25 Aug

Scuba Jargon Buster : What is a Thermocline

Jargon Buster – Thermocline

If you dive frequently, you may have heard the term Thermocline (thermal = temperature/ heat, cline = layer). For someone who has never dived like me, the closest term I know is thermometer. If you are among the non-divers, this info may be of some use when you decide to go diving.

The first time I encountered the word Thermocline was in the PADI Open Water course manual (that I have waded through diligently so that I can start my first Open Water course with Blue Season Bali). In simple English, a thermocline is a layer that separates colder water below from warmer water above. That term alone already fascinates me. I have known water for my whole life.. drinking it, bathing in it.. even our body is 70% water. Never would I have thought that it could come in two separate flavors in one container.  How does this happen?

Here’s the theory .. (inhale) Ocean water is exposed directly to the sun. The heat makes the temperature on the surface warm. The lower part of ocean remains colder, since less sunlight reaches it. Cold water is denser than warm water, because its molecules are more tight (remember your physics lessons?), gravity keeps the layers separated so well, that the book says you can swim in the warmer layer of water, extend your hand below and feel the difference in temperature. (exhale.. very techie talk.. you okay there?)

Scuba Jargon Buster : What is a Thermocline
Diagrams of  water temperature changes by depth

In practice I heard that a thermocline isn’t really just a thin layer, but it actually can have thickness up to a few meter (as diagram above). I snorkeled once before, and to me sea water in itself is enough to make me shiver. With a thermocline, I can only imagine how cold it can be down there. So, if you have dived, and you know more about thermoclines, please share your experience by leaving some comments on this post. Stay tuned for other newbie friendly posts to add to your knowledge repository.

4 Comment
  • Bryony
    Posted at 10:33 am, 31 Aug Reply

    I took my PADi advanced open water while travelling Thailand some two years ago. During my time diving off the amazing island of Koh Tao I came across several thermocline’s, indeed the water does have a noticeable change in temperature, so much so that you could liken it to the feeling you recieve when you put the tip of your toe into an ice cold bath on a hot summers day. The clarity of water visibility differs inside areas of the thermocline too. From a photography point of view the colder more dense water has more particles floating and requires a more intense balancing filter for the camera as the cooler the water, the more intense the drain of colour becomes.

    I hope this information is of some use to you , happy diving 🙂

    • Chilly
      Posted at 11:00 am, 31 Aug Reply

      Whoa.. Thank you for the reply. I think your short reply is more informative than my long post 🙂
      By your description, the temperature must contrast a lot.
      In our FB quiz post, to avoid hypothermia you wear adequate thermal protection or abort a dive when its too cold.
      In practise, how do you keep warm?
      I’m so much more eager to try diving now.

      Speaking about photo clarity in thermoclines, I think that would be a great subject for a blog post.
      Would you like to be our guest blogger for this topic?

      • Bryony
        Posted at 8:23 pm, 31 Aug Reply

        Guest blog sounds good. I would certainly give it my best shot, I fell in love with diving, I hope that any information/ experience I share will inspire others to try it out and appreciate the natural beauty abundant in our worlds waters.

        I have to say there are several methods used by divers to keep warm, the ones listed by yourself above being the most safe and sensible, which should always be used as they truly can safe your life! Please remember diving can quickly turn from fun to life threatening if the correct procedures and training have not been followed!
        That being said there are a few cheeky tricks used by divers world wide, one of the most common and possibly slightly unhygienic is to urinate in your suit. The temperature of your urine will be warmer then the water external to your body and heat the air trapped in the space between your skin and suit, however this is merely for comfort, if the elements are setting in, I simple say ascend immediately in the safest means to a depth that allows you to warm up and safely evaluate the situation, to continue or end the dive.

        My advice would always be to follow what your instructor tells you, apply common sense and always air on the side of caution.

        Tip of the day: Hydrate after every dive, ensure you carry energy foods and a substantial stock of fresh water to keep your body fluids in check.

        • Chilly
          Posted at 1:32 pm, 12 Sep Reply

          Thank you very much.. I will be sending you an email shortly.. And I hope soon we have more active guest blogging platform on Blue Season Bali.
          The cheeky trick.. sounds.. yucky.. but smart none-the-less.
          That tips of the day is great, noted and I’m sure it can come in handy for many other readers out there.
          Thank you again 🙂

Post A Comment

Ready to sign up for this special offer today?

Check out our Instagram for daily promo!