May 3, 2020ARTICLES0 comments

Definition of halocline

In oceanography, a halocline (from Greek hals, halos ‘salt’ and klinein ‘to slope’) is a relatively sharp discontinuity in ocean salinity at a particular depth. In general, water with a higher concentration of salinity sinks below water that is less saline; therefore, saltier haloclines lie below less salty ones.

In the caves in Yucatan this stratification is even bigger because the water changes radically from fresh to salty. This sudden alteration in the salinity of the water results in amazing visual effects and buoyancy changes.

Where all that water comes from?

Saltwater comes from the sea. It is permanently filtering through the very porous limestone rock that conforms the Yucatan Peninsula creating a lense that soaks the Peninsula. 

Fresh water comes from the rain. The water stays for a short time on the surface and quickly crosses the substrate dissolving minerals on its way down to finally lay on top of the lense created by saltwater. 


So, what is  halocline? The layer where these two water masses meet.

But this layer is also a Thermocline as temperature experiences a big variation. In the Riviera Maya saltwater is 3-4° F (about 2 °C) warmer than fresh water what creates a “bathtub effect” when hitting the salty layer that all divers love.

How does it affect diver’s bouyancy?

Through the Archimedes principle, Physics says that the deeper an object submerged in water is, the more negatively buoyant it will get.

But the change from one density to a drastically different one in just a few inches or centimeters strongly affects diver’s buoyancy. Suddenly the surrounding water is much more dense and neutral buoyancy becomes positive. Trying to descend becomes very difficult unless some air is released from the BCD or wing. On the way back up the opposite occurs. Some air has to be added in the BCD to compensate for the decreased density in the water holding the diver. 

Even the most seasoned divers get amazed by this effect the first time they experience it.

No, is not your mask nor your eyes.

Diving in jelly would be an accurate definition of what a diver can see when crossing the halocline. Being below it is also a trick for the eyes. When untouched, the point where the two different waters meet looks perfectly flat, giving the optical impression of being the surface. 

The visual effects created by this layer is one of the biggest features of some of the cenotes in the Riviera Maya, such as Jardín del Eden, also known as Ponderosa.

In order to enjoy these effects being one of the first groups in the water makes a huge difference. When diving cenotes in the Riviera Maya ask your dive shop or guide to go as early as possible. Totally worthy..

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