Question #1064

Ice age - must be true

Started by Lily · started 2013-05-25 18:13 · last activity 2018-06-22 20:30 · 4 replies

I am so lost ... Help! Is water from ocean same as water from sea? I get we learned this in elementary school sea can be attached to or even a part of the ocean -meditarranean sea and atlantic ocean- so ultimately sea water is ocean water and ocean water is sea water... But why distinguish them in the first premise if it is logically not so? Also ... I imagine an ocean and the water is evaporating up from it with o16 easily going up and the heavy o18 dragging behind ... I also imagine sea water same scenario except there are more o18 so more laggers and less easy o16s Normally in the ocean scenario, overall composition remains the same because what goes up much come down - precipitation ... (ignoring the confusion of that does sea water have to do with ocean water). The exception: ice age! What goes up, gets stuck while coming down ... So overall composition is disturbed. Must be true: well in either case (whether sea water or ocean water) both have those lagging o18 guys so no matter what is coming down those o18 guys are abundant?

Replies

  1. Mehran · 2013-05-25 22:28

    Hey Lily, Thanks for your message. Let's breakdown the stimulus first: Basically the ratio of o16 to o18 is higher in vapor than in seawater. So let's use some basic numerical examples: For vapor, let's pretend the ratio of o16 to o18 is 4 to 1 (i.e. 4 parts o16 for every 1 part o18). Now, for seawater, we need this ratio to be smaller, so let's pretend it is 1 to 1 (i.e. one part o16 to o18). Normally, this difference has no effect on the composition of the ocean because this vapor returns to the ocean. During an ice age, however, a large amount of precipitation (i.e. the vapor returning) falls on ice caps, where it is trapped as ice. As such, during an ice age, we would be losing 4 parts of o16 for every 1 part of o18 (i.e. more o16 being removed than o18 but not returning to the ocean because it is falling on ice caps). Therefore, we can conclude that in "a typical ice age" (language directly from the question stem), the concentration of o18 would increase. Hope this helps! Let me know if you have any other questions.

  2. Yang · 2015-12-17 19:02

    Still confused please help! How do you know that o16 was the only part got lost trapped as ice? It's oxygen, don't they lose together? How is possible to separate o16 from o18 while evaporating or losing?

  3. ekaterinaurban@gmail.com · 2018-06-21 20:41

    Since it was an ice age and everything was covered with ice, it is logical to assume the sea would be covered with ice, not only ocean?

  4. Christopher · 2018-06-22 20:30

    @Yang and @ekaterinaurban@gmail.com The issue is not where the o16 or o18 are coming from but where they are both going. The implication of ocean water evaporate including more o16 than o18 is that if nothing replenishes the o16, then eventually the balance of o16 to o18 will lean toward o18 as more o16 is evaporating away. Normally rain made up of seawater would do this, but in the case of an ice age, a large amount of the rain coming from both seawater and ocean water is being frozen and trapped at the ice caps, so there is less o16 being replenished in the ocean which starts leaning toward o18. So the same ratio of o16 to o18 is evaporating from both seawater and ocean water, but rather than that evaporate turning into rain that balances the ocean, it is ending up as ice on the polar ice caps, allowing the ocean to lean toward o18. Does that help?

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