Oxygen Isotope Ratio Cycle - Connection Between Isotopes and Temperature/weather

Connection Between Isotopes and Temperature/weather

18O is two neutrons heavier than 16O and causes the water molecule in which it occurs to be heavier by that amount. The addition of more energy is required to vaporize H₂18O than H₂16O, and H₂18O liberates more energy when it condenses. In addition, H₂16O tends to diffuse more rapidly.

Because H₂16O requires less energy to vaporize, and is more likely to diffuse to the liquid surface, the first water vapor formed during evaporation of liquid water is enriched in H₂16O, and the residual liquid is enriched in H₂18O. When water vapor condenses into liquid, H₂18O preferentially enters the liquid, while H₂16O is concentrated in the remaining vapor.

As an air mass moves from a warm region to a cold region, water vapor condenses and is removed as precipitation. The precipitation removes H₂18O, leaving progressively more H₂16O-rich water vapor. This distillation process causes precipitation to have lower 18O/16O as the temperature decreases. Additional factors can affect the efficiency of the distillation, such as the direct precipitation of ice crystals, rather than liquid water, at low temperatures.

Due to the intense precipitation that occurs in hurricanes, the H₂18O is exhausted relative to the H₂16O, resulting in relatively low 18O/16O ratios. The subsequent uptake of hurricane rainfall in trees, creates a record of the passing of hurricanes that can be used to create a historical record in the absence of human records.