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Geography Class 03

REVISION OF THE PREVIOUS CLASS (05:06 PM)

OCEANOGRAPHY (05:09 PM)

  • Structure of the topic:
  • Distribution of water.
  • Salinity and temperature of the Oceans.
  • Ocean Bottom Relief Features.
  • Ocean Currents.
  • Tides.
  • Coral Reefs.
  • Tsunamis.
  • Ocean Deposits.

DISTRIBUTION OF WATER (05:11 PM)

  • Oceans contain 97.25% of the Earths water.
  • Continents contain 2.75% of the Earths water.
  • Water Presence in  Percentage
    Lakes 0.01
    Soil Moisture 0.005
    Atmospheric Moisture 0.001
    Streams and rivers 0.0001
    Biosphere 0.00008

SALINITY (05:32 PM)

  • The amount of dissolved salts in grams per kilogram of water (Parts per Thousand ‰).
  • The salinity can be classified into different types:
  •  Salinity Chart  
    Freshwater <5‰
    Brackish Water >5‰-24.9‰
    Saline Water and Brine >24.9‰
  • Composition of the Salts:
  • The most dominant salt is Sodium Chloride followed by (in sequence):
  • Magnesium Chloride.
  • Magnesium Sulphide.
  • Potassium Sulphide.
  • Magnesium Bromide.
  • Chlorides and sulphides form the dominant composition of the salts.
  • Sources of Salinity:
  • 1. Terrestrial Source.
  • 2. Submarine Source.
  • 3. Cosmic Source.
  • Terrestrial Sources:
  • When the rock weathers, it is carried either by the river or the fast-blowing winds into the ocean making the water saline.
  • It is the dominant source of salinity.
  • Submarine Source:
  • It is called an immediate source of salinity due to vulcanism.
  • The submarine vulcanism spews huge quantities of Pyroclastic material into the oceanic water making the water saline.
  • Cosmic Source:
  • This is the source of salinity from outer space in the form of meteors and meteorites.
  • Factors affecting salinity:
  • 1. Evaporation:
  • The rate of evaporation depends upon temperature.
  • More the evaporation more the salinity.
  • 2. Influx of the freshwater:
  • The more the influx of fresh water, the lesser will be the salinity.
  • Influx can be of three types:
  • 1. By the rivers;
  • 2. By the rainfall;
  • 3. Thwaing of the ice.
  • Along the mouths of the river, the salinity is very low.
  • In those areas where the rainfall is too high and throughout the year, such areas experience moderate salinity.
  • For example, Equatorial regions.
  • The melting of the ice increases the freshwater Volume by decreasing the salinity.
  • 3. Ocean currents:
  • The definite circulation of the water in the ocean is called oceanic current.
  • The water from the Equatorial region with more salinity is brought to the Polar Region and less saline regions and back from the Polar region, the waters are carried towards the equatorial region maintaining the hydrostatic balance of the ocean.
  • 4. Pressure and the Winds:
  • The Global winds have a profound influence on the salinity.
  • For example, the trade winds blow from East to West of the World due to their frictional force over the water surface drag the water from the East to West of the ocean continuously.
  • This results in the cold upwelling of the water along the Eastern margins of the ocean.
  • Alternatively along the Western margins of the oceans piling up of the warm surface water results in the downwelling.

DISTRIBUTION OF SALINITY (07:15 PM)

  • The world is divided into three major regions:
  • 1. Regions of Moderate salinity.
  • 2. The regions of High Salinity.
  • 3. Regions of low salinity.
  • 1. Regions of moderate salinity:
  • These are the Equatorial regions though the insulation is high, these are called the areas of moderate salinity due to the influx of fresh water by rainfall.
  • 2. Regions of high salinity:
  • These are the tropical and subtropical regions.
  • Evaporation is more than the precipitation is a major condition for such high salinity.
  • For example, Lake Van is in Turkey;
  • Dead Sea between Jordan and Israel;
  • Persian Gulf;
  • 3. Region of low salinity:
  • These are the regions of temperate and Polar regions.
  • Regions include:
  • Baltic Sea;
  • Gulf of Bothnia;
  • Gulf of Riga.

TEMPERATURE OF THE OCEANS (07:48 PM)

  • The average temperature of the oceans in the Northern Hemisphere is 19°C whereas the average temperature of the oceans in the Southern Hemisphere is 16° C.
  • The high temperature in the Northern Hemisphere is due to the presence of more landmass.
  • Factors affecting the temperature of the ocean:
  • 1. Latitude:
  • Temperature decreases from the Equator towards the Poles.
  • The rate of change of temperature per latitude is 0.5°C.
  • On average, the temperature along 20° Latitude is 22°C, along 40° latitude is around 14°C and along 90° Latitude, the temperature is 0°C keeping the seasonal variations as constant.
  • 2. Ocean Currents:
  • A definite circulation of water in the ocean is called ocean current.
  • These circulations maintain the global temperatures by taking the warm Equatorial waters towards the Poles and bringing the Cold Polar waters towards the Equator.
  • 3. Distribution of land and water:
  • More enclosed water bodies experience more thermal range than the less enclosed water bodies.
  • Due to the presence of more landmass in the Northern Hemisphere, the average temperature of the oceans is high at 19°C while in the Southern Hemisphere, it is 16°C.
  • 4. Global Winds:
  • The global wind circulations maintain the global heat balance due to their circulations throughout the Planet.

The topic to be discussed in the next class- Ocean Bottom Relief Features.