PCO 2009- 10 physical chemical oceanography

8/7/2019 PCO 2009- 10 physical chemical oceanography

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Oceanography

Greek word- Oceanus+ graphos meansdescription of oceans. It is scientificinvestigations, exploration and exploitation of

seafood, minerals and energy Oceanography is the scientific study of the

ocean. It is not a single science. There is fourparts viz. Chemical, biological, physical andgeological. Ocean engineering and marinepolicy is also included


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Oceanography

Chemical oceanography is concerned withchemical reactions that occur both in theocean and on the sea floor

Bio. Ocean. Involves the study of distribution and environmental aspects oflife

Physical reactions, such as changes andmotion of sea water are comes under physical oceanography


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Why study of ocean

Hostile and not readily accessibleenvironment that does not easily yield its

secrets Ocean is source of many commerciallyvaluable chemicals

Record of geological and biological history

Important food


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FATHER OF OCEANOGRAPHY

Lt Mathew Fontaine Maury is often calledthe father of oceanography

Maurys maps of ocean currents, seasurface temperature and surface winds areamong his greatest accomplishments


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Ocean basin


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Ocean basin

Ocean basins can be described as saucer likedepressions of the sea bed

They vary in size from relatively minor features

of the continental margin to vast structuraldivisions of the deep ocean The largest ocean basins are 3 to 5 km deep

and stretch from the outer margins of the

continents to the mid ocean ridges Ocean basins cover approximately 71% of theEarths surface or about 361 m km2


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Ocean basin

Their depth is 5000 m and the total volume isabout 1.35 billion km3

There are five major sub divisions of the world

ocean: the Pacific, the Atlantic, the Indian, theSouthern and the Arctic ocean The Pacific, the Atlantic and the Indian oceans

are conventional ocean basins and are bounded

by the continental masses or by ocean ridgesand currents; they merge below 400 Southlatitude in Antarctic circumpolar current, or westwind drift, at the Southern ocean


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Pacific ocean basin

The pacific ocean basin is bounded on theeast by the North and South Americancontinents; on the north by the Bering

Strait; on the west by Asia, the MalayArchipelago, and Australia; and on thesouth by the Southern ocean

It is by far the largest and deepest of theworlds oceans and contains more thanhalf of its free water


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Pacific ocean basin

The pacific is the oldest of the existing oceanbasins, its oldest rocks having been dated atabout 200 m years

The major features of the basin have beenshaped by the phenomenon associated withplate tectonics

The coastal shelf, which extends to depths of

about 180 m, is narrow along North and SouthAmerica, but is relatively wide along Asia andAustralia


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Pacific ocean basin

The east Pacific rise, a mid ocean ridge, extendsfrom the Gulf of California to a point west of thesouthern tip of South America, and rises anaverage of 2130 m above the ocean floor

Along the East Pacific rise, molten rock up wellsfrom earths mantle, adding crust to the plateson each side of the rise. Due to that the oceanplates forced downward, farming deep trenches

called subduction zone The stresses at these areas of subduction areresponsible for the earthquakes and volcanoesthat the Pacific basin the name ring of fire


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Atlantic ocean basin

Second largest ocean basin, the most heavilytraveled, and the most intensely studied,principally because of its importance in the ship

traffic between Europe and North America Occupies 20% of Earths surface, representing

approximately 75 m km2 , this includes itsmarginal seas; Baltic, Black, Caribbean, Davisstrait, Denmark strait, Gulf of Mexico,Mediterranean sea, North sea, Norwegian sea,and almost all of the Scotia sea


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The Atlantic is divided into two nominal sections:North Atlantic and South Atlantic

The ocean is essentially an S- shaped north-

south channel, extending from Arctic ocean inthe North to Southern ocean in the south The Atlantic ocean has an average depth of

3926 m, the deepest point is Milwaukee deep in

the Puerto Rico Trench (8605 m below surface It began to form during the Jurassic period,about 150 m years ago


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Along the American, African and Europeancoasts, there are the continental shelvesof the Atlantic basin


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Indian ocean basin

It is third largest of the five oceans Bounded on west by Africa, on North by Asia, on the

east by Australia and the Australian islands, and on thesouth by the Southern ocean

No natural boundary separates the Indian ocean fromthe Atlantic ocean, but a line about 4020 km long,connecting Cape Agulhas at the southern end ofAfricawith Antarctica

Total area is 68 m km2

, which includes its marginal seas;Adman sea, Arabian sea, Bay of Bengal, GreatAustralian Bight, Gulf of Aden, Gulf of Oman, PersianGulf, Red sea and Strait of Malacca


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Indian ocean basin

The average depth of the basin is about4210 m, although the Java trench reachesa depth of over 7258 m

The Indian basin is also divided in half bythe mid Indian Ocean ridge


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Southern ocean basin

It extends from the coast of Antarcticanorth to 600 South latitude

It is fourth largest ocean of the world Its area is 20 m km2 and includesAmundsen sea, Bellingshausen sea, Rosssea, Weddell sea


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Arctic ocean basin

The smallest of Earths five ocean basin isthe Arctic

It extends from the North pole to theshores of Europe, Asia and North America

The surface waters of the Arctic oceanmingle with those of the Pacific ocean

through the Bering strait, by way of anarrow and a shallow channel The total water area is 14 m km2


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Arctic ocean basin

Approximately one third of the Arcticocean is underlain by continental shelf,which includes a broad shelf north of

Eurasia and the narrower shelves ofNorthAmerica and Greenland

The average depth of the Arctic ocean isonly about 1500 m

The deepest point in the Arctic ocean is5450 m


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Distribution of water and land

Area of earth surface is 510.1 m km2 Land area- 148.8 m km2 (29.2%)

Ocean area- 361.3 m km2 (70.8%)

The world ocean is a continuous water blanketover the earth adjacent to all of the continentsand islands and possesses a generally saltystructure

In the Northern Hemisphere, the world oceanoccupies 61% of the area and in the SouthernHemisphere, 81%


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In one hemisphere the land dominated and inone the water is dominated, water will appear tocover more than half of the area (53%)

The oceanic hemisphere takes up about 91% ofthe area

The land predominates only between latitudes of450 N and 700 N, and to the south from latitudes700 to south pole. Water predominates theremaining part of the Globe


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The shapes of the shorelines, bottom,relief, systems of oceanic currents, tides,atmospheric circulation and a number of

other criteria subdivide the world oceaninto Pacific, Atlantic, Indian, Arctic andSouthern ocean

On the surface of the earth, altitudes lessthan 1000 m and depths from 3000 up to6000 m are predominate


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The water cover of the earth has volume of 1389.5 mkm3 and 97.4% of this consists salt water. Of thisvolume, 96.5% is in the world ocean and 0.9% is in saltyunderground and lake waters

F

reshwater comprises only of 2.6% of the total volume ofthe hydrosphere World ocean contain s 1340.7 m km3 of water, making

up 1/ 800th of the total volume of the earth In the process of exchanging water with the atmosphere

and continents, world ocean annually producesatmospheric precipitation of about 458000 km3, bothrivers and ground water produce 48000 km3 of water

Evaporation from the surface of the ocean produces506000 km3


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Temperature as a physicalenvironmental factor

Temp. is one of the most important factors in anaquatic environment

Radiation from the sun striking the earthssurface of virtually all the energy that heats theocean surface and warms the lower portion ofthe atmosphere

Part of this incoming solar radiation is within thevisible part of the spectrum and provides the

energy to the plants on land and in the ocean After passing into the surface of ocean, most ofthis energy is converted into heat, either raisingwater temperature or causing evaporation


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Temperature as a physicalenvironmental factor

The spectrum of radiant energy from the sun isfiltered once as it passes through theatmosphere and further filtered in the surface

ocean Within first 10 cm of even pure water, virtually allthe infrared portion of the spectrum is absorbedand changed into heat

W

ithin the first meter, about 60% of the enteringradiation is absorbed, about 80% is absorbed inthe first 10 m, only 10% remains at 140 m inclearest subtropical ocean waters


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Heat budget in ocean

Less than 20% of the solar radiation reachingEarth is absorbed by atmospheric gases andclouds, 50% is absorbed by earths surface

mostly the ocean and 31% is reflected back tothe space

The oceans effectively capture a major portion(about 50%) of the suns radiated energy and

transfer much of it to the atmosphere as latentheat of vaporization and as radiation


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Sources of heat in ocean

Solar energy- it is about 300 watt/m2

Geologic source

Heat generated by the radioactive decay ofelements within earth (about 0.1 micro watt/m2)

Heat left over from earths formation

Human induced through burning of fossilfuels (3 milli watt/ m2)


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Output of heat

The evaporation/ precipitation cycle is animportant part of the heat energy releasedinto the atmosphere

About 2/3 is evaporated and 1/3 isradiated


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Temperature distribution in ocean

Max. amount of incoming solar radiation isreceived in low latitudes (the earth receives mostof its heat between 400 N & 400 S, where as

there is a net loss to space in the high latitudesbetween 400 & 900 in both the hemispheres The temperature difference between warmest

and coldest month of the year is small < 30C inlow latitudes (100 N to 100 S)

When sun is over head only 2% of incomingradiation is reflected


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The fall in temperature with increase in depth,results into the increase of density, which givesvital vertical stability to maintain water masses in

the ocean Temperature difference is very limited sincethere is continuous circulation of the water

Surface water has some effect of atmosphere

and reduce with the depth in deep sea temp.constant at 40 C. Deep water temp. is 00 C nearAntarctic and 2- 4 0 C towards the equator


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The surface water of low latitudes, thetemperature is mostly ranging between 26to 300 C. Surface temperature maybecome as high as 350 C in the Persiangulf. In some of the tropical lagoons andintertidal rock pools the temperature may

rise to even 500 C in summers


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Thermocline


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Thermocline

The thermocline (sometimesmetalimnion) is a layer within a body of water or air where the temperature

changes rapidly with depth Below this layer however, the temperature

drops very rapidlyperhaps as much as200 C with an additional 150 m of depth

In the ocean 90% of the water is belowthermocline (consist of equal density)


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Thermocline

Varies with latitude and season. It is permanent intropics, variable in temperate and weak to nonexistent inpolar region

PT formed at depth from 100- 500 m due to equator

ward flow of deep coldwater from poles and the poleward flow of warm water from the surface of equator

Temporary derived mainly due to change in temperatureand it is not stable, formed at the depth of 100 to 150 m

Diurnal- formed very near to the surface (about 10 mdepth) during day and governed by difference in temp.due to diurnal effect


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Density of sea water

Determined primarily by temperature and salinity Decreases with temperature and increases with

salinity

Changing salinity from 19 to 26 ppt at constanttemp. (30 0 C) has the same effect as changingthe temp. from 31 to 12 0 C at constant salinity(20 pot)

Vertically stratified due to change in salinity Densest water at bottom Neutrally stable system when density is same


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Density of sea water

In coastal waters, mixing is commonbecause tidal currents and movement ofwaters

Three general depth zones according todensity i.e. surface, pycnocline and deepzone are formed


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Tolerance to temperature variation

Stenothermal Tolerate only slight

variation of

temperature

Internal bodytemperature fluctuate

Example- marineinvertebrates, marine

fishes, reptiles

Eurythermal Tolerate a wide range

of temperature

Have temperatureregulating mechanism

Example- sea birds,sea mammals,


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Marine invertebrates and fishes


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Temperature and distribution oforganism

No strict and well defined barriers in theoceans

Controlled by latitudes and depth of water Surface water has three groups viz. warm(> 18 0C), cold (< 5 0C) and temperate (5-18 0C) waters

Temperature influence physiological andmetabolic processes directly


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Salinity

Most characteristic feature of sea. Deals withdensity and specific gravity of water

Most of the elements occurring on earth, are

encountered in oceanic water About 84 elements are so for known to makingsea water but only 6 (Chlorine, sodium,magnesium, sulphate, potassium and calcium)

are common Important compounds are MgCl2, MgBr2,MgSO4, CaCO3, CaSO4, K2SO4 and NaCl


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Salinity

The existence of trace elements viz. Co,Ni, Cd etc. are revealed from many marineplants and organisms which are able to

concentrate Sulpher bacteria- sulpher Radiolarians- silica and strontium

Molluscs- Nickel Lobsters and mussels- cobalt


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Salinity

Algae and sponges- Iodine

Certain sea weeds(Gracilaria and

Sargassum)-A

luminium Jelly fishes- Zn, Tin and Pb

Crustacians and molluscs- copper inhaemocyanin

Blood of ascidians and holothurians-vanadium


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Salinity

Calcium is needed by molluscs, corals formaking their shells

Silica is utilized by diatoms andradiolarians for their glossy cells

Presence can be detected by analysingash of marine organism


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Origin of elements

Majority are introduce through cosmicsources (water is best solvent)

Others are introduced through landdrainage

Chemical elements are found to bedeposited at the ocean floor through thedead decay of the marine organism andtheir fresh supply from river drainage


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Major chemical constituents ofocean

Chloride- 19.353 g

Sulphate- 2.511

Bicarbonate- 0.142

Trace- 0.181

Sodium- 10.76 g

Magnesium- 1.287 g

Calcium- 0.41 g

Strontium- 0.0077


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Salinity definition

In 1902, there was an establishment ofInternational Commission headed by Fork,Knudson, and Sorenson, to define the

salinity Salinity is an account of water or a

measure of dissolved solids in grams in

one kg of sea water when all carbonatesare oxidized, Bromine and iodine arereplaced as chloride and all organic mattercompletely oxidized


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Salinity

Salinity is measured in the form ofchlorinity

Chlorinity can be measured by titrating sea

water with AgNO3 using potassiumchromate as indicator

The empirical relationship between salinity

and chlorinity isSalinity (ppt) = 0.03+ (1.805x chlorinity) Here other halides are ignored


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Salinity

The above relationship between salinity andchlorinity is no longer strictly true

For improvement, the International Commissiondecided to prepare a primary standard of known

chlorinity called as normal water and task wasgiven to Hydrographical laboratory,Copenhagen, Denmark

Accordingly 19.4 pot normal water was prepared

and a table was prepared byW

oodsW

holeOceanographic Institution, Masachussats,USAconsisting of relation of salinity, chlorinity andnormal water


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Factors affecting salinity

Evaporation and precipitation are two mainfactors which affect salinity very much

It vary in fixed rate (does not go a widefluctuations)

The salinity change due to mixing processresulted due to horizontal and vertical currents

It can be estimated by S= So + K (E- P) Where S is salinity of surface water, So is

salinity change due to mixing process, E is rateof evaporation, P is rate of precipitation and K isconstant


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Evaporation and precipitation

Total evaporation from earth is 334000 Km3/ yr Out of which 297000 Km3/ yr is the precipitation

received by the ocean directly in a year time

The remaining 37000 Km3

/ yr is supplied by land runoff.

If any change in this ratio, the salinity changedrastically

The average precipitation , falling on the year time is99000 Km3/ yr out of which 37000 Km3/ yr comesthrough ocean evaporation and 62000 Km3/ yr issupplied through evaporation of inland resources


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Conditions required for evaporation

If oceanic surface is warmer than the overlyingair evaporation always takes place

The vapour pressure initially remains greater at

the sea surface than that in the air The evaporation greatly facilitated in such

conditions because the turbulence of air will

developed fully owing to unstable stratificationof very lowest layer of atmosphere


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Conditions required for evaporation

In such conditions, the heat is transferred from warmsurface water to the overlying air till the lowest layer ofatmosphere gets laden with moisture equal to thesurface water

If the air is much colder, it gets rapidly saturated withwater vapour and thus fog or mist is form over thewater surface and when wind blows it carried upwards

The evaporation process can be observed morekeenly near the coast but not over open oceanbecause the necessary temperature gradientdifferences are rapidly eliminated as the distance

increases

Conditions required for advection


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Conditions required for advectionfog

When the sea surface is colder than overlying air,advection fog is formed

Here water vapour is rarely produced and air does notgets saturated with moisture

The direction of heat transfer is reversed here andcondensation takes place in such a way that the heatis brought to the surface oceanic water and heatcarried away from it

The turbulence in the air is greatly reduced and theheat transfer would stop only when vapour content oflowest layer of atmosphere has reached the valueequivalent to heat of vapour pressure at the sea

surface

Salinity of different oceans up to


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Salinity of different oceans up tothe depth of 400- 600 m

Mid Pacific- 35.5 ppt Mid Atlantic- 37.0 ppt North Pacific- 33.7 ppt North Atlantic- 35.3 pot

Red sea- 40.0 pot Inshore waters of Bahamas 155.0 ppt

and West Indies (due to less depth and its enclosedgeographic structure)

Baltic sea 8.0 to 0.0 ppt Gulf of Bothnia (due to narrow

connection with Atlanticocean and North sea)- 8.0 to 0.0 ppt


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Salinity changes at different latitudeand longitude

Salinity varies place to place due to change inaverage evaporation and precipitation rates atdifferent latitude and longitude

Evaporation changes due to change in solar

radiation at different latitudes Surface water salinity is minimum at equator

because the rate the rate of precipitation is morethan the evaporation

The surface water salinity is maximum in theworld oceans between 20 0 N and 20 0 Sbecause in this part evaporation is more thanthat of precipitation


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In temperate region, the melting of icewater get stagnated in the basin there byreducing salinity

At higher latitude the average salinity ismuch lesser

In Indian subcontinent, there is seasonal

fluctuation owing to influence of monsoon,evaporation, precipitation and riverdischarge


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The salinity ofArabian sea and Bay ofBengal is between 36.0 to 36.5 ppt and33.0 to 34.0 ppt

Arabian sea is connected to most aridseas like Red sea and Parsian Gulf

Bay of Bengal receives river discharge

from most of the Indian rivers.


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Types of waves

Wind generating waves- formed due tosea surface due to transfer of energy fromair to the sea surface and resultant

pressure fluctuations create vibration overwater surface to form waves duringturbulent wind conditions

Internal waves- Indirect effect of

atmosphere, formed by bring intointeraction of water of different densitiesand thermal gradients together


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Types of waves

Catastrophic waves- in the form of stormsurges and tidal currents, atmospheric andcosmic influences are also responsible for

creation of such waves


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Ocean waves


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Wave crest and trough


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Waves

Wave length- The horizontal distance betweentwo successive crest or trough (L)

The time required for two successive crests or

two successive troughs to pass a fixed point inspace is called the period T

Wave height (H) is the vertical distance

between crest and succeeding trough


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Waves

Steepness is the wave height divided bythe wave length (H/L)- when wavesteepness exceeds 1/7, wave become

unstable and begin to break by raveling ofover steepened crests

The angle at the crest must be 1200 or

greater for the wave to remain stable


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Characteristic of wave

A wave transfers a disturbance from onepart of a material to another

The disturbance is propagated through the

material without any substantial overallmotion of material itself

The disturbance is propagated without anysignificant distortion of the wave form

The disturbance appears to be propagatedwith constant speed


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Characteristic of wave

When small waves move through deep water,individual bits of water move in circular orbitswhich are vertical and nearly closed

The water moves forward as crest passes, thenvertically, and finally backward as the troughpasses

After each wave has passed, the water parcel isfound nearly in its original position but there issome slight net movement of the water


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Wave forms

All waves are progressive waves Body waves travel through materials Surface waves occur at the interface

between two bodies of fluid (capillary andgravity waves)

Sine waves- crest and trough tend to be

rounded and may be approximated Trochoid waves- crest is more sharplypointed


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Deep water waves

In the deeper water where depth is greaterthan L/2, water parcel move in nearlystationary circular orbits, are known as deep

water waves. The diameter is equal to waveheight. It decreases to one- half the waveheight at a depth of L/9 and is nearly 0 at

the depth of L/2


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Formation of waves

Involve two forces- disturbance and stillwater

Disturbing waves are wind generatingwaves, tides, tsunamis etc. these arealso called as forced waves

Free waves move independently e.g.

explosion generated wave


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Formation of waves

Once a wave has formed , restoring forces actto restore the equilibrium.

For smallest wave (L 1.7 cm, TP < 0.1 sec.) the

dominant restoring force is surface tension For waves with periods between 1 and 5 min.,

gravity is the restoring force

The waves whose period is more than 5 min.,gravity and coriolis forces are the restoringforces


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TSUNAMI

These are long wavelength, shallow water progressivewaves caused by rapid displacement of ocean water

Displacement is caused by sudden vertical movementof the earth along a fault line, also by landslides,

iceberg falling and volcanic eruptions These are shallow and deep water waves (> of the

wavelength) Speed will be calculated as c= gd

When it reaches shore, its wavelength and velocitydecreases, increases wave height while period remainconstant


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Currents

Large scale water movement occurring in the oceanand carrying the water everywhere in the ocean

Winds and unequal heating and cooling are two forces

for causing major currents It contribute to heat transfer from tropics to poles andfrom poles to tropic thereby partially equalizing earthsurface temperature

A

round equator, the surface water carry warm water tothe region of higher latitudes of both the hemisphererespectively


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O i d ld t


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Ocean wise warm and cold watercurrents

South Atlantic Warmwater currents

South equatorial currents bring warm water in Brazil

region as Brazil currents Brazil current brings warm water to Antarctic and

water return to the West Africa coast through Bengulacurrents

Coldwater currents From Antarctic region, the Falkland current and West

wind drift to lower latitude

O i d ld t


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North Pacific Warm water currents

North Pacific current to higher latitude and surplus

water as California current Through Kuroshio current from Japan region,

warm water to higher latitude

Cold water currents

Oyashio, Sub Arctic and Alaska currents fromArctic to low latitudes

O i d ld t


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South Pacific Warm water currents

South Equatorial currents, Peru currents and EastA

ustralian current Cold water currents West wind drift and West Australian currents

Seasonal currents ofNorth Indian region

During summer the continental Asia is greatlywarmed up, the continental air rises anddraws air from the ocean towards land

S l t f N th I di


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Seasonal currents ofNorth Indianregion

The South West monsoon currentreplaces North Equatorial currents

In winter just reverse takes place. TheNorth Equatorial current reappear andmay cause cyclone


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CO


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CO2

Minor constituent of atmosphere and equilibriumconcentration in pure water is small Derived from the atmosphere, respiration of animals and

plants, bacterial decomposition of organic matter,inflowing ground waters which seep into the ponds, lakesand streams and from within the water itself in

combination with other substances Solubility of CO2 is 30 times that of oxygen. It dissolves

in water to produce H2CO3 which dissociates into variousfractions depending upon the pH

Solubility of CO2 is decreases with increase of

temperature 00 C- 1.1 mg/l 100 C- 0.76 mg/l 200 C- 0.56 mg/l 300 C- 0.42 mg/l

CO


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CO2

Reduction of CO2 by photosynthesis, marlforming organism, agitation of water,evaporation and bubble formation

is not appreciably toxic to fish


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P4 and N2 cycles in ocean

In shallow waters nutrients recycle fairly quickly Seasonal variation in phosphorus cycle During winter, when phytoplankton populations

are small, dissolved inorganic phosphorusconcentrations are as high as 0.002 mg/l or more

In spring, P4 level drop sharply. When nutrientlevel drop off, organisms die and release

nutrients or in some cases a zooplankton bloomresults from abundance of plant food and theanimals release nutrients during metabolism


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P4 and N2 cycles in ocean

Dissolved and particulate organic phosphorusreleased by phytoplankton and animals isutilized by bacteria and certain heterotrophicphytoplankton

N2 cycle is more slowly because energy isrequired to fix it in organic form, reduce it, andfinally to oxidize it back to N2

Zooplankton facilitate this process by releasingsoluble organic N2 compounds such as ureaand NH3 which can be taken up byphytoplankton


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Nitrogen

Occurs in combination with other elements suchas ammonia, nitrite and nitrate or free form

Vital for all organisms, helps to synthesizecomplex protein molecules that affect growthand reproduction

They regularly remove complex nitrogencompounds as excreta

On the death, complex nitrogenous compoundsdecomposed into simpler chemical compoundsby bacteria


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Nitrogen

There are two forms of nitrogen elementalor uncombined and inorganic/ organiccompounds

Elemental nitrogen come from atmosphere Solubility of nitrogen varies with

temperature and super saturation causegas bubble disease

Inorganic nitrogen present in the form ofNH3, NO2 and NO3


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Nitrogen

Organic nitrogen constitute about 50% oftotal. Most of it is composed as aminoacid, polypeptides and proteins

Process involve in N2 cycle arenitrification, denitrification andammonification

Nitrogen cycle


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Nitrogen cycle

Phosphorus cycle


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Phosphorus cycle


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Silica

Occurs mainly as orthosilicate in anundissociated condition at the normallyencountered pH values

Most abundant in sedimentary rocks andtherefore, occurs generally in higher concentrations in such regions

Silica is utilized most by diatoms and amajor


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Silica cycle


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PCO 2009- 10 physical chemical oceanography

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Transcript of PCO 2009- 10 physical chemical oceanography