Investigating human geographic origins using dual-isotope (87Sr/86Sr, δ18O) assignment approaches

Human tissue oxygen and strontium isotope values in North America: A data compilation and assessment for forensic geolocation

The use of isotopic analysis for human mobility, geolocation, and forensic identification has become common over the past two decades, yet its effectiveness depends on the availability of well-documented reference data. Many reference data exist in the literature, but the suitability of these data for forensic applications has not been critically assessed. Here, we compile oxygen and strontium isotope data for North American human tissues (hair, nails, bone, and tooth enamel). We review the geographic distribution of these data, evaluate their relationship with the predicted geographic variation, and assess potential sources of bias that may limit the comparability of different datasets in the compilation. A substantial number of data are available for some of these substrates and isotope systems, but in most cases, their geographic distribution is patchy with many areas under sampled. Except for hair Sr isotopes, a robust relationship occurs between human tissue values and modeled local environmental values, suggesting theoretically expected relationships between human tissues and local sources of O and Sr are expressed. These relationships are noisy; we identify several methodological differences that produce systematic biases across the compiled data. Based on these findings, we suggest interpreting forensic isotope data using currently published reference data is problematic. We propose the adoption of consistent metadata reporting and standardized laboratory protocols to enhance the utility of data gathered in future research as these practices could lead to measurable improvements in the strength of forensic interpretations derived from human tissue isotope data.

Diversity of Lifeways in Early Antillean Societies: A Multi-Isotope Approach

OBJECTIVES

In this paper, we sought to examine whether people with different lifeways, as evidenced by their mobility patterns and dietary practices, inhabited the Antilles in early precolonial time. We also aimed to explore spatiotemporal trends.

MATERIALS AND METHODS

New and previously published enamel strontium, oxygen, and carbon isotope data were combined with bone apatite carbon and bone collagen carbon and nitrogen isotope data to assess the mobility and diet of 146 individuals from eight early precolonial sites from Cuba.

RESULTS

At least three patterns of mobility, associated with different dietary signals, were identified. In contrast with the low 87Sr/86Sr and δ13Cen variability found in Canímar Abajo (CA) between bce 1320 and 807, more variability in dietary practices and higher mobility was apparent in later groups. Between bce 116 and 241 ce, individuals from Playa del Mango showed high mobility within the Cauto region, likely associated with food procurement between inland and coastal areas. From at least 174 ce, a moderate pattern of mobility and a diversity of dietary traditions could be observed among groups from western sites. At least three general dietary patterns were observed, ranging from a 100% C3 diet to 70:30 C3/C4 and, in the case of CA, a higher dependence on marine/C4 resources.

CONCLUSIONS

The differences observed in both mobility and diet between and within populations support the notion that groups with different lifeways inhabited the Antilles in precolonial times. This diverse mosaic of cultural traits defies attempts to group them into broad categories for regional studies of biological and cultural traits.

Earliest evidence of sedentism in the Antilles: Multiple isotope data from Canímar Abajo, Cuba

The early populations that inhabited the Antilles were traditionally understood as highly mobile groups of hunters/fishers and gatherers. Although more recent data have demonstrated that some populations engaged in the production of domestic plants and cultivars, questions remain about other aspects of their lifeways, including whether the adoption of domesticates was accompanied by a decrease in residential mobility. The level of sedentism in a population is an instrumental variable to understand community social relations and complexity, adaptations, and lifeways. Here, we combined enamel strontium (87Sr/86Sr), oxygen (δ18Oen), and carbon (δ13Cen) isotopes of 44 human teeth from the site of Canímar Abajo-where the oldest human remains from the insular Caribbean have been reported-to examine the mobility patterns of early Antillean groups. In contrast with traditional narratives, the homogeneous strontium isotope values observed in most individuals from the older funerary area of the site (cal. BC 2237-790) were consistent with the pattern expected for a sedentary population subsisting primarily on local resources obtained close to the coast. The isotopic evidence reveals that between cal. AD 403-1282, the mound was reused for funerary practices by both local communities and nonlocal individuals. The evidence suggests that this period saw higher population mobility, with influxes of individuals from more distant locations and diverse dietary and burial traditions. The isotope results from Canímar Abajo provide the earliest isotopic evidence of populations with low-level residential mobility in the Antilles.

Spatial ecology of moose in Sweden: Combined Sr-O-C isotope analyses of bone and antler

The study of spatial (paleo)ecology in mammals is critical to understand how animals adapt to and exploit their environment. In this work we analysed the 87Sr/86Sr, δ18O and δ13C isotope composition of 65 moose bone and antler samples from Sweden from wild-shot individuals dated between 1800 and 1994 to study moose mobility and feeding behaviour for (paleo)ecological applications. Sr data were compared with isoscapes of the Scandinavian region, built ad-hoc during this study, to understand how moose utilise the landscape in Northern Europe. The 87Sr/86Sr isoscape was developed using a machine-learning approach with external geo-environmental predictors and literature data. Similarly, a δ18O isoscape, obtained from average annual precipitation δ18O values, was employed to highlight differences in the isotope composition of the local environment vs. bone/antler. Overall, 82% of the moose samples were compatible with the likely local isotope composition (n = 53), suggesting that they were shot not far from their year-round dwelling area. 'Local' samples were used to calibrate the two isoscapes, to improve the prediction of provenance for the presumably 'non-local' individuals. For the latter (n = 12, of which two are antlers and ten are bones), the probability of geographic origin was estimated using a Bayesian approach by combining the two isoscapes. Interestingly, two of these samples (one antler and one bone) seem to come from areas more than 250 km away from the place where the animals were hunted, indicating a possible remarkable intra-annual mobility. Finally, the δ13C data were compared with the forest cover of Sweden and ultimately used to understand the dietary preference of moose. We interpreted a difference in δ13C values of antlers (13C-enriched) and bones (13C-depleted) as a joint effect of seasonal variations in moose diet and, possibly, physiological stresses during winter-time, i.e., increased consumption of endogenous 13C-depleted lipids.

Assessment of carbon, oxygen, strontium, and lead isotopic variation in modern Colombian teeth: An application to human identification

Colombia faces the complex humanitarian challenges of locating approximately 100,000 missing persons and identifying thousands who are deceased. Identification is a difficult task in many cases, because the skeletonized bodies are deteriorated, missing person data are unavailable for comparison, and the provenance of the remains is often totally unknown. Isotopic analysis of human tissues (e.g., bone, hair, nails, and teeth) aid in the identification process of unknown individuals because they can provide valuable information on possible geographic origin. This project evaluated the isotopic variability of carbon (C), oxygen (O), strontium (Sr), and lead (Pb) in modern Colombian teeth according to city, department (a political designation similar to "state" in the US or Mexico), and one of four geographically determined regions of origin; and assessed its utility for human identification in Colombia. Isotopic data (O-C-Sr-Pb) were analyzed from modern Colombians originating from the cities of Bogotá, Cali, and Neiva (n = 95); and these data were compiled with published Colombian data of individuals mainly from the city of Medellín (n = 61). Results indicate a wide range and overlap of O-C-Sr-Pb isotopic distribution according to the defined categories. However, differences between coastal and lowland individuals are observed when using δ18 O values, and differences between mountainous regions are observed when using 87 Sr/86 Sr values. In addition, this study suggests that the usefulness of isotopic analysis for unidentified individuals in Colombia would be with assigning them geographically using the designations of North, Central Andes, Eastern Andes, or Southwest Andes versus making classifications at a city or department level.

Stable Isotope Provenance of Unidentified Deceased Migrants-A Pilot Study

In the global migration crisis, one of the challenges in the effort to identify deceased migrants is establishing their region of origin, which facilitates the search for ante mortem data to be compared with the post mortem information. This pilot study explores the potential of using stable isotope analysis to distinguish between individuals coming from West Africa and the Horn of Africa. Six individuals (four of known origin and two of unknown origin) were sampled. δ13CVPDB(keratin), δ15NVPDB(keratin) and δ18OVSMOW(keratin) of hair were analysed using Elemental Analyzers coupled with Isotope Ratio Mass Spectrometry (IRMS). δ18OVSMOW(carbonate) and δ13CVPDB(carbonate) of bone were analysed using GasBench II with IRMS, while 87Sr/86Sr composition was determined in bone and dental enamel using laser ablation multi-collector inductively coupled plasma mass spectrometry. The stable isotope compositions of the individual from the Horn of Africa differed from the other individuals. The differences found between 87Sr/86Sr of enamel and bone and between δ18O and δ13C in bone and hair reflect changes in sources of food and water in accordance with regionally typical migration journeys. The analysis of multiple stable isotopes delivered promising results, allowing us to narrow down the region of origin of deceased migrants and corroborate the information about the migration journey.

Isotopic and proteomic evidence for communal stability at Pre-Pottery Neolithic Jericho in the Southern Levant

As one of the key, long-term occupied sites in the Southern Levant, Jericho was one of the most important early Neolithic centres to witness social and economic changes associated with the domestication of plants and animals. This study applies strontium (87Sr/86Sr), oxygen (δ18O) and carbon (δ13C) isotope analyses to the enamel of 52 human teeth from Pre-Pottery Neolithic (PPN) layers of Jericho to directly study human diet and mobility and investigate the degree of consolidation and the flexibility of social organization of Jericho society in the PPN period. The results indicate only two non-local individuals out of the 44 sampled inhabitants identified by strontium isotope analysis and are consistent with the presence of a largely sedentary community at PPN Jericho with no evidence for large-scale migration. We also construct strontium spatial baselines (87Sr/86Sr map) with local 87Sr/86Sr signatures for the sites across the Southern Levant based on systematic compilation and analysis of available data. In addition, we apply proteomic analysis of sex-specific amelogenin peptides in tooth enamel for sex estimation of the sampled individuals (n = 44), the results of which showed a sex-biased ratio (more male than female detected in this sample pool) in Jericho society during the PPN period, which may be due to the limited sample size or selective ritual practices like particular burial zones used for specific groups. We also pretreated a batch of human bone samples recovered from PPNB Jericho for stable carbon and nitrogen isotope analyses for dietary investigations. However, the extracted collagen showed poor preservation and no valid δ13C or δ15N data were obtained.

Machine learning-based Sr isoscape of southern Sardinia: A tool for bio-geographic studies at the Phoenician-Punic site of Nora

Since prehistoric times, the island of Sardinia-in the western Mediterranean-has played a leading role in the dynamics of human population and mobility, in the circulation of raw materials and artefacts, idioms and customs, of technologies and ideas that have enriched the biological, linguistic and cultural heritage of local groups. For the Phoenician and Punic periods (from the 9th to the 3rd centuries BCE), the ancient site of Nora-in southern Sardinia-represents an emblematic case in the study of migratory phenomena that occurred on the Island from the Iron Age until the Roman conquest. Despite the importance of exploring (and characterising) such movements from a wider bio-cultural perspective, the application of bio-geochemical tools for geographical provenance to the ancient skeletal populations of Sardinia is yet scarce. The present work is the first step towards filling this gap with the development of the first isoscape of southern Sardinia using new bioavailable Sr isotope data and a machine-learning approach. From a geolithological point of view, Sardinia is rather heterogeneous and requires detailed studies to correctly assess the distribution of the isotopic signature of bioavailable Sr. The random forest model employed here to construct the Sr isoscape uses several external environmental and geological variables. The most important predictors are related to age and bedrock type, with additional input from local soil properties. A 10-fold cross-validation gives a mean square error of 0.0008 and an R-squared of 0.81, so the model correctly predicts the 87Sr/86Sr ratio of unknown areas. By using a Bayesian provenance assignment workflow, we tested the isoscape here produced to determine the geographic origin and the mobility of archaeological and modern fauna collected from the Phoenician-Punic site of Nora and the surrounding Pula Plain. Our results indicate that archaeological sheep and goats (87Sr/86Sr < 0.7090) are compatible with areas close to Nora and Pula Plain, in agreement with archaeological evidence of pastoralism in those areas. Modern wild and domesticated fauna (87Sr/86Sr > 0.7090) show compatibility with several natural and anthropogenic locations in southern Sardinia, as expected based on modern species distribution data. Finally, we discuss the large Sr isotopic variability of the Nora baseline, where human mobility studies of human cremated and inhumed individuals are currently underway.

Isotopic and DNA analyses reveal multiscale PPNB mobility and migration across Southeastern Anatolia and the Southern Levant

Growing reliance on animal and plant domestication in the Near East and beyond during the Pre-Pottery Neolithic B (PPNB) (the ninth to eighth millennium BC) has often been associated with a "revolutionary" social transformation from mobility toward more sedentary lifestyles. We are able to yield nuanced insights into the process of the Neolithization in the Near East based on a bioarchaeological approach integrating isotopic and archaeogenetic analyses on the bone remains recovered from Nevalı Çori, a site occupied from the early PPNB in Turkey where some of the earliest evidence of animal and plant domestication emerged, and from Ba'ja, a typical late PPNB site in Jordan. In addition, we present the archaeological sequence of Nevalı Çori together with newly generated radiocarbon dates. Our results are based on strontium (⁸⁷Sr/⁸⁶Sr), carbon, and oxygen (δ¹⁸O and δ¹³C_carb) isotopic analyses conducted on 28 human and 29 animal individuals from the site of Nevalı Çori. ⁸⁷Sr/⁸⁶Sr results indicate mobility and connection with the contemporaneous surrounding sites during the earlier PPNB prior to an apparent decline in this mobility at a time of growing reliance on domesticates. Genome-wide data from six human individuals from Nevalı Çori and Ba'ja demonstrate a diverse gene pool at Nevalı Çori that supports connectedness within the Fertile Crescent during the earlier phases of Neolithization and evidence of consanguineous union in the PPNB Ba'ja and the Iron Age Nevalı Çori.

The forest effect: Biosphere 87Sr/86Sr shifts due to changing land use and the implications for migration studies

This study documents a transect of ⁸⁷Sr/⁸⁶Sr values from a variety of plant, soil and rock samples across the ancient woodland of the Sherwood Forest National Nature Reserve (SFNNR) and into adjoining farmland in Britain. All samples were collected from the Triassic Sherwood Sandstone Group. A shift of +0.0037 in ⁸⁷Sr/⁸⁶Sr values is observed between the average plant from the biosphere of the ancient forest and that of the farmland. This shift is caused by the leaf litter accumulation in the forest, through time, leading to soil acidity that leaches out the carbonate component of the soil. This results in the forest floor soil reflecting only the silicate minerals from the original Sandstone rock formation. We have named this process "the forest effect". Rock samples from boreholes of the Sherwood Sandstone Group, as well as water samples from aquifers and mineral waters from previous studies, further indicate that the change in biosphere ⁸⁷Sr/⁸⁶Sr is a result of the wooded environment rather than the anthropological addition of lime to farmland. The extent of the forest effect will vary with differing lithologies with the most susceptible terrains being those with mixed carbonate-silicate composition, and it may be sufficient to impact the interpretation of animal and human ⁸⁷Sr/⁸⁶Sr in studies of mobility and migration. The model provides an opportunity to understand and assess food procurement strategies and animal management practices in the past, as well as the interaction of humans with their natural environment.

Male mastodon landscape use changed with maturation (late Pleistocene, North America)

Fossil remains usually reveal little about lifetime landscape use beyond place of death, but ever-growing tusks of American mastodons (Mammut americanum) record this fundamental aspect of paleobiology. Using oxygen and strontium isotopes from a serially sampled male mastodon tusk, we reconstruct changing patterns of landscape use during his life. We find clear shifts in landscape use during adolescence and following maturation to adulthood, including increased monthly movements and development of a summer-only range and mating ground. The mastodon died in his inferred summer mating ground, far from landscapes used during other seasons. Mastodons had long gestation times, and late Pleistocene populations lived in harsh, rapidly changing environments. Seasonal landscape use and migration were likely critical for maximizing mastodon reproductive success.

Under harsh Pleistocene climates, migration and other forms of seasonally patterned landscape use were likely critical for reproductive success of mastodons (Mammut americanum) and other megafauna. However, little is known about how their geographic ranges and mobility fluctuated seasonally or changed with sexual maturity. We used a spatially explicit movement model that coupled strontium and oxygen isotopes from two serially sampled intervals (5+ adolescent years and 3+ adult years) in a male mastodon tusk to test for changes in landscape use associated with maturation and reproductive phenology. The mastodon’s early adolescent home range was geographically restricted, with no evidence of seasonal preferences. Following inferred separation from the matriarchal herd (starting age 12 y), the adolescent male’s mobility increased as landscape use expanded away from his natal home range (likely central Indiana). As an adult, the mastodon’s monthly movements increased further. Landscape use also became seasonally structured, with some areas, including northeast Indiana, used only during the inferred mastodon mating season (spring/summer). The mastodon died in this area (>150 km from his core, nonsummer range) after sustaining a craniofacial injury consistent with a fatal blow from a competing male’s tusk during a battle over access to mates. Northeast Indiana was likely a preferred mating area for this individual and may have been regionally significant for late Pleistocene mastodons. Similarities between mammutids and elephantids in herd structure, tusk dimorphism, tusk function, and the geographic component of male maturation indicate that these traits were likely inherited from a common ancestor.

Assessing the preservation of biogenic strontium isotope ratios (87 Sr/86 Sr) in the pars petrosa ossis temporalis of unburnt human skeletal remains: A case study from Saba

RATIONALE

Strontium isotope (⁸⁷ Sr/⁸⁶ Sr) analysis of skeletal remains has become a powerful tool in archaeological studies of human migration and mobility. Owing to its resistance to post-mortem alteration, dental enamel is the preferred sampling material used for ⁸⁷ Sr/⁸⁶ Sr analysis in bioarchaeological provenance research, although recent studies have demonstrated that cremated bone is also generally resistant to diagenesis. This paper presents the results of a pilot study exploring the potential of unburnt petrous bone (pars petrosa) as a reservoir of biogenic (diagenetically unaltered) strontium, as the otic capsule or bony labyrinth within the petrous bone is extremely dense and is thought to be unable to remodel after early childhood, potentially providing an alternative for dental enamel.

METHODS

From an individual from a colonial-era (18th century) site on the island of Saba in the Caribbean for whom previous enamel ⁸⁷ Sr/⁸⁶ Sr results had indicated non-local origins, multiple locations (n = 4) on the petrous were sampled and measured for strontium isotope composition. Saba (13 km² ) has been extensively mapped for baseline strontium isotopes (n = 50) with ⁸⁷ Sr/⁸⁶ Sr varying from ca 0.7065 to 0.7090, whereas enamel ⁸⁷ Sr/⁸⁶ Sr (n = 3) ranged from 0.7104 to 0.7112.

RESULTS

All four petrous ⁸⁷ Sr/⁸⁶ Sr ratios (0.7111-0.7122) are consistently and considerably higher than the local bioavailable range, and very similar to the enamel ⁸⁷ Sr/⁸⁶ Sr. These results provide initial evidence that unburnt petrous bones may preserve biogenic strontium, at least in this specific burial context.

CONCLUSIONS

While more research in diverse burial conditions is needed to validate this observation, if confirmed, it would have broader implications for sample selection strategies in bioarchaeological studies using the strontium isotope method.

A bioavailable strontium (87Sr/86Sr) isoscape for Aotearoa New Zealand: Implications for food forensics and biosecurity

As people, animals and materials are transported across increasingly large distances in a globalized world, threats to our biosecurity and food security are rising. Aotearoa New Zealand is an island nation with many endemic species, a strong local agricultural industry, and a need to protect these from pest threats, as well as the economy from fraudulent commodities. Mitigation of such threats is much more effective if their origins and pathways for entry are understood. We propose that this may be addressed in Aotearoa using strontium isotope analysis of both pests and products. Bioavailable radiogenic isotopes of strontium are ubiquitous markers of provenance that are increasingly used to trace the origin of animals and plants as well as products, but currently a baseline map across Aotearoa is lacking, preventing use of this technique. Here, we have improved an existing methodology to develop a regional bioavailable strontium isoscape using the best available geospatial datasets for Aotearoa. The isoscape explains 53% of the variation (R² = 0.53 and RMSE = 0.00098) across the region, for which the primary drivers are the underlying geology, soil pH, and aerosol deposition (dust and sea salt). We tested the potential of this model to determine the origin of cow milk produced across Aotearoa. Predictions for cow milk (n = 33) highlighted all potential origin locations that share similar ⁸⁷Sr/⁸⁶Sr values, with the closest predictions averaging 7.05 km away from their true place of origin. These results demonstrate that this bioavailable strontium isoscape is effective for tracing locally produced agricultural products in Aotearoa. Accordingly, it could be used to certify the origin of Aotearoa’s products, while also helping to determine if new pest detections were of locally breeding populations or not, or to raise awareness of imported illegal agricultural products.

Neodymium isotopes in modern human dental enamel: An exploratory dataset for human provenancing

This collection presents data on neodymium isotopes from modern dental elements (third molars) of 47 individuals born and raised in the Netherlands, Grenada, Curaçao, Bonaire, Columbia and Iceland. Neodymium isotope composition was successfully analyzed for 40 individuals (ranging between 0.511820 and 0.512773 143Nd/144Nd and -16.0 to 2.6 εNd), with neodymium concentration data available for 23 individuals (ranging between 0.1 and 21.0 ppb). For 37 individuals the dental elements have also been analyzed for strontium isotopes. All analyses were performed on a Thermo Scientific Triton Plus TIMS. Neodymium analyses were performed using 1013 Ω resistors, with samples reanalyzed using 1011 Ω resistors if enough sample was available. Strontium analyses were performed using 1011Ω resistors. A discussion about the applicability of the analysis technique and the results can be found in the article "Evaluation of neodymium isotope analysis of human dental enamel as a provenance indicator using 1013 Ω amplifiers (TIMS)". This dataset is available for verification of the provenance capability of neodymium isotope analysis in archaeological and forensic mobility studies. To ensure the interoperability and reusability of the data, the data is available on the IsoArcH (https://isoarch.eu/) data repository.

Assessing the predictability of existing water-to-enamel geolocation models against known human teeth

Stable isotope analysis of human tissues has become a valuable tool for mapping human geolocation. This study adds to the existing knowledge of the relationship between oxygen stable isotopes in human enamel and drinking water by presenting enamel oxygen values in clinic-extracted human dental enamel with known provenance. The results from this study indicate that the theoretical isotopic relationship between enamel and drinking water oxygen is weak at the city and country-level. Differences of up to 15‰ were observed between predicted drinking water oxygen values using existing models and observed values, highlighting the complexity of using water/enamel conversion equations. The lower isotopic boundary of enamel oxygen values is now understood for Metro Vancouver at δ18Oc(VPDB) = - 11.0‰ and presents the possibility of using stable isotope analysis as an exclusionary tool where individuals falling below threshold value can be identified as non-local. Overall, this study's results support the development of geographical reference maps for human enamel oxygen.

Identification of a female murder victim found in Burgenland, Austria in 1993

In 1993, the skeletal remains of a female corpse were found in Burgenland, Austria. Initial identification of the approximately 25–35-year-old female appeared impossible, but the case was reopened 23 years later. By applying biogeochemical isotope methods to her body tissues, the geographical origin of the unknown corpse could be predicted. The results of the C, N, S, H, Sr, and Pb isotope analyses suggested that the female did not originate from Europe and most likely spent her youth in the northern Caribbean. Using these findings, the police were able to identify the woman within 2 weeks. The female came from the Dominican Republic and resided in Austria for only a short period before she was murdered. This case shows that isotope biogeochemistry investigations can provide the police with crucial information that enables unknown persons to be identified.

Keypoints

C-N-S-H and Sr-Pb isotope analyses were applied to human remains associated with a cold case.

It was possible to determine the region of origin of the unknown deceased individual as the northern Caribbean.

After 23 years, the murder victim was successfully identified.

The last battle of Anne of Brittany: Solving mass grave through an interdisciplinary approach (paleopathology, biological anthropology, history, multiple isotopes and radiocarbon dating)

Mass graves are usually key historical markers with strong incentive for archeological investigations. The identification of individuals buried in mass graves has long benefitted from traditional historical, archaeological, anthropological and paleopathological techniques. The addition of novel methods including genetic, genomic and isotopic geochemistry have renewed interest in solving unidentified mass graves. In this study, we demonstrate that the combined use of these techniques allows the identification of the individuals found in two Breton historical mass graves, where one method alone would not have revealed the importance of this discovery. The skeletons likely belong to soldiers from the two enemy armies who fought during a major event of Breton history: the siege of Rennes in 1491, which ended by the wedding of the Duchess of Brittany with the King of France and signaled the end of the independence of the region. Our study highlights the value of interdisciplinary approaches with a particular emphasis on increasingly accurate isotopic markers. The development of the sulfur isoscape and testing of the triple isotope geographic assignment are detailed in a companion paper [13].

Triple sulfur-oxygen-strontium isotopes probabilistic geographic assignment of archaeological remains using a novel sulfur isoscape of western Europe

Sulfur isotope composition of organic tissues is a commonly used tool for gathering information about provenance and diet in archaeology and paleoecology. However, the lack of maps predicting sulfur isotope variations on the landscape limits the possibility to use this isotopic system in quantitative geographic assignments. We compiled a database of 2,680 sulfur isotope analyses in the collagen of archaeological human and animal teeth from 221 individual locations across Western Europe. We used this isotopic compilation and remote sensing data to apply a multivariate machine-learning regression, and to predict sulfur isotope variations across Western Europe. The resulting model shows that sulfur isotope patterns are highly predictable, with 65% of sulfur isotope variations explained using only 4 variables representing marine sulfate deposition and local geological conditions. We used this novel sulfur isoscape and existing strontium and oxygen isoscapes of Western Europe to apply triple isotopes continuous-surface probabilistic geographic assignments to assess the origin of a series of teeth from local animals and humans from Brittany. We accurately and precisely constrained the origin of these individuals to limited regions of Brittany. This approach is broadly transferable to studies in archaeology and paleoecology as illustrated in a companion paper (Colleter et al. 2021).

A strontium isoscape for the Conchucos region of highland Peru and its application to Andean archaeology

Strontium isotope (⁸⁷Sr/⁸⁶Sr) analysis of human skeletal remains is an important method in archaeology to examine past human mobility and landscape use. ⁸⁷Sr/⁸⁶Sr signatures of a given location are largely determined by the underlying bedrock, and these geology specific isotope signatures are incorporated into skeletal tissue through food and water, often permitting the differentiation of local and non-local individuals in past human populations. This study presents the results of a systematic survey of modern flora and fauna (n = 100) from 14 locations to map the bioavailable ⁸⁷Sr/⁸⁶Sr signatures of the Conchucos region, an area where the extent of geologic variability was previously unknown. We illustrate the necessity to examine the variation in ⁸⁷Sr/⁸⁶Sr values of the different geological formations available to human land use to document the range of possible local ⁸⁷Sr/⁸⁶Sr values. Within the Conchucos region we found significant variation in environmental ⁸⁷Sr/⁸⁶Sr values (0.7078–0.7214). The resulting isoscape represents the largest regionally specific bioavailable ⁸⁷Sr/⁸⁶Sr map (3,840 km²) to date for the Andes, and will serve as a baseline for future archaeological studies of human mobility in this part of the Peruvian highlands.

Bioavailable Strontium, Human Paleogeography, and Migrations in the Southern Andes: A Machine Learning and GIS Approach

The Andes are a unique geological and biogeographic feature of South America. From the perspective of human geography, this mountain range provides ready access to highly diverse altitudinally arranged ecosystems. The combination of a geologically and ecologically diverse landscape provides an exceptional context to explore the potential of strontium isotopes to track the movements of people and the conveyance of material culture. Here we develop an isotopic landscape of bioavailable strontium (87Sr/86Sr) that is applied to reconstruct human paleogeography across time in the southern Andes of Argentina and Chile (31°–34°S). These results come from a macro-regional sampling of rodents (N = 65) and plants (N = 26) from modern and archeological contexts. This “Southern Andean Strontium Transect” extends over 350 km across the Andes, encompassing the main geological provinces between the Pacific coast (Chile) and the eastern lowlands (Argentina). We follow a recently developed approach to isoscape construction based on Random Forest regression and GIS analysis. Our results suggest that bioavailable strontium is tightly linked with bedrock geology and offers a highly resolved proxy to track human paleogeography involving the levels of territories or daily mobility and anomalous events that disrupt home ranges, such as migration. The southern Andes provide an ideal geological setting to develop this approach, since the geological variation in rock age and composition produces distinctive isotopic signatures for each main biogeographical region. Finally, we apply this framework to a set of results from human remains from the Uspallata Valley in Mendoza (Argentina), to assess the incidence of migration in the key period of the consolidation of agropastoral economies between AD 800 and 1400. The application of the isoscape to the values from human remains confirms the persistence of human groups with relatively restricted territories encompassing Uspallata and the adjacent Precordillera between AD 800 and 1500. We also identify a pulse of human migration between AD 1280 and 1420, shortly preceding the Inka conquest. Looking forward, we expect to converge with ongoing efforts in South America to build a continental research framework to track the movement of people, animals, and artifacts across space and time.

Exploring mobility in Italian Neolithic and Copper Age communities

As a means for investigating human mobility during late the Neolithic to the Copper Age in central and southern Italy, this study presents a novel dataset of enamel oxygen and carbon isotope values (δ¹⁸Oca and δ¹³Cca) from the carbonate fraction of biogenic apatite for one hundred and twenty-six individual teeth coming from two Neolithic and eight Copper Age communities. The measured δ¹⁸Oca values suggest a significant role of local sources in the water inputs to the body water, whereas δ¹³Cca values indicate food resources, principally based on C₃ plants. Both δ¹³Cca and δ¹⁸Oca ranges vary substantially when samples are broken down into local populations. Statistically defined thresholds, accounting for intra-site variability, allow the identification of only a few outliers in the eight Copper Age communities, suggesting that sedentary lifestyle rather than extensive mobility characterized the investigated populations. This seems to be also typical of the two studied Neolithic communities. Overall, this research shows that the investigated periods in peninsular Italy differed in mobility pattern from the following Bronze Age communities from more northern areas.

Comparison of strontium isotope ratios in Mexican human hair and tap water as provenance indicators

Deceased undocumented border crossers are some of the most difficult individuals to identify due to the inability to narrow down the region of origin and therefore to obtain family reference samples for DNA comparison. The isotopic compositions of various body tissues have been demonstrated to be useful biomarkers for tracking locations and movements to aid in the identification of human remains. This study closes the large spatial gap of available ⁸⁷Sr/⁸⁶Sr ratios from North America in tap water and presents the first ⁸⁷Sr/⁸⁶Sr human tissue-based ratios from Mexico. The 101 hair samples from 32 locations in Mexico range in ⁸⁷Sr/⁸⁶Sr ratios from 0.70424 to 0.71613 (ΔSr_max-min=0.01189). Furthermore, 151 tap water samples from 51 locations range between 0.70404 to 0.71385 (ΔSr_max-min=0.00981). Overall, small variations in the hair and tap water samples collected from individual locations were recorded (ΔSr_max-min=0.00041 and 0.00034 respectively). Despite the fact that Mexico is one of the largest bottled water consumers in the world, the ⁸⁷Sr/⁸⁶Sr ratios of human hair and tap water correlated strongly (R²=0.87 for location averages and R²=0.80 when using individual data points). These data represent a valuable resource for identifying the provenance of human remains.

Strontium, oxygen, and carbon isotope variation in modern human dental enamel

OBJECTIVES

Isotopic analyses using human dental enamel provide information on the mobility and diet of individuals in forensic and archeological studies. Thus far, no study has systematically examined intraindividual coupled strontium (Sr), oxygen (O), and carbon (C) isotope variation in human enamel or the effect that caries have on the isotopic integrity of the enamel. The inadequate quantification of isotopic variation affects interpretations and may constrain sample selection of elements affected by caries. This study aims to quantify the intraindividual isotopic variation and provides recommendations for enamel sampling methods.

MATERIAL AND METHODS

This study presents the first systematic results on intraindividual variation in Sr-O-C isotope composition and Sr concentration in modern human dental enamel of third molars (affected and unaffected by caries). A multiloci sampling approach (n = 6-20) was used to analyze surface and inner enamel, employing thermal ionization mass spectrometry (TIMS) and isotope ratio mass spectrometry (IRMS). Third molars were analyzed from 47 individuals from the Netherlands, Iceland, the United States, the Caribbean, Colombia, Somalia, and South Africa.

RESULTS

Intradental isotopic variation in modern Dutch dental elements was recorded for Sr, O, and C and exceeded the variation introduced by the analytical error. Single loci and bulk sampling approaches of third molars established that a single analysis is only representative of the bulk Sr isotope composition in 60% of the elements analyzed. Dental elements affected by caries showed twice the variation seen in unaffected dental elements. Caries did not consistently incorporate the isotopic composition of the geographical environment in which they developed.

DISCUSSION

The isotopic variability recorded in unaffected inner enamel indicates that variations greater than 0.000200 for ⁸⁷ Sr/⁸⁶ Sr and larger than 2‰ for δ¹⁸ O and δ¹³ C are required to demonstrate changes in modern Dutch human diet or geographic location.

Isotopic evidence for anthropogenic lead exposure on a 17th/18th century Barbadian plantation

OBJECTIVES

To identify and characterize anthropogenic lead sources on a 17th/18th century Barbadian plantation and to test if lead isotope analyses can be used to identify the geographic origins of first-generation African captives.

MATERIALS AND METHODS

We carried out lead (Pb) isotope analyses on dental enamel samples from 24 individuals from the Newton Plantation Cemetery in Barbados, which had previously been analyzed for strontium (Sr) and oxygen (O) isotope composition (Schroeder et al., American Journal of Physical Anthropology, 2009, 139:547-557) and Pb concentrations (Schroeder et al., American Journal of Physical Anthropology, 2013, 150:203-209.

RESULTS

We are able to identify British Pb sources, and more specifically Bristol/Mendips Pb, as the most likely source of anthropogenic Pb on the plantation, highlighting the impact of the British Atlantic economy on the lives of enslaved peoples in Barbados during the period of plantation slavery. Furthermore, we find that there is only one clear outlier among seven individuals who had previously been identified as African-born based on their enamel Sr isotope composition (Schroeder et al., American Journal of Physical Anthropology, 2009, 139:547-557). All other individuals present a very homogenous Pb isotope composition, which overlaps with that of British Pb sources.

CONCLUSION

Our results indicate that while Pb isotope analyses can help identify and further characterize the sources of anthropogenic Pb in plantation settings, they might not be suited for identifying the origins of African-born individuals in diasporic contexts.

A Framework for Reconstructing Archaeological Networks Using Exponential Random Graph Models

Reconstructing ties between archaeological contexts may contribute to explain and describe a variety of past social phenomena. Several models have been formulated to infer the structure of such archaeological networks. The applicability of these models in diverse archaeological contexts is limited by the restricted set of assumptions that fully determine the mathematical formulation of the models and are often articulated on a dyadic basis. Here, we present a general framework in which we combine exponential random graph models with archaeological substantiations of mechanisms that may be responsible for network formation. This framework may be applied to infer the structure of ancient networks in a large variety of archaeological settings. We use data collected over a set of sites in the Caribbean during the period AD 100-400 to illustrate the steps to obtain a network reconstruction.

Bioavailable 87Sr/86Sr in European soils: A baseline for provenancing studies

We present ⁸⁷Sr/⁸⁶Sr isotope ratios for ~1200 selected soil samples, collected by the GEMAS consortium from grazing (Gr) and agricultural (Ap) soils in Europe with the aim to better understand the strontium isotope distribution in the bioavailable fraction of the top-soil and its potential for provenancing applications. Spatial analysis shows that there is a clear distinction between coastal (<100 km) and non-coastal (>100 km) samples in their variance and that this variance is mirrored in the sodium concentration, suggesting an important but highly variable contribution from seaspray. We present two ⁸⁷Sr/⁸⁶Sr maps at 25 km × 25 km scale: one based solely on the measured data using a classical kriging approach and one based on a Random Forest model using complementary GEMAS data to predict the strontium isotope composition at the remaining 3000+ GEMAS sampling locations, including appropriate uncertainty assessment. Using a forensic Bayesian likelihood ratio approach, a tool was developed in R to create provenancing likelihood ratio maps. The maps delineate areas of high and low likelihood and allow investigators to direct their resources to areas of interest. For actual forensic case work either the measured or the modelled data can be used as reference data for the overall distribution of ⁸⁷Sr/⁸⁶Sr values in Europe.

Evaluation of neodymium isotope analysis of human dental enamel as a provenance indicator using 1013 Ω amplifiers (TIMS)

Human provenance studies employing isotopic analysis have become an essential tool in forensic and archaeological sciences, with multi-isotope approaches providing more specific location estimates compared to single isotope studies. This study reports on the human provenancing capability of neodymium isotopes (¹⁴³Nd/¹⁴⁴Nd), a relatively conservative tracer in the environment. Neodymium isotope ratios have only recently been determined on human remains due to low concentrations in human dental enamel (ppb range), requiring thermal ionisation mass spectrometry (TIMS) using 10¹³ Ω resistors. Dental elements (third molars) from 20 individuals born and raised in the Netherlands were analysed for Nd concentration (n = 12) and Nd isotope ratios (n = 15). The geological control on Nd isotope composition was examined using coupled Nd-Sr isotope analysis of the same third molar. Teeth from different geological environments were also analysed (Caribbean, Columbian, and Icelandic, n = 5). Neodymium elemental concentrations in dental elements ranged between 0.1 and 7.9 ppb (median 0.5 ppb). The Dutch ¹⁴³Nd/¹⁴⁴Nd ratios of the provinces of Limburg and Friesland were between 0.5118 and 0.5121, with Dutch ⁸⁷Sr/⁸⁶Sr ratios in agreement with the previously established local range (0.708–0.710). The current findings were compared to previously published results on Nd concentration and composition from Dutch individuals. The concentration of Nd and ¹⁴³Nd/¹⁴⁴Nd ratios were weakly correlated (R² = 0.47, n = 17) in Dutch human dental enamel. The majority (n = 25, 83.3%) of individuals had Nd and Sr isotope values isotopically indistinguishable from the geological environment in which their third molars formed and mineralised. However, the Nd isotope ratios of the Icelandic individual and several Dutch individuals (n = 4) suggested that Nd in enamel is not solely influenced by geological environment. In order for neodymium isotopes to be quantitatively applied in forensic and archaeological settings further analyses of individuals from various geographical regions with well-defined dietary Nd isotope data are required.

•

First evaluation of the potential of neodymium isotopes for human provenancing

•

Provides insight in Nd concentration and isotope ratios in human dental enamel

•

First study presenting Nd isotope ratios from multiple geological settings

•

First study combining ¹⁴³Nd/¹⁴⁴Nd and ⁸⁷Sr/⁸⁶Sr ratios of the same dental element

•

The use of 10¹³ Ω resistors allows for greater precision analysis of small samples

Flows of people in villages and large centres in Bronze Age Italy through strontium and oxygen isotopes

This study investigates to what extent Bronze Age societies in Northern Italy were permeable accepting and integrating non-local individuals, as well as importing a wide range of raw materials, commodities, and ideas from networks spanning continental Europe and the Mediterranean. During the second millennium BC, the communities of Northern Italy engaged in a progressive stabilization of settlements, culminating in the large polities of the end of the Middle/beginning of the Late Bronze Age pivoted around large defended centres (the Terramare). Although a wide range of exotic archaeological materials indicates that the inhabitants of the Po plain increasingly took part in the networks of Continental European and the Eastern Mediterranean, we should not overlook the fact that the dynamics of interaction were also extremely active on local and regional levels. Mobility patterns have been explored for three key-sites, spanning the Early to Late Bronze Age (1900-1100 BC), namely Sant'Eurosia, Casinalbo and Fondo Paviani, through strontium and oxygen isotope analysis on a large sample size (more than 100 individuals). The results, integrated with osteological and archaeological data, document for the first time in this area that movements of people occurred mostly within a territorial radius of 50 km, but also that larger nodes in the settlement system (such as Fondo Paviani) included individuals from more distant areas. This suggests that, from a demographic perspective, the process towards a more complex socio-political system in Bronze Age Northern Italy was triggered by a largely, but not completely, internal process, stemming from the dynamics of intra-polity networks and local/regional power relationships.

Strontium isotope ratios (87 Sr/86 Sr) of human fingernail clippings reveal multiple location signals

RATIONALE

Strontium isotope ratios (⁸⁷ Sr/⁸⁶ Sr) in human fingernail keratin tissues have been underexplored for region of origin and travel history reconstruction studies. Here we investigated ⁸⁷ Sr/⁸⁶ Sr ratios in fingernail keratin to establish baseline measurements in a resident group and to examine how ⁸⁷ Sr/⁸⁶ Sr ratios changed with relocation.

METHODS

Fingernail clippings were collected from resident (n = 10) and non-resident/traveler groups (n = 4 and n = 4) that were part of a larger study in Salt Lake City (UT, USA) from 2015 to 2016. Strontium abundance and ⁸⁷ Sr/⁸⁶ Sr ratios were determined via multicollector inductively coupled plasma mass spectrometry (MC-ICP-MS). ⁸⁷ Sr/⁸⁶ Sr and oxygen (δ¹⁸ O) isotope ratios from the traveler participants were compared to examine temporal patterns.

RESULTS

Strontium abundance and ⁸⁷ Sr/⁸⁶ Sr ratios in fingernails from the resident group established a baseline against which we could evaluate potential differences in non-resident/traveler groups. Resident ⁸⁷ Sr/⁸⁶ Sr ratios remained constant over the study period and were consistent with previously measured tap waters for the area. ⁸⁷ Sr/⁸⁶ Sr ratio changes in non-resident/traveler groups were rapid and reflected the current location of the individual within 4-5 weeks of arrival. Lastly, δ¹⁸ O and ⁸⁷ Sr/⁸⁶ Sr ratios of the same fingernail clippings did not exhibit similar temporal patterns, since fingernail δ¹⁸ O ratios required more time to attain values characteristic of the new environment.

CONCLUSIONS

Our findings suggest that strontium is incorporated into fingernail tissues differently from hair and this could be advantageous to forensic investigations. We found that ⁸⁷ Sr/⁸⁶ Sr and δ¹⁸ O ratios of the same fingernail clippings revealed two different time points reflecting an individual's residence over short- (4-5 weeks, ⁸⁷ Sr/⁸⁶ Sr ratios) and long-term (3-5 months, δ¹⁸ O values) time scales. It is likely that the ⁸⁷ Sr/⁸⁶ Sr ratios of fingernail clippings reflect exogenous signals that are incorporated through bathing waters and that these signals change rapidly with movement to a new location. Our results may aid future forensic studies in the determination of region of origin in unidentified remains.

A bioavailable strontium isoscape for Western Europe: A machine learning approach

Strontium isotope ratios (⁸⁷Sr/⁸⁶Sr) are gaining considerable interest as a geolocation tool and are now widely applied in archaeology, ecology, and forensic research. However, their application for provenance requires the development of baseline models predicting surficial ⁸⁷Sr/⁸⁶Sr variations (“isoscapes”). A variety of empirically-based and process-based models have been proposed to build terrestrial ⁸⁷Sr/⁸⁶Sr isoscapes but, in their current forms, those models are not mature enough to be integrated with continuous-probability surface models used in geographic assignment. In this study, we aim to overcome those limitations and to predict ⁸⁷Sr/⁸⁶Sr variations across Western Europe by combining process-based models and a series of remote-sensing geospatial products into a regression framework. We find that random forest regression significantly outperforms other commonly used regression and interpolation methods, and efficiently predicts the multi-scale patterning of ⁸⁷Sr/⁸⁶Sr variations by accounting for geological, geomorphological and atmospheric controls. Random forest regression also provides an easily interpretable and flexible framework to integrate different types of environmental auxiliary variables required to model the multi-scale patterning of ⁸⁷Sr/⁸⁶Sr variability. The method is transferable to different scales and resolutions and can be applied to the large collection of geospatial data available at local and global levels. The isoscape generated in this study provides the most accurate ⁸⁷Sr/⁸⁶Sr predictions in bioavailable strontium for Western Europe (R² = 0.58 and RMSE = 0.0023) to date, as well as a conservative estimate of spatial uncertainty by applying quantile regression forest. We anticipate that the method presented in this study combined with the growing numbers of bioavailable ⁸⁷Sr/⁸⁶Sr data and satellite geospatial products will extend the applicability of the ⁸⁷Sr/⁸⁶Sr geo-profiling tool in provenance applications.

Strontium isotope ratios of human hair record intra-city variations in tap water source

The oxygen (¹⁸O/¹⁶O) isotope analysis of hair is commonly applied to reconstruct an individual’s residence history. However, region-of-origin as determined from oxygen isotope values (δ¹⁸O) alone is often spatially indistinct. Adding additional geochemical recorders can refine region-of-origin estimates. In this capacity, strontium (⁸⁷Sr/⁸⁶Sr) isotope analysis has attracted increased interest. While ⁸⁷Sr/⁸⁶Sr reflects the influences of local geology, ⁸⁷Sr/⁸⁶Sr of hair includes both external environmental signals as well as the internal dietary indicators. To better understand the impact of these contributions to the spatial signal encoded within ⁸⁷Sr/⁸⁶Sr of hair, human hair was collected from three locations within Salt Lake City, Utah along with the donor’s sex. The ⁸⁷Sr/⁸⁶Sr and δ¹⁸O of hair and local tap water were measured. There were no significant relationships between sex and either δ¹⁸O or ⁸⁷Sr/⁸⁶Sr of hair, nor between collection location and the δ¹⁸O of hair. However, we found significant associations between collection location and ⁸⁷Sr/⁸⁶Sr of hair. These findings suggest that interactions with local water may be an important source of Sr to human hair and that the ⁸⁷Sr/⁸⁶Sr of hair may have the capacity to record differences in ⁸⁷Sr/⁸⁶Sr of tap waters on small spatial scales.