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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

PREP-SUPPLEMENT: OCEANOGRAPHY

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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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PREP-SUPPLEMENT: OCEANOGRAPHY

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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