S1, E5: A season of complete darkness, and the worst weather anywhere on the planet: midwinter in the Antarctic. The hostile landscape seems completely devoid of life, but under the ice – now filmable using new diving techniques and remote video cameras – life abounds. Ghost-like white fish are kept alive by anti-freeze in their blood and giant sea spiders patrol the sea bed. Most astonishing of all are the Weddell seals, the only seal to over-winter so far south, which scrape breathing holes through ice up to two meters thick and hunt as deep as 600 meters to find fish. In the center of the continent, male Emperor penguins huddle for warmth throughout the winter, each incubating a single egg. The hatching of the chicks heralds the approach of spring – the Antarctic year has come full circle.