Outline draft: The unique, underground waterworlds of Bahamiam blue holes

This discussion topic submitted by Sharon Ambro (ambrosm1@miamioh.edu) at 1:27 am on 3/30/99. Additions were last made on Wednesday, May 7, 2014.

The unique, underground waterworlds of Bahamian blue holes


I. Introduction


II. Folklore of Bahamian blue holes
A. Mer-people
1. To many Bahamian children, "blue holes," are gateways to a mysterious dimension, an underground, underwater world inhabited by mer-people (Palmer, 1986).
2. If you give the correct answer to a question posed by moonlight, you win a visit to their underwater crystal palaces, a lock of hair, and good fortune throughout your life (Palmer, 1986).
3. If you give a wrong answer, your trip will be one way, pulled down into the gaping mouth of the caves, perhaps to feed the "Lusca" (Palmer, 1986).
B. Lusca
1. Fisherman, farmers, and children of the Bahamas know this sea monster as the Lusca-a half octopus, half shark or sometimes half eel, half squid (Palmer, 1987; Palmer, 1985, p. 73).
2. Lusca inhabits the blue holes and draws fishermen and their boats down as it inhales, then exhales the indigestible flotsam (Palmer, 1987).
3. Or some say that the Lusca shoots out his tentacles and captures boats and fishermen that way (Benjamin, 1970).
C. The causes of Lusca
1. "The appetite of the legendary creature" is the result of swift tidal changes that cause whirlpools on inflow, and cold, mushrooming mounds when the currents reverse and blow out of the caves (Palmer, 1987; Palmer, 1990).
2. These whirlpools surge and boil and hold the potential to pull unwary swimmers into the depths of the blue holes (Belleville, 1994).


III. How and when blue holes were formed
· Formed by chemical actions occurring in the mixing zone
· Formed during the ice ages of the last million years or so
A. Bahama Banks
1. More than 5km thick and made of accumulated marine and wind-blown sediments (Palmer, 1986) that represent over a hundred million years of slow sediment accumulation in shallow seas (Palmer, 1985).
2. These horizontal layers of sediment form a limestone platform with a surface area greater than 100,000 square km (Palmer, 1986).
3. Several times in the banks' 150-million year history, it has been exposed and re-flooded as the levels of the oceans rose and fell in response to glacial activity (Palmer, 1986).
4. During these exposed dry spells, the surface of the banks was eroded, leading to the formation of many features typical of exposed limestone, such as caves (Palmer, 1986).
5. As the last glacial period ended, once again raising the level of the sea, the caves flooded, forming the blue holes of today (Benjamin, 1970).
6. Some of the holes are located inland, in freshwater lakes, and some are located in the offshore marine environments, creating somewhat different habitats.
B. Mixing zone
1. When sea levels were at their lowest, the entire Bahama bank was exposed to create a country notably more extensive than the scattered islands of today (Palmer, 1986).
2. During this time, underground freshwater existed in considerable quantities throughout the banks (Palmer, 1986).
3. Now, with current sea levels, only the largest islands have some underground freshwater resources, which create lens-shaped reservoirs (Palmer, 1986).
4. Freshwater sits atop a layer of denser saltwater that has saturated the rock beneath the island surface (Palmer, 1987). This fresh/saline water interface is known as the halocline.
5. Caves form along the base of these lenses, in the chemically aggressive mixing zone between fresh and saline waters (Palmer, 1986).
a. Tidal flow carries the limestone-saturated water out to sea, more freshwater flows down, and more limestone is dissolved (Palmer, 1987).
b. Bacteria, decomposing the organic debris in the freshwater lens, help this process along (Palmer, 1986).
c. The debris forms a layer floating on the denser sea water below-here is where the bacteria decompose the debris, creating a slightly acidic environment, poor in oxygen but rich in carbon dioxide (perfect for dissolving limestone) (Palmer, 1986).
d. A body-sized passage might take 10,000 years to form (Palmer, 1987).
e. As the ice ages came and went and sea levels changed, so did the position of the mixing zone, and caves formed at many different levels beneath the islands (Palmer, 1987), creating extensive horizontal systems of caves of considerable complexity (Palmer, 1986).
f. According to Palmer, the "underside of the Bahamas resemble[s] a gigantic Swiss cheese" (Palmer, 1987).
C. Speleothems
1. When the caves were above sea level (during the Pleistocene Epoch), conditions were often suitable for the formation of stalactites and stalagmites (Palmer, 1986; Belleville, 1994).
2. Speleothems are formed through mineralization and the slow dripping of water laden with calcium carbonate (Belleville, 1994).
3. Rainwater fell on the surface of the exposed Bahama Banks and dripped steadily down into the dry caves and formed galleries of stalagmites and stalactites (Palmer, 1985).
4. Within their crystal cores, speleothems contain a history of climatic change during the ice ages (Palmer, 1985).
5. Dating stalagmites gives a minimum possible age for the caves; dating their host rock gives a maximum one (Palmer, 1986).

IV. Brief history of blue hole exploration
· Story of blue hole exploration based on two islands, Andros (largest but one of the least developed of the Bahamas) and Grand Bahama (home to Freeport/Lucaya, one of the major tourist centers of the islands) (Palmer, 1990).
A. 1960's
1. Beginning in 1958, George Benjamin (died around 1994), a research chemist and amateur spelunker from Toronto, began exploring many of these phenomena for the first time (Belleville, 1994).
2. "Ever since my first encounter with these strange holes, I have felt irresistibly drawn toward their dark mouths. Everyone talked about the blue holes, but no one, apparently, had mustered either the equipment or the curiosity to explore them." (Benjamin, 1970)
3. On the island of Andros, he and a team of skilled divers charted several hundred potential blue hole sites and personally explored 54 holes around the island (Belleville, 1994).
4. Benjamin also became one of the first to explain tidal surges and vortexes in the mouth of the holes (Belleville, 1994).
B. 1980's
1. Robert Palmer, a British cave diver and Geologist at Bristol University, first heard of the Bahamian blue holes and George Benjamin at the annual British caving conference in 1976 (Palmer, 1985).
2. Palmer, who was a novice cave diver, was intrigued by the blue holes, but worked on building his cave diving skills in Britain (Palmer, 1985).
3. It wasn't until 1981 that Palmer and a small British team made their first expedition to Andros (Palmer, 1985).
4. In 1983, Palmer and another team made an expedition to Grand Bahama and another one in 1984 (Palmer, 1985).
5. During this time, British and American cave divers made spectacular discoveries beneath other islands, showing that blue holes are widespread throughout the Bahamas and housed unique ecosystems (Palmer, 1987).
6. Beneath the interior of Grand Bahamas lie the Lucayan Caverns, possibly one of the world's most extensive underwater cave systems with over 10km of explored passages (Palmer, 1990).
a. It holds the distinction of being the world's only underwater cave National Park (presented to the Bahamas National Trust by Sir Jack Hayward in 1982) (Palmer, 1990).


V. Flora and fauna of the Bahamian blue holes
A. Remipedia (found in inland caves)
1. An entirely new genus, order, and class of life (Palmer, 1990).
2. Tiny centipede-like crustacean with a graceful swimming motion discovered in the Lucayan Caverns by biologist Jill Yager in 1979 (Palmer, 1990; Palmer, 1986).
3. Named Remipedia meaning "oar-footed" (Palmer, 1990).
4. Its nearest known relatives became extinct over 150-million years ago when America was still linked to Europe and Africa, and the Atlantic had barely started to form (Palmer, 1990).
B. Lucifuga (Lucifuga speleotes) (found in marine caves)
1. A brotulid, one of a group of stumpy, eel-like fish whose marine relatives inhabit the inside of reefs and crevices in undersea cliffs (Palmer, 1986).
2. The only truly adapted cave fish, which generally inhabits the deeper saline region below the mixing zone (Palmer, 1987).
3. Their eyes have atrophied over the millennia to black spots beneath its pigmentless, pink skin (Palmer, 1986).
C. Inland caves (Lucayan Caverns and eastern Grand Bahama's Zodiac Caverns)
1. Inland caves are "anchialine," meaning they contain saline or brackish water and are subject to some tidal influence, but no direct connection with the sea (Palmer, 1986).
2. They are free from the strong tidal currents and animals of marine blue holes, making them extremely stable environments (Palmer, 1986).
3. The temperature fluctuates by less than one or two degrees Celsius over the year, and the current through the caves is negligible (Palmer, 1986).
4. Decaying organic debris from the forests above floats into these inland holes, and are decomposed by bacteria, creating an organic broth (Palmer, 1986).
5. The bacteria and the remains of the organic debris form the basic diet of the simplest of the cave crustacea: ostracods, copepods, and thermosbanaceans (a little-known order of crustacean, found almost exclusively in caves) (Palmer, 1986).
6. A link or two higher on the food chain is small crustaceans and cirolanid isopods, feeding on sediments and weaker cave fauna (Palmer, 1986).
7. Next are the predators, such as Remipedes, with their sharp mandibles and many pairs of swift-swimming legs (Palmer, 1986).
8. The top of the food chain is cave-adapted fish, such as Lucifuga
D. Marine caves (Andros Island's Conch Sound Blue Hole)
1. Currents carry food, plankton and organic debris, into the caves (Palmer, 1990).
2. These currents bring in food twice daily and encourage rich coral growth around the entrances, and nourish a marine community which stretches inside the caves (Palmer, 1990).
3. Corals, sponges, ascidians, anemones, hydroids, and bryozoans-all sessile organisms-grow in a colorful carpet of life on the walls, roof, and floor of the passages for long distances into the lightless tunnels (Palmer, 1990; Palmer, 1987).
4. They compete for space and access to the nourishing food of current flows (Palmer, 1987).
5. Sponges and hydroids stretch up to three times their normal lengths, streaming two to three feet into the nourishing flow (Palmer, 1987).
6. Hunters, including arrow crabs and shrimp, clean the cave walls of organic debris (Palmer, 1987).
7. The marine cave mouths are home for much of the wildlife that is found on the outer reef, but in comparatively shallow waters (Palmer, 1990).
8. Blue holes provide shelter for a host of reef fish, such as nurse and lemon sharks, which have been found sleeping inside blue holes (Palmer, 1990).
9. Fish are often found swimming upside down because they orient themselves to the nearest solid surface (Palmer, 1987), which is often the roof of the cave if the floor drops to several hundred meters below.


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