Oceanography – The Absorption Of Solar Energy Causes The Upper Layer Of The Ocean To Become Relatively Warmer, Which Reduces Its Density. 

The Vast Water Area On Earth Is Divided Into Four Oceans: 

(A) Pacific Ocean 

(B) Atlantic Ocean 

(C) Indian Ocean 

(D) Arctic Ocean 

Various Seas, Creeks, Troughs And Sub-Gulfs Etc. Are Part Of These Oceans. 

More Than 70 Percent Of The Earth’s Surface Is Covered By Oceans. 

Due To Its Wide Surface, It Receives About 71 Percent Of The Solar Energy. 

The Sea Surface In The Equatorial Regions Is Warmer Than In The Polar Regions. 

There Are Immense Reserves Of Metallic And Non-Metallic Substances Such As Petroleum, Gases, Salts, Manganese, Gold, Diamond, Iron Etc. 

Large Deposits Of Bromine And Sulphur, Which Are Rarely Found On The Surface, Are In Ocean Areas. 

Energy Can Be Obtained From The Ocean In About 90 Ways. 

Important Among These: Wave Energy, Wind Energy, Tidal Energy Etc.

Ocean Floor Relief

The Ocean Floor Is Made Up Of The World’s Largest Mountain Ranges, The Deepest Creeks And The Largest Plains. Accurate Mapping Of The Ocean Floor Has Been Possible With The Help Of Sonar (Sound Navigation And Ranging). Four Major Relief Zones Are Found In The Ocean Floor:

(A) Continental Shell 

(B) Continental Slope 

(C) Abyssal Plain 

(D) Ocean’s Deep

Continental Shelf

The Side Of The Continents That Is Submerged In Ocean Water, The Average Depth Of Water On It Is 100 Fathoms (1 Fathom = 6 Feet) And The Slope Is Between 10 To 3°, Is Called Continental Shelf. 

The Continental Shelf Extends From The Coastline Of The Continents To The Continental Edge. 

The Shallowness Of The Continental Shelf Enables Sunlight To Pass Across The Water, Aiding The Growth Of Small Plants And Other Microscopic Organisms. 

Therefore, They Are Rich In Plankton, Where Millions Of Fish Feed From The Surface And Bottom. 

Seafood Comes Almost Entirely From The Continental Shelf. 

The Continental Coasts Are The Richest Fisheries In The World, Such As The Grand Bank Of Newfoundland, The Dogger Bank Of The North Sea And The Sanda Shelf Of Southeast Asia. 

These Mangroves Are Rich Deposits Of Minerals. A Significant Part Of Petroleum And Natural Gases Come From Them.

Continental Slope

The Zone With A Sharp Slope Between The Submerged Coast And The Deep Oceanic Plain Is Called The ‘Continental Submerged Slope’. 

It Grows Up To 200-3500 Meters Long. Submerged Slopes Are Found On 8.5% Of The Entire Ocean Area.

Canyons And Trenches Are Found In This Area.

Deep Sea Plain

The Oceanic Plain Is The Widest Part Of The Ocean Floor, Whose Depth Ranges From 3000 To 6000 Meters. 

The Expansion Of The Oceanic Plain Is Found On About 75.9% Of The Total Ocean Area.

Ocean Trough

Oceanic Trenches Are The Deepest Parts Of The Oceans, Covering About 7% Of The Ocean Floor. 

The World’s Deepest Trench Is The Mariana Trench, Which Is Located Near The Philippines In The West Pacific Ocean.

Ocean Relief

The Pacific Ocean

It Is The Largest Ocean.

 It Is Spread Over A Third Of The Entire Surface Of The Earth. 

In Size, It Is More Than The Entire Terrestrial Part Of The Earth. 

Its Shape Is Almost Triangular, Whose Apex Can Be Considered To Be Located In The North Towards The Bering Strait. 

It Is Also The Deepest Ocean. 

Most Of This Ocean Is On An Average 7300 Meters Deep. 

More Than 20,000 Islands Are Located In This Ocean. 

These Islands Located In The Ocean Are Made Up Of Coral Reefs And Volcanoes. 

The North Pacific Ocean Is The Deepest Part And The Average Depth Of This Part Is Between 5000-6000 Meters. 

The Mariana Trench Is More Than 10,000 Meters Deep. 

This Is The World’s Deepest Trench, Also Known As The Challenger Trench.

TheAtlantic Ocean

It Has The Longest Coastline. It Is About Half The Size Of The Pacific Ocean And Covers One-Sixth Of The Total Surface Of The Earth. 

It Is In The Shape Of The Letter ‘S’ Of The English Alphabet. 

In This Ocean, The Maximum Number Of Mangroves Are Found. 

The Hudson Bay, The Baltic Sea And The North Sea Magnet Are Located In It.

An Important Feature Of The Atlantic Ocean Is The Mid-Atlantic Ridge Found In It. 

It Is Spread In The Shape Of ‘S’ Parallel To The Ocean From North To South. 

Examples Are Azores Island, Cape Verde Island, Pico Island Etc. 

There Are Also Some Atolls, Such As Bermuda Island And Volcanic Island. Apart From This, There Are Volcanic Islands Like Saint Helena, Tristan Da Cunha, Gough Etc. 

Note: The Labrador Current Flows Through The Northern Coast Of Canada And Joins The Warm Gulf Current. The Union Of These Two Streams, One Hot And One Cold, Forms The Famous Ganges Around Newfoundland. The Union Of These Streams Forms The World’s Most Important Fisheries. It Includes The Grand Banks Region Of The Northwest Atlantic.

The Indian Ocean

The Two Gulfs On Both Sides Of The Indian Peninsula, The Bay Of Bengal And The Arabian Sea, Belong To The Indian Ocean.

There Are Thousands Of Islands In The Indian Ocean, For Example The Maldives And Cocos Islands Are Coral Reef Islands And Mauritius And Reunion Are Volcanic Islands.

NameOceanDeepest PointDepth (In Metres)
1. Mariana DitchWestern PacificChallenger Deep11,034
2. Tonga-Karamadec TrenchSouthern PacificVityaz 11 (Tonga)10,850
3. Kuril-Kamchatka TrenchWestern Pacific10,542
4. Philippine TrenchNorth PacificGalathea Deep10,539
5. Ditch Puerto RicoWestern AtlanticMilwaukee Deep8.648

Salinity And Temperature

One Of The Main Characteristics Of Ocean And Sea Is Its Salinity.

The Amount Of Salt Present In 1000 Grams Of Sea Water Shows The Salinity. 

An Imaginary Line Joining Areas Of Equal Salinity Is Called An Isohaline. 

The Instrument Used To Measure Ocean Salinity Is Called A Salinometer. 

The Salinity Of The Oceans And Lakes Is Very High Because There Is A Continuous Flow Of Salinity In Them From The Rivers. 

Their Water Becomes More Saline Due To Evaporation. 

Salinity Determines The Thermal Expansion Of Sea Water, Temperature, Absorption Of Solar Radiation, Evaporation, Humidity, Etc.

Great Salt Lake (USA)220%
Dead Sea (West Asia)240%
Lek Van (Turkey)330%
SaltPercentage Volume
Sodium Chloride77.8
Magnesium Chloride10.9
Magnesium Sulfate4.7
Calcium Sulfate3.6
Potassium Sulfate2.5


The Temperature Decreases As The Depth Of The Ocean Increases. 

On Average, The Temperature Of The Water At The Surface Of The Ocean Is 26.7 °C And The Temperature Decreases Continuously From The Equator Towards The Pole. 

Oceans In The Northern Hemisphere Show Relatively Higher Average Temperatures Than Oceans In The Southern Hemisphere. 

It Is A Well Known Fact That The Maximum Temperature Of The Oceans Is Always At Their Surface As They Receive Heat Directly From The Sun And It Travels To Their Lower Floors By Convection.

Coral Reefs

A Coral Reef Is Formed By The Consolidation And Assembly Of The Skeletons Of Marine Organisms Such As Coral Or Coral Polyps. 

Coral Reef Is Formed From 25°N Latitude To 25°N. In The Middle Of Latitude, Up To A Depth Of 200-300 Feet, On The Edge Of An Island Or Coast Or On Ocean Platforms, Where The Sun’s Rays Reach, There Is 20°-25°C. The Temperature Is Ideal For Their Growth. 

Both High Salinity And Very Clean Water Are Detrimental To The Growth Of Coral. 

On The Basis Of Shape, There Are Three Types Of Coral Reefs: 

(A) Fringing Reef 

(B) Barrier Reef 

(C) Coral Ring OrAtoll 

Coastal Reef: A Coral Reef Formed Along The Continental Edge Or Island Is Called A Coastal Reef. Example- South Florida, Gulf Of Mannar Etc.

Barrier Coral Reefs: The Coral Reefs Of The Coastal Surface Are Called Barrier Coral Reefs. There Is A Wide But Shallow Lagoon Between The Coastal Surface And The Reefs. The Great Barrier Reef Off The East Coast Of Australia Is 120 Miles Long. 

Atoll: A Horseshoe Or Ring Shaped Coral Reef Is Called An Atoll. It Is Usually Found In An Elliptical Form Around The Island Or Above The Submerged Plateau. The Lagoon Is Found In The Middle Of It. Example- Funfuti Atoll, Fiji Atoll Etc. 

Ocean Currents

The Movement Of Water In The Oceans In A Certain Direction Is Called ‘Current’. The Origin Of Currents In The Oceans Is Possible Due To The Combined Effect Of Many Factors. 

For Example, The Rotation Speed Of The Earth, Variation In Ocean Temperature, Variation In Salinity, Variation In Density, Air Pressure And Winds, Evaporation And Precipitation Etc. 

On The Basis Of Speed , Size And Direction Of Currents , There Are Several Types: 

(A) Drift: When The Surface Water Of The Ocean Moves Forward Due To Wind Velocity, It Is Called Flow. Its Speed And Range Are Not Fixed. Example- North Atlantic And South Atlantic Flows. 

(B) Current: When The Water Of The Ocean Moves At A Fast Speed In A Certain Direction Within A Certain Limit, Then It Is Called Current. Its Speed Is Greater Than The Flow. 

(C) Massive Stream: When The Excessive Water Of The Ocean Moves In A Definite Direction Like The Rivers Of The Surface, Then It Is Called Huge Stream. Its Speed Is Greater Than Both The Flow And The Current. Example-Gulfstream | 

On The Basis Of Temperature, Ocean Currents Are Of Two Types:

(1) Hot Current And

2) Cold Current 

If The Temperature Of The Stream Is Relatively Higher Than The Temperature Of The Water At The Place Where This Stream Reaches, Then It Is Called Hot Stream And If The Temperature Of That Place Is Higher Than The Temperature Of The Stream, Then It Is Called Cold Stream, Generally From The Equator. The Current Going Towards The Poles Is Hot And The Current Coming From The Poles Towards The Equator Is Cold. 

Due To The Coriolis Force, The Deflection Is To The Right In The Direction Of The Current In The Northern Hemisphere And To The Left In The Southern Hemisphere. 

Situated At 20°-40°N And 350-75°West, The Sargasso Sea Is A Sea Surrounded By Currents. That Is, It Has No Coast. 

It Is The Saltiest And Warmest Part Of The Atlantic Ocean.

Importance Of Ocean Current 

Like Atmospheric Circulation, Ocean Currents Also Transfer Heat From The Equator To The Poles. 

By This A Large Body Of Water Is Carried From One Place To Another, Due To Which The Ocean Plays An Important Role In Maintaining The Thermal Balance On The Earth’s Surface. 

These Currents Develop An Extensive Water Circulatory System That Affects All The Oceans. 

Trade Winds Carry Large Amounts Of Water Off The Coast Of Africa And Into The Caribbean And The Gulf Of Mexico. 

Due To Water Logging Here, Hot Water Current Like Gulf Stream Emerges. 

Similarly, The Waters Of The Gulf Stream Are Carried By Westerly Winds To The Coast In Britain And Europe. 

The Prevailing Winds Have The Greatest Effect On The Sea Current Flowing In The East-West Direction. 

The North-South Flow Has The Greatest Effect On The Difference In Temperature, When The Air Flow Is From The Coast To The Sea, Then Cold Water Currents Develop In That Coastal Areas Like Canari And Bengula Currents. 

The Ocean Currents Influence The Climate Of The Coastal Areas. 

They Affect Temperature, Humidity And Rainfall.

East AustralianHot
Peru / HumboldtCold
South EquatorialHot
Al NinoHot
A. Equatorial CurrentHot
Gulf StreamHot
North Atlantic DriftHot
Norwegian StreamHot
Erminger StreamHot
Renal StreamHot
Labrador StreamCold
Canary StreamCold
East Greenland StreamCold
The. Equatorial CurrentHot
Brazilian StreamHot
Antilles CurrentHot
The. Atlantic DriftCold
Falklands StreamCold
Mozambique CurrentHot
The. Fifth Note Of Musical Scale. Monsoon CurrentHot And Temp
U.E. Monsoon CurrentCold And Temporary
Somali StreamCold And Temporary
Fifth Note Of Musical Scale. Australian StreamCold And Stable
The. Indian Ocean CurrentCold


Due To The Forces Of Attraction Of The Sun And The Moon, The Rising And Falling Of Ocean Water In A Periodic Manner Is Called Tide And Ebb Respectively. 

Due To Its Close Proximity To The Earth, The Moon Exerts The Greatest Influence On The Tides. 

The Tide Is Highest When The Sun, Moon And Earth Are In A Straight Line. 

This Condition Occurs On Full Moon And New Moon Days. It Is Called Spring Tide. 

Conversely, When The Sun, The Earth And The Moon Together Form A Right Angle, The Forces Of Attraction Between The Sun And The Moon Act Opposite To Each Other, Due To Which A Low Tide Is Experienced. 

This Situation Occurs On The Ashtami Of Every Month Of Krishna Paksha And Shukla Paksha. 

It Takes 24 Hours And 52 Minutes For The Same Line On The Rotating Earth To Come Down Again Perpendicular To The Moon. 

Hence The Tides Come At Regular Intervals Of 12 Hours And 26 Minutes. Usually The Tides Come Twice A Day, But In Southampton, Located On The South Coast Of England, The Tides Come Four Times A Day. 


Tsunami Is A Japanese Word, Which Means Sea Waves Coming On The Coast. 

They Have Nothing To Do With Tidal Waves. 

It Arises In The Oceans Due To The Effect Of Ocean Earthquakes. 

The Pacific Ocean Is The Most Dangerous In Terms Of Tsunami Waves.

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