Oxygen Isotopes and The Water Cycle

Water molecules tagged with different isotopes of oxygen have different tendencies to evaporate and condense.


Isotopes

An Atom
Source - antonine-education.co.uk 

An element is defined based upon the number of protons contained in its atoms i.e. different elements contain different number of protons in each atom.
With the number of protons being the same, the atoms of an element can contain a different number of neutrons. 
Isotopes are atoms of the same element or compound that differ in the number of neutrons contained in their atoms.


Oxygen Isotopes

8N and 10N Isotopes of Oxygen
Source - mhhe.com

The Oxygen atom has 15 isotopes of which 3 are stable while 12 are unstable (radioactive) with very short half-life. These unstable isotopes have variants, defined on their mode of decay, that increase their number beyond 12.

Stable oxygen Isotopes
Source - web.sahra.arizona.edu

The 3 stable oxygen isotopes have 16, 17 and 18 neutrons in the nucleus of each atom. 
The 16-Neutron isotope is the most abundant - 99.762% of all Oxygen atoms have 16 neutrons in oxygen atoms.


Primary and Secondary Isotopes of Oxygen
The 16-neutron oxygen isotope is known as the primary isotope as it is postulated to have been created by stellar evolution. The 17-neutron and 18-neutron isotopes are called secondary isotopes because their existence requires "seed nuclei" and they are created on earth.


Oxygen Isotopes and the Hydrological Cycle

Isotopes in air, ocean and ice
Source - wwnorton.com

Water molecules are tagged with the different atoms of oxygen. Thus, water molecules can be tagged with oxygen isotopes with either 16 or 17 or 18 neutrons.

Source - eesc.columbia.edu

Glacial ice, the oceans and the vapor in the air, all contain water molecules tagged with the most common 16-neutron isotope. However, concentrations of the 16-neutron isotope are different in ice, oceans and air. This difference is ultimately due to the slightly higher tendency to evaporate, of water molecules tagged with the 16-neutron oxygen isotope.

Oxygen Isotopes and the Water Cycle
Source - web.sahra.arizona.edu

Conversely, there is a slightly higher tendency of water molecules to precipitate (condense) that are tagged with oxygen atoms containing 18 neutrons.
In fact, the different isotopes of oxygen in water molecules seem to influence evaporation and condensation.


Harvesting of moisture (precipitation i.e. rain) contained in air and wind can, thus, be stimulated by the 18-neutron oxygen isotope that can be artificially created.