Scientists will soon be exploring the Green Banana. Sinking more than 130 meters below the ocean’s surface, it is one of the deepest blue holes on Earth.

Amazing structures

Scattered across the ocean, “blue holes” do not swallow up any form of matter that has come to venture too close, like their cousins the black holes with which they have nothing to do. But they are none the less intriguing and just as interesting to study.

These sea chasms dot the waters of the China Sea, the Caribbean and the Atlantic Ocean. Some are very well known, like that of the Great Barrier Reef, or that of Belize. Formed during past ice ages when the sea level was several tens of meters lower, they then gradually filled with water, eventually forming the amazing structures we see today.

These special environments are home to many life forms, including “corals, sponges, molluscs, sea turtles, sharks and more,” says the National Oceanic and Atmospheric Administration (NOAA). The chemistry of the seawater in these holes is also unique and appears to interact with the water table and possibly aquifers. This link contributes to our knowledge of the carbon cycle between groundwater and the surface ”.

However, our knowledge of “blue holes” does not extend much further. And for good reason, their entry points are often too narrow – before widening – which makes it impossible for an automated submersible to enter. In addition, most are also invisible from the surface. Nevertheless, some remain accessible.

Diving off Florida

One of them, the Green Banana, is due to be explored soon as part of a three-year expedition.

This sea sinkhole, which opens about 43 meters below the surface, then sinks more than 130 meters, is one of the deepest on Earth. You will find it approximately 80 km offshore from St. Petersburg, a town on the Gulf Coast of Florida, United States.

The dive is due to take place next month. During their expedition, biologists from Florida Atlantic University, the Georgia Institute of Technology, the Mote Marine Laboratory and the US Geological Society will take several samples in order to identify the different forms of life evolving in this environment.

It will also be a question of understanding whether this ecosystem connects to other wells of the same kind, or if it integrates the groundwater system of Florida.

During this expedition, divers will be accompanied by a robot specially designed to withstand the intense pressures felt at such depths. This machine, which takes the form of a metal mesh, will be equipped with several instruments intended for the observation and analysis of marine biodiversity.

Note that in May and September 2019, a team of divers had already explored the Amberjack hole located off the city of Sarasota, still in Florida.

At the bottom of this well, the divers found the bodies of two sawfishes (the largest was 3.7 meters long), proof that organic remains sometimes fall to the bottom of these structures. On the other hand, they also discovered that many nutrients rose to the surface to nourish a wide variety of organisms.

In addition, these same researchers had also recorded high levels of radon and radium — markers indicating the presence of groundwater.