Extreme Cave Divers Documentary on Cave Diving and Lost Underwater Worlds (Full Documentary)

In the Bahamas, the world's best cave divers plunge into the abyss. They're exploring underwater caves littered with mysteries and divers who didn't get out alive. Per attempt, this is the most dangerous sport on earth. They face cave-ins, blackouts, panic. They do it for the rush, they do it to be first, and they do it to find ancient bones. These caves are blue holes, liquid time capsules, where the past stares right back at you. Now, extreme divers try to solve the mystery of a lost world. But can they survive this alien place? Under pressure, underwater, underground. In the Caribbean Sea, just 96km off the coast of Florida, there is a paradise known as the Bahamas. This is a place full of attractions. They draw millions of tourists each year. But these visitors aren't here for sun or sand, though they may be in for a bit of a gamble. They've come to search for a lost world. They're extreme explorers, astronauts of an inner space called blue holes. Blue holes get their name from the dark blue of their depths. And while they don't look like much at the surface, what seems like a small pond can go hundreds of metres down and spread out into a maze of underwater passages and tunnels. The mystery of their depths beckons the able and the foolhardy alike. On average, 20 divers each year die in caves like this. But to these explorers, it's worth the risk, because blue holes aren't just spectacular. Some preserve the past like a liquid time capsule. Diving them will take the explorers back thousands of years, where there are hints of an ancient lost Bahamas. What did this world look like then, and who lived here? Now, an unprecedented expedition pairs expert cave divers with world-class scientists to find out. There's two options for getting in here right now. One is jump, and I think the second one is jump. National Geographic explorer Kenny Broad, an anthropologist, is the expedition leader. We're trying to get a window into what the past was like, the living past, the geologic past. And you can jump into a blue hole and make finds that change our picture of these islands. They'll do that by exploring seven blue holes in just three weeks on the islands of Andrus and Abaco. The team has come here because the Bahamas may have more blue holes than anywhere else in the world. The potential for discovery is high, the risks even higher. So Kenny has turned to Brian Kaycook to lead the dives. Brian is one of the world's most experienced cave divers. We just want to see what's around that corner. We don't want to stop. Cave divers live to change the map, and occasionally that can get us into trouble. Brian staggered back and below with the lens. Renowned photographer Wes Skiles heads up a film crew who deliver images to document the scientific finds. I'm the eyes of the scientists and the explorers. I know that what I'm shooting is bringing this back to be shared in very important ways, and that's thrilling. Their first task is a shakedown dive. They'll test out the gear and get all the divers prepared for the treacherous labyrinths below. The first thing dive leader Brian Kaycook does when he gets into the hole is lay down a guideline. In cave diving, laying line is the first rule of survival. Without that guideline, your odds of coming out are very slim, and that's what kills most people. Though they can appear crystal clear, blue holes are full of silt. When disturbed, it rises from the floor or even falls from the ceiling and blacks everything out. In this place, it's extremely dense black organic matter, so it's difficult to work in. Just the pressure wave of your body pushing the water in front of you tends to stir stuff up. You have to count on coming out, zero visibility, with your finger on that line feeling your way out. But even that lifeline can turn against you. Line, an inanimate object, a piece of nylon string. You put it underwater in a cave and it comes alive, and it's devious and evil. It's out to kill you. We have lots of stuff on us, and all of those things can become entrapped in the line or caught in the line if we get too close to it or not paying attention to it. If they do get tangled up, cave divers carry knives, usually more than one. They like back-ups, and they like their back-ups to have back-ups. Just to give you a little sense of the redundancy, so you've got knife, knife, another knife. It's actually a parachute cutter. So, my mum's favourite kitchen knife. Don't tell her. Back-up is second nature in this type of diving, where caves that look solid can suddenly fracture at a bubble's weightless touch. Only minutes into the dive, it happens. Brian turns around to see chunks of ceiling fall on Kenny. Kenny loses the line. It was just raining down crumbly rock, and he almost disappeared. We're talking about avalanches. I couldn't read any of my gauges. While filming, Wes is pummeled by the debris. Once it went completely zero-vis, I was trapped in there. Next time you're in your house, turn off all the lights, put a bag over your head and try to find your way out. Your heart rate will go up, and it takes a while. Brian is still on the line. Kenny grabs his leg, and they escape covered in debris. After the limestone rain shower, we decided just to get all the sediment off of us, so we did a couple of barrel rolls. Just kind of let things hang loose. It's just a small taste of what can go wrong. Well, per attempt, this is the most dangerous sport on Earth. I see dead people that are diving with me. I look at people and go, that person is a potential fatality. And down here, with the slightest mistake, potential becomes reality. Out of nowhere, a human arm bone appears. Next, a flashlight. Then a knife strapped to the leg of a 70s-era wetsuit, an orange sleeve and a headless torso. The remains of a diver who died trapped in this cave 30 years ago. He's jammed up like he was trying to find his way out. Nearby, the diver's head, with his dive mask still in place. The presence of the body was known, but it's never been identified. And it's so deep, no-one's ever attempted a recovery. It's really knowing your limits, and that's what keeps you alive, and I think that's what's killed a lot of people in caves. You don't know what's in there. You know no-one's been in a lot of these places, and that's kind of sucking you in. Our human nature is to push into places that we don't know about. And the blue holes of the Bahamas appeal to that curiosity, with their hundreds of kilometres of unexplored passages. The blue holes formed as long as 300,000 years ago, in the middle of the Ice Age, when ice caps expanded and sea levels dropped. Then, sea level was over 120 metres lower, and the Bahamas sat high and dry. Over time, rain carved holes in the limestone base of the Bahamas islands, creating caves. Ocean water settled at the bottom. Fresh water accumulated at the top. Eventually, the deep layer became completely devoid of oxygen, and that's what makes blue holes time capsules. Without oxygen, bones and other hints of the past are preserved. It's one of the main draws for cave explorers. After over an hour, a cave-in and an encounter with a corpse, the shakedown dive ends amid intense relief. LAUGHTER Good God, what a hell. That was one of the most tense 78 minutes that I've spent in a long time. As cave divers often say, a successful dive is one you return from. Then you think you're home free and all of a sudden the cave starts raining at you. We're laughing because we're here to laugh about it. Let's go cry by the van. With their gear and fortitude tested, they're ready to take on a biological cold case thousands of years old. Though the Bahamas are just 96km from the coast of Florida, they have only a tiny fraction of Florida's wildlife. There are no crocodiles or tortoises in the Bahamas, and no big predators of any kind. But it wasn't always this way. David Stedman wants to know why. He's one of the world's top experts on island ecology. He suspects that the Bahamas was once a thriving Eden. And he's here to find proof. We've underestimated the biological potential of islands. Islands used to be teeming with species. The trouble is they're more vulnerable on islands. For centuries, hurricanes have scoured these islands clean. On the surface, there's almost no fossil record of anything. So the best place to find bones may be straight down in a blue hole named Sawmill Sink on Abaco Island. Its high sides give it the look of a natural animal trap. The team thinks it may be a good place to hunt for the remains of animals who lived here in the past. Since Stedman is not a diver, the underwater team will be his eyes and hands, prospecting for bones in another very dangerous place. This is a very disorienting place, Nate, so you'll watch each other. Stay on the line, stay on the line, stay on the line. Before they reach the bottom where fossils would be, they face one more perilous obstacle, a thick layer of poisonous hydrogen sulphide. The naturally orange-tinted solution is actually the excrement of billions of tiny bacteria. They eat organic material, then excrete hydrogen sulphide, forming another deadly barrier to blue hole exploration. The divers can't protect themselves from this poison because it enters through their skin. Here, at about 150 mg per cubic metre, hydrogen sulphide makes the divers' lips tingle and smells like rotten eggs. But prolonged exposure may cause brain damage, so they've got to kick through it fast. Once on the other side, they reach the oxygen-free zone. It's here that the bones of animals that fell into the blue hole should be preserved. We're dealing with sort of an aquatic tar pit. Animals get in there, and as they die, they sink down into the part of the water that has no oxygen in it. Because that water has no oxygen in it, there's nothing to support the microorganisms, the bacteria and fungus and things like that, that normally would decay bones. Prospecting for fossils in a blue hole takes a delicate touch. Even gentle probing can stir up the silt, which could create a dangerous blackout. As he probes, Brian makes a find. It's a shell, the shape of some kind of tortoise. The oxygen-free layer doesn't preserve skin or muscle, but it does maintain shell and bone in almost pristine condition. About six metres away, he finds a bone from another creature. It's a piece of backbone, but whose? And then, up from the muck, comes the answer. A 30-centimetre-long skull loaded with teeth. It's an ancient crocodile, so perfect it looks like it's been kept in a museum. Large animals like these don't exist in the Bahamas today. These finds are evidence that there may have been a lost world here. With these prizes in hand, the team follows the line deeper into the cave. In this part of Sawmill Sink, the cave opens up. Thousands of years ago, when sea levels were lower, this soaring hole was dry and would have made a perfect home for birds. Today, the divers can actually swim up to a ledge where birds might have roosted and start scouting for fossils. On the ledge, they find a bowl-shaped roost. Below it, they set up a grid surrounding a field of tiny bones of many different types. This suggests that the bird roosting here was an owl. The bones are the remains of what he was eating. Since they can't digest bones, owls collect them in their crop and vomit them out in a clump called a pellet. This is a fossil goldmine, the bones of lizards, snakes, bats and small birds, a census of life here thousands of years ago. It will delight David Stedman, waiting for the divers to return. Got it. I can't wait to open these up. Let's see what you have. There may be some associated bones in the sediment that's in the container there too, so we'll be careful with that sediment. OK, got it. Oh, wow. Look at that tortoise. Look at that. It's complete. Complete tortoise. This is cool. Stedman has a hunch there's a link between the tortoise and the crocodile. There's no way, once a tortoise would fall in here, that it's ever going to get out. There's no exit. And you can imagine a crocodile go in to eat the tortoise, and after it ate the tortoise, the crocodile couldn't crawl out of this sinkhole either. This is so neat. No-one has ever seen this animal before. We're the first ones that actually get to touch it and feel it and study it and know that there was something special going on here. Can you imagine what this place once was? Having crocodiles running around here? When Stedman examines the tortoise shell, he makes an astonishing find. Bite marks from a crocodile prove his hunch was right. This is the sort of thing that makes the fossils from these blue holes so spectacular, to have this kind of evidence, not just of what this animal looked like, not just of what the crocodile looked like, but evidence of who is eating who. Then he turns to the finds from near the owl roost. This is sort of the sediment sample of my dreams. Never has owl vomit looked so good. All of a sudden we have a number of complete skeletons to study. We're finding species that nobody knew existed before. With each bone he identifies, the picture of an ancient wild Bahamas is starting to emerge. The three largest bones are the three major leg bones of a flightless rail, an undescribed species of flightless rail, unknown to science. This new species joins the crocodile and tortoise as the list of animals found in Sawmill Sink grows. A lizard. A meadowlark. And a burrowing owl. A Bahamian boa constrictor. And a raptor called a caracara. From just a single bag of sediment, Stedman identifies 35 species previously unknown here. Three are entirely new to science. It's clear that centuries ago, the barren islands of the Bahamas weren't so barren. So what happened? The bones I've picked out so far, every one of them represents a species of bird that isn't on the island anymore. Based on just this tiny sample, it looks like we're on our way to documenting a pretty drastic change. About a thousand years ago, most of these animals mysteriously disappeared. A fossil trail extending back roughly 12,000 years suddenly goes cold. What killed these animals off? In 1492, when Christopher Columbus first made landfall in this hemisphere, it was in the Bahamas. He encountered a people called the Lucayans. The Lucayans descended from people that came from South America around 800 BC and slowly migrated to the Bahamas. At the time, Columbus wrote almost nothing about their rituals or traditions. What little we know today suggests that they thought blue holes were sacred. They believed caves were the birthplace of humankind. And that when someone died, they should be put back inside. In the early 1990s, in a blue hole called Sanctuary on Andrus Island, a diver found human remains that may have been related to the Lucayans' ritual burial. Following up on that lead, the team will search for more remains beginning at Sanctuary. They'll try to determine if there's a link between the Lucayans and the animal die-off that occurred about a thousand years ago. Our goal is to go down there, look for those identifying signs that there are bones, skulls, hopefully recover that and document it all. Joining the team is Michael Pateman, who'll be the first Bahamian and the first archaeologist to dive this hole. I've been looking forward to this since I started archaeology. It's the mystery of the site. It's what can I find? I want to know what's here. Once on the line, the team begins their descent to the point in the cave where, 20 years ago, a diver found human remains. The team is still on their way down to the bone discovery site. On their way down, the team passes through what's called the halocline. This is where fresh water above meets salt water below. Soon, at 80 metres, they're just above the slope where human bones were found and face another potential danger. The surrounding rocks indicate there's been a massive cave-in. That kind of stuff goes on out of sight all the time, where you have chunks coming down. And we're swimming over boulders the size of houses, and you know they came from the ceiling. They know it will happen again, they just don't know when. It's one more detail that makes working in a blue hole more dangerous than any other type of marine archaeology. Archaeology in open water, if you have a problem, you can do immediate ascent up to the surface. If you need to haul material up, it goes straight up to the surface. You can't do any of that in an underwater cave. In spite of the challenges, it pays off, with first a human jawbone and then a skull. For Bahamian archaeologist Michael Pateman, the find leaves its mark. To finally actually go in the site and to see the site, I thought, wow, I can spend hours in here. And to be in the first Bahamian to dive in that blue hole, it's still not sunk in completely yet. By the end of the dive, the team has recovered pieces of three skulls. But critical questions remain. Are they connected to the catastrophic die-off of animals here? And could these skulls belong to the Lucayans, the same people Columbus wrote about? Pateman identifies a deformity in the skulls that seems to confirm their identity. When they were children, the Lucayans bound the foreheads and the backs with boards and then wrapped them. And so that would create this, what you see here, this conical shape. It's a characteristic found only in cultures like that of the Lucayans. And when the skulls are radiocarbon dated, there's an even bigger revelation. The skulls found in the blue holes date from about 800 years ago. By then, the Lucayans were already settling in the Bahamas and having an impact. And the animal die-off that David Stedman identified started about 1,000 years ago. The dates are close enough that it's likely there's a link between the Lucayans and the deaths of the animals here. We have great fossils from about 12,000 years ago up to about when the first people arrived. So when people show up, along with non-native mammals that they bring, whether it's rats, cats, dogs, pigs, things like that, these island species are very poorly adapted to these new super predators. On islands across the world, the most vulnerable species have been wiped out. They're extinct. By exploring the time capsules inside blue holes, these divers have discovered a lost Eden that was, and showed how humanity changed the Bahamas forever. But bones aren't the only prizes preserved in blue holes. Locked in spires like these are secrets about the planet's history, secrets that can only be found in blue holes. So now the team heads for blue holes famous for some of the most spectacular spires in the Bahamas. They'll dive for them in a pair of blue holes on Abaco Island. To find and collect the right type of spire, known as stalagmite, dive leader Brian Kaycook and anthropologist Kenny Broad will face their most technically demanding dive. How deep are we right here, man? Well, right now we're at the surface. You're actually above the surface. But this hole goes 320 feet. Cutting through the solid rock at the base of the stalagmite is going to take a lot of time. The maximum they can stay down with two tanks of regular air is less than two hours. But they need almost three times that for this dive. So they're using a device like astronauts use during a spacewalk, a machine called a rebreather. Rebreathers are computer-controlled devices that let you breathe your own air over and over again. Rebreathers allow us to scrub out carbon dioxide, the bad things that we don't want to rebreathe. So these little tanks will allow us to do a very long deep penetration of a cave. Rebreathers are especially good for cave diving because they release few bubbles, which can dislodge ceiling debris, creating blackouts. But they do have a deadly downside. There's as many as one out of ten rebreathers sold that people have died on. I mean, this is real serious business. It's a very complex piece of equipment. It needs to be prepared properly, you've got to be on your toes, and you need to be monitoring it constantly. On this dive, rebreathers offer Kenny and Brian a tempting but sobering bargain. Nearly unlimited time to work in the deep, at a significant risk of dying on the job. Avoiding that requires intense concentration, and for Kenny, that's the appeal. It's how I can disconnect. I feel like all day I'm attacked by my cell phone, I'm attacked by my email. It's the only place in the world where that has to be shut out. It's the only time you can have 100% concentration, because it's a life or death endeavour. At 45 metres, Brian and Kenny transit a series of rooms girded by stalagmites. These mineral formations grow from the ground up. Some in this cave took more than 200,000 years to form. It started in a dry cave, when water percolated through the ceiling and fell in different spots. Stalagmites are built by the slow accumulation of the minerals and sediments contained in the water. So these beautiful columns are more than geological ornaments. Locked inside is a biography of Earth and its atmosphere. The stalagmites Brian and Kenny are harvesting may help answer critical questions about the history of Earth's climate. That's what geochemist Peter Swart wants to know about. Stalagmites give us a clue to what paleoclimate was many thousands or hundreds of thousands of years ago. Much of what we know about climate history comes from two sources. Sediment samples from the ocean floor and cores taken from glaciers and ice sheets. But stalagmites from these caves have one major advantage in recording climate history. Their location. The Bahamas lie beside the Atlantic Gulf Stream. For millions of years, this current has carried warm, salty waters north, where they cool and sink. That drives ocean circulation, also called the Atlantic Gyre, which shapes the climate. Stalagmites record changes right in the subtropical Atlantic Gyre. So here we're really at the heart of the action. We haven't had that kind of opportunity to see the changes which occur in this region before now. So the stalagmite that Brian and Kenny have cut could provide a goldmine of global climate history. Using that history, Swart may be able to answer a critical question. While most scientists believe that Earth's climate is changing, they are struggling to figure out how fast. This stalagmite could help answer the question. To decode it, Swart first has to cut it lengthways with a diamond saw. Inside, it displays regular bands of growth, like the rings of a tree. Embedded in each band is the climate biography of a specific period. With analysis, Swart can describe how much it rained, what chemicals were in the rain, soil and air, even the temperature. Examination of the stalagmite shows evidence of more than five major climate changes over the last 80,000 years. This corroborates findings in samples taken from ice cores. But then he notices two curious details. First, the way the bands formed suggests that at least one of these climate episodes came on very abruptly. At the end of the last ice age, about 11,000 years ago, conditions changed radically from dry to wet within 50 years. This change was probably accompanied by a rise in temperature and sea level. And Swart notices something else. Some of these climate events are preceded by a mysterious dark band. When he samples the dark bands, he finds iron. So is there some link between iron and climate change? How could that be? The Bahamas are made of coral. There's no iron anywhere. In the blue hole, where they cut the stalagmite, Brian and Kenny notice something that might help solve the mystery. In the cave wall, they found a layer of red sediment. The colour is the key here. The red in the dust means it's loaded with iron. And that means that thousands of years ago, a thick layer of iron-rich red dust covered the island's surface. Repeated rains washed it through the rock, leaving a bright red band. So, how did the red dust get here? One theory suggests it came from the Sahara Desert, some 7,000 kilometres away. During times of extreme drought, towering dust storms gather in the Sahara, pushing dust high into the atmosphere, where it's carried across the Atlantic. When Swart analyses the iron in the stalagmite, he confirms that it's made of Sahara dust, though its red colour has been washed out after thousands of years. And in the dark band, he isn't finding traces of iron, but significant concentrations. Now, the iron was at very low concentrations, with the exception at this boundary here. The areas with the highest concentration of iron correspond almost exactly to the places on the stalagmite where the chemical composition indicates a period of major climate change. That probably means a major Sahara dust event came right before each change, when temperatures and sea levels rose. The fact that Saharan dust storms happen with greater frequency today is raising concerns that history could be repeating itself. Now, we know for the last 40, 50 years, there's been a major drought in Africa. And that's seen an input in the amount of dust which is coming from the Sahara region to the Bahamas. It's estimated that over the past five decades, the Sahara has seen a tenfold increase in large-scale dust storms. If we are witnessing the beginning of a major climate change, it could happen fast, just as it happened in the past. Maybe in as little as a lifetime. We don't worry too much about climate change because it's something that's going to happen after I'm dead. But in actual fact, in some of the records that we've been looking at, we see tremendous changes in a matter of decades. And so when climate changes that fast, obviously it would have tremendous implications for the present-day society. Swart's findings are preliminary, but they do suggest that climate change in the past happened faster than anyone imagined. If such change occurred today, immediate concern would be for the millions of people in areas most affected by sea-level rise, island nations and coastal regions throughout the world. For the expedition team, climate change could pose an immediate threat to the future of blue holes. There's probably no way to keep rising seas from pouring into them, ruining their delicate chemistry. Blue holes are unique repositories of scientific knowledge. Sea-level rise associated with global warming will change that water chemistry, and we're going to lose a lot of valuable information very quickly. We would lose most or all of the fossil record. It would be the equivalent of burning a library. Eventually the sea will rise. Once that happens, all these artifacts will start to deteriorate. So we really feel like we need to get as much information out of these places as we can right now. Losing blue holes is hard to contemplate for the explorers who have touched the depths of this lethal and alluring lost world. You know, I'm not sure I would know how to go on in life if I wasn't able to go to my church underwater. We go down in these places and we're cleansed. When we come up from a dive, the pressure, the challenges, the difficulties, the conflicts, they're gone. We come up from a dive and it is like you're reborn.