There's something even bigger hiding behind the Great Barrier Reef

The reef was mapped using laser data from the Australian Royal Navy. Picture: Australian Hydrographic Service

There is another, larger structure hiding behind the Great Barrier Reef, which was just discovered by Australian scientists.

A new study from James Cook University, the University of Sydney, and Queensland University of Technology revealed massive fields of unusual doughnut-shaped mounds, each up to 300 metres across and 10 metres deep at the centre.

The area was investigated in the 1980s and was predicted to be about 800 square metres. In the new study, the researchers mapped out the reef with an aircraft equipped with LiDar – a detection system that uses light from a laser — to measure the distance between the sensor and the target object.

They created high-resolutions 3D maps of the ocean floor, which showed that the reef is actually over 2,300 square metres — nearly three times the size that it was previously thought to be.

“We’ve known about these geological structures in the northern Great Barrier Reef since the 1970s and 80s, but never before has the true nature of their shape, size and vast scale been revealed,” JCU’s Robin Beaman said.

The vast mounds are made of geological formations created by green algae called Halimeda bioherms

The structures were thought to be much, much smaller. Picture: Australian Hydrographic Service

When these algae die, they form small limestone flakes that build up into large reef-like mounds. Bioherms can also be built with a mixture of marine invertebrates such as corals, mollusks, and gastropods.

The newly discovered bioherm is believed to be about 8,000 years old, and it acts as a sort of geochemical archive for the researchers. It can be used to help understand how climate change and ocean acidification could affect future ecosystems.

In a statement, Beaman said: “What do the 10-20 metre thick sediments of the bioherms tell us about past climate and environmental change on the Great Barrier Reef over this 10,000-year time-scale? And, what is the finer-scale pattern of modern marine life found within and around the bioherms now that we understand their true shape?”

This kind of reef could also potentially provide refuge for sensitive species as oceans get warmer because it is deeper and so the water around the mounds is cooler.

The next steps for investigating the reef include more geophysical surveys and using autonomous underwater vehicles to reveal more about the physical, chemical, and biological nature of the bioherm mounds.

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