Strontium and Oxygen Isotopes for Mobility

Strontium and oxygen isotopes record the geology and water of the place where a person spent childhood, letting bioarchaeologists identify migrants and reconstruct mobility from the chemistry of teeth and bone.

Definition

The use of strontium and oxygen isotope ratios in dental enamel and bone to infer an individual's place of childhood residence and detect geographic mobility in the past.

Scope

This topic covers the use of strontium isotope ratios, which reflect local bedrock geology, and oxygen isotopes, which reflect drinking water and climate, to study residential origin and movement. It addresses how enamel forming in childhood preserves a fixed early-life signal against which later residence can be compared, the need to establish local biologically available baselines, and applications to migration, exogamy, and population movement.

Core questions

• How do strontium and oxygen isotopes encode geographic origin?
• Why does childhood-formed enamel preserve a different signal than later-forming bone?
• How are local biologically available baselines established to identify non-locals?
• What can isotopic mobility studies reveal about migration, exogamy, and social organization?

Key theories

Bioavailable strontium baselines

Price and colleagues' argument that identifying migrants requires characterizing the biologically available strontium of a region—via local fauna or plants—rather than bedrock alone, because available strontium can differ from underlying geology.

Tissue formation timing and the migration signal

The principle that enamel fixes its isotopic composition in childhood and does not remodel, while bone turns over during life, so comparing teeth and bone can reveal movement between childhood and death.

History

Strontium isotope provenancing in archaeology developed through the 1980s and 1990s and was placed on firmer methodological ground by work establishing biologically available baselines around 2000. Combined with oxygen isotopes from drinking water, it became a standard approach for detecting migrants in cemetery populations and reconstructing prehistoric mobility.

Debates

Defining 'local' and interpreting non-local values

How to set the range of expected local isotope values, and how to interpret individuals who fall outside it given overlapping geological zones, mixed water sources, and the difference between short- and long-distance movement.

Key figures

• R. Alexander Bentley
• T. Douglas Price
• James H. Burton
• Julia A. Lee-Thorp

Seminal works

• priceetal2002
• bentley2006
• leethorp2008

Frequently asked questions

Why are teeth especially useful for studying migration?

Tooth enamel forms in childhood and does not change afterward, so it preserves a chemical fingerprint of where someone grew up even if they later moved and died elsewhere.

What does strontium tell you that oxygen does not?

Strontium isotopes mainly reflect the geology of the area where food and water came from, while oxygen isotopes reflect climate and drinking water, so combining them improves the reconstruction of origin.