Physical Geography Notes for Civil Services UPSC PrelimsMain IASIFSIPSIRS(IT)IRS(C&CE) (English) by Vedanta IAS Academy

Author:Vedanta IAS Academy [Academy, Vedanta IAS]
Language: eng
Format: epub
Published: 2021-12-07T22:00:00+00:00

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The temperature structure of oceans over middle and low latitudes can be described as a three layer system from surface to the bottom.

The first layer represents the top layer of warm oceanic water and it is about 500m thick with temperatures ranging between 20° and 25° C. This layer, within the tropical region, is present throughout the year but in mid latitudes it develops only during summer.

The second layer called the thermocline layer lies below the first layer and is characterized by rapid decrease in temperature with increasing depth. The thermocline is 500 -1,000 m thick The third layer is very cold and extends upto the deep ocean floor. In the Arctic and Antartic circles, the surface water temperatures are close to 0° C and so the temperature change with the depth is very slight. Here, only one layer of cold water exists, which extends from surface to deep ocean floor.

The third layer is very cold and extends upto the deep ocean floor. In the Arctic and Antartic circles, the surface water temperatures are close to 0° C and so the temperature change with the depth is very slight. Here, only one layer of cold water exists, which extends from surface to deep ocean floor.

The maximum temperature of the oceans is always at their surfaces. The average temperature of surface water of the oceans is about 27°C and it gradually decreases from the equator towards the poles.

The highest temperature is not recorded at the equator but slightly towards north of it. The average annual temperatures for the northern and southern hemisphere are around 19° C

and 16° C respectively. This variation is due to the unequal distribution of land and water in the northern and southern hemispheres.

SALINITY OF OCEAN WATERS

Salinity is an important property of sea water. It is calculated as the amount of salt (in gm) dissolved in 1,000 gm (1 kg) of seawater. It is usually expressed as parts per thousand (o/

oo) or ppt.

Factors affecting ocean salinity are mentioned below:

(i) The salinity of water in the surface layer of oceans depend mainly on evaporation and-precipitation.

(ii) Surface salinity is greatly influenced in coastal regions by the fresh-water flow from rivers, and in polar regions by the processes of freezing and thawing of ice.

(iii) Wind, also influences salinity of an area by transferring water to other areas.

(iv) The ocean currents contribute to the salinity variations.

Salinity, temperature and density of water are interrelated. Hence, any change in the temperature or density influences the salinity of water in an area.

Highest salinity in water bodies Lake Van in Turkey (330 o/oo).

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