The surface of the Earth is made of land and water. All the water bodies (71%) on the Earth are together called the hydrosphere. The hydrosphere is often called the "water sphere" as it includes all the earth's water found in streams, lakes, the soil, groundwater, and in the air. The hydrosphere interacts with, and is influenced by, all the other earth spheres. The water of the hydrosphere is distributed among several different stores found in the other spheres. Water is held in oceans, lakes and streams at the surface of the earth. Water is found in vapor, liquid and solid states in the atmosphere. The biosphere serves as an interface between the spheres enabling water to move between the hydrosphere, lithosphere and atmosphere as is accomplished by plant transpiration. The hydrologic cycle traces the movement of water and energy between these various stores and spheres.
Distribution of water
The world's oceans contain 97% of the water in the hydrosphere, most of which is salt water. Ice caps, like that found covering Antarctica, and glaciers that occupy high alpine locations, compose a little less than 2% of all water found on earth. Seemingly a small amount, the water stored as ice in glaciers would have a great impact on the environment if it were to melt into a liquid. One fear is that global warming will cause the melting and collapse of large ice sheets resulting in sea level rise. Rising sea levels could devastate coastal cities, displace millions of people, and wreak havoc on freshwater systems and habitats.
Water beneath the surface comprises the next largest store of water. Groundwater and soil water together make up about .5% of all water (by volume). There is a difference between ground water and soil water. Soil water is the water held in pore spaces between soil particles. Soil pore spaces usually are partially void of water most of the time but fill with water after a rain storm. Groundwater, on the other hand, is found where earth materials are saturated throughout the year. That is, the pore spaces are always occupied with water. Both soil and groundwater are very important sources of water. Soil water is available for plants to extract and use. Groundwater is an important source of water for irrigation and drinking water supplies.
Above the surface water is found stored in streams, rivers and lakes. One might expect that given the large rivers that flow across the earth and the huge numbers of lakes that this store would be rather large. Instead, streams, rivers and lakes only comprise .02% of all water in the earth system. In the atmosphere, only about .0001 % of the water in the hydrosphere is found.
The abundance of water on Earth is a unique feature that clearly distinguishes our "Blue Planet" from others in the solar system. Not a drop of liquid water can be found anywhere else in the solar system. It is because the Earth has just the right mass, the right chemical composition, the right atmosphere, and is the right distance from the Sun (the "Goldilocks" principle) that permits water to exist mainly as a liquid. However, the range of surface temperatures and pressures of our planet permit water to exist in all three states: solid (ice), liquid (water), and gas (water vapor). Most of the water is contained in the oceans and the high heat capacity of this large volume of water (1.35 million cubic kilometers) buffers the Earth surface from large temperature changes such as those observed on the moon. Water is the universal solvent and the basis of all life on our Planet. It is an essential life-sustaining resource which led Benjamin Franklin to comment "When the well's dry, we know the worth of water."
The movement of water around, over, and through the Earth is called the water cycle, a key process of the hydrosphere.
A hydrosphere (Greek hydro means "water") in physical geography describes the collective mass of water found on, under, and over the surface of a planet.Contents
The Earth's hydrosphere consists of water in its liquid, solid, and gaseous forms: the ocean (which comprises the bulk of the hydrosphere), other surface waters including inland seas, lakes, and rivers; rain; underground water; ice (as in glaciers and snow); and atmospheric water vapor (as in clouds). The average depth of the oceans is 3,794 m (12,447 ft), more than five times the average height of the continents. The mass of the oceans is approximately 1.35 × 1018 tonnes, or about 1/4400 of the total mass of the Earth (ranges reported: 1.347 × 1021 to 1.4 × 1021 kg
The abundance of water on Earth is a unique feature that distinguishes our "Blue Planet" from others in the solar system. Approximately 70.8[citation needed] percent (97% of it being sea water and 3% fresh water[2]) of the Earth is covered by water and only 29.2 percent is landmass. Earth's solar orbit, vulcanism, gravity, greenhouse effect, magnetic field and oxygen-rich atmosphere seem to combine to make Earth a water planet.
Earth is actually beyond the outer edge of the orbits which would be warm enough to form liquid water. Without some form of a greenhouse effect, Earth's water would freeze. Paleontological evidence indicates that at one point after blue-green bacteria (Cyanobacteria) had colonized the oceans, the greenhouse effect failed, and Earth's oceans may have completely frozen over for 10 to 100 million years in what is called a snowball Earth event.
On other planets, such as Venus, gaseous water is destroyed (cracked) by solar ultraviolet radiation, and the hydrogen is ionized and blown away by the solar wind. This effect is slow, but inexorable. This is one hypothesis explaining why Venus has no water. Without hydrogen, the oxygen interacts with the surface and is bound up in solid minerals.
In the Earth's atmosphere, a tenuous layer of ozone within the stratosphere absorbs most of this energetic ultraviolet radiation high in the atmosphere, reducing the cracking effect. The ozone, too, can only be produced in an atmosphere with a large amount of free diatomic oxygen, and so also is dependent on the biosphere (plants). The magnetosphere also shields the ionosphere from direct scouring by the solar wind.
Finally, volcanism continuously emits water vapor from the interior. Earth's plate tectonics recycle carbon and water as limestone rocks are subducted into the mantle and volcanically released as gaseous carbon dioxide and steam. It is estimated that the minerals in the mantle may contain as much as 10 times the water as in all of the current oceans, though most of this trapped water will never be released.
The water cycle describes the methods of transport for water in the hydrosphere. This cycle includes water beneath the Earth's surface and in rocks (lithosphere), the water in plants and animals (biosphere), the water covering the surface of the planet in liquid and solid forms, and the water in the atmosphere in the form of water vapor, clouds, and precipitation. Movement of water within the hydrosphere is described by the hydrologic cycle. It is easy to see this motion in rivers and streams, but it is harder to tell that there is this motion in lakes and ponds.
The water in the oceans moves as it is of different temperature and salinity on different locations. Surface waters are also moved by winds, giving rise to surface ocean currents. Warm water is lighter or less dense than cold water which is more dense or heavier and salty water is also more dense than fresh water. The combination of the water's temperature and salinity determines whether it rises to the surface, sinks to the bottom, or stays at some intermediate depth.
There are several theories regarding the formation of the hydrosphere on the Earth. The planet contains proportionately more surface water than comparable bodies in the inner solar system. Outgassing of water from the interior of the Earth is not sufficient to explain the quantity of water.
A hypothesis that has gained popularity among scientists is that the early Earth was subjected to a period of bombardment by Comets and water-rich Asteroids. Much of the water on the surface today is thought to have originated from the outer parts of the solar system, such as from trans-Neptunian objects.
During the history of the Earth there have been a series of periods in which a significant portion of the hydrosphere was locked up in the form of glacial ice. It has even been hypothesized that during the Cryogenian period this sea ice extended all the way to the equator. (See Snowball Earth).
In all there are currently believed to have been four major ice ages during the Earth's history. The current ice age began about 40 million years ago, and gained in intensity during the Pleistocene. The most recent withdrawal of the ice sheets occurred only 10,000 years ago.
Life
All currently recognized forms of life rely on an active hydrosphere. The water cycle in the Earth's hydrosphere allows for the purification of salt water into fresh water. Evaporation and wetland swamps serve to remove a large portion of atmospheric pollutants from the atmosphere (ie. acid rain). Through this process the water cycle purifies the gaseous atmosphere. Although most life on the planet exists in the salt water oceans, humans are particularly interested in the hydrosphere because it provides the fresh water we depend upon.
The search for life in other celestial bodies in our solar system is focused on first locating water. The hydrosphere's of other planetary bodies is also the focus of research to find places that humans can inhabit without having to transport all their water with them.
Extinction
Scientists estimate that in approximately 4 × 109 years the Sun will have exhausted the supply of Hydrogen in its core and will evolve into a supergiant. The outer atmosphere will expand significantly and the planet Earth will lie within the photosphere. During this process the surface temperature will rise far above the boiling point of water, and all water on the Earth's surface will evaporate.
Other hydrospheres
A thick hydrosphere is thought to exist around the Jovian moon Europa. The outer layer of this hydrosphere is almost entirely frozen, but current models predict that there is an ocean up to 100 km in depth underneath the ice. This ocean remains in a liquid form due to tidal flexing of the moon in its orbit around Jupiter.
It has been suggested that the moon Ganymede may also possess a sub-surface ocean. However the ice covering is expected to be thicker on Ganymede than on Europa.
(Q.) What is salinity of ocean water?
Salinity is the term used to define the total content of dissolved salts in sea water. It is calculated as the amount of salt (in gm) dissolved in 1,000 gm (1 kg) of seawater.It is usually expressed as parts per thousand. Salinity is an important property of sea water. All waters in nature, whether rain water or ocean water, contain dissolved mineral salts.
(Q.) Name the largest barrier reef of the world. Where it is located?
The largest barrier reef of the world is the Great Barrier Reef which is located at the east coast ofAustralia.
Q.) What is continuous evapotranspiration? The continuous transfer of water into the gaseous state is referred to as the evapotranspiration
Q.) What is hydrography?
Hydrogaphy is the investigation of seas and other bodies of water including charting ocean surface, study of tides, currents etc.
Q.) What do you understand by the term 'Atoll'?
These are low islands found in the tropical oceans consisting of coral reefs surrounding a central depression.It may be a part of the sea (lagoon), or sometimes from enclosing a body of fresh or highly saline water.
Q.) What is continental rise?
The continental rise is an underwater feature found between the continental slope and the abyssal plain. The environment in the continental rise is quit unique, and many oceanographers study it extensively in the hopes of learning more about the ocean and geologic history.
Q.) What is continental slope?
Continental slope is the area which is extended from the continental shelf towards the bottom of the ocean.The gradient of the slope region varies between 2-50.The slope boundary indicates the end of the continents.
(Q.) What is continental shelf? Continental shelf is the extended margin of each continent occupied by relatively shallow seas and gulfs. It is the shallowest part of the ocean. The width of the continental shelves varies from one ocean to another.
Q.) What is submarine canyon? The submarine canyons are the deep gorges of the ocean bottom. They are sometimes found cutting across the continental shelves and slope, often extending from the mouths of large rivers.The Hudson canyon is the best known canyon in the world.
Q.) What is a submarine trench?
It is a long narrow and steep-sided depression of the ocean bottom. They are some 3-5 km deeper than the surrounding ocean floor. They occur at the bases of continental slopes and along island arcs and are associated with active volcanoes and strong earthquakes
(Q.) What do you understand by the term Reef? Reef isa line of rocks in the tidal zone of a coast submergedin high water but partially uncoveredin shallow water.
Q. Distinguish between sea mount and Guyot.
1. Sea mounts are the mountains on the sea floor. Guyots are the hills found on the sea floor
2. Sea mounts are above 1000 meters in height and Guyots are also above 1000 meters in height
3. Sea mounts have conical summits and Guyots have flat tops
4. Sea mounts are of volcanic originand guyots are also of volcanic origin.
5. Some of the sea mounts attain the height of 3000 metes and an ordinary guyot has a diameter of 20-25 km.
(Q.) What are the various components of water cycle? The various component ofwater cycle are as follows:1. Water storage in the oceans2. Water in the atmosphere3. Water storage in ice and snow4. Surface runoff5. Ground-water storage
(Q.) Distinguish between the submarine trenches and the canyon.
1. A submarine trench is a long narrow and steep-sided depression on the ocean bottom. Canyon is a deep gorge on the continental slope.
2. Depth of submarine trences varies from 7000 to 11000 meters. The canyon’s depth varies from 1800 to 2800 meters
3. Submarine trenches are almostwithout sediments. Coarse deposits are found on the canyons.
4. Submarine trenches are result ofendogenic forces. Canyons are found near river mouths and may have been the result of erosion
(Q.) Why do we call the earth the' blue planet'? Our planet earth is called as the blue planetbecause of the availability ofwater in abundance. The water body covers more than 70% of the surface of the earth and the rest of the surface is covered withland area. If we try to look at the hemisphere wise distribution ofsea water, it is seen that the northern hemispherecontains 43% and the southern hemispherecontains 57% of the total sea water.
Q.) Write a short note on ocean basin. Ocean basin is an extensive region of the basin floor, generally lying in a depth range of 2500 to 6000m. It covers about 76.2 % of the ocean areas. The ocean basin floor contains three types of features; abyssal plains, oceanic rise and sea mounts.
(Q.) Name the two major banks of the world? The two major banks of the world are:1. The Doggar bank (Northern sea)2. The Grand bank (Atlantic sea)
Q.) Write a short note on the Abyssal plain. Abyssal plain is an area beyond the continental slope. They are located at the depth of 3000 to 6000 meters. They cover about 40% of the ocean floor. The deposits of fine matter containing bones and shells of minute animals that live and die on the surface of sea are deposited on it. They are found in all the major oceans of the world.
Q.) What are the various processes by which the water moves through the water cycle?
The multiple processes under which the water cycle moves are listed under following heads:
1. Evaporation and Transpiration
2. Condensation
3. Precipitation
4. Infiltration
5. Runoff
Sub-surface runoff
On an average, the ridge has a width ranging between2000-24000 km. There are various abyssal plainsin the mid-oceanic ridge.
Q.) What is continental margin? Continental margin is the term which is commonly used for the area whichcontains continental shelf and continental slope together. Continental shelf is the area which is close to the continent and continental slope is the area which is next to the continental shelf.
So in other words continental margin is a combined term for continental shelf and continental slope.
Q.) What is Thermocline?
Thermocline is the layer of the ocean after which there is a rapid decrease of temperature in the ocean water. The boundary region after which the rapid decrease of temperature is seen is calledthermocline.Thermocline is a second layer of the ocean which is right below the first layer of the ocean and is characterisedby rapid decreasein temperature with increasing depth.The thermocline is 500-1,000m thick.
Q.) Write a note on the role of oceans in hydrological cycle.Draw a suitable diagram. Hydrological cycle is one of the most fundamental cycle that maintains life on the earth. Life on land sustains because of the transfer of water from the great ocean body to the land through the atmosphere. The hydrological cycle depends basically on the inter-relationship between the circulation of ocean waters and that of the atmosphere.
(Q.) Define temperature of the ocean water. Explain the distribution of temperature in the ocean water.
The temperature ofocean water varies from place to place. The temperature of ocean water at the pole ward area remainsvery low.On the other handocean temperature in the equatorial area remains high throughout the year because ofdirect heat from the sun and thus high amount ofinsolation is also recieved in this area.
Distribution of ocean temperature: The distribution of temperature in the oceans can be categorised intotwo categories:
1. Horizontal distribution
2. Vertical distribution
Horizontal distribution of temperature: The horizontal distribution of temperature is theamount of insolation received. The areas which are closer to the equator receive more insolation instead of the areas which are closer to the poles.
The decrease in the temperature is on 0.5º per latitude till the poles. The average temperature of the entire ocean is 17.2 ºC. The average annual temperature for the northern hemisphere is 19.4ºC and for the southern hemisphere it is 16.1ºC.
Vertical distribution of temperature: In the oceans vertical distribution of temperature is more important phenomenon in spite of the horizontal distribution of temperature. The temperature in the polar regions remains low while the middle latitude and the low latitude regions have high variation in the temperature ofocean water
The Vertical temperature distribution can be described inthree layer structure of the temperature in the oceans.
1. First layer: This layer within the tropics is present throughout the year but in mid latitudes it develops only during summer. This is the warm layer which is 20º cand 25º cwarm.
2. Second layer: This is known as the thermocline layer which is just below the first layer. The rapid decrease in temperature with the increase indepth is the major characteristic of this layer.
3. Third layer: This layer is very cold and extends up to the deep ocean floor. Most of the ocean water is contained in this layer.
Q.) Name the deepest trench of oceans.
(Ans) Mariana Trench in Pacific Ocean is the deepest trench of the world.It's maximum depth of about 11,033 meters.
(Q.) Name the major oceanic water bodies.
(Ans) The major oceanic water bodies are as follows:
1. Pacific ocean
2. Atlantic ocean
3. Indian ocean
4. Arctic ocean
Q. State two special features of the Pacific Ocean.
The Pacific Ocean is oval in shape and has greatest length from east to west.
Q.) Describe the bottom relief features of the ocean floor.(Ans) The ocean floorhasvariety of features related to the topography of the oceans bottom. Its vast extended landformsare fragmented in the ocean bottom. The geographers have divided the oceanic part of the earth into four oceans, namely the Pacific ocean, the Atlantic ocean, the Indian ocean and the Arctic ocean. The various seas, bays, gulfs and other inlets are part of these four large oceans.
Classification of the ocean floor:
Broadly we can divide the ocean floor intofour major divisions:
The Continental Shelf
The Continental Slope
The Deep Sea Plain
The Oceanic Deeps
The Continental Shelf: The continental shelf is slightly inclined, inundated zone which structurally forms the border of the continent. It has a gentle slope with the gradient of 1º or even less and its maximum depth is normally 200 meters. It covers about 7.6% in the world’s ocean.
The Continental Slope: At the edge of the continental shelf, the seaward slope becomes steep all of a sudden. This partion with steep slope is known as continental slope. The gradient of the slope varies from 2º to 5º. It extends to a depth of about 3000 meters.
The Deep Sea Plain: The deep sea plains are also known as the Abyssal plains. The gradient of these plains are less than 1º. Their depth varies from 3000 to 6000 meters. These plains cover 40% of the total ocean floor.
Oceanic Deeps or Trenches: A trench is a long, narrow and steep sided depression on the ocean floor. Trenches are the deepest part of the oceans with the usual depth of 6000 meters. So far 57 trenches have been found, out of which 32 are in the Pacific ocean, 19 in the Atlantic ocean and 6in the Indian ocean. They occupy 1.2% area of the oceans.
Other features: In this category other minor bottom relief features are included. They are as follows:
1. Mid oceanic ridges
2. Abyssal plains
3. Submarine Canyons
4. Atolls
Q.) Define salinity. What are the factors that affect the distribution of salinity in the oceans?
(Ans) Salinity is the term used to define the total content of dissolved salts in sea water. It is estimated that one cubic kilometer of sea water contains 41 million tones of salt. The average salinity insea water is about 35 parts perthousand.
Factors Affecting Salinity: Salinity in water is mainly affected by the following factors:
1.Availability of fresh water:Fresh water comes fromriver and the melting of snow. The addition of fresh water leads to the decrease in percentage of salinity in the ocean water.2.Evaporation: Due to evaporation,fresh water of the water body islost and the remaining sediments enhance the salinityof the water.3.Ocean currents: The cold ocean currents which are generated because of the melting of the snow at the pole, carry fresh water and blow towards the equator and degrade the amount of salinity at the tropical areas.
Distribution ofsalinity in the sea water: The distribution of salinity in sea water can be defined in two ways:
Horizontal distribution
Vertical distribution
Horizontal distribution: The horizontal distribution of the salinity inocean can be divided into the following categories:
1. Salinity in the open seas – It is determined by the various factors such as the currents etc. The salinity is highest in the tropics of the cancer and Capricorn.
2. Salinity of partially enclosed sea – Partially enclosed seas like the Mediterranean, Black sea, Baltic seahave comparatively high amount of salinity.
3. Salinity in the enclosed sea – The enclosed seashave highest amount of salinity. No river orwater body merge into these seas so it is the main reason for the high amount of salinity in these areas.
2. Vertical distribution: The vertical distribution of the salinity in the ocean can be determined by depth. With the increase indepth, the amount of salinity increases. So the addition of fresh water or the high amount of evaporation does not affect the vertical distribution of salinity.
(Ans) Ocean temperature is the most important factor which influences various movements of the ocean current. The major factors which control the ocean temperature are as follows:
Latitudes: Latitudes are among the few major factors that control the temperature difference in the oceans. The temperature of the surface water decreases from equator towards the poles because the sun’s rays become more and more slanting towards the poles and thus the amount of isolation decreases towards the poles.
Uneven distribution of land and water: The oceans in the northern hemisphere receive more heat due to their contact with larger extent of land than the oceans in the southern hemisphere.
Prevailing winds: The winds blowing from land towards the ocean drive surface water away from the coasts resulting into upwelling of cold bottom water from below.
Ocean currents: The warm ocean currents keep up the temperature incold areas while the cold ocean current cools down the temperature inwarmer areas. So the ocean currents play an important role in terms of ocean temperature.
Other reasons: Local weather conditions also play an important role in the ocean temperature like local cyclones etc
(Q.) Distinguish between the features of the Pacific Ocean and the Indian Ocean.
The bottom relief of the Pacific and Indian ocean are not similar, though the basic characteristics of these oceans are same but still thereare enough differences. The differences between the Pacific and Indian ocean can be explained as follows:
Basis of differences between Pacific Ocean and Indian Ocean are:
Indian Ocean
1. Extension: The extension of the Pacific ocean is 165 million sq. km. The extension of the Indian ocean is 68.556 million sq. km.
2. Ridge: The mid oceanic ridge is not very extensive here. Some part of ridge is found in the south of the Pacific ocean. There is a broad submarine ridges found on the bottom of the Indian ocean
3. Ocean basin: The pacific ocean has a number of shallow basins. The major basinscan beeasily seen in the Pacific ocean. The mid oceanic ridge divides the ocean into many small basins. Six major basins can be identified in the Indian ocean.
4. Ocean deeps: Thereare 32 deeps in this ocean. The deepest among them is the Mariana Trench which is 11022 meter deep. The ocean deeps are almost absent from this ocean. Some small deeps are often seen in the Indian ocean.
5. Marginal seas: There are a few marginal seas in the Pacific ocean like South China sea etc. Some very important marginal seas are located such as Red sea, Persian, Arabian sea, Bay of Bengal etc.
6. Island: There are more than 20,000 islands in the Pacific ocean. There are some big islands like Madagascar and Sri Lanka.
Q.) Distinguish between the continental shelf and the continental slope.
The continental shelf and the continental slope are the areas which are very close to each other. For a layman, these areas are common but for a geographer, these two areashave very unique characteristics. The differences between the continental shelf and the continental slope can be seen as follows:
Continental Shelf
1. It joins shore line with continental slope.
2. Its slope is very gentle. It is about 2 meter per km.
3. It is a shallow water area. Its depth is less than 200 meters.
4. There are few canyons or deeps in the continental shelves.
5. They have large store of sand and gravel.They are of great use to man, particularly for fishing.
Continental Slope
1. It joins continental shelf with Abyssal Plain.
2. Its slope is very steep. The average gradient is about 4 degrees.
3. Its depth varies from 200 to 2000 meters.
4. Deep canyons are found on the continental slopes.
5. Very few land deposits are found on it.
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