Among the shallow waters of the Lighthouse Reef Atoll in the Belize Barrier Reef System lies an almost perfect circle of deep water known as the Great Blue Hole.
The Great Blue Hole was formed approximately 150,000 years ago and is believed to be the largest blue hole in the world. The hole can reach depths of 407 feet and a diameter of 1,000 feet! Not only is this hole a popular diving spot but it is also an archive of our world’s climate history.
The Great Blue Hole was originally a limestone cave that rose above the low sea level prior to the last glacial ice age.
As the glacial period ended, warmer temperatures began melting the ice glaciers resulting in a rise in sea levels. With the rise of sea levels the once limestone cave became submerged in water. The water pressure became too extreme and lead to the collapse of the roof and development of this vertical underwater cave now known as the Great Blue Hole.
The Great Blue Hole was exposed to divers in 1971 by Jacques Cousteau. In 1972 Cousteau ventured into the hole with his one man submarine to examine the contents of the hole.
There, he studied the stalactites or dripstones that were formed during last glacial ice age and still present within the hole today. In 1997 Robert F. Dill and fellow divers collected samples of these stalactites. The samples were used to perform isotopic dating and study previous sea levels.
Results have shown fluctuations over time in pollen, mercury, and arsenic levels. The expedition also revealed that oxygen is nonexistent at the bottom of the hole and the levels of hydrogen sulfide deters bottom dwelling organisms from inhabiting the bottom sediment.
Stalactites within the Great Blue Hole are pieces of history that can be used in further research to provide documentation of the change in climate, mercury, and arsenic levels throughout Earth’s history.
Great Blue Hole, greatbluehole.net/.
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“Great Blue Hole, Belize : Image of the Day.” NASA, NASA, earthobservatory.nasa.gov/IOTD/view.php?id=37741&src=ve.