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Comment by vanderZwan | Hacker News Reader

> The new data is more reliable, Carré said, for three reasons: the Peruvian coast is strongly affected by El Niño; the shells record ocean temperature, which is the most important parameter for the El Niño cycles; and the ability to record seasonal changes, the timescale at which El Niño can be observed.

Emphasis mine. I'm kind of curious how the shells encode that temperature information. Growth speed? Chemical changes?

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If I recall correctly (and it's been a few years since my oceanography seminar), it has to do with the ratio of component elements in the shells of benthic fauna. They're pulling those elements in as a part of the growth of those structures, and the ratio of different gases changes based on the temperature.

EDIT: Looked it up, I had the gist of it I guess. http://en.wikipedia.org/wiki/Paleothermometer#Mg.2FCa_and_Sr...

I imagine the techniques now are more refined than what is exactly mentioned there.

Semi-related, I got to take sediment cores from a Ramsar wetland while in South Africa in order to pick them apart for pollen to try and indirectly measure early-Holocene temperatures using the ecology as a proxy. Interesting stuff, and fun to be in the field.

FTA: "While in graduate school, Carré had developed a technique to analyze shell layers to get ocean temperatures, using carbon dating of charcoal from fires to get the year, and the ratio of oxygen isotopes in the growth layers to get the water temperatures as the shell was forming."

So it's his own pet technique. How well supported is it by the rest of the scientific community?

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