Summer is short in the Arctic Circle and by early October, the sea ice is beginning to return.
北极圈内的夏季很短暂，到了十月初，海冰又开始出现了。
Sea water starts to freeze at around minus two degree Celsius.
当水温降至摄氏零下二度时，海水就开始冻结。
But it will be some time before the ice is thick enough for polar bears to return to their hunting platform.
不过还要再过一段时间，冰层厚度才足以使北极熊能够重返捕猎平台。
For the bears, this is the toughest time of the year.
对北极熊来说，这是一年中最困难的时期。
Without the sea ice, it's almost impossible for them to catch seals.
没有了海冰，它们想捉到海豹几乎是不可能的。
In autumn, the bears living around Canada's Hudson bay lie in the shores in large numbers waiting for the sea to freeze.
秋天里，加拿大哈德逊湾沿岸的北极熊在岸边大量聚集，等待海面结冰。
These are the southern most polar bears on the planet and they deal with longer and hotter summers than any others.
这些是地球上分布最靠南的北极熊，它们比其它同类要忍受更长也更热的夏季。
Many of these bears will not have eaten for the last five months.
这些熊当中很多都已经有五个月没吃东西了。
Each year, their hunting ground is melting earlier and taking longer to refreeze as winter approaches.
每年，它们的捕猎场都融化得更早，而当冬季再次来临时冻结得又更晚。
With the shorter hunting season out on the ice, polar bears have less time to fatten up.
由于能在冰上捕食的时期较短，这些北极熊积攒脂肪的时间更少了。
Some bears will scavenge for scraps and even eat seaweed.
有些北极熊会捡食残羹剩饭，甚至进食海藻。
But with such meager pickings, for many, autumn is simply waiting game.
但因为食物如此贫乏，很多北极熊秋天里能做的只有等待。
Polar bear is extraordinarily well adapted to deal with its long periods of famine.
北极熊面对长时期的饥饿适应能力极好。
They slow their metabolism right down and by staying inactive, they conserve their energy, awaiting the return of the ice.
它们能大幅降低新陈代谢速度，而通过尽量不动，它们能节省体能消耗静待冰层的形成。
As winter approaches, the sea of northwest Greenland is beginning to freeze.
随着冬季临近，格陵兰岛西北的海面开始冻结。
At first, a soupy mixture of ice crystals and cold water, known as frazil ice, starts developing.
一开始时，初生冰的形成就是粥状的冰晶和冷水的混合物。