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The Dansgaard paper I've seen shows a roughly linear relationship between the delta-O18 in precipitation and mean annual temperature (at a given location). See Figure 3 in the paper.

When converting delta-O18 into a corresponding delta-temperature, is this simple linear relationship assumed? Or is it more complex than that? What caveats or assumptions go into such a conversion?

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  • $\begingroup$ Very inaccurately, because precise measurements of the various isotopes are difficult to make, and you don't know where these isotopes were picked up from before they were precipitated into your Ice core. It might have been the Gulf of Mexico in summer, or the Denmark Straits in winter, so a great variety of sources and temperatures.. $\endgroup$
    – Michael Walsby
    Commented Sep 15, 2019 at 16:58
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    $\begingroup$ Note that the Dansgaard paper cited in the question uses the mean annual temperature at the 'target' not the 'source'. In this case, the 'target' is simply the location of the ice core. (You shouldn't use the comment feature to provide an answer.) $\endgroup$
    – John
    Commented Sep 15, 2019 at 18:09
  • $\begingroup$ The ratio of heavy isotopes to light isotopes in the precipitation depends on the temperature and evaporation rate of the source, not the target. It also depends on the amount of fresh water in the source (fresh water has less of the heavy isotopes). $\endgroup$
    – Michael Walsby
    Commented Sep 15, 2019 at 19:15

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It depends on which latitude you are in. In polar regions, a relatively linear equation can be used. This is because the so-called Liatiude effect has an extreme influence on the 18O signature.

$\delta^{18}\textrm{O} = (0.521 \pm 0.014)t_a - (14.96 \pm 0.21)^0\!\!/\!_{00}$

For further information: https://www.sciencedirect.com/topics/earth-and-planetary-sciences/isotopic-fractionation

However, in latitudes such as those of Europe, there are additional effects that strongly influence the isotopic signature. For example, the intensity of precipitation is responsible for causing the 18O signature to become more negative with increasing rainfall. As far as I know, a paper on this topic will hopefully be published soon, and I will then provide the link.

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