The main types of water masses in latitude. Water masses

The formation of water masses occurs in accordance with the geophysical conditions of individual regions of the World Ocean. In the process of genesis, significant volumes of water acquire a set of characteristic physicochemical and biological properties, which remains practically unchanged within the entire space of their distribution.

Properties

The main properties of water masses include salinity and temperature. Both of these indicators depend on climatic factors due to geographical latitude. Precipitation and evaporation play the main role in changing water salinity. Temperature is influenced by the climate of the surrounding areas and ocean currents.

Types

In the structure of the World Ocean, the following types of water masses are distinguished - bottom, deep, intermediate and surface.

Surface masses are formed under the influence of precipitation and fresh continental waters. This explains the constant changes in temperature and salinity. Waves and horizontal oceanic currents also appear here. The layer thickness is 200–250 meters.

Intermediate water masses located at a depth of 500-1000 meters. They form in tropical latitudes, where there is a high level of salinity and evaporation.

Formation of deep masses caused by mixing of surface and intermediate water masses. This type of water is found in tropical latitudes. Their horizontal speed can be up to 28 km per hour. The temperature at depths over 1000 meters is approximately + 2–3 degrees.

Bottom water masses are distinguished by very low temperatures, constant salinity and high density. This type of water occupies that part of the ocean that is deeper than 3000 meters.

Views

Depending on the territorial location, such types of water masses are distinguished as equatorial, tropical, subtropical, temperate and polar.

Equatorial water masses are characterized by: low density and salinity, high temperature (up to +28 degrees), low oxygen content.

Tropical masses of water are in the zone of influence of ocean currents. The salinity of such masses is higher, since evaporation prevails here over precipitation.

The moderate masses are influenced by rivers, precipitation and icebergs. These latitudes are characterized by seasonal changes in water temperatures, and the average annual gradually decreases towards the poles from 10 to zero degrees.

The salinity level in the polar layers is quite low because floating ice has a strong desalination effect. At a temperature of about -2 degrees, sea water medium salinity freezes (the higher the salinity, the lower the freezing point).

What are water masses?

Answering the question of what water masses are, it makes sense to say about the processes occurring in the transition zones between them. When the masses meet, the waters are mixed, while the denser ones sink to a depth. Such areas are called convergence zones.

In the zones of divergence, the divergence of water masses occurs, accompanied by the rise of water from the depths.

Education

What are water masses and their types? The main types of water masses

30 September 2017

The total mass of all waters of the World Ocean is subdivided by specialists into two types - surface and deep. However, this division is very arbitrary. A more detailed categorization includes the following several groups, distinguished on the basis of territorial location.

Definition

To begin with, let's give a definition of what water masses are. In geography, this designation means a sufficiently large volume of water that is formed in one or another part of the ocean. Water masses differ from each other in a number of characteristics: salinity, temperature, as well as density and transparency. Differences are also expressed in the amount of oxygen, the presence of living organisms. We have given a definition of what water masses are. Now it is necessary to consider their different types.

Water at the surface

Surface waters are those zones where their thermal and dynamic interaction with air occurs most actively. In accordance with the climatic characteristics inherent in certain zones, they are divided into separate categories: equatorial, tropical, subtropical, polar, subpolar. Students who collect information to answer the question of what water masses are, need to know about the depth of their occurrence. Otherwise, the answer in a geography lesson will be incomplete.

Surface waters reach a depth of 200-250 m. Their temperature often changes, since they are formed by the influence of atmospheric precipitation. Waves and horizontal ocean currents are formed in the surface water column. It is here that the largest amount of fish and plankton is found. Between the surface and deep masses there is an interlayer of intermediate water masses. The depth of their location is from 500 to 1000 m. They are formed in areas of high salinity and high levels of evaporation.

Deep water masses

Bottom line deep waters can sometimes reach 5000 m. This type of water masses most often comes across in tropical latitudes. They are formed under the influence of surface and intermediate waters. For those interested in what water masses are, and what are the features of their various types, it is also important to have an idea of the speed of the current in the ocean. Deep water masses move very slowly in the vertical direction, but their horizontal speed can be up to 28 km per hour. The next layer is bottom water masses. They are found at depths of over 5000 m. This type is characterized by a constant salinity level as well as a high density level.

Equatorial water masses

"What are water masses and their types" is one of the compulsory topics of the course comprehensive school... The student needs to know that waters can be assigned to one group or another, not only depending on their depth, but also on their territorial location. The first type mentioned in accordance with this classification is the equatorial water masses. They are characterized by high temperature (up to 28 ° C), low density, low oxygen content. The salinity of such waters is low. There is a belt of low atmospheric pressure above the equatorial waters.

Tropical water masses

They are also quite well warmed up, and their temperature does not change during different seasons by more than 4 ° C. Ocean currents have a great influence on this type of water. Their salinity is higher, since a zone of high atmospheric pressure is established in this climatic zone, and very little precipitation falls.

Moderate water masses

The salinity level of these waters is lower than that of others, because precipitation, rivers, icebergs have a desalinating effect on them. In seasons, the temperature of water masses of this type can vary up to 10 ° C. However, the change of seasons occurs much later than on the mainland. Temperate waters differ depending on whether they are in the western or eastern regions of the ocean. The former, as a rule, are cold, while the latter are warmer due to warming by internal currents.

Polar water masses

What are the coldest water masses? Obviously, they are those that are in the Arctic and off the coast of Antarctica. With the help of currents, they can be carried to temperate and tropical regions. The main features of polar water masses are floating blocks of ice and vast ice spaces. Their salinity is extremely low. In the Southern Hemisphere, sea ice moves to temperate latitudes much more often than it does in the north.

Formation methods

Students who are interested in what water masses are will also be interested in learning information about their education. The main method of their formation is convection, or mixing. As a result of mixing, the water is immersed to a considerable depth, where vertical stability is again achieved. This process can take place in several stages, and the depth of convective mixing can reach up to 3-4 km. The next way is subduction, or "diving". With this method of mass formation, the water is lowered due to the combined action of the wind and surface cooling.

These are large volumes of water that form in certain parts of the ocean and differ from each other. temperature, salinity, density, transparency, the amount of oxygen contained and many other properties. Unlike, in them great importance has vertical zoning.

V depending on depth the following types of water masses are distinguished:

Surface water masses . They run down to the depth 200-250 m... Here water temperature and salinity often change, since these water masses are formed under the influence of the influx of fresh continental waters. In surface water masses are formed waves and horizontal... In this type of water masses, the highest content of plankton and fish.

Intermediate water masses ... They run down to the depth 500-1000 m... Basically, this type of masses is found in tropical latitudes of both hemispheres and is formed under conditions of increased evaporation and a constant increase in salinity.

Deep water masses ... Their lower limit may be before 5000 m... Their formation is associated with the mixing of surface and intermediate water masses, polar and tropical masses. They move vertically very slowly, but horizontally - at a speed of 28 m / h.

Bottom water masses ... They are located in below 5000 m, have constant salinity and very high density.

Water masses can be classified not only depending on the depth, but also by origin... In this case, the following types of water masses are distinguished:

Equatorial water masses ... They are well warmed up by the sun, their temperature changes by no more than 2 ° C and is 27 - 28 ° C. They are desalinated by abundant atmospheric precipitation and flowing into the ocean in these latitudes, therefore the salinity of these waters is lower than in tropical latitudes.

Tropical water masses ... They are also well warmed by the sun, but the water temperature here is lower than in equatorial latitudes, and is 20-25 ° С. Seasonally, the temperature of waters in tropical latitudes changes by 4 °. The temperature of the waters of this type of water masses is greatly influenced by ocean currents: the western parts of the oceans, where warm currents come from the equator, are warmer than the eastern ones, since cold currents come there... The salinity of these waters is much higher than the equatorial ones, since here, as a result of the descending air currents, high pressure is established and little precipitation falls. Rivers also do not have a desalination effect, since there are very few of them in these latitudes.

Moderate water masses ... According to the seasons, the temperature of the waters of these latitudes differs by 10 °: in winter the water temperature fluctuates from 0 ° to 10 ° С, and in summer it changes from 10 ° to 20 ° С. These waters are already characterized by the change of seasons, but it comes later than on land, and is not so pronounced. The salinity of these waters is lower than that of tropical waters, since atmospheric precipitation, rivers flowing into these waters, and entering these latitudes have a desalinating effect. Temperate water masses are also characterized by temperature differences between the western and eastern parts of the ocean: the western parts of the oceans are cold, where cold currents pass, and the eastern regions are warmed by warm currents.

Polar water masses ... They form in the Arctic and off the coast and can be carried by currents to temperate and even tropical latitudes. Polar water masses are characterized by an abundance of floating ice, as well as ice that forms huge ice spaces. In the Southern Hemisphere, in areas of polar water masses, sea ice penetrates into temperate latitudes much farther than in the Northern. The salinity of polar water masses is low, since floating ice has a strong desalination effect.

There are no clear boundaries between different types of water masses, differing in origin, but there are transition zones... They are most pronounced in places where warm and cold currents meet.

Water masses actively interact with: they give it moisture and heat and absorb carbon dioxide from it, release oxygen.

The most characteristic properties water masses are and.

Air masses

Transformation of air masses

The influence of the surface over which air masses pass affects their lower layers... This influence can cause changes in the moisture content of the air due to evaporation or precipitation, as well as changes in the temperature of the air mass as a result of the release of latent heat or heat exchange with the surface.

Tab. 1. Classification of air masses and their properties depending on the source of formation

Tropical

Polar

Arctic or antarctic

Marine

marine tropical

(MT), warm or very

wet; formed

in the Azores region

islands in the North

Atlantic

marine polar

(MP), cold and very

wet; formed

over the Atlantic to the south

from Greenland

arctic (A)

or antarctic

(AA), very cold and dry; forms over the ice-covered part of the Arctic or over the central part of Antarctica

Continental (K)

continental

tropical (CT),

hot and dry; forming over the Sahara Desert

continental

polar (KP), cold and dry; formed in Siberia in

winter period

Transformations associated with the movement of air masses are called dynamic. Air velocities at different altitudes will almost certainly differ, so the air mass does not move as a whole, and the presence of a velocity shift causes turbulent mixing. If the lower layers of the air mass are heated, then instability arises and convective mixing develops. Other dynamic changes are associated with large-scale vertical air movement.

The transformations that occur with the air mass can be indicated by adding one more letter to its basic designation. If the lower layers of the air mass are warmer than the surface over which it passes, then the letter "T" is added, if they are colder, the letter "X" is added. Consequently, with cooling, the stability of the warm sea polar air mass increases, while the heating of the cold sea polar air mass causes its instability.

Air masses and their effect on the weather in the British Isles

Weather conditions in any place on Earth can be considered as a result of the action of a certain air mass and as a consequence of the changes that have occurred to it. Great Britain, located in mid-latitudes, is affected by most types of air masses. She is thus a good example to study. weather conditions caused by the transformation of air masses near the surface. Dynamic changes, caused mainly by vertical air movements, are also very important in determining weather conditions and cannot be neglected in each case.

Polar Marine Air (MPA) reaching the British Isles is usually of the CMPA type, so this air mass is unstable. When passing over the ocean, as a result of evaporation from its surface, it retains a high relative humidity, and as a result of this - especially over the warm surface of the Earth at noon with the arrival of this air mass, cumulus and cumulonimbus clouds will appear, the temperature will drop below average, and in summer there will be showers, and in winter, precipitation can often fall in the form of snow or grains. Gusty winds and convective motions in the air will disperse dust and smoke so visibility is good.

If the marine polar air (MPV) from the source of its formation passes to the south, and then goes towards the British Isles from the southwest, it may well become warm, that is, of the type TMPV; sometimes referred to as "polar sea return air". It brings normal temperatures and weather, an average between the weather, which is established with the arrival of the air masses CMPV and MTV.

Tropical marine air (MTB) is usually of the TMTV type, so it is stable. Having reached the British Isles after crossing the ocean and cooled down, it is saturated (or becomes close to saturation) with water vapor. This air mass brings with it mild weather, the sky becomes cloudy and visibility is poor, fog is not uncommon in the west of the British Isles. When rising above orographic barriers, stratus clouds are formed; at the same time, drizzling rains are common, turning into stronger ones, and on the eastern side of the mountain ranges there are continuous rains.

The continental tropical air mass at its source is unstable, and although its lower layers become stable when it reaches the British Isles, the upper layers remain unstable, which can cause thunderstorms in the summer. However, during winter, the lower layers of the air mass are very stable, and any clouds that form there are of the stratus type. Typically, the arrival of such an air mass causes the temperature to rise well above average, and fog is formed.

With the arrival of the continental polar air in winter, the British Isles have very cold weather. In the source of formation, this mass is stable, but then in the lower layers it can become unstable and, when passing over the North Sea, will be largely "saturated" with water vapor. The resulting clouds are of the Cumulus type, although Stratocumulus can also form. During the winter, the eastern part of the UK can experience heavy rain and snow or snowfall.

Arctic air (AB) can be continental (CAV) or maritime (MAV), depending on the route it has traveled from the source of formation to the British Isles. The KAV passes over Scandinavia on its way to the British Isles. It is similar to the continental polar air, although it is colder and therefore often brings snowfalls with it during the winter and spring periods. Arctic sea air passes over Greenland and the Norwegian Sea; it can be compared to the cold polar sea air, although it is colder and more unstable. In winter and spring, arctic air is characterized by heavy snowfalls, prolonged frosts and exceptionally good visibility.

Water masses and t-s diagram

When determining water masses, oceanographers use a concept similar to that which is applied to air masses. Water masses are distinguished mainly by temperature and salinity. It is also believed that water masses form in a specific area, where they are in the surface mixed layer and where they are affected by constant atmospheric conditions. If the water remains in a stationary state for a long period of time, its salinity will be determined by a number of factors: evaporation and precipitation, the influx of fresh water with river runoff in coastal areas, melting and ice formation in high latitudes, etc. In the same way, its temperature will be determined by the radiation balance of the water surface, as well as the exchange of heat with the atmosphere. If the salinity of the water decreases and the temperature rises, the density of the water will decrease and the water column will become stable. Under these conditions, only a surface water mass of small thickness can form. If, however, salinity increases and the temperature decreases, the water will become denser, sink, and a water mass may form, reaching a significant vertical thickness.

To distinguish between water masses, data on temperature and salinity obtained at different depths in a certain area of the ocean are plotted on a diagram with temperature on the ordinate and salinity on the abscissa. All points are connected to each other by a line in ascending order of depth. If the water mass is perfectly homogeneous, it will be represented by a single point on such a diagram. It is this feature that serves as a criterion for identifying the type of water. The accumulation of observation points near such a point will show the presence of waters of a certain type. But the temperature and salinity of the water mass usually change with depth, and the water mass is characterized by T-S chart a certain curve. These variations may be due to small fluctuations in the properties of water formed at different times of the year and sinking to different depths in accordance with its density. They can also be explained by changes in conditions on the ocean surface in the area where the formation of the water mass took place, and the water may not descend vertically, but along some inclined surfaces of equal densities. Since q1 is only a function of temperature and salinity, lines of equal q1 values can be drawn on the T-S diagram. An idea of the stability of the water column can be obtained by comparing T-S chart with striking isolines q1.

Conservative and non-conservative properties

Having formed, the water mass, like the air mass, begins to move from the source of formation, undergoing transformation along the way. If it remains in the surface mixed layer or leaves it, and then returns again, further interaction with the atmosphere will cause changes in the temperature and salinity of the water. A new water mass can arise as a result of mixing with another water mass, and its properties will be intermediate between the properties of the two original water masses. From the moment the water mass ceases to undergo transformation under the influence of the atmosphere, its temperature and salinity can only change as a result of the mixing process. Therefore, these properties are called conservative.

The body of water usually has certain chemical characteristics, an inherent biota, and typical temperature-salinity ratios (T-S ratios). A useful indicator characterizing the water mass is often the concentration of dissolved oxygen, as well as the concentration of biogenic substances - silicates and phosphates. Marine organisms inherent in a particular water mass are called indicator species. They can remain within a given water mass, because its physical and chemical properties satisfy them, or simply because they, being plankton, are transported along with the water mass from the area of its formation. These properties, however, change as a result of chemical and biological processes in the ocean and are therefore called non-conservative properties.

Examples of water masses

A fairly illustrative example is the water masses that are formed in semi-enclosed reservoirs. The water mass that forms in the Baltic Sea has low salinity, which is caused by a significant excess of river flow and the amount of precipitation over evaporation. In summer, this water mass heats up sufficiently and therefore has a very low density. From its source of formation, it flows through narrow straits between Sweden and Denmark, where it intensively mixes with the underlying water layers entering the straits from the ocean. Before mixing, its temperature in summer is close to 16 ° C, and the salinity is less than 8% 0. But by the time it reaches the Skagerrak Strait, its salinity as a result of mixing increases to a value of the order of 20% o. Due to its low density, it remains on the surface and is rapidly transformed as a result of interaction with the atmosphere. Therefore, this mass of water has no noticeable effect on the open ocean areas.

In the Mediterranean Sea, evaporation exceeds the influx of fresh water, which comes in the form of precipitation and river runoff, and therefore salinity there increases. In the northwestern Mediterranean, winter cooling (associated mainly with winds called the mistral) can lead to convection that engulfs the entire water column to depths of more than 2000 m, resulting in an extremely homogeneous body of water with a salinity of more than 38.4% and a temperature of about 12.8 ° C. When this water mass leaves the Mediterranean Sea through the Strait of Gibraltar, it undergoes intense mixing, and the least mixed layer, or core, of Mediterranean water in the adjacent Atlantic has a salinity of 36.5% 0 and a temperature of 11 ° C. This layer has a high density and therefore sinks to depths of about 1000 m. At this level, it spreads, undergoing continuous mixing, but its core can still be recognized among other water masses of most of the Atlantic Ocean.

In the open ocean, Central water masses are formed at latitudes from about 25 ° to 40 °, and then sink along oblique isopycnals and occupy the upper part of the main thermocline. In the North Atlantic, this water mass is characterized by a T-S curve with an initial value of 19 ° C and 36.7% and a final value of 8 ° C and 35.1%. At higher latitudes, intermediate water masses are formed, which are characterized by low salinity as well as low temperatures. The most widespread is the Antarctic intermediate water mass. It has a temperature of 2 ° to 7 ° C and a salinity of 34.1 to 34.6% 0 and after submersion to about 50 ° S. NS. to a depth of 800-1000 m, it spreads in a northern direction. The deepest water masses form at high latitudes, where water cools down to very low temperatures in winter, often to the freezing point, so salinity is determined by the freezing process. The Antarctic bottom water mass has a temperature of -0.4 ° C and a salinity of 34.66% 0 and spreads northward at depths of more than 3000 m. -The Greenland Sill is undergoing a marked transformation, extends southward and overlaps the Antarctic bottom water mass in the equatorial and southern Atlantic Ocean.

The concept of water masses has played an important role in describing the circulation processes in the oceans. The currents in the depths of the oceans are both very slow and very changeable so that they can be studied through direct observation. But T-S analysis helps to isolate the cores of water masses and determine the directions of their distribution. However, to establish the speed at which they move, other data are needed, such as the stirring speed and the rate of change of non-conservative properties. But they usually cannot be obtained.

Laminar and turbulent flows

Movements in the atmosphere and in the ocean can be classified in different ways. One of them is the separation of motion into laminar and turbulent. At laminar flow fluid particles move in an orderly manner, streamlines are parallel. The turbulent flow is chaotic and the trajectories of individual particles intersect. In a fluid uniform in density, the transition from the laminar to the turbulent regime occurs when the velocity reaches a certain critical value proportional to the viscosity and inversely proportional to the density and distance to the flow boundary. In the ocean and atmosphere, currents are turbulent in most cases. In this case, the effective viscosity, or turbulent friction, in such flows is usually several orders of magnitude higher than the molecular viscosity and depends on the nature of turbulence and its intensity. In nature, there are two cases of the laminar regime. One is a flow in a very thin layer adjacent to a smooth boundary, the other is motion in layers of significant vertical stability (such as, for example, an inversion layer in the atmosphere and a thermocline in the ocean), where the vertical velocity fluctuations are small. The vertical shear of the velocity in such cases is much greater than in turbulent flows.

The scope of the movement

Another way to classify motions in the atmosphere and ocean is based on their separation according to spatial and temporal scales, as well as on the separation of periodic and non-periodic components of the motion.

The largest spatio-temporal scales correspond to such stationary systems as trade winds in the atmosphere or the Gulf Stream in the ocean. Although the motion in them experiences fluctuations, these systems can be regarded as more or less constant elements of circulation, having a spatial scale of the order of several thousand kilometers.

The next place is taken by processes with seasonal cyclicity. Among them, the monsoons and the currents of the Indian Ocean caused by them - and also changing their direction - should be especially noted. The spatial scale of these processes is also of the order of several thousand kilometers, but they are distinguished by a pronounced periodicity.

Processes with a time scale of several days or weeks are usually irregular and have spatial scales of up to thousands of kilometers. These include variations in wind associated with the transfer of different air masses and causing changes in weather in areas such as the British Isles, as well as similar and often associated with the first fluctuations in ocean currents.

Considering motions with a time scale from several hours to one or two days, we encounter a wide variety of processes, some of which are clearly periodic. This may be a daily frequency associated with the daily variation of solar radiation (it is typical, for example, for a breeze - wind blowing from sea to land during the day, and from land to sea at night); it can be daily and semidiurnal frequency, characteristic of tides; this may be the frequency associated with the movement of cyclones and other atmospheric disturbances. The spatial scale of this type of motion is from 50 km (for breezes) to 2000 km (for baric depressions at mid-latitudes).

Time scales, measured in seconds, less often minutes, correspond to regular movements - waves. The most common are wind waves on the ocean surface, with a spatial scale of about 100 m. Longer waves, such as leeward waves, are also encountered in the ocean and in the atmosphere. Irregular movements with such time scales correspond to turbulent fluctuations, manifested, for example, in the form of wind gusts.

The motion observed in some region of the ocean or atmosphere can be characterized by a vector sum of velocities, each of which corresponds to a certain scale of motion. For example, the velocity measured at some point in time can be represented as where and denotes turbulent velocity pulsations.

To characterize the movement, you can use the description of the forces involved in its creation. This approach, combined with the scale separation method, will be used in subsequent chapters to describe different forms movement. Here it is also convenient to consider the various forces, the action of which can cause or influence horizontal movements in the ocean and atmosphere.

Forces can be divided into three categories: external, internal, and secondary. The sources of external forces lie outside the liquid medium. The gravitational attraction of the Sun and Moon, which causes tidal movements, and the force of friction of the wind, fall into this category. Internal forces are related to the distribution of mass or density in a liquid medium. The uneven density distribution is caused by uneven heating of the ocean and atmosphere, and generates horizontal pressure gradients inside the liquid medium. By secondary, we mean forces acting on a fluid only when it is in a state of motion relative to the earth's surface... The most obvious is the frictional force, always against the motion. If different layers of fluid are moving at different speeds, friction between these layers due to viscosity will slow the faster moving layers and accelerate the less fast moving layers. If the flow is directed along the surface, then in the layer adjacent to the boundary, the friction force is directly opposite to the direction of the flow. Despite the fact that friction usually plays a minor role in atmospheric and oceanic movements, it would lead to attenuation of these movements if they were not supported by external forces. Thus, the movement could not remain uniform if other forces were absent. The other two secondary forces are bogus forces. They are associated with the choice of the coordinate system relative to which the motion is considered. This is the Coriolis force (which we have already talked about) and the centrifugal force that appears when a body moves around a circle.

Centrifugal force

A body moving at a constant speed around a circle changes its direction of motion all the time and, therefore, experiences acceleration. This acceleration is directed towards the instantaneous center of curvature of the trajectory and is called centripetal acceleration. Therefore, in order to remain on the circle, the body must experience the action of some force directed towards the center of the circle. As shown in elementary textbooks on dynamics, the magnitude of this force is mu 2 / r, or mw 2 r, where r is the mass of the body, m is the velocity of the body in a circle, r is the radius of the circle, and w is the angular velocity of rotation of the body (usually measured in radians per second). For example, for a passenger riding a train along a curved path, the movement seems to be uniform. He sees that he is moving relative to the surface at a constant speed. However, the passenger feels the action of some force directed from the center of the circle - centrifugal force, and he counteracts this force by leaning towards the center of the circle. Then the centripetal force turns out to be equal to the horizontal component of the reaction of the support-seat or the floor of the train. In other words, in order to maintain its apparent state of uniform motion, the passenger needs the centripetal force to be equal in magnitude and opposite in direction to the centrifugal force.

WATER MASS, the volume of water, commensurate with the area and depth of a reservoir, with a relative homogeneity of physical, chemical and biological characteristics that are formed in specific physical and geographical conditions (usually on the surface of the ocean, sea), which differ from the surrounding water column. Features of water masses, acquired in certain areas of the oceans and seas, remain outside the area of formation. Adjacent water masses are separated from each other by zones of the World Ocean fronts, zones of separation and transformation zones, which are traced by increasing horizontal and vertical gradients of the main indicators of water masses. The main factors in the formation of water masses are the heat and water balances of a given area, respectively, the main indicators of water masses are temperature, salinity and the density depending on them. The most important geographical patterns - horizontal and vertical zoning - appear in the ocean as a specific structure of waters, consisting of a set of water masses.

In the vertical structure of the World Ocean, water masses are distinguished: surface - up to a depth of 150-200 m; subsurface - up to 400-500 m; intermediate - up to 1000-1500 m, deep - up to 2500-3500 m; bottom - below 3500 m. In each of the oceans there are characteristic water masses, surface water masses are named in accordance with the climatic zone where they formed (for example, Pacific subarctic, Pacific tropical, and so on). For the underlying structural zones of the oceans and seas, the name of the water masses corresponds to their geographical area (Mediterranean intermediate water mass, North Atlantic deep, deep Black Sea, Antarctic bottom, etc.). The density of water and the peculiarities of atmospheric circulation determine the depth to which the water mass sinks in the region of its formation. Often, when analyzing the water mass, indicators of the content of dissolved oxygen, other elements, the concentration of a number of isotopes are also taken into account, which make it possible to trace the distribution of the water mass from the region of its formation, the degree of mixing with the surrounding waters, and the time spent out of contact with the atmosphere.

The characteristics of the water masses do not remain constant, they are subject to seasonal (in the upper layer) and long-term fluctuations within certain limits, and change in space. As they move from the area of formation, the water masses are transformed under the influence of the changed heat and water balances, the peculiarities of the circulation of the atmosphere and the ocean, and are mixed with the surrounding waters. As a result, primary water masses are distinguished (formed under the direct influence of the atmosphere, with the greatest fluctuations in characteristics) and secondary water masses (formed by mixing the primary ones, they are characterized by the greatest homogeneity of characteristics). Within the water mass, a core is distinguished - a layer with the least transformed characteristics, which retains the distinctive features inherent in a particular water mass - minimums or maxima of salinity and temperature, the content of a number of chemicals.

When studying water masses, the method of temperature-salinity curves (T, S-curves), the kernel method (study of the transformation of temperature or salinity extremes inherent in the water mass), isopycnic method (analysis of characteristics on surfaces of equal density), statistical T, S-analysis are used. The circulation of water masses plays an important role in the energy and water balance of the Earth's climatic system, redistributing thermal energy and freshened (or saline) waters between latitudes and different oceans.

Lit .: Sverdrup H. U., Johnson M. W., Fleming R. H. The oceans. N. Y. 1942; Zubov N.N. Dynamic Oceanology. M .; L., 1947; Dobrovolskiy A.D. On the determination of water masses // Oceanology. 1961. T. 1. Iss. 1; Stepanov V.N. Oceanosphere. M., 1983; Mamaev OI Thermohaline analysis of the waters of the World Ocean. L., 1987; he is. Physical oceanography: Fav. works. M., 2000; Mikhailov V.N., Dobrovolskiy A.D., Dobrolyubov S.A. Hydrology. M., 2005.

Water masses are large volumes of water that form in certain parts of the ocean and differ from each other in temperature, salinity, density, transparency, the amount of oxygen contained and many other properties. Unlike air masses, vertical zoning is of great importance in them. Depending on the depth, the following types of water masses are distinguished:

Surface water masses. They are located to a depth of 200-250 m. The water temperature and salinity often change here, since these water masses are formed under the influence of atmospheric precipitation and the influx of fresh continental waters. Waves and horizontal ocean currents are formed in surface water masses. In this type of water masses, the highest content of plankton and fish.

Intermediate water masses. They are located down to a depth of 500-1000 m. Basically, this type of mass is found in the tropical latitudes of both hemispheres and is formed under conditions of increased evaporation and a constant increase in salinity. Deep water masses. Their lower boundary can reach up to 5000 m. Their formation is associated with the mixing of surface and intermediate water masses, polar and tropical masses. They move vertically very slowly, but horizontally - at a speed of 28 m / h.

Bottom water masses. They are located in the World Ocean below 5000 m, have constant salinity and very high density.

Water masses can be classified not only by depth, but also by origin. In this case, the following types of water masses are distinguished:

Equatorial water masses. They are well warmed up by the sun, their temperature changes by no more than 2 ° C and is 27 - 28 ° C. They are desalinated by abundant atmospheric precipitation and rivers flowing into the ocean in these latitudes, so the salinity of these waters is lower than in tropical latitudes.

Tropical water masses. They are also well warmed by the sun, but the water temperature here is lower than in equatorial latitudes, and is 20-25 ° С. Seasonally, the temperature of waters in tropical latitudes changes by 4 °. Ocean currents have a great influence on the temperature of waters of this type of water masses: the western parts of the oceans, where warm currents come from the equator, are warmer than the eastern ones, since cold currents come there. The salinity of these waters is much higher than the equatorial ones, since here, as a result of the descending air currents, high pressure is established and little precipitation falls. Rivers also do not have a desalination effect, since there are very few of them in these latitudes.

Moderate water masses. According to the seasons, the temperature of the waters of these latitudes differs by 10 °: in winter the water temperature fluctuates from 0 ° to 10 ° С, and in summer it changes from 10 ° to 20 ° С. These waters are already characterized by the change of seasons, but it comes later than on land, and is not so pronounced. The salinity of these waters is lower than that of tropical waters, since atmospheric precipitation, rivers flowing into these waters, and icebergs entering these latitudes have a desalinating effect. Temperate water masses are also characterized by temperature differences between the western and eastern parts of the ocean: the western parts of the oceans are cold, where cold currents pass, and the eastern regions are warmed by warm currents.

Polar water masses. They form in the Arctic and off the coast of Antarctica and can be carried out by currents to temperate and even tropical latitudes. Polar water masses are characterized by an abundance of floating ice, as well as ice that forms huge ice spaces. In the Southern Hemisphere, in areas of polar water masses, sea ice penetrates into temperate latitudes much farther than in the Northern. The salinity of polar water masses is low, since floating ice has a strong desalination effect.

There are no clear boundaries between different types of water masses, differing in origin, but there are transition zones. They are most pronounced in places where warm and cold currents meet. Water masses actively interact with the atmosphere: they give it moisture and heat and absorb carbon dioxide from it, and release oxygen. The most characteristic properties of water masses are salinity and temperature.

Water masses- These are large volumes of water that form in certain parts of the ocean and differ from each other in temperature, salinity, density, transparency, amount of oxygen and other properties. In contrast, it is of great importance in them. Depending on the depth, there are:

Surface water masses... They are formed under the influence of atmospheric processes and the influx of fresh water from the mainland to a depth of 200-250 m. Here salinity often changes, and their horizontal transport in the form of ocean currents is much stronger than deep transport. Surface waters have the highest levels of plankton and fish;

Intermediate water masses... They have a lower boundary in the range of 500-1000 m. In intermediate water masses are formed under conditions of increased evaporation and constant rise. This explains the fact that intermediate waters occur between 20 ° and 60 ° in the Northern and Southern Hemispheres;

Deep water masses... They are formed as a result of mixing of surface and intermediate, polar and tropical water masses. Their lower limit is 1200-5000 m. Vertically, these water masses move extremely slowly, and horizontally they move at a speed of 0.2-0.8 cm / s (28 m / h);

Bottom water masses... They occupy an area below 5000 m and have constant salinity, very high density, and their horizontal movement is slower than vertical.

Depending on the origin, the following types of water masses are distinguished:

Tropical... They form in tropical latitudes. The water temperature here is 20-25 °. The temperature of tropical water masses is greatly influenced by ocean currents. The western parts of the oceans are warmer, where warm currents (see) come from the equator. The eastern parts of the oceans are colder as cold currents come here. Seasonally, the temperature of tropical water masses changes by 4 °. The salinity of these water masses is much higher than that of the equatorial ones, since as a result of the descending air currents, little precipitation is established and falls here;

water masses... In the temperate latitudes of the Northern Hemisphere, the western parts of the oceans, where cold currents pass, are cold. The eastern regions of the oceans are warmed by warm currents. Even in winter months the water in them has a temperature of 10 ° C to 0 ° C. In summer, it changes from 10 ° C to 20 ° C. Thus, the temperature of the temperate water masses differs by 10 ° C over the seasons. They are already characterized by the change of seasons. But it comes later than on land, and is not so pronounced. The salinity of temperate water masses is lower than that of tropical ones, since the desalination effect is exerted not only by rivers and atmospheric precipitation that fall here, but also entering these latitudes;

Polar water masses... Formed in and off the coast. These water masses can be carried away by currents to temperate and even tropical latitudes. In the polar regions of both hemispheres, water cools down to -2 ° C, but still remains liquid. Further lowering leads to the formation of ice. Polar water masses are characterized by an abundance of floating ice, as well as ice that forms huge ice spaces. It stays in ice all year round and is in constant drift. In the Southern Hemisphere, in the regions of polar water masses, they enter the temperate latitudes much further than in the Northern. The salinity of polar water masses is low, since ice has a strong desalination effect. There are no clear boundaries between the listed water masses, but there are transition zones - zones of mutual influence of neighboring water masses. They are most pronounced in places where warm and cold currents meet. Each water mass is more or less homogeneous in its properties, but in the transition zones, these characteristics can change dramatically.

Water masses actively interact with: they give it heat and moisture, absorb carbon dioxide from it, and release oxygen.

LESSON 9

Topic: Water masses and their properties

goal: to update knowledge about the properties of the waters of the World Ocean; to formulate knowledge about water masses and their characteristic features; promote understanding of the patterns of movement of ocean currents; improve the ability to work with thematic maps of the atlas; develop research ability, the ability to define concepts, make generalizations, draw analogies, establish causal relationships, draw conclusions; educate independence, responsibility, attentiveness.

Equipment: physical map of the world, textbooks, atlases, contour maps.

Lesson type: combined.

Expected results: students will be able to give examples of water masses of different properties, compare their properties; show on the map the largest warm and cold surface currents and explain their movements.

During the classes

І . organizational issues

ІІ ... Updating basic knowledge and skills

Examination homework

Working in pairs

Reception "Mutual questioning", "Mutual check"

Pupils exchange notebooks, and decide, prepared at home, test tasks, check the correctness of their implementation with each other.

Reception "Why Much"

Why do air temperatures change from the equator to the poles?

Why do air masses have different properties?

Why are air masses constantly moving?

Why trade winds are northeast and southeast

direction?

Why are monsoons formed?

Why is the amount of precipitation near the equator, and in tropical latitudes

Reception "Problem issue"

Why isotherms on climate maps change their latitudinal extent to meandering?

III ... Motivation of educational and cognitive activities

Reception "Practicality of the theory"

Now you know that the climate is formed under the influence of three main climate-forming factors that interact with each other and create conditions for the formation of various climatic conditions on Earth.

In the course of studying the characteristics of climate-forming factors, we have repeatedly noted the role of air masses that form over the oceans and bring moisture to the continents. In order to understand what role the oceans play in the formation of the climate and life of the planet as a whole, we will learn more about the main component of the nature of the World Ocean - its water masses.

І V. Learning new material

1 Formation of the concept of "water masses"

Exercise. Remember what air masses are and their types. Similar to the concept of air masses formed in the air ocean, water masses are distinguished in the World Ocean.

Water masses- large volumes of water formed in certain parts of the ocean and differ from each other:

Temperature

Salinity,

Density,

Transparency,

The amount of oxygen and other properties.

According to the regions of their formation, the following types of water masses are distinguished:

Polar,

Moderate,

Tropical,

Equatorial, which in turn are divided into subtypes:

Coastal

Intraoceanic.

Water masses also change with depth: they distinguish

superficial

intermediate,

deep

bottom water masses.

The thickness of the layer of surface water masses reaches 200-250 m. Being in constant contact with the atmosphere, they change most of their characteristics during the year, actively moving in space.

The main properties of water masses are temperature and salinity. .

Conclusion 1... In the World Ocean, significant volumes of water are formed with certain properties - water masses. The properties of water masses change depending on the depth and place of their formation.

2 Updating knowledge about the basic properties of water masses

Working with the map "Average annual salinity of waters on the surface of the World Ocean"

Exercise

1) Determine the regularities of the distribution of the salinity of the surface waters of the World Ocean.

2) Explain the factors behind this distribution.

The average salinity of ocean waters is 35 ‰.

In equatorial latitudes, salinity is slightly reduced due to the intensity of the desalination effect of atmospheric precipitation.

In subtropical and tropical latitudes, salinity is increased- here evaporation prevails over precipitation, increases the concentration of salts.

In temperate latitudes, salinity is close to average.

Salinity decreases in high latitudes due to low evaporation, melting sea ice, river runoff (in the Northern Hemisphere).

The salinity of the surface waters of the oceans under the influence of a number of factors varies within fairly wide ranges - from 31 ‰ in the Gulf of Guinea to 42 ‰ in the Red Sea... At depths over several hundred meters, it almost everywhere approaches 34.8 ‰, and from a depth of 1500 m to the bottom it is 34.5 ‰.

Conclusion 2. The salinity of the surface water masses of the ocean primarily depends on climatic conditions, which vary with geographical latitude. The distribution of salinity is also influenced by currents and the degree of enclosure of sea basins, especially for inland seas.

Exercise... Analyze the map of the indicators of the average annual temperature of the surface waters of the World Ocean and explain the reasons for the changes in these indicators.

In the equatorial latitudes, the surface water temperature throughout the year is 27-28 ° C.

In tropical zones, the average is 20-25 ° C.

However, it is in these latitudes that the highest average annual temperatures were recorded (in the Persian Gulf - 37 ° С, in the Red Sea - 32 ° С).

The temperate latitudes are characterized by seasonal changes in water temperatures, and the average annual gradually decreases towards the poles from 10 to 0 ° С.

In the polar latitudes, the temperature of the ocean waters during the year varies from 0 to -2 ° C. At a temperature of about -2 ° C, the seawater of average salinity freezes (the higher the salinity, the lower the freezing point).

Consequently, the temperature of the surface water layer depends on the climate and decreases from the equator to the poles.

The average temperature of the surface layer of ocean waters is 17-54 ° C. With depth, the water temperature drops rather quickly to a depth of 200 m, from 200 to 1000 m - more slowly. At depths of more than 1000 m, the temperature is approximately 2 ... + 3 ° C.

The average temperature of the entire mass of water in the ocean is 4 ° C.

Oceanic water has a huge heat capacity of 1 m3 of water, cooling by 1 ° C, it can heat more than 3300 m3 of air by 1 ° C.

Conclusion 3... The temperature distribution of the surface waters of the World Ocean has a zonal character. Water temperature decreases with depth.

3 Currents in the World Ocean

Even in ancient times, people established that thanks to the wind that blows over the sea, not only waves arise, but also currents that play huge role in the process of heat distribution on the Earth.

Ocean currents- horizontal displacement of huge water masses in a certain direction over long distances.

Exercise. Compare climatic and physical map, determine the relationship between constant winds and surface currents.

Conclusion 4. The direction of the largest sea currents almost coincides with the main air currents of the planet. The most powerful surface currents are formed by two types of winds: westerly, which blow from west to east, and trade winds, blowing from east to west.

According to the properties of water, warm and cold currents are distinguished. the interaction of atmospheric flows leads to the formation of a system of gyres of surface currents.

V. Consolidation of the studied material

Reception "Geographic workshop" (subject to availability of study time)

Exercise... Using the maps of salinity and temperature of surface waters and the text of the textbook, make a characteristic of the water masses. Enter the results in the table.

Reception "Blitzopros"

What are water masses? Are the types of water masses distinguished in the World Ocean?

What determines the distribution of the salinity of the waters of the World Ocean?

How and why does the water temperature change from the equator to the poles and with depth?

Give examples of currents whose names coincide with the names of the winds that formed.

VІ ... ANDtog lesson, Preflection

What new discoveries have you made for yourself today in the lesson?

VІІ ... HOMEWORK

1. Develop an appropriate paragraph of the textbook.

2. Mark on outline map the largest warm and cold currents of the World Ocean.

3. Get together in groups for the next lesson.

4. Conduct research: "Interaction of the World Ocean, atmosphere

and sushi, its consequences ”. Format the results in the form of a diagram (or a figure) with appropriate comments.

Surface water masses... They are formed under the influence of atmospheric processes and the influx of fresh water from the mainland to a depth of 200-250 m. Here salinity often changes, and their horizontal transport in the form of ocean currents is much stronger than the deep transport. Surface waters have the highest levels of plankton and fish;

Intermediate water masses... They have a lower boundary within 500-1000 m. In tropical latitudes, intermediate water masses are formed under conditions of increased evaporation and constant rise. This explains the fact that intermediate waters occur between 20 ° and 60 ° in the Northern and Southern Hemispheres;

Bottom water masses... They occupy an area below 5000 m and have constant salinity, very high density, and their horizontal movement is slower than vertical.

Depending on the origin, the following types of water masses are distinguished:

water masses... In the temperate latitudes of the Northern Hemisphere, the western parts of the oceans, where cold currents pass, are cold. The eastern regions of the oceans are warmed by warm currents. Even in the winter months, the water in them has a temperature of 10 ° C to 0 ° C. In summer, it changes from 10 ° C to 20 ° C. Thus, the temperature of the temperate water masses differs by 10 ° C over the seasons. They are already characterized by the change of seasons. But it comes later than on land, and is not so pronounced. The salinity of temperate water masses is lower than that of tropical ones, since the desalination effect is exerted not only by rivers and atmospheric precipitation that fall here, but also entering these latitudes;

Polar water masses... Formed in and off the coast. These water masses can be carried out by currents to temperate and even tropical latitudes. In the polar regions of both hemispheres, water cools down to -2 ° C, but still remains liquid. Further lowering leads to the formation of ice. Polar water masses are characterized by an abundance of floating ice, as well as ice that forms huge ice spaces. It stays in ice all year round and is in constant drift. In the Southern Hemisphere, in the regions of polar water masses, they enter the temperate latitudes much further than in the Northern. The salinity of polar water masses is low, since ice has a strong desalination effect. There are no clear boundaries between the listed water masses, but there are transition zones - zones of mutual influence of neighboring water masses. They are most pronounced in places where warm and cold currents meet. Each water mass is more or less homogeneous in its properties, but in the transition zones, these characteristics can change dramatically.

Water masses actively interact with: they give it heat and moisture, absorb carbon dioxide from it, and release oxygen.

Under the influence of certain geophysical factors. The water mass is characterized by a constant and continuous distribution of physicochemical and biological properties for a long time. All components of the water mass form a kind of a single complex that can change or move as a whole. Unlike air masses, vertical zoning plays a rather important role for masses.

The main characteristics of the water masses:

water temperature,
content of biogenic salts (phosphates, silicates, nitrates),
content of dissolved gases (oxygen, carbon dioxide).

The characteristics of the water masses do not remain constant all the time; they fluctuate within certain limits over the seasons and over the years. There are no clear boundaries between the water masses, instead there are transition zones of mutual influence. This can be most clearly observed at the border of warm and cold sea currents.

The main factors in the formation of water masses are the heat and water balances of the region.

Water masses interact quite actively with the atmosphere. They give it heat and moisture, biogenic and mechanical oxygen, and from it they assimilate carbon dioxide.

Classification

Distinguish between primary and secondary water masses. The former include those whose characteristics are formed under the influence of the earth's atmosphere. They are characterized by the greatest amplitude of changes in their properties in a certain volume of the water column. Secondary water masses include those that are formed under the influence of mixing of the primary. They are characterized by the greatest homogeneity.

In terms of depth and physical and geographical properties, the following types of water masses are distinguished:

superficial:
- surface (primary) - up to depths of 150-200 m,
- sub-surface (primary and secondary) - from 150-200 m to 400-500 m;
intermediate (primary and secondary) - the middle layer of oceanic waters with a thickness of about 1000 m, at depths from 400-500 m to 1000-1500 m, the temperature of which is only a few degrees above the freezing point of water; constant boundary between surface and deep waters, which prevents their mixing;
deep (secondary) - at a depth of 1000-1500 m to 2500-3000 m;
bottom (secondary) - deeper than 3 km.

Spreading

Types of surface water masses

Equatorial

Throughout the year, the equatorial waters are strongly warmed by the sun, which is at its zenith. Layer thickness - 150-300 g. Horizontal movement speed ranges from 60-70 to 120-130 cm / sec. Vertical stirring occurs at a speed of 10 -2 10 -3 cm / sec. Water temperature is 27 ° ... + 28 ° C, seasonal variability is small 2 ° C. The average salinity is from 33-34 to 34-35 ‰, lower than in tropical latitudes, because numerous rivers and strong daily rainfalls quite strongly affect, freshening the upper layer of water. Conditional density 22.0-23.0. Oxygen content 3.0-4.0 ml / l; phosphates - 0.5-1.0 μg-at / l.

Tropical

Layer thickness - 300-400 g. Horizontal movement speed ranges from 10-20 to 50-70 cm / sec. Vertical stirring occurs at a speed of 10 -3 cm / sec. The water temperature ranges from 18-20 to 25-27 ° C. Average salinity 34.5-35.5 ‰. Conditional density 24.0-26.0. Oxygen content 2.0-4.0 ml / l; phosphates - 1.0-2.0 μg-at / l.

Subtropical

Layer thickness - 400-500 g. Horizontal speed of movement is from 20-30 to 80-100 cm / sec. Vertical stirring occurs at a speed of 10 -3 cm / sec. The water temperature ranges from 15-20 to 25-28 ° C. Average salinity from 35-36 to 36-37 ‰. Conditional density from 23.0-24.0 to 25.0-26.0. Oxygen content 4.0-5.0 ml / l; phosphates -

Subpolar

The thickness of the layer is 300-400 g. The horizontal speed of movement is from 10-20 to 30-50 cm / sec. Vertical stirring occurs at a speed of 10 -4 cm / sec. The water temperature ranges from 15-20 to 5-10 ° C. Average salinity 34-35 ‰. Conditional density 25.0-27.0. Oxygen content 4.0-6.0 ml / l; phosphates - 0.5-1.5 μg-at / l.

Literature

Emery, W. J. and J. Meincke. 1986 Global water masses: summary and review. Oceanologica Acta 9: -391.
(rus.) Agenorov V.K.On the main water masses in the hydrosphere, M. - Sverdlovsk, 1944.
(rus.) Zubov N.N. Dynamic Oceanology. M. - L., 1947.
(rus.) Muromtsev A.M. The main features of the hydrology of the Pacific Ocean, L., 1958.
(rus.) Muromtsev A.M. The main features of the hydrology of the Indian Ocean, L., 1959.
(rus.) Dobrovolsky A.D. On the determination of water masses // Oceanology, 1961, vol. 1, issue 1.
(German) Defant A., Dynamische Ozeanographie, B., 1929.
(English) Sverdrup H. U., Jonson M. W., Fleming R. N., The oceans, Englewood Cliffs, 1959.

The entire mass of the waters of the World Ocean is conventionally subdivided into surface and deep. Surface waters - a layer 200–300 m thick - are very heterogeneous in their natural properties; they can be called oceanic troposphere. The rest of the waters - oceanic stratosphere, constituting the main mass of waters, more homogeneous.

Surface waters - a zone of active thermal and dynamic interaction

ocean and atmosphere. In accordance with zonal climatic changes, they are subdivided into different water masses, primarily according to their thermohaline properties. Water masses- These are relatively large volumes of water that form in certain zones (foci) of the ocean and have stable physicochemical and biological properties for a long time.

Allocate five types water masses: equatorial, tropical, subtropical, subpolar and polar.

Equatorial water masses(0-5 ° N) form inter-trade countercurrents. They have constantly high temperatures (26-28 ° C), a pronounced layer of temperature jump at a depth of 20-50 m, low density and salinity - 34 - 34.5 ‰, low oxygen content - 3-4 g / m 3, small saturation with life forms. The rise of water masses prevails. In the atmosphere above them there is a belt of low pressure and calm.

Tropical water masses(5– 35 ° N NS. and 0-30 ° S. sh.) are distributed along the equatorial periphery of subtropical baric maxima; they form trade wind currents. The temperature in summer reaches +26 ... + 28 ° С, in winter it drops to +18 ... +20 ° С, and it differs off the western and eastern coasts due to currents and coastal stationary upwellings and downwellings. Upwelling(eng, upwelling- surfacing) - an ascending movement of water from a depth of 50–100 m, generated by off-set winds off the western coasts of the continents in a strip of 10–30 km. Having a low temperature and, in connection with this, a significant oxygen saturation, deep waters rich in biogenic and mineral substances, entering the surface illuminated zone, increase the productivity of the water mass. Downwellings- downdrafts off the eastern coasts of the continents due to the surge of water; they carry heat and oxygen down. The layer of the temperature jump is expressed throughout the year, the salinity is 35–35.5 ‰, the oxygen content is 2–4 g / m 3.

Subtropical water masses possess the most characteristic and stable properties in the "core" - circular areas bounded by large currents. The temperature during the year varies from 28 to 15 ° C, there is a layer of temperature jump. Salinity 36–37 ‰, oxygen content 4–5 g / m 3. In the center of the gyres, the waters sink. In warm currents, subtropical water masses penetrate into temperate latitudes up to 50 ° C. NS. and 40–45 ° S. NS. These transformed subtropical water masses occupy here almost entirely the waters of the Atlantic, Pacific and Indian oceans. As they cool down, subtropical waters give off a huge amount of heat to the atmosphere, especially in winter, playing a very significant role in planetary heat exchange between latitudes. The boundaries of subtropical and tropical waters are rather arbitrary, therefore some oceanologists combine them into one type of tropical waters.

Subpolar- subarctic (50 - 70 ° N) and subantarctic (45–60 ° S) water masses. For them, a variety of characteristics is typical both for the seasons of the year and for the hemispheres. The temperature in summer is 12–15 ° С, in winter 5–7 ° С, decreasing towards the poles. Sea ice almost never happens, but there are icebergs. The temperature jump layer is expressed only in summer. Salinity decreases from 35 to 33 ‰ towards the poles. The oxygen content is 4 - 6 g / m 3, so the waters are rich in life forms. These water masses occupy the North Atlantic and Pacific Ocean, penetrating in cold currents along the eastern coasts of the continents to temperate latitudes. In the southern hemisphere, they form a continuous zone south of all continents. In general, this is the western circulation of air and water masses, a strip of storms.

Polar water masses in the Arctic and around Antarctica, they have low temperatures: in summer about 0 ° С, in winter –1.5 ... –1.7 ° С. Brackish sea and fresh continental ice and their fragments are constant here. There is no temperature jump layer. Salinity 32–33 ‰. The maximum amount of oxygen is dissolved in cold waters - 5–7 g / m 3. At the border with subpolar waters, a sinking of dense cold waters is observed, especially in winter.

Each water mass has its own focus of formation. When water masses meet with different properties formed oceanological fronts, or convergence zones (lat. converge- converge). They usually form at the junction of warm and cold surface currents and are characterized by a sinking of water masses. There are several frontal zones in the World Ocean, but the main ones are four, two in the northern and southern hemispheres. In temperate latitudes, they are expressed off the eastern coasts of the continents at the boundaries of the subpolar cyclonic and subtropical anticyclonic gyres with their respective cold and warm currents: near Newfoundland, Hokkaido, the Falkland Islands and New Zealand. In these frontal zones, hydrothermal characteristics (temperature, salinity, density, current velocities, seasonal temperature fluctuations, sizes of wind waves, amount of fog, cloudiness, etc.) reach extreme values. To the east, due to the mixing of the waters, the frontal contrasts are blurred. It is in these zones that frontal cyclones of extratropical latitudes originate. Two frontal zones also exist on both sides of the thermal equator off the western coasts of the continents between tropical relatively cold waters and warm equatorial waters of inter-trade countercurrents. They are also distinguished by high values of hydrometeorological characteristics, high dynamic and biological activity, and intense interaction between the ocean and the atmosphere. These are areas where tropical cyclones originate.

Is in the ocean and divergence zones (lat. diuergento- deviate) - zones of divergence of surface currents and the rise of deep waters: at the western coasts of temperate continents and above the thermal equator at the eastern coasts of the continents. Such zones are rich in phyto- and zooplankton, are distinguished by increased biological productivity and are areas of effective fishing.

The oceanic stratosphere is divided in depth into three layers, differing in temperature, illumination and other properties: intermediate, deep and bottom waters. Intermediate waters are located at depths from 300–500 to 1000–1200 m. Their thickness is maximal in polar latitudes and in the central parts of anticyclonic gyres, where water subsidence prevails. Their properties are somewhat different depending on the breadth of distribution. The general transport of these waters is directed from high latitudes towards the equator.

Deep and especially near-bottom waters (the thickness of the latter layer is 1000–1500 m above the bottom) are distinguished by high uniformity (low temperatures, oxygen richness) and a slow speed of movement in the meridional direction from polar latitudes to the equator. Especially widespread are Antarctic waters, "sliding" from the continental slope of Antarctica. They not only occupy the entire southern hemisphere, but also reach 10–12 ° N. NS. v Pacific, up to 40 ° N NS. in the Atlantic and to the Arabian Sea in the Indian Ocean.

From the characteristics of water masses, especially surface ones, and currents, the interaction of the ocean and the atmosphere is clearly visible. The ocean gives the atmosphere the bulk of the heat, converting the sun's radiant energy into thermal energy. The ocean is a huge distiller that supplies the land with fresh water through the atmosphere. The heat entering the atmosphere from the oceans causes different atmospheric pressures. Due to the difference in pressure, wind is generated. It causes excitement and currents that transfer heat to high latitudes or cold to low latitudes, etc. The processes of interaction between the two shells of the Earth - the atmosphere and the oceanosphere - are complex and diverse.

As a result of dynamic processes occurring in the oceanic water column, more or less mobile stratification of waters is established in it. This stratification leads to the isolation of the so-called water masses. Water masses are waters characterized by their inherent conservative properties. Moreover, water masses acquire these properties in certain areas and retain them within the entire space of their distribution.

According to V.N. Stepanov (1974), differ: surface, intermediate, deep and bottom water masses. The main types of water masses can, in turn, be subdivided into varieties.

Surface water masses are characterized by the fact that they are formed by direct interaction with the atmosphere. As a result of interaction with the atmosphere, these water masses are most susceptible to: agitation by waves, changes in the properties of ocean water (temperature, salinity and other properties).

The thickness of the surface masses is on average 200-250 m. They are also distinguished by the maximum transfer intensity - on average, about 15-20 cm / s in the horizontal direction and 10 10-4 - 2 10-4 cm / s in the vertical direction. They are subdivided into equatorial (E), tropical (ST and YT), subarctic (SbAr), subantarctic (SbAn), Antarctic (An) and arctic (Ar).

Intermediate water masses are allocated in the polar regions with elevated temperatures, in temperate and tropical regions with low or high salinity. Their upper boundary is the boundary with surface water masses. The lower boundary lies at a depth of 1000 to 2000 m.Intermediate water masses are subdivided into: subantarctic (PSbAn), subarctic (PSbAr), north-Atlantic (PSat), north-Indian Ocean (PSI), Antarctic (PAn) and arctic (PAR) masses.

The main part of the intermediate subpolar water masses is formed due to the subsidence of surface waters in the zones of subpolar convergence. The transfer of these water masses is directed from the subpolar regions to the equator. V Atlantic Ocean subantarctic intermediate water masses pass beyond the equator and are distributed up to about 20 ° N, in the Tikhiy - to the equator, in the Indian - up to about 10 ° S. Subarctic intermediate waters in the Pacific Ocean also reach the equator. In the Atlantic Ocean, they quickly sink and are lost.

In the northern part of the Atlantic and Indian Oceans, the intermediate masses have a different origin. They form even on the surface in areas of high evaporation. As a result, excessively salty waters are formed. Due to their high density, these salty waters experience slow sinking. Added to these are dense salt waters from the Mediterranean Sea (in the North Atlantic) and from the Red Sea and the Persian and Oman Gulfs (in the Indian Ocean). In the Atlantic Ocean, intermediate waters flow beneath the surface layer north and south of the latitude of the Strait of Gibraltar. They spread between 20 and 60 ° N. In the Indian Ocean, these waters spread to the south and southeast up to 5-10 ° S latitude.

The circulation pattern of intermediate waters was revealed by V.A. Burkov and R.P. Bulatov. It is distinguished by an almost complete attenuation of wind circulations in the tropical and equatorial zones and a slight shift of subtropical gyres towards the poles. In this regard, intermediate waters from the polar fronts spread to tropical and subpolar regions. The same circulation system includes subsurface equatorial countercurrents of the Lomonosov flow type.

Deep water masses are formed mainly at high latitudes. Their formation is associated with the mixing of surface and intermediate water masses. They usually form offshore. Cooling down and, accordingly, acquiring a high density, these masses gradually slide down the continental slope and spread towards the equator. The lower boundary of deep waters is located at a depth of about 4000 m. The intensity of deep water circulation was studied by V.A. Burkov, R.P. Bulatov and A.D. Shcherbinin. It weakens with depth. The main role in the horizontal movement of these water masses is played by: southern anticyclonic gyres; circumpolar deep current in the Southern Hemisphere, which provides deep water exchange between the oceans. The speeds of horizontal movement are approximately 0.2-0.8 cm / s, and vertical speeds 1 10-4 to 7 10O4 cm / s.

Deep water masses are subdivided into: the circumpolar deep water mass of the Southern Hemisphere (GCP), the North Atlantic (GSAT), the North Pacific (GST), the North Indian Ocean (GSI) and the Arctic (GAR). Deep North Atlantic waters are characterized by increased salinity. (up to 34.95%) and temperature (up to 3 °) and slightly increased travel speed. Their formation involves: waters of high latitudes, cooled on the polar shelves and sinking with mixing of surface and intermediate waters, heavy salty waters of the Mediterranean, rather salty waters of the Gulf Stream. Their sinking intensifies as they move to higher latitudes, where they experience gradual cooling.

Circumpolar deep waters are formed exclusively due to the cooling of waters in the Antarctic regions of the World Ocean. The northern deep masses of the Indian and Pacific Oceans are of local origin. In the Indian Ocean due to the runoff of saline waters from the Red Sea and the Persian Gulf. In the Pacific Ocean, mainly due to the cooling of waters on the shelf of the Bering Sea.

The bottom water masses are distinguished by the lowest temperatures and the highest density. They occupy the rest of the ocean deeper than 4000 m. These water masses are characterized by very slow horizontal movement, mainly in the meridional direction. Bottom water masses are distinguished by slightly larger values of vertical movement, in comparison with deep water masses. These values are due to the influx of geothermal heat from the ocean floor. These water masses are formed due to the subsidence of the overlying water masses. Among the bottom water masses, the most widespread are the bottom Antarctic waters (PrAn). These waters are well traced by the lowest temperatures and relatively high oxygen content. The center of their formation is the Antarctic regions of the World Ocean and, in particular, the Antarctic shelf. In addition, the North Atlantic and North Pacific bottom water masses (PrSat and PrST) are distinguished.

Bottom water masses are also in a state of circulation. They are characterized predominantly by northward meridional transport. In addition, in the northwestern part of the Atlantic, a southerly current is clearly expressed, fed by the cold waters of the Norwegian-Greenland Basin. The speed of movement of the bottom masses slightly increases when approaching the bottom.

The main types of water masses in latitude. Water masses

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Types

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What are water masses?

What are water masses and their types? The main types of water masses

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