The Secret Life of Ice

Ice is one of the most mesmerising and beguiling substances in the world.

It's very familiar and yet never ceases to be other-worldly.

Always a little bit strange.

Ice is full of contradictions.

It's transparent

but it can glow with colour like nothing on earth.

It's powerful enough to shatter rock and sink ships.

But can just melt away in the blink of an eye.

I'm Dr Gabrielle Walker.

I trained as a chemist, but now I'm a science writer.

And for a long time, I've been obsessed by ice.

Ever since I first set foot on Arctic sea ice,

I've been drawn back year after year.

I've been trying to discover the secrets hidden deep within ice.

I think the ice crystal has something extraordinary to reveal

about how the world works.

How it does that

and what it tells us is what I want to explore in this programme.

-This is it.

-Wow!

-Welcome to Nigarsbreen.

-It's magnificent!

I'm going to find out how something so ephemeral is powerful enough to carve solid rock.

How ice has led to the evolution of some of the most extraordinary creatures on our planet.

This is a really small one.

How ice in space might lead us to discover extra-terrestrial life.

If we've got an ocean underneath the surface of the moon,

that's a place to search for life.

And how its astonishing ability to store ancient atmospheres

is helping us understand our climate.

When they invaded Britain in 1066, this is the air they were breathing!

Do your worst!

And I reveal how its power to preserve our past

and inform our future

lies deep within the ice crystal.

First of all, I've come to southern Norway...

..to visit an enormous glacier called Jostedalsbreen.

It's the biggest piece of ice in continental Europe.

It covers nearly 500 square kilometres of mountain.

Glaciers are one of the most powerful forces in nature.

They turn fragile ice into enormous grinding machines

that can erode mountains.

I'm going to explore one of Jostedalsbreen's many glacial tongues, Nigardsbreen.

I'm meeting local glaciologist, Evan Lowe.

Hello, Evan!

-Hello. Welcome to Jostedalsbreen.

-Thank you.

Gosh, it's gorgeous!

We have a kayak to take us across the lake.

I want to find out exactly what makes glaciers so powerful.

How something as malleable as ice

can carve out such a spectacular landscape.

From the sculpted walls of the valley

to the colour of the lake.

-And full speed onto land.

-Full speed.

Even though it's just ten per cent of the Jostedalsbreen's glacier,

Nigardsbreen covers nearly 50 square kilometres of mountain.

It rises steeply to almost two kilometres above sea level.

Down here in the valley, where the temperatures are warmer than in the high mountains,

the glacier melts abruptly in a ragged wall.

It's only when you get this much ice that you can witness something spectacular.

-This is it!

-Wow!

'Its full range of colours.'

It's magnificent! The blue colour is absolutely amazing.

It's like looking into the heart of the glacier.

Yes, it goes from completely white and all the way to very dark blue,

depending on how the light hits the surface

and how far into the ice the light penetrates

before it's reflected to us.

The surface of the glacier looks white

because its jagged crystals are deflecting sunlight in all directions.

Close up, the ice seems transparent.

But it's not.

Pure ice crystals absorb light at the red end of the spectrum.

So as sunlight travels deeper into the ice,

a new blue light is reflected back.

When it's in a huge chunk like a glacier, it looks blue.

But if you grab a chunk of it, it's just white, ordinary boring ice!

Ice is never boring. Never, ever!

The ice in this front wall is at the end of its journey down the mountain.

It's now at the point of melting away.

Every moment it's changing,

like a moving sculpture.

Melt water is raining down on me

and it's making the most amazing shapes.

You can see it's eating into the walls here

and making all these curves and round parts

and that's why it looks like the moon outside with all those incredible curves.

It's beautiful.

Although glacial ice is a solid,

it actually flows like a river.

It's incredible to think that this much ice

is constantly on the move.

I've been climbing up to see what drives the glacier.

And it's the phenomenal weight of this enormous ice pack,

over nine kilometres long,

and up to 500 metres deep.

Millions of tonnes of ice crammed into this valley.

Built up from layer upon layer of snow,

this monumental river of ice is constantly being topped up

by fresh snowfall.

And that keeps it flowing downhill.

It makes very slow progress. But there is a way to see it move.

A time-lapse camera shows that Nigardsbreen's surface ice

travels at around 275 metres per year,

carving away the rock as it goes.

When you're here, the only clues you see of the glacier's movement

are crevasses.

Deep gashes that split open the surface of the ice.

These open up at the top of the ice.

One of the reasons is the top of the ice is brittle and tough.

Further down, where it's been squeezed, it's plastic and soft.

But as the glacier moves, the brittle part breaks open

and creates these great crevasses.

When a crevasse has opened up in the ice, melt water can gather in it

and start hollowing its way down towards the bedrock.

Here, it carves out a hidden world of icy caverns deep within the glacier.

I'm going to try to abseil right into the heart of the glacier

to see for myself how it moves.

That was amazing!

We're in the engine room of the glacier.

You can see just down here right where the ice melts the ground.

And this is where everything important happens.

I'm getting wet with the melting water,

but it's that that helps the glacier slide on its belly,

one of the things that makes it so dynamic.

Nigardsbreen's temperate mountain climate

means the ice at the lower end of the glacier exists very close to melting point.

As well as the melt water flowing beneath the ice,

which helps lubricate the glacier on its journey down the mountain,

there's melt water within the ice itself,

seeping out of these walls.

That melting water also makes this cave, and other caves like it all around.

I bet this cave wasn't here last year and it probably won't be here next.

It's transient, part of the signs that the glacier is dynamic

and moving and changing all the time.

When you look at the slick blue ice in these caves,

it's hard to imagine it began its life as snowflakes.

But hundreds of years of compression

have gradually turned it into this glittering mass of ice crystals.

Look at that!

The sides of the ice here are just like they were in the cave.

They really look like solid squashed together lumps and cubes.

And here you can really see that.

Like someone's taken a bunch of cubes and squeezed them together.

And that's what I'm walking on. Like walking on a giant Slushie!

Every single one of these ice crystals has an unusual property.

If you throw them into water, they float.

That's something we take completely for granted.

But it's incredibly rare in nature.

It's what helps to make ice special.

And what gives it the power to transform our world.

The secret lies at the heart of the ice crystal.

I'm going to witness the very instant it forms,

with chemist and fellow ice enthusiast, Dr Andrea Sella.

Ice breaks all the rules that we learn.

Andrea believes this moment is key to understanding the mysterious world of the ice crystal

because of the curious way that water turns from liquid to solid ice.

Let me show you something really amazing.

We've got some mineral water here that we've been cooling for a bit.

I want you to take these bottles quite gingerly.

-Take this and bang it on the table.

-Just bang it?

-Bang it.

-There it goes! Look at that!

-Instant ice!

It's spreading out these fingers and shards of ice all the way down.

It's quite amazing. You can see the crystals growing before your very eyes!

Ice is a crystal in which the water molecules are very carefully arranged.

If you think of guards on parade,

all lined up in neat rows, that's what a crystal is, and that's what ice is.

Like any crystal, ice doesn't form spontaneously,

even in this super-cooled water,

which is well below zero degrees centigrade.

It needs a seed, a template.

You need someone to kind of blow the whistle

and provide an initial point, saying start here.

-So I bang it, you get bubbles and each of those bubbles is a place for the crystals to form.

-Absolutely.

You can do it in other ways, too.

Take another bottle, and this time what we'll do

is try dropping another piece of ice into it.

Just pop it in.

Ready, steady...

It's really the ice which is acting as the initial starting point

on which the rest of the ice grows.

It's the way the ice crystal forms that is the key to why it floats.

Water molecules are loosely held together by bonds

which are constantly making and breaking.

When the temperature drops to zero,

these bonds begin to hold. Fast.

Creating a hexagonal lattice, an ice crystal.

In the lattice, the bonds hold the molecules far apart.

It's that sudden opening out

that makes ice lighter, less dense, than liquid water.

In water, the approaches are quite close.

When we get to ice, suddenly it expands a bit.

And we end up with a strangely spacious open structure

which is less dense and therefore it floats.

It's really quite miraculous.

-That's all down to the structure of the crystal?

-Absolutely.

Ice is incredibly special.

The irony is that to us it's completely common.

We take an ice cube and drop it into a drink and it floats.

Well, it is almost unique

in the enormous, the millions of compounds and materials that we know about,

in being a solid that floats on its melt.

If ice didn't float, the world would be a very different place.

Instead of forming on the surface of the ocean,

allowing marine life to survive beneath,

ice would form on the sea bed,

oceans would freeze from the bottom up

and life as we know it might never have evolved at all.

We also wouldn't have developed an elegant British pastime

that began on frozen lakes and rivers hundreds of years ago.

Every Sunday morning, members of the Royal Skating Club

meet at Guildford ice rink to skate in what is called "the English style".

Once considered England's highest form of skating art,

"the English style" originates from the early 19th century.

It combines a Victorian sense of elegance and understatement

with a high level of skill.

Around a centre marked by an orange,

the skaters perform perfectly-shaped geometric figures

in absolute unison, holding their bodies stiff and straight.

Centre change, sub circle.

In keeping with the Victorian horror of showing off,

the challenge is to make these complex manoeuvres look graceful

and effortless.

These are lovely.

Elaine Hooper, historian for the National Ice Skating Association,

has some Victorian pictures of the English Style.

It was very much a more polite style of skating. It was very dignified.

The ladies had long dresses and big hats on and the men had top hats in Victorian times.

That was the style of skating

that evolved on the frozen lakes and rivers

as early as the 1600s.

Over the years, different moves were added when people wanted to make it more difficult.

The English Style developed amongst the upper classes

while Britain was experiencing what became known as "the little ice age".

From the 13th century to the middle of the 19th century,

British winters were up to two degrees cooler.

Many lakes and rivers regularly froze over.

Pepys himself talks about skating with Nell Gwyn on the Thames

in one of the great frost fairs where they would roast hogs and skate.

It was just a way of life then. It was much colder.

The Thames doesn't tend to freeze over now so we can't have that again.

We can skate because of another quality of ice.

Its slipperiness.

This may seem completely normal, but it's actually very rare for a solid.

The reason we can skate is to do with what happens when ice is squeezed by a blade.

The way it reacts to pressure.

So Andrea Sella and I are going to put ice under a lot of pressure

in a classic experiment.

OK, we need to lift it up and get it onto our platform.

-It is pretty heavy.

-I'm strong, don't worry!

Good. There we are.

So now we need to unpack things.

-Ooh, that's lovely!

-Gorgeous!

I'll lift it and you pull.

That's great.

What we're going to do is sling this wire over the top

and hang these two really rather heavy weights,

we're talking about seven kilos here.

There we go.

It's now suspended.

What we have to do is wait for the pressure of the wire

to work its magic on the ice.

As we wait, the wire works its way through the ice.

Almost cutting it in two.

And behind the wire, the ice is sealing up again.

Something very strange is going on.

It's amazing. Look at it!

So how's it gone through the ice like this?

Of course, the wire has the weight on it. And because the wire's very thin,

what it does is apply really quite a large pressure

on a local area of the ice.

We know that ice expands when it freezes

so if you squeeze it, you can drive it back towards that molten state.

So when you put pressure on it, it turns it back to water.

You can re-melt it back to water.

That's one of the key reasons we can skate.

The pressure of the blades is enough to melt the top layer of ice into water

which lubricates the skates.

Friction can also help melt the ice.

In our experiment, as the wire passed through the block,

the ice sealed up behind.

This shows how ice can engulf something solid

leaving barely a trace.

I was expecting the wire to cut through it. And it's completely sealed.

-It looks as though it ought to fall apart.

-It's an extraordinary process.

Effectively, underneath the wire, the ice melts

and then behind it, it re-freezes again.

So this whole process is making the ice

move between those two points on that knife-edge between liquid and solid.

The pressure squeezes it,

-take the pressure off and it freezes again.

-Absolutely.

This formidable ability to swallow up another solid

is a real insight into just how peculiar ice is.

It also explains how ice can do seemingly impossible things

in nature.

In Norway, at the foot of Nigardsbreen,

glaciologist Evan Lowe has some local stories to tell

of how glaciers can engulf things much bigger than a thin metal wire.

From where we're sitting now we can see a place where a farm used to be, 250 years ago.

Until it was knocked down by this glacier behind us

and all the buildings and farm were just swallowed by the glacier.

If something goes into the ice, what happens to it?

A bit further south, there's a plane with a pilot who crashed in the '70s

on top of the glacier.

Before the rescuers could get there, the whole thing was covered by snow.

And it never appeared again.

Some guy calculated that it should come out of the glacier

some 25 years later, but they're still waiting for it.

-No-one's seen any trace of it.

-So there's a plane, body and everything.

Somewhere!

That's a spooky ghost story to tell just before bed!

When it comes to a glacier shaping the landscape,

this ability of ice to absorb things

is a real secret to its strength.

Ice on its own is far too fragile to leave any mark on solid rock.

It can only carve out a valley by picking up tools.

The ice engulfs rocks and boulders as it moves down the mountainside.

They pass through the ice and get dragged along in its underbelly.

Together they scrape and chip away at the rock beneath.

It's easy to imagine that this was once just one big mountain.

And now all this space that we are in now

is the result of the glacier

taking its bites like this during thousands of years.

I like the way you say, "taking bites". The rocks are the teeth of the glacier

and that's what it's using to grind away.

It's still doing it up there, making the valley bigger and wider.

If it were some other solid like steel or rock,

it would just sit there. It couldn't do this.

That's one of the secrets of the ice

that it's strong enough to carry big rocks to work on the surface

but it's also soft enough to move.

Over the thousands of years that Nigardsbreen has been advancing and retreating,

it's been grinding down the rock

like an enormous sheet of sand paper.

Gradually, it's turned boulders and bedrock into dust so fine

that when it's washed into the lake,

it remains suspended there.

And it's the minerals in this dust

that give the lake its colour.

So that piece of ice there has done everything.

It's shaped and smoothed these rocks

and it's made these scrape marks and teeth marks

and down there, the bigger boulders and the pebbles and the silt

all the way through to the colour of the lake,

even the shape of the valley,

everything about everything I see has been dictated and defined by the ice.

But ice itself is ruled by temperature.

That's what determines everything from how long it lasts

to how and where it forms.

And nowhere is this more true than in the sky,

where ice is at its most unpredictable.

Clouds are usually made of water vapour.

But if it's cold enough, you can get clouds entirely made of ice crystals.

When you get ice in the sky, that can cause havoc with the weather.

One of the most treacherous forms of icy weather

is an ice storm.

11 Canadians have been killed and two million are without electricity

after devastating ice storms swept the country.

In 1998, eastern Canada was hit by a massive ice storm,

its worst on record.

Over five days, freezing rain turned into a slick glaze of ice

and built up to 7.5 centimetres thick in some places.

It became heavy enough to bring down trees and power lines.

The ice storm forced the government to declare a state of emergency.

Ice storms can begin high in the atmosphere.

Here, ice crystals grow into delicate snowflakes

with stunningly symmetrical branches.

If snowflakes fall into a warmer band of air,

they'll melt away into rain.

But in the unusual circumstances that lead to an ice storm,

there's much colder air beneath this warm layer

and it's very close to the ground.

As the rain falls through this cold air,

it becomes super-cooled,

ready to freeze again in an instant.

It crystallises as soon as it touches something,

creating layer upon hazardous layer of ice.

MAN: Millions of people here in Montreal are affected.

-WOMAN:

-It's like a war scene, almost.

We're going round house to house suggesting to people that it'll be a while before the power's back

and it might be wise to relocate to a shelter.

The damage cost the country 3 billion.

In some areas, the ice didn't melt for three months.

Temperature is truly the master of ice.

And there's a mysterious phenomenon called hot ice,

which freezes at room temperature.

Hot ice is created by putting water under enormous pressure,

far greater than any glacier on our planet.

This is ice that we wouldn't normally find anywhere on Earth.

Professor Paul Macmillan is going to show me how to make this high-pressure ice.

What we've got is a little drop of liquid water

and it's placed between two diamonds.

Inside here we've got two tiny diamonds that are pressing together.

You're going to turn this knob here very gently.

Because otherwise you'll force the two diamonds together too fast and they'll break.

I'll be very careful.

I'm about to put a tiny drop of water under more pressure

than occurs naturally anywhere on the Earth's surface.

When this gets to around 12,

-I want you to start to watch the screen.

-OK.

-Nine and a half now.

-Yes.

So what's happening is the pressure is going on

-and the diamonds are squeezing that drop of water.

-Yes.

-It's close to 12.

-I would slow it down just a wee bit.

At the moment this is liquid water, but it's really squeezed now.

The pressure's going up...

Look at that!

It's crystals!

-Yeah.

-Oh, that is cool.

-You've just made ice crystals in there.

They're growing as well, not just sitting there.

It's a whole faceful of tiny crystals.

The ice has formed even though it's way above zero degrees.

See the room temperature is 25 degrees.

-So we've made water freeze at 25 degrees C?

-Yes.

These are icebergs floating in dense water.

'The hot ice is at a pressure of 15,000 atmospheres.

'That's 15 times more pressure

'than you find at the bottom of the deepest ocean on Earth.'

What would it be like, then? I know we can't take it out and look at it

or do things with it because it's under that pressure.

But how is it different from real, normal ice?

The first thing is that it doesn't melt at normal temperatures.

This one here, you'd have to take this up to well over 100 degrees centigrade

for it even to start to melt.

So you can go above boiling point and it doesn't melt?

Exactly. This is a high-density form of ice.

The structure is very like a little cube.

You would never get the hexagon snowflake shapes

that you get with normal ice.

'This kind of ice might occur naturally out in space.'

We think that it probably does exist in the solar system,

deep inside some of the icy moons out there

like Titan, which is the large moon of Saturn.

And we know that the pressure inside

gets to these pressure values.

-So it's like having a telescope to look into the heart of Saturn's moon.

-Exactly.

We know already that the surfaces of some of the moons of Jupiter and Saturn

are covered in more normal ice, the type we're familiar with on Earth.

Recently, we've been able to get close enough to see it

in more detail.

And that's revealed something startling.

It might be protecting oceans of liquid water out in space.

Professor Michele Dougherty is a space physicist who explores these outer planets.

It was Jupiter's moon, Europa,

that first attracted her attention

thanks to a surprising photograph taken by the Galileo spacecraft.

This image shows us what looks like an ice shelf

which is floating on a liquid.

We could almost say it was the Antarctic or Greenland.

What you can clearly see are these icebergs which look as if they're moving around on the surface.

The only way for that to happen is for there to be liquid underneath

that's helping shift them around on the icy surface.

By studying data from Galileo,

scientists reckon that Europa's ice is covering an ocean

of liquid water.

If true, this will be an amazing discovery.

But frustratingly, there's no way yet of penetrating the surface

to confirm it.

However, in 1997,

an unmanned probe called Cassini

was sent into space.

Its mission, to explore Saturn, 700 million miles from Earth.

When it flew by a tiny ice-covered moon called Enceladus,

it gave a reading that Michele and her team simply couldn't explain.

So she asked the mission planners if Cassini could make a closer fly-by.

And this revealed a spectacle

that had never been seen before

anywhere in the solar system.

This is the image we took when we went really close to Enceladus.

You can clearly see this large plume of water vapour

coming off from the south pole. A gorgeous image!

As Cassini has shown us that water definitely exists under Enceladus's ice,

that makes it a fantastic place to search for evidence of extra-terrestrial life.

The reason that this discovery is so amazing

is that it's telling us there's water under the surface of Enceladus

and in the plume itself there is water vapour,

there are ice crystals

and there are organic compounds - nitrogen, carbon, hydrogen -

all the things that you need for the basic building blocks of life.

Michele and her colleagues are currently working on building much smaller probes

that will be able to analyse the plumes jetting out from Enceladus.

They'll look for more evidence of life.

Ice in space may bring us one step closer to finding out

if other life forms have evolved in our solar system.

Although icy environments even on our own planet

seem too hostile to support life,

in fact they can be a very favourable place for life to flourish.

Under the sea ice around the edges of the Antarctic continent,

at temperatures that would kill most living things,

live some of the most intriguing creatures on Earth.

In total, I've been to the Antarctic 13 times.

'At the laboratories of the British Antarctic Survey,

'Professor Lloyd Peck studies these creatures to find out

'just how they survive

'and what makes the icy ocean so advantageous for some forms of life.'

If we move down here,

we can see some of our really special animals.

These little fish are called the plunder fish.

I haven't seen this.

-That's a beauty! Is it all right?

-Yeah, they're fine.

If a predator comes along, they open their mouth, push their gill cases out

and push their spines out to stop being eaten.

They breed in our tank. They're one of the classic types of Antarctic fish.

-How cold is it?

-The water is below zero degrees.

But it's sea water so it doesn't freeze.

What you see here is, those animals living there

are permanently living below zero degrees.

-Why don't they freeze?

-Well, the fish would freeze

except for the fact they've got antifreeze in their blood, their tissues and their bodies.

They need antifreeze to live in these temperatures.

-They have antifreeze in their blood?

-They make their own antifreeze. They have antifreeze proteins.

There's antifreeze everywhere because without it,

ice crystals would grow inside their cells and inside their blood

and it would rip their tissues apart.

OK. I've got another animal here to show you.

This is a sea spider.

Oh, look at him!

In Antarctica, the sea spiders get really big.

The biggest ones are 40 centimetres from leg tip to leg tip.

-So that's twice the size of this one?

-About twice the size.

And the biggest sea spiders in the Antarctic

are a thousand, maybe two thousand, three thousand times heavier

-than the biggest sea spiders in Europe.

-Why do they get so big?

Well, the reason they get big is because it's cold!

Two things happen when sea water gets cold.

One is that the amount of oxygen you get in the water goes up.

There's nearly twice as much oxygen in the sea in Antarctica as in the tropics.

Because it's cold, their metabolic rates run much slower than animals elsewhere.

So it's like live cheaper, grow bigger?

Live cheaper, grow bigger. And it's not just the sea spiders.

This is a 40-arm starfish.

-Its Latin name is Labidiaster.

-Oh, my God!

Have a hold of that.

OK? This is a really small one.

The big ones get up to 70, 80 centimetres across. They're huge.

They're one of the big predators in the Antarctic on the sea bed.

There's his stomach. They crawl over the top of animals, put their stomachs out and eat them.

What is it about the ice that makes all these weird adaptations and strange animals?

The ice helps keep the temperature constant in the seas.

What it's done is kept that temperature low and constant

for maybe 25 million years.

So it's not just cold, it's also steady.

It is. The Antarctic Ocean is possibly the most constant temperature place on Earth.

And it's been there for such a long time that animals have been able to adapt to it

in a very fine-scaled way, in a way that hasn't happened anywhere else on Earth.

These creatures are the product of a unique eco-system

that revolves around ice.

By studying how they managed not just to adapt, but to thrive,

we can learn about the impact of cold

and how well icy environments can support life.

Antarctica is the coldest, windiest continent on the planet.

It's covered by the largest single mass of ice on Earth.

Back in the 1950s,

a team of scientists set out with a seemingly impossible dream,

to discover how thick the Antarctic ice sheet was

and what might be lying beneath.

Part of that team was glaciologist, Dr Charles Swithinbank.

He's a legend in the world of Antarctic science.

He's spent a lifetime exploring the heart of the white continent.

-That's it.

-That's you?

That's me. I was mad keen and always have been.

Here was a chance of real adventure and real exploring

in a really unknown part of the Antarctic.

It was Charles' job to try to measure the depth of the ice.

Taking a sled loaded with dynamite out onto the ice,

he and his colleagues set off an explosion at the surface.

They measured how long it took for its echo to bounce back.

From this, they could work out how far it had travelled

and how thick the ice sheet was.

We found thicknesses up to 2,500 metres.

That's nothing nowadays. People have found a lot deeper.

But it staggered us

because here we were, walking over solid ice

without any idea how thick it was.

But as it took a day to make one single measurement,

mapping the whole continent was going to take decades.

Until another ice secret was unlocked by American army engineer, Amory Waite.

In the 1950s, experienced pilots were crashing into the Antarctic ice sheet and no-one knew why.

Waite knew the planes' altimeters used radar to measure how high they were above the ground.

He started hitting ice with different frequencies of radio waves

and realised some of them were going straight through the ice.

This could have given the pilots a false reading of their height.

Waite realised that despite being a solid,

ice was transparent to radar.

Once this was known, planes stopped crashing,

saving countless lives.

But it also revolutionised Charles Swithinbank's job

of surveying the Antarctic ice sheet and the land beneath.

His team could now criss-cross the continent in a plane,

using radar to see through the ice

by bouncing radio waves off the bedrock below.

And he could now take hundreds of readings every second.

It was staggeringly exciting

because we were getting a cross-section of the ice sheet as we flew over it.

We went to a number of places where I'd worked on the ground

and dreamed and wondered how thick the ice was.

And in the matter of a minute -

pow! - we'd measured how thick it was.

It was very, very exciting.

Beneath the white and pristine Antarctic surface,

an entire new world was uncovered.

A world made of valleys, mountains and plateaus

hidden in parts by ice more than four kilometres thick.

And all laid bare thanks to discovering another secret of the ice crystal.

While the Antarctic lies on mountainous bedrock,

on the other side of the world, the Arctic is a treacherous ocean

of floating sea ice,

where exploration has often been driven by commerce.

For hundreds of years, sailors searched for a short and lucrative trade route through these waters

between Europe and the Pacific.

One that would be cheaper than the long route via India and China.

The elusive North-West Passage.

For the expedition that found it, there was a prize of thousands of pounds.

I'm interested in the story of one particular expedition.

It was led by a celebrated naval officer, Sir John Franklin.

But it turned out to be the worst disaster in the history of British polar exploration.

What draws me to this story

is that it plays out like a detective mystery

with ice as the key witness.

And some of the clues are here, at the Scott Polar Research Institute.

This is the leader of the expedition, Sir John Franklin.

In 1845, he was already 59 years old.

He'd fought with Nelson at the Battle of Trafalgar.

He'd been to the Arctic three times and mapped thousands of miles of coastline.

The British public had been captivated by stories of how he and his men

staved off hunger by eating their own leather boots.

Franklin was clearly the man for the job.

Before he set off, he arranged to have portraits taken of himself and his senior officers

with the very latest technology.

Curator Heather Lane has these precious early daguerreotypes

for me to see.

-If you'd like to pick it up and open it.

-I'd love to.

Very happy.

And there he is.

Quite extraordinary to think you're seeing him on the day they set off.

'Franklin had assembled a team of experienced officers to sail with him to the Arctic,

'many of whom had been there before.'

-They all look quite sure of themselves.

-Franklin had been sensible.

He's pulled together a team he knows will actually obey orders

in what are likely to be quite difficult circumstances.

In total, 133 men set sail with Franklin from Kent

in two sturdy ships, the Erebus and the Terror,

both of which had seen service in the Polar regions before.

They were expecting to sail from the Atlantic Ocean

through the ice-bound islands of Northern Canada

to the Pacific Ocean, and return within three years.

They'd refitted these ships with state-of-the-art equipment. They were steam-powered,

they had water purification, they had central heating on board.

They really put a huge amount of effort into ensuring

that this was the expedition that was going to make it all the way through the North-West Passage.

Then suddenly, they disappear.

The ice has swallowed this expedition whole.

And it's the beginning of a great Victorian mystery - what has happened to Franklin and his men?

Over the next few years,

more than 30 rescue missions searched the icy Arctic for survivors

but failed to find any.

It wasn't until 1858 that the likely fate of Franklin's men was confirmed

by a message discovered in a can on a small uninhabited island.

Written by two senior officers,

it announced that Sir John Franklin had died in 1847,

two years after he'd set sail.

Both ships had been abandoned in the ice

and second-in-command Captain Crozier was attempting to lead 105 survivors to safety.

But why had an expedition with experienced Polar navigators

in state-of-the-art ships,

ended up like this?

Well, although the records end here,

the detective story doesn't.

What I find fascinating about the Franklin story

is it doesn't seem to die. Clues keep on showing up in the ice.

And eventually, it would be the ice that would provide the answer.

In 1986, a team of forensic archaeologists

travelled to Beachy Island in northern Canada.

This was where, in 1850,

a search party had found empty food cans,

evidence that the expedition had wintered here.

And not far from them, three graves.

Over two intense weeks, Dr Owen Beatty and his team

exhumed the bodies of able seaman John Hartnell

and Private William Brain

to try to find out how they'd died.

The forensic team had no idea what to expect. What condition the bodies would be in.

They had to pick-axe their way through the frozen ground

which is what the grave-diggers must have had to do when they buried the bodies in the Arctic winter.

They found that the ice had preserved the bodies almost perfectly.

When they released them, using warm water,

there was so little decay, it was relatively easy to investigate how they'd died.

John Hartnell had had tuberculosis, but he was also incredibly thin.

He had no food in his stomach or intestines.

Scattered around the camp, Beatty had found empty cans that had been soldered with lead.

He put two and two together.

He tested the men's bodies

and found dangerously high levels of lead

in their hair, bones and soft tissue.

To date, about 17 more of Franklin's men

have been found to have had toxic levels of lead in their bones.

New research suggest the lead might not have come from the cans at all

but is more likely to have leeched out of the new lead piping in the ship's water system

and contaminated their water.

Lead poisoning is a horrible way to die.

It paralyses your muscles and eats away at your brain and central nervous system.

So then what you get is disorientation and anorexia.

The worst things that can happen if you're trying to survive an Arctic winter.

We know so much about the tragic fate of Franklin and his men

because of the miraculous ability of ice to preserve.

But it doesn't just preserve history by slowing down decomposition.

It also has the ability to preserve something much more delicate than bodies.

And one that might prove even more valuable.

In the Antarctic, teams of scientists have been reaching back into history.

They've been drilling thousands of metres into the ice sheet

to remove columns of ice that can bear witness to our past.

These ice cores preserve air from hundreds of thousands of years ago.

They're helping us understand one of the most complex aspects of nature,

our climate.

I'm with Dr Robert Mulvaney

at the British Antarctic Survey's ice core freezer in Cambridge

where he studies this ancient ice.

So if I take a piece of this out.

Let's put that down on here.

You can probably make out the tiny air balls in there.

It's the magic of the ice that it's able to take these air molecules

-into its matrix without altering them, and release them back to us later.

-A storage box.

-Yes.

What we'll do is cut a piece off and see if we can see the air bubbles.

The deeper you go, the older the ice gets.

Scientists are able to date each layer of ice

from chemical markers within the ice crystal itself.

It's starting to clear. I think you can see the air bubbles in that.

Fantastic, isn't it?

This air is about 1,000 years old!

So when they were invading Britain in 1066,

this is the air they would have been breathing!

-The Saxons and Normans.

-Saxons and Normans.

-That is wild!

-It is, isn't it?

This is quite a long way down in the ice sheet.

This is about 80,000 years old. You can probably see the air in that.

So this is before... This fell as snow and trapped air

before human civilisation?

That's right. Fascinating, isn't it?

As well as preserving past atmospheres,

the ice crystals preserve another important secret.

Tiny variations in their chemistry

reveal the temperature of the climate when they originally formed.

This has allowed us to see in more detail than ever before

how our climate has changed throughout history.

It's also enabled us to explore a link

between temperature and levels of atmospheric carbon dioxide.

Our oldest ice core goes back 800,000 years.

In that period, we've been in and out of an ice age eight times.

And all through that period, the atmosphere and the temperature have been very closely linked.

So as we go into an ice age, the levels of carbon dioxide, greenhouse gases, decrease,

and as come out of an ice age they start to increase.

The ice core record shows that there was a strong relationship between temperature and carbon dioxide.

They've moved in tandem throughout history for 800,000 years.

To many scientists, this historical record supports current theories of global warming,

suggesting that if carbon dioxide levels rise, as they're doing today,

temperatures will also rise.

It's a warning from the past that many find hard to ignore.

And all because of the unique ability of ice

to capture air and preserve it.

Ice is one of the most enigmatic substances in nature.

A solid can pass through it, without leaving a trace.

It can shatter rock and sculpt our planet.

In space, its protective shell may conceal life forms

just waiting to be discovered.

It can last for millions of years

or just melt in an instant.

I'm drawn to ice because of its contradictions.

Although is seems so fragile, it's capable of carving out landscapes and preserving histories,

even giving us warnings about the future of our world.

But what's really struck me about making this programme

is discovering where all that power comes from.

Because actually, the very thing that makes ice seem fragile and vulnerable,

the fact that it's always on the point of disappearing

turns out to be the source of all its strength.

Subtitles by Red Bee Media Ltd