can tell scientists about what climate, air temperature, atmosphere was on our planet not 10 - 20, but 200 - 300 thousand years ago. Even information about the winds that blew in those distant eras remains in the memory of the glaciers. How is all this rich information stored in the ice? It is known that water consists of two chemical elements - hydrogen and oxygen. But oxygen and hydrogen are different - “light” and “heavy.” Ordinary water is formed from the so-called light isotopes, and heavy water is formed from heavy isotopes. Among the many molecules of ordinary water, you can always find several molecules of heavy water - in nature, they are, as a rule, inseparable. But the fact is that the content of heavy water in ice depends on the temperature at which it was formed. The higher the temperature, the more heavy water molecules there are in the ice. Therefore, by measuring the amount of heavy water in the ice, you can quite accurately find out what the temperature was at the time of its formation. Along with water, atmospheric dust that settled on the surface of the ice many thousands of years ago is also stored in the thickness of the glacier. By analyzing it, you can find out what the air was polluted with in those eras, where it was brought from by the winds, whether there were any major volcanic eruptions then, and much more.
Even more interesting records from the glacial record concern the composition of the ancient atmosphere. The problem of air pollution is one of the pressing problems of modern humanity. And you can find out how much the atmosphere has deteriorated only by comparing its modern composition with the one it had long before the advent of man and industry. Where can you find ancient air?
In glaciers. Having fallen to the surface, snow first turns into firn - loose granular ice with a lot of air.
As firn compacts and freezes, it forms ice, and the air bubbles it contains are tightly sealed in the glacial mass. Having isolated these tiny bubbles of ancient air, scientists perform a chemical analysis of them and determine how much carbon dioxide, oxygen, methane and many other atmospheric gases were in it.
The most important and interesting thing is that all the information recorded in the glacial record can be read step by step, year by year, analyzing each annual layer of ice separately and in order. Moving from top to bottom, you can trace how the temperature, pollution and composition of the earth's atmosphere gradually changed, and how climatic conditions on Earth fluctuated over hundreds of thousands of years. In order to find out, it is necessary to drill through a thousand-meter thickness of glaciers, obtain ice samples from different depths and then subject them to analysis in scientific laboratories.
The first hole in the ice was made in the Alps in 1841, and half a century later several alpine holes were already reaching the glacial bed. Nowadays, glacier drilling has become a common activity for researchers. The depth of some wells in Greenland and Antarctica exceeded 2 km.
Drilling ice is very difficult because of its plasticity: as soon as you remove the drill bit, the walls of the hole quickly close. Therefore, the well has to be filled with non-freezing liquid, which has the same density as ice. Usually, either an electromechanical or an electrothermal method is used for drilling, when the ice is melted by a heated drill bit.
A column of ice removed from the glacier during drilling is called a “core”. It is carefully taken to special refrigerated laboratories, where it is studied in detail using the most modern methods of analysis.
The most interesting results so far have come from drilling at the Vostok polar station in Antarctica, which began in the 70s of the 20th century. The Vostok station is located in the central part of East Antarctica at an altitude of 3490 m. The average annual temperature here is -56.6 C, snow accumulates a little more than 2 cm per year. The thickness of the glacier at 3500 m contains ice deposited over hundreds of thousands of years.
Sea ice is classified:
by origin,
according to shapes and sizes,
according to the condition of the ice surface (flat, hummocky),
by age (stage of development and destruction),
according to navigation criteria (ice passability by ships),
according to dynamic characteristics (fixed and floating ice).
By origin Ice is divided into sea, river and glacier ice.
Marine ice is formed from sea water and has a greenish or whitish (in the presence of air bubbles or snow) tint.
Freshwater Ice is carried out from rivers in spring and summer and has a grayish or brownish tint due to inclusions of suspended matter.
Glacier ice (of continental origin) is formed as a result of the calving of glaciers descending into the sea - icebergs, drifting ice islands.
By appearance and shape ices are divided into:
ice needles, formed on the surface or in the water column,
ice lard– accumulation of frozen ice needles in the form of spots or a thin layer of grayish lead color,
snowflake– a viscous mushy mass formed during heavy snowfall on chilled water,
sludge– accumulation of lumps of ice, snow and bottom ice,
Nilas– thin elastic ice crust up to 10 cm thick,
bottle– thin transparent ice up to 5 cm thick, formed from ice crystals or fat in a calm sea,
pancake ice– ice, usually round in shape with a diameter of 30 cm to 3 m and a thickness of up to 10 cm.
According to the age ice happens:
young ice is 15-30 cm thick, has a gray or gray-white tint,
annual ice - ice that has existed for no more than one winter, with a thickness of 30 cm to 2 m.
two-year– ice that reached a thickness of more than 2 m by the end of the second winter,
perennial pack ice is ice that has existed for more than 2 years, more than 3 m thick, blue in color.
By navigation feature ice permeability is assessed on a 10-point scale cohesion ice. Ice concentration (thickness) is the ratio of the area of ice floes and the spaces of water between them in a given area. 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.
According to dynamic characteristics Ice is divided into fixed and floating.
Fixed ice exist in the form fast ice off the coast. The thickness of perennial fast ice off the coast of Greenland is more than 3 m, and off the coast of Antarctica there are tens and even hundreds of meters. The thickness of one-year fast ice in the Arctic Ocean is about 2–3 m, the width is up to 500 km (Laptev Sea).
floating Ice is formed either by freezing of floating ice or as a result of breaking off fast ice.
The term used to refer to any type of floating sea ice drifting ice.
The sizes of drifting ice are different: when the size is more than 500 m in diameter, they are called icyfields, for sizes 100…500m - ice fragmentsfields, with sizes 200...100m - large ice, for sizes less than 20m - , crushed ice.
The movement of ice occurs under the influence of wind or currents, under the influence of which they change their compactness. When the wind blows onshore, the concentration of drifting ice increases; when the wind blows from the shore, the ice thins out. As the speed of currents increases, the ice thins out, and as the speed decreases, the ice accumulates. The accumulation (compression) of ice occurs during the change of tidal currents, and lasts 1-2 hours, after which thinning of the ice is observed. When the water level rises, the ice thins out, and when it falls, it consolidates.
Glacier ice – icebergs(ice mountains) form in areas of the Arctic Ocean and off the coast of Antarctica. Currents carry them to moderate latitudes of both hemispheres. Icebergs sometimes reach enormous sizes. In 1854, in the area of 44°S. 28°W. An iceberg 120 km long and 90 m high was encountered. Only a tenth of the iceberg rises above the water.
About −1.8 °C.
An assessment of the amount (density) of sea ice is given in points - from 0 (clear water) to 10 (solid ice).
Properties
The most important properties of sea ice are porosity and salinity, which determine its density (from 0.85 to 0.94 g/cm³). Due to the low density of ice, ice floes rise above the surface of the water by 1/7 - 1/10 of their thickness. Sea ice begins to melt at temperatures above −2.3°C. Compared to freshwater, it is more difficult to break into pieces and is more elastic.
Salinity
Density
Sea ice is a complex physical body consisting of fresh ice crystals, brine, air bubbles and various impurities. The ratio of the components depends on the conditions of ice formation and subsequent ice processes and affects the average density of ice. Thus, the presence of air bubbles ( porosity) significantly reduces the density of ice. Ice salinity has less of an effect on density than porosity. With an ice salinity of 2 ppm and zero porosity, the ice density is 922 kilograms per cubic meter, and with a porosity of 6 percent it decreases to 867. At the same time, with zero porosity, an increase in salinity from 2 to 6 ppm leads to an increase in ice density only from 922 to 928 kilograms per cubic meter.
Nilas (foreground) in the Arctic
Thermophysical properties
The color of sea ice in large massifs varies from white to brown.
White ice formed from snow and has many air bubbles or brine cells.
Young sea ice of a granular structure with significant amounts of air and brine often has green color.
Multi-year hummocky ice, from which impurities have been squeezed out, and young ice, which froze under calm conditions, often have light blue or blue color. Glacier ice and icebergs are also blue. The needle-like structure of the crystals is clearly visible in blue ice.
Brown or yellowish ice is of river or coastal origin, it contains admixtures of clay or humic acids.
Initial types of ice (ice lard, slush) have dark grey color, sometimes with a steely tint. As the thickness of the ice increases, its color becomes lighter, gradually turning white. When melting, thin pieces of ice turn gray again.
If the ice contains a large amount of mineral or organic impurities (plankton, aeolian suspensions, bacteria), its color may change to red, pink, yellow, up to black.
Due to the property of ice to retain long-wave radiation, it is capable of creating a greenhouse effect, which leads to heating of the water underneath it.
Mechanical properties
The mechanical properties of ice mean its ability to resist deformation.
Typical types of ice deformation: tension, compression, shear, bending. There are three stages of ice deformation: elastic, elastic-plastic, and destruction stage. Taking into account the mechanical properties of ice is important when determining the optimal course of icebreakers, as well as when placing cargo on ice floes, polar stations, and when calculating the strength of a ship’s hull.
Conditions of education
When sea ice forms, small drops of salt water appear between entirely fresh ice crystals, which gradually flow down. The freezing point and the temperature of greatest density of sea water depend on its salinity. Sea water, the salinity of which is below 24.695 ppm (so-called brackish water), when cooled, first reaches the highest density, like fresh water, and with further cooling and without stirring it quickly reaches its freezing point. If the salinity of the water is above 24.695 ppm (salt water), it cools to the freezing point with a constant increase in density with continuous mixing (exchange between the upper cold and lower warmer layers of water), which does not create conditions for rapid cooling and freezing of water, that is, when Under the same weather conditions, salty ocean water freezes later than brackish water.
Classifications
Sea ice in its own way location and mobility divided into three types:
- floating (drifting) ice,
Forecast of changes in ice thickness by 2050
By stages of ice development There are several so-called initial types of ice (in order of formation time):
- intra-water (including bottom or anchor), formed at a certain depth and objects located in the water under conditions of turbulent mixing of water.
Further types of ice in time of formation - nilas ice:
- nilas, formed on a calm sea surface from fat and snow (dark nilas up to 5 cm thick, light nilas up to 10 cm thick) - a thin elastic crust of ice that easily bends on water or swell and forms jagged layers when compressed;
- flasks formed in desalinated water in a calm sea (mainly in bays, near river mouths) - a fragile shiny crust of ice that easily breaks under the influence of waves and wind;
- pancake ice formed during weak waves from icy fat, snow or slush, or as a result of a break as a result of waves of a flask, nilas or so-called young ice. They are round-shaped ice plates from 30 cm to 3 m in diameter and 10-15 cm thick with raised edges due to rubbing and impacts of ice floes.
The further stage of development of ice formation is young ice, which are divided into gray (10-15 cm thick) and gray-white (15-30 cm thick) ice.
Sea ice that develops from young ice and is no more than one winter old is called first-year ice. This first-year ice can be:
- thin first-year ice - white ice 30-70 cm thick,
- average thickness - 70-120 cm,
- thick first-year ice - more than 120 cm thick.
If sea ice has been subject to melting for at least one year, it is classified as old ice. Old ice is divided into:
- residual first-year ice - ice that has not melted in summer and is again in the freezing stage,
- two-year-old - lasted more than one year (thickness reaches 2 m),
- multi-year - old ice 3 m thick or more, which has survived melting for at least two years. The surface of such ice is covered with numerous irregularities and mounds formed as a result of repeated melting. The lower surface of perennial ice is also highly uneven and varied in shape.
Research of sea ice at the North Pole
The thickness of perennial ice in the Arctic Ocean reaches 4 m in some areas.
Antarctic waters mainly contain first-year ice up to 1.5 m thick, which disappears in the summer.
Bottom ice
Bottom ice is an accumulation of ice masses of a loose spongy structure at the bottom of natural watercourses, usually before the start of ice drift.
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See what “Bottom ice” is in other dictionaries:
BOTTOM, bottom, bottom (special). adj. to the bottom. Bottom ice (settled to the bottom). Bottom fishing rod (attached so that the line with the hook reaches the bottom). Ushakov's explanatory dictionary. D.N. Ushakov. 1935 1940 ... Ushakov's Explanatory Dictionary
Ground, grassroots Dictionary of Russian synonyms. bottom adj., number of synonyms: 2 ground (4) ... Synonym dictionary
See bottom. Ozhegov's explanatory dictionary. S.I. Ozhegov, N.Yu. Shvedova. 1949 1992 … Ozhegov's Explanatory Dictionary
Accumulations of inland ice (See Inland ice) at the bottom of non-freezing areas (polynyas) of rivers and lakes... Great Soviet Encyclopedia
I adj. 1. ratio with noun bottom I, associated with it 2. Peculiar to the bottom [bottom I], characteristic of it. 3. Living, growing, located at the bottom [bottom I 1.] or at the very bottom of a reservoir. II adj. 1. ratio with noun sweet clover associated with it 2.… … Modern explanatory dictionary of the Russian language by Efremova