At 1000ft I tried to name the water; blackish-blue, dark grey-blue. The last hint of blue tapers into a nameless grey, and this finally into black. At 1900ft, to my surprise, there was still the faintest hint of dead grey light, 200ft deeper than usual, attesting to the almost complete calm of the surface and extreme brilliance of the day far overhead. At 2000ft the world was forever black.

William Beebe, Half Mile Down, Bermuda, 1934

I remember the milkiness of the water, and that at 18m we had been stopped by what looked like a weird mud floor, even though I was sure I had measured around 47m from the surface earlier. I had touched the floor and received the shock of my life. There was no floor - nothing but warmth.
     I had pulled my hand back so fast that my buddy took a tumble in the water. I had never experienced anything like it. I then buried my hand up to my elbow, then a leg, then submerged up to my waist, but still felt nothing.
     The quasi floor had started moving in waves, like a bowl of jello. This was almost too much, but I had gone in up to my neck, and suddenly everything was as black as night. Was I free-falling, had I come up under a ledge or what
     I had inflated my BC to ascend, and when I popped out, my buddy had told me that the blackness flowed off my head like paint. It was spooky.

That had been my first and only dive in a Black Hole, one of the recently discovered vertical cave systems that form in the larger Bahamian islands. Most are on South Andros, and this one was perfectly circular and 300m across, big enough to be seen on Space Shuttle photographs.
     These are areas of the Bahamian outback that no humans have visited, where the land is composed of carbonate mud, in places metres thick. You cant walk in this stuff, certainly not carrying heavy dive equipment. We had made that first trip by seaplane.
     Black Holes differ from the better-known Blue Holes in that they develop from the surface downwards, and appear to have no direct link to the sea except through rock fractures and porosity, and no lateral passages leading away from the entrance. What develops in a Black Hole would therefore tend to remain stable for long periods of time. But what exactly has developed in the Black Holes
     A year or so later I received an email from an Australian production company called Beyond. It produced a TV series in which a team travelled the oceans filming wild and wonderful things. The ship that gave the series its name, Quest, was coming to the Bahamas to film in Blue Holes. Was I interested My answer was obvious.
     The first phone call revealed that the ship came equipped with toys: a Bell Ranger helicopter, a 12m powerboat, three submersibles and a shark cage. All my Christmases had come at once.
     When I heard about the helicopter, I knew right away what to say when they asked me where I wanted to go and why - back to the Black Hole.
     The team were quickly hooked on the idea. They would arrive in June and spend a few days resupplying the ship.
     As the Quest docked, I was stunned to see two old friends of my late husband, Rob Palmer. I had met them in 1995 while cave-diving in Australia. Ronnie Allum, one of Australias top cave-divers, and Andrew Wright came walking down the plank to greet me. I knew then that it was going to be a great trip.
     I have been on some rustbuckets in my time, but the 60m Quest was at the other end of the spectrum. It had a full dive shop and equipment repair room, a photo-shop and a room for charging batteries. The dining room looked like a small ballroom. The Quest came with a team of engineers, cleaners and cooks.

Captain James Daly was a bit of a mystery man. He showed his face only momentarily during the first few days onboard. What stood out was a bruise on his leg the size of a basketball.
     It seems that his girlfriend of seven years had broken off their relationship. James had drowned himself in drink, fell down the ships stairs and remained unconscious all night. Hes lucky he didnt fall overboard or land on his head, though Im not sure the latter would have done him any damage.
     I loaded almost a tonne of gear onboard - five truckloads - and two kayaks. Two people were coming with me, Cheryl Main, who had expertise in the study of algae, which I thought would be useful, and her boyfriend David, a surveyor who would survey the Black Hole for me. Andrew had promised that after filming we would be left while the Quest filmed on Andros, and I had planned for seven days of sampling.
     It was a 20-hour steam to Deep Creek, South Andros. When I woke from a restless night, the sun was blazing on a smooth ocean. We dropped anchor near a Blue Hole called 4-Shark, and other cave openings along this same fracture system that we had named Luskas Breath and Atlantes.
     We dived these Blue Holes first. As Andrew and Ronnie would not be on this side of the world too often I wanted to see that they were blown away, as indeed they were. But those Blue Holes are another story. Everyone was dead keen to see first-hand what I had been talking about now for weeks.
     We started with a helicopter recce of the Black Hole, 14 nautical miles away. I can fly a plane, but this was my first helicopter ride. Wow, what a sensation, no doors, and to lift off and view the world in this way - I loved it!
     In the five minutes it took to reach Andros, I knew that I had to get my own helicopter licence. This was the only way to see these remote areas.

The landscape rushing past below us was thirsty, soggy, salty and basically unfriendly, but it was sprinkled with these perfectly circular openings.
     I soon stopped saying: Look at that one over there! - there were too many. I was in my element, and I dont think I could have been happier.
     Using the co-ordinates I had given him, James flew up Deep Creek, then veered north. Was that the Black Hole I peered over his shoulder and confirmed his observation. My mind wandered back to my first trip and I grinned at the memory.
     Andrew was impressed by the size of the Black Hole. James flew around it until he found a good spot, and with a hop and jerk we were down. Andrew and I were out of the chopper before James could shut down, and wandered to the edge.
     The sun was no longer high in the sky and the light that bathed this body of water did not say come hither and dive me. Andrew remarked that the water looked evil, and I had to agree.
     We walked round and decided where people could set up their gear and a campsite for my team. I was satisfied and keen to find out what lay beneath the black floor.
     Back on the ship, Andrew announced at dinner that we would be taking the two rigid-hulled boats up Deep Creek as far as possible and that James would pick us up and transport everyone to the Black Hole, to limit chopper airtime.
     He then broke the news that we had only 15 minutes to assemble all the gear we needed - and that we would be able to stay at the Black Hole for only two days. I was launched from bliss to stress. Andrew went on about how he couldnt afford to fly us in and out of the site, or to fly food out.
     This was not good timing. When he finally stopped running his mouth, I told him that I didnt want to be picked up. I was planning on camping out there for the whole time and already had enough food and water packed. This caught him off-guard.
     I had spent a months rent and food for special supplies for sample collection, and now I wasnt going to have time to use it. Andrews neck was looking real snappable.
     Somehow, Cheryl and I managed to get things together. About half an hour later I watched about $50,000 of my equipment head off towards the Black Hole, suspended from a tarp beneath the chopper. My stomach was in knots.
     The following morning around six, we climbed into the boats, James hovering overhead like a giant mosquito. At the entrance to Deep Creek the serious filming began. I soon tired of everything having to be done three times over, though I understood that it was necessary.
     I was one of the first at the Black Hole and set to work on a shelter. The sun was brutal, the dry scrub seeming to huddle in retreat. Everything was light shades of brown to green.

As people arrived, preparations for the dive began. I had my hydrolab, which could measure geochemical parameters such as dissolved oxygen, temperature, pH, salinity and depth. I wanted to try to investigate the black layer before I allowed anyone to dive into it. The last thing I needed was a fatality - I had already been labelled the Black Widow by some people because of past incidents beyond my control.
     From our small inflatable in the middle of the hole I lowered the hydrolab into the water a few centimetres at a time, before finally touching what appeared to be the bottom.
     Back on land, I hooked the lab up to my computer. Andrew joined me as we watched the data move across the screen. I suddenly saw the dissolved-oxygen level drop to nearly zero. Wow! I said.
     What is it asked Andrew.
     I explained that something was consuming the oxygen at this level. It was the level where I had measured the depth of the black layer last time.
     So the layer was still there, and probably contained a very high level of hydrogen sulphide, one of the most poisonous substances to man.
     What I failed to notice was the temperature reading, 37ÂC, and the low pH reading indicating an acid environment.
     The layer had not been hot on my first visit, so I wasnt looking for it. Anyway, I think that if the computer had flashed in big red letters: Dont go!, I would have gone anyway. My curiosity was overwhelming.

A line and buoy had been set in the middle of the hole, and the buoy was secured on a line stretched across the hole. This would be our lifeline back to the surface. Ronnie had the camera set up, we were kitted up, and we swam out to the guideline, slowly descending as we went.
     By the time we reached the line, what greeted our eyes was something I had not seen the last time. The black floor was still there - but there was a white cloud above it. The rope just vanished into it.
     I grabbed the line. Andrew followed and Ronnie was behind, filming. Slowly we slid down the line, Andrew above me. Suddenly I felt the water get hot around my feet. I didnt remember this.
     I slid down a little further. By now my body was half-gone to the camera and I was feeling very concerned. This was not just really warm water; it was uncomfortably hot.

I remembered a place called Jacuzzi Hole which also got this hot, but cooled down again once we got through the layer.
     I hoped that this would happen soon here as well. These layers have had temperatures recorded up to 41ÂC. If it didnt cool soon, we would be toast.
     About shoulder-deep now in this unbelievably hot water, the stench of hydrogen sulphide was almost making me sick. I could feel every cut on my body. I felt Andrews hand on mine and looked up at him. He was shaking his head. It seemed it was all too much for him.
     Hell, it was almost too much for me, but I waved goodbye to Andrew and vanished. I saw nothing but swirling dark purple clouds of something before my eyes. This was not a nice place.
     I began to question the wisdom of my decision to go through this layer, but then I asked myself, would it matter The answer was no. I only hoped that I would survive to tell someone about it.
     Suddenly, almost on cue, the water went crystal-clear and real cold. I landed on a floor which seemed to be composed of a material not unlike jelly. The landscape looked as one would imagine the surface of Mars to look.
     This new false floor was a purple-orange colour. The bits that we had disturbed were floating in my view like sheets of flesh. The surface of the undisturbed portion of the floor appeared to have a scalloped pattern. It was weird.

I was just sitting there, slowly sinking into the floor, when Andrew popped into view. I damn near came out of my gear. I was so absorbed in my surroundings that I had forgotten about him. His eyes were as big as dinner-plates.
     He had promised to follow me to hell and back and, true to his word, he did. I think hell be more careful next time he makes a promise to me.
     Once I had calmed down, I began investigating this jelly floor. I unfolded my metre stick and began to slide it in. I could have lowered the stick till my arm vanished and still not hit the real floor.
     A shiver passed down my spine. Maybe I was being warned that it was time to leave. I was not sure how concentrated the hydrogen sulphide was, but until I knew, I wanted to minimise our exposure.
     I hurried to collect a sample and signalled that it was time to go back. There was no argument from either Ronnie or Andrew. The prospects of passing into that layer again did not excite us but we had no choice if we wanted ever to see the sun again. And that layer was so dense that no sunlight penetrated it. It was like a rock ceiling.
     At the surface, we were bombarded with questions. I looked at the silver ring I was wearing and couldnt believe what I saw. It had turned jet black, as had all the metal clips on my jacket.
     Andrew was babbling to camera as I interrupted him with my observations. I also commented that he smelt like hell, to which he responded: You dont exactly smell like fresh roses either!
     We all had a laugh and began to climb out of the water. It felt good to be in the sun again. I was chilled and wondered how much of this was due to the experience.
     Andrew had seen another big Black Hole slightly to the north-west and wondered if we wanted to go and look before sunset.
     How decadent, I thought, as I threw my gear into the back of the chopper and we climbed in for another adventure. All my Christmases of a lifetime were happening now, and I had forgotten about the earlier stresses Andrew had put me through.

The other site was almost a double hole; a big one, about half the size of the Black Hole, and a small pool, apparently a relatively newly forming hole attached at the side. It was so shallow that the water was still light blue.
     James landed the chopper on a substantial crack. I didnt think this was a good idea, but either he didnt hear me or was just ignoring me.
     All I could think of was, what if this crack lets loose Our only means of escape would be sitting at the bottom of this hole.
     We threw on our gear again. This hole appeared to be very different from the Black Hole. Instead of a soup-bowl rim, its sides dropped sheer from the edge.
     We slowly descended into what again appeared to be a milky layer. We swam along the edge for a while before I saw what appeared to be purple stalactites. I swam up to a group of them.
     They appeared to be hanging precariously on the edge of some recent rock collapse. If these were stalactites, this hole must be a lot older than I had originally thought. Then, as I reached out to touch one of the stalactites with my finger, the whole string of them wobbled.
     In horror I jerked my hand back and tried to absorb what I had witnessed. They were still moving. Goose bumps went down my arms and up my spine. All these new surprises!
     My brain was on serious overload now. I mustered the courage to touch this thing again and realised that these quasi-stals were actually purple bacterial mats, the same substance as made up the floor of the Black Hole.
     Because the rock from which they were suspended was poised at a downward angle, the thick, heavy mats which had formed on the surface were slowly beginning to slide off the edge of the flat rock, forming virtual drip features.
     At some stage they would fall off and settle on the floor with the rest. This was amazing.
     I followed Andrew down. We passed through a warm layer, though nothing like what was in the Black Hole. Five metres further, we passed through another warm layer. There was nothing visible; we simply felt the temperature change.
     This place was spooky. Purple bacterial mats covered everything that faced the surface sun. There appeared to be no passages. After swimming around for about half an hour, we returned to a 6m decompression depth.
     My eyes wandered to the wall, which was supporting the helicopter above. I noticed how big the crack was and how ready it looked to fall over. This was bad. I was now quite eager to get out.
     I was about to point out this crack to Andrew when there was an almighty explosion. I closed my eyes and went into a tuck. I had cracked wall on my mind and I was waiting for the chopper to fall on top of me.
     Nothing. I opened my eyes and looked up. I had forgotten about our surface cover. James had jumped into the water wearing only his sneakers.
     Andrew turned and looked at me and I could see under all his face-gear that he was grinning.
     I just rolled my eyes and thought, boys will be boys. A naked man swimming around with only his volleys on is not a good look; trust me, ladies.
     When I surfaced, James was dressed again, leaning against the chopper with his arms crossed, waiting. I pulled my mask off, spat my regulator out, got out of the water, walked over to James and said, for the camera: Between us girls, Ill blame the cold water. He and everyone else roared with laughter.
     I have since named these two amazing dive sites Aussies Black Holes.
     As we were lifting off, I heard a crack that sounded like lightning popping overhead. I yelled: Go, go go! to James.
     Im not sure they knew what almost happened but I sure did. As we took off, the wall appeared to stay in place but I reckon we shortened its standing life by several thousand years.
     The next morning, I was off into the water to start my sampling, still with hair full of purple bacteria. Andrew was not among the returning group. Seems he was not feeling well. I believe that he was checking body parts to make sure that nothing had fallen off.

And the morning after that, I was jolted out of my bed. As always happens when you want to get out of a tent in a hurry, the zipper stuck.
     I fought with it like a madwoman, watching from my jail as James jumped out of the chopper, rotors still going, and started throwing dive gear into the back. I yelled as I saw my equipment vanish into the rear, but he couldnt hear me.
     As he jumped back into the helicopter, the zipper finally gave up and I shot out as if on fire, running as fast as I could. James, now in the air, must have thought I was waving him goodbye.
     I was madder than hell.
     The rest of my team stood blank-faced. They hadnt understood what had happened, but knew it was bad from the look on my face. I turned to them, politely said: Excuse me, and let go a scream that would peel the varnish off a rock.
     The chopper and Quest were too far away for radio contact. Losing my diving tanks had knocked out a whole range of possible sample collection. I could not return to the bottom for the jelly. And the one sample I did have, the cameraman had accidentally kicked back into the water while trying to record us when we came out.

I had one tank with about a third of the air left with which to collect samples from the water column, and had to blow off all the diving rules about air reserves.
     I didnt care any more. I wanted my samples, and the likelihood of getting into this body of water again soon was unlikely. I wanted to explain all the weird things that were going on here, and I had only today and a little air left.
     We all worked well into the night to get what we could.
     James arrived in the morning, about six. I immediately asked him what the deal was, taking my dive gear back to the ship, and he just mumbled something about Andrew telling him to collect their own gear - though without being told, how could he have known whose gear was whose
     I sat in the co-pilots seat, trying to absorb as much as I could as the Black Hole slowly vanished behind me. I felt sad that this adventure was over.
     Then, suddenly, James asked me if I wanted to fly this bird. Really I asked. Sure, tell me what to do.
     So he explained it to me and I took the controls. What a thrill! I viewed from the sky Atlantes, one of my favourite caves, a dome of water over the opening signalling that the system was blowing. The entrance was full of nurse sharks enjoying the cool waters it exhaled.
     Luska and 4-Shark had domes as well. The string of pearls were in their prime.

Back on the ship, I was so overwhelmed by the experience that I just sat in the co-pilots seat like a drunken fool as the turbines cooled.
     When James shut down the motor, I suddenly popped back into reality.
     High and smiling from my experience, I walked past Andrew. I had taken five steps before it dawned that this was the man I wanted to kill. I turned, caught him and asked him as calmly as I could what he had been playing at.
     Andrew said he had told James to collect only his and Ronnies gear, and had said nothing about mine. Translated to women talk: I screwed up but Im going to let my best mate sink for it.
     There was no point pushing the issue. The window of opportunity was gone and I had to make the best of a cocked-up situation. Andrew and James are still good friends of mine and in the end the misunderstanding didnt hold a light to my recent adventures. I had gotten through the floor of fire and survived.
     What more could I ask for, except a trip back to the Black Hole real soon
 We now know that the water in Black Holes appears black because of the metre-thick microbial layer which lies at around 18-19m, dividing the oxic low-salinity water at the top from denser anoxic saline water.
     Analysis of our purple samples revealed that we had discovered a novel species of bacteria. In October 2003 it was officially named Allocromatium palmeri after my late husband, Robert John Palmer. Rob was the first person to describe the Andros enigma in his book Deep Into Blue Holes, and as he had tried for nearly 20 years to reach this site, my research colleague Dr Rod Herbert at Dundee and I agreed that Rob should receive the honour.
     Other samples are still being analysed. NASAs Johnson Space Centre in Houston has invited me to apply for a summer fellowship to examine the rest of the samples in its state-of-the-art Astrobiology Laboratory, where I hope that more amazing discoveries will be made.
     Another recent discovery I made as principle investigator on the Pacific Rise filming expeditions, sponsored by Titanic director and producer James Cameron, was that macro fauna found in deep waters often appear physically almost identical to samples recovered from Blue Holes and the Black Hole.
     The plan now is to return to the Black Hole and spend the time needed there to collect all the samples required.