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Thermocline Definition

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A thermocline popularly known as the thermal layer or even known as metalimnion in lakes is actually a thin but distinct layer in a large fluid body like in ocean or in the lake. In thermocline, the temperature varies drastically with the depth while it varies less in the layers that are above or below. In the ocean, the thermocline distinguishes the upper mixed layer from the deep water which is quite calmer deep below. 


Majorly depending on the season, turbulent and latitude extension, and also by mixing with the wind, the thermocline may be a semi-permanent feature present in the body of water where they basically occur. 


More about Thermocline

Thermoclines are visible in lakes as well. In cold weather, this layer leads to an occurrence called ‘stratification’. In the summertime, the warm water, which is less dense, will settle on the top of the colder, denser, and deep water, and in between them, a thermocline will be separating both temperature water. 


The warm is known as epilimnion, while the cold layer is called the hypolimnion. This happens as the warm water gets exposed to the direct sun in the daytime, there exists a stable system and little mixing of the warm water and the cold water which occurs particularly in calmer weather.


One result of this kind of stability is that when the summer wears on, there is much lesser oxygen that is below the thermocline. While the water below this thermocline never circulates on the surface and the organisms in the water deplete the availability of oxygen. 


When the winter approaches, the temperature of the surface water will drop, this happens because at nighttime the cooling dominates the heat transfer. Then a point is reached in where the density of the cooling surface water is much greater than the density of the deep water and then the overturning begins when the dense surface water moves down with the gravitational pull. This process is also backed by wind or by any other process like the currents for example which agitates the water.


Thermocline Depth

The thermocline is the oceanic water layer where the water temperature decreases quite rapidly with the increasing depth in them. There is a widespread and permanent thermocline that exists beneath this relatively warmer, well-mixed surface layer, from the depths of about 200 m (or 660 feet) to about around 1,000 m (that is 3,000 feet), where there is an interval of temperatures that diminishes steadily.

Seasonal Thermocline

A thermocline that is formed in the oceans in the summer days at relatively shallow depths, is due to surface heating and for the downward transport of heat which is caused by mixing with the water that is generated by the summer breeze.            

Permanent Thermocline

The permanent thermocline actually refers to the thermocline that is not affected by the seasonal or the diurnal changes in the surface which is by the forcing and is therefore located below the per annum maximum depth of the mixed layer and by the influential potentiality of the atmosphere.

Fishing Thermometer Thermocline

Put the thermocline in a band of water. This is done where the temperature changes rapidly from the hot on top to the cold below. This is often a number of feet thick. For the water properties varying at different temperatures, this forms a barrier that prevents the hot water on the top to mix with the cold water underneath.

This technique is quite important while fishing as the water which is above the thermocline is very hot for the fish to live there, they cannot survive there for long periods of time. This is so because the surface water is exposed to direct sunlight.

While the water below has low oxygen available for the fish. This happens as the oxygen gets into the water by the water plants and by the surface action. The water plants are usually shallow which places above the thermocline. The thermocline acts as a barrier for that oxygen to trickle the water down below.

Hence the fishes like to hang around the thermocline. This allows the fishes to find the balance for the want of oxygen and temperature. Thus, effortlessly the fishes can move to adjust the balance here.

Thermocline Temperature

The temperature measured in the deep ocean may gradually drop with the increasing depth. As the saline water will not freeze until this reaches −2.3 °C (27.9 °F) (which is colder as the depth and pressure increase gradually) the temperature that is below the surface is usually not far from getting zero degrees. Thus, the thermocline varies with increase and decrease in depth.

FAQ (Frequently Asked Questions)

1. What is Stratification?

Ans. Stratification can be defined as the development of relatively stable light which has warm layers above the colder and deeper layers that are within a body of the water vessel. Thermal stratification is also related to the water density and this is affected by the incoming heat, by water depth, and also by the degree of water-column which is in the mixing process.

In the case of Lake stratification, the lakes try to form a separate and distinct thermal layer during the warm season. Thermal stratification occurs generally when the lake water forms a distinct layer by the heating of the sun.

2. Where Does Thermocline Occur?

Ans. The thermocline is the oceanic water layer, here the water temperature decreases quite rapidly with the increase in the depth level. A widespread and permanent thermocline does exist beneath the relatively warm, and well-mixed surface layer, which is from the depth of about 200 m (660 feet) to about 1,000 m (3,000 feet), where the temperature varies and decreases steadily.

3. What is the Difference Between Thermocline and Halocline?

Ans. A halocline is known as the layer which separates two water masses by the difference in their individual density, but this is not caused due to temperature, this mainly occurs when these two bodies of water come together, one with fresh water and the other one with saltwater. Saltier this water, the denser and sinks leaving the fresh water on the surface of the water.