Seasonal variation in kangaroo tooth enamel oxygen and carbon isotopes in southern Australia

Serial sampling of tooth enamel growth increments for carbon and oxygen isotopic analyses of Macropus (kangaroo) teeth was performed to assess the potential for reconstructing paleoseasonality. The carbon isotope composition of tooth enamel apatite carbonate reflects the proportional intake of C₃ and C₄ vegetation. The oxygen isotopic composition of enamel reflects that of ingested and metabolic water. Tooth enamel forms sequentially from the tip of the crown to the base, so dietary and environmental changes during the tooth's formation can be detected. δ¹³C and δ¹⁸O values were determined for a series of enamel samples drilled from the 3rd and 4th molars of kangaroos that were collected along a 900 km north–south transect in southern Australia. The serial sampling method did not yield pronounced seasonal isotopic variation patterns in Macropus enamel. The full extent of dietary isotopic variation may be obscured by attenuation of the isotopic signal during enamel mineralisation. Brachydont (low-crowned) Macropus teeth may be less sensitive to seasonal variation in isotopic composition due to time-averaging during mineralisation. However, geographic variations observed suggest that there may be potential for tracking latitudinal shifts in vegetation zones and seasonal environmental patterns in response to climate change.     

Inverse methods for estimating primary input signals from time-averaged isotope profiles

Mammalian teeth are invaluable archives of ancient seasonality because they record along their growth axes an isotopic record of temporal change in environment, plant diet, and animal behavior. A major problem with the intra-tooth method is that intra-tooth isotope profiles can be extremely time-averaged compared to the actual pattern of isotopic variation experienced by the animal during tooth formation. This time-averaging is a result of the temporal and spatial characteristics of amelogenesis (tooth enamel formation), and also results from laboratory sampling. This paper develops and evaluates an inverse method for reconstructing original input signals from time-averaged intra-tooth isotope profiles. The method requires that the temporal and spatial patterns of amelogenesis are known for the specific tooth and uses a minimum length solution of the linear system Am = d, where d is the measured isotopic profile, A is a matrix describing temporal and spatial averaging during amelogenesis and sampling, and m is the input vector that is sought. Accuracy is dependent on several factors, including the total measurement error and the isotopic structure of the measured profile. The method is shown to accurately reconstruct known input signals for synthetic tooth enamel profiles and the known input signal for a rabbit that underwent controlled dietary changes. Application to carbon isotope profiles of modern hippopotamus canines reveals detailed dietary histories that are not apparent from the measured data alone. Inverse methods show promise as an effective means of dealing with the time-averaging problem in studies of intra-tooth isotopic variation.     

High-resolution δC intratooth profiles in bovine enamel: Implications for mineralization pattern and isotopic attenuation

We present the first high-resolution carbon isotope and carbonate content profiles generated through the thickness of enamel from a steer fed C₃- then C₄-dominant food. Carbonate contents decrease by ∼2 wt% from the enamel surface to the innermost enamel layer, and each carbon isotope profile shows a mixture of enamel portions mineralized over several months. Downward and outward increasing contribution of C₄ food to the enamel δ¹³C values reveal two components of the mineralization gradient: a vertical component from the tip of the tooth crown to the neck, and a horizontal component from the enamel-dentine junction to the outer enamel. We use our results to infer mineralization parameters for bovines and to calculate expected isotopic attenuations for an array of environmental inputs and microsampling strategies, using the model developed by Passey and Cerling [Geochim. Cosmochim. Acta. 66 (2002) 3225-3234]. Although it seems unlikely that any strategy will perfectly isolate discrete time slices, sampling the innermost enamel layer might offer the advantage of significantly reducing the isotope damping that would become independent of the structure of the input signal.     

Oxygen isotopes of bovid teeth as archives of paleoclimatic variations in archaeological deposits of the Ganga plain, India

Oxygen isotope analysis was performed on enamel phosphate of mammalian teeth from archaeological sites Kalli Pachchhim and Dadupur in the central Ganga plain and Charda in the northern Ganga plain. The bulk oxygen isotopic compositions of enamel phosphate from third molars (M3) of Bos indicus individuals belonging to different cultural periods were used to understand the climatic changes during the past 3600 cal yr B.P. Oxygen isotope ratios indicate humid conditions around 3600 cal yr B.P., followed by a trend toward drier conditions until around 2800 cal yr B.P. Then from 2500 to 1500 cal yr B.P. there is a trend toward higher humidity, followed by the onset of a dry period around 1300 cal yr B.P. The study of intratooth δ¹⁸O variations in teeth from different periods demonstrates that the monsoon seasonality was prominent. Spatial changes in the amount of annual rainfall are also reflected in the δ¹⁸O values. Teeth derived from areas with intense rainfall have lighter isotope ratios compared to teeth from regions receiving less rain, but they show similar seasonal patterns. The long-term paleoclimatic variations reflected by fluctuations in bulk δ¹⁸O_p values from M3 teeth match well with the regional paleoenvironmental records and show a good correlation to the cultural changes that took place during this time span in Ganga plain.     

Diagenesis and the reconstruction of paleoenvironments: A method to restore original δO values of carbonate and phosphate from fossil tooth enamel

Intra-tooth δ¹⁸O variations within the carbonate (δ¹⁸Oc) and phosphate (δ¹⁸Op) components of tooth apatite were measured for Miocene and Pliocene hypsodont mammals from Afghanistan, Greece and Chad in order to evaluate the resistance of enamel to diagenetic alteration. Application of water-apatite interaction models suggest that the different kinetic behaviours of the phosphate-water and carbonate-water systems can be used to detect subtle oxygen isotope disequilibria in fossil enamel when intra-individual variations are considered. Selective alteration of the oxygen isotope composition from the carbonate component of Afghan and Greek enamels suggests inorganic isotopic exchange processes. Microbially-induced isotopic exchange for phosphate is demonstrated for the first time in enamel samples from Chad, in association with extensive recrystallization. In Chad, δ¹⁸Op values were derived from partial isotopic exchange with fossil groundwater during early diagenesis. Mass balance calculations using average carbonate content in enamel as a proxy for recrystallization, and the lowest δ¹⁸Op value of dentine as a proxy for the isotopic composition of the diagenetic fluid, indicate that diagenesis can alter δ¹⁸Op by as much as 3‰ in some enamel samples. This diagenetic alteration is also responsible for a decrease in intra-individual variations of up to 1‰ in affected specimens. The effects of diagenesis on δ¹⁸Op values of fossil enamel are not systematic, however, and can only be estimated if sequential δ¹⁸Op and δ¹⁸Oc analyses are performed on fossil enamel and dentine. Reconstruction of large temporal- or spatial-scale paleoclimates based on δ¹⁸Op analyses from mammalian teeth cannot be considered valid if enamel has been affected by bacterial activity or if the data cannot be corrected for diagenetic effects.     

The isotope record of short- and long-term dietary changes in sheep tooth enamel: Implications for quantitative reconstruction of paleodiets

Quantitative reconstruction of paleodiet by means of sequential sampling and carbon isotope analysis in hypsodont tooth enamel requires a precise knowledge of the isotopic enrichment between dietary carbon and carbon from enamel apatite (ε_D-E), as well as of the timing and duration of the enamel mineralization process (amelogenesis). To better constrain these parameters, we performed a series of controlled feeding experiments on sheep ranging in age from 6 to 24 months-old. Twenty-eight lambs and 14 ewes were fed isotopically distinct diets for different periods of time, and then slaughtered, allowing the timing and rate of molar growth to be determined. High resolution sampling and stable carbon isotope analysis of breath CO₂ performed on six individuals following a diet-switch showed that 70-90% of dietary carbon had turned over in less than 24 h. Sequential sampling and carbon isotopic analysis was performed on the first (M₁) and second (M₂) lower molars of four lambs as well as on the third lower molar (M₃) of 11 ewes. The changes in diet were recorded in all molars. We found that the length of enamel matrix apposition is approximately one-quarter of the final tooth length during crown extension, and that enamel maturation spans slightly less than 3 months in M₁, and 4 months in M₂ and M₃. Portions of enamel in equilibrium with dietary carbon were used to calculate ε_D-E values. Animals on grass silage diets had values similar to previous observations, whereas animal switched to pelleted corn diets had values ca. 4‰ lower, a pattern consistent with lower methane production observed for animals fed concentrate diets. The tooth enamel forward model of Passey and Cerling (2002) closely predicted the amplitude of isotope changes recorded in tooth enamel, but slightly underestimated the rate of isotope change, suggesting that the rate of accumulation of carbonate during maturation may not be constant over time. Although stable isotope profiles in tooth enamel represent underdetermined systems, our results demonstrate that they can provide useful information about dietary variability if the mineralization process is taken into account.     

Analysis of coupled Sr/Ca and Sr/Sr variations in enamel using laser-ablation tandem quadrupole-multicollector ICPMS

We present in this study results obtained with a laser-ablation coupled with both a quadrupole and a multi-collector ICPMS. The simultaneous in situ Sr/Ca and ⁸⁷Sr/⁸⁶Sr measurements along growth profiles in enamel allows the concomitant diet and migration patterns in mammals to be reconstructed. Aliquots of the powdered international standard NIST “SRM1400 Bone Ash” with certified Sr and Ca contents, was sintered at high pressure and temperature and was adopted as the reference material for external reproducibility and calibration of the results. A total of 145 coupled elemental and isotopic measurements of herbivores enamel from the Kruger National Park, South Africa, gives intra-tooth Sr/Ca and ⁸⁷Sr/⁸⁶Sr variations that are well larger than external reproducibility. Sr/Ca profiles systematically decrease from the dentine-enamel junction to the outer enamel whereas ⁸⁷Sr/⁸⁶Sr profiles exhibit variable patterns. Using a simple geometric model of hypsodont teeth growth, we demonstrate that a continuous recording of the ⁸⁷Sr/⁸⁶Sr variations can be reconstructed in the tooth length axis. This suggests that the mobility of a mammal can be reconstructed over a period of more than a year with a resolution of a ten of days, by sampling enamel along growth profiles. Our geometric model of hypsodont teeth growth predicts that an optimal distance between two successive profiles is equal to the enamel thickness. However, this model does not apply to the Sr/Ca signal which is likely to be altered during the enamel maturation stage due to differential maturation processes along enamel thickness. Here, the observed constant decreases of the Sr/Ca ratios in the ungulates of Kruger National Park suggests that they did not changed of diet, while some of them were migrating.     

Carbon isotope composition of graptolite periderm and whole-rock from the Aeronian (Silurian, Llandovery) in Wales and Scotland and its use in chemostratigraphy

Here we show the use of graptolite periderm for chemostratigraphic study. Using material from the Aeronian (Silurian) interval from Wales and Scotland as examples, we show that the carbon isotope composition of the periderm (δ¹³C_grap.) provides a signal that is locally different but not consistently so from surrounding whole-rock samples (δ¹³C_whole-rock). Graptolite periderm δ¹³C seems not influenced by astogenetic stage of development or gross rhabdosome type and differences between δ¹³C_grap. from different metamorphic grades are minimal. Taken as a whole, the Aeronian interval examined shows little overall change, but large variations are seen on the small scale, possibly reflecting very local carbon cycling. For carbon isotope stratigraphy in such rocks, therefore, large-scale bulk sampling will likely reduce inhomogeneities and give more reproducible results. Furthermore, in situations (for instance associated with sea level fluctuations) where terrestrial organic matter has been incorporated into the sediment, then graptolite carbon may more faithfully reflect bulk marine organic matter.     

Modelling stalagmite growth and δC as a function of drip interval and temperature

Growth and stable isotope composition of stalagmites are affected by climate changes. To understand the underlying mechanisms, we developed a time dependent multi-box model that describes stalagmite growth and stable isotope fractionation of carbon under disequilibrium conditions. The model takes variations of the drip interval, temperature and the amount of mixing between the impinging drops and the solution on top of the stalagmite into account, which allows to quantify the influence of these parameters. To calculate the variations of δ¹³C, the multi-box model was calibrated by comparison with an existing growth model. The results show that drip interval, temperature and the mixing coefficient do have a significant influence on δ¹³C. However, considering the higher natural variability of the drip interval, this parameter might have the largest influence.     

Oxygen isotopic composition of mammalian skeletal phosphate from the Natufian Period,Hayonim Cave,Israel: Diagenesis and paleoclimate

Recent and fossil (prehistoric, Natufian) gazelle bones, dentin and enamel were analyzed for their oxygen isotopic composition (δ¹⁸O) of the phosphate and carbonate, as well as their crystallinity. Fossil bones and dentin have better crystallinity than recent specimens, indicating diagenetic change. Fossil enamel, on the other hand, is identical in crystallinity to recent enamel, indicating the lack of diagenetic alteration. Comparison of δ¹⁸O of carbonate and phosphate of the skeletal elements suggests that the coexisting phosphate and carbonate of both the recent and fossil specimens are close to isotopic equilibrium. This might suggest that both phases were affected by the same degree of diagenetic alteration, and that comparison of their δ¹⁸O is not useful for the selection of pristine material for paleoclimatic reconstruction purposes. Oxygen isotope analysis of gazelle enamel from the Natufian period from Hayonim Cave, Israel, show depletion in δ¹⁸O in comparison with recent enamel. This depletion is interpreted to represent a colder and/or wetter climate in the Natufian of northern Israel. © 1999 John Wiley & Sons, Inc.     

Assessment of grain-scale homogeneity and equilibration of carbon and oxygen isotope compositions of minerals in carbonate-bearing metamorphic rocks by ion microprobe

Nineteen samples of metamorphosed carbonate-bearing rocks were analyzed for carbon and oxygen isotope ratios by ion microprobe with a ∼5-15 μm spot, three from a regional terrain and 16 from five different contact aureoles. Contact metamorphic rocks further represent four groups: calc-silicate marble and hornfels (6), brucite marble (2), samples that contain a reaction front (4), and samples with a pervasive distribution of reactants and products of a decarbonation reaction (4). The average spot-to-spot reproducibility of standard calcite analyses is ±0.37‰ (2 standard deviations, SD) for δ¹⁸O and ±0.71‰ for δ¹³C. Ten or more measurements of a mineral in a sample that has uniform isotope composition within error of measurement can routinely return a weighted mean with a 95% confidence interval of 0.09-0.16‰ for δ¹⁸O and 0.10-0.29‰ for δ¹³C. Using a difference of >6SD as the criterion, only four of 19 analyzed samples exhibit significant intracrystalline and/or intercrystalline inhomogeneity in δ¹³C at the 100-500 μm scale, with differences within individual grains up to 3.7‰. Measurements are consistent with carbon isotope exchange equilibrium between calcite and dolomite in five of six analyzed samples at the same scale. Because of relatively slow carbon isotope diffusion in calcite and dolomite, differences in δ¹³C can survive intracrystalline homogenization by diffusion during cooling after peak metamorphism and likely represent the effects of prograde decarbonation and infiltration. All but 2 of 11 analyzed samples exhibit intracrystalline differences in δ¹⁸O (up to 9.4‰), intercrystalline inhomogeneity in δ¹⁸O (up to 12.5‰), and/or disequilibrium oxygen isotope fractionations among calcite-dolomite, calcite-quartz, and calcite-forsterite pairs at the 100-500 μm scale. Inhomogeneities in δ¹⁸O and δ¹³C are poorly correlated with only a single mineral (dolomite) in a single sample exhibiting both. Because of relatively rapid oxygen isotope diffusion in calcite, intracrystalline inhomogeneities in δ¹⁸O likely represent partial equilibration between calcite and fluid during retrograde metamorphism. Calcite is in oxygen isotope exchange equilibrium with forsterite in one of four analyzed samples, in equilibrium with dolomite in none of six analyzed samples, and in equilibrium with quartz in neither of two analyzed samples. There are no samples of contact metamorphic rock with analyzed reactants and products of an arrested metamorphic reaction that are in oxygen isotope equilibrium with each other. The degree of departure from equilibrium in analyzed samples is variable and is often related, at least in part, to alteration of δ¹⁸O of calcite during retrograde fluid-rock reaction. In situ sub-grain-scale carbon and oxygen isotope analyses of minerals are advisable in the common applications of stable isotope geochemistry to metamorphic petrology. Correlation of sub-mm scale stable isotope data with imaging will lead to improved understanding of reaction kinetics, reactive fluid flow, and thermal histories during metamorphism.     

Oxygen isotope compositions and magmatic epidote from two contrasting metaluminous granitoids,NE Brazil

Oxygen isotope compositions of mineral separates were determined from two metaluminous granitoids (Emas and São Rafael plutons) from northeastern Brazil. The I-type Emas pluton has high δ¹⁸O (WR) values (11.5–11.8‰), whereas the São Rafael pluton has low δ¹⁸O (WR) values (7.5–8.1‰), but Sr and Nd are characteristics of S-type granitoids. Measured mineral–mineral fractionations suggest continuous sub-solidus inter-mineral isotope exchange among all minerals except zircon. There is a large and consistent quartz–epidote fractionation that gives apparent temperatures that are much lower than anticipated closure temperatures for epidote. Oxygen isotope fractionation between natural zircon and magmatic epidote is opposite to that predicted from theoretical determinations, as δ¹⁸O (epidote) <δ¹⁸O (zircon). An empirical calibration based on these results would suggests a closure T for oxygen in epidote of ~500 °C and Δ(qtz–epi) ~5.19 at 500 °C.     

Iron Isotopic Compositions of Forearc Mantle Peridotites Constrained by Ophiolites from the North Qilian Orogen,Northern Tibet

Previous studies on iron isotope compositions of subduction zone magmas have revealed significant and complex variations that have great bearings on petrogenetic processes in the mantle wedge, e.g., partial melting, fluid metasomatism and redox state. However, interpretations for the fractionations are highly debatable and lack direct constraints from mantle wedge peridotites. This study presents iron isotope compositions for whole rocks and mineral separates in fresh forearc peridotites from the Yushigou ophiolite, North Qilian orogen in northern Tibet. Major and trace element compositions of whole rock and mineral indicate that the peridotites are highly depleted forearc peridotites overprinted by melt metasomatism, in contrast to the long‐holding opinion that the peridotites are derived from mid‐oceanic ridges. The minerals fall on a line with a slope of ～1 on the plot of δ⁵⁶Fe vs. δ⁵⁶Fe, indicating isotope equilibrium between minerals. δ⁵⁶Fe fractionation between olivine and orthopyroxene is within the range of 0～0.05, while fractionation between olivine and spinel is about 0.05～0.10. The fractionation trend between olivine and spinel is opposite to previous theoretical and experimental constraints, which may be due to substantial Cr substitution into the spinel. This indicates that negative correlations between spinel Cr#, fO₂ and spinel δ⁵⁶Fe in previous studies are probably a reflection of gradual Cr enrichment in spinel during melt extraction, and spinel δ⁵⁶Fe values are not a proxy for oxygen fugacity. Whole rock δ⁵⁶Fe values are well correlated with mineral δ⁵⁶Fe values, varying from overlapping with depleted mantle to slightly lower than depleted mantle. Therefore, variations in iron isotope compositions of subduction zone magmas are probably due to combined effect of source heterogeneity and partial melting fractionation.     

Discovery of Early Proterozoic Carbon Isotope Shifts

The authors have detailedly and systematically studied the carbon isotopic composition of Early Proterozoic carbonate rocks. Samples which are all dolomicrite were taken from the Jianancun, Daguandong and Huaiyincun Formations of the Hutuo Group in Wutai County Shanxi Province, North China. A total of 209 samples were analysed for their carbon isotope compositions, and the mean sampling interval was 6.9 m. Carbon isotope analysis clearly shows δ13C shifts at the boundary between the Jian'ancun Formation and Daguandong Formation and near the boundary between the Daguandong Formation and Huaiyincun Formation. Like carbon isotope shifts at the Cretaceous-Tertiary, Permian-Triassic and Precambrian-Cambrian boundaries, the discovery of δ13C shifts in the Early Proterozoic has important significance in further studies on Early Proterozoic biotic evolution, regional and global stratigraphic correlation, and carbon geochemical cycles.     

Experimentally-controlled carbon and oxygen isotope exchange between bioapatites and water under inorganic and microbially-mediated conditions

Modern bone and enamel powders have reacted at 301 K with ¹³C- and ¹⁸O-labelled waters under inorganic and microbial conditions. The aim of the study is to investigate the resistance of stable isotope compositions of bioapatite carbonate (δ¹³C, δ¹⁸Oc) and phosphate (δ¹⁸Op) to isotopic alteration during early diagenesis. Rapid and significant carbon and oxygen isotope changes were observed in the carbonate and phosphate fractions of bone apatite before any detectable change occurred in the crystallinity or organic matter content. These observations indicate that chemical alterations of bone apatite are likely to start within days of death. Enamel crystallites are much more resistant than bone crystallites, but are not exempt of alteration. Non removable carbon and oxygen isotope enrichments were measured in the carbonate phase of bone (50-90%) and enamel (40%) after the acetic acid treatment. This result indicates that a significant part of ¹³C and ¹⁸O-labelled coming from the aqueous fluid has been durably incorporated into the apatite structure, probably through isotopic exchange or secondary carbonate apatite precipitation. As a result, acetic acid pre-treatments that are currently used to remove exogenous material by selective dissolution, are not adequate to restore pristine δ¹³C and δ¹⁸Oc values of fossil apatites. Under inorganic conditions, kinetics of oxygen isotope exchange are 10 times faster in carbonate than in phosphate. On the opposite, during biologically-mediated reactions, the kinetics of oxygen isotope exchange between phosphate and water is, at least, from 2 to 15 times faster than between carbonate and water. Enamel is a more suitable material than bone for paleoenvironmental or paleoclimatical reconstructions, but interpretations of δ¹⁸Op or δ¹³C values must be restricted to specimens for which no or very limited trace of microbial activity can be detected.     

Controls on the stable isotope composition of seasonal growth bands in aragonitic fresh-water bivalves (unionidae)

Water temperature, oxygen isotope composition and the δ¹³C of dissolved inorganic carbon were measured in 2 southern Michigan rivers, the Huron River and Fleming Creek, between late September 1990 and June 1992. The final full year of shell growth in 3 unionids collected in 1992 from these rivers was sampled for stable isotope analysis with a resolution of 30 μm. The δ¹⁸O of both shell nacre and the prismatic layer is accurately predicted by a fractionation relationship developed for biogenic aragonite. High resolution sampling of 3 species and bulk sampling of 3 other species suggest that all unionids adhere to this oxygen isotope fractionation relationship. This relationship is used to show that shell growth ceases below approximately 12°C. In these 2 settings the average δ¹⁸O value of shell (PDB scale) is within 0.5‰ of the average δ¹⁸O of river water (SMOW scale). Unionids can therefore be used in oxygen-isotope-based paleoclimatic and paleohydrologic reconstructions. In contrast, the carbon isotope ratio of shell is not accurately predicted by published fractionation factors between D.I.C. and carbonate. Shell δ¹³C is more negative than predicted values and the offset is highly variable suggesting a significant and variable incorporation of metabolic carbon into the shell carbonate.     

Cyclostratigraphy and high-frequency carbon isotope fluctuations in Upper Cretaceous shallow-water carbonates, southern Italy

Abstract A detailed carbon isotope study has been carried out on a Santonian (Upper Cretaceous) carbonate platform succession that crops out at Monte Sant'Erasmo (southern Italy). Previous centimetre‐scale studies on this succession have shown that high‐frequency eustatic changes, resulting from the Earth's orbital fluctuations, controlled the hierarchical organization of the depositional and early diagenetic features in elementary cycles, bundles (groups of three to five elementary cycles) and superbundles (groups of three or four bundles). The elementary cycles, which correspond to single beds, suggest a control caused by Earth's precession; the bundles and superbundles record the short (≈ 100 kyr) and long (≈ 400 kyr) eccentricity periodicity respectively. The δ¹³C signal of the Monte Sant'Erasmo succession is cyclic in nature and may be considered to be a reliable proxy for the sedimentary evolution (and related sea‐level history) of the analysed sequence. The carbon isotope cyclicity is recorded at bundle and superbundle level, but it is not evident at the scale of the elementary cycles, at least with the sampling interval used in this study. Spectral analysis of the δ¹³C record shows two main peaks corresponding to the short‐ and long‐eccentricity periodicity, whereas the precession signal is not evident in the power spectrum. In addition, lithofacies analysis shows that, in each bundle (and superbundle), higher C isotope values occur in sediments characterized by marine cements, whereas lower values are normally found in more restricted deposits overprinted by early meteoric diagenesis. Early diagenesis, driven by periodic sea‐level fluctuations, developed in either shallow‐subtidal (marine diagenesis) or subaerial‐exposed (meteoric overprint) sedimentary environments and directly influenced the carbon isotope signature. As a consequence, the δ¹³C record at Monte Sant'Erasmo reflects high‐frequency climatic oscillations controlling both environmental and early diagenetic changes. The long‐term isotopic record is similar to that of contemporaneous pelagic sections in England and elsewhere in Italy. It is concluded that the δ¹³C signature of shallow‐water carbonates, such as those of Monte Sant'Erasmo, offers great potential for correlation with coeval sections, including those of the pelagic realm.     

Lithium isotope geochemistry of marine pore waters - Insights from cold seep fluids

Lithium concentration and isotope data (δ⁷Li) are reported for pore fluids from 18 cold seep locations together with reference fluids from shallow marine environments, a sediment-hosted hydrothermal system and two Mediterranean brine basins. The new reference data and literature data of hydrothermal fluids and pore fluids from the Ocean Drilling Program follow an empirical relationship between Li concentration and δ⁷Li (δ⁷Li = −6.0(±0.3) · ln[Li] + 51(±1.2)) reflecting Li release from sediment or rocks and/or uptake of Li during mineral authigenesis. Cold seep fluids display δ⁷Li values between +7.5‰ and +45.7‰, mostly in agreement with this general relationship. Ubiquitous diagenetic signals of clay dehydration in all cold seep fluids indicate that authigenic smectite-illite is the major sink for light pore water Li in deeply buried continental margin sediments. Deviations from the general relationship are attributed to the varying provenance and composition of sediments or to transport-related fractionation trends. Pore fluids on passive margins receive disproportionally high amounts of Li from intensely weathered and transported terrigenous matter. By contrast, on convergent margins and in other settings with strong volcanogenic input, Li concentrations in pore water are lower because of intense Li uptake by alteration minerals and, most notably, adsorption of Li onto smectite. The latter process is not accompanied by isotope fractionation, as revealed from a separate study on shallow sediments. A numerical transport-reaction model was applied to simulate Li isotope fractionation during upwelling of pore fluids. It is demonstrated that slow pore water advection (order of mm a⁻¹) suffices to convey much of the deep-seated diagenetic Li signal into shallow sediments. If carefully applied, Li isotope systematics may, thus, provide a valuable record of fluid/mineral interaction that has been inherited several hundreds or thousands of meters below the actual seafloor fluid escape structure.     

Late Pleistocene climatic change in the French Jura (Gigny) recorded in the δO of phosphate from ungulate tooth enamel

Oxygen isotope compositions of phosphate in tooth enamel from large mammals (i.e. horse and red deer) were measured to quantify past mean annual air temperatures and seasonal variations between 145 ka and 33 ka in eastern France. The method is based on interdependent relationships between the δ¹⁸O of apatite phosphate, environmental waters and air temperatures. Horse (Equus caballus germanicus) and red deer (Cervus elaphus) remains have δ¹⁸O values that range from 14.2‰ to 17.2‰, indicating mean air temperatures between 7°C and 13°C. Oxygen isotope time series obtained from two of the six horse teeth show a sinusoidal-like signal that could have been forced by temperature variations of seasonal origin. Intra-tooth oxygen isotope variations reveal that at 145 ka, winters were colder (? 7 ± 2°C) than at present (3 ± 1°C) while summer temperatures were similar. Winter temperatures mark a well-developed West–East thermal gradient in France of about ? 9°C, much stronger than the ?4°C difference recorded presently. Negative winter temperatures were likely responsible for the extent and duration of the snow cover, thus limiting the food resources available for large ungulates with repercussions for Neanderthal predators.     

Carbon and oxygen stable isotope compositions of late Pleistocene mammal teeth from dolines of Ajoie (Northwestern Switzerland)

Fossils of megaherbivores from eight late Pleistocene ¹⁴C- and OSL-dated doline infillings of Ajoie (NW Switzerland) were discovered along the Transjurane highway in the Swiss Jura. Carbon and oxygen analyses of enamel were performed on forty-six teeth of large mammals (Equus germanicus, Mammuthus primigenius, Coelodonta antiquitatis, and Bison priscus), coming from one doline in Boncourt (~ 80 ka, marine oxygen isotope stage MIS5a) and seven in Courtedoux (51–27 ka, late MIS3), in order to reconstruct the paleoclimatic and paleoenvironmental conditions of the region. Similar enamel δ¹³C values for both periods, ranging from − 14.5 to − 9.2‰, indicate that the megaherbivores lived in a C₃ plant-dominated environment. Enamel δ¹⁸O_PO4 values range from 10.9 to 16.3‰ with a mean of 13.5 ± 1.0‰ (n = 46). Mean air temperatures (MATs) were inferred using species-specific δ¹⁸O_PO4–δ¹⁸O_H2O-calibrations for modern mammals and a present-day precipitation δ¹⁸O_H2O-MAT relation for Switzerland. Similar average MATs of 6.6 ± 3.6°C for the deposits dated to ~ 80 ka and 6.5 ± 3.3°C for those dated to the interval 51–27 ka were estimated. This suggests that these mammals in the Ajoie area lived in mild periods of the late Pleistocene with MATs only about 2.5°C lower than modern-day temperatures.