Original subtitles

Winter in Antarctica.

The temperature has dropped to minus 70 degrees centigrade,

and winds of 120 miles an hour

blow across the desolate icescape.

The centre of Antarctica is in continuous darkness.

Only its fringes see the bleak winter light.

The sea freezes over for hundreds of miles,

effectively doubling the size of the continent.

In winter, the Antarctic is a very lonely place.

As the temperature plummets

and the sea ice forms,

most of the wildlife that came down here to take advantage of the brief summer season

is forced to retreat north again.

Practically nothing stays.

To survive in the deep south at its most bitterly hostile

requires a very special animal with very special adaptations.

Such a creature is the Weddell seal.

No other mammal lives throughout the year

as far south as this.

These seals are just 800 miles from the pole,

and they stay here winter and summer.

Like all Antarctic seals,

they have a thick layer of blubber to insulate them from the cold.

But the real key to their success in surviving here

is their ability to keep open holes in the ice

so that they have access to the sea the year round.

These holes are the only things that break the white monotony

over hundreds of square miles of sea ice.

The seals, with no escape to the open ocean,

are forced to stay near the holes.

Each is a gateway

to and from the underwater world

in which the seals hunt and find shelter.

Underwater, the temperature never drops below minus 1.8 degrees.

The seals retreat down here during the worst winter storms

and so keep comparatively warm.

When you dive beneath the ice,

you enter, within seconds, a totally different world.

Here, within a foot or so

of the gale-swept, savagely cold wilderness above,

illuminated only by the dim blue light filtering through the ice,

there is stability, peace,

and an eerie, unforgettable beauty.

Animals need special adaptations

to live in water that is below zero centigrade.

Most fish would explode if they touched this glacier wall.

Crystals would immediately form in their cells.

These survive because their tissues are loaded with anti-freeze.

Life beneath the ice,

compared with the white desert above,

is extraordinarily rich.

There are all kinds of invertebrates,

including giant jellyfish.

It's a very sheltered place,

for the permanent sea ice overhead

provides year-round protection

from waves and storms.

But food is scarce,

and many of these creatures have become scavengers.

These starfish make a meal of seal faeces.

Weddell seals can dive to 750 metres, possibly more,

in search of food.

At these depths, in permanent darkness,

they encounter a world dominated by stalk sponges.

Growing extremely slowly in the cold,

the Antarctic invertebrates become giants.

Returning from depths

where a human would be crushed,

seals surface suffering none of the effects of deep diving

that can cripple human swimmers.

October in the far south.

Female Weddell seals haul out on the sea ice to give birth.

Imagine the shock of leaving a womb at plus 37 degrees centigrade

and being dropped on the ice into a world of minus 20.

The pup has to suckle and build a layer of blubber

as fast as possible.

It usually doubles its weight in ten days,

for Weddell milk is 60% fat,

one of the richest produced by any mammal.

Remarkably, after one week,

the pup is ready for a swim.

(MOTHER LOWS TO HER PUP)

The mother is anxious to get her pup accustomed to the water

before the weather deteriorates.

At this time, more than any other,

breathing holes are jealously guarded.

Weddells have an especially wide gape

and long canine and incisor teeth,

which enable them to scrape away the ice

that is constantly forming and threatens to close their breathing holes.

Their teeth aren't impervious to this wear and tear

and are gradually worn down,

so that eventually the seal can't eat.

As a consequence, Weddells die at about 20 years,

half the age of other Antarctic seals.

A male defends an underwater territory

and mates with all the females that use his breathing holes.

It's an effective way of acquiring a harem,

because females must have a refuge below the ice

from the extremes of the winter weather.

It might seem that there could not be

a more harsh existence than this,

but the environment here is comparatively constant

and these seals are adapted to it -

protected by a coat of dense hair

and insulated by blubber immediately beneath the skin.

Indeed, Weddells do far better than most other seals.

If they are sufficiently fattened

in the six weeks before they wean,

95% of pups will survive.

These seals, the most southerly in the world,

live in the shadow

of the largest active volcano in Antarctica - Mount Erebus.

Erebus is a mountain of extremes.

In the crater, molten lava bubbles away at 600 degrees centigrade,

and yet, on the summit,

temperatures rarely rise above minus 45 degrees.

Even here, there is life.

The heat of the volcano produces steam

that rises to the rim and melts the snow and ice,

leaving bare patches of rock -

home to heat-loving bacteria and algae.

Another extraordinary example

of how life can survive in the most extreme conditions on Earth.

Behind Mount Erebus,

the trans-Antarctic mountains stretch in a long broad band.

They are the most extensive range on the continent,

running for some 2,000 miles

and separating the great east and west ice caps.

Although many of the peaks are over 4,000 metres high,

most of the range is blanketed

by vast glaciers which fill the valleys.

Hidden among the trans-Antarctic mountains

is one of the continent's greatest surprises -

the dry valleys.

Here is the largest area of bare rock in Antarctica.

It's so arid that falling snow soon evaporates

and never builds up.

The valley below me is the driest place on Earth.

It hasn't snowed or rained here for centuries.

In winter, the temperature falls to minus 52 degrees centigrade

and the ground is permanently frozen to a depth of half a mile.

Conditions are so extreme

that when scientists came to design a vehicle to work on the surface of Mars,

they brought it to this valley in order to test it.

A clue to the factor that creates these conditions

lies in the extraordinary shape of these boulders.

Although they are solid granite,

they have been carved by savage winds that scream down off the ice cap.

These winds are so dry that they instantly absorb

any moisture in the air,

and by doing so desiccate and preserve organic tissues.

This mummified crabeater seal, 70 miles from the sea,

has probably been lying here

for 3,000 years or more.

You might suppose

that a place that can freeze-dry seals' bodies for centuries

would be totally without life.

But even in these extreme conditions,

life does exist.

Pick the right sort of rock -

this is a light porous sandstone -

give it a hit...

...and there, a millimetre beneath the surface,

within the actual fabric of the rock,

a band of green, the colour of life.

It is lichen that has managed to penetrate and colonise

the microscopic spaces between the grains of the porous rock.

It's the only place where it can survive

in these arid, desert-like conditions.

Above the dry valleys,

held back by the trans-Antarctic mountains,

stretches the ice cap itself.

This is the Antarctic plateau,

3,000 metres high.

There can be no more forbidding, hostile, desolate places to be

than up here on the Antarctic plateau.

It's not just that human life here seems insignificant -

it seems totally irrelevant.

A few spots of lichens may grow on boulders

to within 200 miles of the South Pole,

and, in the summer,

maybe one or two particularly adventurous snow petrels

will come up here to try and nest.

But come the winter,

absolutely nothing living

moves up here on the Antarctic plateau.

Even in summer, it is always winter here,

with temperatures averaging minus 30.

1.5 times the size of Australia,

this is the largest area of lifeless wilderness in the world.

Snow petrels, brief visitors here in summer,

are forced to spend the winter hundreds of miles

to the warmer north, at the edge of the frozen sea.

This is the frontier between life in the ocean

and a desert of ice where almost no animals dare go.

But one creature has to cross it -

the Emperor penguin.

In May, when the freezing waters and cold winter temperatures

force other animals to retreat to the warmer north,

Emperor penguins head south.

They make their way to a number of traditional nesting sites.

In this one alone, there may be 25,000 birds.

Emperors are unique.

They are the only birds to lay their eggs directly on ice.

Just hours after the female has produced her single egg,

the male takes it over.

The transfer has to be quick

if the egg is not to freeze.

The male manoeuvres it

into a brood pouch lined with blood vessels

that keep the egg 80 degrees warmer than the outside temperature.

There, under a flap of skin,

it's sealed away for the winter.

When the egg is safely inside the male's pouch,

the females are free to go,

and they start the long trek back across the sea ice, to the open ocean,

leaving their partners to face the coldest conditions on Earth.

With temperatures of 70 below,

and in terrible storms,

the penguins huddle tightly together for warmth.

No other adult penguins are so tolerant of one another,

but for Emperors this is the key to survival.

The co-operation is not random.

Those most exposed on the windward side

move around the huddle to the more sheltered side.

So every bird gets a fair share of the warmth in the middle

and takes its turn in enduring the brunt of the Antarctic weather.

As midwinter approaches,

the sun disappears below the horizon

for the last time this season.

A month of total darkness lies ahead.

Above the huddle, the Southern Lights -

the Aurora Australis -

blaze across the winter sky.

These spectacular displays occur

as subatomic particles, travelling through space,

enter the Earth's magnetic field.

As winter recedes, the huddles begin to break up,

and heat that was trapped within them for so long escapes.

These males, who have not eaten for 115 days,

are close to death by starvation.

(SQUAWKING)

As the sun returns to the southern hemisphere,

the female Emperors,

sleek and fat from months of feeding at sea,

begin the long march back to the rookery.

The sea ice is now at its fullest extent,

and they may have to walk 100 miles to reach their colony.

By now the eggs have hatched

and the tiny chicks are awaiting their first feed.

Each female times her return

to coincide with the hatching of her chick.

A male, having starved for so long,

can give the chick only one meal -

no more than a milky secretion from his gut wall.

If his partner doesn't return

within ten days of the chick hatching,

he will have to abandon it and head to the sea to find food for himself.

(TREMENDOUS DIN)

It's a noisy time in the colony.

The courtship calling that took place before winter

now brings its reward.

After a separation of over three months,

a bird can still recognise its partner's call.

(VARl0US CALLS)

When they find one another,

the pair perform their greeting ritual

to ensure there hasn't been a case of mistaken identity.

Then the female gives their chick its first proper meal -

half-digested fish.

She's very eager to take charge of the chick,

but the male, having cared for it for so long, is reluctant to give it up.

She has literally to push him back to get him to release it.

The transfer is a tricky manoeuvre that must be done fast.

A chick left on the ice for only two minutes will die.

The males, after their four-month ordeal,

near to starvation and desperate to feed,

have to walk 100 miles or so back to the open sea.

Mothers and chicks spend the next few weeks

learning each other's call

and establishing a strong bond

that ensures they will recognise one another in the months ahead

when she returns from feeding trips.

It's early spring and the weather is still variable.

(HOWLING GALE)

Severe storms are a real threat

to the chick's survival.

An abandoned one seeks shelter from passing adults.

One of them seems interested,

but the vital bond between parent and chick isn't there

and eventually the adult walks off.

In fact, the adults do have a strong instinct to protect chicks.

So much so that birds that have not managed to breed

will try to take possession of a stray or abandoned chick.

But this fostering never succeeds

because the adult has no partner to help in rearing the waif.

These desperate unpartnered penguins

will sometimes fight over a chick

and crush it to death.

Mortality is high.

Many eggs don't hatch,

and of those that do, 25% die in the first few months.

Those that survive have to grow fast and fledge

before the sea ice on which they live breaks up beneath them.

These chicks take five months to rear.

Only by incubating the eggs through the harsh winter,

so that the chicks hatch at the very beginning of the short summer,

is it possible for the Emperors to breed every year.

It was to collect an Emperor penguin's egg like this

that men made the first-ever land journey

in the bitter cold darkness of the Antarctic winter.

Bill Wilson, the naturalist on Captain Scott's expedition,

was fascinated by the evolutionary origin of birds

and was convinced that the embryo in an egg like this

would provide conclusive evidence of the link

between the feathers of birds and the scales of reptiles.

So, on 12 June, 1911, in the middle of winter,

he and two companions

left Captain Scott's hut here on Cape Evans

and set out for the Emperor penguin colony on the other side of Mount Erebus,

65 miles away.

It was a trip that became known with some justice

as the worst journey in the world.

The weather was abominable.

Their clothes and harnesses froze solid

and all three suffered terrible frostbite

as they hauled their sledges over heavily-crevassed terrain.

On the return journey, they lost their tent in a violent storm.

By a miracle, they found it again and made it back to the hut alive.

They brought back three eggs and three Emperor penguin skins,

one of which is still here in Scott's hut,

preserved by the Antarctic cold.

Although the connection between birds and reptiles is no longer in doubt,

the eggs did not provide the evidence that Wilson thought they would.

Even so, the journey remains one of the great epic stories

in the annals of polar exploration.

In the next programme,

we'll look at the history of Antarctic exploration in more detail

and also see how people today survive life in the freezer.

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