Scuba diving and thermoclines

Scuba diving through a thermocline isn't dangerous, it's actually quite fascinating. As a scuba diver you probably dived through a thermocline before, perhaps even without knowing what it was. Looking back you may find you've dived through quite some thermoclines. However what are thermoclines? How do you recognise one? And where can you expect to find one? Let's answer these questions.

What is a thermocline?
A thermocline is a distinct layer in a large body of water (think ocean or lake) in which temperature changes more rapidly with depth than it does in the layers above or below. You can visualise it as two separate layers of water which have two different temperatures. Usually the layer above is a bit warmer than the layer below. Thermoclines may be a permanent feature of your scuba dive site or it may be a temporary occurrence. This depends on several external factors like season, location and local weather conditions. 

How to recognise a thermocline?
There are three ways to recognise a thermocline. The easiest way is to the feel it by the drop in temperature while descending on your dive. Suddenly you get a chill as if someone drops a bucket of ice water over your head. You feel an thermocline better when scuba diving in a wetsuit than in a dry suit of course. The drop in temperature is usually only a few degrees so where does that 'chilly' feeling come from. That's because your body is accustomed to a certain water temperature and when this suddenly drops even if it's only 1 degree, this feels 'extremely' cold.

The second way is to use your scuba diving computer. When moving your computer through the two different layers you will see the temperature shift on your computer. 

The third and last method is by seeing the thermocline through your own eyes. So what does a thermocline look like? You can compare it with something else you're probably very familiar with. When it's very hot you can often see the air wrinkle above a road. A thermocline looks almost the same as this wrinkling of hot air. You can only see a thermocline when your eyes are exactly on the spot where the two layers meet each other. Thermoclines may not always be that perfectly visible because the two layers can be mixed up which negates this wrinkling effect.  

Where can you expect thermoclines?
Thermoclines can happen anywhere. I experienced thermoclines while scuba diving in the Caribbean, Iceland and even in a fresh water lake in the Netherlands. Just keep an eye out for that 'chilly' feeling. 


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