But when new born, each cub weighs just six hundred grams.
而每只幼崽刚出生时体重都只有约六百克。
They have no subcutaneous fat and will not survive exposure to the Arctic conditions above ground.
它们没有皮下脂肪，因此如果暴露在北极地面环境下将无法存活。
The family will remain in their den until March when the cubs are big enough to venture outside.
北极熊一家将在洞中一直呆到三月到来，那时幼崽们已经长大得足够外出闯荡了。
Inside the den, it's a snug zero degree Celsius.
洞中的温度是感觉舒适的零度。
Above ground, without the sun's energy, the temperature has plummeted to minus thirty degree Celsius.
而在地面上，因为缺乏太阳的能量，气温已经急剧下降至零下30摄氏度。
Male polar bears do not hibernate and remain active throughout the winter.
公北极熊不进行冬眠，而是在整个冬季都保持活动。
They are solitary animals and each winter they endure months of extreme cold and darkness alone on the sea ice.
它们是独居动物，而每年冬天，它们都独自在海冰上忍受着几个月的严寒与黑暗。
By mid February, an end to the long polar winter is insight.
到了二月中旬，北极漫长的冬季即将结束。
The sun rises above the horizon in Svalbard for the first time in months.
在斯瓦尔巴德群岛的地平线上，几个月以来太阳初次升起。
At first, there is less than two hour sunlight each day.
起初，每天只有不到两小时的阳光。
It will be another month before the days are long enough for the sun's warmth to start melting the froze Arctic Ocean.
还要再过一个月时间，白昼的时长才足以让太阳的热度开始融化冰冻的北冰洋。
Small pools have remained open throughout the winter.
有些小洞整个冬季都不会冻结。
These beluga whales became stranded when the ocean turned to ice in autumn.
这些白鲸在秋季海面结冰时被困在这里。
Like all mammals, they need to breathe oxygen.
它们与所有哺乳动物一样需要呼吸氧气。
The small hole on the ice is maintained by their continuous movement as they rise to the surface to breathe.
冰面上的小洞是靠它们探出水面来进行呼吸这样持续的运动才得以维持。
Open water is miles away, and this tiny pool is their lifeline.
开阔的水面在几公里之外，所以这狭小的洞成了它们的生命线。
They must stay near the hole to breathe, but having already exhausted any food supplies nearby, they are starving.
它们必须留在洞附近以维持呼吸，但是它们已经耗尽了周围的食物因此饥饿异常。
The belugas bear horrible scars and they are not caused by the ice but by predators.
白鲸身上带着可怕的伤痕，但这些并非与冰层碰撞所致而是掠食者留下的。