How do you tell temperature by oxygen isotopes?

Question

How do you tell temperature by oxygen isotopes? In the movie An Inconvient Truth, Al Gore says that by looking at air bubbles in ice they can tell the temperature by the oxygen isotopes. How does that work?

Answer 1

You can look at 018 and 016 ratios, specifically. Since 018 is heavier, it is harder to incorporate into structures, like ice sheets and marine mollusc shells (I study mollusks, it is used in them to determine growth cycles). 018 is enriched in cooler waters, and therefore will be incorporated at a greater rate into ice sheets when we are in a cold cycle.

O18 to 016 ratios provide a reliable proxy, then, and by looking at the relative amounts of each, through which we can determine ocean temperature.

Answer 2

I'm not 100% sure, but I believe the ratio of one isotope to another would give you the age (like carbon dating) and the quantity of dissolved O2 in the water would be indicative of temperature. But I think pressure would also effect it, so ... I'm not 100% sure.

To the best of my knowledge, isotopic decay is not dependent on temperature. I could be wrong. It will be very interesting to learn the correct answer.

Excellent answer, kiddo!