Thermoclines are recognizable zones in bodies of water in which the temperature varies at a much quicker rate.

While thermoclines are seen frequently in oceans, they can also occur in lakes.

Clines in oceanography refers to areas or layers where the properties of the water are different than their surroundings.

You may have heard of pycnoclines or haloclines in your open water course.

  • Haloclines refer to layers that have a distinct change in salinity gradient.
  • Pycnoclines refer to layers that have a distinct change in water density.

Why Do Thermoclines Exist?


Thermoclines exist due to the way water absorbs heat and sunlight. The surface and first few centimeters of water are the warmest.

As you go deeper into the epipelagic zone, heat is lost due to radiation. Ocean movements cause warmth from the sun to be distributed past this layer but eventually ends.

Once this level is reached, the temperature begins to drop off much faster.

Here’s an informative video discussing more about the ocean and its many layers.

Do Thermoclines Vary By The Season?

thermoclines by the seasons

Thermoclines are formed off a variety of conditions, and seasons are certainly one of them.

As you might expect, in summer months thermoclines are often pushed deeper due to the increased average water temperature.

There’s a direct correlation between the stage the sun is in setting and the location or severity of a thermocline.

Interestingly enough, thermoclines can also play a role in the prediction and tracking of hurricanes, but we won’t get into that here.

Why Do Thermoclines Matter For Scuba Divers?

Thermoclines play an important role in the planning of a scuba dive.

While you won’t encounter them on all of your dives, they’re important to consider if you are diving in a location where they are common.

As you may remember from a PADI open water course, we humans consume air much quicker when we are overexerted. Diving in cold water, even with proper gear causes us to use more air.

So, if a dive site you are going to takes place in a thermocline, consider a different approach to the dive such as using a thicker wetsuit.


Thermoclines are an interesting natural phenomenon that can take many new and inexperienced divers by surprise.

I remember the first time I experienced one in Hawaii, and just how apparent the difference was temperature.

Depending on light conditions, it’s also possible to see different shading in the water indicating a thermocline zone is near.

If the dive site you are headed to is known to have thermoclines, it’s very important to both understand and prepare properly for the dive.