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GEOGRAPHYOPTIONAL
by
SHAMIM ANWER
PREP SUPPLEMENTOCEANOGRAPHY
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LEARNING GEOGRAPHY -A NEVER BEFORE EXPERIENCE
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KEYNOTE IAS
PREP-SUPPLEMENT: OCEANOGRAPHY
PHYSICAL GEOGRAPHYOCEANOGRAPHY
INDEX
1. OCEANS AND THEIR
CONFIGURATION..............................................................1-5Atlantic
Ocean, Pacific Ocean & Indian Ocean
2. TEMPERATURE, SALINITY & DENSITY OF OCEAN
WATER...........................6-103. OCEAN DEPOSITS
................................................................................................11-124.
TIDES AND WAVES
.............................................................................................13-155.
OCEAN CIRCULATION
......................................................................................16-216.
MARINE RESOURCES
..........................................................................................227.
CORAL REEFS
.......................................................................................................23-28
Fringing Reefs, Barrier Reefs & Atolls;Coral Reef
Bleaching
8. SEA LEVEL
CHANGE............................................................................................29-309.
MARINE
POLLUTION............................................................................................31-32
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1. OCEANS AND THEIRCONFIGURATION
The oceans are the largest and most prominentfeature on Earth.
In fact, they are the single mostdefining feature of our planet.
Water coversroughly around 70%of Earth'ssurface. The world
ocean is a single inter-connected body of water,which is large
in size and volume. It can be dividedinto five principal oceans-the
Pacific, Atlantic,Indian, and Arctic Oceans and the Southern
orAntarctic Ocean The ocean floor can be dividedint three major
provinces:
(1) Continental margins, which are shallow-waterareas close to
continents,(2) Deep-ocean basins, which are deep-water areasfarther
from land, and(3) The mid-oceanridge, which is composed ofshall
ower are as near the middleofan ocean.
Plate tectonic processes are integral to theformation of these
provinces. Through the processof sea floor spreading, mid-ocean
ridges and deep-ocean basins are created. Elsewhere, as a
continentis split apart, new continental margins are formed.
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Continental Shelf-The continental shelf is definedas a generally
flat zone extending from the shorebeneath the ocean surface to a
point at which amarked increase in slope angle occurs, called
theshelf break. It is usually flat and relativelyfeatureless
because of marine sediment depositsbut can contain coastal islands,
reefs, and raisedbanks. The underlying rock is granitic
continentalcrust. The average width of the continental shelfis
about 70 kilometres, but it varies from a fewtens of meters to 1500
kilometres. The broadestshelves occur off the northern coasts of
Siberiaand North America in the Arctic Ocean. Theaverage depth at
which the shelf break occurs isabout 135 meters. Around the
continent ofAntarctica, however, the shelf break occurs at
350meters. The type of continental margin willdetermine the shape
and features associated withthe continental shelf. For example, the
east coastof South America has a broader continental shelfthan its
west coast. The east coast is a passivemargin, which typically has
a wider shelf. Incontrast, the convergent active margin
presentalong the west coast of South America ischaracterized by a
narrow continental shelf and ashelf break close to shore.Most
commercial exploitation from the sea, suchas metallic-ore,
non-metallic ore, and hydrocarbonextraction, takes place on the
continental shelf.Bank, Shoal & Reef: These marine features
areformed as a result of erosional, depositional andbiological
activity. Also, these are produced uponfeatures of diastrophic
origin. Therefore, they arelocated on upper parts of elevations.A
bank is a flat topped elevation located in thecontinental margins.
The depth of water here isshallow but enough for navigational
purposes. TheDogger Bank in the North Sea and Grand Bank inthe
north-western Atlantic off Newfoundland arefamous examples. The
banks are sites of some ofthe most productive fisheries of the
world.A shoal is a detached elevation with shallowdepths, since
they project out of water withmoderate heights, they are dangerous
fornavigation.
A reef is a predominantly organic deposit madeby living or dead
organisms that forms a moundor rocky elevation like a ridge. Coral
reefs are acharacteristic feature of the Pacific Ocean wherethey
are associated with seamounts and guyots.The largest reef in the
world is found off theQueensland coast of Australia. Since the
reefs mayextend above the surface, they are generalitydangerous for
navigation.Continental Slope -After some depth the slope ofthe
continental shelf suddenly gets much steeper,turning into the
continental slope which lies beyondthe shelf break. It is a
submarine geological featurewhich connects the continental shelf to
the abyssalplain. Together, the continental shelf and slope
areoften referred to as the "continental margin."Submarine canyon
comprises the most outstandingrelief feature of the continental
slope. It looks likea long steep sided V-shaped valley with
tributariessimilar to those of river cut canyons on land.Submarine
Canyons - The continental slope and,to a lesser extent,
thecontinental shelf exhibitsubmarine canyons,which are narrow but
deepsubmarine valleys thatare V-shaped in profile viewand have
branches ortributaries with steep tooverhanging walls. They
resemble canyons formedon landthat are carved by rivers and can be
quitelarge. They are formed due to turbidity currents.
Continental Rise-The continental rise is anunderwater feature
found between the continentalslope and the abyssal
plain.Thisfeature can befound all around the world, and it
represents thefinal stage in the boundary between continents andthe
deepest part of the ocean. The formation of thecontinental rise is
a constant and very slow process.As rivers and streams travel over
land, they pickup sediment, silt, and other material, which
isgradually carried out to sea. Some of thesesediments settle on
the continental shelf, but othersdrift down the continental slope
to form thecontinental rise
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Abyssal Plains - It is a flat depositional surfacesextending
from the base of the continental rise intothe deep-ocean basins.
Theyaresomeofthedeepestand flattest regions on Earth.Abyssal plains
areformed by fine particles of sediment slowly driftingonto
thedeep-oceanfloor.There are several distinctabyssal plains across
the world's oceans. Each onestarts at a continental riseand
continues until itreaches a mid-oceanic ridge, resuming on the
otherside. They cover around 40% of the ocean floor.Volcanic
features such as seamounts, guyots andabyssal hills can be found
here. A submarinemountain peak rising morethan 1000 m aboveocean
floor are knownas "seamount".Flat toppedseamounts are known
as"Guyots". Volcanicfeatures whose height is less than 1000 m
arecalled abyssal hills.
Ocean Trenches-An ocean trench is a geologicalstructure which
occurs undersea along theboundary of a tectonic plate.
Specifically, oceantrenches form along the subduction zones, in
areaswhere one plate is beingsubducted under another.They comprise
the deepest part of the ocean. Thedeepest ocean trench is the
Mariana Trench, in theWestern Pacific Ocean. The deepest point
onEarth's surface 11,022 meters is found in theChallenger Deep area
of the Mariana.The landward side of the trenchrisesasa volcanicarc
that
may produce is lands (suchastheis lands of Japan,an is landarc)
oravolcanic mountain range alongthe margin of a continent (such as
the AndesMountains, a continental arc).
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Mid-Ocean Ridges -It is a continuous, fracture-looking mountain
ridge that extends through allthe ocean basins. They results from
sea-floorspreading along divergent plate boundaries. Theseare
entirely oceanic and composed of basalticlavas.Oceanic
Islands-There are three basic types ofoceanic islands: (1) islands
associated withvolcanicactivitya long the mid-oceanic ridge (2)is
land sassociated with hot spots(suchas theHawaiian Island sin the
Pacific Ocean); and(3)islands that are island arcs and associated
withconvergent plate boundaries (such as the AleutianIslands in the
Pacific Ocean). All three types arevolcanicinorigin.
ATLANTIC OCEANThe Atlantic is roughly half the size of the
PacificOcean and resembles the letter 'S' in shape. It hasprominent
continental shelf with varying width-the largest width occurring
off north-east Americaand north-west Europe. The Atlantic Ocean
hasnumerous marginal seas occurring on the shelves,like the Hudson
Bay, the Baltic Sea and the NorthSea.The most striking feature of
the Atlantic Ocean isthe presence of Mid-Atlantic Ridge which
runsfrom north to the south paralleling the 'S' shape ofthe ocean
itself, dividing the Atlantic into twodeeper basins on the either
side.The ridge is about 14,000 km long and about 4,000metres high.
Several peaks of this ridge projectout of the ocean surface to form
islands of the mid-Atlantic. Examples include Pico Island of
Azores,Cape Verde Island. Also, there are coral islandslike Bermuda
and volcanic islands like Ascension,
Tristan da Cunha, St Helena and Gough.By and large the Atlantic
Ocean lacks in troughsand trenches, which are more characteristic
of thePacific Ocean. North Cayman and Puerto Rico arethe two
troughs and Romanche and SouthSandwich are the two trenches in the
AtlanticOcean.Ridges: Rio Grande Ridge, Wyville-ThompsonRidge, New
found land Ridge, Walv is Ridge,Telegraphic Plateau, Sierra Leone
Ridge,Raykjanes Ridge, Cape Swell, Dolphin Rise,Challenger
Rise.Basins: Labrador Basin, Iberian Basin, Cape-Verde Basin,
Guinea Basin, Sierra LeoneBasin,Cape Basin, Argentina Basin,
AgulhasBasin.Deeps & trenches: Moseley Deep, BuchananDeep,
Valdivia Deep, Romanche Deep, Puerto-Rico Deep, Nares Deep.PACIFIC
OCEANThis part is characterised by maximum depth and
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a large number of deeps, trenches and island areas.Some
well-known trenches are Aleutian, Kuril,from 7,000 to 10,000
metres. There are also a largenumber of seamounts, guyots and
parallel andarcuate island chains in the central part.South-West
Pacific:The average depth of this part is about 4,000 m,and this
part is marked by a variety of islands,marginal seas, and
continental shelf and submarinetrenches. Mariana Trench lies in
this portion andthe Mindanao Trench is also very deep with a
depthof more than 10,000 metres.South-East Pacific:This part is
conspicuous for the absence ofmarginal seas, and has submarine
ridges andplateaus. The Tonga and Atacama are
prominenttrenches.Ridges: Albatross Plateau, Cocos Ridge,
San-Felix-Juan Ridge, Hawaiian Swell, MarcusNeckerRise, Chatham
Rise, Lord Howe Rise,NorfolkRidge, S. Tasmania Ridge.Basins:
Aleutian Basin, E&W Caroline Basin, FijiBasin, E. Australian
Basin, Jeffrey's Basin, S WPacific Basin, SE Pacific Basin,
PacificAtlanticBasin.Trenches: Aleutian Trench, Kuril
Trench,PhilippineTrench, Cape-Johnson Deep, NeroDeep,Mariana
Trench, Tonga-KermadecTrench,Aldrich Deep, Brook Deep, Planet
Deep.INDIAN OCEANThis ocean is smaller and less deep than
theAtlantic Ocean. Since it is completely blocked inthe north by
the Asian landmass, it can beconsidered only half an ocean. It has
few marginal
seas. Linear deeps are almost absent. The onlyexception is Sunda
Trench, which lies to the southof the island of Java.There are a
number of broad submarine ridges inthis ocean, which include the
Lakshadweep-Chagos Ridge, the St. Paul Ridge which widensinto the
Amsterdam St. Paul Plateau, the Socotra-Chagos Ridge, the
Seychelles Ridge, the SouthMadagascar Ridge, the Prince Edward
CrozetRidge, the Andaman-Nicobar Ridge and theCarlsberg Ridge.
These ridges divide the oceanbottom into many basins. Chief among
these arethe Central Basin, Arabian Basin, South IndianBasin,
Mascarene Basin, West Australian andSouth Australian Basins.Most of
the islands in the Indian Ocean arecontinental islands and are
present in the north andwest. These include the Andaman and
Nicobar,Sri Lanka, Madagascar and Zanzibar. TheLakshadweep and
Maldives are coral islands andMauritius and the Reunion Islands are
of volcanicorigin. The eastern section of the Indian Ocean isalmost
free from islands.Ridges: Socotra-Chagos Ridge, St. Paul
Ridge,Seychelles Ridge, Crozet Ridge, Crozet Ridge,Kerguelen Ridge,
Laccadives-Chagos Ridge,Chagos St. Paul Ridge, Kergel-Gausberg
Ridge,Andaman Rise.Basins: Somali Basin, Oman Basin,
NatalBasin,Mauritius Basin, Agulhas Basin,AndamanBasin,
Cocos-Kelling Basin, E. Indian-AntarcticBasin.Trenches: Sunda
Trench, Valdivia Deep,Jeffreydee
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2. TEMPERATURE, SALINITY ANDDENSITY OF OCEAN WATER.
Temperature, salinity and density are the three veryimportant
physical properties of the ocean water.They are not static but
change with the space andtime.These properties affect the physical,
chemicalas well the biological environment of the oceans.
Temperature of the ocean waterThe ocean water gets heated when
it receives heatenergy from the sun and its temperature
rises.Temperature influences the radiation balances andthe heat
budget of the earth, the generalatmospheric conditions and control
the planetarywind belts. Global hydrological cycle to aconsiderable
extent.
Distribution of temperatures in the oceans.-Horizontal
distribution patterns depend upon thefollowing -Latitude-The
temperature of the surfacewater generally decreases as we move from
theequator towards the pole. Because the insolationdecreases as the
sun's rays are vertical throughout
the year and they become more and more slantingtowards the
pole.Unequal distribution of land and water. Oceansin the northern
hemisphere will receive more heatdue to their contact with the
larger extent of landthan the oceans in the southern hemisphere.
Dueto the differential heating of the land and waterthere are
temperature contrasts and the isothermsdo not follow latitudes and
are curved near thecoasts .There curvature is more pronounced in
thenorthern hemisphere due to the extensive landmasses than in the
southern hemisphere whereoceans are more extensive.Prevailing
winds-The winds blowing from theland towards the oceans drive warm
surface wateraway from the coast resulting in cold waterupwelling
from below. It results in the longitudinalvariation of the
temperature. The on shore windspile up the warm water near the
coast and thisraises the temperature. The temperature of theeastern
part of the oceans is lower than that of thewestern part in tropics
due to the prevailing tradewinds there. On the contrary,
temperature is loweron the western coasts than the eastern coasts
inthe temperate zone due to the prevailing westerliesthere.Ocean
currents- Warm ocean currents raises thetemperature of the ocean
water whereas the coldocean current leads to a fall of the
temperature.For example, the Gulf Stream (warm current)increases
the temperature near the east coasts ofNorth America and western
coast of Europe .while
the Labrador Current (cold current) decreases thetemperature
near the north east coasts of NorthAmerica.Mixing of ocean
water-The temperatures of theenclosed waters differ from that of
the openwaters.The enclosed seas located in the lowlatitudes record
relatively higher temperatures than
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the open seas whereas enclosed seas in the higherlatitudes have
lower temperature than in open sea.Vertical distribution-The
surface of the sea waterreceives the largest amount of solar
insolation andhas the highest temperatures. As we go deep intothe
sea the sun's rays are reduced and so does thetemperature. Hence,
there is a fall in temperaturewith the depth. However the rate of
fall is not sameeverywhere.
Temperature layers-There is a boundary margin between the
surfacewaters and the deeper layers. The temperaturestructure of
oceans over middle and low latitudescan be described as a three
layer system fromsurface to bottom.First layer- represents top
layer of warm oceanicwater, temp. Range between 20-25 degrees.
Thislayer within the tropics is present throughout theyear but in
the mid-latitudes it is developed in thesummer only.Second layer-
thermocline layer-The boundaryregion from where there is a rapid
decrease in thetemperature is called the thermocline. About 90%of
the total volume of water is found below thethermocline in the deep
ocean.Third layer- very cold layer and extends up tothe deep ocean
floor.in the arctic and the Antarcticlatitudes, the surface water
temp are close to0degrees and so the temperature change with
depthis very slight. Here only one layer of cold waterexists from
surface to deep ocean floor.
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Salinity of the ocean watersSalinity is the ratio of the mass of
dissolvedsubstances to the mass of the water sample.Salinity is
often expressed in parts per thousand.The distribution of dissolved
salts in the oceansand adjacent seas varies in space and time
Salt Name PercentageNaCl SodiumChloride 77.8MgCl2
MagnesiumChloride 10.9MgSO4 MagnesiumSulphate 4.7CaSO4
CalciumSulphate 3.6K2SO4 PotassiumSulphate 2.5CaCO3
CalciumCarbonate 0.3MgBr2 Magnesium 0.2
Processes Affecting Seawater SalinitySalinity differences are
created only by dilutionor concentration as fresh water is added
orremoved, or as salty water is rejected from sea iceas it freezes.
Adding more water, dilutes thedissolved component and lowers the
salinity of thesample. Conversely, removing water
increasessalinity.Precipitation, runoff (stream discharge),melting
icebergs, and melting sea ice decreaseseawater,however, the
formation of sea ice andevaporation increase seawater salinity
byremoving water from the ocean.Surface salinity distribution-The
salinity ofsurface water varies considerably due to
surfaceprocesses, with the maximum salinity foundnearthe Tropics of
Cancer and Capricorn and themin imumsalinity foundin
high-latituderegions.
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Salinity also varies with depth down to about 1000meters (3300
feet), but below that the salinity ofdeep wateris very consistent.
A haloclineislayerof rapidly changing salinityLowest salinities
occur in the Arctic and Antarcticwhere there is both net
precipitation and seasonalice melt. Highest salinities occur in the
Red Seaand Persian Gulf, both located in the north westernIndian
Ocean, where net evaporation is high. Highsalinity is also found in
the Mediterranean Sea. Inthe open ocean, high salinity occurs in
thesubtropical areas of net. A band of low salinityunderlies the
ITCZ at 10°N.The effect of continental runoff is apparent inlowered
surface salinity near the mouths of majorrivers such as the Amazon
and the Congo and thenumerous large rivers that empty into the Bay
ofBengal, east of India, including the Ganges andBrahmaputra.
Runoff from many rivers around theGulf of Alaska in the north
eastern Pacific andaround the Arctic Ocean is important in
thelowered salinities of high-latitude ocean regionsLatitudinal
Distribution - It decreasesfrom Equatortowards the Poles. The
averagesalinity of N-Hemisphere is 34‰while for S-Hemisphere it
is35‰. In general there is lowsalinity in equatorialzone, high in
tropicalbelt, low in temperate zoneand minimum insub-polar
zone.
LatitudinalZones Salinity(%)10-15N 34.5-3515-40N 35-3640-50N
33-3450-70N 30-3110-30S 35-3630-50S 34-3550-70S 33-34Regional
Distribution - The amount ofsalinityvaries from ocean to ocean,
mainly dueto supplyof fresh water, rapidity of evaporationand
watermixing tendency. The greatestproportion of salt isfound in two
areas whichlie about the Tropic ofCancer and the Tropic
ofCapricorn. From theseregions the salinitydecreases both towards
equatorand the poles.Salinity of the inland seas and lakesis very
highbecause of the regular supply of saltby the riversflowing into
them and the evaporationmakestheir water continuously more and
moresaline.Vertical Distribution of Salinity - Salinity of theocean
decreases or increasestowards the bottomaccording to the natureof
the water mass.In highlatitude salinity increases withdepth due to
densewater found at thebottom. In the middle latitude
salinityincreases with the depth up to 200fathomsand then it
starts decreasing.At equatorsurface salinity is low but justbelow
it greatersalinity is found which againdecreases at thebottom due
to presence ofcold water mass.Seawater Density- Low-density water
existsnearthe surface and higher density water occursbelow. Except
for some shallow inland seas witha high rate of evaporation that
creates high salinitywater, the highest-density water is found at
thedeepest ocean depths As the temperatureincreasesseawater density
decreases and.assalinity increasesseawater density
increasesAspressure increasesseawater density increasesOfthese
three factors, only temperature and salinityinfluence the density
of surface water Cold waterthat also has high salinity is some of
the highest-density water intheworld. Thedensityofseawaterthere
sulto fits salinity and temperature influencescurrent sinthe deep
oceanbecaus ehigh-densitywater sinks belowless-dense water.
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3. OCEAN DEPOSITSThe study of marine deposits is very important
forthe understanding of the rocks exposed on thesurface of the
earth. The unconsolidated sedimentsderived from various sources
like weathering anderosion of continental rocks are transported to
theoceans by rivers, winds etc. volcanic eruption alsoprovide
sediments. Besides, the decay anddecomposition of marine organisms
(both plantsand animals) also contribute sediments to
oceandeposits. The study of oceanic deposits involvesthe
consideration of the sources from whichsediments are derived, the
methods oftransportation from the source to the destination,and the
horizontal and vertical variation in theirdistribution. The marine
sediments continuouslybeing deposited on the ocean floor are
derived fromvarious sources and are distinguished by the natureof
their source regions.
These deposits consist of:1. Terrigenous MaterialUnder the
process of disintegration anddecomposition the terrigenous rocks
constitutingmostly of igneous or sedimentary rocks areshattered
into pieces. These rocks are disintegratedinto smaller fragments
and are carried down tothe sea by rivers as mud and sand.The larger
fragments of the terrigenous origin arelaid down close to the
shore, but the finer sedimentsare carried far away into the ocean.
The distanceto which the rock material travels not only dependsupon
the size of the fragments but also on thestrength of the waves and
ocean currents. On thebasis of texture of the source region, mode
offormation, nature of transporting agency andchemical composition
the sediments are broadlydivided into gravel, sand and mud.Gravel:
It is a coarse material ranging betweenboulders and granules. These
gravels mostly formpebble banks along the coast and are too heavy
tobe transported.Sand: The sand deposits contain fragments
ofdifferent rocks i.e., igneous or sedimentary ormetamorphic,
thoroughly mixed up. But the greater
part of ordinary sand contains grains of quartz,because it is
the most abundant constituent of theearth's crust not subject to
easy disintegration orchemical change. A little finer sediment
rangingfrom very coarse to very fine sand is also the resultof wear
of the rock.Silt, clay or Muds: These deposits in general arefiner
particles much smaller than sand. Clays aresomewhat finer than the
muds and act as a bindingmaterial of sediments. Their proportion
increaseswith the distance from the land. The origin of siltor clay
is generally from the disintegration of thecontinental rock both
sedimentary and plutonic.The silt is then carried by rivers into
the sea, assuspended particles. Muds are finer texture thanthe
sands. They consist to a large extent of minuteparticles of various
rock forming minerals, quartbeing the most abundant. Murray
distinguishesbetween three classes of mud based on the colourof the
sediments ranging from black to white withaddition of blue, yellow,
red or a mixture of allthese.
Blue Mud: It is the most common and widespreaddeposit in the
deeper areas surrounding continentallands, and in partially
enclosed seas. It isconsidered to be mainly formed of land
detritushence carbonate of lime ranges upto 35 percent.Most of the
deposits of blue mud are found alongthe Atlantic, the
Mediterranean, the Atlantic andthe Banda Sea.Red Mud: It is
differentiated from others by thepresence of iron oxide. As
compared to blue mudthis variety is rare. Typical localities of
itsoccurrence are Yellow Sea, the coasts of Brazil,and large areas
of the floor of the Arctic Ocean.Green Mud: It is mostly seen off
high coastsfree from large rivers and their deposits, such asthe
Pacific and the Atlantic coasts of NorthAmerica (South of Cape
Hatteras and Californiaspecially), off the coasts of Japan,
Australia andSouth Africa. As regards the minerals,
percentageglauconite ranges up to 7-8% and carbonate oflime 0.56%.
Green mud is found between 100-
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900 fathoms depth.2. Volcanic ProductThe volcanic material after
chemical andmechanical weathering is transported to the oceanby the
action of running a water and wind. Thesedeposits mainly consist of
lava.3. Organic RemainsOrganic remains are basically of two types:
theNeretic and the Pelagic. The former consists ofdead skeletons of
marine animals and plants andthe latter is a type of algae found in
the openoceanic environment. Neretic matter is depositedmostly on
the continental shelves and are generallycovered by terrigenous
material. These includeshells of molluscs and their fragments,
skeletonsof radiolaria and spicules of sponges, calcareousand
siliceous plant remains.Pelagic deposits consist of matter derived
fromalgae and are mostly in the form of liquid mud,generally known
as ooze. Pelagic materials areoozes which are divided into the two
groups onthe basis of lime and silica contents as follows:I.
Calcareous oozes: contain lime content inabundance and are seldom
found at greater depthbecause of their high degree of solubility.
On thebasis of principal organisms calcareous oozes arefurther
divided into two sub types.(a) Pteropod Ooze: Most of the pteropod
oozesare formed of floating pteropodmulluscs havingthin shells of
generally conical shape. It contain80 per cent of calcium carbonate
and is mostlyfound in the tropical oceans and seas at the depthof
300-1000 fathoms. The main location ofpteropod ooze includes the
western and easternparts of the Pacific Ocean, surrounding of
Azores,Canary Islands, Antiles, mid Mediterraneansubmarine ridge
and Indian Ocean.(b) Globigerina Ooze: Though this ooze isformed
from the shell of a variety of foraminiferabut most of such oozes
are formed of germs calledglobigerina. Globigerina is found mostly
in thetropical and temperate zones of the Atlantic Ocean,on the
eastern and western continental shelves ofthe Indian Ocean and in
the eastern Pacific Ocean.It contains about 65 percent of
calcium.II. Siliceous Ooze: When silica contentdominates, the ooze
becomes siliceous in nature.Silica is derived from group of
protozoa orradiolarian and benthic animals mainly sponges.This ooze
does not dissolve as compared tocalcareous ooze because of less
calcium carbonateand dominance of silica. Thus, such oozes arefound
in both warm and cold water at greaterdepths. This group is further
divided into two
subtypes on the basis of dominance of a particularorganism.(a)
Radiolarian ooze: is formed by the shells ofradiolaria and
foraminifera. Silica predominatesbut calcium carbonate is also
present. Lime contentdecreases with increasing depth and it
absolutelydisappears at greater depth. It covers the largestareas
in the Pacific Ocean.(b) Diatom ooze: is formed of the shells of
verymicroscopic plants containing silica in abundancealso contains
some clay. It is very frequently foundat greater depth in high
latitude. Significant areaof this deposit includes the zone around
Antarcticaand a belt from Alaska to Japan in the N. Pacific,at a
depth of 600-2000 fathoms.III. Inorganic Materials: Majority of
inorganicelements are basically precipitates which fall downfrom
above. These elements fall on the land aswell as in the oceans.
Some of the inorganicelements are transported from the land to
theoceans by various agencies. The inorganicprecipitates include
dolomite, amorphous silica,iron, manganese oxide, phosphate barite
etc.Besides, glauconite, phosphorite, feldspar,phillipsite and clay
minerals are also found.IV. Red clay: Previously considered to be
oforganic origin is the most significant inorganicmatter and very
important member of pelagicdeposits. It covers the largest area of
deep seadeposits. Silicates of alumina and oxides of ironare the
chief constituents of red clay. Besides,calcium, siliceous
organisms and a few mineralare also present. It also contains
decomposedvolcanic material. It may be pointed out that redclay
contains more radioactive substances than anyother marine deposit.
Red clay is widely distributedat the greatest depth in all the
ocean. Its dominantlocation include the zone between 400 N and 400S
in the Atlantic Ocean, eastern part of the IndianOcean and the
North Pacific Ocean covering 129million km2 of area.
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4. TIDES AND WAVESTidesTides are the rise and fall of sea levels
caused bythe combined effects of gravitational forces exertedby the
Moon, Sun, and rotation of the Earth. Thetide producing force of
the moon is slightly morethan twice that of the sun. Moon being
closer hasgreater impact than the sun. However, its
amplitudedepends upon the -movement of the moon,revolving position
of sun and moon with referenceto earth, uneven distribution of
water, irregularbottom topography of the oceans.Tides vary on time
scales ranging from hours toyears due to a number of factors. While
tides areusually the largest source of short-term
sea-levelfluctuations, sea levels are also subject to forcessuch as
wind and barometric pressure changes,resulting in storm surges,
especially in shallow seasand near coasts.Tidal phenomena are not
limited to the oceans, butcan occur in other systems whenever
agravitational field that varies in time and space
ispresent.CharacteristicsTide changes proceed via the following
stages:
• Sea level rises over several hours, covering theintertidal
zone; flood tide." The water rises to its highest level, reaching
hightide.
• Sea level falls over several hours, revealing theintertidal
zone; ebb tide.
• The water stops falling, reaching low tide.Types of tidesHigh
Tide and Low TideBecause the moon is closer to the earth than
thesun, it has the most influence on the tides. In fact,it's fair
to say that tides would not occur if theearth and the moon were not
attracted to each other.The gravitational pull of the moon causes
theoceans and other major water bodies to bulge outtoward the
moon.When the gravitational pull is at its highest point,the result
is high tide, which is the highest level ofthe tide. When the pull
is at its lowest point, wesee low tide, or the lowest level of the
tide. Theearth itself is also pulled toward the moon but withless
strength. This pulls the earth away from thewater on the opposite
side of the earth, makingthe water on that side bulge as well.
Therefore,high tide occurs on both sides of the planet at thesame
time. Meanwhile the earth is rotating. Sothe tides throughout the
day are experienced.
Semidiurnal and Diurnal Tidesif the earth were perfectly round
with no big landmasses, all bodies of water in the world
wouldexperience two nearly equal high tides and twolow tides each
day. This tidal pattern is known assemidiurnal tides. However, the
continents of earthdisrupt water bodies, and so this can
producedifferent tidal patterns. For example, some bodiesof water,
such as the Gulf of Mexico, have diurnaltides, which mean only one
high tide and one lowtide each day.Spring Tides and Neap TidesThe
earth and moon are constantly in motionaround the sun, and all have
their own gravitationalpull. So, when the alignment between the
threebodies changes, it changes the strength of theoverall
gravitational pull and therefore the size ofthe tides.Spring tides
are tides that occur when the earth,moon and sun are aligned,
[syzygy] and the tidalrange between high and low tide is at its
maximum.This happens basically twice a month, during the
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full and new moon phases. At these times, the threebodies are in
line and their gravitational pullsreinforce each other. When the
spring tide ishappening, we see higher than average high tidesand
lower than average low tides.A few weeks after the spring tides,
the neap tidesare observed. These are tides that occur when themoon
and sun are at right angles to the earth's orbit,and the tidal
range between high and low tide is atits minimum. The neap tides
occur when the moonis in its first and last quarter phase. Because
ofthe position of the moon and sun, their gravitationalpulls on the
waters of earth partially cancel eachother out, resulting in
smaller differences betweenthe high and low tides.
Advantages-• Helps in navigation by increasing the water
level
in the rivers. For example the Kolkata port is alsocalled the
tidal port because of this fact.
• Help in the generation of the tidal energy, one ofthe cleanest
sources of energy.
• Rich biodiversity in the form of inter tidal zonesin the form
of mangroves.
• Help in the natural cleansing of the ports.• Helpful to the
ship building industry in many ways.
Disadvantages-• High amount of water intrusion causes
destruction
to a great extent• Low lying areas are affected badly. Tides
causes
floods and submergence of these areas.• Restricts delta
formation as the accumulated
sediments are moved by the tides into the seaWavesWaves
represent a series of parallel crest separatedby troughs. They
travel over a definite directionfor great distances but it's only
the wave motionthat is transported whereas the water
particlesremain at the same places. Waves are
surficialmanifestation of the dynamism induced in the seawater by
the sub aerial forces of the wind anddifference in the atmospheric
pressure.Sculpting seawater into crested shapes, wavesmove water
and energy from one area to another.Waves located on the ocean's
surface arecommonly caused by wind transferring its energyto the
water, and big waves, or swells, can travelover long distances. A
wave's size depends on windspeed, wind duration, and the area over
which thewind is blowing This variability leads to waves ofall
shapes and sizes. The smallest categories ofwaves are ripples,
growing less than one foot (3m) high. The largest waves occur where
there arebig expanses of open water that wind can affect.Places
famous for big waves include, Hawaii;Mavericks, California;
Ireland; and Tahiti. Theselarge wave sites attract surfers,
althoughoccasionally, waves get just too big to surf.They are
generally classified as longitudinal andtransverse waves.
Longitudinal waves haveparticles moving parallel to the line of
propagationand the general motion is to and fro while thetransverse
waves have particles moving back andforth and perpendicular to the
propagation of thewave motion.
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Characteristics of the waves-The crest of the waves is defined
as its highestpart and the trough is the lowest part, whereas
thewave height or the amplitude is the verticaldistance from the
trough to the crest and the wavelength is the horizontal distance
between the crestto crest. The wave velocity is equal to the
distancetravelled by the wave in seconds and the waveperiod is the
time taken between the occurrence ofone wave crest and another at
fixed location.Sea waves are generated mainly by the
frictionalforce of the wind over the sea surface. They arealso
caused by the differences in the atmosphericpressure, temperature,
density and salinity of seawater sea waves are high waves with low
energyrogue waves and storm beakers are high energywaves but they
are local phenomenon and occurrarely.
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5. OCEAN CIRCULATIONOcean currents are masses of ocean water
that flowfrom one place to another. The amount of watercan be large
or small, currents can be at the surfaceor deep below, and the
phenomena that create themcan be simple or quite complex. Simply
put,currents are water masses in motion.Ocean currents are either
wind driven or densitydriven. Wind-driven currents move
waterhorizontally and occur primarily in the ocean'ssurface waters,
so these currents are called surfacecur-rents. Density-driven
circulation, on the otherhand, moves water vertically and accounts
for thethorough mixing of the deep masses of ocean water.
Ocean Surface CurrentsSurface currents occur within and above
thepycnocline to a depth of about 1 kilometre andaffect only about
10% of the world's ocean water.Origin of Surface
CurrentsSimplistically the friction between wind andsurface water
generates the surface ocean currents.During this process very
little amount of windenergy will get transferred to the ocean
surface. Ifthere were no continents on Earth, the surfacecurrents
would generally follow the major windbelts of the world. In each
hemi-sphere, therefore,a current would flow between 0 and 30
degreeslatitude as a result of the trade winds, a secondwould flow
be-tween 30 and 60 degrees latitudeas a result of the prevailing
westerlies, and a third
would flow between 60 and 90 degrees latitude asa result of the
polar easterlies.In reality, however, flow of the ocean
surfacecurrents is influenced by many factors such asdistribution
of continents etc.Main Components of Ocean
SurfaceCirculationSUBTROPICAL GYRES The large, circular-moving
loops of water that are driven by the majorwind belts of the world
are called gyres whichgenerally comprises of four main currents.
Theyrotate clockwise in the Northern Hemisphere andcounter
clockwise in the Southern Hemisphere.World's five subtropical
gyres:
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1. The North Atlantic Subtropical Gyre2. The South Atlantic
Subtropical Gyre3. The North Pacific Subtropical Gyre4. The South
Pacific Subtropical Gyre5. The Indian Ocean Subtropical
The main components of subtropical gyre are:Equatorial Currents
- produced by trade winds ofboth the hemispheres and flow westward.
Theyare called north or south equatorial currents,depending on
their position relative to the equator.Western Boundary Currents -
the Coriolis forcedeflects the Equatorial currents away from
theequator as western boundary currents. Forexample, the Gulf
Stream and the Brazil Currentare western boundary currents. They
carry warmwater to high latitudes.Northern or Southern Boundary
Currents - theyare produced by prevailing westerlies and
liedbetween 30 and 60 degrees latitude. They flowtowards east. In
the Northern Hemisphere, arecalled northern boundary currents; in
the SouthernHemisphere, they are called southern
boundarycurrents.Eastern Boundary Currents -Coriolis force
andcontinental barriers turn Northern or SouthernBoundary Currents
toward the equator, creatingeastern boundary currents .Examples of
easternboundary currents include the Canary Current andthe Benguela
Current. They carry cool water tolower latitudes.
EQUATORIAL COUNTERCURRENTS -Equatorial currents moves large
volume of waterwestward. As a result water piles up along
thewestern margin of an ocean basin, which raisessea level on the
western side of the basin. The wateron the western margins then
flows downhill underthe influence of gravity, creating narrow
equatorial
counter currents that flow to the east counter toand between the
adjoining equatorial currents.SUBPOLAR GYRES Northern or
southernboundary currents eventually move into subpolarlatitudes.
They are driven in a westerly directionby the polar easterlies,
producing subpolar gyresthat rotate opposite the adjacent
subtropical gyres.Subpolar gyres are smaller and fewer
thansubtropical gyres. Two examples include thesubpolar gyre in the
Atlantic Ocean betweenGreenland and Europe and in the Weddell Sea
offAntarctica.Several other factors influence circulation
patternsin subtropical gyres, including Ekman spiral andEkman
transport, geostrophic currents, andwestern intensification of
subtropical gyres.Ocean Currents and ClimateOcean surface currents
directly influence theclimate of adjoining landmasses. For
instance,warm ocean currents warm the nearby air. Thiswarm air can
hold a large amount of water vapour,which puts more moisture in the
atmosphere. Whenthis warm, moist air travels over a continent,
itreleases its water vapour in the form ofprecipitation producing
humid climate in general.
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Conversely, cold ocean currents cool the nearbyair, which is
more likely to have low water vapourcontent. When the cool, dry air
travels over acontinent, it results in very little
precipitationproducing dry climate.Upwelling and
DownwellingUpwelling is the vertical movement of cold,
deep,nutrient-rich water to the surface; downwelling isthe vertical
movement of surface water to deeperparts of the ocean. Upwelling
brings chilled water,rich in nutrients, to the surface resulting
into higherproductivity in that area. Downwelling, on theother
hand, is associated with much lower amountsof surface productivity
but carries necessarydissolved oxygen to those organisms living on
thedeep-sea floor. They provide important mixingmechanisms between
surface and deep waters andare accomplished by a variety of methods
such asdiverging surface water and converging surfacewater etc.
Main Surface Circulation Patterns in EachOceanThe pattern of
surface currents varies from oceanto ocean depending upon the
geometry of the oceanbasin, the pattern of major wind belts,
seasonalfactors, and other periodic changes.Atlantic Ocean
CirculationAtlantic Ocean surface circulation, which consistsof two
large subtropical gyres: the North AtlanticGyre and the South
Atlantic Gyre.THE NORTH AND SOUTH ATLANTICSUBTROPICAL GYRES The
North AtlanticSubtropical Gyre rotates clockwise and the
SouthAtlantic Subtropical Gyre rotates counterclockwise, due to the
combined effects of the tradewinds, the prevailing westerlies, and
the Corioliseffect. The two gyres are partially offset by theshapes
of the surrounding continents, and theAtlantic Equatorial Counter
current moves inbetween them.In the South Atlantic Gyre, the South
EquatorialCurrent reaches its greatest strength just belowthe
equator, where it encounters the coast of Braziland splits in two.
Part of the South EquatorialCurrent moves off along the
north-eastern coastof South America toward the Caribbean Sea andthe
North Atlantic. The rest is turned southwardas the Brazil Current,
which ultimately mergeswith the West Wind Drift and moves
eastwardacross the South Atlantic. The Brazil Current ismuch
smaller than its Northern Hemispherecounterpart, the Gulf Stream,
due to the splittingof the South Equatorial Current. The
BenguelaCurrent, slow moving and cold, flows towards theequator
along Africa's western coast, completingthe gyre.The North
Equatorial Current moves parallel tothe equator in the Northern
Hemisphere, where itis joined by the portion of the South
EquatorialCurrent that turns northward along the SouthAmerican
coast. This flow then splits into theAntilles Current, which passes
along the Atlanticside of the West Indies, and the Caribbean
Current,which passes through the Yucatán Channel intothe Gulf of
Mexico. These masses re-converge asthe Florida Current.
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The Florida Current flows close to shore over thecontinental
shelf. As it moves off North CarolinasCape Hatteras it is called
the Gulf Stream.The Sargasso Sea - The Gulf Stream graduallymerges
eastward with the water of the SargassoSea. The Sargasso Sea is the
water that circulatesaround the rotation centre of the North
Atlanticgyre. The Sargasso Sea can be thought of as thestagnant
eddy of the North Atlantic Gyre. Its nameis derived from a type of
floating marine alga calledSargassum that abounds on its
surface.Southeast of Newfoundland, the Gulf Streamcontinues in an
easterly direction across the NorthAtlantic. Here, one major branch
combines thecold water of the Labrador Current with the warmGulf
Stream, producing abundant fog in the NorthAtlantic. This branch
eventually breaks into theIrminger Current, which flows along
Iceland s westcoast, and the Norwegian Current, which
movesnorthward along Norway s coast. The other major
branch crosses the North Atlantic as North AtlanticDrift, which
turns southward to become the coolCanary Current. The Canary
Current is a broad,diffuse southward flow that eventually joins
theNorth Equatorial Current, thus completing thegyre.
CLIMATIC EFFECTS OF NORTH ATLANTICCURRENTS The warming effects
of the GulfStream are far ranging. The Gulf Stream not
onlymoderates temperatures along the East Coast ofthe United States
but also in northern Europe. Thus,the temperatures across the
Atlantic at differentlatitudes are much higher in Europe than in
NorthAmerica because of the effects of heat transferfrom the Gulf
Stream to Europe. For example,Spain and Portugal have warm
climates, eventhough they are at the same latitude as the
NewEngland states. The warming that northern Europeexperiences
because of the Gulf Stream is as muchas 9°C, which is enough to
keep high-latitudeBaltic ports ice free throughout the year. On
thewestern side of the North Atlantic, the southward-flowing
Labrador Current which is cold and oftencontains icebergs from
western Greenland keepsCanadian coastal waters much cooler. During
theNorthern Hemisphere winter, North Africa'scoastal waters are
cooled by the south-ward-flowing Canary Current and are much cooler
thanwaters near Florida and the Gulf of Mexico.
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Because of the shape and position of India, theIndian Ocean
exists mostly in the SouthernHemisphere. From November to March,
equatorialcirculation in the Indian Ocean is similar to thatin the
Atlantic Ocean, with two westward-flowingequatorial currents
separated by an eastward-flowing Equatorial Counter current. The
shape ofthe Indian Ocean basin and its proximity to thehigh
mountains of Asia cause it to experiencestrong seasonal changes.Not
only does this seasonal changes affect weatherpatterns on land, it
also affects surface currentcirculation in the Indian Ocean. In
fact, thenorthern Indian Ocean is the only place in theworld where
reversing seasonal winds actuallycause major ocean surface currents
to switchdirection. During the winter time northwestmonsoon,
offshore winds cause the NorthEquatorial Current to flow from east
to west andits extension, the Somali Current, flows south
along the coast of Africa. An Equatorial Countercurrent is also
established. During the summertimesouthwest monsoon, the winds
reverse, causing theNorth Equatorial Current to be replaced by
theSouthwest Monsoon Current, which flows in theopposite direction.
The winds cause the SomaliCurrent to reverse as well, which flows
rapidlynorthward and feeds the Southwest MonsoonCurrent. By
October, the northeast trade winds arere-established and the North
Equatorial Currentreappears.The movement of winds during the
summertimesouthwest monsoon also affects sea surfacetemperatures,
which cool near the ArabianPeninsula because of upwelling as water
is drawnaway from shore. This cool water also supportslarge
populations of phytoplankton during thesummer southwest
monsoon.INDIAN OCEAN SUBTROPICAL GYRESurface circulation in the
southern Indian Oceanis similar to subtropical gyres observed in
othersouthern oceans. When the northeast trade windsblow, the South
Equatorial Current provides waterfor the Equatorial Counter current
and the AgulhasCurrent, which flows southward along Africa's
eastcoast and joins the West Wind Drift. Turningnorthward out of
the West Wind Drift is the WestAustralian Current, an eastern
boundary currentthat merges with the South Equatorial
Current,completing the gyre.
Indian Ocean Circulation
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Pacific Ocean Circulation Two large subtropical gyres dominate
thecirculation pattern in the Pacific Ocean, resultingin surface
water movement and climatic effectssimilar to those found in the
Atlantic. However,the Equatorial Counter current is much
betterdeveloped in the Pacific Ocean than in the Atlantic,largely
because the Pacific Ocean basin is largerand more unobstructed than
the Atlantic Ocean.The North Pacific Subtropical Gyre includes
theNorth Equatorial Current, which flows westwardinto the western
intensified Kuroshio Current nearAsia. The warm waters of the
Kuroshio Currentmake Japans climate warmer than would beexpected
for its latitude. This current flows intothe North Pacific Current,
which connects to thecool-water California Current. The
CaliforniaCurrent flows south along the coast of Californiato
complete the loop. Some North Pacific Currentwater also flows to
the north and merges into theAlaskan Current in the Gulf of
Alaska.The South Pacific Subtropical Gyre includes theSouth
Equatorial Current, which flows westwardinto the western
intensified East AustralianCurrent. From there, it joins the West
Wind Driftand completes the gyre as the Peru Current.
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6. MARINE RESOURCESThe ocean environment holds a wealth of
resourcesthat we rely on, from fuel sources to food supplies.The
sea floor is rich in potential mineral andorganic resources. Some
of the marine resourcesavailable to us are as follows:-Petroleum-Of
the non-living resources extractedfrom the oceans, more than 95% of
the economicvalue is in petroleum products.Major offshorereserves
exist in the Persian Gulf, in the Gulf ofMexico, off Southern
California, in the North Sea,and in the East Indies. Future
offshore petroleumexploration will continue to be intense,
especiallyin deeper waters of the continental margins.Hydrocarbons-
The.Hydrocarbons are found insedimentary rocks beneath the seabed,
usuallyalong the edges of continents wheresedimentstransported by
rivers were laid down inthick sequences in the geological past.
Thesesediments also trap dead organic matter from plantsand
animals.The organic matter is turned into oiland methane gas (CH4),
through the action ofelevated temperatures and pressures. The oil
andgas usually form in organic-rich shales. They thenmigrate
through fractures and pool in highly porousand permeable rock
formations, such as sandstonesand limestones, creating a
hydrocarbon reservoir.Gas hydrates- Gas hydrates may represent
afuture source of fuel Gas hydrates are widespreadaround the world
and are usually found incontinental margin sediments.Food-The seas
and oceans contain vast naturalresources that are increasingly
available to humansas technology and scientific
understandingimprove. Fishes are important components ofseafood.
Ocean ranching, whaling, marine farmingare some of the forms for
utilising the searesources.Poly metallic manganese nodules-The
non-living resources of the deep ocean floor areincreasingly
attractive for the mineral industry.Polymetallic manganese nodules
(also knownas manganese nodules) are small potato-sizedlumps of
material precipitated from seawater andsediment pore water at slow
rates over millions ofyears and occur mainly on the deep-seafloor
Theycontain approximately 24% manganese, comparedto 35 to 55%
manganese in land ore bodies, sothey do not offer solid economics
as a manganesesource, Apart from these metals, nodules includetrace
amounts of molybdenum, platinum and otherbasemetalsPhosphates
Phosphorus- bearing compounds(phosphates) occur abundantly
ascoatingsonrocks and as noduleson the continental shelf
and on bank satdepths shallower than 1000 meters(3300
feet).Concentrations of phosphates in suchdeposits commonly reach
30% by weight andindicate abundant biological activity in
surfacewater above where they accumulate. Becausephosphates are
valuable as fertilizers, ancientmarine phosphate deposits that have
been upliftedonto land are extensively mined to supplyagricultural
needs.Biofuels from marine algae-One promisingsource of biofuels
has been identified as marinealgae grown in large open ponds. The
algae wouldbe harvested and turned into a carbon neutral
fuelsourceSandand Gravel- The offshore sand and gravelindustry is
second in economic value only to thepetroleumindustry. Sand and
gravel, which includesrock fragments that are washed out to sea
andshells of marine organisms, is mined byoffshorebarges using a
suction dredge. This material isprimarily used as aggregatein
concrete, as a fillmaterial in grading projects, and on
recreationalbeaches. Off shore deposit sareamajor source ofsand and
gravelin New England, New York, andthrough out the Gulf Coast. Many
Europeancountries, Iceland, Israel, and Lebanon also dependheavily
on such deposits.Some off shore sand andgravel deposits are rich in
valuable minerals.Vitamins and Drugs ResourcesResearches to use
marine organism (plants andanimals) for vitamins and medicines to
curedifferent diseases is going on.Shark oil and codliver oil are
already in use as energy tonics.It is beyond doubt that if the
present rate of growthof world population continues, the demand
forworld supply of food would also increaseproportionately in
future, which cannot be met withland sources alone. Thus, it is
necessary to looktowards marine food resource. It is evident
thatthe pressure on marine resource would increasesin future;
therefore it is necessary to initiatenecessary suitable steps for
exploitation,utilization, conservation and preservation ofmarine
resource.
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7. CORAL REEFSCorals are nothing but calcareous rocks,
formedfrom the skeletons of minute sea animals, calledpolyps. The
polyps extract calcium salts from seawater to form hard skeletons
which protect theirsoft bodies. These skeletons give rise to
corals.The corals live in colonies fastened to the rockysea floor.
New generations develop on skeletonsof dead polyps. The tubular
skeletons growupwards and outwards as a cemented calcareousrocky
mass, collectively called corals. The shallowrock created by these
depositions is called reef.These reefs, later on, evolve into
islands.The corals Occur in different forms and colours,depending
upon the nature of salts or constituentsthey are made of.
Progressive development ofcorals appears over the sea surface in
differentforms over a period of time. Small marine plants(algae)
also deposit calcium carbonate, thuscontributing to coral
growth.Ideal Conditions for Coral Growth1. Corals thrive in
tropical waters-between 30°Nand 30°S latitudes.2. The ideal depths
for coral growth are 45 m to55 m below sea surface, where there is
abundantsunlight available.3. The temperature of water should be
around20°C.4. Clear salt water is suitable for coral growth,while
both fresh water and highly saline water areharmful for polyp
growth.5. Adequate supply of oxygen and microscopicmarine food,
called plankton, is essential forgrowth and existence. As the food
supply is moreabundant on the seaward side, corals grow morerapidly
on the seaward side.Types of Coral Features:Coral reefs can be
classified on the basis of large-scale reef morphology; the size
and shape of areef, and its relation to nearby land (if any).Thisis
usually (but not always) sufficient to clearlydistinguish one type
from the others. There is oftena great deal of overlap among the
major reef types(within a given biogeographic region) in terms
ofthe dominant groups of animals and plants, as wellas their
ecological interactions.There are three major types of coral reefs:
FringingReef, Barrier Reef and Atoll1. Fringing Reef:It is by far
the most common of the three majortypes of coral reefs. It is a
coral platform attachedto a continental coast or an island,
sometimesseparated by a narrow, shallow lagoon or channel.
A fringing reef runs as a narrow belt, 0.5 km to2.5 km wide.
This type of reef grows from the deepsea bottom with the seaward
side sloping steeplyinto the deep sea.Coral polyps do not extend
outwards because ofsudden and large increase in depth. The surface
ofa fringing reef is rough, as it is covered with coralremains
forming a boulder zone or reef flat.2. Barrier Reef:This is the
largest of the three reefs, runs forhundreds of kilometres and is
several kilometreswide. It extends as a broken, irregular ring
aroundthe coast or an island, running almost parallel toit. A
barrier reef is characterised by distant locationof the reef from
the coast with a broader and deeperlagoon, which is sometimes
joined with the seawater through one or more channels cutting
acrossthe barrier reef.A barrier reef is very thick, going even
below 180metres from the surface with the seaward sidesloping
steeply into the deep sea. The surface of abarrier reef is covered
with coral debris, bouldersand sand.The most famous example of this
type ofreef is the Great Barrier Reef off the coast of
north-eastern Australia, which is 1900 km long and 160km wide.
3. Atoll:It is a ring like reef, which, partly or
completely,encloses a lagoon. The lagoon may have a levelsurface,
but the seaward side of the reef slopessteeply into deep sea. The
lagoon has a depth 80-150 metres and may be joined with sea
waterthrough a number of channels cutting across thereef.Atolls are
located at great distances from deep seaplatforms, where the
submarine features may helpin formation of atolls, such as a
submerged islandor a volcanic cone which may reach a level
suitablefor coral growth.Atolls are far more common in the Pacific
than
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any other ocean. The Fiji atoll and the Funafutiatoll in the
Ellice Island are well known examplesof atolls. A large number of
atolls also occur inthe Lakshadweep islands.Distribution of Coral
ReefsThe majority of reef building corals are foundwithin tropical
and subtropical waters. Thesetypically occur between 300 north and
300 southlatitudes.The Indonesian/Philippines archipelago has
theworld's greatest concentration of reefs and thegreatest coral
diversity. Other area of reefconcentration are the Great Barrier
Reef ofAustralia, the Red Sea and the Caribbean, the latterhaving a
much lower diversity than all major Indo-Pacific regions.World's
major coral reef regions:• Caribbean/ western Atlantic• Eastern
Pacific• Central and western Pacific• Indian Ocean• Arabian Gulf•
Red Sea
Theories on Origin of Corals:Various theories have been put
forth to explainthe mode of origin of coral reefs, taking
intoaccount the fluctuation of the Pleistocene sea leveland the
stability of the land concerned. The latterfact analyses three
conditions-a subsiding island,a stationary island and an emerging
land with reefsalong them.Out of the three types of reefs, fringing
reef isperhaps the most simple and easiest to explain.Corals in the
past established themselves alongsuitable submarine structures,
within around 50metres of depth. Upward growth, however, ceasedwhen
the reef reached the low tide level because
coral polyps cannot stand a long exposure toatmosphere, but the
outward growth towards thesea continued.The material eroded by
waves wasconsequently deposited on its surface. The originof the
other two reefs, the barrier and the atoll, isnot so easy to
explain. Hence, there are differentviews on their origin.All the
theories of reef formation can be broadlycategorised into two
groups:1. Subsidence theories2. Non-subsidence theoriesDarwin's
Subsidence Theory:This theory was put forth by Charles Darwin
in1837 and modified in 1842, during his voyage onthe Beagle when it
became clear to him that coralpolyps could grow only in shallow
waters.Darwin assumes that along a suitable platform,coral polyps
flocked together and grew upwardtowards a low water level. The
resulting reef, inthis stable condition, would be a fringing reef.
But,at the same time, Darwin assumes, the sea floorand the
projecting land in coral seas startedsubmerging, and the living
corals found themselvesin deeper waters. Hence, an urge to grow
upwardand outward would be balanced by the subsidenceof the land.As
a result of this, Darwin postulated that thefringing reef, barrier
reefs and atolls are only threestages in the evolutionary growth of
a reef. As theland subsides, the fringing reef would growupwards
and outwards, resulting in the formationof a shallow lagoon.Further
subsidence would convert it into a barrierreef with wide and
comparatively deeper lagoon.The width of the reef is increased due
to the rapidoutward growth of the reef and deposition of
coraldebris along it. The last stage of submergence(comparable to
thousands of feet) results in partialor complete disappearance of
the land and theexistence of a coral ring enclosing a lagoon.In
spite of continued subsidence, Darwin maintainsthat the shallowness
of the lagoon would be dueto the deposition of the sediment from
the nearbysubsiding land. Hence, the lagoon always remainsflat and
shallow.The theory, though simple in its presentation,implies that
the barrier reef and atoll can occuronly in the areas of
submergence, and the greatamount of vertical thickness of coral
material isprimarily due to the subsidence of land andconsequent
upward growth of coral polyps.Evidence in Support of the
Theory:There is much evidence of subsidence in coral
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areas. For example, submerged valleys in the eastof Indonesia
and the coastal areas of Queensland.Had there been no subsidence,
the sedimentproduced by the erosion of coral reefs would havefilled
the lagoons and caused the death of corals.
The material produced by erosion getscontinuously accumulated at
the subsiding lagoonbottom. That is why the lagoons are
shallow.During an experimental boring, done to a depth of340 m in
the island atoll of Funafuti, dead coralswere discovered at these
depths.Only subsidence can explain existence of coralsat this depth
because, generally, corals cannot growbelow 100 metres. Also, these
dead corals showedthe evidence of their having got 'dolomitised'
whichis possible only in shallow waters. All this evidencegoes to
prove the subsidence theory.Evidence against the Subsidence
Theory:Some scientists, have argued that the corals havedeveloped
in places where there is no evidence ofsubsidence. Timor is one
such area. Similarly,lagoons, with depths of 40m to 45m and
manykilometres wide, cannot be explained on the basisof
subsidence.Also, the question arises as to why there is
uniformsubsidence in the tropical and subtropical areasand not so
in other areas.If it is supposed that the coral islands are a
productof subsidence, we will have to assume the existenceof a vast
area in the Pacific Ocean which has
submerged, leaving behind corals as islands. Thereis no evidence
of the existence of such a vast landarea in Pacific Ocean which
existed in the ancienttimes.
Murray's Stand Still TheoryJohn Murray was against the idea of
coralformation due to subsidence of submarineplatform. As per him,
any submarine platformcould be lowered by erosion or built up
bydeposition until it was at a suitable height for coralsto
grow.Then the corals will start growing on this platformleading to
the formation of a fringing reef. Due tothe increased growth on the
outward margin ofthe reef it will turn into a barrier reef.Atolls
are formed due to outward growth of coralsin all directions at the
top of the submarineplatform. In the Lagoon side of the Atoll,
deadcorals are found which get dissolved making thelagoon deeper
and on the other side we'll find livingcorals.He argued that either
by the erosion of volcanichills rising above sea-level or by the
deposition ofsediments on those lying below sea-level, it
waspossible to have an adequate number of shallowsubmarine
platforms on which the reef-buildingcorals could grow.He explained
the existence of corals bellow 30fathom depth by saying that above
this depth reef
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will be formed by living corals, while at greaterdepths mostly
coral debris will be found whichwill be cemented by ocean water.His
theory has been criticised due to the followingreasons:• Existence
of submarine platforms everywhere isdoubtful.• It is difficult to
accept lagoon formation bysolution as sea water is not a good
solvent.• Reefs are found below the depth of 30 fathoms.• The
assumption that both erosion and depositionare active at the depth
of 30 fathoms, does notseem logical.Daly's Glacial Control
Theory:Daly, while studying the coral reefs of Hawaii,was greatly
impressed by two things. He observedthat the reefs were very narrow
and there weremarks of glaciations. It appeared to him that
thereshould be a close relationship between the growthof reefs and
temperature.According to Daly's hypothesis, in the last
glacialperiod, an ice sheet had developed due to the fallin
temperature. This caused a withdrawal of water,equal to the weight
of the ice sheet. Thiswithdrawal lowered the sea level by 125-150
m.The corals which existed prior to the ice age hadto face this
fall in temperature dining this age andthey were also exposed to
air when the sea levelfell. As a result, the corals were killed and
the coralreefs and atolls were planed down by sea erosionto the
falling level of sea in that period.When the ice age ended, the
temperature startedrising and the ice sheet melted. The water
returnedto the sea, which started rising. Due to the rise
intemperature and sea level, corals again startedgrowing over the
platforms which were lowereddue to marine erosion.As the sea level
rose, the coral colonies also rose.The coral colonies developed
more on thecircumference of the platforms because food andother
facilities were better available there thananywhere else.Hence, the
shape of coral reefs took the form ofthe edges of submerged
platforms. A long coralreef developed on the continental shelf
situated onthe coast of eastern Australia. Coral reefs and
atollsdeveloped on submerged plateau tops. After theice age, the
surface of platforms was not affectedby any endogenetic forces and
the crust of the earthremained stationary.
Evidence in Support of Daly's Hypothesis:The experimental
borings done on the Funafutiatoll provide evidence in support of
Daly'shypothesis. Also, in the ice age, all the platformswere cut
down to the sea level by marine erosion.Hence, the depth of these
platforms and that oflagoons with barrier reefs and coral atolls
werealmost equal.Study shows that the depths of the platforms andof
lagoons are equal at all places. The greatestmerit of this
hypothesis is that it needs nosubsidence of the crust, as is the
case with Darwin'shypothesis. Finally, the sea waves and
currentscould have easily cut down the islands andconverted them
into low platforms.Evidence against Daly's Hypothesis:There are
some platforms which are so long andbroad that their formation
cannot be consideredas the work of marine erosion alone. One
suchplatform is the Nazareth Platform-350 km longand 100 km wide.
It is about 600 m higheverywhere.Also, Daly could not explain the
existence s ofcoral colonies at depths of 100 metres. He had
toadmit local subsidence to be able to explain coralcolonies in
some deeper areas. Daly had alsocalculated that the fall of sea
level during the iceage was around 80 metres.It appears that this
calculation is not correct. Infact, the fall of sea level can be
correctly measuredby the angle of walls of submerged
V-shapedvalleys. If calculation is done on this basis, thesea level
should have fallen by more than 80m.Finally, Daly had stated that
the temperature waslowered during the ice age. It must have
causedthe death of corals, but there is no evidence of this
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phenomenon.From the above discussion, it appears that
thehypotheses of Darwin and Daly are notcontradictory but
complementary. Both togetherthrow a lot of light on the
phenomenon.Davis' Application of Physiography to theProblem of
Origin of Coral Reefs:Davis gave his explanation in order to revive
andre-establish the old idea of submergence as appliedto the coral
reef problem. In 1928, he attempted togive concrete physiographic
evidences to explainvarious problems hitherto unsolved.To begin
with, Davis reasserted the validity ofsubmergence. He stressed that
the indented andembayed coastlines found in the coral
seasdemonstrate the submergence of the land.According to him, the
flatness does not denote thetrue bottom of the lagoon, but is only
due to thedeposition of debris. Similarly, the shallowness ofthe
lagoon illustrates the subsidence of the land.Davis has also taken
into consideration the factsof changing sea level. According to
him, loweredsea level on subsiding islands would also createcliffs
and spurs, but most of them would beprotected by reefs along the
shores from waveattack, hence cliffs would not be seen.
Further,subsidence would also drown such cliffs if theywere
formed.
Thus, this theory advocates the old idea ofsubsidence with
renewed application ofphysiography. It is also comprehensive in
itsapplication as it includes the changes of thesealevel as well as
the tectonic changes of thelandmass.In spite of the above evidence,
one fact is leftunexplained, viz. the assumed equal depth of
thelagoons. The flat floor of the lagoon and its shallow
depths may be attributed to the sedimentation, butthis in no
case proves that the original bottom ofthe lagoon, concealed
beneath, may not be showingdifferent depths.Coral reef
bleachingCoral reef ecosystems world-wide have beensubject to
unprecedented degradation over the pastfew decades. Disturbances
affecting coral reefsinclude anthropogenic and natural events.
Recentaccelerated coral reef decline seems to be relatedmostly to
anthropogenic impacts (overexploitation,overfishing, increased
sedimentation and nutrientoverloading. Natural disturbances which
causedamage to coral reefs include violent storms,flooding, high
and low temperature extremes, ElNino Southern Oscillation (ENSO)
events etc.Coral bleaching occurs when the relationshipbetween the
coral host and marine algae, whichgive coral much of their colour,
breaks down.Without the marine algae, the tissue of the coralanimal
appears transparent and the coral's brightwhite skeleton is
revealed.Coral reef bleaching isa common stress response of corals
to many of thevarious disturbances mentioned above.Corals begin to
starve once they bleach. Whilesome corals are able to feed
themselves, mostcorals struggle to survive without their algae.If
conditions return to normal, corals can regaintheir algae, return
to their normal colour andsurvive. However, this stress is likely
to causedecreased coral growth and reproduction, andincreased
susceptibility to disease.
Bleached corals often die if the stress persists.Coral reefs
that have high rates of coral deathfollowing bleaching can take
many years ordecades to recover.Causes of coral bleachingAs coral
reef bleaching is a general response tostress, it can be induced by
a variety of factors,alone or in combination. It is therefore
difficult to
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unequivocally identify the causes for bleachingevents. The
following stressors have beenimplicated in coral reef bleaching
events.TemperatureCoral species live within a relatively
narrowtemperature margin and therefore, low and highsea
temperatures can induce coral bleaching.Bleaching events occur
during sudden temperaturedrops accompanying intense upwelling
episodes,seasonal cold-air outbreaks etc.Solar IrradianceBleaching
during the summer months, duringseasonal temperature and irradiance
maxima oftenoccurs disproportionately in shallow-living coralsand
on the exposed summits of colonies.Sub-aerial ExposureSudden
exposure of reef flat corals to theatmosphere during events such as
extreme lowtides, ENSO-related sea level drops or tectonicuplift
can potentially induce bleaching.Fresh Water DilutionRapid dilution
of reef waters from storm-generatedprecipitation and runoff has
been demonstrated tocause coral reef bleaching.Other causes
includes the increase in theconcentration of inorganic
Nutrients,sedimentation, oxygen starvation caused by anincrease in
zooplankton levels as a result ofoverfishing, ocean acidification,
changes insalinity, sea level change due to global warming,cyanide
fishing etc.
Spatial and temporal range of coral reefbleachingMass coral
moralities in coral reef ecosystemshave been reported in all major
reef provinces sincethe 1870s. The frequency and scale of
bleachingdisturbances has increased dramatically since thelate
70's. This is possibly due to more observersand a greater interest
in reporting in recent years.More than 60 coral reef bleaching
events out of105 mass coral moralities were reported
during1979-1990, compared with only three bleachingevents among 63
mass coral moralities recordedduring the preceding 103 years.
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8. SEA LEVEL CHANGEBy changes in sea level, we mean the
fluctuationsin the mean sea level, i.e., the average level of
thesea surface. Thus, the changes in sea level mayalso be termed as
a relative change in sea level.During a relative rise in sea level,
either the landor the sea surface may undergo upliftment
orsubsidence, or both may rise and fall at the sametime.The major
categories of change in sea level arementioned(i) Eustatic changes
occur when the volume of seawater changes due to factors such as
globalwarming and melting of ice sheets (rise in sealevel) or ice
ages (fall in sea level).(ii) Tectonic changes occur due to a
change in thelevel of land. These changes occur due to thefollowing
factors:(a) Isostatic changes which take place due toaddition or
removal of load, e.g., during ice ages,landmass subsided due to the
tremendous loadexerted by the glacial ice; as a result, there was
anapparent rise in sea level. On the other hand, thelandmass of
Scandinavia is still rising as the glacialice is being removed(b)
Epeirogenic movement occurs due to broadscale tilting of continents
which may result in therise of one part of the continent in
relation to themean sea level even as the other part may
subsidecausing an apparent rise in sea level.(c) Orogenic movement
is related to folding andflexuring (stretching of a part of the
earth's crust)of the lithosphere which results in the formationof
lofty mountains and an apparent fall in sea level.Relevance of the
Study of Sea Level Changes:The study of sea level changes is
important. Itprovides key evidences regarding climate changeand
also enables us to draw a benchmark forestimating the rates of
tectonic upliftment in thepast geological periods. Sea level
directlyinfluences the rate and pattern of erosional
anddepositional processes in the coastal areas. Bystudying the
fluctuations of sea level it becomespossible to assess the
suitability of coastallocations for industrial development.
Thefluctuations in sea level determine the availabilityof land,
particularly in coastal areas, which areimportant for agricultural
purposes. Thesubmergence of land in future could be a disasterfor
the human civilisation as it may endanger ourfood security. By
predicting climate change andthe possible areas to be submerged
under sea, itbecomes possible for the low-lying countries tobuild
coastal dykes and embankments. The task
of mapping of areas likely to be affected by stormsurges and
periodic flooding becomes possible onlyif we know the likely areas
to be affected by futuresea level rise. The construction of tidal
powergeneration units needs suitable locations. Byidentifying the
areas of possible submergence inthe near future it becomes possible
for us to set uptidal power generation plants in suitable
locations.Mechanisms of the Change in Sea Level:The fluctuations of
sea level involve three basicmechanisms: changes in ocean water
volume;changes in ocean basin volume; changes in thegeoid, i.e.,
the shape of the earthChanges in the volume of ocean water: The
presentsea level would rise by about 60 to 75 m if the icein
Antarctica melts, whereas the Greenland ice capwould contribute
about 5 m rise in sea level. It isassumed that, in such a case, the
added load ofocean water would lead to the sinking of the
oceanfloor due to isostatic compensation. So the totalrise of sea
level would be about 40-50 m. However,the isostatic adjustment of
the land and the oceanis still not clear due to lack of data.Change
in the volume of the ocean basin:Changes in the volume of ocean
basin and theresultant changes in sea level were an importantevent
of the Mesozoic Era and the early CenozoicEra.Such changes occur
due to the followingfactors:(i) Changes in the volume of
mid-oceanicridges:An important tectonic cause of sea level
rise,changes in the volume of mid-oceanic ridges mayoccur due to
periodic reorganisation of plateboundaries which cause variations
in the totallength of the ridge system. If the lithosphere iswarm,
the spreading rate increases causing anincrease in ridge volume and
vice versa. The sealevel rises when the oceanic ridge increases
involume.(ii) Accumulation of sediments on the oceanfloor:Sediments
are produced by the denudation ofcontinents and are deposited on
the ocean floor.The deposition of sediments may result in
thesubsidence of the ocean floor and the removal ofsediments either
through subduction or upliftment.If we do not take these two
factors intoconsideration, there will be a rise in sea level dueto
the decreased volume of the ocean basin.(iii) Impact of
orogenesis:As orogenesis causes shortening and thickening
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of continental crust and a reduction in the area ofcontinents,
the sea level falls as a result of anincrease in the volume of the
ocean basin.Short-Term Changes in Global Sea Level: Short-term
changes occur during a year. Commonly,seasonal variations of 5-6 cm
in sea level areobserved in a year. But the fluctuations of sea
levelreach 20-30 cm or more in almost all coastal areasof the
world. Even if the causes of such short-termchanges are not known,
the fluctuations of sea levelmay be due to a complex interaction of
thefollowing factors:(i) Marine water density: Temperature
andsalinity control the density of sea water. Lowtemperature and
high salinity produce high densityof sea water and lower sea level.
It is due to lowertemperature and higher salinity that the
easternpart of the Pacific Ocean has a sea level30-50 cmhigher than
the Atlantic Ocean.(ii) Atmospheric pressure:Low pressure results
in higher local sea level andvice versa. The sea level rises
locally in places oflow pressure because water is sucked in by
theupward moving air mass.
(iii) Velocity of ocean currents:Fast-flowing ocean currents
when taking a curvedpath cause arise in sea level on their outer
fringes.(iv) Ice formation and fall in sea level:During winter the
ocean water trapped in theicecaps of the northern and the
southernhemispheres leads to a fall in sea level.(v) Piling up of
water along windward coasts:A local rise of sea level occurs in the
coastal regionas water is driven towards the coasts by an airmass,
for example, the sea level rises in south andEast Asia during the
monsoon months due tolandward movement of the air mass. The
twentiethcentury has observed short-term global sea levelrise due
to the following factors. Global warmingin the last century due to
anthropogenic activitieshas resulted in thermal expansion of ocean
water.Impact of the sea level fall- changes in the baselevel of
rivers, rejuvenated landforms ,extendedshoreline ,lengthening of
rivers ,death of coralreefs, extension of ice caps.
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9. MARINE POLLUTIONMarine pollution occurs when harmful,
orpotentially harmful, effects result from the entryof the
chemicals, particles, industrial, agriculturaland residential
waste, noise, or the spread ofinvasive organisms into the
oceans.Causes-The various causes of marine pollutionare as
follows-
• Oil- Oil spills cause huge damage to the marineenvironment.
Oil spills penetrate into the structureof the plumage of birds and
the fur of mammals,reducing its insulating ability, and making
themmore vulnerable to temperature fluctuations andmuch less
buoyant in the water. Clean up andrecovery from an oil spill is
difficult and dependsupon many factors, including the type of oil
spilled,the temperature of the water (affecting evaporationand
biodegradation), and the types of shorelinesand beaches
involved.
• Fertilizers- Fertilizer runoff from farms and lawnsis a huge
problem for coastal areas. Nitrogen-richfertilizers applied by
farmers inland, for example,end up in local streams, rivers, and
groundwaterand are eventually deposited in estuaries, bays,and
deltas. These excess nutrients can spawnmassive blooms of algae
that rob the water ofoxygen (eutrophication), leaving areas where
littleor no marine life can exist. Eutrophication hascreated
enormous dead zones in several parts ofthe world, including the
Gulf of Mexico and theBaltic Sea.
• Solid garbage- Solid garbage also makes its wayto the ocean in
the form of Plastic bags, balloons,glass bottles, shoes, and
packaging material.Plastic garbage, which decomposes very slowly,is
often mistaken for food by marine animals. Highconcentrations of
plastic material, particularlyplastic bags, have been found
blocking thebreathing passages and stomachs of many marinespecies,
including whales, dolphins, and seals,puffins, and turtles This
garbage can also comeback to shore, where it pollutes beaches and
othercoastal habitats.
• Sewage disposal- In many parts of the world,sewage flows
untreated, or under-treated, into theocean. For example, 80% of
urban sewagedischarged into the Mediterranean Sea is untreated.This
sewage can also lead to eutrophication. Inaddition, it can cause
human disease and lead tobeach closures
• Toxic chemicals- Almost every marine organism,from the tiniest
plankton to whales and polar bears,is contaminated with man-made
chemicals, suchas pesticides and chemicals used in common
consumer products. Some of these chemicals enterthe sea through
deliberate dumping. For centuries,the oceans have been a convenient
dumping groundfor waste generated on land. Chemicals also enterthe
sea from land-based activities. Chemicals canescape into water,
soil, and air during theirmanufacture, use, or disposal, as well as
fromaccidental leaks or fires in products containingthese
chemicals. Once in the environment, theycan travel for long
distances in air and waterEvidence is mounting that a number of
man-madechemicals can cause serious health problemsincluding
cancer, damage to the immune system,behavioural problems, and
reduced fertility.
• Radioactive Waste-Radioactive waste is alsodumped in the
oceans and usually comes from thenuclear power process, medical use
ofradioisotopes, research use of radioisotopes andindustrial uses.
The difference between industrialwaste and nuclear waste is that
nuclear wasteusually remains radioactive for decades. Theprotocol
for disposing of nuclear waste involvesspecial treatment by keeping
it in concrete drumsso that it doesn't spread when it hits the
ocean floor.The concentration of radioactive waste in theconcrete
drums varies as does the danger to marinelife and humans.
• Underwater noise- Marine life can be susceptibleto noise or
the sound pollution from sources suchas passing ships, oil
exploration seismic surveys,and naval low-frequency active sonar.
Soundtravels more rapidly and over larger distances inthe sea than
in the atmosphere. Marine animals,such as cetaceans, often have
weak eyesight, andlive in a world largely defined by
acousticinformation.
• Ocean Mining- Ocean mining in the deep sea isyet another
source of ocean pollution. Oceanmining sites drilling for silver,
gold, copper, cobaltand zinc create sulphide deposits up to three
and ahalf thousand meters down in to the ocean.Ecosystem is
severely hampered. This permanentdamage dealt also causes leaking,
corrosion andoil spills that only drastically further hinder
theecosystem of the region.
• Major shipping corridors result in direct damageto the marine
environment by anchor drag and theneed for dredging activities to
maintain shippingchannels. Activities at larger ports present a
riskof introduction of species, accidental spills,potential
contamination, and habitat destruction.Pressure from ports, other
marine facilities andrelated infrastructure is expected to
increase.Effects of marine pollution• Effect of Toxic Wastes on
Marine Animals-
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Oil spill is dangerous to marine life in sev-eral ways. The oil
spilled in the ocean couldget on to the gills and feathers of
marine ani-mals, which makes it difficult for them tomove or fly
properly or feed their children.The long term effect on marine life
can in-clude cancer, failure in the reproductive sys-tem,
behavioural changes, and even death.
• Disruption to the Cycle of Coral Reefs- Oilspill floats on the
surface of water and pre-vents sunlight from reaching to marine
plantsand affects in the process of photosynthesis.Skin irritation,
eye irritation, lung and liverproblems can impact marine life over
longperiod of time.
• Depletes Oxygen Content in Water- Most ofthe debris in the
ocean does not decomposeand remain in the ocean for years. It
usesoxygen as it degrades. As a result of this,oxygen levels go
down. When oxygen levelsgo down, the chances of survival of
marineanimals like whales, turtles, sharks, dolphins,penguins for
long time also goes down.
• Failure in the Reproductive System of SeaAnimals- Industrial
and agricultural wastesinclude various poisonous chemicals that
areconsidered hazardous for marine life. Chemi-cals from pesticides
can accumulate in thefatty tissue of animals, leading to failure
intheir reproductive system.
• Effect on Food Chain- Chemicals used in in-dustries and
agriculture get washed into therivers and from there are carried
into theoceans. These chemicals do not get dissolvedand sink at the
bottom of the ocean. Smallanimals ingest these chemicals and are
later
eaten by large animals, which then affects thewhole food
chain.
• Affects Human Health- Animals from im-pacted food chain are
then eaten by humanswhich affects their health as toxins from
thesecontaminated animals gets deposited in thetissues of people
and can lead to cancer, birthdefects or long term health
problems.
Marine environmental management• Environmental impact assessment
should be
undertaken by developers with projects thatare likely to
significantly impact the environ-ment.
• Impacts have to be considered collectively,such as dredging,
nutrient enrichment and theinput of contaminants, and
cumulativelywhere impacts from multiple developmentscontribute to
significant, cumulative loss ordisturbance of habitats.
• Marine and coastal habitat mapping shouldbe incorporated, in
order to estimate the scaleof damage caused due to human activities
geo-graphically.
• Mangrove assessment projects should also beundertaken to
document and assess informa-tion about mangroves, in order to
assist intheir management and conservation.
• Various mitigation measures to be imple-mented to reduce
impacts to benthic habitatsfrom marine pollution and towed
equipment,as well as mitigation to be implemented toreduce impacts
to reef fish, will also mini-mize impacts to corals from various
marineprojects