Thermocline Definition
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.
FAQs on Thermocline
1. What is a thermocline and why is it important in oceanography?
A thermocline is a distinct layer within a large body of water, like an ocean or a lake, where the temperature changes rapidly with increasing depth. This transitional layer separates the warmer, mixed surface water (epilimnion) from the colder, deep water (hypolimnion). It is critically important in oceanography because it acts as a barrier that prevents vertical mixing of water, which impacts nutrient distribution, oxygen levels, and the behaviour of marine ecosystems.
2. At what depth is the thermocline typically found in the ocean?
In most oceans, a permanent thermocline exists at a depth ranging from approximately 200 metres (660 feet) to about 1,000 metres (3,300 feet) below the surface. The exact depth and thickness can vary based on factors like geographical location and season. For instance, a temporary or seasonal thermocline can form at shallower depths during the summer.
3. How does thermal stratification lead to the formation of a thermocline?
Thermal stratification is the process where a body of water separates into layers based on temperature and density. It occurs because the sun's energy primarily heats the surface water, making it warmer and less dense. Wind and waves mix this upper layer, creating a uniformly warm epilimnion. Below this, in the deep, dark hypolimnion, the water remains cold and dense. The thermocline is the transitional zone that develops between these two distinct layers, marking the point where the temperature begins to drop sharply.
4. What is the main difference between a thermocline, a halocline, and a pycnocline?
These three terms describe layers of rapid change in the ocean, but they relate to different properties of water:
Thermocline: A layer with a rapid change in temperature.
Halocline: A layer with a rapid change in salinity (salt content).
Pycnocline: A layer with a rapid change in water density. The pycnocline is typically caused by the combined effects of the thermocline and halocline.
5. Why does the temperature drop so rapidly within the thermocline layer itself?
The rapid temperature drop occurs because the thermocline is a boundary zone that is not effectively mixed. The upper layer is warmed by the sun and mixed by wind, keeping its temperature stable. The deep layer is too far from the surface to be affected by solar heat or wind. The thermocline is sandwiched between them, representing the region where the influence of surface heating abruptly ends. Without mixing to distribute heat downwards, a steep temperature gradient forms.
6. Does the thermocline exist in all bodies of water, such as lakes and polar oceans?
No, the thermocline is not universal. While it is a prominent feature in most of the world's oceans and in many deep temperate lakes (especially during summer), it is weak or absent in certain regions. In polar oceans (Arctic and Antarctic), the surface water is already very cold, so there is little temperature difference with depth, preventing a strong thermocline from forming. Similarly, shallow lakes or constantly mixed water bodies may not develop a stable thermocline.
7. How does the thermocline affect marine life and submarine operations?
The thermocline has significant real-world effects:
For Marine Life: It acts as a physical barrier that traps nutrients in the cold, deep water. This can limit the population of phytoplankton (the base of the marine food web) in surface waters. Many marine animals live their lives entirely above or below the thermocline.
For Submarine Operations: The sharp change in water density at the thermocline can bend or reflect sonar waves, creating a 'shadow zone' where a submarine can effectively hide from sonar detection. It also affects a submarine's buoyancy, requiring adjustments to maintain depth.
8. Does a permanent thermocline exist at extreme depths like the Mariana Trench?
No, a thermocline does not exist at extreme depths like the Mariana Trench. The permanent thermocline is a feature of the upper-to-mid ocean, typically ending around 1,000 metres deep. The Mariana Trench is part of the hadal zone (depths below 6,000 metres), which is located entirely within the deep ocean's hypolimnion. At these extreme depths, the water is uniformly and consistently cold, generally between 1 to 4 degrees Celsius, so there is no significant temperature gradient to form a thermocline.
