5 NATURAL ABUNDANCE OF THE STABLE ISOTOPES ... - Falw.vu

Chapter 72 VSMOW (‰)+ 200meteoric water line:2 = 8 18 + 10 ‰oceanwater 20 40arbitraryfreshwatersevaporated water 2 = 4.5 18 estuarine mixing60escapingvapour8010 8 6 4 2 0 +218 VSMOW (‰)Fig.7.18Relation between 18 and 2 for estuarine mixing and for evaporating surface water.Because the evaporation is a non-equilibrium process, isotope fractionations involved arenot necessarily related by a factor of 8, as is the equilibrium condensation process, thebasis for the meteoric water line (Fig.7.17). As in the preceding figure, the arrowsindicate the direction of change of the isotopic composition of the escaping vapour and ofthe remaining evaporated water.122