Bahamas' 'blue holes' hold wonders and weird science
(javascript:;) (javascript:;) Scientist Kenny Broad
fights to the surface in a sinkhole on Abaco. The caves can contain dangerous
whirlpools.
By _Dan Vergano_ (http://content.usatoday.com/topics/reporter/Dan+Vergano)
, USA TODAY
What lies below the Bahamas in the Caribbean? A veiled world of fossils,
blind creatures and scientific riddles.
In next month's issue of National Geographic magazine, an international
team of cave divers led by anthropologist Kenny Broad of the _University of
Miami_
(http://content.usatoday.com/topics/topic/Organizations/Schools/University+of+Miami)
reveals the mysteries hidden from vacationers' view.
The two-month expedition, paid for by the National Geographic Foundation,
was merely a small slice of time in a years-long effort to uncover the
secrets of this realm, which has been plumbed by researchers for at least
three
decades.
Only a few miles inland from the Bahamas' sparkling coral reefs, the
islands' limestone boasts dozens of submerged caves, "blue holes," some of
them
hidden in what look like island swimming holes linked to the ocean.
But swimming holes they are not. The inland caves on five islands sport
freshwater caps covering heavier saltwater layers, sometimes filled with
clouds of poisonous hydrogen sulfide released by salt-eating microbes, acting
to preserve whatever falls within. Others contain whirlpools powered by the
tides.
"Cave diving is really about knowing your limits," Broad says. "But it
provides one of the most amazing experiences in life, and the scientific
opportunities are tremendous."
Says cave diver and geologist Patricia Beddows of _Northwestern University_
(http://content.usatoday.com/topics/topic/Organizations/Schools/Northwestern
+University) in Evanston, Ill., who was not part of the expedition: "Each
one of these cave diving expeditions, without fail, provides an enormous
amount of information. Cave diving is an extraordinarily powerful tool to
allow us to get into the heart of karst (cave) systems worldwide."
Mysteries within: From a cove on Long Island, the cave known as Dean?s
Blue Hole plunges more than 600 feet into darkness.
Photos by Wes C. Skiles, National Geographic
In submerged caves such as Stargate on Andros island in the Bahamas, the
expedition team reports:
• Specialized "chemosynthetic" bacteria that live without oxygen and feast
on chemical reactions possible only in the caves.
• Stalactite curtains, or "speleothems," that contain a record of past sea
level and climate conditions locked in their structures.
• Fossils of Lucayan tribe members who lived on the islands until the
1500s.
"We've brought scientists from many disciplines together so our results
inform each other's work," Broad says. "The initial exploration is just a
proof of concept. We still have lots of work ahead."
Coastal regions of the Caribbean, such as Florida, Cuba and the Yucatán,
and other regions worldwide contain limestone permeated with caves, Beddows
notes, leading to such blue holes. In addition to their scientific value,
they often serve as freshwater resources for increasing numbers of people in
those regions, which makes investigation of them essential for public
health.
Sea level about 20,000 years ago, during the height of an Ice Age, was
hundreds of feet lower in the Bahamas. The transition has left its mark on the
speleothems and geology of the caves, Broad says, making each one a
laboratory for measuring the effects of past changes in climate.
Each cave diving expedition requires years of preparation, and the results
will affect scientific conclusions for years afterward.
"It's possible to make a direct comparison between what we do and
exploring outer space," Beddows says. Years of training for short
investigations in
a hostile environment are the hallmarks of cave diving science, which she
describes as a "select" discipline, slowly growing in numbers but now
increasingly established.
Alongside the danger, the blue holes of the Bahamas have offered little
allure for divers who in some cases could instead walk to beaches with access
to some of the world's most beautiful coral reefs.
"Why dive into a muddy-looking hole when you can head for the beach?"
Broad says. "But (the holes) are really fascinating places once you start
looking."
_http://www.usatoday.com/tech/science/discoveries/2010-07-21-bahamas21_ST_N.
htm_
(http://www.usatoday.com/tech/science/discoveries/2010-07-21-bahamas21_ST_N.htm)
