Range Of δ13C Values Research Articles

Tianshanbeilu and the Isotopic Millet Road: reviewing the late Neolithic/Bronze Age radiation of human millet consumption from north China to Europe.

The westward expansion of human millet consumption from north China has important implications for understanding early interactions between the East and West. However, few studies have focused on the Xinjiang Uyghur Autonomous Region, the vast geographical area directly linking the ancient cultures of the Eurasian Steppe and the Gansu Corridor of China. In this study, we present the largest isotopic investigation of Bronze Age China (n = 110) on material from the key site of Tianshanbeilu, in eastern Xinjiang. The large range of δ13C values (–17.6‰ to –7.2‰; –15.5 ± 1.2‰) provides direct evidence of unique dietary diversity and consumption of significant C4 resources (millets). The high δ15N results (10.3‰ to 16.7‰; 14.7 ± 0.8‰) likely reflect sheep/goat and wild game consumption and the arid climate of the Taklamakan Desert. Radiocarbon dates from four individuals indicate Tianshanbeilu was in use between 1940 and 1215 cal bc. The Tianshanbeilu results are then analysed with respect to 52 Bronze Age sites from across Eurasia, to investigate the spread and chronology of significant human millet consumption and human migration. This isotopic survey finds novel evidence that the second millennium bc was a dynamic period, with significant dietary interconnectivity occurring between north China, Central Asia and Siberia. Further, we argue that this ‘Isotopic Millet Road’ extended all the way to the Mediterranean and Central Europe, and conclude that these C4 dietary signatures of millet consumption reflect early links (migration and/or resource transfer) between the Bronze Age inhabitants of modern-day China and Europe.

Relationship between leaf functional traits and productivity in Aquilaria crassna (Thymelaeaceae) plantations: a tool to aid in the early selection of high-yielding trees.

Physiological traits are frequently used as indicators of tree productivity. Aquilaria species growing in a research planting were studied to investigate relationships between leaf-productivity traits and tree growth. Twenty-eight trees were selected to measure isotopic composition of carbon (δ13C) and nitrogen (δ15N) and monitor six leaf attributes. Trees were sampled randomly within each of four diametric classes (at 150 mm above ground level) ensuring the variability in growth of the whole population was represented. A model averaging technique based on the Akaike's information criterion was computed to identify whether leaf traits could assist in diameter prediction. Regression analysis was performed to test for relationships between carbon isotope values and diameter and leaf traits. Approximately one new leaf per week was produced by a shoot. The rate of leaf expansion was estimated as 1.45 mm day-1. The range of δ13C values in leaves of Aquilaria species was from -25.5‰ to -31‰, with an average of -28.4 ‰ (±1.5‰ SD). A moderate negative correlation (R2 = 0.357) between diameter and δ13C in leaf dry matter indicated that individuals with high intercellular CO2 concentrations (low δ13C) and associated low water-use efficiency sustained rapid growth. Analysis of the 95% confidence of best-ranked regression models indicated that the predictors that could best explain growth in Aquilaria species were δ13C, δ15N, petiole length, number of new leaves produced per week and specific leaf area. The model constructed with these variables explained 55% (R2 = 0.55) of the variability in stem diameter. This demonstrates that leaf traits can assist in the early selection of high-productivity trees in Aquilaria species.

Evaluation of δ13C in Carbonaceous Aerosol Source Apportionment at a Rural Measurement Site

The stable isotope of carbon, 13C, has been used in several studies for source characterization of carbonaceous aerosol since there are specific signatures for different sources. In rural areas, the influence of different sources is complex and the application of δ13C for source characterization of the total carbonaceous aerosol (TC) can therefore be difficult, especially the separation between biomass burning and biogenic sources. We measured δ13C from 25 filter samples collected during one year at a rural background site in southern Sweden. Throughout the year, the measured δ13C showed low variability (–26.73 to –25.64‰). We found that the measured δ13C did not correlate with other commonly used source apportionment tracers (14C, levoglucosan). δ13C values showed lower variability during the cold months compared to the summer, and this narrowing of the δ13C values together with elevated levoglucosan concentrations may indicate contribution from sources with lower δ13C variation, such as biomass or fossil fuel combustion. Comparison of two Monte Carlo based source apportionment models showed no significant difference in results when δ13C was incorporated in the model. The insignificant change of redistributed fraction of carbon between the sources was mainly a consequence of relatively narrow range of δ13C values and was complicated by an unaccounted kinetic isotopic effect and overlapping δ13C end-member values for biomass burning and biogenic sources. (Less)

A multi-isotope investigation of diet and subsistence amongst island and mainland populations from early medieval western Britain.

ObjectivesThis is the first investigation of dietary practices amongst multiple early medieval populations (AD 500–1000) from Wales and the Isle of Man using carbon, nitrogen, and sulphur isotope analysis. The analysis will illuminate similarities or differences between the diets and subsistence strategies of populations occupying different geographical regions, specifically those living in marginal coastal regions in comparison to inland populations well‐connected to ecclesiastical centres and high‐status settlements.Materials and MethodsOne hundred and two human skeletons were sampled for carbon and nitrogen isotope analysis, and 69 human skeletons were sampled for sulphur isotope analysis from nine cemetery sites from western Britain (Isle of Man = 3, southwest Wales = 4, southeast Wales = 2). Thirteen faunal skeletons from St Patrick's Chapel (southwest Wales) were sampled for carbon, nitrogen, and sulphur isotope analysis.ResultsHuman δ13C values range from −19.4‰ to −21.2‰ (δ13C mean=−20.4 ±0.4‰, 1σ, n = 86), and δ15N values range from 9.1‰ to 13.8‰ (δ15N mean = 10.8 ± 0.9‰, 1σ, n = 86). δ34S values range from 1.2‰ to 18.4‰ (δ34S mean = 11.6 ± 4.5‰, 1σ, n = 66). Significant differences were noted between the mean δ13C, δ15N and δ34S values according to geographic region: Isle of Man (δ13C = −20.7 ± 0.4‰, δ15N = 11.4 ±0.6‰, n = 13/86; δ34S mean = 17.1 ±0.6, n = 4/66), southwest Wales (δ13C = −20.5 ± 0.4‰, δ15N = 11.0 ±1‰, n = 32/86; δ34S = 16.1 ± 2.1, n = 21/66), and southeast Wales (δ13C =−20.3 ±0.4‰, δ15N = 10.4 ±0.7‰, n = 41/86; δ34S= 8.8 ±3‰, n = 41/66). Faunal δ13C values range from −23.1‰ to −21.2‰ (δ13C mean= −22.1 ±0.5‰, 1σ, n = 13), and δ15N values range from 6.3‰ to 9.8‰ (δ15N mean = 7.3 ± 1.1‰, 1σ, n = 13). δ34S values range from 4.7‰ to 18.4‰ (δ34S mean= 16.3 ± 3.6‰, 1σ, n = 13).ConclusionsThe data reveal a reliance on terrestrial protein, however differences are observed between the resource consumption of populations from southwest Wales and the Isle of Man in comparison to the populations from southeast Wales. Populations from the west coast have a marine sulphur signature that reflects their coastal proximity and may also include a reliance on seaweed as a fertiliser/food source. Populations in the southeast were connected to ecclesiastical centres and high‐status settlements and had access to inland‐grown produce. The data add support to the suggestion that δ34S can be used as a mobility indicator.

Characteristics of Ordovician paleokarst inclusions and their implications for paleoenvironmental and geological history in Halahatang area of northern Tarim Basin

The Halahatang area has become a key region for petroleum exploration in the Tarim Basin in recent years owing to its well-developed and extremely heterogeneous Ordovician paleokarst carbonatites. This study explores the geochemical characteristics of the paleokarstification products, various periods of paleokarstification, and paleoenvironmental conditions of the Ordovician carbonates in the Halahatang area. After careful analysis of the rock fabric, the stable carbon and oxygen isotopic composition of the calcites filling paleokarstic fissures were systematically examined, and experimental analysis on fluid inclusions was conducted. The δ18O values were generally negative, ranging from −4.14 to −15.71‰ with an average value of −9.95‰. These values reflect a paleokarstification environment changing from shallow burial to deep burial, the rocks of which were later affected by corrosion. The δ13C (PDB) values range from 2.12 to 4.09‰ with an average value of 0.65‰. This confirms the complexity of the paleokarstification and revealed four different paleoenvironmental conditions: a marine environment with syndiagenesis, weathered crust exposed to a freshwater karst environment, a shallow-burial karst environment, and a deep-burial high-temperature environment. The homogenization temperature of the inclusions indicates the existence of four paleokarstification and calcite infilling periods: buried karstification during the late Hercynian, the Indosinian–Yanshanian, and the Himalayan and karstification by meteoric water during the Caledonian. The results of this study provide new evidence for the prediction and exploration of karst reservoirs.

Diet composition of two common mole‐rat populations in arid and mesic environments in South Africa as determined by stable isotope analysis

AbstractThe common mole‐rat Cryptomys hottentotus hottentotus is a small, subterranean mammal found in southern Africa which lives in social colonies. They harvest their food resources from below ground by extending their burrow systems, and are considered to be geophyte (bulbs, tubers and corms) specialists. This study examines differences in diet composition between populations of common mole‐rats inhabiting arid and mesic areas, by using stable isotope analysis to investigate dietary niches and estimate their reliance on different food resources. We sampled three tissue types, blood, claws and fur, to provide dietary information over different time periods (weeks to months). In addition, we collected and analysed potential food sources adjacent to burrows. We found that the diets of common mole‐rats in both the arid and mesic areas were composed predominantly of geophytes. However, mole‐rats in the arid area had a wider dietary niche, with a larger range in both δ15N and δ13C values which was consistent across all tissue types. Mole‐rats in arid areas also showed a greater reliance on alternative food sources, such as clover and grass, in addition to geophytes comprising 59–69% of the diet in the arid area, compared to 91–92% of the diet in the mesic area. We suggest that the lower geophyte density in the arid area led to a greater reliance on other food resources by the mole‐rats, and that this decrease in diet specialization could be an adaptation to surviving in more arid areas. We demonstrate that stable isotope analyses can be used to examine interpopulation dietary differences within the same species living in contrasting environments.

Carbon dioxide concentration can limit the identification of C4 plants by stable isotope composition

The global expansion of C4 plants during the Late Cenozoic is an important event in the Earth’s environmental-ecosystem evolution. Taking into account the nonglobal expansion of C4 plants, the CO2 concentration is not the only prerequisite for C4 expansion. The direct driving factors for C4 expansion may be associated with regional arid and/or warm seasonal precipitation and temperature variations. However, a large change in the CO2 concentration occurred, varying from 100∼300 to >2000 ppm during geological history; thus, it is necessary to understand the impact of such changes in the atmospheric CO2 concentration on the δ13C values of C3 and C4 plants during different geological periods. In this article, we analyzed the δ13C values for seven C4 and C3 plants grown under different CO2 concentrations for 10, 20, and 30 days. According to our study, the δ13C records for all the C3 and C4 plants show a rapid decrease followed by a slowly stable decreased trend with increasing CO2 concentration when the plants were grown for 10, 20, and 30 days. Comparing with the value averaging about −26 to −27 ‰ for C3 plants and about −12 ‰ for C4 plants, when the CO2 levels reach 20,000 ppm, all of the δ13C values of C4 plants become more negative, varying from −27.5 to −36.1 ‰, which fall into the range of δ13C values for C3 plants. Namely, the increase of carbon dioxide can limit the identification of C4 plants by carbon isotope composition. Thus, the expansion of C4 plants as reconstructed from the geological records of carbon isotopes possibly does not reflect the origin and expansion of C4 plants when atmospheric CO2 concentration was reduced to a threshold value, as previously thought. However, another possible explanation is that the atmospheric CO2 concentration was reduced to a threshold value from which the carbon isotope values of C3 and C4 plants can be distinguished. Therefore, we suggest that it is necessary to understand the δ13C range for C3 and C4 plants, to accurately evaluate the origin and expansion of C4 plants, for geological periods when a high CO2 concentration occurred.

Stable isotope geochemistry of the nitrogen-rich gas from lower Cambrian shale in the Yangtze Gorges area, South China

The organic-rich marine shales from the lower Cambrian Niutitang formation in the Yangtze Gorges area are characterized by their high TOC values (0.54–5.13%), types I and II organic matter, and high Ro values (2.4%–2.6%). Geochemical parameters of 19 gas samples from the lower Cambrian shale formation from well ZD-1 were analyzed in this study. The gases are dominated by methane, with small amounts of ethane and no propane or butane. The δ13C(CH4) values range from −31.7‰ to −27.9‰, the δ13C(C2H6) values range from −35.2‰ to −33.4‰, and the δ2H(CH4) values range from −214‰ to −187‰. Furthermore, carbon isotopic compositions of the alkane gases from the lower Cambrian shale are characterized by δ13C1 > δ13C2; these results indicate that the gases are of thermogenic origin and are oil-derived. Moreover, methane with heavy carbon isotopic and light hydrogen isotopic values may be produced when water reacts with inorganic carbon. The isotopic reversal of alkane gases was probably due to destructive redox reactions at maximum burial resulting in Rayleigh-type fractionation and/or mixing by gases from the same source but at a different maturity. Nitrogen occurs in the analyzed gases at concentrations from 8.15 to 96.52%, and the δ15N(N2) values vary from 3.2 to 7.4‰. The δ15N(N2) values and high illite content suggest that nitrogen was mainly generated during thermal transformation of organic matter and/or from NH4-rich illites of the clayey facies of the lower Cambrian shale. Carbon dioxide concentrations vary from 1.13 to 4.96%, and the δ13C(CO2) values range from −8.9 to −13.6‰. This suggests that carbon dioxide was mainly generated during thermogenic processes of transformation of organic matter. Moreover, the major reason for the change in nitrogen and methane contents in the studied well (ZD-1) is probably due to the development of micro cracks in core samples with high contents of nitrogen. A high nitrogen content may be caused by the strong adsorption capacity of nitrogen, which leads to the retention of nitrogen and the diffusion of methane in shale.

Trophic interactions and food web structure of a subantarctic marine food web in the Beagle Channel: Bahía Lapataia, Argentina

Basic ecological knowledge regarding the importance of different sources of primary production and how it is transferred among consumer species is required to properly manage and conserve subpolar ecosystems that are particularly vulnerable to environmental changes. We used carbon (δ13C) and nitrogen (δ15N) stable isotope analysis to establish a baseline of species interactions and food web structure for the nearshore marine community in Bahia Lapataia, Argentina, an ecosystem that faces many threats, including a recent invasion of exotic chinook salmon. Primary producers and other organic sources (e.g., particulate organic matter) available to the food web were isotopically distinct and had a wide range in δ13C (−31.3 to −5.3 ‰) and δ15N (−0.5 to 13.1 ‰) values. Consumers also showed a wide range of isotope values with mean δ13C and δ15N values ranging from −20.8 to −12.3 ‰ and from 10.5 to 19.6 ‰, respectively. A cluster analysis of these isotope data correctly identified functional groups and expected interactions among species based on independent information. Using Bayesian isotope mixing models, we estimated that the proportional contribution of benthic production, in particular through grazing and the consumption of detritus, was a more important source of energy for primary and secondary consumers than pelagic production. Using stable isotope analysis to continually monitor species interactions and food web structure may prove to be a valuable research and management tool for assessing ecological consequences of different threats in this and other subpolar ecosystems.

Carbon and oxygen isotopic composition of coal and carbon dioxide derived from laboratory coal combustion: A preliminary study

The concentration of carbon dioxide (CO2) in the atmosphere has dramatically increased from the start of the industrial revolution in the mid-1700s to present levels exceeding 400ppm. Carbon dioxide derived from fossil fuel combustion is a greenhouse gas and a major contributor to on-going climate change. Carbon and oxygen stable isotope geochemistry is a useful tool to help model and predict the contributions of anthropogenic sources of CO2 in the global carbon cycle. Surprisingly few studies have addressed the carbon and oxygen isotopic composition of CO2 derived from coal combustion. The goal of this study is to document the relationships between the carbon and oxygen isotope signatures of coal and signatures of the CO2 produced from laboratory coal combustion in atmospheric conditions.Six coal samples were selected that represent various geologic ages (Carboniferous to Tertiary) and coal ranks (lignite to bituminous). Duplicate splits of the six coal samples were ignited and partially combusted in the laboratory at atmospheric conditions. The resulting coal-combustion gases were collected and the molecular composition of the collected gases and isotopic analyses of δ13C of CO2, δ13C of CH4, and δ18O of CO2 were analysed by a commercial laboratory. Splits (~1g) of the un-combusted dried ground coal samples were analyzed for δ13C and δ18O by the U.S. Geological Survey Reston Stable Isotope Laboratory.The major findings of this preliminary work indicate that the isotopic signatures of δ13C (relative to the Vienna Pee Dee Belemnite scale, VPDB) of CO2 resulting from coal combustion are similar to the δ13CVPDB signature of the bulk coal (−28.46 to −23.86‰) and are not similar to atmospheric δ13CVPDB of CO2 (~−8‰, see http://www.esrl.noaa.gov/gmd/outreach/isotopes/c13tellsus.html). The δ18O values of bulk coal are strongly correlated to the coal dry ash yields and appear to have little or no influence on the δ18O values of CO2 resulting from coal combustion in open atmospheric conditions. There is a wide range of δ13C values of coal reported in the literature and the δ13C values from this study generally follow reported ranges for higher plants over geologic time. The values of δ18O (relative to Vienna Standard Mean Ocean Water) of CO2 derived from atmospheric combustion of coal and other high-carbon fuels (peat and coal) range from +19.03 to +27.03‰ and are similar to atmospheric oxygen δ18OVSMOW values which average +23.8‰. Further work is needed on a broader set of samples to better define the relationships between coal composition and combustion-derived gases.

Tooth enamel stable isotopes of Holocene and Pleistocene fossil fauna reveal glacial and interglacial paleoenvironments of hominins in Indonesia

The carbon (δ13C) and oxygen (δ18O) isotope compositions of fossilized animal tissues have become important proxies of paleodiet and paleoenvironment, but such stable isotope studies have not yet been extensively applied to the fossil assemblages of Sundaland (the biogeographical region comprising most of the Indonesian Archipelago). Here, we use the isotope composition of tooth enamel to investigate the diet and habitat of bovids, cervids, and suids from several Holocene and Pleistocene sites on Java and Sumatra. Our carbon isotope results indicate that individual sites are strongly dominated by either C3-browsers or C4-grazers. Herbivores from the Padang Highlands (Sumatra) and Hoekgrot (Java) cave faunas were mainly C3-browsers, while herbivores from Homo erectus-bearing sites Trinil and Sangiran (Java) utilized an almost exclusive C4 diet. The suids from all sites show a wide range of δ13C values, corroborating their omnivorous diet. For the dataset as a whole, oxygen and carbon isotope values are positively correlated. This suggests that isotopic enrichment of rainwater and vegetation δ18O values coincides with an increase of C4-grasslands. We interpret this pattern to mainly reflect the environmental contrast between glacial (drier, more C4) and interglacial (wetter, more C3) conditions. Intermediate herbivore δ13C values indicating mixed C3/C4 feeding is relatively rare, which we believe to reflect the abruptness of the transition between glacial and interglacial precipitation regimes in Sundaland. For seven Homo erectus bone samples we were not able distinguish between diagenetic overprint and original isotope values, underlining the need to apply this isotopic approach to Homo erectus tooth enamel instead of bone. Importantly, our present results on herbivore and omnivore faunas provide the isotopic framework that will allow interpretation of such Homo erectus enamel isotope data.

The isotopic footprint of irrigation in the western Mediterranean basin during the Bronze Age: the settlement of Terlinques, southeast Iberian Peninsula

The isotopic composition of the remains of cereals and pine has been studied, from three different chronological phases from 2140 to 1500 cal bc at the Terlinques site, southeast Iberian Peninsula. The δ13C values range between −24.91 and −21.19 ‰ (V-PDB), with an average of −23.05 ‰ (STD = 0.69). The archaeological cereals show an average isotopic discrimination (Δ13C) with the past atmospheric CO2 of 16.96 ‰, which is much greater than the average Δ13C of 13.89 ‰ of the rainfed Triticeae (wheat and barley) in modern times. However, considering the effect of the atmospheric CO2 concentration, which is included in the WUEi (intrinsic water-use efficiency), this difference is even greater, 77 for archaeological samples versus 144 for present-day rainfed cereals. This could represent some of the earliest evidence of the use of irrigation techniques in Europe. Modern cereals which have been irrigated show a general Δ13C average of 17.17 ‰, very similar to those of the middle Holocene. However, when the WUEi is calculated, the value of 108 indicates that present-day irrigated cereals are more stressed than the archaeological samples. For comparison, we have included pine trees, since these have an extensive root development which is capable of reaching the water table. In the past, both cereals and pine present similar WUEi values (77 vs. 72), however at present only irrigated cereals show similar WUEi values to pine (108 vs. 107). This again suggests irrigation of cereals in the past. The processes of climatic degradation towards drier conditions which started in the middle Holocene could be responsible for the use of land near water sources, on riverbanks and near shallow lakes. According to the isotopic and plant macrofossil data, irrigation or water management techniques were used at the Terlinques site, located close to the Laguna de Villena, a lake which has now dried out.

Carbon isotope stratigraphy and correlation of depositional sequences in the Upper Ordovician Ely Springs Dolostone, eastern Great Basin, USA

Shallow water carbonate shelf strata of the Ely Springs Dolostone accumulated on the western Laurentian margin as relative sea level fluctuated during the Late Ordovician icehouse. The Ely Springs Dolostone is divided into four upper Katian depositional sequences and one Hirnantian sequence. Here we present new carbon isotope data from the Ely Springs in the context of the sequence stratigraphic architecture. These data derive from a shelf transect of five stratigraphic sections exposed in the eastern Great Basin, USA and provide records of carbon cycling on the Laurentian margin prior to and during the Hirnantian glacial maximum. The δ13C values range between −2‰ and +4‰ at each section, and chemostratigraphic tie points occur in all sections of the transect. Intrabasinal correlations based on the δ13C records are consistent with correlations derived from sequence stratigraphy and conodont biostratigraphy. The Ely Springs Dolostone carbon isotope curve can also be correlated with the late Katian (Cincinnatian) composite derived from epicontinental deposits of the Laurentian midcontinent. The globally documented Hirnantian positive carbon isotope excursion (commonly referred to as “HICE”) occurs within the uppermost depositional sequence immediately below a regional unconformity coinciding with peak glacial conditions on Gondwana. The late Katian Elkhorn and Waynseville δ13C excursions are also present in the Ely Springs Dolostone carbon isotope record. The peak value of the Hirnantian carbon excursion increases from 2.6‰ to 3.8‰ across the shallow shelf and reaches 7.3‰ in coeval limestones of the Hanson Creek Formation deposited in a deep dysoxic setting. This lateral gradient is not the result of changes to the δ13C of weathered carbon supplied by rivers, as previously proposed; it may be instead related to authigenic carbonate cement precipitation during early diagenesis of the Hanson Creek strata. That these pervasively dolomitized shallow water carbonates retain δ13C signatures useful for regional and global stratigraphic correlation indicates that δ13C chemostratigraphy may be an appropriate correlation tool for dolostones with few biostratigraphically useful fossils.

Microstructure-specific carbon isotopic signatures of organic matter from ∼3.5 Ga cherts of the Pilbara Craton support a biologic origin

The ∼3.5 Ga Dresser Formation from the North Pole Dome of the Pilbara Craton (Western Australia) contains some of the oldest evidence for life on Earth. Here, we present a detailed study of microstructure-specific carbon isotopic composition of organic matter (OM) preserved in Dresser Formation bedded cherts and hydrothermal chert vein using in situ Secondary-Ion Mass Spectrometry (SIMS). The OM in these rocks occurs mainly as clots that, together with minor fine OM layers and laminae, are considered primary textures formed prior to host rock lithification. Other than rare OM-rich stylolites, no evidence was found for later OM migration beyond the micrometer scale. Average δ13C(OM) values in specific microstructural types range between −33.6‰ and −25.7‰. No correlation is seen between measured δ13C values and H/C ratios in the studied OM microstructures. This lack of correlation and the low metamorphic grade of the rocks studied argue against significant modification of OM isotopic composition by later metamorphic alteration. It is thus concluded that the range of δ13C values found in the samples represents primary OM isotopic variability. Within some individual samples variable δ13C(OM) values are correlated with specific microstructural types. This observation is not consistent with solely abiotic OM formation via Fisher-Tropsch type reactions. When compared with associated δ13C(ankerite) values, average δ13C(OM) values indicate C isotopic fractionation [Δ13C(Ank–OM)] of 25–33‰, which translates to dissolved CO2–OM isotopic fractionation [Δ13C(CO2–OM)] of 20–30‰. This range of Δ13C(CO2–OM) is consistent with enzymatic C fixation via the Calvin cycle utilized by photoautotrophs and the reductive acetyl-CoA pathway utilized by chemolithoautotrophs. Photosynthetic OM formation is supported by the relatively shallow water depth inferred for the Dresser environment and the restricted occurrence of stromatolites to shallow water deposits in this unit, whereas chemolithosynthesis is supported by the abundance of OM in sub-seafloor hydrothermal chert veins. The range of δ13C(OM) values observed in the samples may therefore represent the remains of different organisms utilizing different C-fixation pathways. Other biologic effects, such as the growth rate and density of microbial communities, and further heterotrophic overprinting of the autotrophic biomass may have also contributed to the observed range of δ13C(OM) values.

Evidence for a subduction component in the diamond-bearing mantle of the Siberian craton

Evidence for the involvement of a subduction component in diamond formation is analyzed based on literature data and our studies. Examination of xenoliths of diamondiferous eclogites, including X-ray tomography analysis, testifies to the superposed character of most diamonds. Diamond generation is accompanied by the serious modification of eclogite substratum. Isotope–geochemical data show that the eclogites originated from oceanic-crust rocks. The oxygen isotope compositions of garnets and clinopyroxenes from websterite xenoliths are similar to the mantle average (5.3–5.6‰). The eclogite minerals vary considerably in oxygen isotope composition (δ18O of 5.3 to 12.4‰). Diamonds of eclogitic paragenesis predominate dramatically in the placers of the northeastern Yakutian diamondiferous province. In placer eclogitic diamonds, δ13C varies from −27.2 to −3‰ (n = 28). In diamonds of ultrabasic paragenesis, the range of δ13C values is much narrower (from −7.1 to −0.5‰). All diamonds of variety V have a lighter carbon isotope composition (from −24.1 to −17.4‰). In a wide range of crystals with a contrasting carbon isotope composition, the isotope composition of the rim tends toward the average mantle value. This suggests that the eclogitic diamonds grew first with the participation of carbon from subducted continental crust and finally with the involvement of mantle carbon.

Variation in camelid δ13C and δ15N values in relation to geography and climate: Holocene patterns and archaeological implications in central western Argentina

Camelids are among the largest wild and domestic faunas in South America and represent one of the most important taxa to pre-hispanic South America human populations. Stable isotope data from these animals play an important role in improving our understanding of human paleodiet, past human-animal interactions, Holocene environmental change, and modern camelid management. This paper presents δ13C and δ15N values taken from 91 camelid specimens distributed across western Argentina between 30° and 37° S. These samples come from three desert environments (Andean, Patagonia, and Monte) and include both modern and prehistoric samples. Camelid δ13C values range between −20.3‰ and −10.7‰, while δ15N values vary between 2‰ and 10.2‰. Mean isotope values differ by environmental context, with significant difference in δ13C and δ15N between Patagonian and Monte or Andean deserts. Camelid isotope values also vary with latitude, altitude and longitude, though differences in δ15N are weak, and these geographic differences are tied to climatic variables such as annual mean temperature, annual precipitation, and season of precipitation. When comparing camelid δ13C values from Central-western Argentina with those from Northwest Argentina and Patagonia, we see a latitudinal trend of decreasing δ13C values, with the most negative values occurring in southern Patagonia and the most positive values in Northwest Argentina. Variation in camelid stable isotope values and their association with particular environmental contexts shows their value as a geographic marker and possibly as a paleoecological proxy. These results highlight the need to consider the geographic origin of camelid isotope values when using them to reconstruct human diet.

Reconstructing Diet of the Early Qin (ca. 700–400 BC) at Xishan, Gansu Province, China

AbstractHere we report the bone collagen carbon and nitrogen isotopic results of humans (n = 33) and animals (n = 58) to reconstruct the dietary practices of an early Qin population dating to the Zhou Dynasty (Late Western–Early Eastern period ca. 700–400 BC) at the Xishan site in Gansu Province, China. The humans have a very large range of δ13C (−23.3‰ to −7.1‰) and δ15N (4.3‰ to 10.9‰) values which reflects extraordinarily diverse diets and included individuals with predominately C3 as well as those with exclusive C4 diets. This wide span of isotopic results produced a subtle linear trend (R2 = 0.62) in the human data, which paralleled the animals across the C3 and C4 environmental gradient. However, the majority of the individuals had a predominately C4 diet based on millet with δ15N results only slightly elevated above the animals, except for the pigs and cattle. This is evidence that many of the animals were likely used for their secondary products, labour or as sacrificial offerings and that pork and beef were the main sources of animal protein for the population. High status individuals had elevated δ15N values (10.2 ± 0.6‰) compared to medium (8.9 ± 0.3‰) and lower status (8.8 ± 0.8‰) individuals, possibly related to increased animal protein in the diet. Differences related to gender were also found with females having elevated δ13C (−11.2 ± 1.9‰) and δ15N (9.4 ± 0.8‰) values compared to the males (δ13C = −14.1 ± 4.2‰; δ15N = 7.9 ± 1.9‰), but these results necessitate caution given the large number of individuals that could not be sexed. The results of this study support the view that the early Qin people were a more sedentary society focused on millet agriculture and animal husbandry, and that they were influenced by the pre‐existing populations of the central Gansu region. Copyright © 2015 John Wiley & Sons, Ltd.

Indigenous aliphatic amines in the aqueously altered Orgueil meteorite

AbstractThe CI1 Orgueil meteorite is a highly aqueously altered carbonaceous chondrite. It has been extensively studied, and despite its extensive degree of aqueous alteration and some documented instances of contamination, several indigenous organic compounds including amino acids, carboxylic acids, and nucleobases have been detected in its carbon‐rich matrix. We recently developed a novel gas chromatographic method for the enantiomeric and compound‐specific isotopic analyses of meteoritic aliphatic monoamines in extracts and have now applied this method to investigate the monoamine content in Orgueil. We detected 12 amines in Orgueil, with concentrations ranging from 1.1 to 332 nmol g−1 of meteorite and compared this amine content in Orgueil with that of the CM2 Murchison meteorite, which experienced less parent‐body aqueous alteration. Methylamine is four times more abundant in Orgueil than in Murchison. As with other species, the amine content in Orgueil extracts shows less structural diversity than that in Murchison extracts. We measured the compound‐specific stable carbon isotopic ratios (δ13C) for 5 of the 12 monoamines detected in Orgueil and found a range of δ13C values from –20 to +59‰. These δ13C values fall into the range of other meteoritic organic compounds, although they are 13C‐depleted relative to their counterparts extracted from the Murchison meteorite. In addition, we measured the enantiomeric composition for the chiral monoamines (R)‐ and (S)‐sec‐butylamine in Orgueil, and found it was racemic within experimental error, in contrast with the l‐enantiomeric excess found for its amino acid structural analog isovaline. The racemic nature of sec‐butylamine in Orgueil was comparable to that previously observed in Murchison, and to other CM2 and CR2 carbonaceous chondrites measured in this work (ALH 83100 [CM1/2], LON 94101 [CM2], LEW 90500 [CM2], LAP 02342 [CR2], and GRA 95229 [CR2]). These results allow us to place some constraints on the effects of aqueous alteration observed over the monoamine concentrations in Orgueil and Murchison, and to evaluate the primordial synthetic relationships between meteoritic monoamines and amino acids.

Paleodietary reconstruction using stable isotopes and abundance analysis of bovids from the Shungura Formation of South Omo, Ethiopia

Preservation of the stable carbon isotopic composition of fossil tooth enamel enables us to estimate the relative proportion of C3 versus C4 vegetation in an animal's diet, which, combined with analysis of faunal abundance, may provide complementary methods of paleoenvironmental reconstruction. To this end, we analyzed stable carbon isotopic composition (δ13C values) of tooth enamel from four bovid tribes (Tragelaphini, Aepycerotini, Reduncini, and Alcelaphini) derived from six members of the Shungura Formation (Members B, C, D, F, G, and L; ages from ca. 2.90–1.05 Ma (millions of years ago) in the Lower Omo Valley of southwestern Ethiopia. The bovids show a wide range of δ13C values within taxa and stratigraphic members, as well as temporal changes in the feeding strategies of taxa analyzed throughout the middle to late Pliocene and early Pleistocene. Such variation suggests that the use of actualistic approaches for paleoenvironmental reconstruction may not always be warranted. Alcelaphini was the only taxon analyzed that retained a consistent dietary preference throughout the sequence, with entirely C4-dominated diets. Reduncini had a mixed C3/C4 to C4-dominated diet prior to 2.4 Ma, after which this taxon shifted to a largely C4-dominated diet. Aepycerotini generally showed a mixed C3/C4 diet, with a period of increased C4 diet from 2.5 to 2.3 Ma. Tragelaphini showed a range of mixed C3/C4 diets, with a median value that was briefly nearer the C4 end member from 2.9 to 2.4 Ma but was otherwise towards the C3 end member. These isotopic results, combined with relative abundance data for these bovids, imply that the environment of the Lower Omo Valley consisted of a mosaic of closed woodlands, with riverine forests and open grasslands. However, our data also signify that the overall environment gradually became more open, and that C4 grasses became more dominant. Finally, these results help document the range and extent of environments and potential diets that were available to the four hominin species encountered in the Shungura sequence.

Investigating Dietary Patterns with Stable Isotope Ratios of Collagen and Starch Grain Analysis of Dental Calculus at the Iron Age Cemetery Site of Heigouliang, Xinjiang, China

AbstractHere, we present δ13C and δ15N results for the dietary reconstruction of nomadic pastoralists from the Iron Age (ca. 1000 bc–8 ad) site of Heigouliang. The human (n = 27) δ13C values range from −19.6‰ to −17.0‰ with a mean value of −18.5 ± 0.5‰, and the δ15N results range from 11.5‰ to 13.8‰ with a mean value of 12.4 ± 0.6‰. The results indicated that animals, like sheep, were part of the predominately C3 terrestrial diet, but two individuals have values greater than −18‰ that is indicative of some input of C4 foods in their diets. Because of a lack of faunal samples and to supply complementary information concerning plant consumption, teeth from four individuals were analysed for dental calculus microfossils. Starch grains were found to correspond to Triticeae and Poaceae, possibly including wheat (Triticum aestivum), barley (Hordeum vulgare), highland barley (H. vulgare L var. nudum), foxtail millet (Setaria italica) and/or common millet (Panicum miliaceum). At the population level, no dietary differences were detected between burial owners and sacrificial victims, but variations were found when specific tombs were analysed. In particular, individuals with bone trauma associated with armed conflict also had distinct isotopic signatures possibly suggesting that some of the sacrificial victims could have been captured warriors that were sacrificed for the burial owners. While limited, the results are some of the first from an Iron Age population from Xinjiang and contribute to our understanding of the dietary patterns of this region. Copyright © 2015 John Wiley & Sons, Ltd.