Frozen Planet

Adélie penguins travel to Cape Crozier at the onset of spring to to breed, crossing the sea ice to get to the bare rock of the continent upon which their eggs will be laid. The females are still at sea but the males have arrived early to prepare for their arrival by building nests.

Each male collects pebbles with which he constructs his nest, but they must be wary. To avoid the effort of finding the best stones, some males will attempt to steal pebbles from nearby nests when their builders are otherwise occupied with the task at hand.

The spring sun does bring about warmer temperatures but it also heats the surrounding sea faster than the land. This causes cold air from inland to be pulled out towards the coast, generating powerful and icy katabatic winds that the male penguins have no choice but to endure as they await the arrival of the females.

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A female polar bear emerges from beneath the snow as the rays of the sun hit the high slopes in which she has made her den, for the first time in six months. Up here, her three young cubs are safe from male bears but to continue to nurse them she must soon lead them down to the sea ice where she can catch seals.

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9 out of 10 polar bear hunts end in failure. A male polar bear has been hunting on the sea ice throughout winter but the arrival of spring heralds a new source of prey: seal pups, hidden in dens a metre beneath beneath the surface. He first has to use his keen sense of smell to locate one of these dens and then use his body weight to punch through the ice. Though he comes up empty at the first den he tries, the bear detects a ringed seal pup that has already left its den but is still out on the ice. His luck doesn't change, however; as soon as it senses his presence, it slips into the hole in the ice into the water below.

The white fur of ringed seal pups helps to camouflage them against the sea ice to avoid detection from predators, enabling a mother seal to hunt underwater while her pup remains on the surface. However, the pup makes sure to remain close to its mother's breathing hole and, as soon as it detects danger from an advancing polar bear, slips into the water below.

A female polar bear, having led her two cubs down to the sea ice, begins to search for seals. She's not fed for 4 months and must hunt soon, but it's hard for her to be stealthy with two playful and boisterous cubs make. Her search ends fruitless but still she nurses her cubs on the reserves of milk she has left.

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At the onset of spring, a pod of narwhal arrives at an inlet on Baffin Island in Canada and travels single-file down the leads that have begun to form in the ice. The whales are hoping to be among the first to reach the rich fishing grounds that have remained frozen over through winter. The crack is so narrow that when they encounter another group coming from the opposite direction, the pod is forced to turn around and look for a different path to follow.

By the following week, the bay is mostly ice-free giving the narwhal more space to socialise. The whales brush up against each other, gently clashing their tusks, but what exactly this behaviour means remains a mystery. One suggestion has been that it helps assert each whale's position in the group's hierarchy.

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In spring, the warming Arctic seas spur the growth of plankton, which in turn supports a number of small creatures, including Arctic comb jellies, also known as "sea gooseberries", which move through the water, straining the water for microscopic organisms in their long trailing filaments. Their bodies are covered in tiny plates called cilia which shine in many colours as their undulating bodies catch sunlight.

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Among the smaller organisms supported by the explosion of plankton fuelled by the warming Arctic seas are predatory sea slugs such as Clione limacina. These marine gastropods are on the hunt for Limacina snails.

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The explosion of plankton in warming Arctic seas allows a number of small organisms to flourish, including the sea butterfly Limacina helicina. It glides through the water flapping its wings, avoiding predators such as the Clione limacina sea slug.

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In spring, plankton blooms in the warming Arctic seas which supports vast shoals of Arctic cod, some numbering 500 million fish. This annual event attracts many predators, from seabirds to seals.

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In Canada, the vast shoals of Arctic cod that flourish each spring are a bounty for harp seals in Canada; they share this harvest with many seabirds.

Each spring, the Arctic woolly bear caterpillar is the first insect to emerge on the tundra on Ellesmere Island. The caterpillar feeds voraciously whilst the surrouding vegetation remains ice-free but, this far north, the season is too short for the caterpillar to build up enough reserves to transform into a moth. So, as the temperatures drop in autumn, it succumbs to the encroaching ice, its body freezing solid and its heart stopping beating.

Yet, the next spring, the caterpillar thaws fully and, once again, takes to the tundra to feed. This cycle repeats a further 12 times. Only at the advent of the 14th spring does the caterpillar, now the oldest in the world, begin to create a cocoon to undergo metamorphosis. The moths that emerge will have only days to find a partner and mate before they die.

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The arrival of spring transforms Canada's tundra with fresh growth, which attracts great numbers of migrant birds from the south. Arctic wolves that have survived here in the leaner winter months prior take full advantage of this bounty. A small pack of wolves hunts waterfowl in a small lake before bringing back the remains of successful kills to the six month-old cubs waiting back at the den.

South Georgia is far enough north of the pole that it remains free of sea ice, allowing some animals, such as wandering albatross, to live here year around. Albatross chicks take 13 months to fledge and, for most of this time, they remain sat in their nest, protected from the cold with their thick layer of fluffy down, and fed by both parents on seafood they collect on trips out in the surrounding Southern Ocean.

King penguins are among the few animals that inhabit South Georgia throughout winter to benefit from exclusive access to rich fishing grounds of the surrounding Southern Ocean year round, compared to other birds and mammals that visit seasonally. To survive cold spells, penguin chicks must huddle together in creches for warmth.

Macaroni penguins are among the most numerous of the seasonal visitors to South Georgia. 10 million birds, half the world's population, come here breed.

Wandering albatross pair for life, a courtship that can last 50 years. Every two years, in spring, a pair will first renew their bonds with an elaborate variety of behaviours: spreading their wings, rapping their bills together, and affectionately preening each others' feathers.

In spring, female southern elephant seals in South Georgia become ready to mate again in spring having given birth to pups concieved last year. Each patch of beach is occupied by a single male, who must engage in often bloody battles with rivals to defend his right to breed with his harem of females.

Towards the end of spring, wandering albatross chicks born the previous year are now ready to take to the skies. It takes time for them to adjust to their large wings and not all maiden flights go as planned - one bird ends up in a patch of mud - but eventually, with the right wind conditions, they are able to take off and begin a 5-year journey in the Southern Ocean before they return to land.

Female Adélie penguins arrive at Cape Crozier as the sea ice begins to break, joining the males that arrived prior to build their nests in courtship. Once the eggs are laid, the males are left to incubate them while the females head out to sea to hunt. A group of penguins encounters a pod of killer whales travelling through the area. Luckily, these whales are fish specialists and pass the birds by.

A pod of killer whales travelling through Cape Crozier spooks a group of Adélie penguins as they "spy-hop" out of the water to get a better look at their surroundings. These killer whales are fish specialists and aren't here to hunt the penguins; instead, they're doing this to work out the best routes through cracks in the ice to reach the richer fishing grounds at the coast.