Nitrogen isotopes and the trophic level of humans in archaeology

Human and domesticate animal bone collagen δ¹⁵N values in prehistory differ generally by 3‰ or more from Neolithic to post- Roman times in Northwest Europe, leading to an assumed dietary animal protein fraction of 60–80% using a standard interpretation of δ¹⁵N values. We examine the assumptions on which this model rests and the limitations of our knowledge in the analysis of δ¹⁵N values in archaeology. We have developed a set of models which, with small changes made in assumptions (on the order of 1‰), can produce substantially lower estimates of the dietary animal protein fraction for given δ¹⁵N values. We consider the implications of various dietary animal protein fractions on agricultural carrying capacities and human population densities in prehistory.     

Stable oxygen (δO) and hydrogen (δD) isotopes in ovicaprid dentinal collagen record seasonal variation

Understanding paleoenvironmental conditions, including the frequency and amplitude of seasonal variation, is crucial to understanding a wide array of human behaviors in prehistory. In vertebrate calcified tissue, inorganic oxygen isotopes derived from apatite have been widely used as a proxy for paleoenvironment and seasonality in the archaeological record. However, organic sources of δ¹⁸O and δD in mineralized tissue have remained largely unexplored. Here we measure the oxygen (δ¹⁸O) and hydrogen (δD) composition of dentin collagen sequentially sampled from the lower cheek teeth of four modern ovicaprids from the Baga Gazar'in Chuluu (BGC) region of the Gobi Desert of Mongolia. A significant correlation between trends in hydrogen and oxygen isotope values within individual teeth was identified. The amplitude of isotopic variation observed in sampled tooth dentin is similar to the yearly range of hydrogen and oxygen isotopic variation observed in meteoric precipitation for the region. These data indicate that dentin collagen δ¹⁸O and δD isotopic values reflect seasonal variation in the organic oxygen and hydrogen isotopic composition of diet and ingested water. We argue that paired measurements of dentin collagen δ¹⁸O and δD appear to be reliable seasonal climatic indicators.     

Stable isotopes and diet at Ancient Kerma,Upper Nubia (Sudan)

Carbon and nitrogen stable isotope values were measured from bone collagen extracted from archaeological Nubian human (n = 54) and faunal (n = 61) populations from the site of Kerma, Sudan. Collagen suitable for isotopic analysis was extracted from 22 faunal and 48 human samples from the Eastern cemetery site, dated to the Middle Kerma (c. 2050–1750 BC) and Classic Kerma (c. 1750–1500 BC) periods respectively. The isotopic data indicate that the human dietary regimen included a mix of C₃ and C₄ plant-derived components, with a larger C₄ component than previously reported in archaeological Egyptian Nile Valley populations. Elevated δ¹⁵N values are attributed to consumption of dietary resources from a ¹⁵N-enriched terrestrial ecosystem. The faunal isotope data also indicate the consumption of C₃ and C₄ plants. The large range of δ¹³C values measured in both the human and faunal samples supports previous work suggesting that a significant portion of the populations buried at Kerma may have originated elsewhere, further confirming the Nile Valley as a major corridor for population movement in the region.     

Evaluating bone collagen extraction methods for stable isotope analysis in dietary studies

The specific purpose of this study was to compare three different collagen extraction methods commonly used in isotope laboratories conducting dietary studies. We evaluated their resultant differences in δ¹³C and δ¹⁵N, collagen quality and collagen yield. Our study was based on well-preserved skeletal material from the medieval period in Denmark. Our study shows that there is a systematic significant difference in the yield and the δ¹³C values between the three methods. Using the method of DeNiro and Epstein [DeNiro, M.J., Epstein, S., 1981. Influence of diet on the distribution of nitrogen isotopes in animals. Geochimica et Cosmochimica Acta 45, 341–351] with NaOH as cleaning agent, will, according to our study, give δ¹³C values that are on average ±0.32‰ more positive than using the ultra-filtration method [Brown, T.A., Nelson, D.E., Vogel, J.S., Southon, J.R., 1988. Improved collagen extraction by modified Longin method. Radiocarbon 30 (2), 171–177, modified in Richards, M.P., Hedges R.E.M., 1999. Stable isotope evidence for similarities in the types of marine foods used by late Mesolithic humans at sites along the Atlantic coast of Europe. Journal of Archaeological Science 26, 717–722]. The third method, which is a modified version of the second method, excluded the ultra-filtration step. This method seems to give δ¹³C values that lie in between the other methods. Our study did not show any significant difference in δ¹⁵N values. Although the differences between the methods are very small, we conclude that the use of stable isotope analysis in food determination studies requires adherence to routine methods for preparing and measuring samples.     

Stable isotopic evidence for diet in a Roman and Late Roman population from Leptiminus,Tunisia

This study investigates the diet of the Roman and Late Roman population of Leptiminus on the Mediterranean coast of Tunisia. Stable carbon and nitrogen isotope analysis of human bone collagen and carbonate samples obtained from individuals buried in four cemeteries at Leptiminus was conducted in order to reconstruct the diet of the population, investigate the relative importance of marine vs. terrestrial resources, explore sex-, age-, and status-based variations in diet, examine temporal changes in the types of foods consumed, and compare the diet at Leptiminus with that of other Roman populations. The results of this study indicate that the residents of Leptiminus consumed a diet that was heavily reliant on terrestrial plant resources with the addition of a significant amount of marine resources. There were no significant sex differences in isotope values. In contrast, distinct dietary differences were seen between the adults and children. Nitrogen isotope values suggest that weaning began before the age of two and was completed by about 3 years of age, a finding consistent with previous isotopic studies of Roman samples. A temporal shift in diet is suggested by the nitrogen isotope values measured in samples from the most recent cemetery. A comparison of the data from Leptiminus with that derived from other Roman sites indicates that regional variability in diet existed within the Empire.     

Stable carbon and nitrogen isotope variations in tooth dentine serial sections from Wharram Percy

Here we report δ¹³C and δ¹⁵N measurements of serial sections of human deciduous and permanent tooth dentine from archaeological samples taken from the medieval village site of Wharram Percy, Yorkshire, UK. We found a pattern of enrichment, for both δ¹³C and δ¹⁵N, where the tooth crown was greater than the cervical part of the root, which in turn was greater than the apical portion of the root and the associated rib collagen values. This pattern reflects a decrease in the consumption of isotopically enriched breast milk and the introduction of less enriched weaning foods in the diet. The (mean±SD) difference between the deciduous second molar crowns and corresponding rib samples from the same individuals after 2 years of age was 1.2±0.4‰ for δ¹³C and 3.2±0.8‰ for δ¹⁵N. The δ¹⁵N values are as predicted, but as there were no C₄plants at Wharram Percy, this 1.2‰ enrichment in δ¹³C represents clear evidence of a carbon trophic level effect in collagen from breastfeeding infants. Carbon and nitrogen results also show that the infant diet among those who died in infancy did not differ from those who survived into childhood. This study demonstrates the promise of using dentine serial sections to study the temporal relationships of breastfeeding, weaning, and dietary patterns of single individuals.     

Stable isotope investigations of charred barley (Hordeum vulgare) and wheat (Triticum spelta) grains from Danebury Hillfort: implications for palaeodietary reconstructions

Palaeodietary studies typically focus on the analysis of bone collagen due to the limited availability of plant remains. Isotopic analysis of plant remains, however, allow for a more extensive consideration of the contribution of plants to the human diet and can potentially provide information about the environment in which the crops were grown. This paper reports the results of carbon and nitrogen isotope analyses performed on charred barley and wheat grains recovered from pits within Danebury Iron Age hillfort. To the best of our knowledge, this is the first Iron Age site in Britain from which charred grains have been isotopically analysed. Our results suggest that cereals found at the hillfort were grown in several different environmental contexts. The isotope data demonstrate that the herbivores were not consuming a diet primarily based on grains as the δ¹⁵N values of the grains are very similar to those of the herbivores. Palaeodietary investigations typically assume that humans eating plant protein only would have the same δ¹⁵N value as the local herbivores. This assumption is clearly invalid at Danebury, where the humans and animals appear to have consumed either different parts of the same plants or different plants. Researchers typically interpret high differences between human and animal δ¹⁵N values as indicative of diets high in animal protein, however where major plant resources have δ¹⁵N values similar to those of the herbivores our ability to distinguish between plant and animal sources of protein in the diet is limited. Our research has demonstrated that whenever possible it is desirable to measure the isotopic signatures of potential major plant resources in order to understand past subsistence strategies.     

The distinction between freshwater- and terrestrial-based diets: methodological concerns and archaeological applications of sulphur stable isotope analysis

Sulphur isotopes in archaeological bone collagen are not routinely analysed in palaeodietary studies. Here we investigate the potential contribution that sulphur isotope analysis can provide toward the study of ancient human diet and economy, with particular emphasis on the distinction between freshwater and terrestrial consumers. For material from the Late Bronze Age site of Chicha in the south-western Eurasian forest-steppe, sulphur isotopes effectively separate freshwater and terrestrial animal food resources. The sulphur isotope data coupled with nitrogen isotope values from Chicha reflect a dietary reliance upon freshwater animal protein (fish) for the Late Bronze Age inhabitants. In contrast, sulphur isotope values for freshwater and terrestrial potential food species from the Eneolithic site of Bil'shivtsi in western Ukraine were indistinguishable, demonstrating that δ³⁴S values cannot always be relied upon to identify freshwater and terrestrial consumers. The data from this study support the adoption of δ³⁴S analysis as a standard component of palaeodietary studies; apart from its potential to distinguish freshwater from terrestrial consumers, it can provide supplementary dietary information not evident from the carbon and nitrogen isotope data. In addition, certain indices are considered that may be used to assess the validity of sulphur isotope data, as currently exist for carbon and nitrogen. According to the analysis of modern collagen samples, N:S appears to be a broad indicator of collagen sulphur isotope quality. However, more work needs to be done to establish an effective means by which highly-altered sulphur isotope values can be identified and thereby removed from consideration.     

Stable isotopes and human diet in central western Argentina

Central western Argentina is the southern boundary of prehispanic maize in the archaeological record. This paper explores the stable isotope information from human bone (δ¹³C, from collagen and δ¹³C from apatite) and tooth (δ¹³C from enamel) samples in order to characterize the temporal and spatial trends of these isotopes and to understand them in terms of human diet. We analyzed 104 human individuals from the last 6000 years. Using the Kellner and Schoeninger (2007) model the results shows a high variation in human diet with few human individuals with a notably high significance of C₄ plants (probably maize) as an energy source and these samples have a chronology around ca. 1000 years BP. On the other hand a high variation in an individual’s dietary life history is shown by differences between δ¹³C collagen, apatite and enamel.     

Stable carbon and nitrogen isotope analysis on human remains from the Early Mesolithic site of La Vergne (Charente-Maritime,France)

We report here the results of stable carbon and nitrogen isotope analysis of human and faunal remains from La Vergne (Charente-Maritime, western France), a rare Early Mesolithic burial site (ca. 8500–8000 cal BC). The results for nine humans (average δ¹³C = −19.3‰; δ¹⁵N = 9.4‰) indicate a strongly terrestrial diet, dominated by animal protein, with the possibility of, at best, a slight contribution of marine-derived protein. Given lower sea-levels in the early Holocene, the site would have been some 60–80 km from the sea at the time of its use; nevertheless, contacts with the coast are shown by the presence of numerous marine shell beads in the graves. In the light of the stable isotope results, it is suggested here that such contacts most likely took the form of exchange with coastal communities whose remains now lie underwater.     

Paleodietary analysis of the prehistoric population of the Canary Islands inferred from stable isotopes (carbon,nitrogen and hydrogen) in bone collagen

Nitrogen and carbon isotope compositions were measured in the bone collagen from a total of 86 prehispanic samples of the Canary Islands, and hydrogen in 70, all of them with enough amount of bone collagen, and adequate N and C content. These samples belong to prehistoric population of El Hierro (n = 27), Tenerife (n = 18), and Gran Canaria (n = 41). Isotope compositions were also obtained for prehistoric and modern food resources that were likely consumed by these people. Marked differences were observed among the three islands regarding the three isotopes analyzed: the δ¹⁵N values were highest among the population of Gran Canaria (10.8‰ ± 0.9‰), who also showed the highest δD values (7 ± 8‰). The population of El Hierro showed the highest δ¹³C values (−18.6‰ ± 0.7‰). These data suggest a high consumption of marine products by the population from El Hierro, and also an important consumption of terrestrial meat or marine, piscivore fish, by the population from Gran Canaria, together with domesticated C₃ plants (barley and/or wheat), fruits of Ficus carica and other wild species, and goat products. Additionally, marked differences were observed between men and women, which suggest that women consumed a more vegetal-based diet, a finding which is in agreement with the higher proportion of teeth with carious lesions among women.     

Stable isotope evidence of human diet at the Nukdo shell midden site,South Korea

Carbon and nitrogen stable isotope analysis was undertaken on bone collagen extracted from archaeological human (n = 48) and animal (n = 45) skeletons from the Nukdo site, Location I C, South Korea. This shell midden and grave site is dated from the late Mumun (550–300 BC) to early Iron Age (300 BC-1 AD) periods. The herbivorous mammals fell within the range of C₃ consumers, with average values of δ¹³C = −21.0 ± 0.5‰ and δ¹⁵N = 3.6 ± 0.5‰ for deer (n = 16) and δ¹³C = −20.6 ± 0.5‰ and δ¹⁵N = 4.5 ± 2.0‰ for wild boar (n = 17). Humans from this site averaged δ¹³C = −18.3 ± 0.4‰ and δ¹⁵N = 11.2 ± 0.7‰ for adults (n = 15) and δ¹³C = −18.7 ± 0.7‰ and δ¹⁵N = 12.5 ± 1.1‰ for juveniles (n = 33). These δ¹³C values indicate that there was no significant input of C₄ plants in the human diets and this may be associated with the spread of rice agriculture in the Mumun period. Human bone collagen δ¹³C and δ¹⁵N values indicate that there was some consumption of marine foods, although the main protein sources were from terrestrial foods. The isotope data demonstrate that the humans at Nukdo had mixed diets that included marine and terrestrial protein, including C₃ plants such as rice. Finally, the isotope results from the juveniles indicate that weaning occurred before the age of 1.5 years in this period.     

Stable carbon and nitrogen isotopes of human dental calculus: a potentially new non-destructive proxy for paleodietary analysis

Fifty-eight dental calculus samples from medieval and post-medieval skeletons from Vitoria, Spain, and a single sample from an Alaskan Inuit were tested for stable carbon and nitrogen isotope compositions. There was sufficient carbon and nitrogen concentrations to obtain δ¹³C and δ¹⁵N values, and the samples from Spain produced results that were replicable and comparable to European isotope values based on bone collagen collected from literature sources. The Alaskan Inuit calculus sample yielded a δ¹⁵N value of +17.5‰, well beyond the range of the Spanish samples, but consistent with literature data for modern Greenlandic Inuit consuming a diet rich in marine food. There are several potential sources for carbon and nitrogen in calculus. The results of this study yield stable isotope values consistent with those obtained from other biomaterials used as isotope proxies for paleodietary research, including bone collagen, hair, and fingernails, although further work is necessary to verify the fidelity of calculus as an isotope proxy. Many studies in bioarchaeology are precluded by curatorial concerns regarding the destructive analysis of primary biomaterials. However, calculus is an “add-on”, or secondary biomaterial, that is not an integral part of the dental or skeletal system. Hence, its consumption during analysis is technically not destructive. Therefore, isotope analysis of dental calculus may provide a potential new avenue for paleodietary analysis where the use of other primary biomaterials is precluded.     

Manuring and stable nitrogen isotope ratios in cereals and pulses: towards a new archaeobotanical approach to the inference of land use and dietary practices

This paper explores the impact of animal manure application on the δ¹⁵N values of a broad range of crops (cereals and pulses), under a range of manuring levels/regimes and at a series of locations extending from northwest Europe to the eastern Mediterranean. We included both agricultural field experiments and areas where ‘traditional’ farming is practised. Our aim is to ground-truth interpretation of δ¹⁵N values in archaeobotanical crop remains as evidence of past growing conditions and husbandry practices. The results confirm the potentially radical impact of manuring on δ¹⁵N values in cereals, depending on manuring level, but indicate only a slight effect on pulses, which can fix atmospheric nitrogen. The expected geographical trend towards greater δ¹⁵N with increasing climatic aridity is not apparent, probably because the growing conditions for crops are ‘buffered’ through crop management. Each of these observations has fundamental implications for archaeobotanical interpretation of δ¹⁵N values as evidence of land use practices and (together with analysis of bone collagen/tooth enamel in potential consumers) palaeodiet.     

A palaeodietary investigation of carbon (C/C) and nitrogen (N/N) in human and faunal bones from the Copper Age cemeteries of Varna I and Durankulak,Bulgaria

Stable isotope analyses have been applied to human and faunal bone collagen from the Varna I and Durankulak cemeteries to explore palaeodietary adaptations in the Neolithic and Eneolithic (Copper Age). The results suggest both populations primarily utilised terrestrial, C₃-based diets, despite their proximity to the Black Sea. The wider δ¹⁵N range of the Durankulak humans likely indicates the differential utilisation of terrestrial meat sources, which is probably related to the degree to which primary and/or secondary ovicaprid products were consumed, particularly since ovicaprid δ¹⁵N values differ from other herbivores. The isotopic distribution of Varna I reflects a linear relationship between δ¹⁵N and δ¹³C, suggesting that a minority of individuals enriched in both isotopic parameters supplemented their diets with marine resources. These burials include the well known ‘chieftain’ (burial 43) and show notable material wealth by way of grave goods. At the population level, however, there is no significant correlation between stable isotope values and material wealth at Varna I, a fact with implications for theories regarding emergent social/economic hierarchies in Balkan prehistory. Five burials at Durankulak were found to have relatively enriched δ¹³C and δ¹⁵N values with respect to the rest of the population. These burials reflect a prominently marine-based or mixed terrestrial C₃-based diet that included C₄ inputs, possibly from millet, for which the limitations of stable isotope analysis on bulk collagen are not able to differentiate. AMS dating has shown that these burials belong to a much later period.     

Experimental chemical degradation compared to natural diagenetic alteration of collagen: implications for collagen quality indicators for stable isotope analysis

Stable isotopic ratios from archaeological bone collagen are valid palaeodietary indicators, but depend on sufficiently well preserved molecules and several collagen quality criteria have to be fulfilled (mostly collagen wt%, C%; N%, C/N molar ratio). For a reassessment of these quality criteria, and a better understanding of the chemical degradation of bone collagen, experimentally degraded modern bones and 54 archaeological human bones were investigated. In the course of the experimental degradation, alterations of isotopic ratios were paralleled by altered collagen quality criteria. The contrary was found in the case of the archaeological specimens. This implies that the commonly used collagen quality criteria may be insufficient and do not guarantee that stable isotopic values of the gelatine extracts will still represent the original biological signal.     

Modern and early-middle Holocene shells of the freshwater mollusc Unio, from Çatalhöyük in the Konya Basin, Turkey: preliminary palaeoclimatic implications from molluscan isotope data

Carbon and oxygen isotope ratios in the shells of the freshwater Unio mollusc yield information on the isotopic composition of the water in which the shell was formed, which in turn relates to climatic conditions prevailing during the bivalves’ life span. Here we analysed shells from one modern Unio, from a modern lake shore in Anatolia, and 4 subfossil Unio shells from Çatalhöyük (dated between 7200 BC and 5000 BC, Neolithic and Chalcolithic periods). Sequential carbon and oxygen isotope analysis along the surface of the shells provides information on seasonal or shorter-term variability of lake waters during the lifetime of the organisms. δ¹⁸O values of the modern shell are consistent with it being collected from a dammed portion of the Seyhan River that does not undergo intensive summer evaporation. This is in contrast to many of the surface water bodies in Anatolia which suffer extensive evaporation in the arid summers. δ¹⁸O values of the subfossil shells from the Çatalhöyük middens indicate that the bivalves came from lakes which evaporated extensively during the summer months but were replenished by high winter rainfall, suggesting that the subfossil shells lived in relatively small lakes or ponds. Stable isotope analysis along the growth of freshwater bivalves is one of the few methods for investigating seasonal water fluctuations in the past. These results may alter current interpretations on the environment of Çatalhöyük during the Neolithic, although more work is needed to confirm these initial findings.     

Stable isotopes,diet, and taphonomy: a look at using isotope-based dietary reconstructions to infer differential survivorship in zooarchaeological assemblages

Archaeology has always faced the problem of making informed inferences based on an incomplete record. Zooarchaeological studies of prehistoric hunting and diet offer a clear case in point, where a range of behavioral and taphonomic factors can produce a substantial disconnect between what people actually captured and ate and what archaeologists recover and interpret. We explore this disconnect by presenting stable C and N data for wild faunas, archaeological maize, and three human burials from Fremont-period sites in southeastern Utah, the United States. We use these data to estimate faunal contributions to prehistoric diets and compare the results with previous zooarchaeological analyses of faunas from the same sites. Results for the two approaches differ sharply, with isotopic estimates showing much higher contributions of small and lowland game. We discuss these results in terms of both local prehistory and wider issues of taphonomy and dietary analysis.     

Stable isotope evidence for salt-marsh grazing in the Bronze Age Severn Estuary,UK: implications for palaeodietary analysis at coastal sites

Stable isotope analyses of modern coastal and salt-marsh plant species (‘salt-loving’ plants or halophytes) have demonstrated that these are significantly enriched in ¹⁵N compared to other terrestrial plants. Coastal salt-marshes were far more extensive in the past than they are today. They represented a vast and much-exploited resource in many areas of the UK and north-western Europe and were considered to be prime land for the grazing of animal stock.     

FOCUS: effect of diet and protein source on carbon stable isotope ratios in collagen: follow up to

We analyzed carbon stable isotope data from bone collagen of animals consuming varied experimental diets, including recently published data from Warinner and Tuross [Warinner, C., Tuross, N., 2009. Alkaline cooking and stable isotope tissue–diet spacing in swine: archaeological implications. Journal of Archaeological Science 36, 1690–1697; this journal]. Comparing regression lines for the relationship between collagen and diet δ¹³C, we show that protein source, and not physiology, explains the apparent taxonomic difference between swine and rodents reported in that paper. Our results reveal a complex relationship between whole diet and dietary protein in determining collagen δ¹³C values, such that in many cases, collagen alone may not provide reliable reconstructions of paleodiet. We advocate the simultaneous use of both collagen and apatite δ¹³C, whenever possible, to assess the diets of prehistoric peoples.