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Figure 3.17. Comparison of estimated temperatures at two Greenland sites (Jouzel et al.,
1997).
from the parcel. With these assumptions, the isotope content of this precipitation
is a unique function of the initial isotope mass and water vapor mass within the
air parcel and of the water vapor mass remaining when the precipitation forms.
This model leads to a family of curves like that in Figure 3.15 , with the position
of each curve dependent on the ocean temperature from which the original
evaporation took place. The results correlate with the main features of the global
distribution of isotopes in precipitation, namely, its seasonal and spatial character-
istics, the observed relationships with local temperature or precipitation amount,
and the strong link between d 18 O and d D. However, such a simple model can
only roughly represent the complexity of dynamical and microphysical processes
leading to the formation of individual precipitation events or changes in ocean
surface characteristics, in surface topography, and in atmospheric circulation
associated with important climatic changes, such as the transition between the
Last Glacial Maximum and the Holocene.
3.3.1.2 Temperature estimates from borehole models
According to Cuffey et al. (1995):
''Using both empirical data and physical models for isotope fractionation,
paleoclimatologists have interpreted d 18 O to be a measure of environmental
temperature T at the core site, through a simple relation that we call the isotopic
paleothermometer: d 18 O ¼ AT þ B, where A and B are constants. There are two
obstacles to making this interpretation sound. First, the coecients A and B are
not known a priori because many factors in addition to local environmental
 
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