We’d been through the ringer by the time we arrived at this stop on our expedition. With hair matted to our salted and sunburnt faces, legs covered in bug bites, and eyes glazed over from the exertion of back-to-back dives, we made our way through initial introductions at ECOSUR Research Center in Chetumal, Mexico. But the occasion was far too significant to let our depleted condition hold us back. The team at ECOSUR had just learned about the world’s deepest blue hole. Our eagerness simply exceeded our exhaustion.

A few months prior, we had reached out to Dr. Juan Carlos Alcérreca-Huerta, the lead scientist overseeing and coordinating everything about Taam Ja’, the aforementioned, and now confirmed deepest, blue hole in Chetumal Bay, Mexico. We had read his paper in Frontiers right at its publication and we just so happened to be across the border from him in Belize. Shocked at what we were reading, we were ready to re-route our entire expedition to work with Juan Carlos – salty, sunburnt, bug-bitten and all.

Only hours before sitting down with Juan Carlos, we had done two dives at Taam Ja’ with our greatest depth being 45.5 metres in the 425-metre blue hole that only six people had dived prior. There were just the three members of our team in those isolated waters during these dives, and the feeling could best be described as surreal, other-worldly, equal parts terrifying and mind blowing all at once. The experience was that out of a science fiction movie, exploring a place people had simply never gone before.

Juan Carlos guided us in comprehending the profound sight we had just taken in, which we had spent an entire day capturing both on camera and in our memories. But before there was the discovery of the blue hole, there was the seven-year monitoring project focused on studying the dynamics of the Gulf of Mexico and the Caribbean Sea coordinated by Dr. Laura Carrillo. If it weren’t for that effort, starting back in 2016, the world would still be blind to what sits beneath the surface right off of mainland Quintana Roo.

Juan Carlos and his colleagues have worked closely with Jesús Artemio Poot-Villa, a local fly fisherman, due to his local knowledge of Chetumal Bay and its surroundings. As the project was coming to a wrap, Jesús mentioned an “interesting structure” within Chetumal Bay and invited Juan Carlos to investigate further. Initial explorations of the never-before-seen blue hole in the middle of Chetumal Bay involved the most basic methods like lowering a rock on a rope, initially revealing depths of 30 metres, then 50 metres, and eventually reaching 130 metres without hitting bottom. Subsequently, they deployed specialised instruments for detailed measurements inside the blue hole, all wondering with great curiosity how far they could go.

On Juan’s team, Dr. Óscar F. Reyes-Mendoza and MSc Laura María Flórez-Franco were to head up exploring the blue hole from a diving perspective, enhancing their research and planning navigation strategies to actually see for themselves what they were working with. Their initial efforts concentrated on studying the morphology and layers within the hole. But of course, the pivotal scientific breakthrough came when they accurately determined the true width and depth of the blue hole. It was a significant milestone in 2024 when it was officially on record that Taam Ja’ was deeper than Dragon’s Hole in China – the previous record holder for deepest blue hole in the world.

While sitting at his desk, with little blue hole artifacts all around him, Juan unveiled that the first expedition to Taam Ja’ in 2021 was particularly intriguing due to the unusual calmness observed over the hole, a stark contrast to the chaotic surrounding waves. During this event, the blue hole was ejecting water like a spring, a spectacle Juan Carlos and Jesús have not witnessed since. This moment prompted a deeper investigation into the water layers and their dynamics.

Their initial focus was on accurately measuring the depth and subsequently involving other departments at ECOSUR to explore various aspects such as chemistry and water quality with the inclusion of Dra. Teresa Álvarez-Legorreta and Dr. Joan Sánchez-Sánchez. Their interdisciplinary approach aimed to comprehensively understand the blue hole as best and as fast as they could. Their efforts included extensive measurements to analyse salinity and conduct water testing. Maria played a crucial role in confirming the presence of thermoclines, with sudden temperature changes of 3-4 degrees Celsius observed at different depths. Salinity levels also varied significantly, ranging from 12 to 16 units near the surface to 37 units deeper, similar to the Caribbean Sea. These findings highlighted the nature of the blue hole’s environment, revealing numerous layers of complexity that demanded further investigation.

Traditionally, water temperatures decrease with depth, but a notable and intriguing anomaly was also found beyond 400 metres in Taam Ja’, where the temperature rose by approximately 4 degrees Celsius – a significant deviation for a water mass under such conditions. One hypothesis for why this was happening was hinting at a potential connection with the Caribbean Sea. This would suggest that the blue hole may function as a conduit or the root of a larger geohydrological system, distinct from those developed in Tulum and Cancun. These dynamics could provide insights into understanding broader and unique geological processes shaping the southern coasts of the Mexican Caribbean.

In the vicinity of Taam Ja’ there are two distinct fracture zones: the northern zone characterised by underground large horizontal structures like caverns, passages and conduits connecting cenotes, typical of Tulum and Cancun, and the southern zone with very large vertical structures like what we know as blue holes and exposed karstic manifestations such as lakes and rivers. These fractures delineate geological features that develop along the Mexico-Belize border, including iconic sites like Bacalar. The coastal area of Chetumal Bay also lies within this southern fracture zone, suggesting similarities in geological behaviour, akin to that of Bacalar.

Across the Yucatan Peninsula, a limestone platform sits beneath the landscape, contributing to the formation of cenotes and blue holes with a shared geological origin. However, the southern zone exhibits more similarities with Belize than with the rest of Yucatan. Despite regional distinctions, these formations are unified by the limestone platform, tectonics, and hydrology extending across both fracture zones. The interaction between erosion, sea level fluctuations, and tectonic activity over millennia has shaped the landscape, particularly evident in the unique characteristics of these blue holes. As sea levels rose from approximately 120 meters lower during the last glaciation to their current levels, erosion processes intensified, affecting the integrity of sinkholes’ upper layers. Tectonic forces further influenced these formations.

Recent findings indicate dynamic changes, such as water movements and temperature fluctuations, suggest that Taam Ja’ could act as a pathway or a portal connecting these geological processes. This connectivity potentially extends to the other four blue holes, submerged springs and cenotes in the area, highlighting the interplay of natural forces that continue to shape this remarkable landscape. Although we had been utterly wowed from the moment we first were introduced to this remarkable place – this was the true moment our minds were fully blown. There is so much that we do not know about the place we call home!

The profound depths of blue holes, like the Great Blue Hole in Belize, result from historical sea level fluctuations. These formations mark ancient sea levels from approximately 10,000 years ago, illustrating gradual sea level rise. While some blue holes globally are formed by cave system collapses, the exact formation of extremely deep holes, such as the Taam Ja’ Blue Hole, China’s Dragon’s Hole (also known as Yongle Blue Hole) in China, or Dean’s Blue Hole in the Bahamas, remains uncertain. Despite the proximity of large blue holes in Belize and Mexico, their formation involves a complex interplay of tectonic activity, erosion, and unique limestone geology.

But, what’s so drastically different about the Great Blue Hole and Mexico’s Taam Ja’ is that while the Great Blue Hole is so visually distinct that it can be seen from space, Taam Ja is practically invisible from above (hence its very recent discovery). The reason for this is because the conditions out in Chetumal Bay are less than ideal when it comes to visibility. The local wind-driven waves and the turbidity due to sediment resuspension makes it hard to see what’s hidden beyond five meters below a pycnocline, a water layer where water density varies rapidly with depth, caused by changes in temperature and salinity. This pycnocline acts as a membrane separating the upper mixed water mass layer, characteristic of Chetumal Bay, from the calm and enigmatic waters of Taam Ja’.

When we put up our drone, directly above Taam Ja’s waters, all you could see was rippling wind on its surface with no indication of any such geological marvel. Once we descended past the five metre mark, the visibility opened up and we could see the nearly vertical drop down to depths that are still being discerned even as we speak. The water pressure-measuring instrument used to uncover the depth of Taam Ja’ never actually reached the 500 metre mark on its examination of the hole due to suspected complications with the device. There will be further studies conducted to confirm its actual depth in the coming months, as right now, we do not know how deep this thing goes!

But perhaps the most jarring fact about this hole and those who discovered it is the fact that Jesús and his father knew about its existence 20 years ago. And Jesús clued in Juan Carlos back in 2021, when the team thought it was only sitting at 275 meters. So, it’s safe to say this has been Chetumal’s best kept secret for a long time. As fly fishermen, Jesús and his father weren’t catching fish in the hole when they found it. It wasn’t relevant to the work that they do and it was rendered devoid of life. It wasn’t until Jesús became part of the scientific community that he realised this could be something much bigger, much more important and something much deeper, literally. “This is why local knowledge and science must go hand-in-hand,” Juan said. “Because of Jesús, that’s why you are here meeting us right now!”

The meticulous effort to gather measurements, often extending until sunset, is met with ever-changing conditions and unexpected achievements for the ECOSUR Research Center team. Beyond the historical and cultural significance of the Mayans and cenotes, the exploration of Taam Ja’ in the region opens new perspectives for understanding the Yucatan Peninsula. This journey is not just about scientific exploration but also about weaving a compelling narrative that places us in the history of this remarkable place – a quest to unravel earth’s deepest mysteries and contribute to a greater understanding of the place we call home.

Diving into the blue hole felt like encountering a living entity – it moved and interacted with us in ways that intrigue, mystify and certainly intimidate. For us, there was a constant undercurrent of uncertainty and awe, as we navigated the unknown depths of this unimaginably vast formation. Despite apprehension about the unpredictable nature of this uncharted territory, each of our dives brought a sense of discovery and satisfaction – one we were beyond thankful to be a part of. Maria was the first woman in the world to do scuba gear and dive Taam Ja’, with Marla and I being her subsequent followers. She recounted what it was like diving the site for the first time, and why this has contributed so much to her life’s work.

But she wasn’t alone in saying “her life’s work.” Everyone on the team shared that sentiment as well: that this was a defining moment in their careers and personal lives. Maria, Oscar and Juan Carlos arrived in Chetumal at different times and for different reasons, but their paths converged with the rest of the team at this crucial moment in history. Their collective expertise and experiences in the area merged seamlessly when Jesús proposed the idea of conducting research, to which everyone enthusiastically agreed to by sheer coincidence. And together, they had the once-in-a-lifetime opportunity to realise they were on to a discovery much bigger than just a blue hole.

The culmination of their efforts led to the publication of findings from the ECOSUR records, revealing not just Taam Ja’ but other similarly remarkable structures in the area. This discovery felt like a beckoning call to explore further – an invitation that had been waiting patiently. With all the necessary team members and areas of expertise now united as one, the team conveyed a deep sense of pride. Despite any limitations that stand in their way, their shared passion drives them forward in tackling this pioneering and challenging endeavor that has only just begun.

To read more about what it was like to scuba dive the Taam Ja’ blue hole, visit our story with Scuba Schools International, and for the scientific deep dive, review Juan Carlos’ paper in Frontiers. Thank you to the full team for inviting us to participate in your groundbreaking discovery: Jesús Artemio Poot-Villa, Dr. Juan Carlos Alcérreca-Huerta, Dra. Laura Carrillo, Dra. Teresa Álvarez -Legorreta, Dr. Óscar F. Reyes-Mendoza, Dr. Joan A. Sánchez-Sánchez, MSc Laura María Flórez-Franco and MSc Johnny Valdés.