The Big Freeze Life in the Freezer

Winter in Antarctica. The temperature has dropped to minus 70 degrees Centigrade

and winds of 120 mph 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 lonely place. As the temperature plummets

and sea ice forms, most of the wildlife that came down in 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.

They have thick 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 they have access to the sea the year round.

The seals' 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 is never 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, cold wilderness above,

illuminated by the dim blue light filtering through the ceiling of 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 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 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 constant darkness,

they encounter a world dominated by stalked sponges.

Growing extremely slowly in the cold, the Antarctic invertebrates become giants.

Returning from depths where a human being 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 at minus 20.

The pup has to suckle and build a layer of blubber as fast as possible.

It usually manages to double 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.

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 a very wide gape and long canine and incisor teeth,

enabling them to scrape away the ice which forms and threatens to close their breathing holes.

Their teeth aren't impervious to this wear and tear and are gradually worn down,

so eventually the seal cannot eat.

As a result, 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 as females must have a refuge from the extreme winter weather.

It may seem that there could not be a harsher existence, but the environment is 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're weaned, 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,

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.

It's 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 in Antarctica, running for 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 greatest surprises - the Dry Valleys.

Here is the largest area of bare rock to be found 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 Centigrade and the ground is 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 to test it.

A clue to what creates these conditions lies in the shape of these boulders.

Although they are solid granite, they've been carved by savage winds that scream down off the ice-cap.

These winds are so dry that they absorb any moisture in the air,

and by doing so, they will desiccate and preserve organic tissues.

This mummified crabeater seal, about 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 the bodies of seals 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's a lichen

that has penetrated and colonised 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 Transarctic Mountains, is 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.

Human life here doesn't just seem 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's always winter here, with temperatures averaging minus 30.

1½ times the size of Australia, this is the largest lifeless wilderness in the world.

Snow petrels, brief visitors here in summer, 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 must cross it - the Emperor penguin.

In May, when the freezing waters and the cold winter temperatures force other animals

to retreat to warmer conditions in the 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.

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 eggs 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 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. This ensures

that every bird gets its fair share of 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.

As the sun returns to the southern hemisphere,

the females, sleek and fat from months of feeding at sea, 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's return coincides with the hatching of her chick.

Having starved for so long, a male can give only one meal -

a milky secretion from his gut wall.

If his partner doesn't return within ten days of the chick hatching,

he will be forced to abandon it and head for the sea

to find food for himself.

SHRILL CRIES

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 3 months, a bird can still recognise its partner's call.

SHRILL CRIES

When they find one another,

the pair perform their greeting ritual to ensure that there hasn't been a case of mistaken identity.

Then the female gives their chick its first proper meal - half-digested fish.

She is 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 forming a strong bond to ensure 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.

Severe storms are a real threat

to the chick's survival. One that has been abandoned seeks shelter from passing adults.

One of them seems interested, but the vital bond between parent and chick simply isn't there,

and eventually the adult walks off.

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

and 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 must 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 Antarctic 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

that men made the first-ever land journey in the bitter cold darkness of the Antarctic winter.

Bill Wilson, the naturalist on Scott's expedition, was fascinated by the evolutionary origin of birds.

He thought that the embryo in an egg would provide conclusive evidence

of the link between the feathers of birds and the scales of reptiles.

So on June 12th, 1911, in midwinter,

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 suffered terrible frostbite as they hauled their sledges over heavily crevassed terrain.

They lost their tent in a violent storm. By a miracle, they found it again and made it back to the hut.

They brought back three eggs and three penguin skins,

one of which is here in Scott's hut, preserved by the Antarctic cold.

Although the link between birds and reptiles is no longer in doubt, the eggs didn't provide the evidence.

Even so, the journey remains one of the great epic stories in the annals of polar exploration.

Subtitles by Calum Short BBC Scotland 1993