By combining cutting-edge technologies such as infrared spectrometry, Raman spectrometry and chromatography, our scientists are able to detect and identify the organic remains found in ancient amphorae and pottery. The techniques developed by CIRAM enable us to characterize oils, fermented beverages, resins, fats and perfumes, so as to understand the dietary and cosmetic habits of ancient peoples.

Organic residues: understanding old habits and practices

Organic residues found in dishes, vases and flasks provide clues to food customs and ancient cooking methods, for example. But they can also provide information about trade in Antiquity or the Middle Ages, as well as ancestral burial practices. CIRAM laboratories have an analytical network that covers a wide spectrum of investigations, from the identification of major product families (oil, fat, resin, etc.) to the discovery, in the best of cases, of ancient cooking recipes.

Organic residue analysis methods

Fourier transform infrared spectroscopy, in ATR mode or under microscopy, is used to identify the major families of organic compounds. For example, the presence of oil, animal fat or natural resin can be characterized. Mineral matter, however, can provide a spurious signal, preventing identification of the organic compounds present. For this reason, infrared spectrometry will usually be used as a preliminary step. CIRAM teams will generally couple FTIR spectrometry with other analysis techniques, such as chromatography or Raman spectrometry.

GC-MS coupling to locate and identify substances

Gas chromatography (GC) coupled with mass spectrometry (MS) is the technique dedicated to the study of organic compounds. Chromatography separates compounds in a sample, while mass spectrometry identifies compounds according to their mass. This GC-MS coupling enables the precise identification and quantification of many substances present in very small quantities, or even in trace amounts. Using GC-MS analysis, our scientists can characterize most of the molecules present in an archaeological mixture or organic residue. It is the nature of these molecules, combined with their concentration, that enables us to trace them back to the material used: olive oil, walnut starch, animal fat, tannin...

Complementary analytical techniques for the analysis of certain residues

Although Raman spectrometry is more suited to the study of mineral matter, it is nonetheless an interesting method for archaeometry, as it is non-invasive and requires no sample pre-treatment.

This analysis provides very good spatial resolution, making it possible to study samples on a very small scale (spots of a few µm). Raman spectrometry can be used on its own, or in conjunction with FTIR spectrometry or GC-MS chromatography. In fact, the residues found in ancient pottery are so complex that it is generally necessary to use different complementary analytical techniques.

Carpology for the study of seeds and fruits that have been discovered

Carpology is the study of seed and fruit remains found in ancient containers or archaeological sediments. Analysis of these plant residues provides information on human activities and ancestral lifestyles. Even when charred, CIRAM scientists are able to identify the nature of these seeds, and thus understand their use and reconstruct environments.

Palynology, the study of pollen and spores

Palynology is the study of pollen and spores released by plant species. Coupled with carpology and anthracology, these techniques enable us to reconstruct environments and climates. Observations made using light microscopy or electron microscopy will make it possible to determine the size and shape of pollen grains or spores, the number and shape of apertures, ornamentation, wall structure... and thus define the plant family, genus and, in the best case, species.

CIRAM laboratories, specialists in carbon-14 dating and archaeometric analysis.

CIRAM, a specialist in carbon-14 dating and archaeomaterials analysis, offers a meticulous examination of organic residues. To deliver relevant and accurate results, we interpret the results and remain at your disposal to discuss hypotheses according to your needs.

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.

Carbon-14 is a radioactive isotope present in all living organisms. This isotope allows for the dating of a large number of organic materials found in archaeological contexts.

Specialists in AMS carbon-14 dating, our scientists perform laboratory analysis of materials such as wood, bone and charcoal, as well as peat and other organic sediments. Discover our peat analysis methods for precise dating of all your organic residues.

Valuable information thanks to C14 peat analysis

Peat bogs, which have been present in some areas for over 10,000 years, provide valuable information on environmental changes such as climate and anthropological changes.

For example, it is important to be able to define chronologically the start of turfigenesis on an archaeological site in order to carry out a paleo-environmental reconstruction.

Thanks to the distribution of the dates obtained and their comparison with geomorphological, paleoecological and archaeological data, it is possible to trace the evolution and changes in landscapes and societies.

While radiocarbon dating is the most suitable method for the chronological setting of peat bogs and other sediments, there are several methodological problems.

Different types of peat

We can analyze and date many types of peat and organic sediments. For accurate results, we take care to eliminate macro-rests.

For silty peats that do not contain macro-rests, we use organic sediment.

Fibrous peat (the most common in the samples we analyze) is a mixture of decomposing plant remains and silty peat. For this type of peat, we extract the fibrous part, which undergoes ABA (acid-base-acid) treatment to eliminate carbonates and humic and fulmic acids.

Sediment and peat analysis methods

Methods differ between silty peats and fibrous peats.

Silty peat is first sieved to 100 microns to remove micro-rests. Silty peats and the insoluble fraction of humic sediments are treated exclusively with acid to remove carbonates.

Fibrous peats are first treated with acid, then alkaline and finally washed with acid to remove carbonates and humic acids.

It is also necessary to sieve the soluble fraction of humic sediments to remove macro-rests. Once the fraction is clean, we use a hot acid treatment, repeated if effervescence persists, followed by an alkaline treatment. Our scientists recover only the alkaline solution by centrifugation or filtration. Finally, an acid treatment is applied until precipitation.

As a general rule, the acid-washed and sieved organic sediment fraction will give a more accurate dating.

Results and calibration

Our scientists systematically calibrate the analyses using international standards. There is a difference between the gross age and the calibrated dates, depending on the data and the estimated age of the peat. Gross age is expressed in BP years, i.e. before 1950. We always convert raw ages into calibrated dates, which are corrected by the calibration curve.

CIRAM laboratories can help you interpret your results

CIRAM's laboratories are committed to delivering results that are in line with the realities of the field, and always provide a detailed commentary to address your specific issues. We are also at your service to provide additional information and discuss the results in order to advance your research and meet your needs in relation to the archaeological context.

Follow-up of results, dialogue between professionals and proximity, CIRAM laboratories deliver serious expertise in collaboration with you.

Isotopes are found everywhere in the environment, in plants via sediments and water, and in animal tissues (and therefore in human tissues) through eating, drinking and breathing. The analysis of stable isotopes, such as those of carbon, nitrogen, strontium, etc., makes it possible to study the diets of an individual or group of individuals, and to determine where an individual grew up or lived for the last twenty to twenty-five years of his or her life.

Strontium is abundant in nature, found mainly in rocks and sediments. As sediments are eroded and dispersed in water and food resources, it is absorbed by the body and incorporated into bone tissue. The isotopic ratio of strontium varies from one geographical region to another. Consequently, the analysis of strontium isotope ratios in bones or teeth can be used to determine the geographical origin of an individual, or to measure the homogeneity of a group of individuals.

Bone and teeth are the most frequently analyzed tissues, as they are hard and can be preserved for a long time in archaeological contexts. Bone is made up of two components: an organic matrix composed mainly of collagen, and an inorganic mineral matrix composed mainly of calcium phosphates. Bone is a living tissue that constantly renews itself as we grow and age. However, this process is very slow, and dense cortical bone reflects approximately the last ten to fifteen years of an individual's life. Teeth are also composed of organic and mineral materials, but tooth enamel does not renew itself. Teeth are therefore very useful in determining the environment of an individual's early years. Moreover, by comparing the teeth and bones of the same individual, it is possible to determine whether he or she has migrated from one region to another since childhood. Teeth show where a person lived during childhood, and bones show where they lived in the years leading up to death.

The principle is to compare the 87Sr/86Sr ratio of bone and/or dental enamel with that of the environment (sediments) around the archaeological site and in neighbouring regions (with different geological substrates). This will enable us to discuss the geographical origin of the food ingested by the individuals.

The selection of materials will respect, as far as possible, the preservation of archaeological remains while meeting the study's needs. Sampling of bone fragments should preferentially be carried out on cortical bone. The study must involve several subjects to be relevant, and we will always attempt to select the same anatomical part. For dental tissue studies, depending on the inter- or intra-individual study issues, we will perform either an analysis per tooth or a multi-analysis per layer. The analysis will be carried out using a multi-collector mass spectrometer, with or without laser ablation coupling.

Animal tooth samples are cleaned with ethanol and placed on a glass slide to remove the outer enamel surface. For the specific case of herbivore teeth, we will choose analysis zones at the base, middle and top of each tooth, in order to assess the enamel formed at different times in the individual's life. The spectrometer is coupled to a laser system, equipped with an ablation cell (LA-ICP-MS). For laser ablation analysis, 500 µm long line scans are applied, with a circular spot size of 100 µm and a translation speed of 5 µm/s. We use several internal reference materials of bioapatite, as well as apatite and carbonate.

Strontium analysis is invaluable for studying the movement of populations. Thanks to our experienced scientists and state-of-the-art equipment, strontium analysis is a specialty of CIRAM laboratories.

The to carbon-14 dating is an essential method in archaeology. It allows for the determination of the age of organic artifacts (wood, coals, bone…). Regarding marine organisms, this method encounters unique challenges due to the reservoir effect, a phenomenon that makes interpreting results difficult. In this article, we we will explain this concept, the correction methods used by scientists, and the limitations of C14 dating in marine environments.

The reservoir effect in C14 dating of marine organisms

Origins and mechanisms of the reservoir effect

The reservoir effect is a variation in carbon-14 (C14) concentration between terrestrial and marine organisms. This difference poses unique challenges for dating marine samples. Unlike atmospheric carbon, which is uniformly distributed and rapidly recycled, seawater has significantly lower C14 levels. This C14 deficit can be explained by several factors.

First,the exchangeof carbon between the atmosphere and the ocean is a slow process due to the large mass of the oceans and the low solubility of carbon dioxide in water. Furthermore, ocean currents and water mass stratification lead to a circulation of carbon that varies with depth and latitude. On the other hand, the ocean contains significant amounts of old carbon, particularly in the form of dissolved carbonate that has not been in recent contact with the atmosphere. This old carbon can have several origins, such as the dissolution of carbonate rocks or submarine volcanism, contributing to an apparent "aging" of marine organisms.

Consequences of the reservoir effect: the reservoir age

The consequences of the reservoir effect lead to an "aging" of the age of marine organisms when they are dated using carbon 14. Marine organisms incorporate less C14 than their terrestrial counterparts due to reduced levels of C14 in seawater. Indeed, marine organisms start with a radiocarbon "clock" already offset compared to that of terrestrial organisms at the time of their death.

This difference, known as the "reservoir age", averages 400 years for surface ocean waters. However, reservoir age is not constant and can vary according to various geographical and environmental factors, such as water depth, proximity to freshwater sources, and the geochemical composition of water masses. For example, waters in estuaries or deltas show significant variations in carbon-14 concentrations due to mixing between fresh and marine waters, which impacts reservoir age. Similarly, C14 concentration varies according to latitude: polar waters often have higher reservoir ages due to slower circulation and low exchange with the atmosphere.

Scientists correct reservoir effect

Calibration methods with reference samples

Scientists rely on reference samples to compensate for shifts caused by the reservoir effect and thus obtain more accurate dating. One frequently used method is to compare results obtained on marine shells whose year of death is known. These shells from well-dated archaeological contexts or recent collections are used to calibrate the ages measured in C14. Using this reference point, researchers can adjust the results obtained for samples from the same region or of the same type, taking into account local variations in reservoir age.

Another key repository in this calibration process is the Marine 2020 Reservoir Database. This resource compiles data on reservoir ages observed around the world and provides corrective factors specific to different geographical locations. Scientists can then cross-reference the data from the sample under study with the information in this database, in order to apply an appropriate correction, taking into account the environmental and geographical particularities of the area concerned. This approach makes it possible to refine dating and reduce the margins of error associated with the reservoir effect.

Use of isotope ratio mass spectrometry (IRMS)

Isotope ratio mass spectrometry (IRMS) is an advanced technique used to analyze stable isotopes of carbon and nitrogen in samples. This technique is particularly useful for differentiating between sources of organic matter, identifying whether a sample comes from a terrestrial or marine environment. Isotope analysis therefore determines whether a correction for reservoir effect should be applied or not.

Using IRMS, archaeological dating laboratories can also refine the necessary corrections. For example, stable carbon isotopes can be used to detect the specific isotopic signatures of different carbon sources, such as those derived from marine or terrestrial photosynthesis. This process is essential for samples of uncertain origin, such as objects carved from organic materials of mixed or undetermined origin. Researchers can apply more precise corrections, reducing the uncertainties associated with the reservoir effect thanks to this improved knowledge of the isotopic composition of such samples.

Outlook for the reservoir effect

Geochemical models and reservoir age estimation

Another promising analytical method for improving age estimates of marine samples is the use of advanced geochemical models. These models integrate data on ocean circulation, atmospheric exchange, and spatial and temporal variations in ocean carbon-14 concentrations. These models can be used to calculate region-specific reservoir ages, adjusted for variables such as latitude, depth and ocean currents, taking into account the complex dynamics of oceanography.

The use of geochemical models offers greater precision in estimating reservoir ages by modeling the physical and chemical processes that influence the distribution of carbon 14 in the oceans. These take into account elements such as carbonate dissolution, circulation of deep water masses and ocean-atmosphere interactions. Researchers obtain more reliable estimates of the age of marine samples by applying these models, even in complex environments such as estuaries and deltas.

Carbon-14 dating of marine organisms is a complex yet essential field in archaeology. It requires precise methods to correct for reservoir effects. While limitations remain, technological and methodological advances are continually improving the accuracy of these dates.

Scientists from CIRAM laboratories offer this type of analysis and are available to guide you in your dating issues. If you wish to carry out a dating, you canrequest a studyto benefit from our expertise and obtain precise answers to your archaeological questions.