WEBVTT 00:00:02.440 --> 00:00:04.560 Travelling close to the sea floor, 00:00:04.560 --> 00:00:09.840 we're going to take a journey to the very bottom of the deep sea. 00:00:09.840 --> 00:00:13.880 To a world separate from the mid-water above. 00:00:23.680 --> 00:00:25.560 At around 300 metres, 00:00:25.560 --> 00:00:30.720 the drop-off levels out and we move onto the continental slope. 00:00:32.960 --> 00:00:36.680 This stretches for about 150 miles from the coast, 00:00:36.680 --> 00:00:42.320 sloping in a gentle gradient down to a maximum depth of 4,000 metres. 00:00:43.280 --> 00:00:48.360 Water temperatures drop below four degrees centigrade, 00:00:48.360 --> 00:00:53.320 and the pressure reaches 400 times that at the surface. 00:00:58.720 --> 00:01:02.240 Without the lights of the submersible, 00:01:02.240 --> 00:01:05.280 it would be completely dark. 00:01:05.280 --> 00:01:10.560 The water is crystal clear because there's so little organic matter. 00:01:10.560 --> 00:01:16.040 Only 3% of potential food at the surface reaches here. 00:01:19.240 --> 00:01:23.560 At first sight, it appears a lifeless desert. 00:01:23.560 --> 00:01:28.840 But take a closer look and you notice a network of tracks. 00:01:28.840 --> 00:01:31.000 There is life even down here. 00:01:34.440 --> 00:01:39.200 These animals would die immediately if brought to the surface in nets. 00:01:39.200 --> 00:01:43.280 You can only see them behaving normally from submersibles. 00:01:43.280 --> 00:01:45.600 Many are new to science. 00:01:50.120 --> 00:01:53.800 The deep sea floor is dominated by echinoderms - 00:01:53.800 --> 00:01:57.640 sea cucumbers, brittle-stars and sea urchins. 00:01:57.640 --> 00:02:01.160 There are literally millions of them, 00:02:01.160 --> 00:02:03.240 marching across the sea bed, 00:02:03.240 --> 00:02:06.240 hoovering up edible particles in the sediment. 00:02:07.800 --> 00:02:10.640 They come in all shapes and sizes. 00:02:10.640 --> 00:02:15.440 Though thinly spread, the deep ocean floor is so vast 00:02:15.440 --> 00:02:19.560 these are among the most numerous animals on the planet. 00:02:19.560 --> 00:02:24.040 Their spikes are good for locomotion and defence, 00:02:24.040 --> 00:02:26.160 but not so good for mating. 00:02:28.680 --> 00:02:34.000 Finding a mate in this largely empty sea floor could be a problem. 00:02:34.560 --> 00:02:36.920 Some urchins stay in herds, 00:02:36.920 --> 00:02:40.040 to be sure they're never too far from a potential partner. 00:02:42.600 --> 00:02:46.880 Rocky outcrops provide good anchorage for animals 00:02:46.880 --> 00:02:49.400 that rely on food that might drift past. 00:02:49.880 --> 00:02:55.840 These sea lilies look like plants, but are, in fact, animals. 00:02:57.080 --> 00:03:02.520 Their long stalks ensure their umbrella of feeding tentacles 00:03:02.520 --> 00:03:06.080 are positioned to best effect in the current. 00:03:06.080 --> 00:03:09.080 Particles are swept onto the arms 00:03:09.080 --> 00:03:12.240 and carried to a mouth in the middle. 00:03:14.280 --> 00:03:15.840 These sudden movements 00:03:15.840 --> 00:03:20.840 swat away tiny amphipods that try to steal the sea lily's captures. 00:03:29.120 --> 00:03:33.720 Coral reefs are not supposed to exist in total darkness. 00:03:33.720 --> 00:03:38.840 But recently, a new kind of coral was found as deep as 2,000 metres. 00:03:38.840 --> 00:03:42.440 In the cold waters of a Norwegian fjord 00:03:42.440 --> 00:03:47.800 there was a deep-sea reef 30m high and 200m long. 00:03:48.640 --> 00:03:51.360 This coral gets no energy from the sun, 00:03:51.360 --> 00:03:54.440 so it has to be efficient in catching food. 00:03:54.440 --> 00:03:58.280 Its polyps are far larger than those of shallow-water corals. 00:04:04.640 --> 00:04:10.120 These are, in fact, the largest coral polyps in the ocean. 00:04:10.120 --> 00:04:14.160 They belong to the deep-sea mushroom coral. 00:04:15.120 --> 00:04:19.640 Their 3cm-long tentacles can catch far larger prey 00:04:19.640 --> 00:04:21.600 than other corals can. 00:04:25.240 --> 00:04:28.000 This necessity to capture every particle of food 00:04:28.000 --> 00:04:30.360 in this near-desert 00:04:30.360 --> 00:04:33.320 has radically changed many animals. 00:04:34.320 --> 00:04:37.200 Most tunicates are filter feeders, 00:04:37.200 --> 00:04:40.320 but this one has become a predator 00:04:40.320 --> 00:04:44.280 and its greatly-enlarged siphon has been converted into a trap. 00:04:55.480 --> 00:04:59.760 Most sea cucumbers stay firmly on the bottom. 00:04:59.760 --> 00:05:03.120 But not this extraordinary deep-sea species. 00:05:07.240 --> 00:05:09.880 Its skirts of skin 00:05:09.880 --> 00:05:14.680 allow it to swim hundreds of metres above the sea floor. 00:05:27.080 --> 00:05:31.080 Eventually, it will descend and, with luck, 00:05:31.080 --> 00:05:33.640 land on fresh feeding grounds. 00:05:41.320 --> 00:05:46.360 This, though, has to be the most extraordinary animal design of all. 00:05:46.360 --> 00:05:48.880 It's a polycheate worm 00:05:48.880 --> 00:05:52.520 and you'd expect the long body to be stuck on the sediment. 00:05:55.640 --> 00:06:00.560 This worm - alone in its group - swims in the open water. 00:06:04.880 --> 00:06:08.360 Propelling itself with its yellow frill, 00:06:08.400 --> 00:06:11.640 it finds new sources of food 00:06:11.640 --> 00:06:14.840 or maybe escapes from a predator. 00:06:20.400 --> 00:06:25.400 This is chimaera, a relative of the sharks, less than a metre long. 00:06:27.120 --> 00:06:30.560 Sensory pits on its chin help it hunt prey on the bottom, 00:06:30.560 --> 00:06:34.760 while its surprisingly large eyes may help it spot bioluminescence. 00:06:43.680 --> 00:06:45.920 Large fish are rare down here. 00:06:45.920 --> 00:06:49.320 There's simply not enough live prey to sustain them. 00:06:49.320 --> 00:06:51.040 Most have become scavengers. 00:06:51.040 --> 00:06:55.200 A dead tuna has attracted a deep sea conger eel... 00:06:56.960 --> 00:06:58.560 .. and a sixgill shark. 00:06:59.800 --> 00:07:02.480 These monsters grow to eight metres long. 00:07:17.160 --> 00:07:19.520 Sixgills are living fossils. 00:07:19.520 --> 00:07:23.840 For 150 million years, they've existed unchanged, 00:07:23.840 --> 00:07:27.520 living in water as deep as 2,500m. 00:07:30.600 --> 00:07:35.800 Very few people have ever been lucky enough to glimpse these sharks 00:07:35.800 --> 00:07:39.080 and we know almost nothing about their behaviour. 00:07:46.680 --> 00:07:51.040 The body of a tuna is a substantial meal, but occasionally, 00:07:51.040 --> 00:07:55.320 a really gigantic corpse drifts down to the deep-sea floor. 00:08:00.280 --> 00:08:04.040 This is the freshly dead carcass of a 30-tonne grey whale. 00:08:04.040 --> 00:08:07.520 It's resting on the sea floor a mile down. 00:08:07.520 --> 00:08:11.040 It's only been on the bottom for six weeks 00:08:11.040 --> 00:08:14.560 but already it has attracted hundreds of hagfish. 00:08:16.640 --> 00:08:21.840 These ancient scavengers are often the first to discover a fallen body 00:08:21.840 --> 00:08:24.640 and are attracted from miles around. 00:08:29.200 --> 00:08:32.400 They lack jaws, and rasp at the flesh 00:08:32.400 --> 00:08:35.960 with two rows of horny teeth on each side of their mouths. 00:08:41.360 --> 00:08:46.440 Next to arrive, a sleeper shark, a real deep-sea specialist. 00:08:46.440 --> 00:08:49.280 They grow to over seven metres long 00:08:49.280 --> 00:08:52.440 and have never been filmed at such a depth before. 00:08:56.520 --> 00:09:00.280 The gaping wounds in the whale's flank are its work. 00:09:08.120 --> 00:09:10.960 Unlike the hagfish, it has powerful jaws, 00:09:10.960 --> 00:09:14.240 so is able to rip off huge chunks of meat. 00:09:21.160 --> 00:09:25.960 Sharks, hagfish and a whole succession of deep-sea scavengers 00:09:25.960 --> 00:09:30.440 will feast on the carcass for years before all its nutriment has gone. 00:09:33.840 --> 00:09:36.800 18 months later, when we returned to this whale, 00:09:36.800 --> 00:09:40.440 all that was left was a perfect skeleton, stripped bare. 00:09:48.840 --> 00:09:51.160 It was almost as if a museum specimen 00:09:51.160 --> 00:09:53.640 had been carefully laid out on the sea floor. 00:09:58.640 --> 00:10:02.000 At first, the skeleton seemed totally abandoned, 00:10:02.000 --> 00:10:05.480 but even after so long, there was still some flesh left in the head. 00:10:11.240 --> 00:10:14.120 Hagfish have a skeleton of cartilage 00:10:14.120 --> 00:10:18.960 and are so flexible that they can tie themselves into knots 00:10:18.960 --> 00:10:21.680 and get a better purchase on the flesh they feed on. 00:10:27.760 --> 00:10:30.960 But smaller organisms had fed here. 00:10:30.960 --> 00:10:34.800 A band of white bacteria had formed on the mud 00:10:34.800 --> 00:10:36.600 outlining the shape of the whale. 00:10:37.720 --> 00:10:40.360 And on the skeleton itself, 00:10:40.360 --> 00:10:45.560 colonies of bacteria extract energy from the bones. 00:10:48.320 --> 00:10:51.600 Most remarkably, and in huge abundance, 00:10:51.600 --> 00:10:55.960 polychaete worms were collecting the last edible fragments. 00:10:55.960 --> 00:10:58.320 These are a new species that, so far, 00:10:58.320 --> 00:11:01.720 have only been found on the fallen bodies of whales. 00:11:03.440 --> 00:11:09.080 Scientists have found 178 different animals on one whale vertebra, 00:11:09.080 --> 00:11:11.840 most of which have been found nowhere else. 00:11:13.120 --> 00:11:15.160 This whale, lying over a mile down, 00:11:15.160 --> 00:11:19.160 was not filmed from a submersible with an acrylic sphere. 00:11:19.160 --> 00:11:22.160 Such craft can't go as deep as this. 00:11:23.680 --> 00:11:27.920 To withstand the pressure here, you need a far stronger submersible. 00:11:27.920 --> 00:11:32.760 This is Alvin, a sphere with just enough room in it 00:11:32.760 --> 00:11:37.960 for a pilot and two observers. Its walls are made of titanium. 00:11:37.960 --> 00:11:39.920 The viewing ports have to be tiny. 00:11:39.920 --> 00:11:44.440 Any larger and the submersible would implode under the pressure here. 00:11:47.040 --> 00:11:53.200 Alvin can dive to 4,500m, three miles below the surface. 00:11:57.360 --> 00:12:01.640 Around 3,000 metres, the continental slope finally flattens out 00:12:01.640 --> 00:12:03.960 and joins the abyssal plain. 00:12:03.960 --> 00:12:07.400 This covers over half the Earth's surface. 00:12:07.400 --> 00:12:09.920 Mostly it's completely flat, 00:12:09.920 --> 00:12:14.960 but, in places, it's gashed by huge trenches, hundreds of miles wide. 00:12:20.840 --> 00:12:24.560 The deepest of these is the Mariana trench, 00:12:24.560 --> 00:12:29.240 which drops to over seven miles below sea level. 00:12:34.800 --> 00:12:40.720 Only five manned submersibles can reach the abyssal plain. 00:12:40.720 --> 00:12:44.320 Between them so far, they have explored less than 1% of it. 00:12:47.320 --> 00:12:52.320 1,000 times fewer large animals live here than on the continental slope, 00:12:52.320 --> 00:12:55.360 but in places, hundreds of brittle stars 00:12:55.360 --> 00:12:57.960 march over the sea bed, in search of food. 00:13:01.320 --> 00:13:05.760 Fish have been found right down to the bottom of the deepest trenches. 00:13:05.760 --> 00:13:09.960 Most come from one family, the aptly named rat-tails. 00:13:12.320 --> 00:13:14.960 They forage near the sea floor 00:13:14.960 --> 00:13:18.200 and use their battery of sensory pits 00:13:18.200 --> 00:13:21.520 to follow odour trails from rotting carcasses. 00:13:21.520 --> 00:13:26.840 They travel long distances across the abyssal plain in search of food, 00:13:26.840 --> 00:13:29.680 but others prefer to sit and wait. 00:13:33.640 --> 00:13:35.000 This is a tripod fish. 00:13:35.000 --> 00:13:38.960 It supports itself on two specially adapted fin rays 00:13:38.960 --> 00:13:42.320 and can sit motionless for hour after hour. 00:13:42.320 --> 00:13:47.440 It does have tiny eyes, but it's almost totally blind. 00:13:47.440 --> 00:13:52.240 It locates potential prey with a pair of fins behind its head, 00:13:52.240 --> 00:13:54.960 which are sensitive to even tiny movements. 00:14:01.880 --> 00:14:06.400 We know more about the moon's surface than about the abyssal plain. 00:14:07.360 --> 00:14:11.040 Every dive still produces complete surprises. 00:14:16.760 --> 00:14:20.640 This deep-sea octopus is about the size of a beach ball 00:14:20.640 --> 00:14:22.920 and has been nicknamed Dumbo. 00:14:34.000 --> 00:14:38.880 An umbrella of skin between its tentacles and its flapping ears 00:14:38.880 --> 00:14:43.080 allow Dumbo to hover effortlessly over the sea floor 00:14:43.080 --> 00:14:45.720 as it searches for food. 00:15:02.360 --> 00:15:04.520 Right in the middle of the abyssal plain 00:15:04.520 --> 00:15:09.000 lie the largest geological structures on our planet... 00:15:15.680 --> 00:15:18.440 ..the mid-ocean ridges. 00:15:24.120 --> 00:15:26.760 Rising almost two miles off the sea floor, 00:15:26.760 --> 00:15:32.920 the ridges extend for 28,000 miles, the largest mountain chain on Earth. 00:15:38.040 --> 00:15:44.120 When submersibles finally succeeded in reaching the ridges in the 1970s, 00:15:44.120 --> 00:15:49.120 they found an extraordinary world with miles of once molten rock 00:15:49.120 --> 00:15:53.400 that had welled up from the deep in the past and had now solidified. 00:15:58.320 --> 00:16:00.320 They discovered towering chimneys, 00:16:00.320 --> 00:16:03.440 pouring out water as hot as molten lead. 00:16:29.760 --> 00:16:34.600 At the surface, water becomes steam at 100 degrees centigrade, 00:16:34.600 --> 00:16:37.600 but down here, under the immense pressure of the ocean, 00:16:37.600 --> 00:16:41.960 it remains liquid at temperatures as hot as 400 degrees centigrade. 00:16:47.720 --> 00:16:52.200 A submersible has to move carefully. Disaster is very close, 00:16:52.200 --> 00:16:55.880 when surrounded by such enormous temperatures and pressures. 00:16:57.120 --> 00:17:01.480 And here, where the water is loaded with hydrogen sulphides 00:17:01.480 --> 00:17:06.000 poisonous to normal life processes, they found living creatures. 00:17:10.640 --> 00:17:14.120 Some of the chimneys were encrusted with white tubes. 00:17:14.120 --> 00:17:18.840 The tubes were inhabited by a new species of polychaete worm 00:17:18.840 --> 00:17:22.560 that was exposed to temperatures as high as 80 degrees centigrade. 00:17:25.560 --> 00:17:29.280 No other animal on Earth was known to tolerate such high temperatures, 00:17:29.280 --> 00:17:33.440 so the scientists call them Pompeii worms. 00:17:34.480 --> 00:17:39.360 But this was just the beginning. Nearby, there were chimneys 00:17:39.360 --> 00:17:43.040 completely covered by whole communities of different organisms. 00:17:43.800 --> 00:17:48.320 The bottom of the vent was encrusted with large mussels. 00:17:50.280 --> 00:17:53.120 There were swarms of white crabs 00:17:53.120 --> 00:17:58.600 and dominating the chimney were hundreds of bright red tube worms, 00:17:58.600 --> 00:18:02.160 each two metres long and four centimetres wide. 00:18:04.160 --> 00:18:06.400 Until these creatures were discovered, 00:18:06.400 --> 00:18:10.320 all life on earth was thought to be dependent on the sun. 00:18:10.320 --> 00:18:13.760 But here in the darkness of the deep, 00:18:13.760 --> 00:18:18.800 they discovered a density of life that derived no energy from the sun. 00:18:25.320 --> 00:18:27.720 So, what do they live on? 00:18:27.720 --> 00:18:31.480 The answer was found within the tube worms themselves. 00:18:31.480 --> 00:18:35.760 They were full of specialised bacteria, that are able to derive 00:18:35.760 --> 00:18:39.320 energy from the sulphides pouring from the vents. 00:18:43.560 --> 00:18:46.960 The worms' plumes were red with haemoglobin 00:18:46.960 --> 00:18:51.280 that carries sulphides and oxygen down to the bacteria. 00:18:51.280 --> 00:18:57.080 These bacteria are the primary source of energy for the life here. 00:18:57.080 --> 00:18:59.600 The mussels were packed with them. 00:18:59.600 --> 00:19:04.400 As green plants are the basis of life for animals living in the sun, 00:19:04.400 --> 00:19:07.040 these bacteria and other microbes 00:19:07.040 --> 00:19:12.120 are at the foot of the food chain on which over 500 species depend. 00:19:17.800 --> 00:19:20.400 Crabs and shrimps feed off bacteria 00:19:20.400 --> 00:19:24.240 and even try to steal pieces of tube worm plumes. 00:19:31.000 --> 00:19:34.560 Since the vents were first visited by biologists in 1979, 00:19:34.560 --> 00:19:38.480 a new species has been described every ten days. 00:19:39.560 --> 00:19:45.160 At the top of the food chain, fish that never stray far from the vents. 00:19:45.160 --> 00:19:49.520 But they, or their descendants, will move eventually, 00:19:49.520 --> 00:19:53.640 for we know that individual vents are only active for a few decades. 00:20:08.200 --> 00:20:13.040 Such a density of life, living in such harsh conditions, 00:20:13.040 --> 00:20:16.520 in the middle of a vast, and otherwise barren, abyssal plain, 00:20:16.520 --> 00:20:19.800 astounded the biologists who first saw it. 00:20:23.640 --> 00:20:27.280 It seemed to them that here was evidence of how life on this planet, 00:20:27.280 --> 00:20:30.480 which certainly started in the sea, might have begun. 00:20:35.840 --> 00:20:40.600 Deep-sea submersibles made an even more extraordinary discovery 00:20:40.600 --> 00:20:42.200 in 1990. 00:20:53.080 --> 00:20:57.000 Over half a mile down, at the bottom of the Gulf of Mexico, 00:20:57.000 --> 00:21:02.280 they came across what appeared to be an underwater lake over 20m long, 00:21:02.280 --> 00:21:04.200 with its own sandy shore. 00:21:05.520 --> 00:21:09.840 Around its edge there even seemed to be a tide line. 00:21:09.840 --> 00:21:13.800 But this couldn't be, of course. This was under water. 00:21:15.480 --> 00:21:20.240 In fact, the lapping edge was created by a soup of salty brine, 00:21:20.240 --> 00:21:22.920 far heavier than the surrounding sea water, 00:21:22.920 --> 00:21:26.480 and the sand was made up of hundreds of thousands of mussels. 00:21:28.520 --> 00:21:32.000 Once again, in the midst of a totally barren sea bed, 00:21:32.000 --> 00:21:37.600 a rich oasis of life, totally independent of the sun's energy. 00:21:41.440 --> 00:21:46.560 The source of energy this time was methane, 00:21:46.560 --> 00:21:48.320 bubbling out of the sea bed. 00:21:48.320 --> 00:21:51.560 Again, the mussels carried special bacteria 00:21:51.560 --> 00:21:54.720 capable of fixing the methane's energy. 00:21:54.720 --> 00:21:56.680 Just like the hot vents, 00:21:56.680 --> 00:22:00.680 a complete ecosystem had developed, based on the bacteria. 00:22:00.680 --> 00:22:05.360 There was an enormous variety of completely new species - 00:22:05.360 --> 00:22:11.400 shrimps, weird squat lobsters and bright red polychaete worms. 00:22:20.360 --> 00:22:23.440 These oases were called cold seeps 00:22:23.440 --> 00:22:26.480 and were surprisingly similar to the hot vents. 00:22:31.680 --> 00:22:35.400 The geological processes in the sea floor that produce methane 00:22:35.400 --> 00:22:38.680 can also result in the release of hydrogen sulphides. 00:22:38.680 --> 00:22:44.840 It was hardly surprising, then, that nearby they found tube worms. 00:22:46.680 --> 00:22:52.080 Extensive fields of tube worms, that stretch for hundreds of metres. 00:22:52.080 --> 00:22:57.200 This new species also uses bacteria to fix energy from sulphides, 00:22:57.200 --> 00:23:00.400 but it extracts them directly from the ground. 00:23:04.400 --> 00:23:09.440 Their beautiful gills are only used to supply oxygen to the bacteria. 00:23:12.480 --> 00:23:17.200 Amazingly, these tube worms are over 200 years old. 00:23:17.200 --> 00:23:22.480 Hot vent tube worms are the fastest growing invertebrates in the sea, 00:23:22.480 --> 00:23:25.040 but these appear to be far slower. 00:23:25.040 --> 00:23:30.240 All the more reason to protect your gills from biting amphipods. 00:23:32.560 --> 00:23:37.760 The energy sources exploited by the hot vent animals may suddenly fail, 00:23:37.760 --> 00:23:42.840 but here life can enjoy a more stable geological future. 00:23:46.920 --> 00:23:50.880 To discover, within ten years, two new ecosystems 00:23:50.880 --> 00:23:55.720 both independent of the sun's energy, has been quite extraordinary. 00:23:55.720 --> 00:24:00.520 So far we have explored just 1% of the deep ocean floor. 00:24:00.520 --> 00:24:03.960 Who knows what is still out there to be discovered? 00:24:11.800 --> 00:24:14.680 The waters of the deep ocean are so clear 00:24:15.200 --> 00:24:18.320 it looks as if these pictures were filmed in a tank. 00:24:18.320 --> 00:24:20.840 Nothing could be farther from the truth. 00:24:20.840 --> 00:24:26.520 These tube worms live a mile down, where pressure is so great 00:24:26.520 --> 00:24:31.960 that a large polystyrene cup attached to the submersible was crushed down 00:24:31.960 --> 00:24:34.400 to this tiny thimble. 00:24:34.400 --> 00:24:37.800 It's a pressure that could kill a human immediately 00:24:37.800 --> 00:24:42.200 and only a handful of submersibles worldwide can dive that deep. 00:24:42.200 --> 00:24:47.480 To add camera equipment, then to film remotely from the capsule, 00:24:47.480 --> 00:24:49.440 seems almost impossible. 00:24:49.440 --> 00:24:52.800 But with the help of some highly-professional submarine crews, 00:24:52.800 --> 00:24:57.200 our Blue Planet teams did bring back these extraordinary pictures 00:24:57.200 --> 00:24:59.240 from another world. 00:25:06.400 --> 00:25:08.200 'You have permission to surface.' 00:25:09.840 --> 00:25:14.760 The Johnson Sea Link submersible surfaces after a successful dive. 00:25:14.760 --> 00:25:18.360 In the Gulf of Mexico, it's used in the oil industry 00:25:18.360 --> 00:25:20.520 to survey the sea floor. 00:25:22.440 --> 00:25:25.400 But on this occasion, Blue Planet cameraman Mike DeGruy 00:25:25.400 --> 00:25:27.520 has been filming a remarkable phenomenon 00:25:27.520 --> 00:25:30.600 over half a mile down on the sea floor. 00:25:30.600 --> 00:25:33.800 He can hardly contain his excitement. 00:25:33.800 --> 00:25:36.760 The place is amazing. You're travelling across the mud, 00:25:36.760 --> 00:25:41.000 there's nothing, except the odd fish, sea cucumber swimming around. 00:25:41.000 --> 00:25:45.640 You come up to the mussels - a band about eight feet wide - 00:25:45.640 --> 00:25:49.640 encircling what looks like a black hole. 00:25:49.640 --> 00:25:52.520 You're literally floating on salt. 00:25:52.520 --> 00:25:56.040 The sub is trying to sink and it bounces off the top. 00:25:56.040 --> 00:25:57.400 You can't get any lower. 00:25:57.400 --> 00:26:02.320 Mike is describing a unique new community of animals 00:26:02.320 --> 00:26:04.800 first discovered in 1990. 00:26:04.800 --> 00:26:07.320 A super-salty lake under the sea 00:26:07.320 --> 00:26:09.400 which has never been documented. 00:26:09.400 --> 00:26:13.160 It's an extremely dangerous place for the unwary. 00:26:13.160 --> 00:26:17.560 Fish will come swimming across the mussels and think, 00:26:17.560 --> 00:26:19.960 "This is interesting." Into the lake they go. 00:26:19.960 --> 00:26:25.800 When they hit the top, they start gaping, roll over on their side. 00:26:25.800 --> 00:26:28.440 I've got a shot of one barely making it across. 00:26:28.440 --> 00:26:34.000 He makes it and lives. It must be full of dead animals. 00:26:34.000 --> 00:26:35.920 It's a fantastic place. 00:26:37.080 --> 00:26:39.720 Mike's task for his last dive was to film 00:26:39.720 --> 00:26:44.880 creatures called tube worms, that live around pockets of gas 00:26:44.880 --> 00:26:47.800 seeping from the sea bed 1,000 metres down. 00:26:50.480 --> 00:26:53.440 At 6.00am the next morning, the Sea Link sets off 00:26:53.440 --> 00:26:56.000 on Mike's dive to find the tubeworms. 00:26:56.000 --> 00:26:59.920 All the lights and cameras are fitted and checked. 00:26:59.920 --> 00:27:04.840 All Mike can do is hope everything works out 1,000 metres down. 00:27:16.640 --> 00:27:19.640 The journey down will take 20 minutes. 00:27:19.640 --> 00:27:23.360 The submersible has enough power for six hours' work. 00:27:23.360 --> 00:27:27.680 The crew inside have constant contact with the mothership. 00:27:27.680 --> 00:27:29.200 One seven six. 00:27:29.200 --> 00:27:33.720 The only sense they have that they're descending 00:27:33.720 --> 00:27:36.080 comes from quickly diminishing light. 00:27:42.040 --> 00:27:46.040 - 1-84 at 600 feet. - Roger that. 00:27:46.040 --> 00:27:48.920 By 500m, most of the light from the surface has gone 00:27:48.920 --> 00:27:53.280 and strange creatures start to pass by. 00:27:59.080 --> 00:28:04.480 We're sitting on the bottom. Our depth is 17-55, 1-7-5-5. 00:28:04.480 --> 00:28:11.080 Temperature is seven degrees, visibility is 30-35 feet. 00:28:11.080 --> 00:28:14.360 I've got zero to one tenth... 00:28:16.560 --> 00:28:19.800 Below 500 metres, creatures like this rabbit fish 00:28:19.800 --> 00:28:23.560 exist in a world where daylight never penetrates. 00:28:27.080 --> 00:28:29.440 Filming moving animals with a submersible 00:28:29.440 --> 00:28:32.240 requires a lot of skill from the pilot, 00:28:32.240 --> 00:28:36.320 since it's very easy to disturb the ancient silt on the sea bed. 00:28:39.240 --> 00:28:41.280 At least tube worms don't move around 00:28:41.280 --> 00:28:44.840 and Mike had a few hours to concentrate on high quality images 00:28:44.840 --> 00:28:47.480 before the submersible's batteries ran down. 00:28:51.200 --> 00:28:53.920 First, the lights attached to the manipulator arm 00:28:53.920 --> 00:28:56.120 had to be positioned to get the right look. 00:28:58.160 --> 00:29:01.680 But the real challenge was the big close-ups. 00:29:01.680 --> 00:29:05.640 At high magnifications every tiny movement is crucial. 00:29:05.640 --> 00:29:08.520 Eventually, he was satisfied. 00:29:08.520 --> 00:29:10.040 Oh, that's beautiful. 00:29:19.440 --> 00:29:23.480 These beautiful creatures take 200 years to grow to this size, 00:29:23.480 --> 00:29:26.920 and, for millions of years they have evolved in the deep sea, 00:29:26.920 --> 00:29:30.440 out of the sight of mankind, until now.