0:01:04 > 0:01:11Winter in Antarctica. The temperature has dropped to minus 70 degrees Centigrade
0:01:11 > 0:01:16and winds of 120 mph blow across the desolate icescape.
0:01:18 > 0:01:23The centre of Antarctica is in continuous darkness.
0:01:23 > 0:01:27Only its fringes see the bleak winter light.
0:01:27 > 0:01:34The sea freezes over for hundreds of miles, effectively doubling the size of the continent.
0:01:34 > 0:01:40In winter, the Antarctic is a lonely place. As the temperature plummets
0:01:40 > 0:01:46and sea ice forms, most of the wildlife that came down in the brief summer season
0:01:46 > 0:01:49is forced to retreat north again.
0:01:49 > 0:01:52Practically nothing stays.
0:01:52 > 0:01:57To survive in the deep south at its most bitterly hostile
0:01:57 > 0:02:02requires a very special animal with very special adaptations.
0:02:02 > 0:02:05Such a creature is the Weddell seal.
0:02:06 > 0:02:12No other mammal lives throughout the year as far south as this.
0:02:12 > 0:02:19These seals are just 800 miles from the Pole and they stay here winter and summer.
0:02:19 > 0:02:23They have thick blubber to insulate them from the cold.
0:02:23 > 0:02:31But the real key to their success in surviving here is their ability to keep open holes in the ice
0:02:31 > 0:02:35so they have access to the sea the year round.
0:02:35 > 0:02:43The seals' holes are the only things that break the white monotony over hundreds of square miles of sea ice.
0:02:43 > 0:02:50The seals, with no escape to the open ocean, are forced to stay near the holes.
0:02:50 > 0:02:55Each is a gateway to and from the underwater world
0:02:55 > 0:03:03in which the seals hunt and find shelter. Underwater, the temperature is never below minus 1.8 degrees.
0:03:03 > 0:03:10The seals retreat down here during the worst winter storms and so keep comparatively warm.
0:03:20 > 0:03:27When you dive beneath the ice, you enter, within seconds, a totally different world.
0:03:27 > 0:03:33Here, within a foot or so of the gale-swept, cold wilderness above,
0:03:33 > 0:03:38illuminated by the dim blue light filtering through the ceiling of ice,
0:03:38 > 0:03:44there is stability, peace and an eerie, unforgettable beauty.
0:04:23 > 0:04:30Animals need special adaptations to live in water that is below zero Centigrade.
0:04:30 > 0:04:38Most fish would explode if they touched this glacier wall. Crystals would form in their cells.
0:04:38 > 0:04:44These survive because their tissues are loaded with anti-freeze.
0:04:46 > 0:04:53Life beneath the ice compared with the white desert above is extraordinarily rich.
0:04:53 > 0:04:58There are all kinds of invertebrates including giant jellyfish.
0:05:25 > 0:05:33It's a very sheltered place, for the sea ice overhead provides year-round protection from waves and storms.
0:05:33 > 0:05:40But food is scarce and many of these creatures have become scavengers.
0:05:40 > 0:05:44These starfish make a meal of seal faeces.
0:05:48 > 0:05:54Weddell seals can dive to 750 metres, possibly more, in search of food.
0:05:54 > 0:05:57At these depths in constant darkness,
0:05:57 > 0:06:02they encounter a world dominated by stalked sponges.
0:06:03 > 0:06:10Growing extremely slowly in the cold, the Antarctic invertebrates become giants.
0:06:18 > 0:06:24Returning from depths where a human being would be crushed,
0:06:24 > 0:06:32seals surface suffering none of the effects of deep diving that can cripple human swimmers.
0:06:37 > 0:06:40October in the far south.
0:06:40 > 0:06:46Female Weddell seals haul out on the sea ice to give birth.
0:06:54 > 0:07:01Imagine the shock of leaving a womb at plus 37 degrees Centigrade and being dropped on the ice
0:07:01 > 0:07:04into a world at minus 20.
0:07:32 > 0:07:37The pup has to suckle and build a layer of blubber as fast as possible.
0:07:37 > 0:07:44It usually manages to double its weight in ten days for Weddell milk is 60% fat -
0:07:44 > 0:07:48one of the richest produced by any mammal.
0:07:48 > 0:07:53Remarkably, after one week, the pup is ready for a swim.
0:08:05 > 0:08:13The mother is anxious to get her pup accustomed to the water before the weather deteriorates.
0:08:24 > 0:08:31At this time, more than any other, breathing holes are jealously guarded.
0:09:00 > 0:09:05Weddells have a very wide gape and long canine and incisor teeth,
0:09:05 > 0:09:13enabling them to scrape away the ice which forms and threatens to close their breathing holes.
0:09:13 > 0:09:19Their teeth aren't impervious to this wear and tear and are gradually worn down,
0:09:19 > 0:09:22so eventually the seal cannot eat.
0:09:22 > 0:09:29As a result, Weddells die at about 20 years, half the age of other Antarctic seals.
0:09:29 > 0:09:37A male defends an underwater territory and mates with all the females that use his breathing holes.
0:09:37 > 0:09:44It's an effective way of acquiring a harem as females must have a refuge from the extreme winter weather.
0:09:47 > 0:09:55It may seem that there could not be a harsher existence, but the environment is constant,
0:09:55 > 0:09:58and these seals are adapted to it -
0:09:58 > 0:10:05protected by a coat of dense hair and insulated by blubber immediately beneath the skin.
0:10:06 > 0:10:11Indeed, Weddells do far better than most other seals.
0:10:11 > 0:10:18If they are sufficiently fattened in the six weeks before they're weaned, 95% of pups will survive.
0:10:23 > 0:10:29These seals, the most southerly in the world, live in the shadow
0:10:29 > 0:10:35of the largest active volcano in Antarctica - Mount Erebus.
0:10:38 > 0:10:41Erebus is a mountain of extremes.
0:10:41 > 0:10:46In the crater, molten lava bubbles away at 600 degrees Centigrade,
0:10:46 > 0:10:54yet on the summit, temperatures rarely rise above minus 45 degrees. Even here, there is life.
0:10:54 > 0:11:01The heat of the volcano produces steam that rises to the rim and melts the snow and ice,
0:11:01 > 0:11:06leaving bare patches of rock - home to heat-loving bacteria and algae.
0:11:06 > 0:11:13It's another extraordinary example of how life can survive in the most extreme conditions on earth.
0:11:27 > 0:11:34Behind Mount Erebus, the Trans-Antarctic Mountains stretch in a long broad band.
0:11:34 > 0:11:40They are the most extensive range in Antarctica, running for 2,000 miles
0:11:40 > 0:11:44and separating the great East and West ice-caps.
0:11:47 > 0:11:52Although many of the peaks are over 4,000 metres high,
0:11:52 > 0:11:57most of the range is blanketed by vast glaciers which fill the valleys.
0:12:14 > 0:12:22Hidden among the Trans-Antarctic Mountains is one of the greatest surprises - the Dry Valleys.
0:12:22 > 0:12:27Here is the largest area of bare rock to be found in Antarctica.
0:12:27 > 0:12:31It's so arid that falling snow soon evaporates
0:12:31 > 0:12:34and never builds up.
0:12:34 > 0:12:41The valley below me is the driest place on earth. It hasn't snowed or rained here for centuries.
0:12:41 > 0:12:49In winter, the temperature falls to minus 52 Centigrade and the ground is frozen to a depth of half a mile.
0:12:49 > 0:12:56Conditions are so extreme that when scientists came to design a vehicle to work on the surface of Mars,
0:12:56 > 0:13:00they brought it to this valley to test it.
0:13:00 > 0:13:07A clue to what creates these conditions lies in the shape of these boulders.
0:13:07 > 0:13:15Although they are solid granite, they've been carved by savage winds that scream down off the ice-cap.
0:13:15 > 0:13:21These winds are so dry that they absorb any moisture in the air,
0:13:21 > 0:13:26and by doing so, they will desiccate and preserve organic tissues.
0:13:26 > 0:13:31This mummified crabeater seal, about 70 miles from the sea,
0:13:31 > 0:13:34has probably been lying here
0:13:34 > 0:13:37for 3,000 years or more.
0:13:37 > 0:13:39You might suppose that a place
0:13:39 > 0:13:46that can freeze-dry the bodies of seals for centuries would be totally without life.
0:13:47 > 0:13:52But even in these extreme conditions, life does exist.
0:13:52 > 0:14:00Pick the right sort of rock - this is a light porous sandstone - give it a hit...
0:14:01 > 0:14:06and there, a millimetre beneath the surface
0:14:06 > 0:14:14within the actual fabric of the rock - a band of green, the colour of life. It's a lichen
0:14:14 > 0:14:21that has penetrated and colonised the microscopic spaces between the grains of the porous rock.
0:14:21 > 0:14:28It's the only place where it can survive in these arid, desert-like conditions.
0:14:28 > 0:14:30Above the Dry Valleys,
0:14:30 > 0:14:35held back by the Transarctic Mountains, is the ice-cap itself.
0:14:35 > 0:14:40This is the Antarctic Plateau, 3,000 metres high.
0:14:49 > 0:14:54There can be no more forbidding, hostile, desolate places to be
0:14:54 > 0:14:58than up here on the Antarctic Plateau.
0:14:58 > 0:15:03Human life here doesn't just seem insignificant,
0:15:03 > 0:15:05it seems totally irrelevant.
0:15:06 > 0:15:14A few spots of lichens may grow on boulders to within 200 miles of the South Pole,
0:15:14 > 0:15:21and in the summer, maybe one or two particularly adventurous snow petrels
0:15:21 > 0:15:24will come up here to try and nest.
0:15:24 > 0:15:27But come the winter,
0:15:27 > 0:15:33absolutely nothing living moves up here on the Antarctic Plateau.
0:15:37 > 0:15:44Even in summer it's always winter here, with temperatures averaging minus 30.
0:15:44 > 0:15:511½ times the size of Australia, this is the largest lifeless wilderness in the world.
0:15:51 > 0:15:58Snow petrels, brief visitors here in summer, spend the winter hundreds of miles to the warmer north,
0:15:58 > 0:16:01at the edge of the frozen sea.
0:16:07 > 0:16:14This is the frontier between life in the ocean and a desert of ice where almost no animals dare go.
0:16:14 > 0:16:19But one creature must cross it - the Emperor penguin.
0:16:30 > 0:16:37In May, when the freezing waters and the cold winter temperatures force other animals
0:16:37 > 0:16:44to retreat to warmer conditions in the north, Emperor penguins head south.
0:16:54 > 0:16:56They make their way
0:16:56 > 0:17:00to a number of traditional nesting sites.
0:17:00 > 0:17:05In this one alone, there may be 25,000 birds.
0:17:07 > 0:17:13Emperors are unique. They are the only birds to lay their eggs directly on ice.
0:17:24 > 0:17:29Hours after the female has produced her single egg,
0:17:29 > 0:17:36the male takes it over. The transfer has to be quick if the egg is not to freeze.
0:17:36 > 0:17:41The male manoeuvres it into a brood pouch lined with blood vessels
0:17:41 > 0:17:47that keep the eggs 80 degrees warmer than the outside temperature.
0:17:47 > 0:17:52There, under a flap of skin, it's sealed away for the winter.
0:17:55 > 0:18:04When the egg is safely inside the male's pouch, the females are free to go and they start the long trek
0:18:04 > 0:18:11back across the sea ice to the open ocean, leaving their partners to face the coldest conditions on Earth.
0:18:28 > 0:18:35With temperatures of 70 below, and in terrible storms, the penguins huddle tightly together for warmth.
0:18:35 > 0:18:39No other penguins are so tolerant of one another,
0:18:39 > 0:18:44but for Emperors, this is the key to survival.
0:18:48 > 0:18:51The co-operation is not random.
0:18:51 > 0:18:56Those most exposed on the windward side move around the huddle
0:18:56 > 0:19:00to the more sheltered side. This ensures
0:19:00 > 0:19:05that every bird gets its fair share of warmth in the middle
0:19:05 > 0:19:10and takes its turn in enduring the brunt of the Antarctic weather.
0:19:18 > 0:19:21As midwinter approaches,
0:19:21 > 0:19:27the sun disappears below the horizon for the last time this season.
0:19:27 > 0:19:30A month of total darkness lies ahead.
0:19:36 > 0:19:42Above the huddle, the southern lights, the "aurora australis",
0:19:42 > 0:19:44blaze across the winter sky.
0:19:44 > 0:19:52These spectacular displays occur as subatomic particles, travelling through space,
0:19:52 > 0:19:55enter the Earth's magnetic field.
0:20:15 > 0:20:19As winter recedes, the huddles begin to break up
0:20:19 > 0:20:24and heat that was trapped within them for so long escapes.
0:20:24 > 0:20:31These males, who have not eaten for 115 days, are close to death by starvation.
0:20:43 > 0:20:48As the sun returns to the southern hemisphere,
0:20:48 > 0:20:55the females, sleek and fat from months of feeding at sea, march back to the rookery.
0:20:55 > 0:21:03The sea ice is now at its fullest extent and they may have to walk 100 miles to reach their colony.
0:21:12 > 0:21:15By now, the eggs have hatched
0:21:15 > 0:21:20and the tiny chicks are awaiting their first feed.
0:21:20 > 0:21:25Each female's return coincides with the hatching of her chick.
0:21:25 > 0:21:30Having starved for so long, a male can give only one meal -
0:21:30 > 0:21:33a milky secretion from his gut wall.
0:21:33 > 0:21:38If his partner doesn't return within ten days of the chick hatching,
0:21:38 > 0:21:43he will be forced to abandon it and head for the sea
0:21:43 > 0:21:45to find food for himself.
0:21:51 > 0:21:54SHRILL CRIES
0:21:57 > 0:22:05It's a noisy time in the colony. The courtship calling that took place before winter now brings its reward.
0:22:05 > 0:22:11After a separation of over 3 months, a bird can still recognise its partner's call.
0:22:13 > 0:22:17SHRILL CRIES
0:22:27 > 0:22:30When they find one another,
0:22:30 > 0:22:38the pair perform their greeting ritual to ensure that there hasn't been a case of mistaken identity.
0:22:38 > 0:22:45Then the female gives their chick its first proper meal - half-digested fish.
0:22:48 > 0:22:56She is very eager to take charge of the chick, but the male, having cared for it for so long,
0:22:56 > 0:23:02is reluctant to give it up. She has literally to push him back
0:23:02 > 0:23:04to get him to release it.
0:23:10 > 0:23:15The transfer is a tricky manoeuvre that must be done fast.
0:23:15 > 0:23:21A chick left on the ice for only two minutes will die.
0:23:45 > 0:23:52The males, after their four-month ordeal, near to starvation and desperate to feed,
0:23:52 > 0:23:57have to walk 100 miles or so back to the open sea.
0:23:58 > 0:24:03Mothers and chicks spend the next few weeks learning each other's call
0:24:03 > 0:24:10and forming a strong bond to ensure they will recognise one another in the months ahead
0:24:10 > 0:24:13when she returns from feeding trips.
0:24:21 > 0:24:25It's early spring and the weather is still variable.
0:24:33 > 0:24:36Severe storms are a real threat
0:24:36 > 0:24:43to the chick's survival. One that has been abandoned seeks shelter from passing adults.
0:24:43 > 0:24:50One of them seems interested, but the vital bond between parent and chick simply isn't there,
0:24:50 > 0:24:53and eventually the adult walks off.
0:24:54 > 0:25:00In fact, the adults do have a strong instinct to protect chicks,
0:25:00 > 0:25:07and birds that have not managed to breed will try to take possession of a stray or abandoned chick,
0:25:07 > 0:25:10but this fostering never succeeds
0:25:10 > 0:25:15because the adult has no partner to help in rearing the waif.
0:25:39 > 0:25:44These desperate unpartnered penguins will sometimes fight over a chick
0:25:44 > 0:25:47and crush it to death.
0:26:00 > 0:26:03Mortality is high.
0:26:03 > 0:26:10Many eggs don't hatch, and of those that do, 25% die in the first few months.
0:26:10 > 0:26:15Those that survive must grow fast and fledge
0:26:15 > 0:26:20before the sea ice on which they live breaks up beneath them.
0:26:37 > 0:26:45These chicks take five months to rear. Only by incubating the eggs through the harsh Antarctic winter
0:26:45 > 0:26:50so that the chicks hatch at the very beginning of the short summer
0:26:50 > 0:26:55is it possible for the Emperors to breed every year.
0:26:55 > 0:26:59It was to collect an Emperor penguin's egg
0:26:59 > 0:27:06that men made the first-ever land journey in the bitter cold darkness of the Antarctic winter.
0:27:06 > 0:27:14Bill Wilson, the naturalist on Scott's expedition, was fascinated by the evolutionary origin of birds.
0:27:14 > 0:27:19He thought that the embryo in an egg would provide conclusive evidence
0:27:19 > 0:27:24of the link between the feathers of birds and the scales of reptiles.
0:27:24 > 0:27:28So on June 12th, 1911, in midwinter,
0:27:28 > 0:27:34he and two companions left Captain Scott's hut here on Cape Evans and set out
0:27:34 > 0:27:41for the Emperor penguin colony on the other side of Mount Erebus, 65 miles away.
0:27:41 > 0:27:48It was a trip that became known, with some justice, as the worst journey in the world.
0:27:48 > 0:27:53The weather was abominable. Their clothes and harnesses froze solid
0:27:53 > 0:28:00and all suffered terrible frostbite as they hauled their sledges over heavily crevassed terrain.
0:28:00 > 0:28:08They lost their tent in a violent storm. By a miracle, they found it again and made it back to the hut.
0:28:08 > 0:28:13They brought back three eggs and three penguin skins,
0:28:13 > 0:28:18one of which is here in Scott's hut, preserved by the Antarctic cold.
0:28:18 > 0:28:26Although the link between birds and reptiles is no longer in doubt, the eggs didn't provide the evidence.
0:28:26 > 0:28:33Even so, the journey remains one of the great epic stories in the annals of polar exploration.
0:29:03 > 0:29:08Subtitles by Calum Short BBC Scotland 1993