Bahamian Caves

They are beautiful, otherworldly, full of secrets, and can kill you. It takes bravery and special training to venture into the hydrogen sulfide atmosphere of the Bahama caves known as inland blue holes. Those who dare are looking for the chemistry of how our earth supports evolving life.

Offshore flooded caves, so-called ocean blue holes, are extensions of the sea, subject to the same heavy tides and host to many of the same species found in the surrounding waters. Inland blue holes, however, are unlike any other environment on Earth, thanks largely to their geology and water chemistry. In these flooded caves, such as Stargate on Andros Island, the reduced tidal flow results in a sharp stratification of water chemistry. A thin lens of fresh water—supplied by rainfall—lies atop a denser layer of salt water. The freshwater lens acts as a lid, isolating the salt water from atmospheric oxygen and inhibiting bacteria from causing organic matter to decay. Bacteria in the zone just below the fresh water survive by exploiting sulfate (one of the salts in the water), generating hydrogen sulfide as a by-product. Known on land as swamp or sewer gas, hydrogen sulfide in higher doses can cause delirium and death.

These strange but natural environments are threatened by both rising sea levels and people who use them for garbage dumps.

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Also:

Could "blue holes" offer clues about the biology of extraterrestrials?

In the Bahamas' submerged inland caverns, or "blue holes," a thin layer of fresh water separates oxygen from salt water. This creates a submerged, oxygen-free environment that could resemble underground water pockets on Mars or the seas of Europa.

In the blue holes of the Bahamas, the anoxic salt waters supports ecosystems that are completely unique to individual caverns. This diversity and ability to thrive in aquatic, oxygen-free environments could offer insights into both Earth's early conditions and the anatomy of extraterrestrial life that could exist within our solar system. Says astrobiologist Jenn Macalady of Penn State's Department of Geosciences:

"The universe is made of the same elements and habitable planets are likely to share many of the same characteristics, like a temperature range conducive to life and the presence of water [...] We analyzed the DNA of microbes from five inland blue holes and didn't find any shared species [...] Some of these organisms use tricks we used to think were chemically impossible [...] If we can understand precisely how these microbes are making a living, we know what to look for on oxygen-free worlds."

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