Water at the sites of evaporation is assumed to follow the Craig-Gordon
model, so Δ18Oe can be derived from
equilibrium fractionation (ε+), the ambient to
intercellular air vapor mole fraction
(e a/e i), the kinetic
fractionation (εk), and air vapor enrichment
(Δ18Ov; Eqn. 4)
(Craig & Gordon 1965;
Dongmann et al. 1974;
Flanagan et al. 1991).