Saturday, March 29, 2014

Bahamian Blue Holes

Man O War Cay

Halocline is the zone where salt water and fresh water meet.  In a vertical column of water, fresh water will sit on top of salt water because it is less dense.  If an object falls into such an aquatic vertical column, it can remain suspended in the halocline and decompose in this suspension.  It is a paleontologist’s delight.   

Yesterday, we were on the ferry from Marsh Harbor to Man O War Cay in the Abaco Island chain in northern Bahamas when we met Nancy Albury, a paleontologist whose passion is the study of Bahamian blue holes.  We were on our way to a talk she was giving entitled, New Discoveries from Blue Holes, Caves, and Beach Sands: Are clues from our past charting our future?  Craig is a patient companion when I drag him to these kinds of events but even he was excited about this one.  The attraction: the discovery of perfectly preserved Cuban Crocodile skeletons at the bottom of the Abacos blue holes.  The Cuban Crocodile (affectionately hereby known as CC) is the one that even the scientists at the Crocodile Conservation Center in St. Augustine, Florida give a wide berth to.  CC is nasty.   It doesn’t have the more common sideways, elbows-out kind of crawl that other crocs have.  Instead, it moves more upright on its legs with its feet forward making it fast and aggressive.  Our fascination with crocs and alligators was piqued when we visited the Center a couple of years ago and to have the croc raise its head again was reason enough to catch the ferry to another island to learn more from Nancy.  She generously gave us a private audience on the ferry with her stash of bat specimens, crocodile and tortoise bones, and stories of living on and exploring these islands.

The thing is, CC doesn’t live in the Bahamas anymore.  Nor do 22 bird species whose remains were part of the 43 avian species found at the bottom of the blue holes here.  A blue hole is a deep chasm in the earth or ocean where fresh water is trapped on top of salt water.  The salt-water source is from the bottom of the hole, and is typically fed from cave systems and tunnels that lead out to and in from the ocean.  Bahamian blue holes are particularly remarkable for the clues they are providing about geological, biological, and sociological history.  The Bahamas archipelago was once high and dry, and dotted with stalactite and stalagmite column filled land caves.  Water levels here are presently 425 feet higher than they were at the peak of the last ice age.  As sea levels rose, these caves were filled with layered saline and fresh water, and perfectly protected by the halocline layer of trapped hydrogen sulfide gases.  Flora and fauna that are 1500 years old are still green as they lie suspended in the halocline.  Nancy showed us the bright blue wing of an insect that was also centuries old. 

The once terrestrial (land locked) ecosystem is frozen in time and the tricky part is getting access to it.   Nancy and her colleagues are cave divers of the extreme kind who weave in and out of the kilometers long cave systems, looking for clues in skeletal remains, coral remnants, seeds, plants, and insects.  Human remains have also been discovered and are speculated to be the now extinct Lucayans, South Americans who lived here a thousand years ago.   Nancy’s work is highlighted with superb photos at  National Geographic has also profiled Nancy's discoveries.  

We have anchored at the northern end of the Bahamas in the Abacos, joining the parade of North American cruisers heading back north.  We have been captive at Marsh Harbour for a week, until the heavy surfs at the cut entrances between the islands and the Atlantic Ocean settle down.  The secure holding of our anchor enables us to leave the boat without worry and take the local ferry across the Sea of Abacos to Man O War Cay and colonial Hope Town on Elbow Cay.  After meeting Nancy, a beach is no longer just a beach.  It is another revelation of the topography and history of these islands.

Hope Town, Elbow Cay, Abacos, Bahamas

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