I'm standing at the north pole, the very top of the earth. Up here, is easing sea while the polar regions are so cold. The sun never rises higher enough in the sky to warm my back. And those rays do strike the surface, eventually reflected back from these white wildness. But the fundamental problem is that there's no sun here at all for half the year.

The polar winter is unrivaled in its harshness, a night that lasts for months. Only the toughest day as temperatures plunge to minus 70 degree centigrade. And yet, the greatest challenge survive here is not the cold, but the extreme swings between the seasons.

When the sun finally returns, an extraordinary transformation begins. This frozen world begins to melt away. The polar sping bings a brief opportunity for life. By summer, the sun no longer sets and works its magic for 24 hours a day. Now it's a race to breed before the sun departs. By autumn, all but the hardest abandon the poles and the ice extends script. And the sea closes down for the long polar winter until once again the sun returns.

It's spring in the high arctic and the sun illuminates a giant frozen ocean, the first stop on our journey. The most powerful land predator is on the prowl.