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 Ocean Relief & Salinity

OCEANS- RELIEF AND MOVEMENT OF OCEAN WATER

In general, the ocean floor can be divided into four major divisions:

  1. The Continental Shelf.
  2. The Continental Slope.
  3. The Continental Rise.
  4. The Abyssal Plain.

Besides, there are many associated features including ridges, hills, seamounts , guyots, trenches, canyons, deep and fracture zones.

1. The Continental Shelf :- The Continental Shelf is a gentle seaward sloping surface extending from the coasts towards the open sea. The shelf is generally formed by the drowning of part of a continent with a relative rises in the sea level or marine deposition beneath the water. The seaward edge of the continental shelf is usually 150-200 metres deep. The average a width of Continental Shelf is about 70 kilometres and mean slope is less than one degree.

The continental shelves are mostly covered by sediments derived from rocks on land. Marine food comes almost entirely from them. About 20 percent of the world production of petroleum and gas comes from shelves.

2. Continental Slope: - At the edge of the continental shelf, the seaward slope becomes considerably steep, the angle of slope varying from 2 to 5 degrees. This steep slope, which descends to a depth of about 3660 metres the mean sea level, is known as continental slope.

3. Continental Rise: - where the continental slope ends, the gently sloping continental rise begins. The continental rise has an average slope of between 0.5° to 1° and its general relief is low. With increasing depth the continental rise becomes virtually flat and it merges with the abyssal plain.

4. Abyssal Plain:-Beyond the continental risse lie the deep sea plains known as the abyssal plains or abyssal floors. They are areas of deep ocean floor found at a depth of 3000 to 6000 metres. They occupy about 40 percent of the ocean floor. Abyssal Plains are more common where land derived sediments are in great supply. The irregular topography is buried forming relatively flat areas due to the large supply of sediments.

Submarine Ridges :- submarine ridges are mountain ranges a few hundreds kilometre in length on the floors of oceans. The submarine ridges of high relief form the longest mountain system on the earth. Their summit may rise above sea level forming islands.

Abyssal Hills :- The deep sea floor also contains thousands isolated abyssal hills, seamounts and guyots. A submarine mountain or peak rising more 1000 metres above floor is known as a seamount. Flat topped seamounts as known as guyots . All these features are of volcanic origin.

Submarine Trenches and Deeps :- these are the deepest part of the oceans with their bottoms far below the average level of the ocean floors. A long, narrow and steep sided depression on the ocean bottom is called a Trench. They are usually 5,500 metres in depth and lie along the fringes of the deep sea plain. They are believed to have result from down faulting of down folding of the earth’s. crust and are, therefore, of tectonic origin. The Trenches generally run parallel to the bordering fold mountain or the island chains.

Submarine Canyons:- Submarine canyons are deep gorges on the ocean floor. They are strikingly deep valleys with steep slopes that form long, conclave profiles. They occur around all the coasts of the world and are mainly restricted to the continental shelf, slope and rise.

SALINITY
It is defined as the total amount of solid material in gram contained in one    kilogram of sea water and is expressed as part per thousand. It is measured by electric salinity meter.

  • The average salinity in the oceans and sea is 35%. Very high salinity is recorded in inland seas and lakes. Lake Van in Turkey records the highest salinity.
  • The origin of salinity is attributed to erosion of earth’s crust by dissolving action of running water, produced by rain, river, constant washing of sea shore and agencies which causes erosion in the oceanic crust and volcanic ash which contains minerals like Calcium, Boron, Iodine etc.
  • Salinity is excessive in region of high temperature, strong winds and less rainy days. For example, it is comparatively lower in the equatorial region due to high relative humidity.
  • Influx of fresh water by river reduces the salinity and so there is less salinity near the months of rivers.
  • In spite of high temperature salinity is less in equatorial region because of high rainfall. Around the poles there is a belt of low salinity because of addition of fresh water in the form of iceberg and excessive snow falls.

HORIZONTAL DISTRIBUTION OF SALINITY

It decreases from Equator towards the Poles. In general there is low salinity in equatorial zone, high in tropical belt low in temperature zone and minimum in sub-polar zone.

  • Amount of salinity varies from oceans to ocean, mainly due to supply of fresh water, rapidity of evaporation and water mixing tendency.
  • The greatest evaporation of salt is found in two areas which lie about the Tropic of Cancer and the Tropic of Capricorn from these regions the salinity decreases both onwards equator and the poles.
  • Salinity of the inland seas and lakes is very high because of the regular supply of salt by the rivers flowing into them and the evaporation makes continuously more and more saline.

VERTICAL DISTRIBUTION OF SALINITY

Salinity of ocean decreases of increases towards the bottom according to the nature of the water mass.

  • In high latitude salinity increases with depth due to dense water found at the    bottom. In the middle latitude salinity increases with the depth up to 366 metres and then it starts decreasing..
  • At equator surface salinity is low but just below it greater salinity is found which again decreases at the bottom due to presence of cold water mass.
The document Ocean Relief and Salinity - Physical Geography, UPSC, IAS. | Geography (Prelims) by Valor Academy is a part of the UPSC Course Geography (Prelims) by Valor Academy.
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FAQs on Ocean Relief and Salinity - Physical Geography, UPSC, IAS. - Geography (Prelims) by Valor Academy

1. What is ocean relief and how does it impact physical geography?
Ans. Ocean relief refers to the variations in the shape and form of the ocean floor. It includes features such as underwater mountains, valleys, plateaus, and trenches. Ocean relief plays a significant role in shaping the physical geography of the Earth's surface. It affects ocean currents, wind patterns, and the distribution of marine life. The presence of underwater mountains and plateaus can influence the movement of ocean currents, causing upwelling and downwelling, which impact temperature and nutrient distribution. Trenches and valleys can affect the flow of water and sediment deposition. Therefore, understanding ocean relief is crucial in studying and analyzing the physical geography of the Earth.
2. How does salinity affect ocean ecosystems and marine life?
Ans. Salinity refers to the concentration of dissolved salts in water. It plays a vital role in ocean ecosystems and has a direct impact on marine life. Salinity affects the density and buoyancy of seawater, which, in turn, influences the movement of ocean currents and the mixing of nutrients. Different marine organisms have varying tolerance levels for salinity. Some species, like marine plants and invertebrates, are adapted to live in highly saline environments, while others, such as freshwater fish, cannot survive in high salinity. Changes in salinity levels due to factors such as evaporation, precipitation, and freshwater input from rivers can disrupt the balance of marine ecosystems, leading to the displacement or extinction of certain species.
3. How does ocean relief contribute to the formation of ocean currents?
Ans. Ocean relief plays a crucial role in the formation and behavior of ocean currents. Underwater mountains, plateaus, and trenches can act as barriers or pathways for the movement of ocean water. When ocean currents encounter these relief features, they can be deflected or channeled, leading to the formation of different current systems. For example, the Gulf Stream, a powerful warm ocean current in the Atlantic Ocean, is influenced by the presence of the underwater mountain range known as the Mid-Atlantic Ridge. Additionally, ocean relief can create areas of upwelling or downwelling, where nutrient-rich water rises or sinks, respectively, influencing the productivity and biodiversity of marine ecosystems.
4. How does ocean salinity vary across different regions of the world?
Ans. Ocean salinity varies across different regions of the world due to various factors. One of the main factors is the balance between evaporation and precipitation. In regions with high evaporation rates and limited rainfall, such as the subtropics, salinity tends to be higher. Conversely, areas with high precipitation, such as the equatorial regions or near river mouths, often have lower salinity. Another factor is the influence of freshwater input from rivers. The salinity near river mouths is often lower due to the mixing of freshwater. Additionally, ocean circulation patterns and the presence of currents can also affect salinity levels. For example, in the North Atlantic, the Gulf Stream brings warm, saline water from the tropics, increasing salinity in that region.
5. How does ocean salinity impact global climate and weather patterns?
Ans. Ocean salinity plays a role in global climate and weather patterns through its influence on ocean circulation and the water cycle. Salinity affects the density of seawater, which, in turn, influences the sinking and rising of water masses. This process, known as thermohaline circulation, plays a crucial role in redistributing heat around the planet and regulating climate. Changes in salinity can disrupt this circulation, leading to alterations in climate patterns. Additionally, salinity affects the water cycle by influencing the evaporation and condensation rates of seawater. This can impact the formation of clouds, rainfall patterns, and the distribution of heat in the atmosphere. Therefore, understanding ocean salinity is essential for studying and predicting global climate and weather phenomena.
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