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Oxygen isotope analysis


Oxygen isotope analysis determines the proportions of the stable isotopes 16O and 18O. The isotope ratio is given as a Delta (δ) value, i.e. as the deviation of the isotope ratio in the sample from that of a standard isotopic composition.

At CEZA, oxygen isotope analysis is carried out mainly on human or animal enamel in order to investigate mobility and seasonality as part of bioarchaeometric investigations. The starting point is the isotopic composition of the oxygen in meteoric water (precipitation), which varies both seasonally and regionally, by temperature, altitude and distance from the sea.


Human and animal mobility is a core topic of bioarchaeometry. Oxygen isotope analysis is often combined with strontium isotope analysis on tooth enamel in order to identify persons of a non-local origin or to investigate seasonal mobility of people with their herds of domesticated animals.

The analyses usually aim to identify people who did not spend the first years of their lives at the place where their mortal remains were found. This knowledge is fundamental for addressing questions regarding the mobility of individuals or the composition of funeral communities. Respective research interests include the identification of historic persons, residential rules, or testing hypotheses regarding a non-local origin of people based on grave goods or grave architecture.

The oxygen isotope values of different tooth crowns mineralised in early or late childhood or several samples taken sequentially from the same tooth, may also inform on the duration of breastfeeding.

Series of samples from high-crowned animal teeth (e.g. from cattle, sheep, goats or horses) reveal systematic variations of the isotope composition along the tooth crowns, mirroring temperature differences between summer and winter (seasonality). Enamel from the positions of the maxima and minima of these seasonality curves may be used for strontium isotope analysis, which informs on herding on pastures of different geological conditions in the course of seasonal mobility in animal husbandry.

Oxygen isotope ratios in precipitation and ice cores indicate long-term temperature changes and are among the best established climate indicators.


The oxygen isotope values (18O/16O or δ18O) of teeth and bones reflect the isotope composition of water ingested as drinking water and through food. This is ultimately due to precipitation, whose isotope values depend on temperature, altitude, latitude and distance from the sea. The reason for the spatial variation is isotope fractionation, which also plays a role in metabolic processes in the body and the incorporation of oxygen into bones and teeth. Because in animals, including humans, these processes take place at a constant body temperature, regression equations can be used to infer the values of bones and teeth from those of drinking water.

Oxygen isotope ratios in skeletal remains are determined either for the oxgygen bound in the phosphate group or for the structural carbonate in the mineral fraction of bones and teeth (hydroxyapatite). The δ18O values of both components correlate and bear similar information, if the sample material is not diagenetically altered during burial. The phosphate bond is chemically more stable than that of the structural carbonate, so that the former is generally less susceptible to diagenetic alteration.

With regard to data evaluation, analytical data for the phosphate group has the advantage that most regression equations tend to estimate δ18O values of the drinking water based on the phosphate values. In contrast, data for the structural carbonate must first be converted into potential phosphate values, which adds uncertainty.

Advantages of oxygen isotope analysis on the structural carbonate are the less complex preparation of samples and the simultaneous determination of carbon isotope values which contain dietary information.

Modern analysis and consistently applied quality control allows for a highly precise and accurate determination of the isotopic composition of the sample material by means of an isotope ratio mass spectrometer. Systematic analyses of standard materials ensure high quality data collection. The latter are materials with certified or long-term documented isotope compositions, which are analysed in the same way as the samples. Their isotope compositions allow an assessment of the correctness and precision of the analysed results of the actual materials to be examined. For an optimal traceability of the analytical quality, data reports include the analytical values of the standard materials.


The analysed isotope ratios of analysis which fulfill the quality criteria need to be interpreted with regard to the archaeological or climate historical questions posed.

In order to address human mobility, the isotope ratios must first be assessed in regard to their correlation with the local isotope range for the respective site and evaluated in the context of a presumed local or non-local origin of the sampled individual. Then, the oxygen isotope data of the human or animal enamel are compared with those of the isotope composition of precipitation or river and lake water. For this purpose, the isotope values of teeth or bones need to be converted into those of the metoric water or vice versa using linear regressions. Uncertainties regarding the differentiation between local and non-local values result from gradual transitions of the isotope ratios of the meteoric water, seasonal variability, variation among different years, possible long-term climate changes as well as from the availability of several regression equations for humans and animals of the same species. Oxygen isotope data generally tends to differentiate on a large scale between climatically different regions.

Possible further restrictions with regard to data interpretation result from diagenetic changes in the sample material during burial, which can affect bone in particular, but also tooth enamel. The oxygen bound to the structural carbonate is usually more susceptible to these influences than the oxygen bound to the phosphate group.

One of the greatest challenges is the spatial assignment of the isotope values identified as being non-local to a possible location of origin. Similar climatic and environmental conditions cause similar isotopic compositions of water in different regions, which may be located at considerable distances from each other. This fact may prevent the recognition of non-local individuals or offer several alternative options of provenance assignments. The information potential of oxygen isotope data benefits from precise research questions and hypotheses as well as from being part of interdisciplinary studies in which different data strands are integrated to answer complex questions.

Sample properties

Tooth enamel is the most common sample material to investigate research questions of bioarchaeometry. The optimum sample size for pre-treatment and analysis is approx. 12 mg of enamel or bone powder.

We recommend submitting complete teeth, along with information regarding their anatomical position in the jaw. We will separate the required amount of sample. Remaining material may be returned upon request.

Human teeth

If the teeth to be investigated are part of larger series, e.g. from a cemetery, they should be selected as uniform as possible regarding their anatomical position, resp. period of enamel formation. To examine human mobility based on one tooth per individual, we recommend using enamel that is mineralised after the end of the breastfeeding period, approx. from the age of 3 years. Suitable teeth include second molars, premolars or wisdom teeth (3rd molars). Due to breastmilk consumption, teeth that form earlier in childhood (1st molars, front teeth or deciduous teeth) may have slightly higher δ18O values than to be expected when drinking water. This fact may lead to misinterpretations regarding a possible non-local origin. Early forming teeth should therefore only be selected if no later forming teeth are available.

For studies in which childhood mobility is of interest, both early and later forming teeth from the same individuals may be included (e.g. 1st molars and wisdom teeth) of the same individual. Comparing the analytical data from both also reveals the breast-feeding effect, which may also be investigated very specifically by a higher-resolution sampling strategy with several analyses on the same tooth.

Animal teeth

Animal teeth should be submitted as complete as possible, along with information regarding the animal species and the anatomical position of each tooth.

For serial sampling, enamel powder that is distributed along the tooth crowns is milled from the teeth in horizontally alligned grooves of a few millimetres distance from each other.

Alternatively, an average value of the enamel of the entire crown height may be determined.

General remarks

Samples shall be submitted individually packed and along with information regarding their anatomical position. The informative potential of oxygen isotope analysis benefits from precise research questions and hypotheses as well as from their integration into interdisciplinary studies that combine different data sets to investigate complex questions.