In this article, we discuss the use of stable carbon and nitrogen isotopes (δ13C and δ15N) in bone collagen. Thanks to these methods, it is possible to identify the environment from which individuals have drawn their resources, as well as their relative positions in the food web. Stable isotope analysis not only reveals a group's food choices, but also socio-cultural and economic distinctions. Our laboratory scientists propose individual and collective dietary trends based on information from each individual.
Determining diet using stable carbon and nitrogen isotopes
Carbon-14 dating is not the only technique used in archaeometry. Stable isotope analysis of carbon and nitrogen also provides a wealth of information. As far as plants are concerned, our scientists distinguish between two types of photosynthesis:
- In C3 for woody trees, rice, cotton or wheat which have a δ13C lower than -20 ‰ ;
- In C4, such as grass, corn or sugarcane, which have a δ13C of between -10 and -20%.
We also use the isotopic ratio of nitrogen 15 and 14 to determine the origin of proteins.
Thanks to stable carbon and nitrogen isotopes, it is possible to determine the diet of a person or animal. We know, for example, whether they were carnivores, herbivores or omnivores. We can also determine whether the diet was more terrestrial or marine in origin.
Determining the state of preservation of the bone material, an important step in exploiting the samples
By quantifying carbon and nitrogen concentrations and analyzing the C/N ratio, it is possible to assess the state of preservation of the organic bone material, collagen. If collagen is in a poor state of preservation, the samples cannot be processed. Only a C/N in the 2.9 to 3.6 range will reveal a state of preservation compatible with reliable carbon-14 dating and isotopic study.
Interpretation of results
The results of carbon and nitrogen stable isotope analysis provide valuable information such as :
- Origin of animal proteins (predominantly meat, milk/dairy products or fish);
- Importance of cereals and legumes in ancient times.
It is also possible to compare results with different groups of individuals to detect different habits and to understand archaeological issues. Our scientists interpret the results and work with you to resolve your hypotheses.
CIRAM laboratories use a vario ISOTOPE select elemental analyzer (EA) from ELEMENTAR, which measures carbon and nitrogen concentrations (atomic %). This is a high-temperature combustion unit, up to 1200°C. The weighing range is from 20 µg to 300 mg. Concentration range is up to 7 mg absolute for carbon and up to 10 mg absolute for nitrogen. External accuracy (1s) is less than 0.1% for carbon and nitrogen. The elemental analyzer is the IRMS gas injection system. ELEMENTAR's IRMS isoprime precisION is an isotope ratio mass spectrometer that measures the stable isotope ratios of carbon (13C/12C) and nitrogen (15N/14N) expressed in per thousand (‰). External precision (1s) is 0.1 ‰ for δ13C and 0.15 ‰ for δ15N.
CIRAM, leader in dation and analysis since 2005
Stable isotope analysis is a goldmine for understanding the dietary and social habits of a group of individuals, but to be reliable it must be carried out on a significant corpus of individuals, otherwise the results cannot be representative.
CIRAM, laboratory dating and analysis since 2005, accompanies all its results with a complete, documented report. Our teams of researchers are always ready to listen to your needs and to work closely with you in the field.
