行星地球第六集：冰雪世界 Ice Worlds

[00:26.90]Both poles of our planet are covered with ice. [00:30.76] [00:31.08]They're the largest and most demanding wildernesses of all. [00:35.83] [00:37.52]Nowhere else on Earth is seasonal change so extreme. [00:42.04] [00:42.30]It causes the ice to advance and retreat every year [00:47.87] [00:48.88]and all life here is governed by that. [00:53.24] [01:10.47]When the first polar explorers headed south [01:14.02] [01:14.11]giant cathedrals of ice marked their entry into uncharted territory. [01:20.17] [01:24.16]Passing the towering spires they must've wondered what unearthly sights lay in store. [01:30.72] [01:34.78]As they battled on the ice became increasingly dominant [01:38.75] [01:38.86]but nothing could have prepared them for the ice world that finally loomed into view. [01:45.65] [01:50.61]Terra incognita - the unknown land. [01:55.43] [02:07.06]At the southernmost extreme of our planet the continent of Antarctica [02:11.71] [02:11.81]is as large as the United States of America. [02:15.22] [02:21.33]Ninety percent of all the world's ice is found here. [02:25.78] [02:28.35]This frozen world is largely deserted until the start of spring. [02:35.32] [02:39.61]Adelie penguins [02:41.63] [02:42.36]in a hurry. [02:44.43] [02:49.70]The clock is ticking. [02:51.93] [02:52.16]Instead of waiting for the summer melt the new arrivals hasten south over the frozen sea. [02:58.56] [03:10.03]They have come here to breed but polar summers are so short [03:14.29] [03:14.48]they must be in position before the thaw starts. [03:18.77] [03:23.40]As the sea ice retreats life can journey farther south. [03:28.49] [03:34.18]Antarctic waters are so rich that visitors come from far and wide to harvest them. [03:41.22] [03:48.27]Vast numbers of chinstrap penguins come ashore to breed. [03:53.89] [04:01.46]No bird will lay their eggs directly onto ice [04:05.40] [04:05.50]so bare rock is a vital commodity. The best patches are worth the climb. [04:12.33] [04:16.85]The clifftops are soon stained pink with the droppings of tens of thousands of nesting penguins. [04:24.24] [04:32.31]Only in a land almost entirely covered in ice could bare rock be reckoned an oasis. [04:39.97] [04:41.69]Some will travel into the heart of the continent to find it. [04:46.17] [04:47.77]These are noon attacks the exposed peaks of vast mountain ranges buried in ice over a mile deep. [04:57.39] [04:58.90]The eerie silence here is only broken in spring. [05:04.18] [05:10.64]The snow petrels have arrived and are courting. [05:14.86] [05:21.82]Antarctic petrels now join the most southerly colony on Earth. [05:27.26] [05:28.68]The birds have flown inland for over three hundred miles [05:32.09] [05:32.11]to reach this breeding site. [05:34.59] [05:39.13]Once their eggs have hatched they'll be forced repeatedly to make the 600 mile round trip [05:44.55] [05:44.56]to gather food in the ocean. [05:46.60] [05:48.79]First though valuable nesting places must be defended from property thieves. [05:54.52] [06:01.17]After laying their eggs the petrels take time out to clean their plumage. [06:06.64] [06:27.03]The south polar skua is a formidable opportunist [06:31.82] [06:35.15]but the skuas have not chanced upon the petrels [06:38.47] [06:38.92]they've been waiting for them. [06:41.58] [06:44.82]These birds do not need to go to the ocean for their food. [06:49.93] [07:06.52]The skuas can survive further south than any other predator [07:10.66] [07:10.66]by exploiting the petrels' desperate need for bare rock. [07:15.14] [07:25.41]Even at the height of summer less than 3% of Antarctica is free of ice [07:30.72] [07:30.77]and nearly all of that exposed rock is found in one place [07:35.34] [07:35.68]the Antarctic Peninsula. [07:38.26] [07:44.42]It's long arm extends further north than the rest of the continent, so spring arrives here first. [07:51.54] [08:05.21]The thaw unlocks sheltered bays [08:08.36] [08:08.36]that provide refuge from the relentless battering of the southern ocean. [08:13.86] [08:17.55]In the depths something stirs... [08:21.83] [08:44.84]Humpback whales. [08:46.84] [08:46.89]They have travelled over 5000 miles to reach these waters. [08:52.17] [08:58.32]The whales are harvesting krill [09:01.02] [09:01.07]shrimp like creatures that begin to swarm here as soon as the ice retreats. [09:06.74] [09:20.35]Diving into the heart of the swarm [09:22.80] [09:22.94]teams of whales spiral around each other in close coordination. [09:28.09] [09:30.86]Now they turn and blasting air from their blowholes and ascend towards their prey. [09:36.98] [09:38.55]The krill becomes concentrated as the spiralling net of bubbles draws inwards. [09:44.29] [10:10.77]The team of whales work around the clock for the bloom is short lived. [10:15.65] [10:15.81]Summer is already fading and the whales will soon be forced north as winter returns. [10:23.07] [10:26.07]The sun's influence diminishes and the ocean starts to freeze. [10:31.20] [10:31.43]The greatest seasonal change on our planet is underway. [10:36.91] [10:41.42]The ice grows at an extraordinary rate advancing two and a half miles a day. [10:47.06] [10:47.32]In a matter of weeks the continent effectively doubles in size. [10:52.68] [10:55.52]Life flees from Antarctica... [10:59.23] [11:04.99]but one creature is just arriving. [11:08.11] [11:12.76]Every winter Emperor penguins leave the comfort of their ocean home and begin a remarkable journey. [11:21.13] [11:22.55]They head towards their breeding grounds almost a hundred miles inland. [11:28.65] [11:50.30]Eventually the emperor penguins reach the place where they were hatched [11:54.75] [11:54.93]an area sheltered by icebergs trapped in the frozen ocean. [11:59.40] [12:00.49]Here they will raise the next generation [12:03.87] [12:10.05]but first each must find a mate. [12:13.36] [12:16.15]Males begin to serenade [12:19.28] [12:23.07]and if a female replies they pair up, posing like statues. [12:28.99] [12:32.72]New couples quickly form a strong bond [12:35.98] [12:36.07]they seem oblivious to the noisy crowd around them. [12:40.36] [12:42.20]To cement their relationship the male steps out with his female. [12:47.22] [12:56.70]The brief courtship complete there isn't a moment to loose. [13:01.22] [13:01.29]With so much pressure to perform any male would struggle to stay on top. [13:06.85] [13:14.31]Several weeks later and it seems that most couplings were successful [13:19.24] [13:20.12]but producing the egg has taken it's toll. [13:24.07] [13:24.37]The females no longer have the energy to incubate. [13:28.09] [13:29.91]The male takes over. [13:31.70] [13:31.97]It's still minus 20 degrees centigrade, so the transfer must be done quickly or else the egg will freeze. [13:39.14] [13:39.30]With no bare rock to nest on the male tucks the egg into a special pouch [13:44.36] [13:44.45]where he can keep it warm. [13:46.52] [13:47.20]It requires an extraordinary piece of teamwork. [13:50.76] [13:54.92]Driven by hunger, the exhausted females now return to the ocean on their own [14:00.50] [14:00.70]repeating the epic journey they made with the males only a month before. [14:06.31] [14:11.69]Now the sun barely appears above the horizon. [14:15.50] [14:16.13]As the day shortens, it's warmth is withdrawn from the continent. [14:21.35] [14:31.81]With the females gone the colony undergoes a strange transformation. [14:37.46] [14:38.03]The males shuffle into groups, their eggs still tucked away above their feet. [14:44.30] [14:46.52]They lock together in tightly packed huddles as they struggle to keep warm. [14:52.10] [14:55.69]Speeding up the action reveals how these huddles constantly shift and change [15:00.64] [15:00.64]as each penguin works it's way towards the warmer interior. [15:06.01] [15:06.79]Crammed into this scrum, the birds are remarkably good natured, but they have to be. [15:12.57] [15:12.75]If the huddle breaks even for a moment, precious heat escapes. [15:18.09] [15:35.51]It's imperative they reform as quickly as possible [15:39.46] [15:39.60]for only by as acting as one can the males withstand the elements, and protect their eggs. [15:46.34] [15:50.95]But their greatest test lies ahead. [15:54.44] [15:54.85]As winter advances, frequent blizzards drive the temperature down. [15:59.95] [16:00.50]It's now 60 degrees below zero. [16:05.40] [16:07.08]The birds at the edge of the huddle [16:09.39] [16:09.46]bear the brunt of the hundred mile an hour winds [16:12.21] [16:12.39]and so provide shelter to those taking their turn in the middle. [16:17.25] [16:25.24]Abandoned by the sun the males are left alone with their eggs [16:29.46] [16:29.46]to face the coldest darkest winter on Earth. [16:34.47] [16:40.94]At the northern extreme of our planet [16:43.80] [16:43.82]the sun rises for the first time in months, illuminating a very different ice world. [16:51.47] [16:53.62]Unlike Antarctica, the Arctic is a vast frozen sea surrounded by land. [17:01.09] [17:02.43]Here winter is coming to an end [17:05.51] [17:05.83]but this bleak wilderness remains locked in ice. [17:11.46] [17:17.72]Eider ducks break the silence. [17:20.65] [17:20.81]They have stayed here braving the northern winter, instead of flying south to warmer climes. [17:27.93] [17:30.98]Flocks forty thousand strong sweep across the frozen wastes. [17:36.88] [17:49.47]They all have the same goal [17:51.94] [17:52.01]a polinear, a permanent hole in the sea ice kept open throughout the winter by strong ocean currents. [17:59.98] [18:03.36]This unusual duck pond provides an overnight sanctuary [18:08.01] [18:08.06]and when day breaks a rare chance to feed. [18:12.35] [18:23.92]Just ten meters beneath the ice, the sea floor is carpeted with dense mussel beds. [18:31.04] [18:32.25]These can only be reached during a brief lull in the currents. [18:36.22] [18:36.35]The ducks must quickly prise the mussels free before the tide starts to turn. [18:42.78] [18:48.72]The window of opportunity is short. [18:51.29] [18:51.47]As the current begins to build it's up up and away. [18:56.60] [19:07.29]These permanent holes in the ice provide seafood throughout winter. [19:13.44] [19:14.75]The diners attract others. [19:17.34] [19:23.42]In the Arctic, any breach in the icy barrier can be a lifeline. [19:28.59] [19:32.45]Musk oxen create their own. [19:34.70] [19:36.11]These giants have the strength to smash through the frozen crust [19:40.28] [19:40.39]to graze on the vegetation below. [19:43.32] [19:47.22]These icebreakers create an opening for other over winterers. [19:52.19] [19:53.08]Flocks of ptarmigan make unusual grazing companions for the musk oxen [19:58.16] [19:58.46]whose entourage grows throughout the day. [20:01.25] [20:09.89]This odd assembly of vegetarians doesn't go unnoticed. [20:15.09] [20:15.84]An arctic fox. [20:17.61] [20:22.85]The musk oxen have recently given birth. [20:26.46] [20:26.87]For the fox, it's a chance to scavenge [20:30.59] [20:36.99]but half a ton of mad hairy cow is not to be trifled with. [20:42.55] [20:51.42]The calves are born well before the spring melt [20:54.44] [20:54.44]giving them a head start when summer finally arrives. [20:59.66] [21:02.68]It must get to grips with it's new ice world [21:06.10] [21:06.53]benign one minute life threatening the next. [21:10.51] [21:16.22]Even in spring winds chill to the bone. [21:20.17] [21:23.08]The calf must stay close to it's mother to avoid getting lost in the sudden blizzard. [21:28.73] [21:37.93]Arctic wolves. [21:40.44] [21:43.89]In the whiteout, the threat is almost impossible to detect [21:47.79] [21:47.88]but the musk oxen instinctively retreat to higher ground. [21:51.98] [22:07.03]Forming a defensive ring around their calves [22:10.30] [22:10.38]the adults present a barricade that few hunters could breach [22:14.53] [22:16.84]but the wolves need not risk injury today. [22:20.61] [22:22.38]A calf has been left behind in the panic. [22:26.13] [22:38.48]With each passing day the sun climbs higher in the sky [22:42.94] [22:43.09]and it's rays strike the Arctic more directly. [22:46.68] [22:47.54]It's spring and new life stirs. [22:52.06] [22:55.78]The polar bear cubs emerge from the den in which they were born. [23:00.01] [23:00.39]Their mother stretches her legs after five months under the snow. [23:05.87] [23:10.43]They're just two months old [23:12.32] [23:12.66]and instinctively follow her lead. [23:16.06] [23:30.72]A steep slope makes the best site for a den [23:34.19] [23:34.28]but it's a tricky place to take your first steps. [23:38.75] [23:56.75]It may look like fun, but this is serious training for the task ahead. [24:02.10] [24:02.28]There's no food on the slopes [24:04.15] [24:04.15]and the family will need to head out across the frozen sea, before the mother's milk runs dry. [24:10.54] [24:16.69]Two weeks later they're ready. [24:19.94] [24:20.62]Out on the sea ice the female can hunt for seals [24:24.66] [24:24.82]but it will take all her mothering skills to keep her cubs safe [24:28.95] [24:29.13]in this dangerous world of ice. [24:32.56] [24:46.78]The annual melt has begun. [24:50.37] [24:51.54]This is a challenging time for the bear family. [24:55.06] [24:55.33]One out of every two cubs do not survive their first year out on the ice. [25:01.53] [25:11.61]As the sun's influence increases, the sea ice seems to take on a life of it's own. [25:17.60] [25:25.47]Glacial melt waters pour from the land [25:28.33] [25:28.51]mingling with the sea and speeding up the thaw. [25:32.51] [25:37.23]The seascape is in constant flux, as broken ice is moved on by winds and currents. [25:44.49] [25:52.95]The ice is becoming too weak to support a male polar bear. [25:59.03] [26:05.89]He attempts to spread his weight [26:08.56] [26:08.65]but the ice that has supported him all winter is rapidly disintegrating. [26:13.92] [26:15.62]Each year as the climate warms the Arctic holds less ice. [26:20.39] [26:20.59]This is a disaster for polar bears. [26:23.61] [26:23.65]Without it's solid platform, they can't hunt the seals they need in order to survive. [26:30.19] [26:32.71]This may be a glimpse of the unstable future [26:36.16] [26:36.16]faced by this magnificent creature. [26:39.42] [27:11.56]As the ice disappears seabirds return to the high Arctic. [27:17.30] [27:24.95]Little auks arrive in their millions. [27:28.80] [27:30.76]In some ways these birds are the penguins of the north. [27:34.93] [27:34.98]The seek bare rock on which to lay their eggs and they look rather like penguins too. [27:40.70] [27:46.50]Unlike Antarctica, the Arctic can be reached by land based predators [27:51.68] [27:51.70]which is why little auks have kept the ability to fly. [27:55.92] [28:00.60]They use scree slopes to protect their eggs, burrowing up to a meter beneath the rocks. [28:07.41] [28:13.33]At the height of summer the sun never sets [28:16.57] [28:16.57]but just skims the horizon before rising again. [28:20.66] [28:25.88]Migrants return to the Arctic from far and wide. [28:30.44] [28:30.85]They've come to make the most of the brief flush of food [28:34.09] [28:34.23]and to produce their young. [28:36.36] [28:37.81]Sandhill cranes have travelled all the way from New Mexico. [28:42.94] [28:47.80]Their chicks join the growing band of youngsters exploring the tundra. [28:53.72] [29:00.10]For a few months each year the Arctic becomes the land of the midnight sun [29:05.77] [29:06.02]and twenty four hours of daylight allow animals to feed around the clock. [29:11.40] [29:12.72]The arctic fox finally has enough food to raise her large family. [29:18.57] [29:32.87]If you choose to nest in the open you must be prepared for a fight. [29:37.98] [29:46.38]Arctic skuas will see off any trespassers even large vegetarians. [29:52.34] [30:36.57]The male polar bear's ice world has finally vanished beneath him. [30:42.93] [30:53.62]While the female is still kept on land by her dependent cubs [30:58.40] [30:58.45]the male can take to the sea in search of food. [31:02.01] [31:02.17]Ducking and diving, he hopes to ambush seals resting on the remaining fragments of ice. [31:09.43] [31:35.01]In these new surroundings he is a surprisingly adept swimmer. [31:41.00] [31:50.82]Once an extremely rare sight [31:53.53] [31:53.53]polar bears have recently been seen over sixty miles from the shore. [31:58.97] [32:11.86]There is now no turning back for this bear. [32:15.72] [32:15.97]He's forced to head out into deeper water. [32:20.39] [32:27.18]His giant front paws help him to fight the ocean currents. [32:32.56] [32:52.41]He seems at home in the sea but he cannot swim indefinitely. [32:58.06] [33:00.94]He will drown if he doesn't find land somewhere in this vast ocean. [33:06.75] [33:33.21]Walruses are now gathering on low lying islands. [33:37.32] [33:37.71]They gave birth on sea ice [33:40.07] [33:40.07]but with this platform now gone, they need a new place to haul out and nurse their young. [33:46.60] [33:48.42]After several days at sea the male bear finally makes landfall [33:53.41] [33:53.50]drawn by pungent smells emanating from the island. [33:58.43] [34:05.82]By the end of summer the bear has lost half his weight. [34:10.09] [34:10.38]With the ice long gone he is forced onto land in search of food. [34:16.06] [34:24.52]There will be no easy meals on this island. [34:28.06] [34:28.51]Walruses are the largest seals in the world. They weight over a ton [34:33.10] [34:33.14]and are armed with tusks a meter long. [34:36.41] [34:39.25]Exhausted from his swim the bear must regain his strength. [34:44.44] [34:50.66]The next day a sea fog shrouds the island. [34:54.52] [34:54.75]The walruses sense that they're in danger. [34:58.13] [35:00.72]Using the fog as cover the bear approaches the herd. [35:05.35] [35:09.91]The adults close ranks around their young, presenting a wall of blubber and hide. [35:16.49] [35:26.09]He tests the barrier but it stands firm. [35:28.36] [35:29.26]It appears that the world's largest land carnivore has met his match. [35:34.44] [35:41.83]There must be a chink in the armor somewhere. [35:44.40] [35:48.62]Not here. [35:49.82] [35:58.65]This female walrus is shielding her pup, if can just prise her off. [36:03.85] [36:10.81]The bears claws and teeth can't penetrate her thick hide. [36:15.49] [36:23.79]With the herd retreating to water the bear must move quickly. [36:28.27] [36:33.23]Having failed with one he heads straight for another. [36:37.02] [36:53.91]The chance of his first meal in months is slipping away. [36:58.31] [37:05.07]He seems increasingly desperate. [37:07.27] [37:13.24]It's now or never. [37:15.22] [37:16.13]He must avoid the stabbing tusks if he's to win. [37:20.07] [37:26.68]The flailing walrus is immensely powerful and drags the bear away from the shallows [37:32.17] [37:32.26]towards the safety of the herd. [37:34.64] [37:49.80]It slips from his grasp. [37:52.30] [38:00.29]Only at the height of summer when bears are on the verge of starvation [38:04.80] [38:05.07]will they risk attacking such dangerous prey. [38:08.89] [38:12.38]It was a gamble that this bear took, and lost. [38:16.81] [38:19.35]The stab wounds he received from the walrus are so severe that he can barely walk. [38:26.50] [38:30.60]The walruses are calm again [38:32.90] [38:33.24]seemingly aware that the injured bear no longer poses a threat to them or their young. [38:39.86] [38:54.73]Unable to feed this bear will not survive. [38:59.65] [39:11.32]If the global climate continues to warm [39:14.31] [39:14.56]and the Arctic ice melts sooner each year [39:17.42] [39:17.67]it's certain that more bears will share this fate. [39:22.05] [39:42.99]At the southern end of our planet [39:45.49] [39:45.58]fiery ribbons are illuminating the winter skies. [39:49.37] [39:49.60]<i>The aurora australis. [39:52.77] [39:55.45]This light brings no warmth to the male penguins who are still huddling [40:00.85] [40:01.08]defying the coldest conditions on the planet. [40:04.89] [40:17.85]Their ordeal is drawing to a close. [40:22.12] [40:28.77]Thirty days after it last set the sun rises once more on Antarctica. [40:35.91] [40:56.95]Their appalling trials have all been for this. [41:01.56] [41:16.85]Each father has just one meal left inside him. [41:21.62] [41:21.80]He's been saving it all winter. [41:25.09] [41:25.86]This single feeding will sustain the chicks for a few more days [41:31.01] [41:31.53]but the males have not eaten for nearly four months. [41:34.57] [41:34.58]If they do not eat soon they and their chicks will die. [41:39.70] [41:49.03]But there is hope on the horizon. [41:52.30] [42:03.73]The females are returning, and their bellies are full with fish. [42:09.91] [42:15.22]As they approach, waves of excitement ripple through the huddle. [42:20.41] [42:27.74]Each female calls to her mate, and he, recognizing her song, trumpets back. [42:35.12] [42:37.64]Reunited, at last. [42:40.43] [42:43.38]The mother feeds her chick for the first time. [42:47.39] [42:50.73]She's keen to start parenting [42:53.02] [42:53.75]but the father needs persuading to surrender the chick he's been caring for all winter. [42:59.67] [43:03.71]He must now put his chick at risk. In these temperatures it could freeze in seconds. [43:10.13] [43:13.54]The male will have to let go. [43:16.35] [43:22.64]Eventually, the transfer to the mother is safely made. [43:26.72] [43:41.17]The chicks grow quickly on a diet of fish and squid. [43:46.44] [43:59.24]Soon they're keen to explore, but always with mother in tow. [44:04.93] [44:06.79]This chick is less fortunate. [44:09.02] [44:09.13]It's mother has not returned to claim it. [44:13.17] [44:14.33]Another orphan is searching for a new family, but this female already has a chick of her own. [44:21.39] [44:29.28]Some orphans receive too much mothering from penguins whose own chicks have not survived. [44:35.14] [44:35.32]The urge to parent is so strong, that they will compete with one another to adopt any chick they find. [44:42.40] [44:47.12]Many of these squabbles will end in tragedy [44:49.84] [44:50.05]as the poor chick is trampled to death. [44:53.86] [45:04.89]Those chicks that do have parents quickly learn survival skills. [45:10.54] [45:11.54]Even in spring, they must huddle together for warmth [45:14.74] [45:14.78]just as their fathers did in the depths of winter. [45:18.23] [45:22.23]A group of chicks has got lost in the blizzard. [45:25.88] [45:31.98]Cold and disorientated they search for the colony. [45:36.25] [45:42.35]It will not be long before the storm claims it's first victims. [45:47.44] [46:05.52]By early summer, the chicks are surprisingly well developed [46:10.31] [46:10.51]and now look ready to take on the world. [46:14.37] [46:15.48]Those that survived their first year have the best possible start in life [46:20.09] [46:20.18]thanks to the extraordinary hardships endured by their parents. [46:25.56] [46:25.72]Parents who battled with the Antarctic winter, and won. [46:31.80] [46:40.40]In the Arctic the two polar bear cubs are now independent of their mother [46:45.62] [46:45.69]and they briefly reunite where their home ranges overlap. [46:50.98] [46:56.88]Their time together will be fleeting. [46:59.67] [46:59.99]Most of their lives are now spent alone [47:02.82] [47:02.96]wandering the vast tracts of frozen ocean. [47:06.84] [47:34.66]Following their mother, has prepared them for life at the pole [47:39.18] [47:39.29]an ever changing land ruled by ice. [47:44.28] [47:45.30]Whether they are ready for the bigger changes that have begun to shape the ice worlds of our planet [47:50.48] [47:50.70]remains to be seen. [47:54.99]

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