PT1.S3.Q11 - Ice age

moonstars5678

Had originally picked C and read this thread that was very helpful in visualizing the stimulus: https://7sage.com/discussion/#/discussion/7343.

However, I'm still having trouble with AC B and C.

1) For B, I had originally read it as the concentration of O18 INCREASED (so if it was at 90L after the evaporation, then in the ice age, it was actually at 150L), rather than the concentration of O18 in the ice age ocean is just higher than that of the interglacial period.

2) Could someone explain why C is wrong? It seems to align with the stimulus?

help

samk

C is wrong because the ratio of oxygen 16 to oxygen 18 in vaporized seawater (and thus in the precipitation) is the same in both glacial and interglacial periods (ice and and non ice age), the stimulus does not mention anything about that ratio changing in the precipitation between those two periods.

So the snow and rain that falls is the same in both periods in their makeup of oxygen 18 and 16.

moonstars5678

@samk If there's a higher amount of O16 evaporating in the seawater during the glacial periods, doesn't that necessarily mean that there's less in the non ice-age periods?

The way I'm understanding the stimulus is this:
"Water vapor evaporated from the ocean contains a greater proportion of O16 and smaller proportion of O18 than does seawater" - so let's say 10:1 O16 to O18 ratio in the water vapor

"During the ice age however, a large amount of precipitation falls on ice caps, where it is trapped as ice" - so the 10:1 O16 to O18 ratio means that there's progressively less O16 in the water vapor so if O16 and O18 are red and blue, the water is getting progressively more blue. Meaning, if there's more O18 in the water, then there's less O16 to evaporate so the ratio changes to 5:1?

So C would be wrong because the rain and snow would actually contain more O18 and not more O16 than in interglacial periods (given most of the O16 is trapped in ice)?

help

nye8870

a) It just doesn't say this
b) there is just no way to know the concentration of seawater, the stim only speaks to the vapor.
c) are we even talking about "seawater" anymore? It doesn't contradict, but is it supported?
d) to be blunt- If the atmosphere has more land to dump on, less will make it back to the sea. "During an ice age, however, a large
amount of precipitation falls on ice caps, where it is
trapped as ice." *Seems supported. CORRECT
e) more slowly? Whats our time frame. Pace not in play. Wrong

moonstars5678

@nye8870 the right answer is B...not D