The temperature-depth profile for the ocean water shows how the temperature decreases with the increasing depth.
Vertical distribution of temperature is determined by calculating the difference between surface water temperature and water temperature at specified depths. Horizontal distribution of temperature is determined by calculating monthly or seasonal means for specified depths.
The profile shows a boundary region between the surface waters of the ocean and the deeper layers.
The boundary usually begins around 100 – 400 m below the sea surface and extends several hundred of metres downward.
This boundary region, from where there is a rapid decrease of temperature, is called the thermocline.
About 90 per cent of the total volume of water is found below the thermocline in the deep ocean.
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 characterised 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.
