Scientists Dive to the Bottom of Mysterious ‘Blue Hole’ Off the Coast of Sarasota, Florida

(Courtesy of Mote Marine Laboratory)

A scientific dive team explored a little-studied underwater phenomenon known as a “blue hole,” a sort of sunken underwater oasis surrounded by barren sea floor, about 30 miles off the coast of Sarasota, Florida, in May and September 2019.

Blue holes are a lot like sink holes on land but occur on the bottom of the ocean. They can sometimes drop hundreds of feet below the surrounding ocean floor, and are also complex, unique, and fascinating hotbeds of biodiversity, unlike the above topography, with an abundance of plants and animals.

The site of this particular dive was dubbed the “Amberjack Hole,” and the team of explorers consisted of scientists from Mote Marine Laboratory, Florida Atlantic University/Harbor Branch, and Georgia Institute of Technology and the U.S. Geological Society, with support from NOAA.

(Courtesy of Mote Marine Laboratory)

(Courtesy of Mote Marine Laboratory)

They deployed both divers and a survey platform called the “benthic lander” equipped with various scientific instruments and weighing 600 pounds (approx. 272 kg) to the bottom of Amberjack Hole—whose rim is 113 feet (34 meters) deep, while the hole drops down another 237 feet (72+ meters); they documented life, carbon, nutrients, and microscopic life throughout the environment, and sediments at its bottom, and collected 17 water samples.

Blue holes can contain organisms large and small, including “corals, sponges, mollusks, sea turtles, sharks, and more,” according to NOAA. They also found two dead smalltooth sawfish (endangered) on the bottom.

Interestingly, the high inorganic carbon content found in Amberjack supports life such as microbes, which are able to cycle the carbon back into the environment in a form accessible to other organisms.

(Courtesy of Mote Marine Laboratory)

(Courtesy of Mote Marine Laboratory)

These findings also suggest that nutrients are rising up from the blue hole for the ecosystem above to make use of, contributing to a positive feedback cycle. They found the seawater chemistry in these holes appears to interact with groundwater, a finding that could contribute to the study of carbon cycling between groundwater and the surface.

These holes have largely gone unstudied by science because of their inaccessibility, and reports of their existence came mostly from fishermen and divers, NOAA says. Not only are blue holes often hundreds of feet deep, but their narrow openings also restrict certain types of submersible equipment from entering.

A diver’s view descending into Amberjack Hole. (Courtesy of Mote Marine Laboratory)

Divers explore the bottom of Amberjack Hole. (Courtesy of Curt Bowen)

The team’s “mission,” according to NOAA, is to determine the following:

Whether these submersed sinkholes are connected to Florida’s groundwater or if there is groundwater intrusion into the Gulf of Mexico

If a particular blue hole is secreting nutrients and thus affecting an area’s primary production

Whether microenvironments harbor unique or new species of microbes

If the Amberjack site should become a protected area

The team plans another dive in August 2020 and May 2021 at a different, and even deeper, site known as Green Banana, whose rim lies at a depth of 155 feet (47 meters) and bottom drops to 425 feet (130 meters). The “hourglass” configuration of the hole also presents new technical challenges for the deployment of the lander; but the divers will otherwise employ the same approach as Amberjack.

(Courtesy of Curt Bowen)

(Courtesy of Curt Bowen)

(Courtesy of Curt Bowen)

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