Blue holes are massive undersea sinkholes that are considered hotspots of microbial biodiversity. And while marine scientists are captivated by their potential from a research perspective, laypeople seem pretty riveted by these sinkholes too.
Mostly existing in the form of vertical caves, blue holes can sometimes comprise hundreds of meters long, horizontal cave formations that extend like ‘arms’ from vertical caves. Blue holes are believed to have been formed during the later ice ages due to the erosion of limestone terrains by rain and chemical weathering. As the sea levels rose with time, water rushed into them, and filled them up — and some of these depressions even got immersed underwater. Inside these blue holes, oxygen is scarce and sunlight is available only near the surface, and that brings us to the most interesting part about blue holes: life inside these unique marine formations has adapted to the low-oxygen environment. In fact, life forms in blue holes use sulfate, instead of oxygen, during photosynthesis.
Blue holes offer interesting evolutionary insights into what life was possibly like on Earth millions of years ago when the oceans were anoxic, or without oxygen. But they also help scientists understand what life could be like on other planets, which are considered unfit for the survival of most of Earth’s species due to the absence of oxygen and sunlight. In fact, this week, as part of an ongoing three-year research project, a multi-institutional team of scientists is gearing up to explore a blue hole called ‘Green Banana’ off the coast of Florida, which is located 425-feet-deep in the ocean floor.
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“Little is known about blue holes due to their lack of accessibility and unknown distribution and abundance. The opening of a blue hole can be several hundred feet underwater, and for many holes, the opening is too small for an automated submersible,” the National Oceanic and Atmospheric Administration (NOAA) said. This makes manual expeditions necessary. However, expeditions into blue holes can be dangerous too. Sources estimate that between 130 to 200 divers have died during a fifteen-year period from 1997 to 2012 at an Egyptian blue hole on the coast of the Red Sea.
The fact these ecosystems that exist on present-day Earth, and yet resemble life in either pre-historic times, or life on other planets, has captured our collective imagination. In addition, the fact that we know so little about them only makes them more mysterious. This is similar to our obsession with black holes, which act as reminders of the fact that there are mysteries in the universe that science has barely scratched the surface of.
