The Blue Holes of the Bahamas—An Incredible Underworld

by Larry Smith

Looking down, the opening into the cavern beneath could be distinctly seen and it was evident, as the tide was flowing, that this ocean-hole communicated with other caverns at a distance, possibly on the island of Andros, and that the water was being sucked down through the opening to find its way into unknown parts.

There are deep, well-like depressions filled with salt water and connected with the ocean by subterranean passages. They ebb and flow with the tide, support marine life, and in all essential features resemble the submarine ocean-holes, except that they occur on land, usually removed some distance from the sea.

-- the Bahama Islands, by Drs George Shattuck and Benjamin Miller, 1905

The Bahamas are like no other group of islands in the world, scientists say. They were formed about 150 million years ago - as the Atlantic Ocean began to fill the space where Africa and North America were once joined. The islands that exist today are little more than the tips of fossilised sand dunes.

Deep drilling has established that virtually all of the rocks that make up the Bahamas platform - to a depth of at least 19,000 feet - were formed in shallow water as layers of sediment. As these layers gradually subsided under the weight of new deposits, they were converted into limestone. Winds blew the top layers into vast sand dunes, and by the end of the last glacial period - about 12,000 years ago - the geography of the Bahamas was more or less complete.

Over the millennia, sea levels have risen and fallen as the ice sheets expanded and contracted. According to the geography textbook, Bahamian Landscapes, by Neil Sealey, the evidence for this includes fossilised reefs found on dry land with corals that normally live at depths of 20 feet, while off the coast of Bimini peat from a drowned marsh has been dredged from 10 feet of sea water and dated to about 4300 years ago.

When sea levels were lower, rainwater eroded the limestone rocks to form solution holes that gradually expanded into huge underground systems. These caves were described as early as 1725 by the great English naturalist Mark Catesby, and the marine caves known as blue holes were first recorded on sea charts in 1843. But it is only in very recent times that explorers have been able to visit this mysterious underworld.

Experts say the entire Bahamas platform is riddled with cracks and fissures like the holes in a piece of Swiss cheese, and everything is tidally connected. In 1947, for example, oil prospectors drilling off Andros encountered caverns at a depth of more than 10,000 feet and had to abandon their test, along with thousands of feet of drill pipe which fell into the void.

Today, scientists are making unprecedented discoveries in Bahamian blue holes, although only about 20 per cent have been explored over the past 50 years. The original Lucayan inhabitants of our islands used them as sacred burial sites - the remains of 16 Amerindians were found in a blue hole on Andros, for example - but modern Bahamians prefer to use them as dumps. Divers have found everything from cars and appliances to household garbage and used diapers clogging many inland blue holes.

The most significant blue hole site in the Bahamas these days is Sawmill Sink in South Abaco, where scientists have opened an extraordinary window into the past. Their finds have included the earliest Lucayan bones (dated to about a thousand years ago) as well as highly preserved animal and plant remains dating back 12,000 years to the end of the last glaciation.

In many cases, leaves that settled to the floor of the cave are still green, while seeds and insect wings are intact. The most compelling finds have been the skeletons of giant tortoises and the fearsome land crocodiles that once hunted them. Both animals were extirpated after the arrival of humans. The tortoises were similar to those remaining in the Galapagos Islands while the crocodiles are closely related to a Cuban species that barely survives today.

This long-dead prehistoric world was described in detail at two recent events - the Abaco Science Alliance conference on January 7 organised by Abaco Friends of the Environment, and a special public meeting last week sponsored by the Bahamas National Trust and the Antiquities, Monuments & Museums Corporation, which has overall responsibility for the Sawmill Sink research.

"More than any other single site, Sawmill Sink lets us learn how the plant and animal life of the Bahamas has changed through time," Florida Museum of Natural History curator Dr David Steadman told the Abaco science conference. "By going back in time we can see how impoverished island life is today, and this can help us set more ambitious goals for restoration that are different from the way things are today. This has revolutionised our understanding of what these islands were like."

Scientists are currently studying the best-preserved giant tortoises in the region, found with every individual bone intact; the remains of some 54 crocodiles (as well as crocodile tooth marks on a tortoise shell); as many as 40 bird species, many of which are extinct on Abaco today; and a 20,000-year-old bat skeleton encrusted in minerals.

The unusual state of preservation is the result of the complete absence of oxygen in the cavern's undisturbed salt-water depths. But these conditions do not always apply when divers visit a Bahamian blue hole. In fact, BEC recently bulldozed several unexplored blue holes during road-building for the Wilson City power plant now under construction south of Marsh Harbour.

"Many inland blue holes have already been polluted and are full of trash," AMMC project director Nancy Albury said at the BNT meeting last Wednesday. "This destroys both the water chemistry and the unusual biology of these sites, so we are looking for these caves everywhere in the islands to see what can be done to protect them."

The BNT meeting discussed a proposal now being drafted to set aside a nine-mile area around Sawmill Sink (west of the Abaco highway near Crossing Rocks) as a special conservation area. Town meetings are still being held and precise boundaries have yet to be drawn, but the proposal is expected to go to the prime minister's office by mid-year. The area is on Crown land and incorporates four inland blue holes, which experts believe are interconnected.

Explorers have used terms like "elemental beauty", "magically diverse" and "enchanted voids" to describe the ethereal world of these underwater caverns. BNT members were treated to a spectacular video of a cave diver gliding effortlessly through vast crystal formations in perfectly clear water. Footage like this will be aired in a National Geographic/Nova documentary on PBS this February and photo spreads will appear in National Geographic Magazine's August edition.

National Geographic is a major sponsor of a scientific expedition that has made a series of discoveries at Sawmill Sink and other blue holes in the country. It is led by marine biologist and cave diver Dr Kenny Broad of the University of Miami. The expedition comes under the auspices of the AMMC, a public corporation that is responsible for archaeological research and curation in the Bahamas.

Besides Broad and Steadman, the expedition includes Jennifer Lynn Macalady, an astrobiologist from Penn State University who studies the origin of life; and Dr Tom Iliffe, a marine biologist from Texas A & M in Galveston whose work has led to the discovery of more than 250 new species in submerged caves around the world; and Nancy Albury of the AMMC.

These scientists have been accompanied by a top-drawer film crew led by Wes Skiles, while the technical side is led by veteran cave diver Brian Kakuk, who operates a Bahamian-owned adventure diving and training facility in Abaco. Last summer the team criss-crossed the Bahamas exploring submerged caverns, conducting original research and producing spectacular videos and stills for print, broadcast, online and educational applications.

The incredible fact is that the blue holes under our islands are probably the last place on Earth that humans can physically go to explore. "They are truly a final frontier," said Brian Kakuk, who was at the BNT meeting last week, "and our team is thoroughly documenting this frontier for the first time."

The Lucayans regarded blue holes as windows into the world of their ancestors. And according to their mythology, the sun, the moon and the Taino race itself came from these caves, the oldest (so far) of which has been dated by the expedition's scientists to 350,000 years ago by analysis of a mineral formation known as a speleothem.

Today, we are fortunate to have stumbled upon the scientific treasures contained in these blue holes before they are lost forever due to careless disregard. And we should remember that anything we put into these holes - given our Swiss cheese underpinning - will come back to haunt us by damaging our critical fresh water resources.

•In the wake of the humanitarian crisis in Haiti, Tough Call urges readers to support the petition calling on finance ministers and development agencies to cancel Haiti's existing $890 million debt and ensure that new aid is provided in the form of grants. This is an initiative of an advocacy group called One International co-founded by the Irish musician, Bono, to fight extreme poverty and preventable disease around the world. The French squeezed blood out of a stone by demanding reparations (equal to $21 billion today) after the world's first successful slave revolt in 1804. It's time to pay that back.

Comments

[Rick Lowe]

Two thumbs up!
The Rotary Club of East Nassau, through the generosity of the Nassau community, cleaned up the blue hole at RM Bailey park at one point.
Another group put an enclosure around it, but things have returned to normal at the site...dumping etc.
It's good to see renewed interest in preserving these beautiful sites.
Check this blue dive in Abaco out:
http://bit.ly/8GWVkn
It's an incredible world down there.

[Brian Kakuk]

Thanks for the excellent article Larry. We hope that everyone will join us in our efforts to conserve these amazing sites which are truly one of the Bahamas most impressive natural wonders.

Brian Kakuk
Bahamas Caves Research Foundation
www.bahamascaves.com