Scientists have not yet reached the bottom of the Taam Ja blue hole in Mexico’s Chetumal Bay; According to new measurements, this hole may be connected to a labyrinth of underwater caves and tunnels. Researchers have discovered that the Taam Ja Blue Hole in Mexico is the deepest underwater hole in the world, and they have yet to reach the bottom.

New measurements show that the Taam Ja Blue Hole (TJBH), located in Chetumal Bay on the southeast coast of the Yucatan Peninsula, extends at least 1,380 feet (420 meters) below sea level.

That’s 480 feet (146 m) deeper than what scientists documented when they first discovered the blue hole in 2021, and 390 feet (119 m) deeper than the previous record holder, the 990-foot (990-foot) Sansha Yongle Blue Hole. Also known as the Dragon Hole in the South China Sea.

“A scuba diving expedition was conducted on December 6, 2023, to determine the environmental conditions prevailing at TJBH,” researchers wrote in a study published Monday (April 29) in the journal Frontiers in Marine Science. During the expedition, researchers took measurements using a conductivity, temperature and depth (CTD) profiler, which includes an array of probes that read water properties in real time through a cable and transmit them to the surface. The data showed that the Taam Jah blue hole “is the deepest known blue hole in the world, and its bottom has not yet been reached,” researchers wrote in the study.

The profiler also identified different layers of water within the blue hole, including a layer below 1,312 feet (400 m), where temperature and salinity conditions are similar to the Caribbean Sea and adjacent coastal reef lagoons. According to the research, this suggests that TJBH may be connected to the ocean through a secret network of tunnels and caves.

Blue holes are water-filled vertical caves or sinkholes found in coastal areas where the bedrock consists of soluble materials such as limestone, marble or gypsum. They form when surface water seeps through the rock, dissolving minerals and widening cracks, eventually causing the rock to collapse. Famous examples include the Dinah Blue Hole in the Bahamas, the Dahab Blue Hole in Egypt, and the Great Blue Hole in Belize.

Initial measurements of TJBH were made using sonar, a device that sends sound waves to the bottom of the water and measures the rate of return to calculate distance. However, there are limitations to the blue hole echo drilling technique due to fluctuations in water density and the unpredictable shape of each hole, which may not be exactly vertical.

“Due to instrument limitations during scientific exploration in 2021, it was not possible to verify the maximum depth,” the researchers wrote in the study.

The CTD instrument used for the latest study also could not find the bottom of the blue hole because it could only work to a depth of 1,640 feet (500 m). According to the study, scientists lowered the profiler to this depth, but the cable to which it was attached may have been dragged in underwater currents or hit a ledge that stopped the device at a depth of 430 meters.

Next, scientists plan to “resolve the maximum depth of the TJBH and the possibility that it forms part of an underwater complex and potentially an interconnected system of caves and tunnels,” the researchers write.

“The depths of TJBH may also hold biodiversity that needs to be discovered,” they added.