Underwater Universe (2011) s01e04 Episode Script
Tides and Currents of Death
Ocean tides and currents-- colossal forces created by the motion of the planet itself.
It's a lot of power, and it's distributed over the whole world.
Caught in their grip, there can be no escape.
Here comes the waves, and they travel fast.
4 of the earth's most dangerous tides and currents.
Rip currents are completely unpredictable.
They seem to come out of nowhere.
But which poses the greatest threat to mankind? If the ocean ever quit moving, life would end.
It's as simple as that.
It happened before and could happen again.
Tides and currents of death in the underwater universe.
Underwater Universe 1x04 Tides and Currents of Death The Earth's oceans-- spanning 1/5 of the globe; vast, powerful, and deeper than the continents are tall.
When you look at the ocean, it looks like it's sitting still, but the fact is that the ocean is valuable to Earth because it moves things around.
The forces within the underwater universe that keep the ocean moving are its tides and currents.
Shaped by the pull of the moon and the spin of the Earth, they are the circulatory system of the planet.
It moves temperature around, it moves food around.
Without motion, the ocean won't work.
It has to keep moving to do what it has to do to generate life.
But as these powerful surges of water sustain life, they can also take it away.
The water in the ocean is 800 times denser than the air in the atmosphere.
Water weighs so much more than air does that the energy associated with the water is orders of magnitude larger.
If you have winds that go at 150 miles per hour, that is the same energy as water going at 6 miles per hour.
Getting in the way of that much force can be deadly to humans.
Of all the tides and currents in the underwater universe, 4 are the most dangerous to man, each more destructive than the last.
The final and most powerful has the greatest potential to kill.
It once triggered a mass extinction, wiping out 90% of all life on Earth.
Could it do it again? The first is the Gulf Stream, the most powerful current in the Atlantic.
When we talk about currents, all we are talking about is the horizontal movement of water.
Whereas tides are the vertical, up and down movement, currents are horizontal.
62 miles wide and up to 3,900 feet deep, the Gulf Stream transports warm water from the Gulf of Mexico to the North Atlantic.
The Gulf Stream starts near the equator.
So the Gulf Stream brings up warm water up along the North American coast and then moves into the middle of the Atlantic.
The winds that blow off of that bring that warmth over to Europe and cause Europe's climate to be much warmer than at the same latitude over in Canada.
This heated ocean river can play havoc with climate, navigation, and people's lives.
Fort Lauderdale, Florida.
Ernest Norman earns a living as an advertising salesman, but fishing is his passion.
In 1981, he and his friend John Ensinger are out fishing with another man, Alex Temes, on a borrowed 36-foot cruiser.
John, when he was going to the Bahamas, he invited me along, and I couldn't pass up that trip.
I didn't think twice I just went with him.
We were gonna spend 2 or 3 days over there.
John a qualified Captain, and Ernest has been fishing the waters around Florida his whole life, although neither has been as far as the Bahamas.
Neither one of us had done that trip.
With that nice boat, we figured it'd be a simple run across because it was only 55 miles off Fort Lauderdale.
All's we did is filled the tanks with gas, filled our coolers with ice, put in the bait, put in our tackle, some food and water, and headed for Bimini.
We didn't even check the ocean.
We thought it was flat calm.
But the Gulf Stream is unpredictable at best.
If you take a look at satellite data, you will frequently see clouds just forming right over the Gulf Stream itself.
It really is like a ribbon flowing through the ocean, interacting with the atmosphere over it, that create clouds, and then clouds create low-pressure systems, and you spin up storms.
It's a very potent weather maker.
Usually it's about 80 degree fahrenheit water, which will really help the storm get going.
Once you get to that temperature, the conditions are kind of set up such that the storm can really start to maximize.
9:30 p.
m.
Ernest, John, and Alex are halfway to Bimini when the winds begin to howl.
The seas were running anywhere from 6 top 10 feet, mixed with wind chop.
And that boat just started coming apart at the seams.
It wasn't even two minutes, we were flooded.
It was time to get out of that boat.
Ernest tosses two $25 rubber rafts, purchased on a whim just hours earlier, into the sea.
Then he and the others plunge in after them.
A minute and a half from that time, that boat was down.
And after it sunk, you could look down in the deep blue and the lights were all still on in the boat.
And all of a sudden, it blinked a couple times and went out and was gone.
The 3 men are now at the mercy of one of the fastest currents on the planet.
The Gulf Stream, bigger than all the Earth's rivers combined, is set in motion by winds blowing across the Atlantic.
Most of the currents in the ocean are driven by winds.
The wind has a force on it.
And it drags the surface of the ocean in one particular direction.
Though winds are its engine, the Earth's rotational force dictates the Gulf Stream's path.
So Earth is a spinning planet, the way our experiments are spinning.
The Earth is spinning much faster than the fluid moves on top of the Earth.
When you push a bit of fluid, the way we're pushing it out of a tube here, it bends to the right, turning into a circular motion.
So what we can see is the effect of the huge earth on the very small scale.
The influence of the Earth's spin on fluid is called the Coriolis force.
As the Gulf stream bends, it connects with another current to form a giant loop.
On this side, we have the Gulf Stream.
On this side, we have the Canary current.
The water in the North Atlantic is moving around in a great big circle that oceanographers call a gyre.
This gyre is actually smashed up against the U.
S.
East Coast, causing a very fast return flow to the North.
Currents tend to follow the shape of the sea floor and flow along it, just as a race car goes around a curve, tends to bank up against the edge of a racetrack.
The Gulf Stream banks against the eastern coast of the United States at a brisk 5 miles per hour--faster than a man can walk.
But that same current doubles in speed in the area where Ernest and his friends are now adrift.
Here, warm water from the Gulf of Mexico is funneled through the Florida Straits.
They're bounded on the North by Florida, and they're bounded on the South by Cuba.
And there's an extraordinary amount of water that has to go through the Florida Straits that then becomes the Gulf Stream.
And a way to think about that is that if we have a certain amount of water that's going through a hose and we constrict the area in which it can go, the velocities are going to become much, much larger for the same volume to go through that area.
The power of this rushing current is working against Ernest and his friends.
It is quickly, inexorably dragging them due north, away from land, away from rescue.
We were completely lost at sea.
4 of the oceans' most powerful tides and currents are potentially lethal to man.
The first is the Gulf Stream.
For Ernest Norman, John Ensinger, and Alex Temes, it's now their biggest enemy.
The 3 men are adrift off the coast of Florida in two $25 rubber rafts.
Ernest and John are crowded into one, Alex alone in the other.
We're going out with the Gulf Stream.
It's taking us further off shore.
We were probably off Hobe Sound.
There was no more lights.
So the only thing we could do was keep paddling and keep paddling.
Next day, the sun came up.
We figured, oh, boy, we're in bad shape.
In the Straits of Florida, the current is very strong.
So if you're in a small boat out there and in the stream, and something happens, you're gonna be carried northward up to 5 knots, quite fast.
Over 24 hours after their boat sinks, the 3 men have yet to be rescued.
Exhausted, confused, they argue about what to do.
"Alex," he says, "you're going the wrong way.
" And I said, "Alex, the wind is northeast.
Just follow the wind.
It'll take you to the beach.
" But following the wind means crossing a very powerful current.
The only other option is to let the Gulf Stream carry them north.
The question is, how far north? This broad stretch of the Gulf Stream continues uninterrupted until it hits North Carolina's Cape Hatteras.
That area is called the graveyard of the Atlantic.
It's an incredibly stormy region where you've got currents going all kinds of different directions, and so it's very hard for sailors to navigate through that area.
Two ocean rivers collide just off of Cape Hatteras: The Gulf Stream and the Labrador Current.
The Labrador Current, it's really, really cold.
It's right above freezing.
Now, when it meets the Gulf Stream, you have the really, really warm waters and the really, really cold waters.
Those two combine to create really stormy, really foggy, really rainy conditions.
In waters like these, flimsy rubber rafts won't stand a chance.
Finally, Alex Temes makes a decision.
He was in his life raft by himself, and he started paddling due north.
And I said to John, "well, that's his problem.
Can't do anything about it.
" So me and John kept paddling.
Paddled all that day.
Ernest and John are paddling across a current packing as much force as winds blowing 125 miles per hour.
To paddle on a raft 60 miles in calm ocean, where there's no waves, where there's no currents, is an extraordinary feat.
I mean, that's like running a couple of marathons.
Now, add on to that, you have a current that is pushing you towards the north.
I really can't think of anything that would compare to that.
We were dehydrated and tired and hallucinating, and I didn't think I was ever going to make it in.
I thought it was, this was it.
Then, at midnight on day 3, they spot something on the horizon: Land.
I crawled up on the beach, and I was never so happy in my life.
If it wasn't for that northeast wind, we would have probably got stuck in that Gulf Stream and it would have kept us out there because it kept just pulling you north, pulling you north.
It takes the third man, Alex Temes, another 36 hours and 101 miles to make landfall further north.
The 3 men barely escape the grip of the Gulf Stream, but not all are so lucky.
The Gulf Stream claims a dozen victims over the course of a year.
But the next contender has claimed dozens in one day.
The second of the deadliest tides and currents in the underwater universe are extreme tides, specifically the notorious Tides of Morecambe Bay on the northwest coast of England.
The tide range is about 30 feet, and when the tide pulls back, 120 square miles of mudflats are now revealed, and the shoreline pulls back 7 miles.
It is the largest expanse of intertidal mudflats and sand in the U.
K.
And a tempting stroll for visitorsUntil the tide turns.
Due to the nature of the bay and the gullies and the channels, the water can come in behind you.
So for the unwary, they're thinking the tide is still well away from them.
But actually what happens is that the gullies fill in from behind you and cut you off.
The bay is an ever-shifting maze of gullies and channels carved into quicksand, and an incoming tide races back with such force that few can escape it.
People don't realize, if the tides are running high, it comes in at the speed of a galloping horse.
You cannot swim when it comes in.
You cannot swim.
The tide is too fast, and it isn't just clear water.
It's like sand and mud, moving sand all the time, see? With each tidal cycle, 107 billion cubic feet of water floods the bay at 10 miles per hour.
Standing in the way of an incoming tide is the equivalent of being struck by winds blowing 250 miles per hour.
It comes in so quickly, it can encompass you and drown you.
You can be over your head in literally no time.
Though Morecambe Bay's powerful tides are part of the arsenal of the underwater universe's deadly forces, they are born in the heavens.
Tides are generated by a balance between two forces.
There's the gravitational force of the Moon or the Sun, and then there's the centrifugal force of the fact that the Earth and the Moon are rotating around their center of gravity.
Now, these two forces generate a bump of water between the Earth and the Moon and a bump of water on the other side of the Earth.
Now, the Earth turns underneath this bump of water.
And as the Earth gets right underneath the bump of water, you get high tides, and as you get far away from it, you get low tides.
So it may be a bit counterintuitive that the Earth bulges out both toward the Moon and away from the Moon, and so as the Earth rotates in one 24-hour period, a given point on Earth will go through two high tides and two low tides in general, not just one.
Because the time it takes for two tidal cycles to complete is usually a bit longer than 24 hours, the time for high and low tide changes each day.
However, the cycle is completely predictable.
We've known exactly how the Moon orbits the Earth for quite a long time.
So when you say tides are predictable, they're as predictable as the sun coming up the next day.
Yet over the centuries, visitors to Morecambe Bay have ignored the power of the tides and paid with their lives.
In response, royal guides are appointed to escort travelers across the bay.
Without knowing the tide times, you must never leave the safety of the shore without going with someone that has local knowledge.
I would never, ever go out in that bay without writing the tide times on my hand, because there are so many people, what time does the tide come in? That's reassuring to them.
But even today, not all visitors know to use a guide.
February 5, 2004.
The temperature was round about 6 degrees.
The wind speed was 20 to 25 miles an hour.
Quite foreboding.
Even more ominous, the Moon is almost full.
A Spring high tide is scheduled for that evening.
The Sun's tides on Earth reinforce the Moon's tides on Earth.
Now, when the Moon is in this position, roughly in a straight line with the Earth and the Sun, you get a Spring tide because the Sun's tidal effect adds to the Moon's tidal effect.
You have extreme tides, high high tides, low low tides, so those are called Spring tides.
23 Chinese immigrants, men and women, take to the sands, getting ready for a profitable night's work.
These Chinese immigrants were out there on the mudflats digging up cockles, which is a delicacy in terms of shellfish that can bring in a lot of money.
The money in this case will go to a gang leader.
The workers have little choice.
Many are here illegally.
And most of them weren't fishermen.
They were just, you know, out to make as much money as they could.
For 6 hours, well past nightfall, the immigrants work a cockle bed some distance from shore.
The cockle beds that were producing at that time were around about 3 or 4 miles out into the bay, which is a good hour's, hour and a half walk if you were going to go by foot.
By now, the incoming spring tide is well on its way, and the wind has picked up.
The first calls came into the Coast Guard from one of the lifeboat crew in Morecambe who had seen some lights out in the bay and realized that they shouldn't have been out there at that time with an incoming tide.
The Chinese immigrants are still hard at work, unaware that a wall of water is minutes away.
February 5, 2004.
23 Chinese immigrants are hard at work harvesting shellfish on the mudflats, unaware that a spring tide is racing toward them.
There was just no chance that night.
I knew how the tide would come in.
See, it comes up the river first, which was behind them.
They wouldn't be able to hear it.
It was blowing.
10 minutes later, the men and women are surrounded.
Worse, the deep channel they crossed earlier is now a raging torrent.
The fast, incoming tide had cut them off very, very quickly, and the route back to the shore that they'd taken to get out to the cockle beds would have changed with the incoming tide.
Funneled through the narrow opening of the bay, the massive tide is flooding the 120 square miles of shallow sandbanks with enormous force.
There can be something called a tidal bore.
The speed of the tide coming in depends on the depth of water.
So as the water rises, it will travel faster.
So the tide at the beginning edge of this wave gets slowed down while the tide behind catches up.
The water begins to pile up on itself, like snow pushed by a shovel.
The phenomenon can happen in both inlets and rivers.
One of the best known tidal bores occurs in the Qiantang River in China.
The Qiantang River has the perfect storm of the exact right geometry, the exact right tides, that it has a tidal bore that hurdles up the river.
Known to locals as the "Black Dragon," many have felt its bite and been swept away.
[People screaming.]
Morecambe Bay, February 5.
At first, the water was here, and then the water was here, and then the water was here.
You may not be aware of how quickly it's moving up.
And so once it gets up to here, you're done.
There were actually newspaper accounts of them desperately calling on their cell phones.
[Indistinct cell phone conversation.]
And the fear as the water was rising, higher and higher, literally 7 feet an hour.
Rescuers, some in hovercrafts, try frantically to reach them.
It was difficult because of the weather conditions.
Visibility was quite poor.
And a very confused state of affairs because the information was very scant.
So it was a difficult search and rescue to mount.
Some of the men and women try to swim the 4 miles to shore in the freezing water.
Hypothermia sets in very, very quickly.
The normal temperatures in February are around about 6 degrees for the sea temperatures.
Which only gives really around about an hour to two hours survivability at best.
We searched right through the night and never gave up hope.
Unfortunately, it was only when the tide started to recede that the bodies started to appear out on the cockle beds.
The tides of Morecambe Bay claim 23 victims that night, deaths that could have been prevented had the victims understood the lethal power of extreme tides.
I never slept a wink that night, thinking about it.
To date, we've managed to retrieve 22 of those 23 bodies.
The tide comes in so quickly in Morecambe Bay, it's always a hazardous area, and if you're out too long, then you're going to get yourselves in difficulty.
Extreme tides show little mercy to the unwary, but the threat they pose to humans is no match for the serial killer lurking off beaches around the world.
The Hawaiian Islands are home to some of the most beautiful-- and deadly--stretches of coastline in the world, none more so than on the northernmost island of Kauai.
Here, spectacular beaches mask some of the most dangerous rip currents in the world.
Number 3 in the underwater universe's most treacherous tides and currents: The rip currents of Kauai.
Rip currents are completely unpredictable.
You don't know when they're going to happen.
You don't know exactly where.
They seem to come out of nowhere.
A swimmer that is caught in a rip current at first may not even know that they're in one.
But then they'll start getting this feeling like, "hey, I'm moving," and look back towards the shore and start to panic.
Worse than any predator, they kill over 100 people in America each year.
By contrast, only 4 people die from shark attacks each year worldwide.
Rip currents occur when the receding flow of water from breaking waves is concentrated in one area.
What generates rip currents are waves coming and breaking on the shore.
It has to come back somehow.
And so if it's constantly redirected into a specific place, then you're going to get really, really strong rip currents.
The most important aspect of it is the shape of the sea floor.
The sea floor shape varies with hills and valleys.
And it's on these hills where the surf focuses.
And that creates a pileup.
And then gravity pulls that water towards the side where the valleys are located, and then out to sea.
Woody Peeples is an emergency room physician in Bend, Oregon.
Off duty, he shares a love of sports with his two boys, Jack, age 10, and Connor, age 12.
They're very adventurous.
They're a little crazy sometimes, but they've always been able to get themselves out of trouble in situations, and they've learned a lot over the years, being adventurous.
March 2010.
The family is vacationing on Kauai's Napali Coast.
My wife had to go back early.
So the boys and I were on our own for the last two days of the vacation.
The surf was huge that day, and so we chose not to go near the water.
Woody and his boys play it safe and set off on an 11-mile hike instead.
I have an adventurous streak as well, but I try to temper that with good judgment when things are not looking good.
A few hours into the hike, they reach Hanakapiai Beach.
I read all the signs coming in.
There's one sort of ghastly sign that recounts something like 80 deaths at this beach, warning not to go near the water.
It's very ominous.
What makes this location particularly dangerous is the fact that there's no offshore reefs.
So the waves release their full force right near the shore.
But the power of the waves isn't always obvious.
You have a sandy beach.
It's beautiful.
You want to go cool off.
There's no waves coming at that moment.
Let's go hit it.
And as soon as you get in, here comes the waves, and they travel fast.
And before you know it, you're swept out to sea.
We were a little bit tired from the hike.
We had our lunch.
The water looked reasonable near the shore, and I knew the boys were kind of wading in the water.
And the next thing I knew, somebody screamed, "is that your little son way out there?" I looked up, and I saw that he was probably 50 yards out.
Then my big son went in to try and get him.
In less than 20 seconds, Connor is also dragged away.
I quickly ran up the beach, and I dove in, and I went after them.
I couldn't come back without them.
Rip currents can move at up to 8 feet per second.
That's 5 1/2 miles per hour.
By contrast, the fastest swimmer in the world swims at just 4.
7 miles per hour.
They're excellent swimmers, but they were moving away from me.
Immediately, they disappeared around the corner to the left, and they were gone.
The third of the ocean's deadliest tides and currents are the rip currents of Hawaii's northernmost island of Kauia.
It didn't take very long for me to get caught in the rip as well.
As soon as my feet left the bottom, I was moving.
Emergency physician, Woody Peeples searches frantically for his two missing sons, swept out to sea moments before.
I was moving at a real good clip toward the corner of this cliff, and as soon as I came around the corner, as far as I could see, were waves the size of city buses coming down and smashing against these vertical cliffs.
Once they're pulled offshore, there most likely will be some long shore current, and they'll immediately be in front of these steep sea cliffs.
And the next beach access could be as much as 6 miles away.
If the waves come in at an angle, the water tends to start being pushed down the shoreline, down the coast in what we call long shore current.
Hawaii is known for its large waves, and large waves can bring even more water into shore and can create very strong long shore currents.
These long shore currents are now dragging Woody and his boys perilously close to the cliffs.
Miraculously, I looked and I could see Jack's head.
I started screaming as loud as I could.
I'm not sure whether he got pushed toward me a little, or whether I was able to swim faster than the rip, but within 5 minutes or so, I was able to reach him.
But father and son have yet to escape the grip of the current.
If you've ever been in a relatively fast-moving river, that's what it feels like.
You're standing on a treadmill and trying to walk against it.
That's like the current is flowing against you and you're trying to keep up with it.
Now, the object on the treadmill is to get tired.
You're trying to exercise.
But if this treadmill is going faster and faster and you don't think you can keep up with it, you're going to be swept right off the back, what do you do? You step off on the side.
Carefully, of course, but you step onto the side where it's not moving and you get out of the fast-moving tread.
That's what you have to do in a rip current, essentially.
The only way to do it is swim sideways, parallel to the shore.
Woody and Jack use what energy they have left swimming to the cliffs.
I tried to launch him as high as I could onto this rock face.
He grabbed a handhold, and I was able to push him up onto a tiny ledge.
Then I pulled myself up to where Jack was and immediately started searching to see if I could find Connor.
12-year-old Connor has been in the water some 20 minutes.
The weight of the swimmer shouldn't really matter.
I think the most important aspect is their endurance and also their mind.
Are they gonna panic? Because you can tread water for a long time, if you're calm.
Even novice swimmers that know the basics can tread water for at least 15 to 30 minutes.
Finally, Woody spots Connor clinging to a nearby rock.
And miraculously, there he was, probably 20-25 feet away from us, and I was able to shout to him.
He saw us up there.
I climb down and pull him over.
After 2 1/2 hours, rescuers arrive with a Zodiac and a helicopter and bring the family to safety.
As far as I'm concerned at this point, I could die.
I didn't care what happened to me.
I was just so glad my kids were safe.
His boys are exhausted from the ordeal.
It feels like a treadmill almost.
It feels like a river that's going really, really fast.
And like you're trying to swim forward but you're just going backward.
And even when it's shallow, you still can't do anything, like, it's still pulling you.
If there was panic, or if anybody had given up, we'd all be dead.
Absolutely.
Although rip currents pose a threat to individuals caught in their grip, there is one current so vast and powerful that should anything interrupt its flow, it could mean the end of almost all life on planet Earth.
It happened before, some 250 million years ago And some experts believe it could happen again.
The fourth and final tide or current that poses the biggest potential threat to mankind is the great ocean conveyor, the earth's most powerful current.
The global ocean conveyor belt, known by scientists as the thermohaline circulation, is a set of currents that actually carries warm water northward, near the surface, throughout the entire Atlantic Ocean.
It then sinks to great depth and spreads south, eventually touching all the ocean basins.
The great ocean conveyor acts as the planet's circulatory system.
The great ocean conveyer is crucial for life as we know it today because it brings heat from the equator up towards the poles.
It brings nutrients up from the depths up to the surface where they can be used.
It takes oxygen at the poles and brings it down and distributes it through all of the bottom of the ocean.
It was the same in prehistoric times.
250 million years ago, and the planet is heating up.
Back in the Permian times, all of the Continents were together in this supercontinent called Pangaea.
And really, the other side of the world was this super Pacific Ocean, if you like.
We call it Panthalassa.
It spans 3/4 of the Earth's surface.
Within Panthalassa, the Tethys Sea is a vast, shallow body of water almost surrounded by Pangaea.
The planet was teeming with life.
The oceans were teeming with life.
We had very large herbivores on land.
There were sharks, which probably reached up to 5 meters in length.
And thenThey all start to die.
Of course the $64 million question is what exactly happened.
Long before the age of dinosaurs, the biggest current on Earth--the great ocean conveyor--is about to trigger the world's most catastrophic mass extinction.
If you were snorkeling in the late Permian seas, you would have seen beautiful crystal-clear lagoons with beautiful fish and corals.
In the immediate aftermath, you'd have seen nothing.
You wouldn't have been able to see the hand in front of your face.
It begins not in the oceans, but on land.
250 million years ago, volcanoes in what is now Siberia start to blow and continue to blow for 700,000 years.
The eruptions that happened in Siberia were the largest in earth history.
An enormous amount of lava was extruded onto the Earth's surface, and with the lava comes gases.
One of those crucial gases that comes out of volcanoes is carbon dioxide.
And carbon dioxide, as we know, is a greenhouse gas.
Greenhouse gases act like insulation around the planet, trapping heat from the sun.
Soon, temperatures soar by as much as 54 degrees.
Eventually, of course, it will have an effect on the oceans.
Water temperature is a key factor in keeping the great ocean conveyor moving.
You've got currents near the equator that move from the equator to the poles.
Once they get to the poles, that water gets colder, and colder, and colder.
And cold water is denser than warm water, so that cold water sinks.
And then it goes back from the poles towards the equator.
And so, it's like a conveyer belt.
See what happened when you generate these two water masses.
One is a A simple experiment shows how differences in water density generates motion.
As you can see red dye is added on one side, an ice cube dyed blue on the other.
So now we're going to turn on the light that will simulate the sun at the equator heating up the surface water.
So, warming up this water here at the equator, and its generating this warm water that wants to ride on the surface all the way to the North Pole, where some ice is melting, and it's forming this dense, cold- water plume.
This cold, dense water will flow on the bottom of the ocean and return to the equator.
One other ingredient affects the density of seawater: Salt.
The saltier the water, the heavier it is.
Around the North Atlantic, when you have ice formation, all of the ice pushes out all of the salt.
And so that water there is both cold and really salty, and so it sinks very, very quickly.
The sinking water in the North Atlantic is what drives the circulation throughout the entire oceans.
250 million years ago, the excess carbon dioxide in the air heating up the Earth is also heating up the oceans.
The great ocean conveyor is the first casualty.
The great ocean conveyor belt is driven by cold, deep, dense water, and if the ocean is warmer, then less deep water would form.
The conveyor belt would be slowed up by this gradual warming.
Another reason is if the ice sheets are melting, flooding the ocean with some fresh water, that would also tend to slow up the conveyor belt.
Fresh water is less dense and so quickly dilutes the salty water at the poles and stops it from sinking.
The great ocean conveyor slows to a crawl.
The ocean conveyor transports more than just heat.
The ocean is very good at storing things like carbon, oxygen, other gases.
As temperature increases in the ocean, it can't hold on to as much of the gases.
So it can't hold onto carbon dioxide.
It can't hold on to oxygen.
With no oxygen, most marine life gives its last gasp and dies.
Fossil evidence paints a bleak picture.
Here we have the healthy ocean.
It's also relatively thick bedded.
Animals have churned through the sea floor looking for food particles.
So in contrast, this is your unhealthy ocean.
No animals have burrowed through the sediment.
So the rock types look very, very different.
When the great conveyor stops circulating the ocean's hot and cold water, the planet suffers drastic extremes of weather.
Pangea, the Earth's only continent, becomes unlivable.
It took only a few thousands of years or maybe 10,000 years for almost 90% of the species on the planet to become extinct.
It is the most severe extinction event in Earth's history.
[Thunder.]
And because it takes many more years for the volcanic activity to stop, it takes the planet a painfully long time to crawl back to life.
Best guess--that it took about 5 million years.
The great ocean conveyor once brought the world to its knees, simply by shutting down.
Now, the oceans are heating up again.
Could the future hold a similar fate? The oceans are gaining heat faster than any other part of the climate system, about 20 times faster than the land, atmosphere and ice parts of the system combined.
As more people burn fossil fuels, more greenhouse gases are being released into the atmosphere.
The heat added to the ocean in the past 18 years is equivalent to the energy released by 2 billion atomic bombs.
As the planet heats up, the overturning is likely to slow down.
It would be tough for the overturning to come to a screeching halt in say, 6 months.
But over the course of years or decades, we can definitely expect a change in the overturning circulation, as the planet heats up.
If the ocean conveyer belt stopped, that would make the poles much, much colder.
It would make around the equator much, much warmer.
So our climate would be very, very different.
Could the planet be headed toward another extinction event? Many, many paleontologists, geologists, scientists, zoologists think that we're in the middle of an extinction event now.
We're fooling around with a system we don't really know very well and with potential devastating effects.
If the ocean ever quit moving, life would end.
It's as simple as that.
It's a lot of power, and it's distributed over the whole world.
Caught in their grip, there can be no escape.
Here comes the waves, and they travel fast.
4 of the earth's most dangerous tides and currents.
Rip currents are completely unpredictable.
They seem to come out of nowhere.
But which poses the greatest threat to mankind? If the ocean ever quit moving, life would end.
It's as simple as that.
It happened before and could happen again.
Tides and currents of death in the underwater universe.
Underwater Universe 1x04 Tides and Currents of Death The Earth's oceans-- spanning 1/5 of the globe; vast, powerful, and deeper than the continents are tall.
When you look at the ocean, it looks like it's sitting still, but the fact is that the ocean is valuable to Earth because it moves things around.
The forces within the underwater universe that keep the ocean moving are its tides and currents.
Shaped by the pull of the moon and the spin of the Earth, they are the circulatory system of the planet.
It moves temperature around, it moves food around.
Without motion, the ocean won't work.
It has to keep moving to do what it has to do to generate life.
But as these powerful surges of water sustain life, they can also take it away.
The water in the ocean is 800 times denser than the air in the atmosphere.
Water weighs so much more than air does that the energy associated with the water is orders of magnitude larger.
If you have winds that go at 150 miles per hour, that is the same energy as water going at 6 miles per hour.
Getting in the way of that much force can be deadly to humans.
Of all the tides and currents in the underwater universe, 4 are the most dangerous to man, each more destructive than the last.
The final and most powerful has the greatest potential to kill.
It once triggered a mass extinction, wiping out 90% of all life on Earth.
Could it do it again? The first is the Gulf Stream, the most powerful current in the Atlantic.
When we talk about currents, all we are talking about is the horizontal movement of water.
Whereas tides are the vertical, up and down movement, currents are horizontal.
62 miles wide and up to 3,900 feet deep, the Gulf Stream transports warm water from the Gulf of Mexico to the North Atlantic.
The Gulf Stream starts near the equator.
So the Gulf Stream brings up warm water up along the North American coast and then moves into the middle of the Atlantic.
The winds that blow off of that bring that warmth over to Europe and cause Europe's climate to be much warmer than at the same latitude over in Canada.
This heated ocean river can play havoc with climate, navigation, and people's lives.
Fort Lauderdale, Florida.
Ernest Norman earns a living as an advertising salesman, but fishing is his passion.
In 1981, he and his friend John Ensinger are out fishing with another man, Alex Temes, on a borrowed 36-foot cruiser.
John, when he was going to the Bahamas, he invited me along, and I couldn't pass up that trip.
I didn't think twice I just went with him.
We were gonna spend 2 or 3 days over there.
John a qualified Captain, and Ernest has been fishing the waters around Florida his whole life, although neither has been as far as the Bahamas.
Neither one of us had done that trip.
With that nice boat, we figured it'd be a simple run across because it was only 55 miles off Fort Lauderdale.
All's we did is filled the tanks with gas, filled our coolers with ice, put in the bait, put in our tackle, some food and water, and headed for Bimini.
We didn't even check the ocean.
We thought it was flat calm.
But the Gulf Stream is unpredictable at best.
If you take a look at satellite data, you will frequently see clouds just forming right over the Gulf Stream itself.
It really is like a ribbon flowing through the ocean, interacting with the atmosphere over it, that create clouds, and then clouds create low-pressure systems, and you spin up storms.
It's a very potent weather maker.
Usually it's about 80 degree fahrenheit water, which will really help the storm get going.
Once you get to that temperature, the conditions are kind of set up such that the storm can really start to maximize.
9:30 p.
m.
Ernest, John, and Alex are halfway to Bimini when the winds begin to howl.
The seas were running anywhere from 6 top 10 feet, mixed with wind chop.
And that boat just started coming apart at the seams.
It wasn't even two minutes, we were flooded.
It was time to get out of that boat.
Ernest tosses two $25 rubber rafts, purchased on a whim just hours earlier, into the sea.
Then he and the others plunge in after them.
A minute and a half from that time, that boat was down.
And after it sunk, you could look down in the deep blue and the lights were all still on in the boat.
And all of a sudden, it blinked a couple times and went out and was gone.
The 3 men are now at the mercy of one of the fastest currents on the planet.
The Gulf Stream, bigger than all the Earth's rivers combined, is set in motion by winds blowing across the Atlantic.
Most of the currents in the ocean are driven by winds.
The wind has a force on it.
And it drags the surface of the ocean in one particular direction.
Though winds are its engine, the Earth's rotational force dictates the Gulf Stream's path.
So Earth is a spinning planet, the way our experiments are spinning.
The Earth is spinning much faster than the fluid moves on top of the Earth.
When you push a bit of fluid, the way we're pushing it out of a tube here, it bends to the right, turning into a circular motion.
So what we can see is the effect of the huge earth on the very small scale.
The influence of the Earth's spin on fluid is called the Coriolis force.
As the Gulf stream bends, it connects with another current to form a giant loop.
On this side, we have the Gulf Stream.
On this side, we have the Canary current.
The water in the North Atlantic is moving around in a great big circle that oceanographers call a gyre.
This gyre is actually smashed up against the U.
S.
East Coast, causing a very fast return flow to the North.
Currents tend to follow the shape of the sea floor and flow along it, just as a race car goes around a curve, tends to bank up against the edge of a racetrack.
The Gulf Stream banks against the eastern coast of the United States at a brisk 5 miles per hour--faster than a man can walk.
But that same current doubles in speed in the area where Ernest and his friends are now adrift.
Here, warm water from the Gulf of Mexico is funneled through the Florida Straits.
They're bounded on the North by Florida, and they're bounded on the South by Cuba.
And there's an extraordinary amount of water that has to go through the Florida Straits that then becomes the Gulf Stream.
And a way to think about that is that if we have a certain amount of water that's going through a hose and we constrict the area in which it can go, the velocities are going to become much, much larger for the same volume to go through that area.
The power of this rushing current is working against Ernest and his friends.
It is quickly, inexorably dragging them due north, away from land, away from rescue.
We were completely lost at sea.
4 of the oceans' most powerful tides and currents are potentially lethal to man.
The first is the Gulf Stream.
For Ernest Norman, John Ensinger, and Alex Temes, it's now their biggest enemy.
The 3 men are adrift off the coast of Florida in two $25 rubber rafts.
Ernest and John are crowded into one, Alex alone in the other.
We're going out with the Gulf Stream.
It's taking us further off shore.
We were probably off Hobe Sound.
There was no more lights.
So the only thing we could do was keep paddling and keep paddling.
Next day, the sun came up.
We figured, oh, boy, we're in bad shape.
In the Straits of Florida, the current is very strong.
So if you're in a small boat out there and in the stream, and something happens, you're gonna be carried northward up to 5 knots, quite fast.
Over 24 hours after their boat sinks, the 3 men have yet to be rescued.
Exhausted, confused, they argue about what to do.
"Alex," he says, "you're going the wrong way.
" And I said, "Alex, the wind is northeast.
Just follow the wind.
It'll take you to the beach.
" But following the wind means crossing a very powerful current.
The only other option is to let the Gulf Stream carry them north.
The question is, how far north? This broad stretch of the Gulf Stream continues uninterrupted until it hits North Carolina's Cape Hatteras.
That area is called the graveyard of the Atlantic.
It's an incredibly stormy region where you've got currents going all kinds of different directions, and so it's very hard for sailors to navigate through that area.
Two ocean rivers collide just off of Cape Hatteras: The Gulf Stream and the Labrador Current.
The Labrador Current, it's really, really cold.
It's right above freezing.
Now, when it meets the Gulf Stream, you have the really, really warm waters and the really, really cold waters.
Those two combine to create really stormy, really foggy, really rainy conditions.
In waters like these, flimsy rubber rafts won't stand a chance.
Finally, Alex Temes makes a decision.
He was in his life raft by himself, and he started paddling due north.
And I said to John, "well, that's his problem.
Can't do anything about it.
" So me and John kept paddling.
Paddled all that day.
Ernest and John are paddling across a current packing as much force as winds blowing 125 miles per hour.
To paddle on a raft 60 miles in calm ocean, where there's no waves, where there's no currents, is an extraordinary feat.
I mean, that's like running a couple of marathons.
Now, add on to that, you have a current that is pushing you towards the north.
I really can't think of anything that would compare to that.
We were dehydrated and tired and hallucinating, and I didn't think I was ever going to make it in.
I thought it was, this was it.
Then, at midnight on day 3, they spot something on the horizon: Land.
I crawled up on the beach, and I was never so happy in my life.
If it wasn't for that northeast wind, we would have probably got stuck in that Gulf Stream and it would have kept us out there because it kept just pulling you north, pulling you north.
It takes the third man, Alex Temes, another 36 hours and 101 miles to make landfall further north.
The 3 men barely escape the grip of the Gulf Stream, but not all are so lucky.
The Gulf Stream claims a dozen victims over the course of a year.
But the next contender has claimed dozens in one day.
The second of the deadliest tides and currents in the underwater universe are extreme tides, specifically the notorious Tides of Morecambe Bay on the northwest coast of England.
The tide range is about 30 feet, and when the tide pulls back, 120 square miles of mudflats are now revealed, and the shoreline pulls back 7 miles.
It is the largest expanse of intertidal mudflats and sand in the U.
K.
And a tempting stroll for visitorsUntil the tide turns.
Due to the nature of the bay and the gullies and the channels, the water can come in behind you.
So for the unwary, they're thinking the tide is still well away from them.
But actually what happens is that the gullies fill in from behind you and cut you off.
The bay is an ever-shifting maze of gullies and channels carved into quicksand, and an incoming tide races back with such force that few can escape it.
People don't realize, if the tides are running high, it comes in at the speed of a galloping horse.
You cannot swim when it comes in.
You cannot swim.
The tide is too fast, and it isn't just clear water.
It's like sand and mud, moving sand all the time, see? With each tidal cycle, 107 billion cubic feet of water floods the bay at 10 miles per hour.
Standing in the way of an incoming tide is the equivalent of being struck by winds blowing 250 miles per hour.
It comes in so quickly, it can encompass you and drown you.
You can be over your head in literally no time.
Though Morecambe Bay's powerful tides are part of the arsenal of the underwater universe's deadly forces, they are born in the heavens.
Tides are generated by a balance between two forces.
There's the gravitational force of the Moon or the Sun, and then there's the centrifugal force of the fact that the Earth and the Moon are rotating around their center of gravity.
Now, these two forces generate a bump of water between the Earth and the Moon and a bump of water on the other side of the Earth.
Now, the Earth turns underneath this bump of water.
And as the Earth gets right underneath the bump of water, you get high tides, and as you get far away from it, you get low tides.
So it may be a bit counterintuitive that the Earth bulges out both toward the Moon and away from the Moon, and so as the Earth rotates in one 24-hour period, a given point on Earth will go through two high tides and two low tides in general, not just one.
Because the time it takes for two tidal cycles to complete is usually a bit longer than 24 hours, the time for high and low tide changes each day.
However, the cycle is completely predictable.
We've known exactly how the Moon orbits the Earth for quite a long time.
So when you say tides are predictable, they're as predictable as the sun coming up the next day.
Yet over the centuries, visitors to Morecambe Bay have ignored the power of the tides and paid with their lives.
In response, royal guides are appointed to escort travelers across the bay.
Without knowing the tide times, you must never leave the safety of the shore without going with someone that has local knowledge.
I would never, ever go out in that bay without writing the tide times on my hand, because there are so many people, what time does the tide come in? That's reassuring to them.
But even today, not all visitors know to use a guide.
February 5, 2004.
The temperature was round about 6 degrees.
The wind speed was 20 to 25 miles an hour.
Quite foreboding.
Even more ominous, the Moon is almost full.
A Spring high tide is scheduled for that evening.
The Sun's tides on Earth reinforce the Moon's tides on Earth.
Now, when the Moon is in this position, roughly in a straight line with the Earth and the Sun, you get a Spring tide because the Sun's tidal effect adds to the Moon's tidal effect.
You have extreme tides, high high tides, low low tides, so those are called Spring tides.
23 Chinese immigrants, men and women, take to the sands, getting ready for a profitable night's work.
These Chinese immigrants were out there on the mudflats digging up cockles, which is a delicacy in terms of shellfish that can bring in a lot of money.
The money in this case will go to a gang leader.
The workers have little choice.
Many are here illegally.
And most of them weren't fishermen.
They were just, you know, out to make as much money as they could.
For 6 hours, well past nightfall, the immigrants work a cockle bed some distance from shore.
The cockle beds that were producing at that time were around about 3 or 4 miles out into the bay, which is a good hour's, hour and a half walk if you were going to go by foot.
By now, the incoming spring tide is well on its way, and the wind has picked up.
The first calls came into the Coast Guard from one of the lifeboat crew in Morecambe who had seen some lights out in the bay and realized that they shouldn't have been out there at that time with an incoming tide.
The Chinese immigrants are still hard at work, unaware that a wall of water is minutes away.
February 5, 2004.
23 Chinese immigrants are hard at work harvesting shellfish on the mudflats, unaware that a spring tide is racing toward them.
There was just no chance that night.
I knew how the tide would come in.
See, it comes up the river first, which was behind them.
They wouldn't be able to hear it.
It was blowing.
10 minutes later, the men and women are surrounded.
Worse, the deep channel they crossed earlier is now a raging torrent.
The fast, incoming tide had cut them off very, very quickly, and the route back to the shore that they'd taken to get out to the cockle beds would have changed with the incoming tide.
Funneled through the narrow opening of the bay, the massive tide is flooding the 120 square miles of shallow sandbanks with enormous force.
There can be something called a tidal bore.
The speed of the tide coming in depends on the depth of water.
So as the water rises, it will travel faster.
So the tide at the beginning edge of this wave gets slowed down while the tide behind catches up.
The water begins to pile up on itself, like snow pushed by a shovel.
The phenomenon can happen in both inlets and rivers.
One of the best known tidal bores occurs in the Qiantang River in China.
The Qiantang River has the perfect storm of the exact right geometry, the exact right tides, that it has a tidal bore that hurdles up the river.
Known to locals as the "Black Dragon," many have felt its bite and been swept away.
[People screaming.]
Morecambe Bay, February 5.
At first, the water was here, and then the water was here, and then the water was here.
You may not be aware of how quickly it's moving up.
And so once it gets up to here, you're done.
There were actually newspaper accounts of them desperately calling on their cell phones.
[Indistinct cell phone conversation.]
And the fear as the water was rising, higher and higher, literally 7 feet an hour.
Rescuers, some in hovercrafts, try frantically to reach them.
It was difficult because of the weather conditions.
Visibility was quite poor.
And a very confused state of affairs because the information was very scant.
So it was a difficult search and rescue to mount.
Some of the men and women try to swim the 4 miles to shore in the freezing water.
Hypothermia sets in very, very quickly.
The normal temperatures in February are around about 6 degrees for the sea temperatures.
Which only gives really around about an hour to two hours survivability at best.
We searched right through the night and never gave up hope.
Unfortunately, it was only when the tide started to recede that the bodies started to appear out on the cockle beds.
The tides of Morecambe Bay claim 23 victims that night, deaths that could have been prevented had the victims understood the lethal power of extreme tides.
I never slept a wink that night, thinking about it.
To date, we've managed to retrieve 22 of those 23 bodies.
The tide comes in so quickly in Morecambe Bay, it's always a hazardous area, and if you're out too long, then you're going to get yourselves in difficulty.
Extreme tides show little mercy to the unwary, but the threat they pose to humans is no match for the serial killer lurking off beaches around the world.
The Hawaiian Islands are home to some of the most beautiful-- and deadly--stretches of coastline in the world, none more so than on the northernmost island of Kauai.
Here, spectacular beaches mask some of the most dangerous rip currents in the world.
Number 3 in the underwater universe's most treacherous tides and currents: The rip currents of Kauai.
Rip currents are completely unpredictable.
You don't know when they're going to happen.
You don't know exactly where.
They seem to come out of nowhere.
A swimmer that is caught in a rip current at first may not even know that they're in one.
But then they'll start getting this feeling like, "hey, I'm moving," and look back towards the shore and start to panic.
Worse than any predator, they kill over 100 people in America each year.
By contrast, only 4 people die from shark attacks each year worldwide.
Rip currents occur when the receding flow of water from breaking waves is concentrated in one area.
What generates rip currents are waves coming and breaking on the shore.
It has to come back somehow.
And so if it's constantly redirected into a specific place, then you're going to get really, really strong rip currents.
The most important aspect of it is the shape of the sea floor.
The sea floor shape varies with hills and valleys.
And it's on these hills where the surf focuses.
And that creates a pileup.
And then gravity pulls that water towards the side where the valleys are located, and then out to sea.
Woody Peeples is an emergency room physician in Bend, Oregon.
Off duty, he shares a love of sports with his two boys, Jack, age 10, and Connor, age 12.
They're very adventurous.
They're a little crazy sometimes, but they've always been able to get themselves out of trouble in situations, and they've learned a lot over the years, being adventurous.
March 2010.
The family is vacationing on Kauai's Napali Coast.
My wife had to go back early.
So the boys and I were on our own for the last two days of the vacation.
The surf was huge that day, and so we chose not to go near the water.
Woody and his boys play it safe and set off on an 11-mile hike instead.
I have an adventurous streak as well, but I try to temper that with good judgment when things are not looking good.
A few hours into the hike, they reach Hanakapiai Beach.
I read all the signs coming in.
There's one sort of ghastly sign that recounts something like 80 deaths at this beach, warning not to go near the water.
It's very ominous.
What makes this location particularly dangerous is the fact that there's no offshore reefs.
So the waves release their full force right near the shore.
But the power of the waves isn't always obvious.
You have a sandy beach.
It's beautiful.
You want to go cool off.
There's no waves coming at that moment.
Let's go hit it.
And as soon as you get in, here comes the waves, and they travel fast.
And before you know it, you're swept out to sea.
We were a little bit tired from the hike.
We had our lunch.
The water looked reasonable near the shore, and I knew the boys were kind of wading in the water.
And the next thing I knew, somebody screamed, "is that your little son way out there?" I looked up, and I saw that he was probably 50 yards out.
Then my big son went in to try and get him.
In less than 20 seconds, Connor is also dragged away.
I quickly ran up the beach, and I dove in, and I went after them.
I couldn't come back without them.
Rip currents can move at up to 8 feet per second.
That's 5 1/2 miles per hour.
By contrast, the fastest swimmer in the world swims at just 4.
7 miles per hour.
They're excellent swimmers, but they were moving away from me.
Immediately, they disappeared around the corner to the left, and they were gone.
The third of the ocean's deadliest tides and currents are the rip currents of Hawaii's northernmost island of Kauia.
It didn't take very long for me to get caught in the rip as well.
As soon as my feet left the bottom, I was moving.
Emergency physician, Woody Peeples searches frantically for his two missing sons, swept out to sea moments before.
I was moving at a real good clip toward the corner of this cliff, and as soon as I came around the corner, as far as I could see, were waves the size of city buses coming down and smashing against these vertical cliffs.
Once they're pulled offshore, there most likely will be some long shore current, and they'll immediately be in front of these steep sea cliffs.
And the next beach access could be as much as 6 miles away.
If the waves come in at an angle, the water tends to start being pushed down the shoreline, down the coast in what we call long shore current.
Hawaii is known for its large waves, and large waves can bring even more water into shore and can create very strong long shore currents.
These long shore currents are now dragging Woody and his boys perilously close to the cliffs.
Miraculously, I looked and I could see Jack's head.
I started screaming as loud as I could.
I'm not sure whether he got pushed toward me a little, or whether I was able to swim faster than the rip, but within 5 minutes or so, I was able to reach him.
But father and son have yet to escape the grip of the current.
If you've ever been in a relatively fast-moving river, that's what it feels like.
You're standing on a treadmill and trying to walk against it.
That's like the current is flowing against you and you're trying to keep up with it.
Now, the object on the treadmill is to get tired.
You're trying to exercise.
But if this treadmill is going faster and faster and you don't think you can keep up with it, you're going to be swept right off the back, what do you do? You step off on the side.
Carefully, of course, but you step onto the side where it's not moving and you get out of the fast-moving tread.
That's what you have to do in a rip current, essentially.
The only way to do it is swim sideways, parallel to the shore.
Woody and Jack use what energy they have left swimming to the cliffs.
I tried to launch him as high as I could onto this rock face.
He grabbed a handhold, and I was able to push him up onto a tiny ledge.
Then I pulled myself up to where Jack was and immediately started searching to see if I could find Connor.
12-year-old Connor has been in the water some 20 minutes.
The weight of the swimmer shouldn't really matter.
I think the most important aspect is their endurance and also their mind.
Are they gonna panic? Because you can tread water for a long time, if you're calm.
Even novice swimmers that know the basics can tread water for at least 15 to 30 minutes.
Finally, Woody spots Connor clinging to a nearby rock.
And miraculously, there he was, probably 20-25 feet away from us, and I was able to shout to him.
He saw us up there.
I climb down and pull him over.
After 2 1/2 hours, rescuers arrive with a Zodiac and a helicopter and bring the family to safety.
As far as I'm concerned at this point, I could die.
I didn't care what happened to me.
I was just so glad my kids were safe.
His boys are exhausted from the ordeal.
It feels like a treadmill almost.
It feels like a river that's going really, really fast.
And like you're trying to swim forward but you're just going backward.
And even when it's shallow, you still can't do anything, like, it's still pulling you.
If there was panic, or if anybody had given up, we'd all be dead.
Absolutely.
Although rip currents pose a threat to individuals caught in their grip, there is one current so vast and powerful that should anything interrupt its flow, it could mean the end of almost all life on planet Earth.
It happened before, some 250 million years ago And some experts believe it could happen again.
The fourth and final tide or current that poses the biggest potential threat to mankind is the great ocean conveyor, the earth's most powerful current.
The global ocean conveyor belt, known by scientists as the thermohaline circulation, is a set of currents that actually carries warm water northward, near the surface, throughout the entire Atlantic Ocean.
It then sinks to great depth and spreads south, eventually touching all the ocean basins.
The great ocean conveyor acts as the planet's circulatory system.
The great ocean conveyer is crucial for life as we know it today because it brings heat from the equator up towards the poles.
It brings nutrients up from the depths up to the surface where they can be used.
It takes oxygen at the poles and brings it down and distributes it through all of the bottom of the ocean.
It was the same in prehistoric times.
250 million years ago, and the planet is heating up.
Back in the Permian times, all of the Continents were together in this supercontinent called Pangaea.
And really, the other side of the world was this super Pacific Ocean, if you like.
We call it Panthalassa.
It spans 3/4 of the Earth's surface.
Within Panthalassa, the Tethys Sea is a vast, shallow body of water almost surrounded by Pangaea.
The planet was teeming with life.
The oceans were teeming with life.
We had very large herbivores on land.
There were sharks, which probably reached up to 5 meters in length.
And thenThey all start to die.
Of course the $64 million question is what exactly happened.
Long before the age of dinosaurs, the biggest current on Earth--the great ocean conveyor--is about to trigger the world's most catastrophic mass extinction.
If you were snorkeling in the late Permian seas, you would have seen beautiful crystal-clear lagoons with beautiful fish and corals.
In the immediate aftermath, you'd have seen nothing.
You wouldn't have been able to see the hand in front of your face.
It begins not in the oceans, but on land.
250 million years ago, volcanoes in what is now Siberia start to blow and continue to blow for 700,000 years.
The eruptions that happened in Siberia were the largest in earth history.
An enormous amount of lava was extruded onto the Earth's surface, and with the lava comes gases.
One of those crucial gases that comes out of volcanoes is carbon dioxide.
And carbon dioxide, as we know, is a greenhouse gas.
Greenhouse gases act like insulation around the planet, trapping heat from the sun.
Soon, temperatures soar by as much as 54 degrees.
Eventually, of course, it will have an effect on the oceans.
Water temperature is a key factor in keeping the great ocean conveyor moving.
You've got currents near the equator that move from the equator to the poles.
Once they get to the poles, that water gets colder, and colder, and colder.
And cold water is denser than warm water, so that cold water sinks.
And then it goes back from the poles towards the equator.
And so, it's like a conveyer belt.
See what happened when you generate these two water masses.
One is a A simple experiment shows how differences in water density generates motion.
As you can see red dye is added on one side, an ice cube dyed blue on the other.
So now we're going to turn on the light that will simulate the sun at the equator heating up the surface water.
So, warming up this water here at the equator, and its generating this warm water that wants to ride on the surface all the way to the North Pole, where some ice is melting, and it's forming this dense, cold- water plume.
This cold, dense water will flow on the bottom of the ocean and return to the equator.
One other ingredient affects the density of seawater: Salt.
The saltier the water, the heavier it is.
Around the North Atlantic, when you have ice formation, all of the ice pushes out all of the salt.
And so that water there is both cold and really salty, and so it sinks very, very quickly.
The sinking water in the North Atlantic is what drives the circulation throughout the entire oceans.
250 million years ago, the excess carbon dioxide in the air heating up the Earth is also heating up the oceans.
The great ocean conveyor is the first casualty.
The great ocean conveyor belt is driven by cold, deep, dense water, and if the ocean is warmer, then less deep water would form.
The conveyor belt would be slowed up by this gradual warming.
Another reason is if the ice sheets are melting, flooding the ocean with some fresh water, that would also tend to slow up the conveyor belt.
Fresh water is less dense and so quickly dilutes the salty water at the poles and stops it from sinking.
The great ocean conveyor slows to a crawl.
The ocean conveyor transports more than just heat.
The ocean is very good at storing things like carbon, oxygen, other gases.
As temperature increases in the ocean, it can't hold on to as much of the gases.
So it can't hold onto carbon dioxide.
It can't hold on to oxygen.
With no oxygen, most marine life gives its last gasp and dies.
Fossil evidence paints a bleak picture.
Here we have the healthy ocean.
It's also relatively thick bedded.
Animals have churned through the sea floor looking for food particles.
So in contrast, this is your unhealthy ocean.
No animals have burrowed through the sediment.
So the rock types look very, very different.
When the great conveyor stops circulating the ocean's hot and cold water, the planet suffers drastic extremes of weather.
Pangea, the Earth's only continent, becomes unlivable.
It took only a few thousands of years or maybe 10,000 years for almost 90% of the species on the planet to become extinct.
It is the most severe extinction event in Earth's history.
[Thunder.]
And because it takes many more years for the volcanic activity to stop, it takes the planet a painfully long time to crawl back to life.
Best guess--that it took about 5 million years.
The great ocean conveyor once brought the world to its knees, simply by shutting down.
Now, the oceans are heating up again.
Could the future hold a similar fate? The oceans are gaining heat faster than any other part of the climate system, about 20 times faster than the land, atmosphere and ice parts of the system combined.
As more people burn fossil fuels, more greenhouse gases are being released into the atmosphere.
The heat added to the ocean in the past 18 years is equivalent to the energy released by 2 billion atomic bombs.
As the planet heats up, the overturning is likely to slow down.
It would be tough for the overturning to come to a screeching halt in say, 6 months.
But over the course of years or decades, we can definitely expect a change in the overturning circulation, as the planet heats up.
If the ocean conveyer belt stopped, that would make the poles much, much colder.
It would make around the equator much, much warmer.
So our climate would be very, very different.
Could the planet be headed toward another extinction event? Many, many paleontologists, geologists, scientists, zoologists think that we're in the middle of an extinction event now.
We're fooling around with a system we don't really know very well and with potential devastating effects.
If the ocean ever quit moving, life would end.
It's as simple as that.