Coming up next on Jonathan Bird's Blue World, Jonathan explores a deep and mysterious Blue
Hole in the Bahamas.
Hi, I'm Jonathan Bird and welcome to my world!
The Bahamas are famous in the diving world for their natural formations called Blue Holes.
A Blue Hole is typically a somewhat round hole in the ground filled with water.
They are often quite deep.
Many Bahamian islands are covered in hundreds of these Blue Holes.
Blue Holes were formed during the last ice age when sea levels were much lower than they
are today.
Rain, combining with carbon dioxide in the atmosphere creates a mild acid called Carbonic
Acid, otherwise known as acid rain.
When rainwater collects in a small depression, it slowly starts eating away the soft limestone
of which the Bahamas islands are mostly made.
Over tens of thousands of years, the hole gets bigger and deeper.
At the end of the last ice age, as the Earth warmed, the sea levels rose, and with it,
the water table.
The Blue holes filled with water.
I have come to Andros in the Bahamas to dive a little-known Blue hole called Cousteau’s
Blue Hole.
It’s called that because Jacques Cousteau himself dove here!
My adventure begins at Small Hope Bay Lodge in North Andros.
Today I won’t be using their dive boats…because we get to this dive site with a truck!
Small Hope Bay Lodge divemaster Dennis Burrows is taking me on an adventure to a remote area
of Andros.
We drive through the mangroves to the local highway.
Then it’s into the forest on a road which appears to be barely more than a trail.
A rain storm passes through, making our journey a little wet.
But it just adds to the adventure!
Small Hope Bay Lodge owner Jeff Birch has come along to tell me a little bit about Cousteau’s
Blue Hole.
What do we know about Cousteau’s Blue Hole here?
Well, what we know is that Cousteau’s Blue Hole is one of the very unique blue holes
of the…of what I call the round “swimming type” blue holes because it’s safe to
dive from a recreational perspective, not only from a cave structure perspective.
And that is very very unique.
I finally get my first look at Cousteau’s Blue Hole.
It looks like a small, circular pond.
But this is no ordinary pond.
Some of these Blue Holes are so deep, that before scuba divers started exploring them,
they thought they were bottomless.
Cousteau’s Blue Hole does have a bottom, but it’s about 400 feet below.
So it’s about 4 times deeper than it is wide!
The shore around the blue hole is mostly limestone, but there are a few muddy places, and Cameraman
Tim just found one!
Awww!
Get a shot of that!
Get a shot of that Birdman!
Oh yeah, I forgot to tell you about that!
Unbelievable!
Once Tim has been extricated from the mud, it’s time to carry our gear down the path
from the road.
It’s a lot of work, but at least the sun came out!
In the golden light of late afternoon, our team suits up and prepares to make a dive
before the sun gets too low.
Todd takes a set of powerful video lights to help lighting the wall and overhangs.
Then it’s my turn to get in.
Next Cameraman Tim joins us.
Dennis will be our divemaster.
He has done this dive many times and knows where to find lots of interesting stuff!
The water at the surface is quite green.
Sunlight near the surface allows plankton to grow, making the water murky.
And the water is fresh.
As we sink deeper, the sunlight drops off quickly and we turn on our video lights.
By 50 feet, there is very little light.
By 70 feet there is almost no ambient light at all.
Dennis leads our team along the vertical wall, with Todd close behind lighting the place
up.
We have reached a layer called a halocline where the freshwater above meets the salt
water from the ocean below.
In this layer, where oxygen-rich water from above meets oxygen-poor water from below,
microbial action creates clouds of fine minerals that float in the water.
Dennis leads us to a ledge with a deposit that looks like rusty sediment.
Above it on the wall are rusty looking stains made by iron-oxidizing bacteria.
They break down iron from the rock into rust, which falls down and collects on the shelf
below.
This is the same kind of bacteria that makes rusty stains in sinks and toilets.
The deeper we go, the clearer the water gets.
At 90 feet, the walls are clean white limestone.
At a hundred feet, we come across a layer of sediment that looks a little bit like a
chocolate layer cake.
It’s called a microbial mat, and it’s made of sulfate-reducing bacteria.
These bacteria consume organic material like leaves that fall into the Blue Hole.
They operate in anaerobic conditions, meaning where there is very little to no oxygen.
In a sense, this type of bacteria essentially breathes sulfate--which it gets from the calcium
sulfate that naturally occurs in seawater.
The result is toxic hydrogen sulfide, and this thick mat of decomposed organic material.
The oxygen level in the water at this depth is very low because it is all consumed by
other forms of bacteria that require oxygen to decompose the organic matter in the water.
Between that and the hydrogen sulfide in the water, fish just can't survive down here.
Soon we start making our way up towards the surface again.
In the shallows, algae can live because there is sunlight and no hydrogen sulfide.
The algae make oxygen and fish can live here too, although there aren’t many.
I manage to find a single fish sitting on a ledge.
You have to wonder how fish ever got here in the first place!
Because the limestone walls of the blue hole are being slowly but constantly dissolved
by the water, it has become quite porous.
In fact, if I touch it, it crumbles in my hand like a piece of dried toast.
It’s hard to believe that solid rock can become so fragile!
Just under the surface of the water--less than ten feet deep--the bottom is completely
covered in what looks like an encrusting sponge.
But it’s not sponge at all.
When I touch it, bubbles are released, potentially indicating that there is some type of decomposition
going on within it.
It appears to be some type of microbial mat that has yet to be identified by scientists.
Even here in shallow water, there are scientific discoveries to be made!
We end the dive at sunset.
We have seen some amazing and weird phenomena in Cousteau’s Blue Hole.
I would have never guessed there was so much going on in a small Blue Hole like this one.
It just goes to show there is no limit to the amazing things to be seen in the Blue
World.