Mar 20, 2006 — By Tim Gaynor
TULUM, Mexico (Reuters) - The ancient Maya once believed that Mexico's jungle sinkholes containing crystalline waters were the gateway to the underworld and the lair of a surly rain god who had to be appeased with human sacrifices.
Now, the "cenotes," deep sinkholes in limestone that have pools at the bottom, are yielding scientific discoveries including possible life-saving cancer treatments.
Divers are dipping into the cenotes, which stud the Yucatan peninsula, to explore a vast underground river system.
Hefting air tanks, guidelines and waterproof lamps, they have so far mapped 405 miles of channels that form part of a huge subterranean river delta flowing into the Caribbean sea, and they are only just starting.
Scientists investigating the network of caverns and galleries, formed by rainwater passing through porous limestone, have found a wealth of early archeological relics and prehistoric animal bones.
They also have identified dozens of new aquatic species specially adapted to extreme environmental conditions which could have medical applications.
In the Riviera Maya, a strip of Caribbean tourist resorts including the world-famous archeological site of Tulum, there are more than 500 cenotes. Some are open to the jungle, while others have tiny eye-like holes letting in sunlight and jungle roots.
Their waters have filtered through sponge-like limestone which leaves them so transparent that divers say they feel like they are floating in space. The pools range in depth from a few feet (a meter) to an abyss where explorers have still not touched bottom at over 500 feet.
"It is proving to be a totally unique environment," said marine biologist Tom Iliffe of Texas A&M University. "We are finding things down there including forms of life that no one had ever guessed existed, and there is a lot more work to be done."
BLIND FISH AND MAMMOTHS
The Yucatan sits on a limestone plateau where rainwater percolates down to nonporous rock below ground. Over millions of years, underground river systems have formed that flow out to the sea through caves.
The region's 7,000 to 8,000 cenotes were formed when caves collapsed in on themselves. The resulting sinkholes became a vital water source and a focus for Mayan sacrifices to honor Chac, the volatile, crocodile-like rain deity.
In recent years, biologists delving into the underlying river systems, which unlike the sinkholes are jet-black because of the lack of sunlight, have identified 40 entirely new species, mostly blind shrimps and fish which have adapted to life in the system's harsh conditions, where dissolved oxygen and food are scarce.
Among the startling discoveries are microorganisms that live in the transitional zone where the fresh water rivers flow out into the Caribbean, and salt-water sponges which may contain anti-tumor compounds.
"Research is at an early stage, but it is quite possible that the bacteria and sponges may have potential biomedical applications including cures for cancer," Iliffe told Reuters in a telephone interview. "There is a great deal of scientific excitement about it."
Other finds made by divers roaming the deep, dark corridors include the bones of giant jungle sloths, rabbits and even mammoths dating back beyond the last Ice Age.
"When you come up and tell people there are elephants down there they really think you've gone crazy," said Sam Meacham, an underwater explorer and conservationist.
THREATENED BY DEVELOPMENT
In the past three decades the population of the Riviera Maya has soared 10-fold to close to 1 million people, as tourists from the United States, Europe and Mexico flock to the palm-fringed strip to soak up the sun.
Environmentalists say that the explosive development has been only patchily regulated and warn that waste produced by resort hotels and service towns in the area is already polluting the complex underground oasis.
"It's totally the Wild West, when what is needed is carefully planned, sustainable development," said Meacham, who runs the Quintana Roo Water Systems Research Center, a local non-profit group that raises consciousness about water issues in schools.
Water conservation will be a key issue when ministers, hydrologists and environmentalists from around the world meet at the World Water Forum in Mexico City from March 16-22.
Meacham says human sewage is pumped deep underground, and that at least one water system in the Yucatan has been polluted with fecal matter. The impact of 250 tonnes of trash dumped in landfills each day has yet to be evaluated.
The hundreds of tourists who dive and snorkel each day in any of a dozen cenotes and caves open to the public are also unwittingly destroying the ecosystems before they can be properly understood, Iliffe says.
"Fish are following the divers into the caves and they gobble up all the life, and they (the caves) are left biologically sterile," he said.
"When you consider that they could possibly lead to a cure for cancer, it is essential to conserve them."