“I could give you a bunch of rational, scientific, and conservation reasons, but it’s the feeling of being somewhere that no one has been before, drifting through this most peaceful, delicate, inner space, with all my focus on the task at hand,” said Kenny Broad of why he is drawn to the extreme and often dangerous discipline of exploring underwater caves. But Broad, who holds a PhD in anthropology from Columbia University and is a professor at the University of Miami, also sees the scientific knowledge gained by probing these rarely charted territories. Broad was in the Bahamas studying “blue holes” when I caught up with him over email.
When did you become interested in exploring underwater caves? I grew up in Florida, which is made up of limestone — the best type of rock for extensive cave formation. My neighbor was a professional diver, so at about 11 years old I realized you can breathe underwater and escape the confines of gravity, and basically I became addicted early on. As I received more formal training, the mysterious aura of cave diving was always in the background, and I was introduced to some of the cave-diving pioneers when I was about 19 years old and quickly realized that there was another world right beneath my feet.
What can underwater caves tell us about the environment and/or geological history? Many of the caves, what are referred to as “blue holes” in the Bahamas, “cenotes” in Mexico, or “sinkholes” in the U.S., are really time capsules along many dimensions. The cave formations, stalagmites, and sediments in particular are recorders of environmental history such as temperature and rainfall. The speleothems form when the cave was dry during past ice ages and the sea level was much lower, so sometimes we find the caves inland and sometimes in the coastal areas. With these samples, we can do geochemical analyses to reconstruct past climate, going back hundreds of thousands of years. This allows us to better understand natural climate variability and thus make more sense of what is happening now as we put greenhouse gasses into the atmosphere.
The microbial life in some of these caves can also help us understand what some of the earliest forms of life were like going back over three billion years as some of these sinkholes are modern-day equivalents of the ancient, primordial oceans that life evolved out of. They are also earthly analogs for environments that may exist on other planets, so the astrobiologists are also studying these extremophile forms of life.
The biogeochemistry in some of these caves are salt water and anoxic (no oxygen), thus they are the ideal medium for preserving fossils. Beyond the scientific value, these caves are windows into our freshwater reservoirs — aquifers. Diving in them can shed light on what’s arguably our most critical resource, fresh water. Blue holes are one-stop shopping for geology, biology, and paleontology and for understanding the extent of and the threats to our drinking water supply.