Blue holes are more than just `blue cave entrances` into the depths of the ocean. They carry a world of secrets and fossils that is up to man to discover, writes Aisha Masoom Ali Syed

Exploring nature has been one of the greatest fantasies of mankind. Human beings have spent thousands of years searching for the hidden facts of the universe but the more they unveil, the further they seem to be from the truth.

Water covers up to 71 per cent of the earth`s surface and nurtures within is folds an enormous amount of life. The seas and oceans make up a silent world with its own unique chemistry. The `blue holes` are one of the most mysterious and eye-catching splendours of the oceans.

A  VOYAGE OF DISCOVERY

Blue holes are found in different parts of the world, but the greatest number is found near the Bahamas that consists of around seven hundred islands. The Bahamas platform is a popular scuba diving spot - rich in limestone and carbonate sand which is also a reason for the formation of a large number of blue holes in this region.

Stephanie Schwabe and James L. Carew`s publication Blue Holes An Inappropriate Moniker for Water-Filled Caves in the Bahamas reveals that Mark Catesby, a naturalist, had described the blue holes in literature as far back as 1725. However, the first visual description of these `marine-caves` was given in 1950 using scuba. According to this publication, Dr George Benjamin and his son George went scuba diving and brought images which clearly describe these holes to be more than just `blue cave entrances`.

The world`s deepest blue hole, the Dean`s Blue Hole is in Long Island, Bahamas. It sinks 202 metres down the ocean, having a roughly circular look and a diameter of about 25 to 35 metres.

THE BLUE LOOK

Blue holes were named after their striking dark blue colour, appearance and depth, in sharp contrast to the

white/aqua blue waters of the shallows, as seen from land or a helicopter. They usually appear to be perfectly circular on the surface and their deep waters are usually anoxic. The name typically does not cover the scientific significance of these holes.

However, according to an important paper on blue holes, written by Mylorie et al, titled Blue Holes, he defines them to be vertical openings in the carbonate rock deep under the sea that exhibit complex morphologies, ecologies and water chemistries.

FORMATION

Blue holes in their simplest form can be described as the caves formed due to the chemical weathering and acid rains. In which, when the ice melts resulting in the sea level raise that follows on to the submerging of the caves known as — the blue holes.

Raymond Chang, in his chemistry book, writes about the formation of sinkholes, stalagmites and stalactites, which are varieties of limestone formation. Fantastic rock formations, called stalactites, hang icicle-like from the cavern`s ceiling, and stalagmites, the columns that rise from the cavern`s floor, having principal mineral as limestone (CaCO3).

Limestone is rather insoluble in water, but dissolves readily in acidic water. Since moisture of the soil normally contains acids, along with dissolved carbon dioxide from the atmosphere, therefore, most of the groundwater dissolves limestone, and forms ions of calcium and bicarbonate. When acidic surface water seeps underground, they slowly dissolve away limestone deposits; the resulting depressions in the landscape are called `sink holes`.

This dissolution produces underground caves. When a solution containing ions of calcium and bicarbonate drips through the cracks of a cave, where the partial pressure of carbon dioxide (CO2 ) is lower, the solution becomes super saturated in CO2 which escapes from the solution, and limestone is precipitated out in the form of stalagmites and stalactites inside the caves.

Thus, when the sea level rises due to the temperature changes on earth, these caves submerge in water giving birth to the `blue holes`.

A DEEPER LOOK

Diving into the blue holes is exciting, an experience full of beauty and adventure. Nowadays, the term scuba (an acronym for `Self Contained Underwater Breathing Apparatus`) is not only used as an acronym, but it is also referred as underwater swimming. Scuba is quite different from the conventional fresh water dive, and is characterised by exploration of the caves within the water and the layers of salt.

The sea water chemistry determines the presence of marine life in water but environmental changes has led the aquatic life suffer a lot. Due to this, scientists believe that sea water chemistry will change in the coming decades, ultimately altering marine life.

The environment of blue holes is not suitable for marine life due to the anoxic waters. According to the study, The Water Beetles of the Miller, blue hole Sandusky County, Ohio, are “uninhabitable to the aquatic organisms because of the lack of oxygen, food, shelter and salty waters”.

FOSSILS TREASURES

The well-preserved fossils were found from the Sawmill Sink Blue Hole, on Great Abaco Island, Bahamas. The water chemistry of blue holes makes it a perfect ground for the conservation of fossils due to the salty, less-oxygen water which keeps bacteria away from decomposing the organic remains.

The Proceedings of the National Academy of Sciences USA (PNAS) published a detailed report on the fossil excavation. According to this report, in 2004, Brian Kakuk, a consultant for the Bahamas museum, discovered an entire skeleton of a tortoise and also found the first Sawmill Sink fossil which is a 2,500 year old giant tortoise shell in an excellent condition.

The other fossils details are

150 plus identifiable Squamate reptile bones.

• Two major plant fossils in Sawmill Sink were found which were the tropical dry evergreen forest known as “coppice” and a tropical pine-dominated woodland called “pineland” or “pineyard”.

• Crocodiles were the most abundantly found vertebrates, with specimens including skulls, lower jaws and partial to nearly complete postcranial skeletons.

• Around10 species of birds were also found.

SAVING

Nature has left beautiful signs for mankind in these blue holes and he just needs to explore and preserve them. Many organisations are working to explore and save the blue holes and the aquatic chemistry of these holes.

The responsibility of saving Mother Nature lies on individuals as well, therefore, every one of us should contribute for its betterment and discovery.

Those who are interested in knowing more about these unbelievable and fantastic creations of nature can log on to www.bahamascaves.com.