The Value of Excess

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Science  01 Jul 2005:
Vol. 309, Issue 5731, pp. 15
DOI: 10.1126/science.309.5731.15f

The surface air temperature record of Greenland has been reconstructed mostly from analyses of the isotopic composition of H and O of the water in ice cores. A number of other factors besides average temperature can influence those proxies, however, such as the seasonality and origin of precipitation. Masson-Delmotte et al. (p. 118) measured the deuterium excess of ice from Greenland Ice Core Project (GRIP) samples in order to constrain the source and seasonality of the precipitation for the last full glacial cycle. Earth's orbital obliquity is an important control on the latitudinal temperature gradient between the source and site of precipitation, and moisture sources shifted to the south during cold periods.

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