OCEANS
Earth: Water World
70 % of Earth’s surface is covered with water. If all the water on Earth
is evenly spread then the depth of the water layer would be about 3.7
km! Luckily the topography of Earth is more complicated and 98% of
water are stored in basins, making possible the land mass.
“How inappropriate to call
this planet Earth, when
clearly it is Ocean.”
– Arthur C. Clarke –
Five Main Ocean Basins
The Pacific Ocean is
the largest and has
the greatest depth.
The Indian Ocean, largely
a southern hemisphere
body, is slightly smaller than
the Atlantic.
The Southern
Ocean lies below 60
degrees south.
The Arctic Ocean is about
7 percent of the size of the
Pacific.
The Atlantic Ocean is
about half the size of the
Pacific and not quite as
deep.
The Pacific Ocean
The Pacific Ocean is the largest of the world's five oceans
Area: 155.6
million square km; that is, 28 % of the global surface – larger than the
total land area of the world
Terrain: The ocean floor in the eastern
Pacific is dominated by the East Pacific Rise, while the western Pacific is
dissected by deep trenches, including the Mariana Trench, which is the
world's deepest place
Deepest point: Challenger Deep in the Mariana
Trench –11,022 m.
Southern Ocean
The Southern Ocean, a body of water between 60 degrees south latitude
and Antarctica, is the fourth largest of the world's five oceans
Area:
20.3 million sq km
Terrain: The Southern Ocean is deep – 4,000-5,000 m
over most of its extent with only limited areas of shallow water. It holds
the world's largest ocean current – the Antarctic Circumpolar Current
(21,000 km in length), transporting 130 million cubic metres of water per
second, which is 100 times the flow of all the world's rivers
Deepest
point: 7,235 m at the southern end of the South Sandwich Trench.
Atlantic ocean
The Atlantic Ocean is the second largest of the world's five oceans
Area: 76.8 million square km
Terrain: The ocean floor is dominated by
the Mid-Atlantic Ridge, a rugged north-south underwater mountain range
stretching down the entire Atlantic basin
Deepest point: Milwaukee
Deep in the Puerto Rico Trench – 8,605 m.
Arctic Ocean
The Arctic Ocean is the smallest of the world's five oceans
Area: 14.1
million square km
Terrain: The ocean floor is about 50 per cent
continental shelf (the highest percentage of any ocean) with the
remainder a central basin interrupted by three submarine ridges (Alpha
Cordillera, Nansen Cordillera and Lomonosov Ridge)
Deepest point:
Fram Basin – 4,665 m.
Indian Ocean
The Indian Ocean is the third largest of the world's five oceans
Area:
68.6 million square km
Terrain: The ocean floor is dominated by the
Mid-Indian Ocean Ridge and subdivided by the Southeast Indian Ocean
Ridge, the Southwest Indian Ocean Ridge and Ninety-east Ridge
Deepest point: Java Trench – 7,258 m.
Origin of Oceans
Oldest sedimentary rocks found in
Greenland suggest that the early
seas were formed about 3,800
million years ago.
It is held that ice laden comets and
water vapour trapped inside the
nascent Earth condensed and
resulted into oceans.
Salinity
Salinity is the total amount
of solid material dissolved in
water, usually expressed as
parts per thousands.
Most of the salt in
seawater is sodium
chloride, common table
salt.
Chemical weathering
of rocks on the
continents is the main
source of elements
found in seawater.
Elements from Earth’s
interior also seep into
seawater.
Salinity Varies
Very high
Very low
Low
Very low
Low
Natural Processes that Affect Salinity
Makes the seawater more
saline and more dense.
Adds fresh water and makes the
sea water less saline and less
dense.
Ocean Temperature
The average temperature of the oceans is 17ºC. The ocean’s surface water
temperature varies with the amount of solar radiation received, which is primarily
a function of latitude. The tem is between -2 to 32 !
Temperature Variation with Depth
The layer between the
deep water and
surface layer is called
‘thermocline’.
Temperatures at
hydrothermal vents
can be as high as
100°C.
The top 3 m of the ocean hold
as much heat as our entire
atmosphere. Temperature of
the ocean drops suddenly as
you go deeper.
Most of the seawater at the
deep is at freezing
temperature of -4°C.
The thermocline is the layer of ocean water between about 300 metres
and 1,000 metres where there is a rapid change of temperature with depth.
Ocean Facts
Area
(million sq km)
Salinity
(ppt)
Temperature
( Degree C)
Global
393.9
34.72
3.81
Arctic
14.0
34.71
-0.19
106.4
34.93
4.2
Indian
73.5
34.75
3.9
Pacific
179.7
34.61
3.6
20.3
34.63
2.5
Atlantic
Southern
Surface Current
Ocean current is the mass of ocean water that flows from one place to
another. Surface currents are movements of water that flow horizontally in the
upper part of the ocean’s surface.
Surface currents develop from friction between the ocean and the wind that blows
across its surface. One “rule of thumb” holds that wind blowing for 12 hrs at 100 cm per
sec will produce a 2 cm per sec current (about 2% of the wind speed).
Mystery of Atlantic Ships
Benjamin Franklin was the Deputy
Postmaster
General
of
the
American colonies and was told of
complaints that westward mail
from Europe to America took
weeks longer than the east-bound
ships from America. He being not
just a diplomat but also a keen
scientist
investigated
the
phenomena.
One of the most famous and
massive ocean currents, the Gulf
Stream, was thus ‘accidentally’
discovered.
Gulf Stream
On examination of the ships’ records with the help of Capt. Timothy Folger he
found that it was indeed true that onward journey from Europe took two weeks
longer than the return journey. Compiling the drift data from various ships that
sailed the Atlantic he was able to accumulate information on the ocean currents
off the US East Coast. Thus he identified the ‘Gulf Steam’, which he called a ‘river
in the ocean’ and depicted it in a map prepared in In the 1769.
Surface Currents
Currents are like rivers in
the oceans. They can carry
enormous
amounts
of
water. For example, the
Antarctic
Circumpolar
Current can transport 100
million cubic metres of
seawater per second! Some
currents containing mud
travel at speeds of 4 m/sec.
They are known to have
transported blocks weighing as much as 9,000 kg!
Water currents transport
heat, sediment particles,
dissolved
oxygen
and
nutrient elements from one
place to another.
The Somali Current, off Africa's
eastern coast, is unusual because it
reverses direction twice a year. From
May to September it runs north; from
November to March it runs south.
Gyres
Gyres are huge circular-moving current systems that dominate
the surfaces of the oceans.
The Coriolis Effect is the deflection of currents away from their
original course as a result of Earth’s rotation.
Mechanism of Surface Current
Winds driven by uneven solar heating
and Earth spin drives ocean currents.
Due to surface winds water
moves in different
directions.
Gyres
Surface winds, Sun’s heat, Coriolis
Effect and gravity circulates the ocean
surface clockwise in Northern
hemisphere and anti-clockwise in
Southern hemisphere.
Four interconnected
currents result in a
gyre.
Deep Water Currents- Ocean conveyor belt
Density currents are vertical currents of ocean water that result
from density differences among water masses.
Cold and salty water would
rush to deep ocean…..
and combine
with cold water
off Antarctica…..
and then emerge as upswelling south of India and
Pacific.
Once at surface,
the water is
heated up and
travels west
again.
moves east, channelled by deep
sea trenches and mid ocean
ridges
An increase in seawater density can be caused by a decrease in temperature or an
increase in salinity.
Ocean Conveyor Belt
The deep ocean conveyor belt transports nutrients and heat across the globe.
As can be seen in the map, Europe is about 10 degrees hotter than the rest of
the places in the same latitude due to the heat transported by the ocean’s
conveyor belt .
Waves and Surf
Most ocean waves obtain their energy
and motion from the wind.
The height, length, and period
that are eventually achieved by a
wave depend on three factors: (1)
wind speed, (2) length of time the
wind has blown, and (3) fetch –
distance wind travelled in open
water.
Circular orbital motion allows
energy to move forward
through the water while the
individual water particles that
transmit the wave move around
in a circle.
Breaking waves occur as a wave moves onto shore. As the waves touch the bottom, wave
speed decreases. The decrease in wave speed results in a decrease in wavelength and an
increase in wave height.
Tides
Gravitational attraction of Sun and Moon causes the ocean water to bulge
resulting in tides.
Watch the animation
Tides
During New and Full Moon phases the
Moon, Sun, and Earth are aligned
causing a greater gravitational pull on
Earth. This results in higher high tides
and lower low tides, which are known
as Spring Tides.
But when Sun and Moon are at
angle tides caused are highest
low tide and lowest high tide
Oceans as a Source of Water Vapour
Makes rain and monsoon possible….
How are Cyclones formed
Cool air rushes in
to fill the void.
Due to rotation of
the Earth on its
axis, the air is
bent inwards and
then spirals
upwards with
great force. The
swirling winds
rotate faster and
faster, forming a
huge circle about
2,000 km across.
At the centre of the storm is a calm,
cloudless area called the eye, where
there is no rain, and the winds are
fairly light.
As the cyclone
builds up it
moves. Warm,
moist air
sustains it. The
strongest winds
and heaviest
rains are found
in the towering
clouds. Winds
can reach
speeds of up to
200 km/h, pumps
out about two
million tonnes of
air per second.
Cyclones develop over warm seas near the Equator. Air heated by the sun rises
very swiftly, which creates areas of very low pressure. As the warm air rises, it
becomes loaded with moisture which condenses into massive thunderclouds.
Cyclones, Hurricanes….
Due to Earths rotation and Coriolis force cyclones rotate anti clockwise in
northern hemisphere and clockwise in southern hemisphere
Due to Global
warming as the sea
surface temperature is
increasing, the
intensity of cyclones
and hurricanes are
expected to increase
resulting in severe
damage
Hurricane Katrina (2005)
that hit US anti-clockwise
swirl
Cyclone Larry (2006) that
hit Australia with clockwise
swirl.
It is said that we know lot more about Moon than what is
under the oceans.
The entire surface of the
Moon has been mapped.
Till recently large part of the world map
was just coloured blue – as we had
scant knowledge of what is beneath it.
Developments in technology made
possible to look at the ocean surface.
Mapping the Ocean Floor
Ocean floor is mapped by using SONAR (an acronym for
sound navigation and ranging). It is also referred to as echo
sounding. Sonar works by transmitting sound waves toward
the ocean bottom.
Today Satellites Help
Satellites
are
able
to
measure small differences
by bouncing microwaves off
the ocean surface. Using
this
new
technology,
scientists have discovered
that the ocean surface is not
perfectly flat. Differences in
the height of the ocean
surface are caused by
ocean-floor features.
Unravelling the Ocean Floor
Deepest point 11,033 m
in the Mariana Trench in
the western Pacific.
Mauna Kea, Hawaii, rises 10,203 m from its base
on the ocean floor; only 4,170 m are above sea
level.
The Great Barrier Reef, measuring about
2,000 km, is the largest living structure on
Earth. It can be seen from the Moon.
The Antarctic ice sheet that
forms and melts over the
ocean each year is nearly
twice the size of the United
States
The largest single feature on
Earth, the ocean ridges 64,000
km long, weaves its way
through all the major oceans.
Cross-section of a Typical Ocean
The ocean basin floor is the deepocean floor between the continental
margin and the oceanic ridge.
A continental margin is the zone of
transition between a continent and the
adjacent ocean basin floor.
Deep-ocean trenches form at the sites of plate convergence where one
moving plate descends beneath another and plunges back into the mantle.
Ocean Floor Features
An abyssal
plain is a very
level area of
the deepocean floor,
usually lying
at the foot of
the
continental
rise.
Computed Ocean
surface features
A seamount is
an isolated
volcanic peak
that rises at least
1,000 metres
above the deepocean floor, and
a guyot is an
eroded,
submerged
seamount.
Sonar readings based on
which ocean floor is
mapped in detail
Continental Shelf
A continental shelf is the gently sloping submerged surface
extending from the shoreline. Continental shelves contain
important mineral deposits, large reservoirs of oil and natural
gas, and huge sand and gravel deposits.
Layers of Ocean Water
Oceanographers generally recognise a three-layered structure in most parts
of the open ocean
Deep Zone: Sunlight never reaches this zone. Temperatures are just
a few degrees above freezing. Constant high-density water. More
than 90% of the living space in oceans exists in the deep ocean
known as the abyss.
Mixed Zone: Shallow (300 to 450
meters) Zone of mixing and Sunwarmed zone
Transition zone: Between surface
layer and deep zone
Life In Ocean
From microscopic life forms
thousands of which can be fitted
into millimetre to the largest
mammal – blue whale – 33 metres
across, are abundant in oceans.
Marine life comes in different
shapes and sizes.
Oceans contain 99% of the living space on the planet. 80 %
of life on Earth is found under the ocean surface. Less
than 10% of that space has been explored by humans.
Life Form Differs as You go Deep
Because of the threedimensional
space
available in ocean it is
estimated that available
living space for marine
organism is 250 times
greater than for that on
land. Yet most of the
marine organisms are
concentrated near the
surface, in the upper 200
m
where
sunlight
penetrates.
Life in Ocean
The photic
zone is the
upper part of
the ocean into
which sunlight
penetrates.
The pelagic zone is open zone of
any depth. Animals in this zone
swim or float freely.
The benthic zone is the marine-life
zone that includes any sea-bottom
surface regardless of its distance
from shore.
The abyssal plain is a subdivision of the benthic zone
characterised by extremely high pressures, low
temperatures, low oxygen, few nutrients, and no sunlight.
Adaptation to Ocean Features
Life in ocean is specially adapted to the
saline condition as well as the massive
pressure in the ocean,
Hydrothermal Vents
Hydrothermal vents form along mid-ocean ridges. These are zones where mineralrich water, heated by the hot, newly-formed oceanic crust, escapes through cracks
in the oceanic crust into surrounding water. These vents harbour communities of
organisms found nowhere else on Earth. Unique organisms found here produce
food through chemosynthesis – process using chemical energy to create inorganic
nutrients – as distinct from photosynthesis.
Giant Tube worms
Indian coast
• India's coast is 7,517 km long; of this distance, 5,423 km- mainland
2,094 km Andaman, Nicobar, and Lakshadweep Islands.
• 43% of mainland coast is sandy beaches, 11% rocky coast including cliffs,
and the rest 46% mudflats or marshy coast.
• Among notable coastal features of India are the marshy Rann of Kutch in
western India, and the alluvial Sundarbans delta, which India shares with
Bangladesh.
• India has two archipelagos: the Lakshadweep, coral atolls off India's
south-western coast; and the Andaman and Nicobar Islands, a volcanic
chain in the Andaman Sea.
• About 26% of Indian population live within 100 kms of the coast.
• The area of continental shelf is about 372424 km2. The territorial sea
extends to 193834 km2 while the claimed exclusive economic zone is
2103415 km2.
• 3036 km2 of coastal region is mangrove forest and there are about 1930
km2 of wetland in the coastal region.
• Total fish catch during 2000 was about 2773092 metric tons which
provided about 5 kg per capita per year.
Ocean’s Bounty
The most economically important resource is, of course, salt!
Oil and natural gas are the main
energy products currently being
obtained from the ocean floor. Gas
hydrates are compact chemical
structures made of water and natural
gas. Most oceanic gas hydrates are
created when bacteria break down
organic matter in ocean-floor
sediments.
Other major resources from the ocean floor include
sand and gravel, evaporative salts, and manganese
nodules (hard lumps of manganese and other metals
like cobalt, copper, and iron) that precipitate around a
small object. The offshore sand-and-gravel industry is
second in economic value only to the petroleum
industry.
Economic Importance of Oceans
More than 90 % of the trade between
countries is carried by ships and
about half the communications
between nations use underwater
cables. Fish supply the greatest
percentage of the world's protein
consumed by humans. Most of the
world's major fisheries are being
fished at levels above their maximum
sustainable yield; some regions are
severely overfished.
Oceans Sustain Life
Three-quarters of the world's mega-cities are by the sea. By 2010,
80% of people will live within 50 km of the coast. More than 3.5
billion people depend on the ocean for their primary source of
food. In 20 years, this number could double to 7 billion.
Oceans Under Threat
Over the past decade, an average of 600,000 barrels of oil a year has been
accidentally spilled into the oceans from ships. More oil reaches the
oceans each year as a result of leaking automobiles and other non-point
sources than spills. Eighty per cent of all pollution in seas and oceans
comes from land-based activities. Plastic waste kills up to 1 million sea
birds, 100,000 sea mammals and countless fish each year. Plastic
remains in our ecosystem for years harming thousands of sea creatures
everyday. Death and disease caused by polluted coastal waters costs the
global economy US$12.8 billion a year. The annual economic impact of
hepatitis from tainted seafood alone is US$7.2 billion.
Ocean may die…
Change in sea surface pH caused by
anthropogenic CO2 between the 1700s to 1990s
Due to increase in Carbon dioxide levels in the atmosphere the levels of carbon uptake
in sea has increased leading to acidification of ocean. Between 1751 and 1994 surface
ocean pH is estimated to have decreased from approximately 8.179 to 8.104 (a change
of -0.075). If such trend continues it will cause immense damage to life in ocean
Save Our Oceans; Save our Seas…
End of Slide Show
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