CLIMATOLOGY

Taking an Ice Core's Temperatures

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Science  10 Nov 2000:
Vol. 290, Issue 5494, pp. 1053-1055
DOI: 10.1126/science.290.5494.1053e

Most of our understanding of high-latitude surface air temperature variations during the past 450,000 years comes from the isotopic compositions of oxygen (δ18O) and hydrogen (δD) in polar ice cores. The credibility of these proxies is supported not only by theoretical considerations but also by observations that the δ18O of modern snow in Greenland reflects local surface temperature. However, it is also well known that factors other than temperature affect the isotopic composition of snow. Borehole measurements of ice sheet temperatures have shown that the true temperature difference between the last glacial maximum and the present is nearly twice what was inferred from the isotopic composition of ice and modern isotope-temperature calibrations.

Hendricks et al. have looked at the processes involved in the isotopic fractionation of atmospheric moisture with a one-dimensional meridional model of water vapor transport. They discuss the importance of several factors on the isotopic composition of snow, including evaporative recharge of moist air masses, transport by eddy diffusion, the equator-to-pole temperature gradient, and distance from the ocean. Understanding the significance of these parameters may allow the isotopic record to be reconciled with results from physical studies. — HJS

Global Biogeochem. Cycles14, 851 (2000).

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