New approaches to paleothermometry from isotopes in precipitation

Abstract:

Water isotope ratios in precipitation have been used as paleothermometers for at least 50 years. Most temperature reconstructions using isotope ratios rely on the empirical observation of a correlation between isotope ratios and temperature. While this approach is supported by theoretical considerations, it is nevertheless inherently imprecise because the correlation arises from myriad processes in the atmosphere that cannot be direclty quantified. In this talk, I will discuss two major innovations in the use of isotope ratios to obtain paleotemperature from ice cores. First, the measurement of very high resolution isotope records allows for the determination of the diffusion length (the amount of isotope diffusion that has occurred), which is strongly dependent on temperature. Second, the novel measurement of the third naturally occuring isotope of oxygen -- oxygen 17 -- allows the measurement of the oxygen-17 excess, which provides new constraints temperature because it depends strongly on the temperature-dependent supersaturation. Both these approaches have a stronger theoretical foundation than the tradiational $\delta^{18}O$ method, and have the potential to be both more accurate and precise.