Introducing δSr analysis in archaeology: a demonstration of the utility of strontium isotope fractionation in paleodietary studies

Isotopic methods are widely used in archaeology to investigate paleodiet. Here, we present a new method to identify trophic level in archaeological human populations and to investigate paleodiet. We demonstrate that strontium isotope compositions (reported as δ^88/86Sr) vary in a mass-dependent manner with increasing trophic level and can elucidate paleodiet in archaeological human populations. We present new mass-dependent strontium isotope data from tooth enamel and bone from individuals buried during the Late Intermediate Period (c. AD 1000–1300) in the large cemeteries of Chiribaya Alta, Chiribaya Baja, San Gerónimo, and El Yaral in the Ilo and Moquegua Valleys of southern Peru. We compare these data to radiogenic strontium isotope data (⁸⁷Sr/⁸⁶Sr) and light stable isotope data (δ¹⁵N_col and δ¹³C_col) from the same individuals to investigate geologic variability in strontium sources as well as marine food consumption among the Chiribaya. Our results demonstrate the utility of measurements of strontium isotope fractionation as a new tool for archaeological investigation of paleodiet. Importantly, this new technique can be used to generate paleodietary (δ^88/86Sr) and paleomobility (⁸⁷Sr/⁸⁶Sr) data from the same specimen, minimizing destructive analyses of invaluable archaeological material, and provides a new way to examine paleodiet through hydroxyapatite, which is particularly important when collagen is poorly preserved.     

Tracing population mobility in the Aegean using isotope geochemistry: a first map of local biologically available Sr/Sr signatures

Strontium isotope ratio (⁸⁷Sr/⁸⁶Sr) analysis of archaeological human skeletal remains is an efficient method of investigating past population movement and residential mobility by determining probable geographical origins for the individuals examined. For this to be achieved, however, a map of biologically available ⁸⁷Sr/⁸⁶Sr signatures across the region investigated is needed. This paper presents a first such map for the Aegean, based on ⁸⁷Sr/⁸⁶Sr values recovered mainly from archaeological animal dental enamel and modern snail shells from sites largely distributed in the southern part of this region. Although not exhaustive, this comprehensive dataset of local biologically available ⁸⁷Sr/⁸⁶Sr signatures shows a marked difference between Mainland sites of the Pindos and Parnassos zones and the islands of south-eastern Aegean crossed by the Sub-Pelagonian zone (0.70808–0.70869), and sites in the central Cyclades and the north-eastern Aegean islands falling into the Attic-Cycladic metamorphic belt and the Vardar zone, respectively (0.70926–0.71187). Biologically available ⁸⁷Sr/⁸⁶Sr values from sites on central Euboea in the Pelagonian zone, south-eastern Attica and the western Cyclades in the Attic-Cycladic metamorphic belt, and on Crete in the Gavrovo zone are also relatively high (0.70853–0.70931), but lower than those recorded for the central Cyclades and the north-eastern Aegean.     

Sr/Sr variability in Puerto Rico: geological complexity and the study of paleomobility

The temptation to use biogeochemical techniques to resolve issues of paleomigration is evident and well intentioned. Knowledge of radiogenic strontium isotope baselines in a region of interest is a sine qua non of such archaeological studies of paleomobility. Here, we present the first detailed study of baseline ⁸⁷Sr/⁸⁶Sr values for the island of Puerto Rico. The high degree of ⁸⁷Sr/⁸⁶Sr variability present in this corpus of modern Puerto Rican bedrock and terrestrial malacological samples (0.70406–0.70909) is a testament to the complex geology of that island. This diversity of ⁸⁷Sr/⁸⁶Sr values makes parsing issues of origin a difficult and highly contingent task. Given these complexities, regional studies seeking to assess paleomigration by such isotopic means should proceed with a great deal of caution.     

Spatial variation of biologically available strontium isotopes (Sr/Sr) in an archipelagic setting: a case study from the Caribbean

This paper presents the results of strontium (Sr) isotope analysis of modern and archaeological animal remains and modern plant samples from the Caribbean region. The goal is to assess if patterns of human mobility can be determined from the archaeological record in an archipelagic setting. The range of variability and spatial distribution of biologically available strontium isotope signatures is reported and data evaluated to determine if sufficient heterogeneity exists to permit the identification of mobility despite the presence of potentially large contributions of marine strontium in island and coastal ecosystems. The (is)landscape is divided into several sub-regions based on the age and lithology of underlying geology and the variability of ⁸⁷Sr/⁸⁶Sr ratios is reported as; mean ⁸⁷Sr/⁸⁶Sr ± 2 standard deviations, number of samples: 1) Volcanic and Intrusive rocks (0.7077 ± 0.0019; n = 162); 2) Cretaceous–Miocene Limestone (0.7085 ± 0.0009; n = 50); 3) Pliocene–Quaternary Limestone (0.7091 ± 0.0004; n = 54); 4) Sedimentary Deposits (0.7094 ± 0.0015; n = 16); 5) Metamorphic Deposits (0.7104 ± 0.0014; n = 6). There are substantial differences between expected ⁸⁷Sr/⁸⁶Sr values based on associated geology and measured ⁸⁷Sr/⁸⁶Sr in flora and fauna samples. These differences emphasize the importance of focusing on bioavailable strontium, as opposed to geological proxies, for estimations of Sr isotope ranges, especially in archipelagic environments. While some overlap exists between the ⁸⁷Sr/⁸⁶Sr ranges of certain sub-regions, other sub-regions possessed limited variation and could be distinguished based on strontium isotope data. This spatial patterning of biologically available strontium indicates that strontium isotope analyses can be successfully applied to the archaeological study of human mobility within the Caribbean region.     

Migration in the Nile Valley during the New Kingdom period: a preliminary strontium isotope study

The value of strontium isotope analysis in identifying immigrants at numerous archaeological sites and regional areas has been demonstrated by several researchers, usually by comparing ⁸⁷Sr/⁸⁶Sr values of human tooth enamel and/or bone with the local strontium isotope signature determined by faunal and environmental samples. This paper examines the feasibility of using ⁸⁷Sr/⁸⁶Sr ratios to investigate residential mobility in the Nile Valley region, specifically at the New Kingdom period (∼1050–1400 BC) archaeological site of Tombos (ancient Nubia). Archaeological and textual information regarding this period indicates that immigrant Egyptians and local native Nubians were likely interacting at this site during a period of Egyptian colonial occupation. The results of this study suggest that non-local individuals may be distinguished from locals using ⁸⁷Sr/⁸⁶Sr values and that colonial agents in the Tombos population were probably both local native Nubians and immigrants.     

Oxygen and strontium isotopes as provenance indicators of fish at archaeological sites: the case study of Sagalassos,SW Turkey

In this paper, we investigate the potential use of oxygen and strontium isotope ratios (δ¹⁸O_p and ⁸⁷Sr/⁸⁶Sr) measured in archaeological fish enamel as provenance indicators. δ¹⁸O_p and ⁸⁷Sr/⁸⁶Sr were measured in a suite of archaeological carp remains recovered from the Anatolian townsite of Sagalassos dated to the Early Byzantine period (AD 450–650) and compared to that of modern fish, river and lake waters from the Anatolian region. We used sequential leaches in weak acetic acid to remove diagenetic Sr from fossil tooth enamel, monitoring the effectiveness of this approach by measuring the Sr/Ca ratios of the leachates via an isotope dilution thermal ionization mass spectrometry method (ID-TIMS). δ¹⁸O_p values mostly excluded a riverine origin. ⁸⁷Sr/⁸⁶Sr ratios of one fish overlapped with the ⁸⁷Sr/⁸⁶Sr signatures of two lakes in the Anatolian region, and at least one lake (Gölcük) could be removed as a candidate owing to a very distinctive ⁸⁷Sr/⁸⁶Sr signature not found in any of the fish remains. Most of the tooth samples analyzed could not be assigned a precise geographical origin since the ⁸⁷Sr/⁸⁶Sr ratios measured in enamel did not match that of any of the local lakes selected as potential origin. This result suggests that carp may have originated from lakes that have not yet been sampled, although this conclusion is not supported by other archaeological evidence. Alternatively, the lack of correspondence between lakes and fish Sr isotope ratios highlights several possible sources of uncertainties including spatial heterogeneity in ⁸⁷Sr/⁸⁶Sr ratio within a lake, the contribution of dietary strontium to the ⁸⁷Sr/⁸⁶Sr ratio of fish tooth enamel, and post-mortem alteration of the tooth Sr isotope signal during fossilization. In spite of the high precision of the strontium isotope analyses and the wide range of variation in the surface waters of the Anatolian lakes and rivers, this method may remain limited to distinguishing between lakes situated in regions of bedrock of very distinct age and geology until these sources of uncertainty are more fully investigated.     

Contribution of strontium to the human diet from querns and millstones: an experiment in digestive strontium isotope uptake

The question of whether rock grit ingested unintentionally from querns, metates or millstones, or deliberately through pica or geophagy, is bioaccessible in the human gut has not been addressed in archaeological strontium (Sr) isotope studies. This study employed the unified bioaccessibility method and determined that ingested rock grit can provide bioaccessible ⁸⁷Sr/⁸⁶Sr, but that unintentional consumption is unlikely to constitute > 1% of the diet (by mass) and will not significantly change, that is, by > 0.001, human skeletal ⁸⁷Sr/⁸⁶Sr. The use of locally or non‐locally sourced querns or millstones will not affect the interpretation of archaeological human ⁸⁷Sr/⁸⁶Sr values in Britain.     

Provenancing East Mediterranean cedar wood with the <Superscript>87</Superscript>Sr/<Superscript>86</Superscript>Sr strontium isotope ratio

⁸⁷Sr/⁸⁶Sr isotope ratios of cedar wood from forests in the East Mediterranean have been compiled in order to investigate the feasibility of provenancing archaeological cedar wood finds. Cedrus sp. forests furnished a great amount of wood in antiquity, for purposes ranging from ship to temple construction, and for fashioning cult statues and sarcophagi. The ⁸⁷Sr/⁸⁶Sr signatures of archaeological cedar samples may be compared with the preliminary dataset presented here to help determine the geographic origin of wooden artifacts. Sample sites include two forest areas in the Troodos Massif of Cyprus, five in the Lebanon, and two in Turkey’s Taurus Mountains. Sr ratios for wood varieties (i.e., early heartwood, late heartwood, sapwood, and twig wood) demonstrate relative uniformity between the xylem types frequently recovered from archaeological contexts. As such, this pilot study also assesses important issues of archaeological sampling and the geographical factors that influence Sr uptake in cedar trees of this region. While the regional signatures are distinct in most cases, small sample sizes and range overlap indicate the need for additional methods to make a case for a certain source forest. Alone, this method continues to be best used to disprove assumed wood provenances.     

Strontium isotope analysis of Neolithic and Copper Age populations on the Great Hungarian Plain

The strontium isotope ratio (⁸⁷Sr/⁸⁶Sr) is used in archaeological studies to identify major events of population movement in prehistory such as migration, conquest, and inter-marriage. This study shows that the strontium isotope method can be expanded to identify more subtle shifts in prehistoric human mobility. ⁸⁷Sr/⁸⁶Sr isotope ratios were analyzed in dental enamel from human and faunal specimens from the Late Neolithic and Copper Age on the Great Hungarian Plain. The archaeological record indicates that several aspects of life changed during the transition from the Late Neolithic to the Copper Age (ca. 4500 BC) in Hungary; evidence for increased interaction over a wide geographical area, less resource pooling and the use of secondary products has been used to support the idea that local populations became more mobile, perhaps due to the adoption of an agro-pastoral economy. Results from this study identify a change in the range of strontium isotope values from the Late Neolithic to the Copper Age from a very narrow range of values to a much broader range of values, which suggests that changes in how land and resources were utilized on the Great Hungarian Plain affected incorporation of strontium into the skeletal system. This study indicates that the strontium isotope ratio is a valuable tool for identifying more subtle changes in prehistoric behavior such as a shift to a more pastoral economy.     

HUMAN MOBILITY AT THE EARLY NEOLITHIC SETTLEMENT OF VAIHINGEN,GERMANY: EVIDENCE FROM STRONTIUM ISOTOPE ANALYSIS*

As evidence concerning human mobility during the transition to agriculture in central Europe, we present the results of strontium isotope analysis of human skeletons from the Neolithic village of Vaihingen, Germany. We find significantly more ‘non‐local’⁸⁷Sr/⁸⁶Sr values from humans buried in a Neolithic ditch surrounding Vaihingen than from those buried within the settlement. These results fit with previous studies showing a correlation between burial circumstances and strontium isotope signatures from LBK cemeteries of southwestern Germany ( Price et al. 2001 ; Bentley et al. 2002 ). A pilot study of Neolithic animal teeth from Vaihingen suggests that either ‘local’⁸⁷Sr/⁸⁶Sr signatures were more variable than the analysed human bones suggest, or that these domestic animals themselves were mobile, perhaps ranged by mobile pastoralists.     

Baseline bioavailable strontium isotope values for the investigation of residential mobility and resource-acquisition strategies in prehistoric Cambodia

Strontium (Sr) isotope ratios (⁸⁷Sr/⁸⁶Sr) measured in human skeletal material can increase one's understanding of the residential behaviour and resource-acquisition strategies of past populations. The paper maps bioavailable ⁸⁷Sr/⁸⁶Sr variation in 183 plant and soil samples across Cambodia. Bioavailable ⁸⁷Sr/⁸⁶Sr, as measured in plants, differs significantly between four major geological units. The data set will support future investigations of skeletal material from Cambodian archaeological sites. Baseline ⁸⁷Sr/⁸⁶Sr data should be applied judiciously to skeletal populations, and in concert with other lines of evidence, to identify potential geographical outliers rather than to ascribe specific locations from which individuals may have moved.     

THE POTENTIAL OF CARBONIZED GRAIN TO PRESERVE BIOGENIC 87SR/86SR SIGNATURES WITHIN THE BURIAL ENVIRONMENT*

Carbonized grains survive for millennia in many archaeological contexts. Their stable structure raises the possibility that they preserve biogenic strontium isotope signatures. This hypothesis was investigated using short‐term, laboratory experiments with modern grain immersed in Chalk solution. HCl leaching removed > 95% of secondary alteration from charred grain, and isotope ratios close to the starting value were recovered. This could not be achieved with uncharred grains. HCl leaching of archaeological carbonized grains produced comparable levels of decontamination. Although preliminary, these results suggest that strontium isotope analysis of archaeological carbonized grains from calcareous burial contexts could be used to investigate ancient trade and agriculture.     

Reconstructing ancient Maya animal trade through strontium isotope (87Sr/86Sr) analysis

This study explores the potential for using strontium isotope analysis (⁸⁷Sr/⁸⁶Sr) to study ancient Maya animal exchange. Traditional zooarchaeological methods of studying trade rely on the identification of animals found outside their natural geographic or habitat ranges. Isotopic analysis provides an additional means of identifying and sourcing non-local animals. ⁸⁷Sr/⁸⁶Sr values from Maya zooarchaeological remains indicate that regional and long-distance transport and exchange of animal goods was more common than previously recognized. Widely distributed animals including deer and peccary were among the animals exchanged, which questions their common interpretation as locally-acquired resources. The isotopic results contribute to our understanding of how animal products were integrated into Maya economic and exchange networks. The research is also relevant to human mobility studies in Mesoamerica.     

Baseline data for Andean paleomobility research: a radiogenic strontium isotope study of modern Peruvian agricultural soils

While the use of radiogenic strontium isotope values to examine paleomobility is increasingly common in the Andes, and beyond, many questions about baseline variability remain. To better understand baseline radiogenic strontium isotope compositions in the Andes, we present new ⁸⁷Sr/⁸⁶Sr values from Peruvian soil samples. Modern soil samples were collected from agricultural fields from the following areas in central and southern Peru: Arequipa, Atico, Camaná, Chala, Cusco, Ica, Ilo, Lima, Mejía, Moquegua, Nazca, Ocoña, Palpa, Pisco, Puno, Tacna, and Yauca. Samples were partially dissolved to better approximate the bioavailable strontium. Radiogenic strontium isotope values from the partially dissolved soil samples range from ⁸⁷Sr/⁸⁶Sr?=?0.70202 to 0.71894 and, for all soil samples, have a mean of ⁸⁷Sr/⁸⁶Sr?=?0.70773?±?0.00166 (1σ, n?=?114). In general, the ⁸⁷Sr/⁸⁶Sr values measured for soil samples collected from modern agricultural fields reflect the expected ⁸⁷Sr/⁸⁶Sr values based on bedrock geology. Comparing our new soil data with published radiogenic strontium isotope data for bedrock, soil, water, and faunal samples provides constraints on the regions in the Andes that can, and cannot, be distinguished through radiogenic strontium isotope analysis.     

IN‐SITU ELEMENTAL AND Sr ISOTOPE INVESTIGATION OF HUMAN TOOTH ENAMEL BY LASER ABLATION‐(MC)‐ICP‐MS: SUCCESSES AND PITFALLS*

Trace element and Sr isotope data were obtained by laser ablation‐ and solution mode‐(MC)‐ICP‐MS analysis for tooth enamel from remains excavated at the New Kingdom period Egyptian colonial and Nubian cemetery site of Tombos (Sudan). Elemental abundances determined by both methods of ICP‐MS analysis yielded comparable values; however, ⁸⁷Sr/⁸⁶Sr values obtained by laser ablation were higher compared to their solution mode counterparts. This discrepancy is related to the production of a molecular interference—Ca + P + O (overlaps ⁸⁷Sr); hence the higher ⁸⁷Sr/⁸⁶Sr values recorded during ablation analyses. Laser ablation studies of enamel may provide relatively precise ⁸⁷Sr/⁸⁶Sr values rather quickly but cannot be used for accurately deciphering historical population migrations.     

Strontium isotopes and human mobility in prehistoric Denmark

The principles behind the strontium isotopic system are an important tool for archaeologists tracing human migration and patterns of movement in prehistory. However, there are several scientific challenges of analytical nature, as well as those which relate to unknown parameters inherent to the interpretation of such data. One prerequisite is the knowledge of the range of strontium isotopic ratios that best characterize the bioavailable fractions of a particular area of interest. The study reported here attempts to establish a baseline for strontium isotope signatures valuable for Denmark (excluding the island of Bornholm) and particularly for the use in archaeological investigations. We present strontium isotope ratios of bones and teeth from modern mice contained in owl pellets, of snail shells, and of archaeological fauna samples. We compare these ratios with median strontium isotope signatures characterizing human enamel populations from archaeological sites within Denmark. The fauna samples reported here range from ⁸⁷Sr/⁸⁶Sr = 0.70717 to 0.71185 with an average of 0.70919, and human enamel defines a range from ⁸⁷Sr/⁸⁶Sr = 0.7086 to 0.7110 with an average of 0.7098. In both datasets, we observe a small difference between the baseline values for the western (Jutland) and eastern (Funen, Zealand, and the southern islands) parts of Denmark. We therefore propose two slightly different baseline ranges with a partial overlap for the isotopic signatures of bioavailable strontium fractions within Denmark, namely a range of ⁸⁷Sr/⁸⁶Sr = 0.7078–0.7098 for the western area and a range of ⁸⁷Sr/⁸⁶Sr = 0.7089–0.7108 for the eastern parts.     

87Sr/86Sr: a New Discriminant for Provenancing Neolithic Porcellanite Artifacts from Ireland

Antrim porcellanite (thermally metamorphosed Tertiary laterite) was the most common raw material used in the production of stone implements during the Neolithic in Ireland and was worked at two localities in North Antrim: Tievebulliagh, near Cushendall and Brockley on Rathlin Island.Attempts have been made to provenance material from these two known sources, the most successful to date being the use of geochemical data (Sr and Yppm). Here we present a new geochemical discriminant—Sr isotopic data—which reveal that Tievebulliagh and Brockley porcellanites are distinctive. Present-day⁸⁷Sr/⁸⁶Sr ratios form two discrete groupings ranging from 0·705894±25–0·706443±24 at Tievebulliagh and 0·704088±27–0·704587±25 at Brockley. A coherent relationship between⁸⁷Sr/⁸⁶Sr and Sr (ppm) reiterates the use of Sr content as a discriminant and illustrates the geochemical variability of Sr between these two sources.Although this is a destructive technique,⁸⁷Sr/⁸⁶Sr represents the best discriminant to date for Antrim porcellanites and will enable definitive provenancing of porcellanite artifacts from Ireland with important archaeological implications.     

Isotopic evidence for Middle Horizon to 16th century camelid herding in the Osmore Valley,Peru

Archaeological and zooarchaeological data indicate that camelid pastoralism was a subsistence and economic mainstay of Middle Horizon and more recent cultures in the Osmore region of southern Peru. However, it is not known whether camelids were primarily herded in highland puna pastures or near lower elevation sites in the middle valley or along the coast. This research examines the elevation of archaeological camelid herding in the Osmore Valley using stable isotope analysis. Stable carbon (δ¹³C) and nitrogen (δ¹⁵N) isotope ratios were measured on 28 archaeological camelid bone samples from the Middle Horizon sites of Cerro Baúl and Cerro Mejía, the Late Intermediate site of Yaral and the late pre‐Hispanic to Colonial period site of Torata Alta. Twenty‐three archaeological camelids have δ¹³C and δ¹⁵N values similar to five modern camelids maintained in highland puna pastures. In contrast, three camelids from the high status Wari site of Cerro Baúl, and two from Yaral have unexpectedly high δ¹³C and/or δ¹⁵N values outside the expected range for camelids pastured in highland puna habitats. The results may be explained by differences in foddering practices, altitudinal herding range or climatic conditions. Strontium isotope ratios (⁸⁷Sr/⁸⁶Sr) were also assessed to infer pasture elevation using the camelid remains from Cerro Baúl (n = 11). One individual in this sub‐sample exhibits a non‐local ⁸⁷Sr/⁸⁶Sr value indicative of an origin in the highland puna region east or south of Lake Titicaca. It was not possible to further distinguish between camelids herded in lower to middle elevation habitats outside the Lake Titicaca basin using ⁸⁷Sr/⁸⁶Sr values. This study suggests that multiple isotope proxies may be used to identify animals primarily pastured in lowland coastal versus highland puna (> 4000 masl (meters above sea level)) habitats, but are less useful at distinguishing between animals pastured in lower to middle elevation settings. Copyright © 2010 John Wiley & Sons, Ltd.     

Reduced Population Variance in Strontium Isotope Ratios Informs Domesticated Turkey Use at Chaco Canyon,New Mexico,USA

Traditionally, strontium isotopes (⁸⁷Sr/⁸⁶Sr) have been used as a sourcing tool in numerous archaeological artifact classes. The research presented here demonstrates that ⁸⁷Sr/⁸⁶Sr_bioapatite ratios also can be used at a population level to investigate the presence of domesticated animals and methods of management. The proposed methodology combines ecology, isotope geochemistry, and behavioral ecology to assess the presence and nature of turkey (Meleagris gallopavo) domestication. This case study utilizes ⁸⁷Sr/⁸⁶Sr_bioapatite ratios from teeth and bones of archaeological turkey, deer (Odocoileus sp.), lagomorph (Lepus sp. and Sylvilagus sp.), and prairie dog (Cynomys sp.) from Chaco Canyon, NM, USA (ca. A.D. 800–1250). Wild deer and turkey from the southwestern USA have much larger home ranges and dispersal behaviors (measured in kilometers) when compared to lagomorphs and prairie dogs (measured in meters). Hunted deer and wild turkey from archaeological contexts at Chaco Canyon are expected to have a higher variance in their ⁸⁷Sr/⁸⁶Sr_bioapatite ratios, when compared to small range taxa (lagomorphs and prairie dogs). Contrary to this expectation, ⁸⁷Sr/⁸⁶Sr_bioapatite values of turkey bones from Chacoan assemblages have a much lower variance than deer and are similar to that of smaller mammals. The sampled turkey values show variability most similar to lagomorphs and prairie dogs, suggesting the turkeys from Chaco Canyon were consuming a uniform diet and/or were constrained within a limited home range, indicating at least proto-domestication. The population approach has wide applicability for evaluating the presence and nature of domestication when combined with paleoecology and behavioral ecology in a variety of animals and environments.     

A strontium isotope analysis on the relationship between ritual tooth ablation and migration among the Jomon people in Japan

Distinct patterns can be discerned in the extensive ritual tooth ablation found among the human skeletal remains of the Late–Final Jomon period (ca. 3200–2800 cal BP) in Japan. Based on comparative observations of sex and grave patterns in the skeletal remains, two major patterns in ritual tooth ablation, termed type 4I and type 2C, have been assigned to locals and immigrants, respectively. In order to test this hypothesis, strontium (Sr) isotope (⁸⁷Sr/⁸⁶Sr) analyses were performed on human skeletal remains from the Yoshigo shell mound in Aichi Prefecture, central Japan. Plants in the surrounding area were also examined to illustrate the geographic ⁸⁷Sr/⁸⁶Sr distribution. The Sr isotopic variation in human tooth enamel (⁸⁷Sr/⁸⁶Sr = 0.70868–0.71028) was greater than that in human bones (⁸⁷Sr/⁸⁶Sr = 0.70871–0.70943). Individuals with higher Sr isotope ratios in their tooth enamel than seawater Sr values of 0.7092 can be identified as immigrants (36% of population). The presence of these isotopically identified immigrants between both type 2C and type 4I individuals does not support the previous hypothesis. The intra-population ⁸⁷Sr/⁸⁶Sr distribution of tooth enamel of type 2C individuals showed a significantly higher mean ratio than that of type 4I individuals, suggesting a higher proportion of immigrants among the former.