Cenotes are the natural sinkholes resulting from the collapse of limestone and filled with fresh water. Cenotes have played a significant role in the lives of the Mayan Indians of the Yucatan area and continue to do so today. Because this particular region of Mexico is fairly dry, with relatively no rivers or streams on the land surface, the underground water beds provide an important source of water for the mayan populations. The Mayas were able to utilize the opening of the cenotes to retrieve water much like Westerners use a well. Because these underground water systems were very extensive and deep, it is not surprising that the Mayan civilizations built around cenotes were able to thrive.
Entrance to the cavern in cenote Tajma Ha ©Marina Kudrya
Most (if not all) cenotes are linked into systems through their caves. For example, Dos Ojos system is one of the largest cave systems in the world and contain the deepest known cave passage in the state known as El Pit (~120m). The deeper parts of El Pit later were connected with another cave system called Sac Actun, what made the total length of the combine system almost 320km.
Our guide in cenote Tajma Ha ©Marina Kudya
Dos Ojos cave system connects to the ocean naturally and marine water intrudes the caves depending on the tide; at the same time large volumes of groundwater flow towards a nearby coastal bedrock lagoon. Inside cenotes where the salt and fresh water meet a halocline phenomenon can be seen: a location in the water where there is a sharp change in salinity.
Halocline ©Marina Kudrya
In all deep cenotes at the depth around 30m there is a hydrogen sulphide layer. Hydrogen sulphide is a layer of toxic gas that has been released in decomposing process of fallen vegetation, but could not go up to the surface. Thus it was trapped in the water column. Below the hydrogen sulphide layer is a anoxic layer of salt water from the ocean.
Hydrogen sulphide layer in El Pit ©Marina Kudrya
There is no such vibrant fauna in cenotes as one may find on a coral reef, simply because it not much food there. Sometimes there are small fish or freshwater turtles.
My dive buddy observes underwater vegetation in El Pit ©Marina Kudrya
Although the area of the cavern is within the natural daylight zone of the cave entrance, divers need to be within 60m of the nearest open water. As well each diver must be equipped with a minimum of one light, which stays on during the entire dive.
Our dive guide in a light spot ©Marina Kudrya
Overall diving in cenotes is a very unique experience where every diver can find something of an interest to them, be that a cavern or cave, and explore the wonders of this underworld.
Openings in Tajma Ha ©Marina Kudrya