0:00:02 > 0:00:05They cover two thirds of our planet.
0:00:07 > 0:00:11They hold clues to the mysteries of our past.
0:00:11 > 0:00:15And they're vital for our future survival.
0:00:16 > 0:00:19But the secrets of our oceans have remained
0:00:19 > 0:00:23largely undiscovered until now.
0:00:23 > 0:00:25I am with a six gill shark.
0:00:25 > 0:00:28Yes, yes!
0:00:28 > 0:00:32Explorer Paul Rose is leading a team of ocean experts
0:00:32 > 0:00:36on a series of underwater science expeditions.
0:00:36 > 0:00:41For a year the team has voyaged across the world to build up
0:00:41 > 0:00:43a global picture of our seas.
0:00:43 > 0:00:46We are doing some pretty uncharted research here.
0:00:46 > 0:00:49That is psychedelically purple!
0:00:49 > 0:00:53We are here to try and understand the earth's oceans,
0:00:53 > 0:00:54and put them in a human scale.
0:00:56 > 0:01:00Our oceans are changing faster than ever.
0:01:00 > 0:01:04I've never seen ice like this before.
0:01:04 > 0:01:06There's never been a better time
0:01:06 > 0:01:10to explore the last true wilderness on earth.
0:01:20 > 0:01:22The team is about to explore...
0:01:22 > 0:01:23the mighty Atlantic.
0:01:25 > 0:01:30This vast sea is the second largest of the world's oceans.
0:01:33 > 0:01:36It dominates the western hemisphere
0:01:36 > 0:01:39and covers a fifth of the planet's surface,
0:01:39 > 0:01:42forty-one million square miles.
0:01:42 > 0:01:45Its northern boundary is the Arctic,
0:01:45 > 0:01:48its southern boundary is the Antarctic. To the west,
0:01:48 > 0:01:51you've got the whole Americas and to the east of course
0:01:51 > 0:01:56you've got Africa and northern Europe so I mean, it's a sea of extremes.
0:01:59 > 0:02:02It's the youngest of the great oceans but one of the most
0:02:02 > 0:02:07influential, with an enormous impact on our climate.
0:02:09 > 0:02:12The Atlantic is a critical ocean,
0:02:12 > 0:02:15not just because it's such a beautiful vast and varied place,
0:02:15 > 0:02:19but because it's so important for the health of the planet.
0:02:20 > 0:02:23But it's now under threat.
0:02:23 > 0:02:26Increasing commercialisation of its rich resources
0:02:26 > 0:02:29is changing it dramatically.
0:02:31 > 0:02:35The Atlantic is more than I think many people realise.
0:02:35 > 0:02:39It's being lost before we even, I think, grasp its full significance.
0:02:41 > 0:02:43The team is here to investigate
0:02:43 > 0:02:48how man is endangering our crucial relationship with this ocean.
0:02:51 > 0:02:55We are three and a half billion years back in time.
0:02:55 > 0:03:00Tooni Mahto is a marine biologist and oceanographer.
0:03:00 > 0:03:06On this expedition she'll brave the alien world of our prehistoric seas
0:03:06 > 0:03:10to explore how the oceans transformed our planet.
0:03:12 > 0:03:17It's dark and gloomy, and just very lifeless by the looks of things.
0:03:19 > 0:03:22Maritime archaeologist Dr Lucy Blue
0:03:22 > 0:03:28will investigate how conquering the Atlantic helped change our history.
0:03:28 > 0:03:33It's clearly a hugely important highway in terms of connecting continents,
0:03:33 > 0:03:36but also in terms of the early seafaring activities
0:03:36 > 0:03:40in this particular part of the Atlantic Ocean.
0:03:41 > 0:03:45And environmentalist Philippe Cousteau, grandson of
0:03:45 > 0:03:47ocean pioneer Jacques Cousteau,
0:03:47 > 0:03:50will examine how we are threatening the future of this ocean.
0:03:52 > 0:03:55It's like seeing a polar bear on the plains of Africa.
0:03:55 > 0:03:57It just doesn't belong here.
0:03:57 > 0:03:59And he'll become human bait
0:03:59 > 0:04:02in an experiment to protect a top predator.
0:04:02 > 0:04:06Sharks everywhere!
0:04:08 > 0:04:12The team has come to the heart of the Atlantic Ocean,
0:04:12 > 0:04:14to the tropical waters of the Bahamas.
0:04:17 > 0:04:21Here there are unique marine environments, which can reveal
0:04:21 > 0:04:24this ocean's past and its complex future.
0:04:27 > 0:04:30So the probe, you'll both be handling the probe.
0:04:30 > 0:04:34For their first mission, the team is planning to explore one
0:04:34 > 0:04:38to discover what our planet's earliest oceans were like.
0:04:38 > 0:04:42We really only know this much about what we're going to find
0:04:42 > 0:04:46on this dive. We really, genuinely don't know much about this at all.
0:04:56 > 0:05:01They're heading to a strange marine environment, one of the only places
0:05:01 > 0:05:07in the world where dark toxic waters mimic the earth's first oceans.
0:05:07 > 0:05:09There it is, Tooni.
0:05:10 > 0:05:14It's called the black hole.
0:05:14 > 0:05:17This could well be the most dangerous dive we make.
0:05:17 > 0:05:22It looks like a giant pupil looking up at us.
0:05:22 > 0:05:26Formed by chemical erosion over many thousands of years, this
0:05:26 > 0:05:31isolated black hole has developed conditions similar to the seas of
0:05:31 > 0:05:34three and a half billion years ago.
0:05:40 > 0:05:42The team wants to find out what
0:05:42 > 0:05:47those early seas were really like by diving deep into these waters.
0:05:47 > 0:05:51There's only ever been three scientific expeditions here,
0:05:51 > 0:05:56so this is a great opportunity to actually get in the water and try and
0:05:56 > 0:05:59glean more understanding about this almost isolated environment.
0:06:01 > 0:06:04Though it's relatively unexplored,
0:06:04 > 0:06:08there's one thing scientists do know about this deep water pool
0:06:08 > 0:06:12- that like our early oceans, parts of it are toxic and dangerous.
0:06:14 > 0:06:17I understand there's a layer down there
0:06:17 > 0:06:21and this layer is kind of suspended around about twenty metres.
0:06:21 > 0:06:24It's a metre deep and in that layer
0:06:24 > 0:06:28is very high concentrations of poison - hydrogen sulphide,
0:06:28 > 0:06:31and under that I have no idea what to expect whatsoever.
0:06:32 > 0:06:35Lucy and Philippe will be at the surface taking
0:06:35 > 0:06:38temperature and oxygen readings
0:06:38 > 0:06:41to monitor the conditions as Tooni and Paul descend.
0:06:43 > 0:06:47We're going to drop the sensor down with the divers, and kind of record
0:06:47 > 0:06:50on the way down so we can get an idea, hopefully,
0:06:50 > 0:06:52of what's going on down there.
0:06:54 > 0:06:57It's a deep dive into toxic chemicals.
0:06:57 > 0:07:00Dive safety supervisor Richard Bull is worried.
0:07:00 > 0:07:05Quite frankly, I'm a bit twitchy about it, all right?
0:07:05 > 0:07:08Don't forget you can bail out at any point.
0:07:08 > 0:07:10If you're a bit twitchy, get out of there.
0:07:10 > 0:07:13It's better to be stood up here wishing you were in there,
0:07:13 > 0:07:16than in there wishing you were stood up here, OK?
0:07:16 > 0:07:18Tooni and Paul, you're looking out for each other.
0:07:18 > 0:07:22You are each other's standby, all right?
0:07:22 > 0:07:25I'm not sure it's going to be that pleasant down there
0:07:25 > 0:07:28and if it's not that pleasant, I want my wing man on standby.
0:07:28 > 0:07:30I'm yours, don't worry.
0:07:31 > 0:07:33Two...one...
0:07:43 > 0:07:46Man, that really is looking over the precipice isn't it?
0:07:47 > 0:07:53We're just suspended perfectly over this huge black hole
0:07:53 > 0:07:56and it, it feels as if it's drawing us down.
0:07:56 > 0:07:59Paul and Tooni plan to spend longer in the black hole
0:07:59 > 0:08:02than anyone has before.
0:08:02 > 0:08:06No-one can be absolutely certain what the effects will be.
0:08:08 > 0:08:11Tooni, here's the science kit coming down.
0:08:11 > 0:08:13How deep are you right now?
0:08:14 > 0:08:18Yeah we're now at fifteen metres, Philippe.
0:08:20 > 0:08:23They keep going down. So far,
0:08:23 > 0:08:29the dive has been completely normal, but then they reach eighteen metres.
0:08:29 > 0:08:32Wow - Philippe, the temperature has just soared
0:08:32 > 0:08:35by...by about six degrees.
0:08:35 > 0:08:38Yeah Philippe, my head feels quite normal,
0:08:38 > 0:08:42but my legs are really, really hot,
0:08:42 > 0:08:44and I'm getting some kind of strange layer.
0:08:44 > 0:08:47What are you showing up there for temperature?
0:08:48 > 0:08:52It's just zipped up to about 30 degrees C.
0:08:52 > 0:08:55We're reading some interesting figures here on the probe.
0:08:55 > 0:08:59It seems that the temperature has spiked quite considerably.
0:08:59 > 0:09:01It's just in a metre.
0:09:01 > 0:09:04That's amazing. Usually the deeper you go, the colder it gets.
0:09:04 > 0:09:07This is, this is incredible.
0:09:07 > 0:09:10- I've never even heard of anything like that before.- No, nor have I.
0:09:11 > 0:09:15To find out what's causing the sudden rise in temperature,
0:09:15 > 0:09:17they descend even further.
0:09:18 > 0:09:20Oh, my goodness, it's purple!
0:09:22 > 0:09:24This is bizarre.
0:09:26 > 0:09:30That is psychedelically purple.
0:09:30 > 0:09:34It's like being in an outer space chemical soup.
0:09:36 > 0:09:38As a marine biologist,
0:09:38 > 0:09:41Tooni recognises what the purple cloud must be.
0:09:41 > 0:09:46We're right in the middle of a layer of purple sulphur bacteria.
0:09:50 > 0:09:53They contain a pigment, which they use to trap sunlight,
0:09:53 > 0:09:56and that pigment is purple.
0:09:58 > 0:10:03The bacteria absorb the sunlight's energy to photosynthesise,
0:10:03 > 0:10:07but not all the energy is absorbed.
0:10:07 > 0:10:12And the reason it's warm is because purple sulphur bacterium
0:10:12 > 0:10:16are not particularly good for trapping that sunlight so about
0:10:16 > 0:10:2170% of the energy of the sun is just dissipated as heat.
0:10:22 > 0:10:26Bacteria like these were one of the few life forms that
0:10:26 > 0:10:29could survive in our early seas,
0:10:29 > 0:10:34but when they photosynthesise, some produce a poisonous byproduct...
0:10:34 > 0:10:36hydrogen sulphide.
0:10:36 > 0:10:41In high concentrations, that's as deadly as cyanide.
0:10:47 > 0:10:49Oh, God, I can smell it in my face mask.
0:10:50 > 0:10:52Oh, it really smells.
0:10:52 > 0:10:55None of their face is exposed to the water.
0:10:55 > 0:11:00What's happening is their skin is actually absorbing the hydrogen sulphide,
0:11:00 > 0:11:03and circulating through their body into their sinuses and
0:11:03 > 0:11:05that's how they're smelling it.
0:11:05 > 0:11:10To discover more about conditions in our early oceans,
0:11:10 > 0:11:14Paul and Tooni need to find out what's below this toxic layer.
0:11:15 > 0:11:17It can't possibly get any worse.
0:11:17 > 0:11:20Let's go down another half a metre or so.
0:11:24 > 0:11:27Oh, man, it's absolutely pitch black.
0:11:29 > 0:11:32Like somebody's just sucked all the light away.
0:11:32 > 0:11:35And the bacteria just above us have actually sucked all the
0:11:35 > 0:11:40light out so no sunlight energy reaches this layer.
0:11:40 > 0:11:45This is why the black hole appears so dark from the surface.
0:11:45 > 0:11:50Then Lucy discovers something else.
0:11:50 > 0:11:54The oxygen levels have gone from 7.8 at the surface
0:11:54 > 0:11:56all the way down to 0.18.
0:11:56 > 0:11:59- Wow!- I know that's... - Paul, Tooni, surface.
0:11:59 > 0:12:05We're also noticing on the probes that the oxygen level has dropped considerably.
0:12:07 > 0:12:10There's almost no oxygen in the water here.
0:12:10 > 0:12:16The layer of bacteria acts as a barrier, preventing the sunlight
0:12:16 > 0:12:19and oxygenated water above from getting down here.
0:12:21 > 0:12:25These are the conditions they have been looking for.
0:12:27 > 0:12:29What Paul and I are swimming through
0:12:29 > 0:12:33is what the oceans would have once been like - dark and gloomy,
0:12:33 > 0:12:39very, very little oxygen and just lifeless, by the looks of things.
0:12:42 > 0:12:45With its high concentration of sulphur bacteria
0:12:45 > 0:12:47and no light or oxygen,
0:12:47 > 0:12:53this body of water is as close as we can now get to our ancient oceans.
0:12:56 > 0:13:01We are now three and a half billion years back in time.
0:13:02 > 0:13:07The oceans formed when the earth was about two hundred million years old.
0:13:09 > 0:13:12They were a series of hot, oxygen-free pools
0:13:12 > 0:13:17with very little life, dotted across the barren volcanic landscape.
0:13:17 > 0:13:22They remained that way for over a billion years.
0:13:22 > 0:13:26I'm getting some weird sensations on my skin.
0:13:26 > 0:13:29It's really really tingling.
0:13:29 > 0:13:31After just twenty minutes,
0:13:31 > 0:13:35their bodies have started to react to this harsh environment.
0:13:35 > 0:13:40It's having some weird effect on our skin.
0:13:40 > 0:13:43I can almost feel my hair burning.
0:13:43 > 0:13:47I need to get this suit off, cos I am itching in here.
0:13:47 > 0:13:49These chemicals have really made me itch.
0:13:53 > 0:13:56Dive safety supervisor Richard Bull has heard enough.
0:13:56 > 0:13:59It's time to get them out.
0:13:59 > 0:14:02- Tooni, surface.- There's too much we don't know about down there.
0:14:02 > 0:14:05We don't know how the gas affects them, we don't know
0:14:05 > 0:14:10how it affects the equipment, just so many ifs and buts.
0:14:10 > 0:14:11We're coming up.
0:14:20 > 0:14:23How was it?
0:14:23 > 0:14:25Everything about it is weird.
0:14:25 > 0:14:28- It's getting warmer and warmer and warmer.- As you go deeper?
0:14:28 > 0:14:31To the point of it being oddly, unhealthily warm.
0:14:31 > 0:14:33Oh, look at that!
0:14:33 > 0:14:37That's where the metal's been oxidised by the bacteria.
0:14:37 > 0:14:40This is a brass clip and this is a brass-bodied pressure gauge.
0:14:40 > 0:14:42Just noticed they've both gone off.
0:14:42 > 0:14:46But it's no surprise to see some, some other manifestation
0:14:46 > 0:14:49of that chemical reaction there, because it's pretty powerful.
0:14:52 > 0:14:54That's how our oceans were, not
0:14:54 > 0:15:00these wonderful live masses of water covering 70% of our surface.
0:15:00 > 0:15:04They were like that weird place. That's where we started.
0:15:04 > 0:15:08And so it's fantastic to be in a bit of water that is exactly
0:15:08 > 0:15:11the same as our oceans were three and a half billion years ago.
0:15:11 > 0:15:13I mean, you know, top that.
0:15:24 > 0:15:27Since then, the Atlantic and all our oceans
0:15:27 > 0:15:30have changed beyond recognition.
0:15:30 > 0:15:33They are now abundant with life.
0:15:33 > 0:15:36Divers coming down.
0:15:36 > 0:15:41To find out how that happened, Tooni and Paul are about to dive
0:15:41 > 0:15:45with the creatures which triggered that great transformation.
0:15:46 > 0:15:48Here in the Bahamas
0:15:48 > 0:15:53is one of only two places on earth where they still survive.
0:15:55 > 0:15:58They are the oldest life form on earth.
0:15:59 > 0:16:04I am really looking forward to diving on the organisms that were
0:16:04 > 0:16:09instrumental in creating our modern oceans, and so I'm really keen to go
0:16:09 > 0:16:12and see almost the seat of all life.
0:16:14 > 0:16:16Everyone ready? OK, go!
0:16:25 > 0:16:28They may look like lifeless rocks but this
0:16:28 > 0:16:31is actually a thriving colony
0:16:31 > 0:16:35of the life form that oxygenated our planet's atmosphere...
0:16:37 > 0:16:38..stromatolites.
0:16:41 > 0:16:44They've been around for three and a half billion years
0:16:44 > 0:16:47which is over three-quarters of the earth's history -
0:16:47 > 0:16:49quite phenomenal.
0:16:49 > 0:16:54It's hard to believe, isn't it? These simple rock-shaped things
0:16:54 > 0:16:58are actually one of the engines that turned the planet into the
0:16:58 > 0:17:00life-giving place that it is.
0:17:02 > 0:17:06Billions of bacteria live on the surface of these mounds
0:17:06 > 0:17:10and build up by binding particles in the water.
0:17:11 > 0:17:13The bacteria catch the sediment
0:17:13 > 0:17:18that's brought with the currents and they just form these large boulders,
0:17:18 > 0:17:23and they just lay down more and more of this sandy substance,
0:17:23 > 0:17:27and get larger and larger over time.
0:17:27 > 0:17:30The stromatolites came to dominate the early seas
0:17:30 > 0:17:34and were the first life form to do something extraordinary.
0:17:34 > 0:17:38The bacteria are called cyanobacteria, and they
0:17:38 > 0:17:42actually photosynthesise in the same way that plants and algae do.
0:17:42 > 0:17:48They take carbon dioxide and water and, using the energy from sunlight, they make oxygen.
0:17:51 > 0:17:54By producing oxygen, the stromatolites started
0:17:54 > 0:18:00to transform the planet, and even now, billions of years later,
0:18:00 > 0:18:05they're still producing it as Tooni can prove with a fluorometer.
0:18:06 > 0:18:09The fluorometer gives an indirect measurement
0:18:09 > 0:18:13of the amount of oxygen that the stromatolites are producing.
0:18:13 > 0:18:16Just the skin of this, just the outer layer is the stuff
0:18:16 > 0:18:18that's alive and gives off oxygen.
0:18:22 > 0:18:27So if you want to hold that bit, arm there, on a flat surface.
0:18:29 > 0:18:33And the reading here is 0.5.
0:18:35 > 0:18:39This is significantly less than an average plant produces...
0:18:40 > 0:18:44..but because there were so many colonies of stromatolites
0:18:44 > 0:18:48spread across all our early oceans, they had a huge impact.
0:18:51 > 0:18:56The oxygen they produced seeped into the atmosphere
0:18:56 > 0:18:59and, after two billion years, reached the levels we have today.
0:19:02 > 0:19:07The seas became oxygenated and more complex life could thrive.
0:19:09 > 0:19:13It was the fact that they were pumping huge amounts of oxygen into the atmosphere
0:19:13 > 0:19:16which meant that modern day life
0:19:16 > 0:19:21and very complex life forms such as myself and Paul could evolve.
0:19:31 > 0:19:34- We are the ultimate time travellers. - Yeah, talk about time travel!
0:19:34 > 0:19:39We've experienced the ancient ocean and the modern ocean within the space of a day.
0:19:39 > 0:19:41Perfect.
0:19:50 > 0:19:52For hundreds of thousands of years,
0:19:52 > 0:19:56the rich life in the modern oceans has been a vital resource for man,
0:19:56 > 0:20:00but today we're increasingly threatening it.
0:20:04 > 0:20:07OK guys, white board... we've got it sussed here.
0:20:07 > 0:20:10An easy trip, anchor tonight...
0:20:10 > 0:20:13Philippe is going to investigate a growing problem
0:20:13 > 0:20:16that is changing balance of life here -
0:20:16 > 0:20:19an alien species brought to this ocean by man.
0:20:23 > 0:20:27Invasive species are having a devastating effect
0:20:27 > 0:20:30on more and more of our oceans.
0:20:32 > 0:20:37In this part of the Atlantic, the invader is the lionfish.
0:20:39 > 0:20:42Probably one of the top five environmental crises we're facing
0:20:42 > 0:20:44today is invasive species,
0:20:44 > 0:20:47and lionfish is really the poster child of that here,
0:20:47 > 0:20:49in the Atlantic ocean.
0:20:49 > 0:20:52I love diving with lionfish, you know?
0:20:52 > 0:20:55I've done it many times in the Pacific ocean where they belong,
0:20:55 > 0:20:57not in the Atlantic, not here in the Bahamas.
0:21:03 > 0:21:04Three... two...
0:21:04 > 0:21:06one.
0:21:11 > 0:21:13Philippe wants to discover
0:21:13 > 0:21:17how the lionfish could be affecting the Atlantic ocean.
0:21:19 > 0:21:23Native to the warm waters of the Pacific and Indian oceans,
0:21:23 > 0:21:27lionfish live mainly around coral reefs.
0:21:39 > 0:21:43- Wait, Luce!- Have you got one? - Right here.
0:21:45 > 0:21:48It's like seeing a polar bear on the plains of Africa.
0:21:48 > 0:21:50It just doesn't belong here.
0:21:53 > 0:21:57The fish are popular in aquariums
0:21:57 > 0:22:02so scientists suspect that unwanted pets may have been released by
0:22:02 > 0:22:04their owners into Atlantic waters.
0:22:04 > 0:22:08The first sightings began about twenty years ago.
0:22:08 > 0:22:12- Here's one here, look.- They're clearly doing very, very well.
0:22:12 > 0:22:16You can see this other one right up here, just sitting on the ledge.
0:22:16 > 0:22:19They're everywhere - it's unbelievable.
0:22:19 > 0:22:22There's more of them than anything else.
0:22:25 > 0:22:30These ornate fish are one of the ocean's most poisonous creatures.
0:22:30 > 0:22:33They have spines on their fins.
0:22:33 > 0:22:36At the base of these spines are venom glands
0:22:36 > 0:22:38containing a neurotoxin.
0:22:38 > 0:22:43When the spine punctures a victim, the toxin is released.
0:22:45 > 0:22:47Old wives' tales would say
0:22:47 > 0:22:52that fishermen who would grab lionfish and try and pull them out
0:22:52 > 0:22:54of their nets would get stung
0:22:54 > 0:23:01and they would throw themselves overboard and commit suicide because the pain was so excruciating.
0:23:06 > 0:23:11But the venomous spines aren't the real danger here.
0:23:11 > 0:23:16So far on this dive, the lionfish is the only relatively large fish
0:23:16 > 0:23:18that Philippe and Lucy have seen.
0:23:18 > 0:23:22These invaders are skilled and efficient hunters
0:23:22 > 0:23:26that decimate the native fish population.
0:23:26 > 0:23:30He's eyeballing something. He's just kinda sneaking up on it.
0:23:30 > 0:23:33Whoa! Did you see that, he just went after something?
0:23:33 > 0:23:34Yeah!
0:23:35 > 0:23:38Wow! That is so rare.
0:23:38 > 0:23:41Typically, lionfish are nocturnal feeders
0:23:41 > 0:23:43and for him to have done that, it just shows
0:23:43 > 0:23:48just how voracious and deadly these creatures are.
0:23:52 > 0:23:54And because they're new here,
0:23:54 > 0:23:59the native fish don't yet recognise them as predators.
0:23:59 > 0:24:02All the little fish swimming around it, they're just sort of
0:24:02 > 0:24:07hanging out, so the idea of identifying it as a predator -
0:24:07 > 0:24:10they haven't acknowledged that as yet.
0:24:10 > 0:24:13Look at them, they're almost following it at the moment.
0:24:14 > 0:24:19Lionfish target young fish, which are easily caught.
0:24:19 > 0:24:24The native fish population is in danger of being wiped out.
0:24:24 > 0:24:27That was the problem in action.
0:24:27 > 0:24:31This is bad news for the health of this ecosystem, bad news for
0:24:31 > 0:24:34potentially important fish and for the other creatures that live here
0:24:34 > 0:24:38that are part of the natural order of this food chain.
0:24:39 > 0:24:41And it's getting worse.
0:24:41 > 0:24:45Lionfish have few natural predators in the Atlantic
0:24:45 > 0:24:48so their population is exploding.
0:24:48 > 0:24:51From just a handful 20 years ago,
0:24:51 > 0:24:53there are now countless lionfish
0:24:53 > 0:24:58and they've spread from the Caribbean as far north as Rhode Island.
0:25:03 > 0:25:07For me, it was just the way that the other fish were just sort of hanging
0:25:07 > 0:25:12out around them as if they had no fear or any indication that
0:25:12 > 0:25:15- they were their predators. - They were everywhere.
0:25:15 > 0:25:17I was looking for grouper, for parrot fish.
0:25:17 > 0:25:22I was keeping my eye out for things that should be here and I didn't see
0:25:22 > 0:25:26any of them in the abundancy that I saw lionfish. That's very worrying.
0:25:26 > 0:25:29I don't think there's anything we can do about it,
0:25:29 > 0:25:32I really don't, except for try and learn so that
0:25:32 > 0:25:34if it happens again with another species,
0:25:34 > 0:25:37we're a little more prepared to deal with it.
0:25:37 > 0:25:41I think that's about all we can... we can hope for, which isn't much.
0:25:45 > 0:25:48There's no sign of this Atlantic invasion stopping,
0:25:48 > 0:25:53and it's far from the only example of man's impact on this ocean.
0:25:54 > 0:25:59Later in the expedition the team will dive with sharks to protect
0:25:59 > 0:26:04these top predators - victims of increased commercial fishing here.
0:26:10 > 0:26:14These waters are being changed by man, but they brought the
0:26:14 > 0:26:19first settlers to these islands, over thirteen hundred years ago.
0:26:24 > 0:26:27It's clearly a hugely important
0:26:27 > 0:26:31highway in terms of that whole sort of migration of people out of South
0:26:31 > 0:26:35America, and slow colonisation of various islands in the Caribbean
0:26:35 > 0:26:38and in this part of the Atlantic ocean.
0:26:44 > 0:26:50Today, maritime archaeologist Dr Lucy Blue is travelling inland,
0:26:50 > 0:26:54in search of the lost civilisation of the Lucayans.
0:26:56 > 0:27:00The Lucayans were an ancient people who travelled here
0:27:00 > 0:27:02from South America on wooden rafts,
0:27:02 > 0:27:06using the ocean currents and prevailing winds.
0:27:11 > 0:27:16Lucy will be the first archaeologist to investigate a sea cave
0:27:16 > 0:27:18thought to be a Lucayan burial site.
0:27:21 > 0:27:24This is the first time in 20 years or so, that anybody's been allowed
0:27:24 > 0:27:29to go back and have a look and see if indeed anything still remains there.
0:27:32 > 0:27:36Very little is left of the Lucayans' ancient civilisation.
0:27:38 > 0:27:41Could this cave hold evidence of their rich history?
0:27:42 > 0:27:45This watery state, it's really quite atmospheric,
0:27:45 > 0:27:47quite peaceful, actually, isn't it?
0:27:47 > 0:27:51Sort of fitting that you bury your dead there, in a way.
0:27:54 > 0:27:57Hopefully, my expertise in the archaeological remains will
0:27:57 > 0:28:01add something to an understanding - assuming there's anything there.
0:28:01 > 0:28:04We're still not sure we're actually going to find anything.
0:28:16 > 0:28:19Wow! And into the depths we descend.
0:28:22 > 0:28:26That is just like the hand of God touching the cavern.
0:28:28 > 0:28:31Finding anything won't be easy.
0:28:31 > 0:28:35This underground labyrinth of caverns extends for many miles
0:28:35 > 0:28:38and eventually joins the ocean.
0:28:43 > 0:28:48The limestone structure of the Bahamas being so porous
0:28:48 > 0:28:52and fragile creates these vast cave systems.
0:28:53 > 0:28:57The Lucayans' creation legend tells how they were trapped in
0:28:57 > 0:29:01a watery cave until the sun and the moon freed them.
0:29:04 > 0:29:09So caves were sacred places and used for burial.
0:29:15 > 0:29:16What about there?
0:29:18 > 0:29:21Ahh! Look at this.
0:29:22 > 0:29:25That's really eerie.
0:29:30 > 0:29:34Deep within the cave, Lucy spots something remarkable.
0:29:36 > 0:29:38Tooni, Tooni, come in, come in.
0:29:44 > 0:29:49It's incredible to think this could have been here for over 1,400 years
0:29:49 > 0:29:51just lying here...
0:29:53 > 0:29:55..in its watery grave.
0:29:56 > 0:30:01I can't see any other sort of burial artefacts,
0:30:01 > 0:30:05no bits of pottery but unfortunately we can't get too close.
0:30:05 > 0:30:07I might just go a little bit closer.
0:30:08 > 0:30:11But is this skull Lucayan?
0:30:11 > 0:30:13One feature would prove it.
0:30:14 > 0:30:20Apparently they used to strap planks of wood on the skull, and this would
0:30:20 > 0:30:22give it a very pronounced shape.
0:30:22 > 0:30:26It was supposed to be a sign of, you know, beauty. It's a
0:30:26 > 0:30:30bit like, you know, when the Japanese bind their kids' feet,
0:30:30 > 0:30:31it's the same sort of effect.
0:30:35 > 0:30:39And actually it does look like it's had that on its head.
0:30:42 > 0:30:45The characteristic flat forehead
0:30:45 > 0:30:48shows this really is the skull of a Lucayan.
0:30:53 > 0:30:57It's thought the bodies were dropped into the caves from openings above,
0:30:57 > 0:31:02but to Lucy, the position of the body suggests another possibility.
0:31:04 > 0:31:09The Lucayans themselves were actually really confident free divers,
0:31:09 > 0:31:14and so they could've actually carried the body, placed it in this position.
0:31:14 > 0:31:18To me it looks very deliberately placed.
0:31:21 > 0:31:26But while the Atlantic transported the Lucayan settlers here,
0:31:26 > 0:31:28it also brought about their demise
0:31:28 > 0:31:34when, hundreds of years later, other races migrated across this ocean.
0:31:34 > 0:31:38The Lucayan people lived here quite peacefully until the Europeans
0:31:38 > 0:31:40arrived, Columbus and his men.
0:31:40 > 0:31:45They took a population of roughly 60,000 people and
0:31:45 > 0:31:48enslaved them, and if they refused to be enslaved,
0:31:48 > 0:31:50then they shot them.
0:31:53 > 0:31:55After Spanish colonisation,
0:31:55 > 0:32:00European diseases and mass suicides in response to slavery took their toll.
0:32:00 > 0:32:04Within a generation, the Lucayan peoples no longer existed.
0:32:10 > 0:32:12I felt very privileged
0:32:12 > 0:32:16looking at somebody in their, in their final resting place.
0:32:16 > 0:32:20When you find the remains of people that lived, you know, sort of
0:32:20 > 0:32:24- 1,400 years ago or something. - A vanished civilisation.
0:32:24 > 0:32:26Yeah, that makes it very special.
0:32:34 > 0:32:39Today, the Atlantic still has a great influence on our lives.
0:32:39 > 0:32:41It's one of the most important oceans for
0:32:41 > 0:32:43regulating the planet's climate,
0:32:43 > 0:32:48because it carries one of the world's strongest ocean currents...
0:32:48 > 0:32:50the Gulf Stream.
0:32:50 > 0:32:55Here's the whole huge Atlantic, you know - icebergs either end,
0:32:55 > 0:33:00and here's the Bahamas, with the most powerful current on earth.
0:33:05 > 0:33:08Originating in the Gulf of Mexico,
0:33:08 > 0:33:12it flows north along the east coast of the United States
0:33:12 > 0:33:14before arcing away to the north-east
0:33:14 > 0:33:18and driving right across the entire north Atlantic.
0:33:20 > 0:33:23The Gulf Stream moves a hundred times as much water
0:33:23 > 0:33:26as all the rivers on earth.
0:33:28 > 0:33:32It gets some of the power to do that right here in the Bahamas.
0:33:32 > 0:33:36Where we are in the Bahamas, the Gulf Stream coursing up through that
0:33:36 > 0:33:42narrow bit between Florida and us, the gun barrel of the Gulf Stream.
0:33:43 > 0:33:4830 million cubic metres of water per second are squeezed
0:33:48 > 0:33:53through this narrow channel and forced out of the other end.
0:33:53 > 0:33:55And Paul is going to investigate
0:33:55 > 0:33:58just what effect that has on this current.
0:33:58 > 0:34:01- Ready to rock?- All set.
0:34:01 > 0:34:05We'll all go together, cos with this current if someone gets in first, gone.
0:34:20 > 0:34:25It's going that way and there's no force of man that can stop it.
0:34:27 > 0:34:32It's here that the current is at its fastest.
0:34:32 > 0:34:36The power generated as it's forced through the gap is immense.
0:34:39 > 0:34:43This huge current runs right across the Atlantic ocean
0:34:43 > 0:34:46and it's one of the great engines
0:34:46 > 0:34:48that drives the world's climate.
0:34:52 > 0:34:54The Gulf Stream takes warm water
0:34:54 > 0:35:00from the southern Atlantic and moves it into the northern hemisphere.
0:35:02 > 0:35:07It moves more heat each day than the world's power stations produce in a
0:35:07 > 0:35:10year - enough to warm northern Europe
0:35:10 > 0:35:14and raise the air temperature in Britain by ten degrees.
0:35:17 > 0:35:21The Gulf Stream in the Atlantic ocean is driving our weather.
0:35:21 > 0:35:27That gives you an idea of the scale and power of this whole system.
0:35:28 > 0:35:31We need to get up there, cos he's going to be low on air by now.
0:35:36 > 0:35:38I tell you what, I knew I was going fast,
0:35:38 > 0:35:42but I couldn't tell you how fast.
0:35:42 > 0:35:44You could sense the power.
0:35:50 > 0:35:54Man learned how to harness this current and the winds
0:35:54 > 0:35:56to travel around the Atlantic.
0:35:56 > 0:36:00For hundreds of years, this ocean was central to the discovery of
0:36:00 > 0:36:03new worlds and colonial expansion.
0:36:05 > 0:36:06It's clearly a hugely important
0:36:06 > 0:36:11highway in terms of connecting continents but also in terms of the
0:36:11 > 0:36:14early seafaring activities in this particular part
0:36:14 > 0:36:16of the Atlantic ocean.
0:36:19 > 0:36:23This ocean has been especially important in shaping the history
0:36:23 > 0:36:28of Britain and the United States, bringing settlers, trade, even war.
0:36:32 > 0:36:37Lucy wants to investigate a battle between Britain and America by
0:36:37 > 0:36:42identifying a significant shipwreck, one that might be the HMS Southampton.
0:36:42 > 0:36:46There are so many incidences of shipwrecks in this area.
0:36:46 > 0:36:50I mean the Bahamas in Spanish means shallow waters. We don't know...
0:36:50 > 0:36:54The war was a dispute over Atlantic trade routes between England
0:36:54 > 0:36:59and America in 1812, shortly after the War of Independence.
0:37:01 > 0:37:05A shipwreck has been found on a reef near Conception Island.
0:37:07 > 0:37:10It's not been mapped at all, not been surveyed extensively.
0:37:10 > 0:37:14It certainly hasn't been excavated so it hasn't really been investigated.
0:37:16 > 0:37:21Lucy wants to find out if this wreck is the HMS Southampton.
0:37:23 > 0:37:27She wasn't actually that big, only about 120-odd feet, carrying 32 guns.
0:37:27 > 0:37:29That's a lot of guns for 120 feet.
0:37:29 > 0:37:34I know, and a crew of nearly 200 or something. It must have been actually quite cramped.
0:37:34 > 0:37:37Awfully close, and they spent a lot of time at sea back then.
0:37:37 > 0:37:40I know, totally. It will be interesting to see if that compliment
0:37:40 > 0:37:44of guns and anchors and everything actually are reflected on the seabed.
0:37:48 > 0:37:52But the weather may scupper their plans.
0:37:52 > 0:37:54THUNDER RUMBLES
0:37:58 > 0:38:02We should be prepared for some kind of jiggery-pokery with the schedule
0:38:02 > 0:38:05- or maybe not even making it. - Oh, really?
0:38:05 > 0:38:08- Yeah, they're talking, you know, gale force.- Really?
0:38:08 > 0:38:11Yeah. So...
0:38:11 > 0:38:12And how long is that likely to last?
0:38:12 > 0:38:15Well, we don't, well, we don't even need gale force.
0:38:15 > 0:38:20If it's on the edge of 20 knots, it'll be on the edge of our diving capability.
0:38:25 > 0:38:30The weather moves in and conditions deteriorate rapidly.
0:38:32 > 0:38:36This is just not what we want at all.
0:38:38 > 0:38:41And, as ever it's a tight schedule, so if we don't get a move on...
0:38:44 > 0:38:47As well as the shipwreck, they also need to fit in a
0:38:47 > 0:38:52challenging dive with sharks, so they decide to press on.
0:38:53 > 0:38:57After hours of forging through choppy seas,
0:38:57 > 0:38:59they finally get near the shipwreck.
0:39:04 > 0:39:08It's not getting any better and this boat's rocking and it's
0:39:08 > 0:39:12blowing like crazy, so it's not making our job any easier.
0:39:12 > 0:39:15With the wind, the current and this position,
0:39:15 > 0:39:16it's a bit marginal really.
0:39:23 > 0:39:25In these conditions,
0:39:25 > 0:39:29it's easy to see how a ship could founder on this reef.
0:39:34 > 0:39:39Now Lucy can finally try to discover whether it is the Southampton.
0:39:43 > 0:39:46Well, there's an anticipation, but also you just don't know
0:39:46 > 0:39:51what you're going to find do you? So that's, that's quite exciting really.
0:39:58 > 0:40:04Several metres down, conditions are much better
0:40:04 > 0:40:09so Lucy and Philippe start their detective work.
0:40:09 > 0:40:13I'm just trying to find any clues of the wrecking of the ship.
0:40:13 > 0:40:16I'm trying to see if I can find any of the cannon or the anchor.
0:40:21 > 0:40:24A-ha, look!
0:40:24 > 0:40:27- Philippe, Philippe, Philippe! - Look at that!
0:40:27 > 0:40:30Look, you can see one, two...
0:40:30 > 0:40:33there's loads of cannon all over the place.
0:40:38 > 0:40:41Any exposed wood will long have rotted away,
0:40:41 > 0:40:45but there are artefacts spread over a wide area.
0:40:45 > 0:40:49Once you've trained your eyes, there are cannon everywhere.
0:40:49 > 0:40:51Another one over there.
0:40:51 > 0:40:53They're just lying here.
0:40:53 > 0:40:55Here's another one here.
0:40:57 > 0:41:00I've never seen so many cannon in such a concentrated area
0:41:00 > 0:41:02on a ship before.
0:41:04 > 0:41:08Just, just look at the size of this thing.
0:41:08 > 0:41:10I mean, it's about as long as I am.
0:41:12 > 0:41:15But are these cannons from the Southampton?
0:41:15 > 0:41:18The Southampton had 32 guns.
0:41:18 > 0:41:21There were 26 of these 12 pounders,
0:41:21 > 0:41:24I think this is a 12 pounder. We need to measure it.
0:41:24 > 0:41:27The 12 pound guns on the HMS
0:41:27 > 0:41:32Southampton were said to be between six-and-a-half and seven feet long.
0:41:33 > 0:41:36That's six foot seven.
0:41:36 > 0:41:40- So this is the right kind of cannon then, Lucy?- I think so, I think so.
0:41:43 > 0:41:46Ah, the other thing that's quite distinguishing
0:41:46 > 0:41:51about this...is that the 12 pounders from this era
0:41:51 > 0:41:55have these little sort of rings attached to their ends, so...
0:41:55 > 0:41:59which was quite unusual. Not many of the cannons had
0:41:59 > 0:42:01these so that looks like one of the
0:42:01 > 0:42:06types of cannon that the vessel would have been originally consigned with.
0:42:06 > 0:42:11The cannons alone aren't enough for a positive identification.
0:42:11 > 0:42:14Lucy needs to find more evidence.
0:42:17 > 0:42:21- Philippe, look, look, look, look! - It's huge! This is just incredible.
0:42:21 > 0:42:24I mean you can see this anchor just sitting here.
0:42:25 > 0:42:27It's a British anchor.
0:42:27 > 0:42:30You can see because of the V shaped arms at the bottom of the
0:42:30 > 0:42:34anchor, this is very distinctive of British naval vessel anchors.
0:42:34 > 0:42:37If it was from an American vessel, it would have been
0:42:37 > 0:42:39more rounded at the base.
0:42:40 > 0:42:46It's just another clue, in a way, as to understanding if this is the wreck of the HMS Southampton.
0:42:51 > 0:42:53I would have expected maybe
0:42:53 > 0:42:57to find a pile of chain or something attached to the anchor that, I mean
0:42:57 > 0:43:00that would have been iron that should still be here.
0:43:00 > 0:43:03No, no, not for this period, because they would have been using ropes
0:43:03 > 0:43:06rather than chains to actually haul the anchor.
0:43:11 > 0:43:17She probably would have thrown these anchors aground as she wrecked here during the night.
0:43:19 > 0:43:22By the morning they realised there was no saving the vessel
0:43:22 > 0:43:24and they had to abandon ship,
0:43:24 > 0:43:28so again another clue to confirming this is the HMS Southampton.
0:43:30 > 0:43:35The size of the cannons, along with the type and position of the anchors
0:43:35 > 0:43:39have convinced Lucy this is the HMS Southampton.
0:43:39 > 0:43:44It's a record of the November night in 1812 when, towing a captured
0:43:44 > 0:43:47American ship to Jamaica, she hit this reef and sank.
0:43:52 > 0:43:56It brings to life an event and a particular battle that has been
0:43:56 > 0:44:01forgotten a lot in our, in our histories - both UK and America.
0:44:04 > 0:44:08The war was finally resolved with a treaty, signed in 1814.
0:44:08 > 0:44:12Neither side was victorious but it confirmed the status
0:44:12 > 0:44:16of the United States as a fully independent nation.
0:44:19 > 0:44:21You know what this impresses upon me?
0:44:21 > 0:44:26I mean the Atlantic played a huge role in that war alone,
0:44:26 > 0:44:29not to mention many, many others.
0:44:29 > 0:44:31Such a vast, critical ocean.
0:44:33 > 0:44:37It is like a snapshot in time which basically the ocean has preserved
0:44:37 > 0:44:39for us to come and investigate,
0:44:39 > 0:44:42and so in a way the ocean actually holds a story, which
0:44:42 > 0:44:44we are very unlikely to find in any other context.
0:44:49 > 0:44:54The Atlantic has helped shape our distant and more recent past.
0:44:54 > 0:44:56Now the expedition is heading north-west,
0:44:56 > 0:44:58to investigate its future.
0:45:00 > 0:45:03We're heading for north Bimini, aren't we?
0:45:03 > 0:45:08Yeah we're gonna come off the banks so we need to get down here and drop the anchor overnight.
0:45:11 > 0:45:15The future of the Atlantic is being shaped by man.
0:45:15 > 0:45:18The effects of large scale commercial fishing
0:45:18 > 0:45:20are damaging this mighty ocean.
0:45:20 > 0:45:24In the last decade, some fish stocks have fallen by 95%.
0:45:26 > 0:45:30One fish is particularly hard-hit - the shark.
0:45:32 > 0:45:35How many sharks do we catch every year? Who was it who said...
0:45:35 > 0:45:37it must have been you, Philippe.
0:45:37 > 0:45:43Human beings catch between 70, we estimate between 70 and 100 million sharks every year.
0:45:43 > 0:45:46- Million?- 70 to 100 million sharks a year.
0:45:47 > 0:45:52Some sharks are caught for their fins, used in shark-fin soup.
0:45:53 > 0:45:55But millions of sharks are by-catch,
0:45:55 > 0:46:00caught unintentionally by big commercial fishing operations.
0:46:00 > 0:46:03Sharks are so critical, and they are the apex predator.
0:46:03 > 0:46:06They help to weed out the sick and the diseased, make sure that
0:46:06 > 0:46:10the fisheries and the food chain beneath them is healthy and viable.
0:46:10 > 0:46:14And when they remove sharks from that, you know, that chain,
0:46:14 > 0:46:18it has just disastrous effects on the entire ecosystem.
0:46:20 > 0:46:24So the team is going to dive with sharks to investigate
0:46:24 > 0:46:26a pioneering technique,
0:46:26 > 0:46:30a shark repellent that could help protect these vital creatures.
0:46:37 > 0:46:39It's coming up slowly, it's a small one.
0:46:39 > 0:46:43Philippe and Tooni are going to team up with scientists from the shark
0:46:43 > 0:46:46lab at the Bimini Biological Field Station.
0:46:46 > 0:46:48For the last 25 years,
0:46:48 > 0:46:51they've been monitoring the population here, catching
0:46:51 > 0:46:57and then releasing the sharks once they've collected their data.
0:46:57 > 0:46:59There is a shark caught on one of the hooks.
0:46:59 > 0:47:04I mean it's giving a good thrash in the water so it's still alive and obviously fine.
0:47:07 > 0:47:09To track the diminishing population,
0:47:09 > 0:47:12they need to attach an identity tag to this shark.
0:47:12 > 0:47:16Philippe is going to monitor the process underwater.
0:47:16 > 0:47:18We've got to be very, very careful.
0:47:18 > 0:47:22It's gonna be an upset shark and it's happened before that
0:47:22 > 0:47:25they can break free from a line so we're going to give a lot of space
0:47:25 > 0:47:28and a lot of berth and a lot of respect.
0:47:39 > 0:47:41Looks like a tiger shark.
0:47:41 > 0:47:45That is a tiger shark all right.
0:47:45 > 0:47:49Tiger sharks are known to be one of the more dangerous sharks in the world.
0:47:49 > 0:47:52I normally would never get this close to a tiger shark.
0:48:02 > 0:48:03Woah!
0:48:06 > 0:48:09That was a close call there.
0:48:09 > 0:48:12That's why you've got to be really careful.
0:48:12 > 0:48:15So we're doing a data tag basically.
0:48:17 > 0:48:19As sharks become more threatened,
0:48:19 > 0:48:23tags can help identify when and where they are being fished.
0:48:23 > 0:48:26Do I push it in?
0:48:26 > 0:48:28There you go, pull it out, pull the wood out.
0:48:28 > 0:48:30There you go, then the tag stays in, you see?
0:48:30 > 0:48:34This shark has been caught deliberately, for research,
0:48:34 > 0:48:38but commercial fisheries catch countless sharks unintentionally.
0:48:38 > 0:48:41Long lines are set up by commercial fisherman,
0:48:41 > 0:48:45miles and miles and miles long, with thousands of hooks laid along them.
0:48:45 > 0:48:50Sharks are often left for a long period on those lines and they die.
0:49:02 > 0:49:04She wanted to give me a little goodbye present.
0:49:04 > 0:49:08And off she goes! She looks good.
0:49:09 > 0:49:14Millions of these predators are caught on commercial lines.
0:49:14 > 0:49:18So the hunt is on for an effective way of preventing sharks
0:49:18 > 0:49:20from getting trapped on them.
0:49:34 > 0:49:39Paul and Lucy have joined scientists who've developed a material
0:49:39 > 0:49:41they believe will repel sharks.
0:49:41 > 0:49:46This is the very stuff right here. It's an alloy, a mixture of metals.
0:49:46 > 0:49:50The hope is that hooks made of the repelling metal could
0:49:50 > 0:49:56be used on long line fishing hooks, so fewer sharks end up as by-catch.
0:49:56 > 0:49:59The metal is electropositive.
0:49:59 > 0:50:03It produces a charge that's conducted by salty water.
0:50:03 > 0:50:05Well, done.
0:50:05 > 0:50:07OK, let him settle down a bit.
0:50:07 > 0:50:09So I'll grab him, OK?
0:50:09 > 0:50:14Lucy and Paul are going to test the metal on a juvenile lemon shark.
0:50:14 > 0:50:18Lucy has been shown a handling technique to help the experiment,
0:50:18 > 0:50:21putting the shark in a coma-like state.
0:50:21 > 0:50:23I'm going to try and basically
0:50:23 > 0:50:26turn him on his back so we've got to try and move him over.
0:50:26 > 0:50:28Or her, I don't know.
0:50:28 > 0:50:30Be ready for her,
0:50:30 > 0:50:31steady as you go.
0:50:37 > 0:50:39When the tail becomes immobile...
0:50:39 > 0:50:42- Then she's out.- And basically when she's not moving at all.
0:50:42 > 0:50:44OK, so she's totally out of it at the moment.
0:50:47 > 0:50:50In this state, the shark is very unresponsive.
0:50:51 > 0:50:55Paul is going to bring a small piece of the metal close to its head.
0:51:02 > 0:51:03Are you ready, Lucy?
0:51:07 > 0:51:10Time to see if the shark will react to the metal.
0:51:20 > 0:51:21Holy smoke!
0:51:21 > 0:51:27OK, ha-ha! OK, it works.
0:51:28 > 0:51:32I think that's definitely a conclusive experiment.
0:51:32 > 0:51:33So it works.
0:51:33 > 0:51:38Even in a comatose state, the shark sensed the metal, and was repelled by it.
0:51:38 > 0:51:41So if you've got a set of fish hooks made of this stuff,
0:51:41 > 0:51:43you can do selective fishing.
0:51:43 > 0:51:45You're gonna get more of what you do wanna catch
0:51:45 > 0:51:48and less, or hopefully none, of what you don't wanna catch.
0:51:51 > 0:51:54The expedition is coming to a close.
0:51:55 > 0:51:59But there's one final shark mission for Tooni and Philippe.
0:52:08 > 0:52:11Chum - a mixture of mashed-up dead fish -
0:52:11 > 0:52:14has been spread in the water.
0:52:14 > 0:52:18It's attracted blacktip and Caribbean reef sharks.
0:52:18 > 0:52:20Oh, we've got sharks.
0:52:20 > 0:52:22There are some sharks out here.
0:52:22 > 0:52:25We can see their fin tips just going round the water.
0:52:31 > 0:52:33They're going to test another shark repellent,
0:52:33 > 0:52:38a liquid that could be attached in time-release pouches to long lines.
0:52:41 > 0:52:44To make the conditions for the experiment authentic,
0:52:44 > 0:52:48it's got to be carried out in open water, teeming with adult sharks.
0:52:50 > 0:52:54Philippe and Tooni will dive in amongst the sharks,
0:52:54 > 0:52:57and release the repellent by hand.
0:52:59 > 0:53:02There are some big sharks down there, actually.
0:53:02 > 0:53:04They're a good couple of metres,
0:53:04 > 0:53:06which I don't think I was quite expecting.
0:53:06 > 0:53:09I was expecting slightly smaller sharks to be honest.
0:53:11 > 0:53:15Caribbean reef and blacktip aren't the most aggressive of sharks
0:53:15 > 0:53:18but the chumming has attracted quite a few.
0:53:18 > 0:53:23One, two, three, four, five, six...
0:53:23 > 0:53:25and the small one out the back is seven.
0:53:26 > 0:53:29That's bizarre, that makes my heart go a bit funny.
0:53:29 > 0:53:33It's quite a bizarre sensation to be sitting on the side of a boat,
0:53:33 > 0:53:38about to sort of drop backwards into a pool teeming with sharks.
0:53:40 > 0:53:44Safety divers and first aiders are standing by.
0:53:50 > 0:53:52Oh!
0:53:52 > 0:53:54Oh, my goodness!
0:53:54 > 0:53:59Sharks everywhere, all around us.
0:54:00 > 0:54:03This is just incredible.
0:54:04 > 0:54:07Oh, God, she's having a good look at me.
0:54:17 > 0:54:20Whoa! that was close.
0:54:21 > 0:54:24That was close.
0:54:26 > 0:54:28Shark chaos!
0:54:28 > 0:54:32More and more sharks are gathering.
0:54:32 > 0:54:35This should be the stuff that really scares them off.
0:54:35 > 0:54:41It is essentially distilled tissue from sharks, from dead sharks.
0:54:42 > 0:54:46Scientists realised sharks are driven away
0:54:46 > 0:54:49by the smell of rotting shark.
0:54:49 > 0:54:53As you can see, they're kind of circling us a lot right now.
0:54:53 > 0:54:56You can see them getting a
0:54:56 > 0:54:59little bit ticked off at each other, a little bit
0:54:59 > 0:55:01aggressive towards each other.
0:55:04 > 0:55:07Philippe and Tooni decide to release the repellent.
0:55:07 > 0:55:12This is the first time this repellent has been tested like this.
0:55:12 > 0:55:15This isn't a game, this is serious business.
0:55:23 > 0:55:26Sharks have a very acute sense of smell,
0:55:26 > 0:55:29but it takes a few minutes for the liquid to disperse.
0:55:37 > 0:55:41One by one, the sharks leave.
0:55:41 > 0:55:45They keep just swimming further and further away from us.
0:55:45 > 0:55:49Clearly they didn't like something.
0:55:49 > 0:55:55All the other fish are still here, but the sharks have disappeared.
0:55:57 > 0:56:00They're not showing much signs of coming back, either.
0:56:02 > 0:56:05The experiment's been a complete success,
0:56:05 > 0:56:10and could play a vital role in protecting sharks in all our oceans.
0:56:14 > 0:56:15Fantastic!
0:56:15 > 0:56:20The sharks kind of do an in, sense something and out again.
0:56:20 > 0:56:22Yeah definitely, definitely.
0:56:22 > 0:56:24I'd like to say that I smell of shark repellent.
0:56:24 > 0:56:28- Oof!- It's really quite disgusting!
0:56:32 > 0:56:35I think it's a great, great piece of science.
0:56:35 > 0:56:38It could be impregnated into wet suits or sunscreens and it's just,
0:56:38 > 0:56:41it's like widening the gap between sharks and people.
0:56:41 > 0:56:44I think this is how science can come together
0:56:44 > 0:56:46to have practical applications for conservation,
0:56:46 > 0:56:49and ultimately we have healthier more sustainable oceans.
0:56:58 > 0:57:03The end of the shark dive is also the end of the Atlantic expedition.
0:57:06 > 0:57:08A journey in which this ocean revealed
0:57:08 > 0:57:11how all our oceans once looked.
0:57:14 > 0:57:18And how they were responsible for bringing life to our planet.
0:57:18 > 0:57:23I've spanned three and a half billion years of the ocean's evolution in
0:57:23 > 0:57:26one trip and that's quite something.
0:57:27 > 0:57:34This ocean has played a critical role in our history, but it's
0:57:34 > 0:57:38difficult to assess the impact we could be having on its future.
0:57:39 > 0:57:44The Atlantic is just being abused and I don't think anyone knows what the consequences are,
0:57:44 > 0:57:48but we know that the consequences, whatever they are, are very serious.
0:57:48 > 0:57:51We can't continue to take it for granted.
0:58:02 > 0:58:06Next time, the team explores the Indian Ocean.
0:58:06 > 0:58:09They'll find out how manta rays survive shark attacks.
0:58:09 > 0:58:13There's a shark bite, right there.
0:58:13 > 0:58:16Discover the consequences of its treacherous currents.
0:58:16 > 0:58:19She hit this reef behind us and broke her back.
0:58:19 > 0:58:25And explore an underwater lab that could save coral reefs.
0:58:43 > 0:58:47Subtitles by Red Bee Media Ltd
0:58:47 > 0:58:50E-mail subtitling@bbc.co.uk