# PM IAS GS 1 SYNOPSIS

Approach:
• Giving a brief introduction, discuss the vertical and latitudinal (horizontal) distribution of temperature in ocean waters.
• Enumerate the factors responsible for the above distribution.
• Use appropriate examples wherever necessary.
The study of temperature of the oceans is important for studying the movement of large volumes of water, distribution of marine organisms, other properties such as salinity. This distribution pattern of temperature of ocean water can be studied in two ways:
Vertical distribution (from surface water to the bottom):
The temperature-depth profile for the ocean water shows how the temperature decreases with the increasing depth. The temperature structure of oceans over middle and low latitudes can be described as a three-layer system from surface to the bottom.

1. The first layer represents the top layer of warm oceanic water with temperatures ranging between 20° and 25° C. Within the tropical region, it is present throughout the year but in midlatitudes, it develops only during summer.
2. The second layer called the thermocline layer lies below the first layer and is characterized by rapid decrease in temperature.
3. The third layer is very cold and extends up to the deep ocean floor. Here the temperature becomes almost stagnant.
In the polar regions, the surface water temperatures are close to 0° C and so the temperature changes with the depth are very slight.
Horizontal distribution (temperature of surface water):
• The average temperature of surface water of the oceans is about 27°C and it gradually decreases from the equator towards the poles.
• The rate of decrease of temperature with increasing latitude is generally 0.5°C per latitude (Figure).
4. • The oceans in the northern hemisphere record relatively higher temperature than in southern hemisphere.
• The horizontal temperature distribution is shown by isothermal lines, i.e., lines joining places of equal temperature. Isotherms are closely spaced when the temperature difference is high and vice versa.

The factors, which affect the distribution of temperature of ocean water are as follows:
• Latitude: The temperature of surface water decreases from the equator towards the poles because the amount of insolation decreases pole-ward.
• Unequal distribution of land and water: The oceans in the northern hemisphere receive more heat due to their contact with larger extent of land than the oceans in the southern hemisphere.
• Prevailing wind: The winds blowing from the land towards the oceans drive warm surface water away from the coast resulting in the upwelling of cold water from below. Contrary to this, the onshore winds pile up warm water near the coast and this raises the temperature.
• Ocean currents: Warm ocean currents raise the temperature in cold areas while the cold currents decrease the temperature in warm ocean areas. For example: Gulf stream (warm current) raises the temperature near the eastern coast of North America.
• Enclosed sea: The enclosed seas in the low latitudes record relatively higher temperature than the open seas; whereas the enclosed seas in the high latitudes have lower temperature than the open seas.