Mysterious deep ‘blue hole’ off Florida’s Gulf coast sparks search for signs of life

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A diver’s view looking up to the opening of Amberjack Hole. (AJ GONZALEZ / MOTE MARINE LABORATORY / NOAA)

Off the coast of Florida, deep at the bottom of the ocean, are massive, bright blue holes that appear to glow from within. What the unexplored holes contain has remained largely a mystery — but now, scientists want to change that.

Researchers are flocking to a 425-foot-deep “blue hole” off Florida’s Gulf Coast next month in search of signs of life, among other things. The hole has been dubbed “Green Banana.”

Green Banana is located about 155 feet below the water’s surface, according to the National Oceanic and Atmospheric Administration (NOAA). It was first discovered not by researchers or scientists, but by fishermen and recreational divers, and is similar to sinkholes found on land.

NOAA said that there are many underwater sinkholes, springs and caverns scattered across Florida’s Gulf continental shelf — but they have no idea how many exist or where to find them. While they vary in size, shape and depth, most are believed to host a large abundance of diverse plants and animals.

In May and September 2019, a team of scientists from Mote Marine Laboratory, Florida Atlantic University/Harbor Branch, Georgia Institute of Technology and the U.S. Geological Society, with support from the NOAA Office of Ocean Exploration and Research, explored a 350-foot-deep blue hole called “Amberjack Hole,” located about 30 miles off the coast of Sarasota. In August 2020 and May 2021, the same team plans to explore “Green Banana.”

Last year’s missions marked the most in-depth blue hole investigations ever conducted. After deploying divers and more than 600 pounds of equipment into Amberjack Hole, the team found carbon, nutrients and microscopic life lurking inside.

The team even discovered two dead, but still intact, small tooth sawfish — an endangered species — at the bottom of the hole. Researchers were able to recover the remains of one of the 12-foot-long creatures for examination.

While much of the seafloor is a barren wasteland, blue holes offer an “oasis” of diverse marine life, including corals, sponges, mollusks, sea turtles, sharks and more, NOAA said. But little is known about blue holes in general, due to their inaccessibility — many are located hundreds of feet underwater, with relatively small openings.

The next mission will present even more challenges than the first. Not only is “Green Banana” deeper than Amberjack, but, “the configuration of the hole is somewhat hourglass-shaped, creating new challenges for the lander deployment and water sampling,” NOAA said.

In addition to searching for unique or new species during the mission, scientists are looking to explore the holes’ role in the global carbon cycle, a possible connection between the sinkholes and Florida’s groundwater, nutrient secretion from the hole that could be affecting the surrounding area and whether or not to make the holes protected areas.

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