我们还遇到过无冰的水面，我们不得不游着前进。

We came across open water which we had to swim across.

youdao

这就是为什么我们很难准确预测最早什么时候能看到无冰的北极。

That's what makes it so difficult to predict exactly how rapidly we might see the Arctic go ice-free.

youdao

据推测，北极夏日无冰的开始年份，最早为急迫的2013年，最晚2050年。

Estimates range from 2013-terrifyingly soon-to 2050 for the first year when the Arctic is free of ice in summer.

youdao