Download World Geography Hydrosphere Tides Ocean

HYDROSPHERE, OCEANS AND
TIDES
Revision
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Chapter 12.
Hydrosphere comprises of
ALL WATER
In the Earth’s
Atmosphere
On surface of the
Earth
Under the ground
Water Vapour = 0.001%
Is very important for life
2.15% as ice sheets in the North
and South Poles; 0.00171% in
Rivers and Lakes
97.2% in Oceans
Difficult to estimate
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Hydrosphere and Atmosphere
• Both have a layered structure
• Both have different dimensions of height and
depth
• The pressure, density and temperature
changes at different depths in both structures.
Example: At the lowest depths of oceans even
at the Equator, is near freezing degrees.
• However, the chemical content of water does
not change due to temperature and pressure.
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Chemical composition of Water
• Chemical composition of water depends
upon whether the water is fresh or salty.
• Fresh water is needed for living beings, and
for agriculture.
• It is found in lakes, rivers, and under the
ground. Brooks, and geysers are natural
sources of underground water.
• Man extracts underground water through
wells and pumps. In last 50 years this has
resulted in overuse of underground water.
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An Ocean is the great body of water on Earth’s surface
• 71 % is Ocean
on Earth
• 29% is land on
Earth
61% is
Ocean in
Northern
Hemisphere
81% is
Ocean in
Southern
Hemisphere
39% is Land
In Northern
Hemisphere
19 % is land
in Southern
Hemisphere
• Southern
Hemisphere is
called Ocean
Hemisphere
• Northern
Hemisphere is
called Land
Hemisphere
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Ocean floor, and movement such as
Ocean currents, Tides, and Waves
• Ocean along the coasts, slopes gently at 180
meters , to a depth of 100 km almost to the
floor of the ocean. In certain places this slope
is for a few km only, and remain far from the
floor.
• This slope of land along the coast line, is the
submerged extension of the Continent and is ,
therefore, called the ‘Continental Shelf’.
• The Sonar wave technology is used to
measure the depth of the shelf and the floor.
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Continental Shelf
Continental
Shelf gently
slope at 180 m.
Temperature
Varies only
At the surface
30 to 23 degree C
Falls with
increasing
depth
To depth of 100
km
Depth 4 km
to 6 km
1) Fishing Grounds
In Newfoundland
And North Sea
2) 25% Off shore
petroleum
and natural gas Bombay High and North
Sea
Mid Ocean
ridges
Near freezing
Temperature
exists near the
ocean floor
Ocean Floor
with Abyssal
plains that are
Deep sea plains
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Salinity of Sea water = 35 grams per Kg
or 35 per thousand or 35%
Maximum in
the Dead Sea
At 240 per
thousand
Evaporation
Fresh water from
rivers
From rains
Oceans have
sufficient salt
Arctic Ocean
lowest at 20 per
thousand
Arabian Sea 38
per thousand
Bay of
Bengal30 per
thousand
Caspian Sea salt
water lake – no
outflow
Gangetic
sundarbands 20 per
thousand
To cover all land with a
100 metre thick layer
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Spring and Neap Tides – New and Full Moon
Spring tide is higher
than normal and
occurs on New and
Full Moon days
Fishermen depend
heavily on tides and tidal
water is trapped to make
salt
Neap Tide in 1st and last
quarter when moon is at
right angles to the earth
- Low tide
Tides carry away silt from coastal
regions and are now used to
general Tidal Energy
Spring tides enable large
ships to enter a harbour,
and Neap tides help them
to go out of a harbour
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Tidal waves break and form a
wall of water called ‘Bores’. In an
estuary Bores can be very
dangerous , as in Hoogly River
(India) Amazon River and in
North China
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Seven Seas, Open and Closed Lakes
Arabian
Sea
China
Persian
Gulf
Sea
East
African
Sea
Red
Sea
Mediter
ranean
Sea
West
African
Sea
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Ocean Currents – regular horizontal or vertical movement of water from one
part of the Ocean to another , resulting from action of Density and Winds
• Currents are streams of water that move on the surface
of oceans in a definite direction and have a clear
boundary. They may be thousands of kilometres in
length and can be up to 200 km wide.
• Winds help in this movement.
• Warm Currents originate at Equator and flow towards
the Poles
• Cold Currents flow from the Poles towards the Equator
• Due to currents and Tides, the Oxygen in the Oceans
gets evenly distributed in the Water, otherwise life in
depths will not survive – as in the Dead Sea
• Temperatures are higher at the Equator and the
imbalance causes the movement due to convection.
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The Coriolis Effect is the deflection of winds and ocean
currents due to rotation of the Earth - see diagram on page
59 of the text book.
• The Coriolis effect is the creation of the Spiral at 900
degrees from the direction of the wind. It has the
overall effect of moving a large mass of ocean water,
above the depth of frictional resistance.
• The water is affected by surface winds that drive the
sub-surface layers at an angle to the wind.
• Each layer moves at a slower speed than the layer
above it, but the angle against the wind is larger for
each layer.
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Important Warm Ocean Currents
• 1. The Gulf Stream is a warm current, in
Atlantic Ocean from Gulf of Mexico, that moves
in north-western direction due to Westerly
winds, to wash the coasts of England and
France.
• Along the eastern coast of USA, in
Newfoundland, the Gulf Stream meets the cold
Labrador current, creating dense fogs. The
Labrador current from Arctic Ocean is a cold
current, that diverts the Gulf Stream towards
the coast of Europe.
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Important Warm Ocean Currents
2. The Kuro Shio Current: is a warm current in the Pacific
Ocean , that moves as the North Pacific Drift, to keeps
the eastern coast of Japan warm and free from ice.
Towards north it meets the cold Oya Shio Current.
3. The North Pacific Drift is moved by the Westerly
winds towards the western coast of Canada and
Alaska.
4. The Oya Shio Current or the Kurile Current in Arctic
Ocean flows from Japan and makes the western coast
of Japan and coast of Asia, very cold.
5. It is similar to the Labrador Current in the Atlantic
Ocean along the north eastern coast of USA.
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Role of Oceans in Earth’s Climate
• Sun’s heat causes evaporation of vast
quantities of water from the Oceans every
day.
• The water vapour laden air is lighter, and
therefore, rises up , to cool down and form
clouds.
• Clouds move with the winds towards land
and cause rain.
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Role of Oceans in Earth’s Climate
• In the Oceans, evaporation causes convention
current to build up under the surface of water. This
causes ocean currents .
• Ocean currents transfer heat from lower latitudes
to higher latitudes. This helps in balancing global
temperatures, by absorbing heat in summer and
releasing it in winter (?)
• Oceans have a moderating influence on climate of
coastal regions.
• However, in regions where cold currents merge
with warm currents, fog are generated. Many ship
wrecks are caused by them.
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