# RBSE Class 11 Geography Notes Chapter 19 Ocean: Relief, Temperature and Salinity

Go through these RBSE Class 11 Geography Notes Chapter 19 Ocean: Relief, Temperature and Salinity contain important concepts so that students can score better marks in the exam.

## Rajasthan Board RBSE Class 11 Geography Notes Chapter 19 Ocean: Relief, Temperature and Salinity

→ Water is found on approximately 71% part of the earth, which is called the Hydrosphere.

→ Such amount of water is not present in any planet other than the earth. On this basis the earth is also known as Aquatic Planet.

→ The average and actual depth of the oceans is more than the average height of the landmasses.

→ In oceans, the deepest trench is the Mariana Trench (11033 meters) which is located in
the Pacific Ocean.

→ The average depth of oceans is 3808 meters, while the average height of continents is 840 meters.

Landforms of Oceans

• Like the land, mountains, plateaus, plains and deep trenches are found also below the sea level.
• Similar landforms are not found in the oceans present in the world.
• Pacific Ocean is the largest ocean of the world which covers about 1/3 part of the earth. In the triangular shape, it is 18000 km wide from east to west, and 16740 km. long from north to south.
• More than 20000 islands found in the Pacific Ocean are classified into three parts : Melanesia, Micronesia and Polynesia.
• Many troughs, long ridges, plateaus and scarps are found in the Pacific Ocean.
• Atlantic Ocean is extended in the shape of letter ‘S’ of English. Developed countries of the world are located at both sides of this ocean.
• Equator line divides the Atlantic Ocean into two parts. The North Atlantic Ocean located in its northern part is 5400 km. wide, and the South Atlantic Ocean located in its southern part is 9600 km. wide. Many troughs and deeps are found in the Atlantic Ocean.
• In the north of the Indian Ocean, part of Gondwana Land, Peninsular India, Plateau of Africa, western part of Australia and Continental Shelf are found.
• Sunda Trench, faults and rift valleys are found at many places in the Indian Ocean.
• Due to the cover of snow in most time of the year in the Arctic Ocean, adequate information is not available about it.
• Many islands, seas and ridges are present in the Arctic Ocean.

Relief

• The physical forms of the upper surface of the earth: mountain, plateau, plain etc. physical landscapes are called the Relief.
• Surface relief features originate due to the interactions between the processes like tectonic movement, volcanic eruption, erosion and deposition.
• Like the continents, the oceans are also the First Order Relief. The relief features of Ocean Bottom are classified into four parts: Continental Shelf, Continental Slope, Deep Sea Plain and Oceanic Deeps.
• Continental Shelf is that submerged part of the continent whose slope ranges between 1 degree to 3 degree and whose maximum depth is 100 fatham.
• Continental Slope usually has a slope of 2 degree to 5 degree. It extends up till the depth of 3600 to 9100 meters.
• The slope becomes very gentle on the end of the continental slope and the marine plain starts which is called the Deep Sea Plain.
• The deeps with the maximum depth found on the ocean floor are called the Oceanic Deeps.
• Oceanic deeps are classified into trenches and troughs.

Oceanic Temperature

• The temperature of oceanic water is important for marine vegetation and living creatures.
• Sun is the most important source of the temperature of oceanic water.
• In the factors affecting temperature of oceanic water, the latitudes, distribution of water and land, duration of day, clean atmosphere, distance of the earth from sun, number of sunspots and ocean currents are included.
• The temperature of the surface water decreases on moving towards the north and south poles from the equator.

Horizontal Distribution of Oceanic Temperature

• The temperature of ocean water decreases along with the increasing latitudes.
• On latitudinal basis, the temperature varies in different oceans.
• The rate of reduction in temperature towards the poles is half degree Celsius per latitude.

Vertical Distribution of Oceanic Temperature

• Vertical distribution of temperature in ocean water depends on the amount of heat absorption, horizontal displacement of water through water currents and vertical motion of water.
• In ocean water, the sunrays provide heat by entering down to 25 meters depth. After this depth, the effect of sun’s radiation becomes negligible.
• From the surface of ocean water towards the depth, the temperature declines with a rapid speed till the depth of 2000 meters. After this depth, the rate of decline in temperature reduces significantly.

Oceanic Salinity

• The amount of salinity found in ocean water is called Oceanic Salinity. It is usually expressed as the amount of salt present in per thousand grams of water (%).
• The average salinity of Ocean water is about 35 per thousand (%), that is, about 35 grams salt is present in one thousand grams of ocean water.
• The main source of oceanic salinity is the earth, The sources causing salt accumulation in oceans are the rivers, oceanic waves, winds and volcanic eruptions.
• The ratio of the weight of oceanic water and the weight of substances dissolved in it is called the Oceanic Salinity.
• In the salts found in the oceans, sodium chloride, magnesium chloride, magnesium sulphate, calcium sulphate, potassium sulphate, calcium carbonate and magnesium bromide are mainly included.
• In the factors affecting the oceanic salinity, evaporation, water availability through the rainfall, arrival of river water, prevailing winds, oceanic currents, transmission of oceanic water, etc. are included.

Horizontal Distribution of Oceanic Salinity

• In tropical regions, uneven distribution of salinity is found. Distribution of salinity is not even in the open seas, surrounded seas and partially-surrounded seas.
• The amount of salinity is the highest in tropical regions. Salinity decreases on moving from these regions towards the equator and the poles.
• Lines joining the places with similar salinity in the oceanic regions are called Isohalines.
• More salinity is found due to the reasons like lack of rainfall, less arrival of river water, high temperature, more evaporation, etc.
• Salinity is 238 per thousand grams in the Dead Sea, 170 per thousand grams in the Caspian Sea and 330 per thousand grams in Van Lake of Turkey.

Vertical Distribution of Oceanic Salinity

• There is no definite trend in the distribution of salinity towards the depth.
• In the polar regions, salinity is less on the surface and it increases towards the depth. In the mid latitudes, salinity increases till the depth of 400 meters.
• In the equatorial regions, salinity is less on the surface, it increases till the depth of one thousand meters and after that it again starts reducing.
• Variations are found in the salinity, based on the depth of seas.

### Ocean: Relief, Temperature and Salinity Notes Important Terms

→ Hydrosphere: The entire aqueous part located on the earth which is different from the lithosphere and atmosphere. Various aqueous parts in the form of sea, lakes, rivers, ice sheets, etc. are included under it.

→ Planet: Celestial body of the solar system moving in an elliptical orbit around the sun and is illuminated with the sunlight. There are a total of 8 planets in the solar system in which Mercury is closest to the sun.

→ Mount Everest: The world’s highest mountain peak which is part of the Himalayas. Its certified height is 8848 meters (8850 meters according to the latest data).

→ Deeps: The deepest part of the ocean bottom which is found in the limited area of the oceanic bottom, whose edges are with steep slope.

→ Melanesia: A group of islands of New Guinea, Bismarck, Solomon, Fiji, New Caledonia, Maluku, Vanuatu. It is extended in the shape of a balloon.

→ Micronesia: A part of the Pacific Ocean in which Mariana, Caroline, Marshall and Kiribati Islands are included.

→ Polynesia: A group of islands located in the south of Pacific Ocean in which Hawaian, Tuvalu, Samoa, Cook, Tonga, Kermadec, New Zealand, Australia, Society Islands, etc. are included. It is extended in the form of a triangle.

→ Trough: A trough is a low area between two big waves on the ocean. Depression or trench found on the bottom of ocean is also called a trough.

→ Ridge: High and narrow hill with a steep slope. Ridge located in the sea is called internal sea ridge.

→ Escarpment or Scarp: An escarpment is a steep slope or high cliff that forms as an effect of faulting or erosion and separates two relatively levelled areas having different elevations.

→ Fault: Fault is a planar or gently curved fracture in the rocks of the earth’s crust, where compressional or tensile forces cause relative displacement of the rocks on the opposite sides of the fracture.

→ Rift Valley: A steep-sided valley formed by the downward displacement of a block of the earth’s surface between nearly parallel faults.

→ Erosion: Erosion is the gradual destruction and removal of rock or soil by different natural forces. The flowing surface water, underground water, seawater, wind, glacier, etc. are the main factors of erosion.

→ Deposition: The process of the accumulation of sediments or materials on a place carried from some other places by natural agents like flowing water, winds, glacier, etc.

→ Continental Shelf: Edges of the continents with gentle slope which remain submerged in seawater. The maximum depth of water on it is found to be 200 meters (600 feet) and the average slope from coast to sea is between 1 degree and 3 degree.

→ Ocean Canyon: Extreme deep and narrow oceanic troughs found in marine parts.

→ Continental Slope: A steep slope separating a continental shelf and a deep ocean basin.

→ Fatham: British unit of measuring ocean depth which is mostly used to measure the depth of ocean.

→ Temperate Zone: The zone located between the Tropics and the Frigid Zone on earth Jis the Temperate Zone. It is found in both the hemispheres between 23$$\frac{1}{2}$$ degree and 66$$\frac{1}{2}$$ degree latitudes.

→ Isohaline: The line joining the points with the similar salinity of ocean water on the map.

→ Mid Latitudes: Latitudes located between Cancer Circle and Arctic Circle (23$$\frac{1}{2}$$ degree to 66$$\frac{1}{2}$$ degree North Latitude) and Capricorn Circle and Antarctic Circle (23$$\frac{1}{2}$$ degree to 66$$\frac{1}{2}$$ degree South Latitude).

→ Open Sea: The expanse of sea that is not controlled by any country is called the High Sea.

→ Internal Sea: The sea found on the lithosphere part which is surrounded by the land from all sides is called Internal Sea.