656
Paul eta!'
The stable isotopes deuterium and oxygen-I 8
have been incorporated into a number of atmospheric models, e.g. the LMD model (Joussaume et
al. 1984; loussaume and 10uzeI1993), the NASAl
GISS model (louzel et al. 1987), the ECHAM
model (Hoffmann and Heimann 1993; Hoffmann
1995) and the GENESIS model (Mathieu 1996). As
these four models account for the various
fractionation processes that occur at the sea surface and all succeeding stages ofthe hydrological
cycle, they provide a tool for calculating the isotopic
content of precipitation oP as well as of evaporation oE (luillet-Leclerc et al. 1997). Prior to their
development there was no method to estimate 8E
independently (Craig and Gordon 1965).
The 8 value that is commonly used to express
the isotopic composition of a water sample is defined by
o = (Rsample / Rstandard -1)·1000%0,
(1 )
where R"mp'e and R,'andacd refer to the isotope
ratio 2H/tH or 1S0/ 16 0 in the water sample and in
the standard. Thus positive 8 values indicate an
enrichment of the heavy isotopic species relative
to the standard, and negative 0 values indicate their
depletion. The generally used standard is the Standard Mean Ocean Water (SMOW, Craig 1961) or,
more recently, the Vienna Standard Mean Ocean
Water (V-SMOW, Gonfiantini 1978).
ur ace wa er
~AAIWO%o
Northern Hemisphere
Fig. 1. Sketch of the global 8180 cycle. In our simulations, only the oceanic part has been considered so far.
Paul eta!'
The stable isotopes deuterium and oxygen-I 8
have been incorporated into a number of atmospheric models, e.g. the LMD model (Joussaume et
al. 1984; loussaume and 10uzeI1993), the NASAl
GISS model (louzel et al. 1987), the ECHAM
model (Hoffmann and Heimann 1993; Hoffmann
1995) and the GENESIS model (Mathieu 1996). As
these four models account for the various
fractionation processes that occur at the sea surface and all succeeding stages ofthe hydrological
cycle, they provide a tool for calculating the isotopic
content of precipitation oP as well as of evaporation oE (luillet-Leclerc et al. 1997). Prior to their
development there was no method to estimate 8E
independently (Craig and Gordon 1965).
The 8 value that is commonly used to express
the isotopic composition of a water sample is defined by
o = (Rsample / Rstandard -1)·1000%0,
(1 )
where R"mp'e and R,'andacd refer to the isotope
ratio 2H/tH or 1S0/ 16 0 in the water sample and in
the standard. Thus positive 8 values indicate an
enrichment of the heavy isotopic species relative
to the standard, and negative 0 values indicate their
depletion. The generally used standard is the Standard Mean Ocean Water (SMOW, Craig 1961) or,
more recently, the Vienna Standard Mean Ocean
Water (V-SMOW, Gonfiantini 1978).
ur ace wa er
~AAIWO%o
Northern Hemisphere
Fig. 1. Sketch of the global 8180 cycle. In our simulations, only the oceanic part has been considered so far.