Huge dark blue circle in the middle of the turquoise Caribbean sea has a diameter of 300 meters and a depth of 125 meters; see shipping pictures on site
The mysteries surrounding the Belize’s Great Blue Hole it has always attracted the interest of divers and also of scientists who study the oceans. OR Big blue holeas it is known in English, it is a cave that was formed hundreds of thousands of years ago when the sea level was lower than today. As the ocean rose, it was submerged, but retained the stalactites (sedimentary rock formations that form on the ceiling of caves), later surrounded by marine animals.
It is a phenomenon not seen elsewhere in nature that has become one of the most breathtaking areas. It is located on the Lighthouse Reef Atoll, 80 kilometers off the coast of Belize. Village, which was part of the Mayan civilization, is located on the northeastern coast of Central America. It is very small, about the size of Sergipe and has 290 kilometers of coastline and borders Mexico, Guatemala and Honduras.
The Great Blue Hole may not be the only blue hole in the world, but it’s the only one that can be seen from space, according to an image captured by NASA. United States Aerospace Agency (NASA) on March 24, 2009. “The large blue hole appears in the center of the image, surrounded by a lighter-colored ring caused by uplifting corals,” NASA said at the time.
The huge dark blue circle in the middle of the turquoise Caribbean Sea has a diameter of 300 meters and a depth of 125 meters. In addition to the unusual shape and crystal clear water, the environment rich in marine life attracts tourists from all over the world.. Coral atolls often shimmer with vibrant shades of turquoise, teal, peacock blue, or aquamarine. This unusual site in Belize is designated a World Heritage Site by the United Nations Educational, Scientific and Cultural Organization (Unesco).
Discovering the blue hole of Belize
In November 2018, the Submarines Aquatica sent a submarine with three researchers on board to explore the blue hole of Belize for three weeks. “We traveled to explore and document a geological phenomenon in support of conservation science. We mapped the great blue hole using high-resolution sonar,” said Erika Bergman, oceanographer and the submarine’s chief pilot at the time.
During the mission, the team focused on specific points such as stalactite caves. According to her, the straight vertical sections of the wall are free from erosion because sea levels rose rapidly during the few decades between phases. “Preserved from the disturbance of time and isolated in darkness, the hole holds clues to a very natural part of our planet’s life cycle. It is these terraces and stalactites that we set out to map,” the oceanographer said.
The expedition also included Mark Atherton, a sonar specialist at Kongsberg Mesotech. With equipment that works by emitting sound waves and is used to locate objects on the ocean floor, it has been possible to create a 3D map.
“We deployed a dual-axis sonar to our vessel. This unit was used to scan the entire well in high resolution from the surface. We also mounted a multibeam sonar directly to the front of the submarine and used it for navigation.” Erika explained.
In this way it was possible to create a high-resolution three-dimensional sonar image of the interior of the great blue hole. “Some of the targets we were particularly interested in studying in detail were stalactite caves that were about 50 meters deep. These huge stalactites are now fully embedded,” said the submarine’s chief pilot.
“As pilots, we navigate with vision and sonar because visibility is often limited to the maximum range of our lights combined with the turbidity of the water (darkness), anywhere between zero and 24 meters depth, for example. We create mind maps of places where we have been and have used the estimate to ship,” he added.
At a depth of 88 meters, the expedition observed a layer of calcium carbonate, where a large coral reef grew in what was then the shallow waters of the Caribbean. At a depth of 124 meters, the expedition found evidence of small stalactite or stalagmite formations, which were covered with sand.
In addition to the sonar chart, an instrument was used to measure sea conductivity, temperature and depth, as well as dissolved oxygen. “The collected data shows that under the layer of hydrogen sulfide (H2S) at a depth of 91 meters, the bottom is completely anoxic – there isn’t a drop of oxygen down there.
This is also evidenced by the ‘snail graveyard’, a section of the blue hole where we observed hundreds of dead snails that likely fell into the hole and were unable to escape the steep walls or survive long without oxygen,” he said Hydrogen sulphide is a colorless and malodorous, toxic, flammable and highly corrosive gas.
“Sulphur- and sulfate-reducing bacteria living in anoxic environments like this ocean sinkhole use sulfates to oxidize organic matter. Hydrogen sulfide is a waste product of this natural biochemical process. Another possible contributor to layer thickness and the density of H2S could be the prevalence of algae sargasso. This brown seaweed contains a high concentration of sulfuric compounds and was prolific throughout the Caribbean in 2016 and 2018,” Erika said.
The oceanographer also spoke about his diving experience with Rachel Graham, founder of MarAlliance. “She told me about a shark monitoring project where they found that hammerheads regularly visit the blue hole, along with reef sharks. And they never swim into the H2S layer, they always stay just above it,” she said.
Mechanically, the team also learned how to protect the equipment used on the expedition. “We learned that up to 0.5 percent hydrogen sulfide in solution is acceptable when in contact with carbon steel surfaces. But 1.5 percent or more is detrimentally corrosive,” he said.
There is still much to unveil and reinforce about the challenges and importance of environmental conservation, but according to the oceanographer, every moment counts. “Our experiences in this place make exploration very valuable,” concluded the expert.
Source: Terra
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