Is the Deep Ocean Cold? All You Need to Know

A large percentage of the ocean is yet to be explored. However, the areas we have been able to explore have yielded very exciting results. These facts about the ocean are guaranteed to pique your interest if you are someone who spends a great deal of time studying the water body. 

One of these is the ability of the deep ocean to remain cold regardless of the amount of water pressure found there. It is said that the deep ocean, below 200 meters in depth, is found to have a temperature of around 4 degrees celsius, meaning 39 degrees fahrenheit. 

This difference in temperature affects different aspects of the ocean, most of which will be explored in this article.

Why is the Deep Ocean Cold?

There are many reasons why the deep ocean is a colder place than the shallower parts of the waterbed. 

Weight of Cold Water

Since cold water is denser than warm water, it tends to sink to the bottom. This case is also true for the ocean where the deeper you go into the ocean, the colder it will get. While colder water rests at the bottom of the ocean, the warmer kind stays at the surface. 

Wind influences cause the warm water to enter into a complex dance with the colder, denser water named the Global Conveyor Belt.

The Earth’s Core

You may be wondering how the deep ocean remains cold regardless of how the core of the planet Earth is hotter than the further away parts of our home planet. 

It is important to note that while the inside of the Earth continues to get hotter and hotter as you go deeper, the transfer of this energy has a very minuscule effect on the deep ocean. The effect is barely measurable. This keeps the core of the Earth and the deep ocean, lying within the core, cooler.

This is because, if you disregard ocean currents, the heat flow from these transfers of energy would take years to take any actual effect on the deep ocean and its temperatures. 

However, when considering ocean currents, it is important to understand that the water density causes the deep ocean to continue to cool more and more over time.

Lack of Sunlight

Finally, one of the main reasons the deep ocean remains cold is because the deeper we go into the ocean the less sunlight there is. 

This means that the bottom of the ocean sees no sun at all. The lack of heat energy being transferred makes the deep ocean cool and high pressure.

The Role of Pressure

Most people, when asking why the deep ocean is so cold, wonder why pressure doesn’t heat up the bottom of the ocean as we realize that the pressure of water gets higher the further down we go. There are two reasons for this.

High Pressure Does Not Equal High Temperatures

People often assume that, regardless of what stage of matter an element is in, adding pressure to an object or element will cause it to heat up. 

However, this does not always hold true. Most people believe this because of the oversimplification of the ideal gas law, however, it is important to remember that water is almost entirely incompressible. 

This means that it does not respond to pressure the same way another element would.

Compression Increases Temperature

As we’ve established, pressure does not equal high temperatures. However, compression does. Since the kinetic energy of the molecules in water does not occur because of friction, it can be understood that it is incompressible. 

This means that unless the ocean experiences sudden and rapid changes in water pressure, it is unlikely for the deep ocean water to be anything but cold. 

The Role of Evaporation

Because the sun heats the top layer of the ocean, this layer evaporates, causing the ocean’s surface level to cool down. The colder the water gets, the heavier it becomes. 

Once the density has reached a certain point, water starts to sink into the ocean, leaving warm water to take its place at the top again. This makes it so warm water always remains on the ocean’s surface while the cooler water continues to sink till it becomes part of deep water.

Since the heat flow is low, when disregarding currents, this flow level would take years to heat up the ocean water by 1 degree Celsius. 

Deepest Ocean

The deepest ocean that humans have discovered is the Antarctic Bottom Water (AABW). This water body is found under 4000 meters of all ocean basins connected to the Southern Ocean. 

It is also the coldest ocean standing at a whopping -0.8 to 2 degrees Celsius.


The ocean is a fascinating wonder of the Earth that humans have continued to explore over the centuries. There is much to be learned from and about the water body, for instance, the cold, dense, deep ocean phenomenon.

While there is still so much of the deep ocean that is still unknown to humankind, the things we know are fascinating. 

While the deeper ocean remains cool at all times, the water’s temperature might change over a certain amount of time. Look out for your weather channels to learn more about the wonder that is the ocean.

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