Lecture 23 & 24 : Geography

Topics Covered in this Lecture

  1. Major relief feature of Ocean
  2. Minor relief Feature Of Ocean
  3. Factor affecting Temperature Variations in Ocean.
  4. Horizontal and vertical Distribution of Temperature in Ocean.
  5. Ocean Salinity :- Factors for Variations and Distribution
  6. Signification of Ocean Salinity

Distribution of water resources in the world-

Distribution                              % water

Oceans and seas                        97.25%

Ice caps and glaciers                  2.05%

Ground water                              0.68%

Lakes                                             0.01%

Soil moisture                                0.005%

Rivers (least fresh water)           0.0001%

Isthmus V/S strait

  • Ocean bottom floor is an outcome of volcanic, tectonic, erosional, Depositional processes, and their interactions. The majority of the ocean floor consists of abyssal or deep-sea plains. Having a depth of 3 to 6 kilometers. These abyssal plains or the floor of the ocean have the world’s largest mountain ranges (MOR). Deepest trenches and largest plains it is divided into two parts-

  • Continental margins which consist of the continental shelf and continental slope.

  • Deep-sea plains which consist of ocean deeps or trenches, MOR, seamounts, guyots.

Continental shelf

It is a region of the extended margin of a continent occupied by shallow sea and gulf (it is a bigger, bay is smaller  3 sides land).

  • The average slope/ gradient is around or even less. The gentle slope continuous up to a point where the Steepness suddenly increases giving rise to the continental slope. This point is known as shelf break. The shelf occupies 7.5% of the total area of oceans and has an average width of 80 kilometers.

  • The widest continental shelf is in Atlantic Gujarat has the widest continental shelf in India wider continental shelf in the Western coast as compared to the Eastern coast.

Characteristics of continental shelf-

  • The Continental shelf is wider where big rivers enter the sea depositing large amounts of sediment.

Example- mouths of Ganga, Godavari, Krishna, kaveri.

  • Continental shelf are very wide in the coast of submergence.

Example- Western coast except Kerala.

  • Continental shelf are wider when coastal areas are submerged due to rise in sea level.

  • In the regions where fold mountains run parallel to the coast line continental shelf is very narrow or absent.

Example- Western coast of North and South America.

Importance of continental shelf-

  • As these are the photic zones. Photosynthesis occurs in the regions of the continental shelf and hence marine plants grow mostly on the continental shelf. Biodiversity(variety) bio productivity is very high in these regions.

  • Therefore, the continental shelf is the most important source of food from the sea.

  • In the regions where the continental shelf is very wide as well as there’s a mixing of warm and cold ocean currents are the richest fishing grounds of the world.

Example- Grand banks, Canada, (port – nova Scotia) also famous for apples.

  • Wider continental shelf is also the regions of Energy as well as mineral resources.

Example- Bombay high , bassein high.

  • Wider continental shelf also increase the height of waves and tides and therefore are important for wave and tidal energy.

Example- gulf of Kamba Or cambay 

  • The Bay of fundi in Canada has the highest tidal range in the world.

  • They are potential sites for mineral exploration.

Example- The Arabian sea is rich in Polymetallic nodules especially in Manganese, iron, gold, and copper.

  • They are important for tourism activities.

Continental slope-

An area of a steep slope with a department varying between 200 to 3000 meters is known as continental slope. Due to the steepness of the slope. Sediments roll down from the slope and sometimes accumulate at the bottom forming continental rise.

Submarine canyons –

These are deep valleys cutting the continental shelf and slope found on the mouth of big rivers.

Example- Ganga, Brahmaputra sub Marine cannyon (deepest on earth).

Abyssal plains-

These are the flattest and comparatively featureless plains at the depth of 3 to 6 kilometers. They are concerned with very fine sediment composed of clay and silt.

Syria, Israel, Lebanon, turkey (area surrounding Mediterranean Sea).

Abyssal plains divided into-

  • Ocean trenches – subduction zone/ Benioff, found in the regions of convergent plate Boundary, deepest parts on the earth. The largest number of ocean trenches – Pacific > Atlantic> Indian – Sunda/ java trench/Mariana, Deepest in Atlantic – nares trenches or Puerto Rico.

  • MOR – parallel mountain chains, it represents the divergent plate Boundary. Some Parts even reach above the ocean surface. Example – Icelandic plateau.

  • Seamount– isolated mountains with pointed summits/ peaks rising the seafloor, volcanic in origin are known as sea mountains. Example – Hawaii Islands. A flat-topped seamount that is submerged, henceforth, is known as guyots

Topics Covered in this Lecture

  1. Sea Waves
  2. Factor of Ocean Currents.
  3. Currents of Atlantic Pacific and Indian Ocean.
  4. Significance of Ocean Currents.
  5. Tides :- Formation and Types.
  6. Significance of Tides.

Movement of ocean water in a definite direction with definite velocity forming a gyre (circulation) which is similar to rivers on the land is Ocean current. A larger ocean current is known as stream while the ocean current which bifurcates in many directions is drift.

Factors affecting ocean current-

  • Rotation of the earth and Coriolis force – the North and the South equation current originated due to the rotation of the earth. Coriolis or deflective force deflects the ocean current to right and left in the northern and southern Hemisphere respectively. Due to the convergence of two great.

    Example – currents water level increases in the Eastern part of continent and the Western part of oceans and some water moves backward as weak counterexample – currents.
  • Winds – the wind is the single most important factor that carries the water from the oceans in different directions. In the North  Indian ocean, the direction of the winds determines the direction of ocean currents.

  • Temperature, density, and salinity of the water – warm water from the tropics expand becomes less dense and flows towards the polar regions as surface currents while the cold polar being denser sinks and flows towards the equator as sub surfaces current. The salinity of the ocean water also affects density. Water with high salinity is denser and it tends to sink down and water with low salinity is lighter.
  • Configuration of the ocean floor – the depth of ocean water relief, the height of MORs. Affects the direction of ocean current. Example – MORs defects the ocean current to the right in the northern hemisphere and vice versa in the Southern Hemisphere.

  • Configuration if coastline – line ocean current are deflected due to the shape of the coastline. Example – due to the shape of the Brazilian coast and Caribbean is the South example- current is bifurcated into Memerous sub currents.


Warm current –

  1. North equator current
  2. South equator current
  3. Equator counter current
  4. Florida current
  5. Gulf Stream

Cold current

  1. Labrador current
  2. Canary current
  3. Benguela current


Flows through the Gulf of Mexico. It exists comes out through strait of Florida to join Antilles, current and form Gulf Stream.

The Gulf Stream is Bifureated into numerous branches which are collectively known as North Atlantic drift. North Atlantic drift is responsible for warning effect in the higher Latitudes giving rise to the British type of climate.

A branch of North Atlantic drift enters the Arctic regions and hence Russian port of Murmansk is ice-free throughout the year.


In the Indian Ocean, as it is an enclosed ocean the current system is not well developed. Here the currents are controlled by the direction of winds. Hence during the southwest monsoon. We have warm southwest monsoon currents. While during the North-East monsoon, we have warm North-East monsoon current. Thus the North Indian Ocean is the only ocean that does not have cold ocean current.


Sometimes after the gap of generally 7-8 years the upwelling if Peru/ Humbolt current stops hence warm counter. Equator water.

For example- water replaces the cold water and this warm counter equator water is known as El Nino.

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