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The d18O of firn and ice from polar ice cores can be used to reconstruct
paleotemperatures. The ice d18O-temperature relation is positively
correlated, i.e. warmer temperatures during precipitation lead to higher
d18O values. This is opposite to the fractionation behaviour during the
formation of carbonates, where increasing temperatures lead to decreasing
d18O.
In the case of the carbonates this behaviour can be explained by the
decreasing magnitude of the fractionation factor with increasing
temperatures, leading to less enrichment of 18O in the crystals at higher
temperatures (because the vibrational energy differences between the heavy
and light isotopes become less important at higher temperatures).

Does anybody know if there is a simple explanation for the opposite
temperature/fractionation relation of the water vapour -> ice/snow system?

Florian Boehm



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Florian Boehm
GEOMAR
Forschungszentrum für Marine Geowissenschaften
Wischhofstr. 1-3, D-24148 Kiel
Germany
email: [log in to unmask]
http://www.geomar.de/~fboehm/
Tel.: (49)431-600-2104
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