PT1.S3.Q11 - The right answer still seems suspect...

cjosephmedrano-1-1

My understanding is that in normal times, water vapor from ocean contains a heavier proportion of oxygen-18. However, if that water vapor is not retuning to the Ocean during ice ages, but getting trapped in glaciers, wouldn't that mean the ocean has LESS o-18? I guess I'm assuming the water vapor is taking O-18 out of the ocean. But even if that's not assumed, what warrant do we have to say the ocean has more O-18 than usual?

Ashley2018-1

I'll try my best but I think this is a question that I would likely POE under timed conditions...so we know that water vapor contains a higher proportion of O2 and a lower proportion of O-18 compared to sea water and this normally doesn't matter since, as the stimulus says, the water vapor eventually returns to the ocean via rain. However, during an ice age, the water vapor no longer returns to the ocean and becomes trapped in icebergs instead. We don't know the exact proportion of the O2 and O-18 in the seawater but it doesn't matter. Because the water vapor is no longer returning to the ocean, it means that a disproportionate amount of O2 is being taken from the ocean, which means that the ocean now contains a greater share of O-18.