δ18O (Delta-18-O)
Definition
The ratio of oxygen-18 to oxygen-16 in a sample expressed in per-mil deviation from the Vienna Standard Mean Ocean Water (VSMOW) standard. More negative values indicate lighter, more depleted water typical of high-latitude or high-altitude precipitation.
- Measures
- 18O/16O ratio in a sample
- Reference standard
- VSMOW (Vienna Standard Mean Ocean Water)
- Interpretation
- More negative = lighter, more depleted water
- Application
- Isotope geolocation (isoscapes)
Common questions
Why is high-latitude or high-altitude precipitation more depleted in 18O?+
As air masses travel poleward or upward and cool, the heavier 18O-containing water molecules condense and fall out of the vapor first, leaving the remaining precipitation progressively more depleted in 18O.
What forensic question does δ18O typically help answer?+
Comparing a sample's δ18O signature, such as from hair or water, against regional isoscape reference maps helps narrow down the geographic region where a person or object most likely originated or recently resided.
Related terms
- δ2H (Delta Deuterium)
- The ratio of deuterium to hydrogen in a sample expressed in per-mil deviation from VSMOW. Covaries with δ18O along the global meteoric...
- Global Meteoric Water Line (GMWL)
- The linear relationship δ2H = 8 × δ18O + 10 that describes the global co-variation of O and H isotopes in precipitation....
- Isoscape
- A map of isotope ratio variation across a geographic area, derived from systematic sampling of soil, water, plant, or mineral material; used...
- OIPC (Online Isotopes in Precipitation Calculator)
- A web-based tool and database compiling the IAEA GNIP station network data and providing interpolated δ18O and δ2H predictions for any geographic...
- Tissue-Specific Incorporation
- The principle that different tissues record isotope signals over different time windows: enamel permanently records childhood; hair records month-by-month recent history; bone...