What is the Earth's hydrosphere: description, diagram, components and human influence

Hydrosphere (from Greek hydro - water and sphaira - ball) - the water shell of the Earth. It consists of the oceans, land waters - rivers, lakes, glaciers, as well as groundwater that is everywhere: on land, deeper than lake and sea depressions, under the thickness of mountain and continental ice.

The concept of the hydrosphere was first introduced in scientific literature E. Suess in 1875, who understood it as a single water shell of the planet, mainly consisting of the waters of the oceans. In 1910, a broader interpretation was presented by J. Murray; he included the waters of rivers and lakes, the atmosphere, the cryosphere and the biosphere into the hydrosphere. Such a broad interpretation of the hydrosphere was not unconditionally accepted by researchers. The differences between subsequent definitions of the hydrosphere concerned mainly its continuity, the lower and upper boundaries of its distribution, and the possibility of referring chemically and biologically related waters to it.

In the Earth sciences, the hydrosphere is understood as a discontinuous surface shell, consisting of the water of the seas and oceans, surface water land masses, temporary and permanent streams, solid water in the form of snow and ice. Along with the surface, there is also an underground hydrosphere, which includes ground and underground, including artesian waters. total weight water in the hydrosphere is estimated at 2 * 10 24 g. In the World Ocean, it accounts for about 67%, in the lithosphere - about 30%, in continental ice and groundwater - a little more than 2%, and in land waters - about 1%.

The hydrosphere of the land is made up of rivers, lakes, swamps, glaciers, snow cover and The groundwater.

Rivers are permanent watercourses that collect atmospheric precipitation and groundwater from vast areas ( watersheds) and producing a huge geological work. They erode the rocks of the land and carry the destroyed particles from one place to another. Rivers have great importance for humanity. They fertilize the soil and level the earth's surface, they are transport highways, they provide electricity.

Each river during the year is characterized by an alternation of floods (floods) and low level water (low water). The amount of water during floods increases tenfold. The time of manifestation of the flood and its duration depend on the feeding of the rivers.

Important characteristics of rivers are surface runoff and water discharge. Under the channel runoff is understood the amount of water carried by the river flow for a certain period of time. The solid runoff of a river is the amount of solid and dissolved substances moved by the river over a certain period of time.

Water moving along the uneven surface of the earth in the form of slope runoff, accumulating, forms streams. The water collected in streams has a greater volume and greater velocity and begins to act as an erosive agent. Streams change the configuration of the primary slopes, eroding ravines, turning them into small valleys. The greatest erosion occurs on slopes devoid of vegetation.

Lakes - natural reservoirs in relief depressions (hollows), having a tectonic, glacial, river (oxbow lake), sinkhole, volcanic or artificial origin, filled with stagnant or weakly running water and not connected to the oceans. Lakes occupy about 2.5% of the land area. The largest of them are the Caspian Sea, the Upper North America, Victoria in Africa, Aral in Central Asia, Baikal In Siberia.

Most of the lakes are located in areas of Quaternary glaciation - the lakes of the Scandinavian Peninsula and the north of the European part of Russia, the north of the USA and Canada. There are lakes in all natural areas regardless of terrain height. The highest mountain lake is Lake Titicaca in the Andes (altitude 3812 m above sea level), and the lowest occurrence is the Dead Sea in the Arabian Peninsula (395 m below sea level). The deepest lake is Baikal (1741 m).

Swamps - excessively wet areas earth's surface overgrown with moisture-loving vegetation. The total area of ​​swamps on the Earth's surface is 2 million km2. They are located in areas where the groundwater level is near the surface. By location and conditions water supply distinguish between raised, intermediate, lowland and coastal swamps. Raised bogs are located on leveled watersheds, on river terraces and on the slopes of hills. They are fueled precipitation. Intermediate marshes are fed by both precipitation, and groundwater. lowland swamps located in relief depressions and often appear on the site of shallow and overgrown lakes. They feed on precipitation, groundwater and surface water. Seaside swamps occupy low-lying sea coasts in areas with humid climate. In areas with tropical climate they are covered with mangroves and sometimes flooded by the tides.

Wetlands play an important hydrological role and are stable sources of rivers. They regulate floods and contribute to the self-purification of river waters.

Glaciers form in places with low negative temperatures as a result of many years of accumulation of snow masses. They are present in all high mountain areas, in Antarctica, Greenland and on the polar islands. Glaciers occupy 16.1 million km2, or 11% of the land area, and their total ice volume is 30 million km3.

The altitude position of glaciers depends on the climate. They occupy the lowest position in the subpolar regions and descend to the level of the World Ocean, forming icebergs (Greenland, Antarctica).

Glaciers are divided into terrestrial ice sheets, shelf and mountain. Among the latter, valley, peretny, car, hanging, hatching are distinguished. Feature glaciers - their ability as a result of viscoplastic flow and under the influence of gravity to move from areas of nutrition. The speed of movement of glaciers varies greatly. Almost a quarter of the land is occupied soil ice or permafrost soils.

The bulk of Russia's glaciers are concentrated on the Arctic islands (Novaya Zemlya, Severnaya Zemlya, Franz Josef Land, Wrangel Island, New Siberian Islands) and in mountainous regions (Greater Caucasus, Altai, mountains of Kamchatka, South and Northeast Siberia, Koryak Highlands, Sayans, Urals, Stanovoy Ridge).

Groundwater is one of the natural resources on which the lives of a significant part of the population currently depend the globe. Under the earth's surface is about 37 times more water than in all the rivers, lakes and swamps of the world. The bulk of groundwater is of atmospheric origin. However, in addition to it, there is buried (relict) water that has been preserved between rock particles since sedimentary rocks arose, and magmatic (juvenile) water, that is, water coming from molten magmatic bodies.

Groundwater supplies many cities, it is widely used in agriculture and industry. Wells, springs and artesian wells provide an average of about 150 million m 3 of water per day.

In areas composed of easily permeable and soluble rocks, caves and cavities appear, and karst funnels and depressions form on the surface. Bizarre forms of the earth's surface in places where karst sinkholes develop are called karst relief. It is characterized by a network of numerous short ravines and hollows, karst dips, fields and karst valleys. Under the ground there are karst galleries, voids, grottoes and caves. flowing along the bottom underground rivers and there are cascades of underground waterfalls.

In areas of young volcanic activity, underground thermal waters are found. They pour out to the surface in the form thermal springs and geysers.

Reservoirs are artificially created water landscapes of the surface hydrosphere. According to R.K. Klige, land is characterized by a negative water balance. According to the scientist, the annual reduction in the volume of lakes and groundwater is 38 and 108 km 3 respectively. Losses of lakes are compensated by the creation of reservoirs, canals and irrigation systems. Technogenic lakes include reservoirs created in the channels major rivers in connection with the construction of hydroelectric stations, with the help of which the river flow is regulated.

Reservoirs are classified according to different principles. According to the conditions of water accumulation, it is customary to single out: reservoirs in river valleys blocked by dams; reservoir lakes regulated by dams; bulk reservoirs; reservoirs in places where groundwater comes out, including in karst conditions; reservoirs created in estuaries and coastal areas of the sea, separated from it by dams.

The world's water reserves on Earth are colossal. The total volume of the hydrosphere, according to the latest data given in the table, is about 1390 million km 3. If all the waters of the hydrosphere are evenly distributed over the surface of the Earth, its layer will have a thickness of about 2.5 km (Table 1).

Table 1 - World water reserves

Parts of the hydrosphere	Distribution area, million km 2	Volume of water, thousand km 3	Water layer, m	Share in world reserves, %
From the total water supply	From fresh water
World Ocean
Groundwater (gravitational and capillary)
Mostly fresh groundwater
soil moisture
Glaciers and permanent snow cover. Including:
In Antarctica
In Greenland
On the arctic islands(Canadian Arctic Archipelago, new earth, northern land, Franz Josef Land, Svalbard)
IN mountainous areas outside the Arctic and Antarctic
Ground ice in the permafrost zone
Water reserves in lakes Including:
In fresh
in salty
swamp waters
Waters in riverbeds
Biological water (water contained in living organisms and plants)
Water in the atmosphere
Total water supply
fresh water

It is assumed that this amount of water remains virtually unchanged during geological time, despite the continued inflow of water from the mantle and from the Cosmos (ice nuclei of comets, meteor matter, dust ...) and its loss due to the decomposition of water by photosynthesis and the dissipation of light gases into space. However, the ratio of its individual species listed in Table 2.1 cannot be considered constant and absolutely accurate. It changed in different periods the life of the earth. The data available in the literature on the ratio of parts of the hydrosphere are somewhat different (Figure 1).

Picture 1 - Water resources Earth

IN modern era the main water reserves are concentrated in the World Ocean (96.5%). Fresh water in the hydrosphere is only 2.58% of the total water reserves. Most fresh water is contained in the glaciers and snow cover of Antarctica, the Arctic and mountainous countries (1.78% of the volume of the hydrosphere or 69.3% of the fresh water reserves on Earth). If all the ice is evenly distributed over the surface of the globe, it will cover it with a layer of 53 m, and if these masses of ice are melted, then the level of ice will be evenly distributed over the surface of the globe, it will cover it with a layer of 53 m, and if these masses of ice are melted, then the ocean level will rise by 64 m. Glaciers occupy a special place in the water cycle on Earth, because. they retain moisture in a solid state for many years. On average, a snowflake that falls on a glacier rests there for more than 8,000 years before it turns back into water and enters the active water cycle.

Huge reserves of water are accumulated in the lithosphere. Share of fresh groundwater from general stock fresh water on Earth is 29.4%. Rivers account for 0.006%, fresh lakes - 0.25%, water contained in the atmosphere - 0.03% total fresh water. The share of fresh water suitable for water supply accounts for 4.2 million km 3, or only 0.3% of the volume of the hydrosphere.

An interesting fact is that the largest storage of surface fresh water is Lake Baikal, which contains 1/5 of the world's total surface fresh water reserves. This can be supported by another example. If we assume that the water reserves will be withdrawn from the lake, then the filling of the vacated volume of the lake with all the flowing rivers would occur only in 250-300 years, provided that the water from the lake would not be spent on runoff and evaporation.

VContinental waters 1

V.1 The concept of the hydrosphere 1

V.2 Groundwater 2

V.4 Use of rivers. Channels. Reservoirs 5

V.6Marshes 7

1. inland waters

1. The concept of the hydrosphere

Hydrosphere- water shell of the Earth. It includes all chemically unbound water, regardless of its state of aggregation. The hydrosphere consists of the World Ocean and land waters. The total volume of the hydrosphere is about 1400 million km 3, and the main mass of water - 96.5% - is the water of the World Ocean, salty, undrinkable. Inland waters account for only 3.5%, of which more than 1.7% is contained in the form of ice and only 1.71% in liquid state(rivers, lakes, groundwater). The remaining volume of the Earth's water shell, or hydrosphere, is in a bound state in the earth's crust, in living organisms and in the atmosphere (approximately 0.29%).

Water- a good solvent, a powerful vehicle. It moves huge masses of substances. Water is the cradle of life, without it the existence and development of plants, animals and man, his economic activity is impossible. The hydrosphere is an accumulator of solar heat on Earth, a huge pantry of mineral and human food resources.

The hydrosphere is one. Its unity lies in the common origin of all natural waters from the Earth's mantle, in the unity of their development, in spatial continuity, in the interconnection of all natural waters in the system of the World water cycle (Fig. V.1).

World water cycle- this is a process of continuous movement of water under the influence of solar energy and gravity, covering the hydrosphere, atmosphere, lithosphere and living organisms. From the earth's surface, under the influence of solar heat, water evaporates, and most of it (about 86%) evaporates from the surface of the oceans. Once in the atmosphere, water vapor condenses during cooling, and under the influence of gravity, the water returns to the earth's surface in the form of precipitation. A significant amount of precipitation falls back into the ocean. The water cycle, in which only the ocean and the atmosphere take part, is called the small, or oceanic, water cycle. The land is involved in the global, or large, water cycle: the evaporation of water from the surface of the ocean and land, the transfer of water vapor from the ocean to land, the condensation of vapor, the formation of clouds and precipitation on the surface of the ocean and land. Next is the surface and underground runoff of land waters into the ocean (Fig. V.1). Thus, the water cycle, in which, in addition to the ocean and the atmosphere, land also takes part, is called the global water cycle.

Rice. V.1. World water cycle

In the process of the world water cycle, its gradual renewal takes place in all parts of the hydrosphere. So, underground waters are updated for hundreds of thousands and millions of years; polar glaciers for 8-15 thousand years; waters of the World Ocean - for 2.5-3 thousand years; closed, drainless lakes - for 200-300 years, flowing - for several years; rivers - 12-14 days; atmospheric water vapor - for 8 days; water in the body - in a few hours. The global water cycle connects all the outer shells of the Earth and organisms.

Land waters- is part of the water shell of the Earth. These include groundwater, rivers, lakes, glaciers and swamps. Land waters contain only 3.5% of the total world water reserves. Of these, only 2.5% is fresh water.

The hydrosphere is the body of water between the Earth's atmosphere and the earth's crust, represented by a combination of oceans, seas and continental water masses. The hydrosphere covers 70.8% of the earth's surface. The volume of the hydrosphere is 1370300000 km 3, which is 1/800 of the total volume of the planet. The mass of the hydrosphere is 1.4 ∙ 10 +18 tons, of which 98.31% is in the oceans, seas and groundwater, 1.65% is in the continental ice of the polar regions, and only 0.045% is in fresh waters rivers, swamps and lakes. A small proportion of water is found in the atmosphere and living organisms. Chemical composition hydrosphere approaches the average composition sea ​​water. The hydrosphere is in continuous interaction3 with the atmosphere, the earth's crust and the biosphere.

World water cycle

The water cycle is a process of circulation of water in a geographical envelope, which combines water into a single interconnected system and is the most important component of the metabolism in nature. The main factors that determine this process are solar radiation and gravity. The main components of the cycle are the evaporation of water, the transfer of water vapor over a distance, condensation (thickening) of water vapor, precipitation, infiltration (leakage) of water into the soil and runoff.

The essence of the cycle is that under the influence solar radiation From the surface of the Earth (oceans, land), water evaporates and enters the air in the form of water vapor. Air currents carry it over long distances. In the air, water vapor condenses and turns into droplet-liquid water, which returns as precipitation back to the surface of the Earth.

Depending on the features and scales, large, or general, and small cycles.

A small circulation is a circulation over separate oceans, continents or their parts. Over the oceans, it occurs according to the scheme: ocean - atmosphere - ocean. Water from the ocean in the form of water vapor enters the atmosphere, where it condenses and falls to the surface of the ocean.

The local, or inland, moisture circulation, which occurs only within the land, is also small. The scheme of its movement: land - air - land. Water evaporates from land (from various water bodies, soils, vegetation, etc.), enters the air, condenses, and again returns to land as precipitation.

Until recently, it was believed that as a result of local moisture circulation (repeated circulation of water that comes from the oceans to the continents with air), the number of opals greatly increases. From this came the idea to increase local moisture circulation in order to increase the amount of precipitation in arid regions. This idea is still relevant today. But in Lately it has been proved that the amount of opals does not increase much from local moisture circulation. Water vapor that enters the air from the surface of the land, air currents quickly beyond the boundaries of the continents. Precipitation as a result of local moisture circulation does not exceed 1/3 of all precipitation. However, they are also of great importance for the formation of landscapes.

The big cycle is a complicated process. It includes land and oceans and occurs according to the scheme: oceans - atmosphere - land - oceans. Here the circle closes with a passage through the land, on which the water, before returning to the ocean, passes a series difficult stages. Part of the water that falls on the land surface flows down in the form of surface runoff (through rivers), part seeps into the ground, where it forms an underground runoff and nourishes vegetation. Part of the water, evaporating from land (from soils, water basins) is released into the air. A lot of water returns from the continents to the atmosphere through transpiration (evaporation) by plants (from 200 to 400 g of water is transpired for each gram of dry matter created by the plant), etc.

So sooner or later, in one way or another, the water that comes out of the ocean and falls over the land returns to the ocean again and closes the cycle.

The water cycle in nature is of great importance. The energy of waters that have fallen on land during the cycle is manifested in the formation of relief, erosion of coasts, etc. The water cycle is a powerful conductor from the sea to land. As a component of metabolism, it leads organic life on Earth. Thanks to the water cycle on Earth, there is water on land.

Hydrosphere- from Latin - water shell. For the first time, the concept of the hydrosphere was introduced into scientific literature by E. Suess in 1875, who understood it as a single water shell of the planet, mainly consisting of the waters of the oceans. In 1910, a broader interpretation was presented by J. Murray; he included the waters of rivers and lakes, the atmosphere, the cryosphere and the biosphere into the hydrosphere. Such a broad interpretation of the hydrosphere was not unconditionally accepted by researchers. The differences between subsequent definitions of the hydrosphere concerned mainly its continuity, the lower and upper boundaries of its distribution, and the possibility of referring chemically and biologically related waters to it.

The most physically substantiated is the definition by I.A. Fedoseeva: in a broad sense, the hydrosphere is a continuous shell of the globe, extending down to the upper mantle, where, under conditions high temperatures and pressure, along with the decomposition of water molecules, their synthesis is continuous, and upwards - approximately to the height of the tropopause, above which water molecules undergo photodissipation (decomposition). A narrower definition can be given: the hydrosphere is a continuous shell of the Earth containing water in all three states of aggregation within the World Ocean, cryosphere, lithosphere and atmosphere, which is directly involved in the planetary moisture cycle (hydrological cycle (HC)).

IN general sense HC is a continuous process of circulation and redistribution of all types of natural waters between separate parts of the hydrosphere, establishing certain relationships between them at different scales of averaging. HC provides interconnection and unity of the hydrosphere.

The hydrosphere and the HC are a single self-regulating system consisting of four reservoirs: the ocean, the cryosphere (the Earth's shell containing water in the solid phase), the lithosphere (the surface and ground waters of the land) and the atmosphere.

Over 96% of the hydrosphere are seas and oceans; about 2% - groundwater, about 2% - glaciers, 0.02% - land waters (rivers, lakes, swamps). The total volume of the Earth's hydrosphere is over 1 billion 500 million km3. Of these, in the oceans and seas - 1370 million km 3, in groundwater - about 60 million km 3 in the form of ice and snow - about 30 million km 3, in inland waters- 0.75 million km 3, and in the atmosphere - 0.015 million km 3.

The volume of the hydrosphere is constantly changing. According to scientists, 4 billion years ago its volume was only 20 million km 3, that is, it was almost 7 thousand times less than the modern one. In the future, the amount of water on Earth, apparently, will also increase, given that the volume of water in the Earth's mantle is estimated at 20 billion km 3 - this is 15 times more than the current volume of the hydrosphere. It is believed that the flow of water into the hydrosphere will be carried out from the deep layers of the Earth and during volcanic eruptions.

According to data that takes into account only the proven reserves of groundwater, only 2.8% of the entire planet is fresh water; of which 2.15% is in glaciers and only 0.65% in rivers, lakes, groundwater. The main mass of water (97.2%) is salty. Hydrosphere - single shell, since all waters are interconnected and are in constant large or small cycles. Complete renewal of water occurs in different ways. The waters in the polar glaciers are renewed in 8 thousand years, groundwater - in 5 thousand years, lakes - in 300 days, rivers - in 12 days, water vapor in the atmosphere - in 9 days, and the waters of the World Ocean - in 3 thousand years.

The hydrosphere plays a very important role in the life of the planet: it accumulates solar heat and redistributes it on Earth; Precipitation comes from the oceans to land.

Behind geological history Significant changes took place in the hydrosphere, but little is known about them. It is calculated that in ice ages the amount of ice increased sharply, and due to this, there was a decrease in volume and a decrease in the level of the World Ocean by tens of meters. At present, the hydrosphere is engulfed in unprecedented speed and size transformations associated with human technical activities. About 5 thousand km 3 of water is used annually, and 10 times more is polluted. Some countries have begun to experience shortages of fresh water. This does not mean that there is not enough of it on Earth: it's just that a person has not yet learned how to use it rationally.

The hydrosphere interacts with the lithosphere. This is evidenced by erosive and accumulative processes associated with the work of water. The hydrosphere also interacts with the atmosphere: clouds consist of water vapor evaporated from the surface of the seas and oceans. The hydrosphere also interacts with the biosphere, since living beings inhabiting the biosphere cannot live without water. Interacting with various shells of the planet, the hydrosphere acts, in turn, as part of the integral nature of the earth's surface.

The total water reserves on the Earth during the period of time measured by geological epochs practically do not change, since the flow of water from the earth's interior and outer space to the Earth's surface is very small and is practically compensated by the irretrievable loss of water due to the photodissipation of water vapor in the upper atmosphere. Therefore, the hydrosphere is a quasi-closed system.

Back in 1914, J. Gregory in his work "The Formation of the Earth" wrote that the fundamental difference between the northern and southern hemispheres is the most conspicuous "feature in the plan of the Earth." And indeed, first of all, the figure of the Earth itself is asymmetric, and the northern semi-axis is 70-100 m longer than the southern one, so the polar compression northern hemisphere less than the South. Asymmetry of the North and Southern hemispheres is that the land in the Northern Hemisphere is 39%, and in the Southern - 19%. The uneven distribution of water and land affects many planetary processes, entails asymmetry in the distribution of the components of the geographic envelope and, consequently, the biosphere.

J. Gregory noticed that in 19 out of 20 cases, opposite the land on the opposite side of the Earth, there is water. Lots of water! Our planet, blue from space (due to water), should have been called the planet Water. However, at medium depth MO 3704 m and the diameter of the Earth 12 756 km its layer is only 0.03% of the diameter of the Earth.



Hydrosphere- from Latin - water shell. For the first time, the concept of the hydrosphere was introduced into scientific literature by E. Suess in 1875, who understood it as a single water shell of the planet, mainly consisting of the waters of the oceans. In 1910, a broader interpretation was presented by J. Murray, he included the waters of rivers and lakes, the atmosphere, the cryosphere and the biosphere into the hydrosphere. Such a broad interpretation of the hydrosphere was not unconditionally accepted by researchers. The differences between subsequent definitions of the hydrosphere concerned mainly its continuity, the lower and upper boundaries of its distribution, and the possibility of referring chemically and biologically related waters to it.

The most physically justified is the definition of I. A. Fedoseev: in a broad sense, the hydrosphere is a continuous shell of the globe, extending down to the upper mantle, where, under conditions of high temperatures and pressure, along with the decomposition of water molecules, their synthesis continuously takes place, and upwards - approximately to a height tropopause, above which water molecules undergo photodissipation (decomposition).

A narrower definition can be given hydrosphere - a continuous shell of the Earth containing water in all three states of aggregation within the World Ocean, cryosphere, lithosphere and atmosphere, which is directly involved in the planetary moisture cycle (hydrological cycle).

In a general sense, the hydrological cycle is a continuous process of circulation and redistribution of all types of natural waters between separate parts of the hydrosphere. The hydrological cycle ensures the interconnection and unity of the hydrosphere.

The hydrosphere and the hydrological cycle is a single self-regulating system consisting of four reservoirs: the ocean, the cryosphere (the Earth's shell containing water in the solid phase), the lithosphere (the surface and ground waters of the land) and the atmosphere.

All four reservoirs of the hydrosphere (ocean, continents, cryosphere and atmosphere) are interconnected through a continuous process of circulation and redistribution of natural waters. Despite the closed nature of the system, there is a constant redistribution of water between reservoirs, leading to a change in the water reserves in each individual reservoir over time.

The world ocean occupies 71% of the Earth's surface, land - 29%. The waters of the World Ocean form a continuous body of water, from all sides surrounding the continents separated by it. The uneven distribution of water and land affects many planetary processes, entails asymmetry in the distribution of the components of the geographic envelope and, consequently, the biosphere.

In 1928, the International Hydrographic Bureau adopted the division of the World Ocean according to a number of features into four oceans: the Atlantic, Indian, Pacific and Arctic. The Second International Oceanographic Congress considered it possible to single out the fifth ocean - the Southern.

The Pacific Ocean has the largest area, accounting for almost half of the entire area of ​​the World Ocean and exceeding the area of ​​all the continents and islands. It is also the deepest ocean.

The smallest is the Northern Arctic Ocean, whose area is 12 times less than the area Pacific Ocean. The Arctic Ocean is the only ocean that is completely in the polar region, and therefore has a specific hydrological regime.

The share of shallow depths (up to 500 meters) is only 9.6% of the entire water area of ​​the World Ocean, and the share of the shelf (depths up to 150-200 meters) accounts for less than 7%. Depths of 3000-6000 meters predominate on 73.8% of the area of ​​the World Ocean.

In each ocean, seas can be distinguished - fairly large areas of the ocean, limited by the shores of the continents, islands, bottom elevations and having their own hydrological regime. The area of ​​the seas is 10% of the area of ​​the World Ocean, and the volume of water in them is about 3% of the volume of the World Ocean. According to their location and physical and geographical conditions, the seas are divided into three main groups: inland, marginal and interisland.