Stable-isotope ratio reporting and fractionation
An isotope delta compares a specified sample isotope ratio with the same ratio in a stated reference.
Key knowledge
An isotope delta compares a specified sample isotope ratio with the same ratio in a stated reference. Equilibrium and kinetic fractionation can change isotope partitioning between substances; mixing also changes measured ratios. A delta is a relative ratio difference, not an absolute isotope abundance or a unique process diagnosis.
Values and equations
δ = Rsample/Rreference − 1; δ‰ = 1000δ
- Rsample,Rreference
- same specified isotope amount ratio in sample/reference 1
- δ
- relative isotope-ratio difference 1
- δ‰
- numerical delta reported per mil ‰
Conditions and scope
- State isotope pair, reference scale and reporting multiplier; δ is dimensionless and a per-mil numerical value multiplies it by 1000.
- Fractionation factors require a stated ratio ordering, substances and conditions.
Sources · 2
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
- Compilation of Minimum and Maximum Isotope Ratios, isotope-delta and fractionation definitionsTyler B. Coplen and collaborators — U.S. Geological Survey, Water-Resources Investigations Report 01-4222 (2002)Textbook chapter · PDF
- Explanation of Isotope UnitsU.S. Geological Survey, Scientific Investigations Report 2012-5126Textbook chapter · PDF
Evidence and review
Read indexed report sections containing the explicit delta equation and reference-scale definitions; complete PDF fetch was unavailable, so no claim of checking full report tables or values.
2026-10-10 · Independent AI editorial review: All36 Life-authored Earth compact statements/conditions/displayed equations and all81 origin semantic links read; all36 author exact-source matrix rows and exclusions assessed. All18 inherited Earth compact records read for combined inventory. Targeted independent actual primary sections listed below; not every source body or proof independently reread. AI editorial reference review, not human certification/field proficiency or whole-field completion. Receipt: earth-life-independent-content-review.1.
Entry details
Permanent link to this entry ↗- Record identity
- uni-earth-isotope-delta
- Revision
- core.1
- Structured reference record
- University core expansion