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Файл:Fundamentals of Geography. Study guide
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Hydrosphere. The water balance of Earth. World Ocean
41
of mineral and organic origin, which are in suspended state. The transparency
of seawater depends on the content of suspended colloidal particles. Near
continents, there is more suspended material and the transparency of the water decreases there.
“Since water is the most powerful heat sink of the Sun, the scales given above
determine naturally the main role of the oceans in regulating the climate on the
planet. The world ocean reflects about 8 % of solar radiation from its surface. Due
to the high specific heat capacity of water, there is no drastic temperature drop on
the continents. A giant thermostat – the ocean – does not allow continents to over-
heat in summer and supercool in winter.
Ocean waters are heated mainly in the area of equatorial belt (about the band
from 15 ° S to 30 ° S). Ocean currents containing a huge amount of heat play an
important role in the transfer of heat from the equator to the poles. The average
speed of surface currents is about 0.1–0.2 m/s, and in some areas it reaches 3 m/s
(the Gulf Stream).
The average temperature of the entire water column of the World Ocean is
5.7 °C, except the Arctic basin. This is 22.7 °C higher the average atmospheric
temperature by mass.
Speaking about oceans, the average temperature of the water column: in the
Indian is 6.7 °C, in the Atlantic is 5.6 °C, in the Pacific equals to 4.7 °C. The
warmest water surface has been recorded in the Pacific Ocean (19.4 °C), and the
coldest is under the ice layer of the Arctic Ocean (0.75 °C).
Temperature contrasts caused by atmospheric circulation, contrasts of salinity
and uneven heating of the water surface, gravitational forces and their "differences" from the attraction of the Moon and the Sun, and other factors make water
masses of the World Ocean to move a lot. The problem of explaining the modern
circulation of the waters of the World Ocean at the present time cannot be considered as solved even if we take into account very good and promising hypotheses”
(Bobkov, 2012).
“Groundwater forms hydraulic systems, creating layers containing pores,
cracks and other voids, filled with water. These layers are located between
the water-resistant layers. According to the vertical section of the earth's
crust, there are three main zones that differ in the periods of exchange with
surface waters that make up the hydrosphere: an intensive exchange zone
Topic 5
42
located to a depth of 0.5 km, with a period of complete exchange with surface
waters within 1–100 years; the zone of impeded water exchange is at a depth
of 1.5–2 km – with an exchange period of tens and hundreds of thousands of
years; and the zone of passive exchange is at a depth of more than 2 km, with
a period of complete renewal in millions of years. Water mineralization increases from 1 % in the upper zone up to 3,5 % in the deepest layers of the
earth's crust.
As well as other components of the hydrosphere, groundwater represents
the equilibrium of the "water – gases" system containing oxygen and nitrogen
(the active exchange zone), as well as gases in the soil and carbon dioxide. If
you move deeper, you can find hydrogen sulfide, methane and carbon dioxide
in large quantities. Groundwater is perhaps the most unexplored part of the hydrosphere. It is not accidentally that the assessment of the mass of these waters
is ambiguous and comes from determination of water reserves in layers from
2 to 5 km deep. At the same time, the practice of drilling deep wells (in particular, the deepest in the world on the Kola Peninsula in our country, which are
12 km deep) shows that water in the bowels of Earth can exist deeper than 10 km,
being liquid. As it deepens under the influence of high temperature, vaporous
water is formed in the bowels of the earth's crust, and then a steam-water mixture,
which turns into special state and becomes a kind of water plasma” (Astvatsa-
turov, 2006).
The next largest component of the hydrosphere is glacial and snow massifs
in solid state. “The main mass of ice (about 2.6×1022 g of water) is concentrated
in modern glaciers, including the Antarctic ice sheet – 2.4×1022g, Greenland –
0.2×1022g, the rest is in the Arctic, mountain and other snow-ice covers. Snow
and ice surfaces constantly occupy 102.6 million km2 or about 8 % on land and
sea, and in winter periods of the Northern Hemisphere they reach up to 20 % of
the Earth's surface area. The mass of ice is concentrated in the polar and adjacent
(subpolar) regions of our planet – in the Arctic and Antarctic” (Astvatsaturov,
2006). “These huge areas, hit by frosts all year round, have a significant difference, that is in the fact that at the North Pole, under an icy three-meter layer,
there is a multi-kilometer ocean water column, and in Antarctica, under an ice
shell 3–4 km thick, there is a continent (this is the highest continent on the planet,
in terms of geographical location, which determines the severity of the climate,
Hydrosphere. The water balance of Earth. World Ocean
43
where the temperature goes down -80 °C, and the wind speed is up to 80 m/s)”
(Astvatsaturov, 2006).
“The average air temperature in winter in the Central Arctic is -36 °C, and in
the warmest months it is about 0 °C. The climate of Antarctica is much harsher
than weather conditions in the Arctic zone, since conditions in the Arctic in winter are almost similar to ones in Antarctica in summer. At first glance, this is
paradoxical, since in summer Antarctica receives about 7 % more solar heat than
the Arctic (Earth in its rotation around the Sun in June is in aphelion, and in
December in perihelion). This phenomenon is explained by the following: there
is a continent at the South Pole, which is the highest above sea level among the
six continents of Earth (the average height of Antarctica is 2000 m, and the next
highest Asia is 900 m), in this respect the thickness of the continental ice in
the central part, near the geometric center of the continent is 3000–4000 m. The
height of the surface of the ice sheet in the Central Arctic, in the waters of the
Arctic Ocean is only a few meters and almost corresponds to sea level. Due to
the difference in heights, Antarctica on average should be 13 °C colder than the
Arctic (on the tops of the ice mountains and even higher by 25–28 °C). In addition, the Arctic Ocean is freely linked with the Atlantic Ocean over a vast area
between the northern part of Europe and Greenland. Powerful streams of warm
Atlantic water penetrate under the ice of the Arctic Ocean, making the Arctic
climate milder. Equally importantly, the largest rivers of North America and Eurasia flow into the Arctic Ocean, bringing additional heat to the Arctic. The water
temperature in the Arctic Ocean in winter under the ice is about -1 °C (at a salinity of 30 %), and at a depth of more than 100 m it’s about 10 °C” (Astvatsaturov,
2006).
“Seasonal snow cover plays an important role in the thermal regime of the
planet and the flow of rivers, which on average occupies over 40 million km2.
Among the small components of the hydrosphere, first, these are the waters of
lakes, the total mass of which is estimated to be 2.8×1020 g. The area of all
lakes (salty and fresh) on our planet is slightly more than 2 million km2. The
list of largest lakes in the world includes the Caspian Sea, which area is 371 thousand km2. The largest accumulation of large lakes is located in North America,
where Great Lakes were formed in the areas of ancient glaciation and tectonic
faults of the earth's crust. The largest freshwater lake in the world with an
Topic 5
44
area of 82.1 thousand km2 is Lake Verkhnee. But in terms of water volume
(11.6 thousand km3) and maximum depth (406 m), Lake Verkhneye is behind
Lake Baikal (24.0 thousand km3 and 1741 m) and Lake Tanganyika (18.9 thousand km3 and 1435 m). The next in the list is Lake Victoria in Africa which is
69.0 thousand km2 and the Aral Sea with the sadly tragic fate which is 51.0 thou sand
km2. Lake Ladoga, the largest lake in Europe, has an area of 17.7 thousand km2,
the greatest depth is 230 m, then Lake Onega – 9.7 thousand km2. The deepest
lakes in the world are Baikal (1741 m deep), and Tanganyika in Africa (1435 m deep).
The salinity of the lakes is very diverse, and in terms of the concentration of
dissolved substances, they are closer to groundwater than to the ocean. Lake
Victoria in Africa is considered to be the saltiest lake, the water of which is
11 times saltier than the ocean, and Lake Balkhash in Kazakhstan is of rare
quality, the western part of the lake is fresh, and the eastern part is brackish”
(Astvatsaturov, 2006).
There are 2.85 million lakes in Russia: “131 lakes with a surface area of
100 to 1000 km2, 27 lakes with an area of more than 1000 km2 and about
50 thousand lakes with an area of 1 to 100 km2. Swamps are a small part of the
hydrosphere, characterized by a specific selection of vegetation adapted to increased moisture and lack of oxygen in the water. The total area of swamps and
wetlands is about 3 million km2, of which up to 2 million km2 account for the
territory of our country. The mass of water in the swamps is approximately estimated to be 1×1020 g. The soil waters of the hydrosphere provide moisture to
vegetation and subsurface organisms. According to the scientist-hydrologist
M. I. Lvovich, the mass of soil water is 1.0–0.8×1013g” (Astvatsaturov, 2006).
“The rivers of the world, unlike other components of the hydrosphere, are
very diverse according to their characteristics. Such long rivers as the Nile and
the Amazon (more than 6 thousand km long each) together are as long as their
length almost equals to the diameter of our planet, followed by the Mississippi
with Missouri and Yangtze in terms of length. However, regarding the basin
area, the Ob River and the Irtysh River are the second in the world after the two
rivers – the Amazon and the Mississippi with the Missouri; and in terms of
water consumption at the mouth these two “giants” are followed by the Congo
River – 41 thousand m3/s, and the Yangtze – 34 thousand m3/s” (Astvatsaturov,
2006) (Table 5).
Hydrosphere. The water balance of Earth. World Ocean
45
Table 5
The largest rivers in the world
(according to Mikhailov, Dobrolyubov, 2017)
River
Length,
кm
The area of
the river ba-
sin, thousand. кm2
Water con-
sumption in
the river
mouth, m3/s
Continent
Amazon
(with Maranion)
6437
6915
200000
South
America
Mississippi
(with Missouri)
5971
3268
18000
North
America
Nile
6671
2870
3000
Africa
Yangtze
5800
1808
34000
Asia
Ob (with Irtysh)
5410
2990
12800
Asia
The Yellow River
(or Huang He )
4845
771
1500
Asia
Mekong
4500
810
14800
Asia
Amur
4444
1855
10900
Asia
Lena
4400
2490
16800
Asia
Congo
4370
3820
41000
Africa
The speed of water flow in rivers varies from 0.5–1.0 m/s on the plains to
10 m/s in the mountain streams, and it’ seven times higher in waterfalls.
River waters, usually fresh (with rare exceptions associated with feeding rivers with underground salt water), create a diverse river network on the land surface. So, there are more than fifty large rivers with a length of more than 1000 km
on Earth with a total length of 180 thousand km of their channels. On the territory
of Russia there are about 150 thousand rivers which are 10 km long.
On the territory of our country, water objects are located extremely unevenly,
more than 4/5 of the total river flow is in the basins of the largest rivers of Siberia
Topic 5
46
and the Far East – the Ob, Yenisei, Lena, Amur, etc., while the most populated
part of European Russia, as well as the arid regions of Central Asia and Kazakhstan have relatively small water resources.
However, using indirect methods, hydrologists have calculated that about
2,120 km3 of water is simultaneously concentrated in the beds of all rivers
of the world (at an average water level). Every year, rivers carry more than
45 thousand km3 of water into the ocean. This is relatively small volume,
amounting to about two volumes of the waters of Lake Baikal or the Great
American Lakes. The distribution of river waters across continents is very uneven. Thus, in Europe and Asia, where about 70 % of the world's population
live, only 39 % of the world's river water supply is concentrated.
For a long period in history fresh springs absolutely satisfied the needs of human society in drinking water. However, in the second half of the twentieth century, rapid population growth and the development of scientific and technological
progress led to a sharp increase in freshwater consumption. As a result, there is an
acute problem of shortage of fresh water in the most developed industrial areas of
many countries of the world. A huge amount of water is consumed for industrial
needs in various industries – for agriculture, energy complexes, household needs,
etc. More than 1/3 of the world's population is already experiencing deficiency of
fresh water. Fresh water has become an export item (examples: Hong Kong, transporting water from China, people of the whole of Algeria live thanks to imported
water, etc.). There is no doubt that the consumption of fresh water for the most
diverse needs of mankind will increase in the future, so water is the most precious
recourse in our time. In this regard, an extremely important issue (task) of human
society, in general, is how to stop pollution and preserve water resources.
Practical tasks
Write a report on the water object in your region, that is located the closest to
the place where you live. What role does this water object play? Give its hydrological characteristics.
Project tasks
1. Analyze the water exchange activity of various elements of the water balance.
2. How is the salinity of sea waters formed, what does it depend on, and what
does it affect?
3. What role do ice sheets and polar ice play in the biosphere?
47
T O P I C 6
Th e Ea r th’ s bio s phe r e
The biosphere is a kind of shell of Earth containing the biota of living organisms, that part of the planet's substance which continuously exchanges with
these organisms. The term was first introduced by Austrian scientist E. Suess
(1875), and the modern doctrine of the biosphere was developed by Academician V. I. Vernadsky (1926). He meant that the biosphere was the area of existence
of living matter, which included the lower part of the atmosphere, the entire hydrosphere and the upper part of the lithosphere.
V. I. Vernadsky (in 1978) wrote: "... on the Earth's surface there is no chemical
force more constantly acting, and therefore more powerful in its final products
than living organisms taken as a whole." Thus, he illustrated the huge role of living
organisms in various processes which occur in the biosphere. He also the idea formulated for the first time that the human factor in the development of the biosphere
had become dominant. Therefore, in modern conditions, the doctrine of the biosphere has been of practical importance. Humans, with ever-increasing technical
capabilities, sometimes take too much from nature, without taking into account its
limited ability to reproduce its resources. V. I. Vernadsky's doctrine about the biosphere serves as a scientific foundation for the development of a number of modern global environmental problems.
The substance of the biosphere consists of heterogeneous elements which are
not geologically accidental: living matter, biogenic, inert, biotic, substance in
radioactive decay, etc. (Vernadsky, 1987; Savenko, 2004). Thus, biogenic matter
(substance) (coal, oil, gas, limestones, peat, etc.) is a product made by or of life
forms, and is a source of extremely powerful potential energy. Inert substance is
formed by processes in which living matter did not take part; bioinert substance
is formed simultaneously by stagnant processes and living organisms (weathering
crust, soils, natural waters).
The living substance of the planet. The living matter of the planet is the
most active form of matter in the Universe, it performs colossal geological work
in the biosphere, completely transforming the upper shells of Earth during the
period of its existence. V. I. Vernadsky calculated the total biomass of living
Topic 6
48
matter of the biosphere for the first time i.e. 1015 tons. However, this value
turned out to be somewhat overestimated, it was clarified by the latest calculations made by N. I. Bazilevich, L. E. Rodina and N. N. Rozova (Table 6).
Table 6
Biomass of organisms of Earth
(according to Bazilevich et al., 1971)
Location
Groups of organisms
Weight, tonn
Ratios, %
Continents
Green plants
2,4*1012
99,2
Animals and
microorganisms
0,02*1012
0,8
Total:
2,42*1012
100,0
Oceans
Green plants
0,0002*1012
6,3
Animals and
microorganisms
0,0030*1012
93,7
Total:
0,0032*1012
100,0
Totally in
the biosphere
2,4232*1012
As it can be seen from Table 6, the mass of living matter on the surface of
continents is 800 times higher than the biomass of the World Ocean. On the continents, green plants (99,2 %) strongly predominate in their mass over animals. In
the ocean, the opposite ratio is observed: 93,7 % of the biomass is accounted for
by animals – heterotrophic organisms. This is due to the fact that in the marine
environment there are the most favorable conditions for animals to eat. The smallest plant organisms that make up phytoplankton and live in the illuminated zone
of the seas and oceans are quickly eaten by marine animals and, thus, the transition
of organic substances from plant to animal form dramatically shifts the biomass
towards the predominance of animals.
The Earth's Biosphere
49
Currently, 1.75 million animals and 500 thousand plants are recorded on Earth,
and the most important representatives are given in Table 7.
Table 7
The number of species of the main types of plants and animals
(according to Voitkevich, Vronsky, 1996)
Plants
Animals
Alga
35 000
Protozoans
30 000
Bacteria and fungi
105 000
Sponge
5000
Lichens
26 000
Coelenterates
9000
Bryophyte
25 000
Flatworms
27 000
Club – moss family
970
Nematode
(roundworms)
500 000
Equisetophyta
30–35
Shellfish
107 000
Fernlike
10 000
Arthropods
(except insects)
50 000
Gymnosperms
600
Insects
1 000 000
Angiosperms
250 000
Chordal
46 000
The type of chordates includes the most highly organized animals: fish –
19,000 species, amphibians – 4,300, reptiles – 6,300, birds – 9,000 and mammals –
about 4,000 species. For comparison, we will indicate the number of some animals
in Russia: fish – 2,800 species, reptiles – 92, birds – 720, mammals – 328 species
(Vronsky, 1989).
The circulation of substances in the biosphere is a recurring process of transformation and motion of matter in nature, having a cyclical character. The general
circulation of substances includes separate processes (the circulation of water,
gases, chemical elements), which are not completely reversible, as there is dispersal of matter, changes in its composition, etc. With the evolution of life on Earth,
living organisms began to play a huge role in the circulation of matter (cycles of
nitrogen, oxygen, carbon, phosphorus, sulfur etc.).
Topic 6
50
Global impact, comparable to geological processes, is made by human activity
which, eventually, leads to the development of new migration ways for substances
and changing of those which have existed in nature, to the appearance of new compounds etc. (Vronsky, 1991). A detailed study of all the links of the cycle of substances in the biosphere is a necessary condition for preserving habitable environment.
The water cycle. This is a process of continuous, coupled motion of water on
Earth, occurring under the influence of solar radiation, gravity, vital activity of
living organisms, as well as human economic activity. There are small and large
water cycles. Speaking about a small water cycle, water evaporated from the surface of the ocean partially returns to it, and partially is transferred to the ground.
Here, water falls out in the form of precipitation, feeding rivers and reservoirs,
seeps into soils and underlying rocks, but eventually returns to the ocean by rivers
and underground runoff. According to the calculations made by M. I. Lvovich
(1986), water exchange activity of various parts of the hydrosphere (number of
years) is the following: ocean – 3000, groundwater – 5000, polar glaciers – 8000,
land surface water – 7, rivers – 0.03 and atmospheric vapor – 0.027 years. It can
be seen that the slowest part of the water cycle is the polar glaciers, and the greatest
exchange activity, after atmospheric moisture, is characterized by river waters,
which change on average every 14 days.
The biological cycle. Ecological groups of organisms take part in it such as:
producers (green plants), consumers (animals, part of microorganisms) and decomposers (bacteria, fungi, microorganisms). Recent studies have shown that the
flow of biological elements such as nitrogen, phosphorus, sulfur through populations of microorganisms in the cycle is much higher than through populations of
plants and animals.
An important indicator of the intensity of the biological cycle is the rate of
circulation of chemical elements. The ratio of the mass of the plant litter to the part
of the litter fall that forms the plant litter serves as an indicator of the rate of decomposition of the litter fall and the release of elements. The higher this index is,
the lower the intensity of the biological cycle is in this ecosystem. According to
V. A. Kovda, the largest value of the index (more than 50) is characterized by
swampy forests and tundra. In the dark coniferous forests of the taiga, the index is
10–17, in broad–leaved forests 3–4, in savannas – no more than 0.2. In humid
tropical forests, plant wastes (residues) practically do not accumulate (the index is
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