Enamel δ18O Values Research Articles

Past rainfall patterns in Southeast Asia revealed by microanalysis of δ18O values in human teeth

Variations in human subsistence and settlement patterns have been documented at Holocene archaeological sites across Island and Mainland Southeast Asia. Although climate is frequently invoked as a causal mechanism underlying this variation, direct evidence of ancient rainfall variability on the scale of human lifetimes has thus far been elusive. Here we use a novel time-resolute method for in situ measurement of human tooth enamel δ18O values (n = 2629 near-weekly measurements sampling 51 years) to assess past rainfall seasonality patterns in Southeast Asia. Seasonal fluctuations in enamel δ18O values of ancient humans from several different periods are compared to modern rainfall recorded in Vietnam, Philippines, and Indonesia by the Global Network in Isotopes in Precipitation (GNIP). The likelihood that the ancient humans reflect local precipitation patterns is established through measurement of bulk enamel 87Sr/86Sr ratios. Comparison of the archaeological individuals and the modern rainfall datasets shows that the seasonal variabilities in ancient δ18Oenamel are consistent with seasonal variabilities in modern δ18Oprecip across the study locations (highest in Vietnam, lowest in Indonesia, intermediate in the Philippines). Strong seasonal δ18Oenamel trends in four of five hunter-gatherers from Con Co Ngua, Vietnam, facilitate the inference of birth approximately six months prior to the onset of monsoons, consistent with tropical subsistence societies where food availability correlates with rainfall. High-resolution analysis of human tooth enamel represents a powerful new tool for seasonality reconstructions across different regional and climatic settings.

The Impact of Contact: Isotope Geochemistry Sheds Light on the Lives of Indigenous Australians Living on the Colonial Frontier in Late 19th Century Queensland

Here, we report the first attempt to use isotope geochemistry to improve understanding of the experiences of Indigenous Australians living on the colonial frontier in late 19th century CE Australia. In the study, we analysed strontium (87Sr/86Sr), carbon (δ13C), and oxygen (δ18O) isotope ratios from the tooth enamel and dentine of six individuals who died in Normanton, Queensland, in the 1890s. The study was a collaboration between scientists and the local Traditional Owners, the Gkuthaarn and Kukatj people, and was carried out to promote truth and reconciliation. The enamel 87Sr/86Sr results suggest that the individuals moved to Normanton from three geologically distinct regions during the period of European expansion into the Gulf of Carpentaria, Cape York. This is consistent with the oral histories and historical documents, which suggest that many Indigenous people in the Gulf Country were displaced to camps on the outskirts of towns like Normanton because of European settlement. The δ13C values we obtained indicate that the individuals mostly ate C4 plants and/or C4-plant-consuming herbivores. When combined with the fact that some of the individuals’ teeth had dental caries, this suggests that the individuals may have had regular access to introduced foods. The enamel δ18O values are high compared to an international comparative sample, at 0.72–4.69‰ VPDB. We suspect the elevated values are due to a combination of a high degree of preferential loss of 16O through evaporation of surface water, the amount effect associated with the Australian monsoon, and high prevalence of introduced infectious diseases. Together, the results of our study demonstrate that isotopic analysis of human remains has the potential to further illuminate the effects of European colonisation on Indigenous people in Australia. Perhaps most importantly in connection with this, our study’s results show that isotopic analyses of human remains can provide surprisingly detailed information about the lives of a category of Indigenous Australians who rarely appear in the documents written by early ethnographers and colonial officials—subadults. That the analysis of the skeletal remains of Indigenous Australians can now contribute to the truth and reconciliation process is an unexpected, interesting, and welcome development in the story of bioarchaeology in Australia.

Seasonality of precipitation in the southwestern United States during the late Pleistocene inferred from stable isotopes in herbivore tooth enamel

The late Pleistocene was a climatically dynamic period, with abrupt shifts between cool-wet and warm-dry conditions. Increased effective precipitation supported large pluvial lakes and long-lived spring ecosystems in valleys and basins throughout the western and southwestern U.S., but the source and seasonality of the increased precipitation are debated. Increases in the proportions of C4/(C4+ C3) grasses in the diets of large grazers have been ascribed both to increases in summer precipitation and lower atmospheric CO2 levels. Here we present stable carbon and oxygen isotope data from tooth enamel of late Pleistocene herbivores recovered from paleowetland deposits at Tule Spring Fossil Beds National Monument in the Las Vegas Valley of southern Nevada, as well as modern herbivores from the surrounding area. We use these data to investigate whether winter or summer precipitation was responsible for driving the relatively wet hydroclimate conditions that prevailed in the region during the late Pleistocene. We also evaluate whether late Pleistocene grass C4/(C4+ C3) was higher than today, and potential drivers of any changes.Tooth enamel δ18O values for Pleistocene Equus, Bison, and Mammuthus are generally low (average 22.0 ± 0.7‰, 2 s.e., VSMOW) compared to modern equids (27.8 ± 1.5‰), and imply lower water δ18O values (−16.1 ± 0.8‰) than modern precipitation (−10.5‰) or in waters present in active springs and wells in the Las Vegas Valley (−12.9‰), an area dominated by winter precipitation. In contrast, tooth enamel of Camelops (a browser) generally yielded higher δ18O values (23.9 ± 1.1‰), possibly suggesting drought tolerance. Mean δ13C values for the Pleistocene grazers (−6.6 ± 0.7‰, 2 s.e., VPDB) are considerably higher than for modern equids (−9.6 ± 0.4‰) and indicate more consumption of C4 grass (17 ± 5%) than today (4 ± 4%). However, calculated C4 grass consumption in the late Pleistocene is strikingly lower than the proportion of C4 grass taxa currently present in the valley (55–60%). δ13C values in Camelops tooth enamel (−7.7 ± 1.0‰) are interpreted as reflecting moderate consumption (14 ± 8%) of Atriplex (saltbush), a C4 shrub that flourishes in regions with hot, dry summers.Lower water δ18O values, lower abundance of C4 grasses, and the inferred presence of Atriplex are all consistent with general circulation models for the late Pleistocene that show enhanced delivery of winter precipitation, sourced from the north Pacific, into the interior western U.S. but do not support alternative models that infer enhanced delivery of summer precipitation, sourced from the tropics. In addition, we hypothesize that dietary competition among the diverse and abundant Pleistocene fauna may have driven the grazers analyzed here to feed preferentially on C4 grasses. Dietary partitioning, especially when combined with decreased pCO2 levels during the late Pleistocene, can explain the relatively high δ13C values observed in late Pleistocene grazers in the Las Vegas Valley and elsewhere in the southwestern U.S. without requiring additional summer precipitation. Pleistocene hydroclimate parameters derived from dietary and floral records may need to be reevaluated in the context of the potential effects of dietary preferences and lower pCO2 levels on the stability of C3 vs. C4 plants.

Palaeoecological and palaeoenviromental reconstruction of the upper Miocene vertebrate karstic site of Corral de Lobato, central-eastern Spain

We report stable isotopic analyses for dental enamel of fossil mammals from the Miocene (~7.1 Ma, MN13, middle Turolian) Corral de Lobato locality, Guadalajara, Spain, and compare it with adjacent localities of the Iberian Range. This multidisciplinary research allows the assessment of the palaeoenvironmental, palaeoecological and palaeoclimatic conditions that were in place in the central-eastern area of the Iberian Peninsula at this time. Herbivore tooth enamel δ13C values point to the presence of two environments: open woodland/arid C3 grassland and woodland/mesic C3 grassland. We infer the most probable diets of the two carnivores analysed, indicating a partition of resources and habitats. Tooth enamel δ18O values from the obligate drinkers indicate that all of them would have drunk water with similar evaporation rates except for the suid Hippopotamodon major, although its distinct δ18O values may be influenced by its omnivorous diet. Comparing Corral de Lobato taxa with those from other semi-contemporaneous (MN12–MN13) localities of the nearby Teruel Basin, δ13O values point to more arid conditions in Corral de Lobato while lower values of δ18O are most likely related to the karst origin of water bodies. Possibly, the difference between the isotopic compositions of Corral de Lobato and adjacent localities results from the combined effect of palaeotopography and a global climate pulse about 7 Ma.

OXYGEN ISOTOPE PROFILES OF UPPERMOST JURASSIC VERTEBRATE TEETH AND OYSTER SHELLS: A RECORD OF PALEOENVIRONMENTAL CHANGES AND ANIMAL HABITATS

ABSTRACTHigh resolution oxygen isotopes profiles of well-preserved uppermost Jurassic oyster shells and vertebrate (ichthyosaur and fish) teeth from Central Poland were obtained using a microdrill and an ion microprobe (SHRIMP IIe/MC). Internal variability of δ18O values of oyster shells (-1.7 to 1.3‰ VPDB) collected from the offshore interval of the studied section is greater than that determined previously from bulk oysters. Relatively high δ18O values of the studied oysters may be linked to a slight increase in the salinity of the mid-Polish basin. Low δ18O values of co-occurring ichthyosaur tooth enamel substantiate endothermy of these reptiles. An observed ontogenetic increase in the ichthyosaur enamel δ18O values (from ∼ 19.4 to ∼ 21.6‰ VSMOW) may be a result of long distance migrations although the effect of metabolic factors at rising body mass cannot be completely excluded. It is postulated that δ18O values of the latest portion of the ichthyosaur tooth enamel can be used for the calculation of ancient water oxygen isotope composition and verification of oxygen isotope temperatures. High δ18O values of the enameloid of Caturus lungfishes (23.6 to 26.5‰ VSMOW) collected from an upper part of the studied section, which was deposited in a restricted lagoonal environment after a marine regression, are probably a result of a high evaporation rate. The fishes could have breathed atmospheric air and withstood episodes of water hypoxia. Internal oxygen isotope records of the shells and teeth are promising proxies for studies of the paleoenvironment and activity of animals.

Paleoecology of Aphelops and Teleoceras (Rhinocerotidae) through an interval of changing climate and vegetation in the Neogene of the Great Plains, central United States

The Rhinocerotidae was one of most widespread and abundant mammalian groups in North America during the Oligocene and Miocene but were extinct by the early Pliocene. Potential drivers of extinction include the expansion of C4 grasslands, cooling climate, and increased seasonality. Here we examine potential changes in the relative abundance of two common genera, Aphelops and Teleoceras, from the middle Miocene to the Pliocene of the Great Plains. We also use stable isotopes in tooth enamel to test whether Great Plains rhinoceroses were able to incorporate C4 vegetation into their diet after the expansion of C4 grasslands. Relative abundance of rhinoceroses fluctuates during the middle to late Miocene but then rapidly declines at the end of the Miocene around 6.5 Ma, coinciding with the expansion of C4 grasslands on the Great Plains. Stable carbon isotopes indicate that both Aphelops and Teleoceras were predominantly C3 feeders for most of their history. During C4 expansion some individuals were able to adapt to modest C4 consumption but were not as successful as contemporaneous horses. Our results suggest that the extinction of rhinoceroses was associated with environmental stress related to diminishing food resources following the expansion of C4 vegetation, possibly coupled with a shorter growing season as climate cooled. In addition, tooth enamel δ18O values in rhinoceroses do not support the interpretation that Teleoceras, a “hippo-ecomorph”, had a semi-aquatic lifestyle. Tooth enamel δ18O values reflect a strong latitudinal temperature gradient, suggesting that rhinoceroses effectively track δ18O values in surface waters and are potentially useful for paleoclimatic reconstructions.

Oxygen isotope analyses of ungulate tooth enamel confirm low seasonality of rainfall contributed to the African Humid Period in Somalia

During the African Humid Period (AHP), between ~14 and 5 ka, north and eastern Africa were much wetter and greener than they are today. Although the AHP has long been attributed to an increase in rainfall driven by orbital forcing, many details regarding the timing, pacing, and contributing moisture sources remain to be determined, especially for eastern Africa. Recent research suggests that both Atlantic and Indian Ocean moisture contributed to the AHP in eastern Africa. Large mammalian faunas from two Late Pleistocene/Holocene rockshelter sites in southern Somalia, Gogoshiis Qabe and Guli Waabayo, provide an unusual opportunity to investigate the AHP in an area of eastern Africa that is orographically isolated from Atlantic Ocean moisture. To track changes in aridity at these sites, we used the oxygen isotope aridity index, which exploits the difference in tooth enamel oxygen isotope (δ18O) values between evaporation insensitive obligate drinkers and evaporation sensitive non-obligate drinkers to calculate a water deficit value. Water deficit values calculated from dik-dik (Madoqua spp.; non-obligate drinkers) and warthog (Phacochoerus spp.; obligate drinkers) tooth enamel δ18O values at Gogoshiis Qabe and Guli Waabayo are in agreement and progressively increase toward the present. Additionally, two of three direct dated serially-sampled warthog teeth (ID 4032 and 4033) from Guli Waabayo demonstrate low seasonality of rainfall during much of the AHP (range in δ18O ≤ 1.8‰). One tooth (ID 4035) with high amplitude variability in δ18O values (3.1‰) dates to 8470 ± 66 cal yr B.P., a period identified as a lowstand in several lake level records. Our results suggest that regions isolated from Atlantic Ocean moisture likely experienced a less-pronounced AHP than those receiving moisture from multiple sources but indicate less seasonal variability than present. Our findings also support the presence of climate variability within the AHP.

Late Middle Pleistocene ecology and climate in Northeastern Thailand inferred from the stable isotope analysis of Khok Sung herbivore tooth enamel and the land mammal cenogram

Paleoecological and paleoclimatic records based on the stable isotopes of mammalian tooth enamel are poorly known in mainland Southeast Asia during the Pleistocene. Khok Sung in Northeastern Thailand is a late Middle Pleistocene terrace deposit, tentatively dated either as 213 ka or 188 ka, yielding 15 described mammalian taxa with especially abundant and complete fossil remains. To investigate paleodiets and habitats of these ancient mammals and to understand the corresponding regional climate, we performed an analysis of stable carbon and oxygen isotopes extracted from tooth enamel carbonate of various mammalian taxa, coupled with the cenogram method. The enamel δ13C values of Khok Sung mammals indicate a variety of diets, ranging from pure C3 to C4 plants, suggesting that C4 grasses were a major component of local Thai ecosystems during the late Middle Pleistocene. The stable isotopic distinction between C3 and C4 plants suggests that the Pleistocene wildlife habitats ranged from closed forests to open grasslands for the Khok Sung area. Moreover, differences within sympatric Pleistocene herbivores such as proboscideans, rhinoceroses, and cervids characterize possible niche partitioning by minimizing interspecific overlap. Paleoclimatic interpretations based on the intra-tooth variability in enamel δ18O values from large mammals and on the cenogram analysis reflect significant seasonal variations in precipitation and temperature, and humid conditions, for the Khok Sung locality. Compared to modern environments in Thailand, it is apparent that C4-dominated grasslands were more widespread at that time when anthropic impacts on the ecosystems were presumably absent or minimal.

Paleodietary change and its implications for aridity indices derived from δ18O of herbivore tooth enamel

A large body of research provides reconstructions of ancient water deficit—the difference between potential evapotranspiration and precipitation—using an aridity index derived from the δ18O values of tooth enamel from evaporation sensitive (ES) and evaporation insensitive (EI) mammalian herbivores. The former are typically ruminants that obtain most of their water from leafy dicots (the δ18O of their enamel reflects evaporation of leaf water), whereas the latter are non-ruminants dependent on surface water (the δ18O of their enamel reflects local meteoric water). Use of the index requires that fossil taxa are correctly classified as ES or EI. This study examines how paleodietary change can influence such classifications. In modern ruminant ungulates, dependence on drinking water is related to the proportion of grass versus dicots in the diet. This means that paleodietary change in ruminant ungulates should be associated with shifts in drinking behavior, altering enamel δ18O values and biasing the aridity index. Such bias is evident in estimates of water deficit derived from the enrichment of enamel δ18O in fossil Tragelaphini relative to Hippopotamidae from East African fossil sites spanning the last ~4.4Myr. Elevated grass consumption (measured by enamel δ13C) in the former is associated with reduced enrichment of enamel δ18O relative to the latter, translating to lower estimates of water deficit. In conducting such analyses of fossil ungulates, the diet of those ungulates must be screened to ensure consistency with the assumptions of the method.

Aridity and hominin environments

Aridification is often considered a major driver of long-term ecological change and hominin evolution in eastern Africa during the Plio-Pleistocene; however, this hypothesis remains inadequately tested owing to difficulties in reconstructing terrestrial paleoclimate. We present a revised aridity index for quantifying water deficit (WD) in terrestrial environments using tooth enamel δ18O values, and use this approach to address paleoaridity over the past 4.4 million years in eastern Africa. We find no long-term trend in WD, consistent with other terrestrial climate indicators in the Omo-Turkana Basin, and no relationship between paleoaridity and herbivore paleodiet structure among fossil collections meeting the criteria for WD estimation. Thus, we suggest that changes in the abundance of C4 grass and grazing herbivores in eastern Africa during the Pliocene and Pleistocene may have been decoupled from aridity. As in modern African ecosystems, other factors, such as rainfall seasonality or ecological interactions among plants and mammals, may be important for understanding the evolution of C4 grass- and grazer-dominated biomes.

Stable isotope dietary reconstructions of herbivore enamel reveal heterogeneous savanna ecosystems in the Plio-Pleistocene Malawi Rift

The Plio-Pleistocene expansion of Eastern Africa savanna ecosystems was a major driver for morphological and behavioral innovations in hominin evolution. Most evidence for hominin ecosystem reconstructions originates from the Eastern Rift in today's Somali-Masai Endemic Zone. We provide stable carbon (δ13C) and oxygen (δ18O) isotope data from 22 bovid, equid, suid, hippopotamid and elephant teeth from the southern part of the East African Rift and supplement these by δ18O values of present-day meteoric water. This region (Karonga Basin, Malawi) hosts remains of Homo rudolfensis and Paranthropus boisei. It is situated between hominin-bearing sites in Eastern and Southern Africa and therefore fills an important geographical gap for hominin evolution.Tooth enamel δ13C and δ18O data of 14 large-bodied mammalian herbivore species from Units 2 and 3 (ca. 4.3 to 0.6Ma) in the Chiwondo Beds provide information about foraging strategies and vegetation patterns. Our stable isotope data reflect C3-dominated ecosystems that permitted access to open C4-environments for migratory mammals. Many analyzed taxa show evidence for mixed diets with high abundances of C3-biomass consumption; only selected bovids were specialized grazers.δ18O of present-day meteoric water reflects rainfall amount and seasonality, elevation, and lake evaporation. δ18O values of Karonga Basin herbivore enamel are generally low and cover values similar to present-day drinking water, indicating both, evaporated and freshwater sources. Comparison of δ13C values from the Karonga Basin with other Eastern African herbivore communities reveals significant differences in dietary patterns with much more generalized mixed C3/C4, and pure C3 feeding behaviors in the Malawi Rift. Similarly, enamel δ18O values are lower than in most Plio-Pleistocene Eastern African herbivores, suggesting more humid conditions. Collectively, our data support models in which early hominin foraging activity included access to C3-dominated biomes, complicating traditional interpretations linking early human evolutionary innovations to a shift towards savanna habitats.

Stable isotopic composition of fossil mammal teeth and environmental change in southwestern South Africa during the Pliocene and Pleistocene

The past 5millionyears mark a global change from the warmer, more stable climate of the Pliocene to the initiation of glacial–interglacial cycles during the Pleistocene. Marine core sediment records located off the coast of southwestern Africa indicate aridification and intensified upwelling in the Benguela Current over the Pliocene and Pleistocene. However, few terrestrial records document environmental change in southwestern Africa over this time interval. Here we synthesize new and published carbon and oxygen isotope data of the teeth from large mammals (>6kg) at Langebaanweg (~5millionyears ago, Ma), Elandsfontein (1.0–0.6Ma), and Hoedjiespunt (0.35–0.20Ma), to evaluate environmental change in southwestern Africa between the Pliocene and Pleistocene. The majority of browsing and grazing herbivores from these sites yield enamel δ13C values within the range expected for animals with a pure C3 diet, however some taxa have enamel δ13C values that suggest the presence of small amounts C4 grasses at times during the Pleistocene. Considering that significant amounts of C4 grasses require a warm growing season, these results indicate that the winter rainfall zone, characteristic of the region today, could have been in place for the past 5millionyears. The average δ18O value of the herbivore teeth increases ~4.4‰ between Langebaanweg and Elandsfontein for all taxa except suids. This increase may solely be a function of a change in hydrology between the fluvial system at Langebaanweg and the spring-fed environments at Elandsfontein, or a combination of factors that include depositional context, regional circulation and global climate. However, an increase in regional aridity or global cooling between the early Pliocene and mid-Pleistocene cannot explain the entire increase in enamel δ18O values. Spring-fed environments like those at Elandsfontein may have provided critical resources for mammalian fauna in the mid-Pleistocene within an increasingly arid southwestern Africa ecosystem.

Eocene–Oligocene latitudinal climate gradients in North America inferred from stable isotope ratios in perissodactyl tooth enamel

The Eocene–Oligocene transition (~34Ma) was one of the most pronounced episodes of climate change of the Cenozoic. In order to investigate this episode of global climate cooling in North America, we analyzed the carbon and oxygen stable isotope composition of the carbonate component of 19 perissodactyl (horse and rhino) tooth enamel samples from the Eocene–Oligocene rocks of the Cypress Hills Formation (southwestern Saskatchewan, Canada); we then compared the results with previously published data from the US Great Plains (Nebraska, South Dakota, and Wyoming).Average (±1σ) perissodactyl enamel δ13C values (vs. V-PDB) in the Eocene (−8.8±0.3‰) and Oligocene (−9.0±0.3‰) are indistinguishable, suggesting no major change in mean annual precipitation in Saskatchewan across the transition. The δ13C values in Saskatchewan indicate the presence of arid ecosystems and are slightly higher than those in the US Great Plains, suggesting drier conditions at higher latitudes. With respect to oxygen isotopes, average (±1σ) perissodactyl enamel δ18O values (vs. V-SMOW) in the Eocene (19.8±2.0‰) and Oligocene (20.1±3.6‰) are also indistinguishable, suggesting no change in the δ18O of meteoric precipitation across the transition in Saskatchewan. Enamel δ18O variability is much larger in the Oligocene vs. Eocene, indicating a large increase in temperature seasonality. This increase in enamel δ18O variability is much larger than that recorded in the US Great Plains, suggesting that higher latitudes are more sensitive to major episodes of climate change with respect to temperature seasonality. Finally, our data indicate no major change in the Oligocene vs. Eocene latitudinal gradient in local water δ18O in North America, which suggests no change in mean annual temperature gradients across the transition. This result supports the hypothesis that ascribes the climate change of the transition to a drop in atmospheric pCO2 because climate models show that this mechanism produces uniform cooling at mid-latitudes.

Diet, residential origin, and pathology at Machu Picchu, Peru

Pathological conditions in human skeletal remains provide a wealth of information about archaeological populations, but many are limited in their interpretive significance by their nonspecific etiologies. This study analyzes three common pathological conditions known to manifest in infancy and childhood in the skeletal population from Machu Picchu, Peru (N = 74) with published carbon, nitrogen, oxygen, strontium, and lead isotopic data (Turner et al.: J Archaeol Sci 36 (2009) 317-332; Turner et al.: Chungara: Revista de Antropología Chilena 42 (2010) 515-524) to distinguish early-life diet from residential origins as significantly associated with pathologies among the site's inhabitants. Analyses of variance indicate highly significant variation between enamel δ(18)O values, which serve as a rough proxy of local environment, and both cribra orbitalia (CO) and porotic hyperostosis (PH), generally understood to be markers of anemia. Results tentatively suggest that individuals manifesting these lesions may have lived closer to the arid coasts; however, no significant variation was found in parameters of diet (enamel δ(13) C(carbonate), dentin δ(13) C(collagen), dentin δ(15)N) by either CO or PH, suggesting that the primary factors causing anemia may have been more significantly related to residential origin rather than diet. Linear enamel hypoplasia (LEH) frequency significantly varied by both dietary and residential parameters, supporting models of LEH formation from a synergy of dietary and environmental factors. These results support previous research on the etiology of PH in the Andes; they also represent a useful approach to refining site-specific interpretations of pathological conditions in archaeological populations, and exploring etiological variation between populations.

Stable isotope evidence for seasonal consumption of marine seaweed by modern and archaeological sheep in the Orkney archipelago (Scotland)

The use of seaweed as fodder for domestic animals during winter has been suggested for the North Atlantic isles in prehistory with reference to a historically attested practice. We tested the use of stable isotope analysis in tooth enamel bioapatite to detect seasonal consumption of seaweed on modern sheep from the Orkney archipelago, with no contribution, seasonal contribution or exclusive contribution of seaweed to diet. There was no overlap between the δ13C of local terrestrial vegetation and marine plants available on the shore. Sheep relying on seaweed had enamel δ13C values as high as −3·1‰, differing from grazing sheep with enamel δ13C values comprised between −17·7‰ and −15·1‰. Seaweed consumption was also reflected in lower amplitudes of intra-tooth variation in enamel δ18O values (0·3‰ to 1·8‰ in seaweed-eating sheep; 3·6‰ to 4·1‰ in grazing sheep), likely due to ingestion of oceanic water. The protocol was applied to archaeological assemblages from the same archipelago. A winter consumption of seaweed was detected in one sheep from the Neolithic site of Point of Cott and one sheep from the Iron Age assemblage of Mine Howe. No contribution of seaweed to the sheep diet was shown at the Late Norse site of Earl's Bu.

Evidence of Cenozoic environmental and ecological change from stable isotope analysis of sirenian remains from the Tethys-Mediterranean region

Sirenians (sea cows: manatees and dugongs) have been primary consumers in tropical and subtropical shallow-water marine ecosystems for more than 50 m.y. Though fossils of the earliest sirenians have been recovered from the Caribbean, sirenians are thought to have originated in the Tethys-Mediterranean region, which underwent significant climate change over the course of the Cenozoic. Application of stable isotope analysis can provide new insight into how diet and habitat preferences were affected by climate change and how these ecological changes correlate with diversity patterns for this region. Tooth enamel was sampled from 57 specimens of sirenians from the Tethys-Mediterranean and adjacent seas spanning the Eocene to Pliocene. Enamel δ13C values across this time interval were consistently high and indicative of diets composed mostly of marine seagrasses. In contrast, enamel δ18O values showed significant change over time and across the region. Sirenians from southern sites (i.e., Egypt, Libya) had significantly higher mean δ18O values than specimens from most European locations, suggesting variation in salinity within the Tethys-Mediterranean. The range in enamel δ18O values increased from the Paleogene through the Neogene, but enamel δ13C values remained steady, indicating that changes in environmental conditions did not necessarily coincide with major changes in dietary preferences. Declines in sirenian taxonomic diversity in the late Miocene were likely due to the rapid climate and oceanographic changes during the latter half of the Cenozoic and their impacts on available dietary resources. Elevated δ13C and δ18O values in Mediterranean sirenians during the Messinian salinity crisis corroborate the hypothesis of ecophenotypic dwarfing in these animals.

Stable isotopes in fossil mammals, fish and shells from Kunlun Pass Basin, Tibetan Plateau: Paleo-climatic and paleo-elevation implications

We report the results of a stable isotope study of a late Pliocene fauna recently discovered in the Kunlun Mountain Pass area (∼4700 m above sea level) on the northern Tibetan Plateau. The δ13C values of enamel samples from modern herbivores from the Kunlun Pass Basin range from −14.8 to −10.6‰, with a mean of −12.0±0.7‰, indicating pure C3 diets consistent with the current dominance of C3 vegetation in the area. In contrast, enamel samples from fossil herbivores yielded δ13C values of −5.4‰ to −10.2‰ (with a mean of −7.9±1.3‰), significantly higher than those of modern herbivores in the area. The higher δ13C values indicate that these ancient herbivores, unlike their modern counterparts, had a variety of diets ranging from pure C3 to mixed C3/C4 vegetation. The local ecosystems in the Kunlun Pass area in the late Pliocene likely included grasslands that had small amounts of C4 grasses. The δ18O values of enamel from large herbivores shifted to higher values after the late Pliocene, indicating a significant change in the δ18O of local meteoric water. We estimate that there has been approximately 3.2‰ increase in annual δ18O values of meteoric water since ∼2–3 Ma, most likely driven by changes in the regional hydrological cycle possibly as a result of tectonic and climate change. The δ18O values of fossil fish teeth/bones and gastropod shells, along with abundance of aquatic plants and other invertebrate fossils, clearly indicate that the Kunlun Pass Basin once had plenty of water and was occupied by a freshwater lake in the late Pliocene. Our isotope data from both terrestrial and aquatic fossils suggest that the Kunlun Pass Basin was a hospitable place with a much warmer and wetter climate in the late Pliocene, very different from today's rock desert and cold steppe environments. The mean annual temperature in the late Pliocene estimated from the δ18O of fossil bone carbonate and paleo-water was about 10±8 °C, much higher than the present-day mean annual temperature in the basin. If valid, the estimated temperature change would imply that the elevation of the basin has increased by ∼2700±1600 m since ∼2–3 Ma.

A stable isotope aridity index for terrestrial environments

We use the oxygen isotopic composition of tooth enamel from multiple mammalian taxa across eastern Africa to present a proxy for aridity. Here we report tooth enamel delta(18)O values of 14 species from 18 locations and classify them according to their isotopic sensitivity to environmental aridity. The species are placed into two groups, evaporation sensitive (ES) and evaporation insensitive (EI). Tooth enamel delta(18)O values of ES animals increase with aridity, whereas the tooth enamel delta(18)O values of EI animals track local meteoric water delta(18)O values, demonstrating that bioapatite delta(18)O values of animals with different behaviors and physiologies record different aspects of the same environment. The enrichment between tooth enamel delta(18)O values of ES and EI animals records the degree of (18)O enrichment between evaporated water (ingested water or body water) and source water, which increases with environmental aridity. Recognition of the ES-EI distinction creates the opportunity to use the (18)O composition of bioapatite as an index of terrestrial aridity.

Mapping Human Movement using Stable Oxygen Isotopic Ratio Mass Spectrometry: Potential Application to Forensic Science Demonstrated by a Modern Horse-Human Study

ABSTRACTThe utility of stable oxygen isotope analysis for demonstrating human migration has been developed and demonstrated on archaeological human populations. The application of this approach to tracking human movement has seldom been applied within forensic science. This paper gives results from a stable oxygen isotope assessment of extant modern human and horse enamel δ18O values recovered from tooth enamel. The human and horses were all constrained to known geographic locales for the period of tooth formation and compared to UK and global precipitation values for δ18O. It was found that human and horse values track one another and horse can be used with some confidence as a human proxy. UK values were constrained geographically and outlier values to the UK were identified between Iceland and the Sudan. For application within the realm of forensic science more research is required to understand the regionalized contribution of hydrology to a catchment and the potentially confounding contribution of mixed water sources. However, as a tool to track human movement within forensics there is clear utility.

Immigration, Assimilation, and Status in the Ancient City of Teotihuacan: Stable Isotopic Evidence from Tlajinga 33

AbstractStable carbon isotope ratios in bone collagen and oxygen isotope ratios in bone and enamel phosphate from 25 individuals from the residential compound of Tlajinga 33 were used to examine the possibility that the inhabitants, who were craft producers, may have accepted immigrants to maintain either their ability to reproduce themselves as a social group or their level of economic productivity. Bone δ18O and δ13C values provide a long-term picture of geographic identity and diet, and enamel δ18O values provide a snapshot of geographic location during particular tooth development. A considerable proportion (29 percent) of the Tlajinga 33 inhabitants grew up elsewhere, but the majority of these immigrants had dwelt in Teotihuacan for many years before their death. Neither geographical relocation nor dietary differences are significantly associated with gender. The social position of foreigners appears to have been generally high. For example, the occupants of Tomb 50 appear to have come from elsewhere, possibly West Mexico, but foreigners were also found in lower status contexts such as middens. The stable isotope ratios reflecting long-term dwelling at Teotihuacan suggest that social status was achieved, which supports current archaeological evidence. Furthermore, the lack of dietary differences between immigrants and native Teotihuacanos may also imply political and/or ethnic assimilation.