There was a period of excessive warmth which melted some of the polar ice.

有段时期温度过高，融化了极地的部分冰层。

《柯林斯英汉双解大词典》

The answer seems to be that, simply, late August is the period when polar bears in northern Alaska head north on to the sea ice, and that is what she was doing.

答案看起来是这样的：就因为八月底是阿拉斯加北部的北极熊游向北方的海冰的特定时段，文中这只母熊也正是这样做的。

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The study found that there are still a long-term polar drift and cycle of about 30 years of long-period oscillation.

经研究，发现地极还存在长期的漂移和周期约30年的长周期摆动。

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