Final answer:
In colder climates near the poles, atmospheric water is stored as ice. Lighter isotopes of oxygen evaporate and become stored in ice sheets on continents, causing a decrease in their concentration in the remaining water vapor.
Step-by-step explanation:
In colder climates, such as near the poles, atmospheric water is increasingly stored as ice. The lighter isotopes of oxygen, such as oxygen-16 (¹60), preferentially evaporate from the oceans and become stored in ice sheets on continents. This causes a decrease in the concentration of lighter isotopes in the remaining water vapor.