A male polar bear walks slowly across a windy sea ice in the north of Svalbard. When viewed from afar, he appears white on white, which is precisely where the point is. The bear is actually not white. Each guard hair is transparent, hollow, and will scatter light, while the underlying skin is jet black to absorb whatever light reaches the high Arctic.

He is known to scientists as Ursus maritimus or the sea bear, and is the largest land-living carnivore today. Adult males weigh 300 to 800 kilograms and are 200 to 250 centimetres long from nose to tail; and the females are approximately half the size, weighing 150 to 300 kilograms and measuring 100 to 150 centimetres in length. The species is sexually dimorphic; the males have broad heads and are much heavier on the shoulders. The body is thinner, the neck longer and the skull flatter, all advantageous for slipping through the water and pushing its head into seal breathing holes, when compared with the brown bear.

That's the marine life that's visible in all its detail. There is a thick layer of blubber under the fur, with a thick inner coat. Their paws are huge, frequently 30 centimetres wide, and their soles are hairy, like snowshoes, to help them grasp ice. Even the claws remain short and curved – more suited to holding seal skin than to rooting. Polar bears are officially considered marine mammals as they spend much more of their year on the frozen ocean than on dry land.

Their world revolves around the pole and passes through five countries: Canada, U.S. in Alaska, Greenland, Norway and Russia. There are 19 known subpopulations which ride the sea ice seasonality. A few bears remain in contact with the fast ice throughout the winter. Others take to the pack for thousands of kilometres and float with floes from Beaufort Sea to Siberia. Many arrive on shore when their summer platform is burned, subsisting on stored fat.

That waiting is possible thanks to seals. Ringed seals and bearded seals supply most of the calories, taken most often by still-hunting. A bear will find a breathing hole and position itself downwind and will lie perfectly still for one hour or longer waiting for a seal to come up for air. Then it attacks, pulls the animal onto the ice and feeds from the blubber, leaving the rest for Arctic foxes and gulls. The gaps are filled by walrus and beluga carcasses, and occasionally by a bird or an egg; but fat-rich seal blubber is the energy needed to sustain a female while she is nursing her cubs during long fasts.

The ice calendar is followed for reproduction. Mating takes place in April and May, and the fertilized egg is not implanted until the autumn. The pregnant female burrows a maternity den into a snow drift in October or November on land or sometimes on a stable pack ice. The young are born in December or January, with one or usually two being born blind, each weighing less than a kilogram. For months the mother does not eat or drink within the den, turning her fat into milk. Families start to form in March or April and cubs remain with her for approximately two and a half years, during which they are taught how to locate holes and how to interpret the ice.

It is difficult to come up with numbers in this giant habitat, but the IUCN classifies polar bears as vulnerable, with a population of about 22,000 – 31,000 animals worldwide. Not all subpopulations are faring the same. The sea ice area of the Southern Beaufort Sea group off Alaska and western Canada has been on a downward trend due to increasing ice-free seasons. The greatest long-term stress is from sea ice loss caused by climate change, which can reduce hunting duration and increase the amount of time bears spend on land and their exposure to humans, diet quality, and cub survival. The species is under threat from pollution and industry, and is listed as threatened under the U.S. Endangered Species Act.

Wild bears live for 15 to 18 years, with some females reaching their late twenties. In zoos they can last for 30. They swim for hours without stopping and have been recorded swimming for over 100 kilometers without stopping; they are able to smell a seal almost a kilometre away. The bear is nanook for Inuit people, named for the respect and caution that these people have held for it since time immemorial, as seen in stories, hunting and place names.

Repeat the same male when light dims. He stops at a pressure ridge and breathes, before taking a seat next to a dark hole. He will wait. The ice and the seal and the bear have come together for at least 120,000 years. The difference now is that the platform is no longer fixed, but rather changes depending on the time held each spring.