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The Taam Ja’ Blue Hole (Agujero azul Taam Ja) in Chetumal Bay, situated at the border of the Mexican state of Quintana Roo and Belize, to the south, has been determined to be much deeper than originally thought. So deep, in fact, that it is now considered to be the world’s deepest blue hole, taking the mantle from the ‘Dragon Hole’ – also known as the Yongle Blue Hole – located near the Paracel Islands in the South China Sea.
The Taam Ja’ Blue Hole, first properly documented in 2023 was estimated to have a maximum depth of 274.4m below sea level. By way of comparison, the famous Blue Hole of Belize, which lies approximately 150km south-east of Chetumal Bay, is just 124m deep
Measurement of the Taam Ja’ Blue Hole’s depth was performed using echo-sounding – or sonar – in which acoustic pulses are transmitted into the depths and the interval between the pulse and its echo measured to determine the distance to the surface.
Echo sounding, however, can be limited by changes in the density of water which can be caused by sudden changes in water temperature (thermoclines) or salinity (haloclines), both of which will be very familiar to divers who have spent time in Mexico’s cenotes.
It appears this is the case with the Taam Ja’ Blue Hole, as a physical CTD (conductivity, temperature and depth) device lowered by cable from a support vessel reached depths of 416m and 423.6m on the two occasions it was deployed, without encountering the bottom. That’s at least 119m deeper than the 301m Dragon Hole – or more than three Belize Blue Holes stacked on top of each other.
The team noted that the CTD measuring device was not able to reach the full extent of its 500m-long tether. This appeared to be because the device descended at an angle of approximately 30 degrees from the vertical, although the team was unable to ascertain if this was due to the shape of the sinkhole, or strong underwater currents.
The scientists also report encountering a pycnocline – a boundary separating water layers of different densities – at around 250m below sea level. The presence of the pycnocline at this depth, coupled with a ‘non-linear’ shape of the sinkhole, might therefore explain why the previous echo-sounding measurements were unable to penetrate beyond this level.
Although the Taam Ja’ Blue Hole is now confirmed as the deepest sinkhole on record, it is still part of the same karst structure – in which water-soluble bedrock such as limestone and gypsum is dissolved to form underground water channels – as the famous cenotes of the Yucatán peninsula.
Analysis of salinity levels in the depths of Taam Ja’ suggests there is a similar network of channels deep underground which connects it to the Caribbean Sea, and possibly other blue holes and cenotes in the surrounding area.
The complete paper, ‘Recent records of thermohaline profiles and water depth in the Taam ja’ Blue Hole (Chetumal Bay, Mexico)’ by Juan Carlos Alcérreca-Huerta et al, is published in Frontiers in Marine Science
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