Alaska: Earth's Frozen Kingdom

A mother sea otter nursing her fluff-ball baby through the early, chilly days of spring and black bear cubs emerge from their den.

Some grizzly bears come up with an ingenious way to fatten up during the short summer months whilst a young caribou calf joins a vast herd on its huge migration.

The eight month-long winter takes a grip on Alaska as we discover how life survives in 24 hours a day darkness until the sun returns.