苦思冥想的og 9 中的一句话，请帮忙解释

annwangwangqxwz

A recent discovery makes such a determination possible: relative land-ice

volume for a given period can be deduced from the ratio of two oxygen isotopes, 16 and 18, found in ocean sediments. Almost all the oxygen in water is oxygen 16, but a few molecules out of every thousand incorporate the heavier isotope 18. When an ice age begins, the continental ice sheets grow, steadily reducing the amount of water evaporated from the ocean that will eventually return to it. Because heavier isotopes tend to be left behind when water evaporates from the ocean surfaces，the remaining ocean water becomes progressively enriched in oxygen 18.

请教这句话应该怎莫解释。以前的讨论看了，可是不能够理解。the amount of water 后面的eveprated 是什莫成分，ocean 后面的that 指的是water 吗？

当冰期开始的时候，大陆冰层开始上升，这就减少了从海中蒸发而又回到海中的水的量。 这里为什莫就可以判定剩下的海水中氧18就会变多？不是冰期开始后，要蒸发的海水少了吗？如果少了，氧16也不会随蒸发还跑掉呀？。。。

请教！！！

leonchan

1.“the amount of water 后面的eveprated 是什莫成分”evaporated修饰water；“ocean 后面的that 指的是water 吗？”是。

2.氧18跑的慢，不就留下来了么。

3.这句不理解，并不影响解题；我觉得阅读的时候没有必要这么死扣句子语法，你只要知道冰<-->海水<-->氧18三者之间有一个大致的联系；如果此处出了细节题，考到说冰啊海水啊氧18氧16啊之间如何如何发生关系，再回来看不迟啊。

一孔之见，欢迎拍砖。

fuyun

the amount of water (which was ) evaporated from the ocean

that-----water

When an ice age begins, the continental ice sheets grow, steadily reducing the amount of water evaporated from the ocean that will eventually return to it. Because heavier isotopes tend to be left behind when water evaporates from the ocean surfaces，the remaining ocean water becomes progressively enriched in oxygen 18.

冰期开始后，本来应该循环回海里的蒸发掉的水变成陆地冰层的一部分了, isotope 16蒸发留在陆地冰层，heavier isotopes 18留在海中，所以ratio发生变化

swlfx

同意fuyun的解释和翻译。

在这里，冰川季开始的时候，并不意味着海水的蒸发减少了，只是说这些从海水中蒸发的水气变成了ICE，然后导致 ice sheets grow ，并且因此回到大海中的水（含O16相对更多）减少了，最终导致剩下的海水中重水（含O18相对更多）比例提高。