Blue Hole In South China Sea Declared World's Deepest Underwater Sinkhole


Robin Andrews

Science & Policy Writer

You can fit entire skyscrapers inside this beast. Luo Yunfei/CNSPHOTO/VCG/Getty Images

How low can you go? Blue holes, large marine sinkholes that are open to the surface, range in depth from tens to hundreds of meters deep, but it looks like one in China – the so-called Dragon Hole – may take the top (or should that be the bottom?) spot.

Although it’s been known about before, a brand new marine survey has revealed that it’s far deeper than previously thought. At a staggering depth of 300.89 meters (987 feet), it could fit more than three Statue of Liberties inside it, or one single London Shard skyscraper. The previous record was Dean’s Blue Hole in the Bahamas, which has a depth of 202 meters (663 feet).


The local government has vowed to conserve the blue hole for future generations. “We will strive to protect the natural legacy left by the Earth,” Xu Zhifei, vice mayor of Sansha City, told Xinhua.

Dragon Hole is located within a major coral reef named Yongle within the Xisha Islands. Locals have long called it the “eye” of the South China Sea, and according to a 16th century Chinese legend, this sinkhole is where an ancient hero’s golden staff, a weapon called Ruyi Jingu Bang, comes from. It was stolen by the Monkey King from the underwater kingdom of Ao Guang, the Dragon King of the East Sea.

The Dragon Hole. euronews via YouTube

Sadly, as with other blue holes around the world, this one wasn’t carved out by an architecturally savvy dragon. Many are thought to have been dissolved by acidic rainwater, which fell on carbonate beds when they were exposed to the surface during the last glacial maximum.


Over time, these beds collapsed in on themselves, forming the original sinkholes. When the glaciers melted and sea levels rose, they flooded these holes with seawater. It’s not completely clear why blue holes form precisely where they do, but it’s not surprising that they tend to form near or in coral reefs, which are massive repositories of carbonate rocks.

Their terrestrial equivalents are known as cenotes, which contain fresh groundwater as opposed to briny seawater. In both cases, complex networks of horizontal tunnels can extend out from the primary vertical shaft, forming labyrinthine wonderlands ripe for exploration.


The Great Blue Hole of Belize. Wollertz/Shutterstock

This particular underwater sinkhole was explored by a submarine robot named VideoRay Pro 4, which used a cutting-edge depth sensor to verify the depth of the undersea portal. It was controlled by scientists working with the Sansha Ship Course Research Institute for Coral Protection, which is based in China.


In its shallower segment, Dragon Hole is home to at least 20 different species of marine life. However, the mechanical explorer found that below 100 meters (328 feet) depth, the hole is void of almost any oxygen, which means that the vertical tunnel is deadly to most life along two-thirds of its length.

Still, there could be microorganisms below this depth that survive without needing oxygen to convert food into energy. If they are thriving in this anoxic environment, rather than just existing, then they are known as “extremophiles,” and are likely to be either bacteria or a closely-related group of microbes called archaea.

So far, no extremophiles – or magical staffs – have been found at the bottom of Dragon Hole, but life has been found in far stranger places within the ocean, from hydrothermal vents and exposed mantle rocks to super salty deadpools.

French freediver Guillaume Néry jumps into Dean’s Blue Hole, the previous record holder. Guillaume Néry via YouTube


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