It causes the ice to advance and retreat every year. 使得冰盖面积每年都在扩大和缩小

1. Both poles of our planet are covered with ice.
   地球的两极都被冰覆盖着
2. They're the largest and most demanding wildernesses of all.
   是最大、最荒凉的无人区
3. Nowhere else on Earth is seasonal change so extreme.
   两极地区的季节变化非常极端
4. It causes the ice to advance and retreat every year.
   使得冰盖面积每年都在扩大和缩小
5. And all life here is governed by that.
   这里的一切生命都受其影响
6. When the first polar explorers headed south,
   第一批极地探险家前往南方时候
7. giant cathedrals of ice marked their entry into uncharted territory.
   经过这里的冰山就标志他们进入了未知领域

来自《行星地球 第一季 第六集 Planet Earth S01E06 冰雪世界》第 4 行