Fishermen in Chetumal Bay, in the south of the Yucatan Peninsula (between Mexico and Belize), have known about its existence for decades and some scientists had carried out preliminary studies. But it was not until September 2021 that the first immersions of divers and detailed analyzes with echo sounders, conductivity, temperature and depth profilers were carried out; and images were taken of the interior of the blue hole known as Taam ja' (deep water, in the Mayan language).
The results of this first major study indicate that the Taam ja' reaches 274.4 meters below sea level, thus becoming "the second deepest known blue hole in the world", according to the scientific team responsible for the investigation. in an article presenting the results published in the journal Frontiers Marine Sciences (February 23, 2023).
The Taam ja' blue hole has an almost circular shape on its surface, covering an area of approximately 13,690 m2. The sides of the blue hole are nearly vertical (>80°) and form a large conical structure covered by biofilm, sediment, limestone, and gypsum ledges. The mouth of the blue hole is located between 4.5 and 5 meters below sea level, so the properties of the surface water change significantly with the tides. The water column inside this blue hole also shows great variations in conditions such as oxygen concentration, chemistry, temperature, and biological formations.
The researchers analyzed changes in the water at different depths and reported hydrographic profiles showing a stratified water column within the blue hole consisting of a very low-oxygen or hypoxic layer (between 5 and 20 meters below sea level). ); then a layer called chemocline, where there are masses of water with different properties of salinity and oxygen (between 50 meters and 80 meters below sea level) and below a layer where dissolved oxygen is depleted and is called anoxic layer ( below 110 meters below sea level).
The author team of the study, with Juan C. Alcérreca-Huerta (researcher at the National Council of Science and Technology-El Colegio de la Frontera Sur de México) as the first author, explains in their article that coastal karstic formations (blue holes) have little explored by the global marine scientific research community. This was one of the reasons why they decided to start this project.
Data from fishermen and superficial scientific studies encouraged this team to "explore the geomorphometric and physicochemical characteristics of a submerged blue hole in the large tropical estuary of Chetumal Bay, off the southeast coast of the Yucatan Peninsula, Mexico."
