Frozen Planet

Summer brings many challenges for polar bears. Cubs born in winter have never seen the sea ice break up before and are wary of taking their first swim, while their mother is completely at home in the water.

The trouble for the swimming adult bears, however, is that hunting is made all the more difficult - the seals they're searching for have the advantage.

For one male bear leaving the water to rest on an ice floe, drying off is easy; his fur is so dense that he's able to shake off most of it in a few seconds and whatever's left is quickly absorbed by the ice on which he rolls.

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Bearded seals finds it easier to evade hunting polar bears during the summer. With so little ice left, the predators are forced into entering the water, where the seal has the advantage.

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Snowy owls make their nests on the bare ground in the Alaskan tundra. The male works tirelessly to bring lemmings to his mate and their owlets; over the course of the season, he will catch over 1,000 of them. The owlets can't swallow the lemmings whole so the parents first tear the meal into smaller pieces.

As the chicks grow bigger, they become vulnerable to predatory skuas, such as the pomarine jaegers that circle the skies above. The mother defends against a skua as it swoops down towards the chicks by leaping up to intercept the attacker with her talons outstretched.

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Lapland longspurs nest on the bare ground in the Alaskan tundra. The chicks are able to leave the nest within just 10 days of hatching, because their parents maintain such a constant supply of food for their brood.

A pomarine jaeger circles the skies above the Alaskan tundra looking for easy prey such as snowy owl chicks that aren't yet able to fly.

Even after finding a target, the jaeger must contend with the chicks' mother, who vigorously defends her chicks by leaping up to intercept the jaeger as it swoops down with its talons outstretched.

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On Ellesmere Island, a pair of Arctic wolves tracks down a musk ox herd on the move, searching for fresh grazing. With the hungry cubs back at the den growing quickly in the summer months, it falls to the parents to tackle such large prey to provide for them.

The hunters attempt to panic the herd into scattering so they can more easily pick out a weaker target. They manage to isolate a calf, and work together to wear it down to the ground to deliver a killing bite. But the rest of the herd, now regrouped, charges back and encircles the calf, forcing the wolves to retreat.

With a wall of sharp-horned adults now between them and the calf, the wolves give up the hunt and return to their cubs empty-handed. The pack leave their den behind to find better hunting opportunities elsewhere on the tundra while the season lasts.

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King penguins, returning from the sea with food, must find their chicks amongst the 400,000 birds nesting on South Georgia's northern coastline, somehow recognising their own chick's call amongst the chorus.

In summer, temperatures on land can reach 17°C. The penguins' thick coat of feathers, usually the perfect adaptation for braving the cold, now become a burden in the heat of the sun. The adults cope by simply lying flat on the beach to expose their feet - the only part of their body not covered in feathers - to cool in the breeze, or by taking a dip in the ocean.

The chicks, however, won't be able to swim properly for another two months. They instead gather at a shallow pool of water that has become thick with mud, which they coat their bodies with as they wade through. Water in mud evaporates slowly, which helps them stay cooler for longer.

Elephant seals on the beaches of South Georgia cope with the summer sun by flinging wet sand onto their bodies.

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Crabeater seals are one of the most abundant mammals on the planet. Over 15 million live in the Antarctic Peninsula, the surrounding waters of which are enriched by blooms of algae and krill in the summer.

There are 300 million tonnes of krill in the Southern Ocean, supporting almost all Antarctic life. This staggering number of organisms is only possible because algae that has been trapped in the sea ice during winter is released in great quantities during the summer melt.

The krill have specialised interlocking hairs on their front legs which they use to collect algae.

Humpback whales are among the visitors drawn to the Antarctic Peninsula each summer by the explosion of krill.

They feed by driving the crustaceans to the surface before lunging sideways to engulf their prey, often swimming together in groups so that one whale can collect the overspill from another's.

Antarctic minke whales are drawn to the Antarctic Peninsula each summer by explosion of krill. Here, they are prey for killer whales, that specialise in hunting whales.

One lone minke whale is chased by a pod of killers. The minke's streamlined body and short dorsal fins allow it to swim for hours, but its pursuers work in a team, to match the minke's endurance.

Eventually, the whale succumbs to repeated attempts by the killers to batter and bite it, eventually being flipped over and dragged underwater.

Some killer whales in Antarctica specialise in hunting other whales. One pod finds a lone minke whale and gives chase, flanking the prey on either side as it attempts to flee.

Though the minke can swim for hours, the killers are able to match its endurance by working as a team. As the outriders on either side of the minke tire, other members of the pod switch in. As their quarry tires, they begin to ram into it and tear chunks to wear it down further.

Eventually, after a two hour chase, the pod is able to flip the minke over and drag it underwater where, unable to breathe, it drowns.

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