Long-term data set analysis of stable isotopic composition in German rivers

NASA Astrophysics Data System (ADS)

Reckerth, Anne; Stichler, Willibald; Schmidt, Axel; Stumpp, Christine

2017-09-01

Stable isotopes oxygen-18 (18O) and deuterium (2H) are commonly used to investigate hydrological processes in catchments. However, only a few isotope studies have been conducted on a large scale and rarely over long time periods. The objective of this study was to identify the spatial and seasonal variability of isotopic composition in river water and how it is affected by geographical and hydrological factors. The stable isotopic composition of river water has been measured in nine large river catchments in Germany for a time period of 12 years or 26 years. We conducted time series and correlation analyses to identify spatial and temporal patterns of the isotopic composition in the rivers. Further, we compared it to isotopic composition in local precipitation and catchments characteristics. In the majority of the rivers, the spatial and temporal patterns of precipitation were directly reflected in river water. The isotopic signals of the river water were time shifted and show attenuated amplitudes. Further deviations from isotopic compositions in local precipitation were observed in catchments with complex flow systems. These deviations were attributed to catchment processes and influences like evaporation, damming and storage. The seasonality of the isotopic composition was mainly determined by the discharge regimes of the rivers. We found correlations between isotopic long-term averages and catchment altitude as well as latitude and longitude, resulting in a northwest-southeast gradient. Furthermore, it was shown that long-term averages of d-excess were inversely related to flow length and catchment size, which indicates that evaporation enrichment has an impact on the isotopic composition even in catchments of humid climates. This study showed that isotopic composition in rivers can serve as a proxy for the local precipitation and can be utilized as an indicator for hydrological processes even in large river basins. In future, such long time series will help to also understand the impact of changes in the hydrological cycle on the larger scales. They can also be used for calibration and validation of flow and transport models at catchment and sub-catchment scale.

Stable water isotope patterns in a climate change hotspot: the isotope hydrology framework of Corsica (western Mediterranean).

PubMed

van Geldern, Robert; Kuhlemann, Joachim; Schiebel, Ralf; Taubald, Heinrich; Barth, Johannes A C

2014-06-01

The Mediterranean is regarded as a region of intense climate change. To better understand future climate change, this area has been the target of several palaeoclimate studies which also studied stable isotope proxies that are directly linked to the stable isotope composition of water, such as tree rings, tooth enamel or speleothems. For such work, it is also essential to establish an isotope hydrology framework of the region of interest. Surface waters from streams and lakes as well as groundwater from springs on the island of Corsica were sampled between 2003 and 2009 for their oxygen and hydrogen isotope compositions. Isotope values from lake waters were enriched in heavier isotopes and define a local evaporation line (LEL). On the other hand, stream and spring waters reflect the isotope composition of local precipitation in the catchment. The intersection of the LEL and the linear fit of the spring and stream waters reflect the mean isotope composition of the annual precipitation (δP) with values of-8.6(± 0.2) ‰ for δ(18)O and-58(± 2) ‰ for δ(2)H. This value is also a good indicator of the average isotope composition of the local groundwater in the island. Surface water samples reflect the altitude isotope effect with a value of-0.17(± 0.02) ‰ per 100 m elevation for oxygen isotopes. At Vizzavona Pass in central Corsica, water samples from two catchments within a lateral distance of only a few hundred metres showed unexpected but systematic differences in their stable isotope composition. At this specific location, the direction of exposure seems to be an important factor. The differences were likely caused by isotopic enrichment during recharge in warm weather conditions in south-exposed valley flanks compared to the opposite, north-exposed valley flanks.

Isotopic composition of high-activity particles released in the Chernobyl accident.

PubMed

Osuch, S; Dabrowska, M; Jaracz, P; Kaczanowski, J; Le Van Khoi; Mirowski, S; Piasecki, E; Szeflińska, G; Szefliński, Z; Tropiło, J

1989-11-01

Gamma spectra were measured and activities of the detected isotopes were analyzed for 206 high-activity particles (hot particles, HPs) found in northeastern Poland after the Chernobyl accident. The isotopic composition of HPs observed in gamma-activity is compared with that of the general fallout and core inventory calculations. Particle formation and a process of depletion in Ru and Cs isotopes are discussed. On the basis of a search performed a year later, some comments on the behavior of HPs in the soil are made.

The stable isotope composition of nitrogen and carbon and elemental contents in modern and fossil seabird guano from Northern Chile - Marine sources and diagenetic effects.

PubMed

Lucassen, Friedrich; Pritzkow, Wolfgang; Rosner, Martin; Sepúlveda, Fernando; Vásquez, Paulina; Wilke, Hans; Kasemann, Simone A

2017-01-01

Seabird excrements (guano) have been preserved in the arid climate of Northern Chile since at least the Pliocene. The deposits of marine organic material in coastal areas potentially open a window into the present and past composition of the coastal ocean and its food web. We use the stable isotope composition of nitrogen and carbon as well as element contents to compare the principal prey of the birds, the Peruvian anchovy, with the composition of modern guano. We also investigate the impact of diagenetic changes on the isotopic composition and elemental contents of the pure ornithogenic sediments, starting with modern stratified deposits and extending to fossil guano. Where possible, 14C systematics is used for age information. The nitrogen and carbon isotopic composition of the marine prey (Peruvian anchovy) of the birds is complex as it shows strong systematic variations with latitude. The detailed study of a modern profile that represents a few years of guano deposition up to present reveals systematic changes in nitrogen and carbon isotopic composition towards heavier values that increase with age, i.e. depth. Only the uppermost, youngest layers of modern guano show compositional affinity to the prey of the birds. In the profile, the simultaneous loss of nitrogen and carbon occurs by degassing, and non-volatile elements like phosphorous and calcium are passively enriched in the residual guano. Fossil guano deposits are very low in nitrogen and low in carbon contents, and show very heavy nitrogen isotopic compositions. One result of the study is that the use of guano for tracing nitrogen and carbon isotopic and elemental composition in the marine food web of the birds is restricted to fresh material. Despite systematic changes during diagenesis, there is little promise to retrieve reliable values of marine nitrogen and carbon signatures from older guano. However, the changes in isotopic composition from primary marine nitrogen isotopic signatures towards very heavy values generate a compositionally unique material. These compositions trace the presence of guano in natural ecosystems and its use as fertilizer in present and past agriculture.

The stable isotope composition of nitrogen and carbon and elemental contents in modern and fossil seabird guano from Northern Chile – Marine sources and diagenetic effects

PubMed Central

Pritzkow, Wolfgang; Rosner, Martin; Sepúlveda, Fernando; Vásquez, Paulina; Wilke, Hans; Kasemann, Simone A.

2017-01-01

Seabird excrements (guano) have been preserved in the arid climate of Northern Chile since at least the Pliocene. The deposits of marine organic material in coastal areas potentially open a window into the present and past composition of the coastal ocean and its food web. We use the stable isotope composition of nitrogen and carbon as well as element contents to compare the principal prey of the birds, the Peruvian anchovy, with the composition of modern guano. We also investigate the impact of diagenetic changes on the isotopic composition and elemental contents of the pure ornithogenic sediments, starting with modern stratified deposits and extending to fossil guano. Where possible, 14C systematics is used for age information. The nitrogen and carbon isotopic composition of the marine prey (Peruvian anchovy) of the birds is complex as it shows strong systematic variations with latitude. The detailed study of a modern profile that represents a few years of guano deposition up to present reveals systematic changes in nitrogen and carbon isotopic composition towards heavier values that increase with age, i.e. depth. Only the uppermost, youngest layers of modern guano show compositional affinity to the prey of the birds. In the profile, the simultaneous loss of nitrogen and carbon occurs by degassing, and non-volatile elements like phosphorous and calcium are passively enriched in the residual guano. Fossil guano deposits are very low in nitrogen and low in carbon contents, and show very heavy nitrogen isotopic compositions. One result of the study is that the use of guano for tracing nitrogen and carbon isotopic and elemental composition in the marine food web of the birds is restricted to fresh material. Despite systematic changes during diagenesis, there is little promise to retrieve reliable values of marine nitrogen and carbon signatures from older guano. However, the changes in isotopic composition from primary marine nitrogen isotopic signatures towards very heavy values generate a compositionally unique material. These compositions trace the presence of guano in natural ecosystems and its use as fertilizer in present and past agriculture. PMID:28594902

The ruthenium isotopic composition of the oceanic mantle

NASA Astrophysics Data System (ADS)

Bermingham, K. R.; Walker, R. J.

2017-09-01

The approximately chondritic relative, and comparatively high absolute mantle abundances of the highly siderophile elements (HSE), suggest that their concentrations in the bulk silicate Earth were primarily established during a final ∼0.5 to 1% of ;late accretion; to the mantle, following the cessation of core segregation. Consequently, the isotopic composition of the HSE Ru in the mantle reflects an amalgamation of the isotopic compositions of late accretionary contributions to the silicate portion of the Earth. Among cosmochemical materials, Ru is characterized by considerable mass-independent isotopic variability, making it a powerful genetic tracer of Earth's late accretionary building blocks. To define the Ru isotopic composition of the oceanic mantle, the largest portion of the accessible mantle, we report Ru isotopic data for materials from one Archean and seven Phanerozoic oceanic mantle domains. A sample from a continental lithospheric mantle domain is also examined. All samples have identical Ru isotopic compositions, within analytical uncertainties, indicating that Ru isotopes are well mixed in the oceanic mantle, defining a μ100Ru value of 1.2 ± 7.2 (2SD). The only known meteorites with the same Ru isotopic composition are enstatite chondrites and, when corrected for the effects of cosmic ray exposure, members of the Main Group and sLL subgroup of the IAB iron meteorite complex which have a collective CRE corrected μ100Ru value of 0.9 ± 3.0. This suggests that materials from the region(s) of the solar nebula sampled by these meteorites likely contributed the dominant portion of late accreted materials to Earth's mantle.

Sm-Nd and Rb-Sr Ages for MIL 05035: Implications for Surface and Mantle Sources

NASA Technical Reports Server (NTRS)

Nyquist, L. E.; Shih, C-Y.; Reese, Y. D.

2007-01-01

The Sm-Nd and Rb-Sr ages and also the initial Nd and Sr isotopic compositions of MIL 05035 are the same as those of A-881757. Comparing the radiometric ages of these meteorites to lunar surface ages as modeled from crater size-frequency distributions as well as the TiO2 abundances and initial Sr-isotopic compositions of other basalts places their likely place of origin as within the Australe or Humboldtianum basins. If so, a fundamental west-east lunar asymmetry in compositional and isotopic parameters that likely is due to the PKT is implied.

Millimeter-scale variations of stable isotope abundances in carbonates from banded iron-formations in the Hamersley Group of Western Australia

NASA Technical Reports Server (NTRS)

Baur, M. E.; Hayes, J. M.; Studley, S. A.; Walter, M. R.

1985-01-01

Several diamond drill cores from formations within the Hamersley Group of Western Australia have been studied for evidence of short-range variations in the isotopic compositions of the carbonates. For a set of 32 adjacent microbands analyzed in a specimen from the Marra Mamba Iron Formation, carbon isotope compositions of individual microbands ranged from -2.8 to -19.8 per mil compared to PDB and oxygen isotope compositions ranged from 10.2 to 20.8 per mil compared to SMOW. A pattern of alternating abundances was present, with the average isotopic contrasts between adjacent microbands being 3.0 per mil for carbon and 3.1 per mil for oxygen. Similar results were obtained for a suite of 34 microbands (in four groups) from the Bruno's Band unit of the Mount Sylvia Formation. Difficulties were experienced in preparing samples of single microbands from the Dales Gorge Member of the Brockman Iron Formation, but overall isotopic compositions were in good agreement with values reported by previous authors. Chemical analyses showed that isotopically light carbon and oxygen were correlated with increased concentrations of iron. The preservation of these millimeter-scale variations in isotopic abundances is interpreted as inconsistent with a metamorphic origin for the isotopically light carbon in the BIF carbonates. A biological origin is favored for the correlated variations in 13C and Fe, and it is suggested that the 13C-depleted carbonates may derive either from fermentative metabolism or from anaerobic respiration. A model is presented in which these processes occur near the sediment-water interface and are coupled with an initial oxidative precipitation of the iron.

Magnesium isotope evidence that accretional vapour loss shapes planetary compositions

PubMed Central

Hin, Remco C.; Coath, Christopher D.; Carter, Philip J.; Nimmo, Francis; Lai, Yi-Jen; Pogge von Strandmann, Philip A.E.; Willbold, Matthias; Leinhardt, Zoë M.; Walter, Michael J.; Elliott, Tim

2017-01-01

It has long been recognised that Earth and other differentiated planetary bodies are chemically fractionated compared to primitive, chondritic meteorites and by inference the primordial disk from which they formed. An important question has been whether the notable volatile depletions of planetary bodies are a consequence of accretion1, or inherited from prior nebular fractionation2. The isotopic compositions of the main constituents of planetary bodies can contribute to this debate3–6. Using a new analytical approach to address key issues of accuracy inherent in conventional methods, we show that all differentiated bodies have isotopically heavier magnesium compositions than chondritic meteorites. We argue that possible magnesium isotope fractionation during condensation of the solar nebula, core formation and silicate differentiation cannot explain these observations. However, isotopic fractionation between liquid and vapour followed by vapour escape during accretionary growth of planetesimals generates appropriate residual compositions. Our modelling implies that the isotopic compositions of Mg, Si and Fe and the relative abundances of the major elements of Earth, and other planetary bodies, are a natural consequence of substantial (~40% by mass) vapour loss from growing planetesimals by this mechanism. PMID:28959965

Comparing spatial and temporal patterns of river water isotopes across networks

EPA Science Inventory

A detailed understanding of the spatial and temporal dynamics of water sources across river networks is central to managing the impacts of climate change. Because the stable isotope composition of precipitation varies geographically, variation in surface-water isotope signatures ...

Stable Isotope Systematics in Grasshopper Assemblages Along an Elevation Gradient, Colorado

NASA Astrophysics Data System (ADS)

Kohn, M. J.; Evans, S.; Dean, J.; Nufio, C.

2012-12-01

Insects comprise over three quarters of all animal species, yet studies of body water isotopic composition are limited to only the cockroach, the hoverfly, and chironomid flies. These studies suggest that oxygen and hydrogen isotopic compositions in body water are primarily controlled by dietary water sources, with modification from respiratory and metabolic processes. In particular, outward diffusion of isotopically depleted water vapor through insect spiracles at low humidity enriches residual body water in 18O and 2H (D). Stable isotope compositions (δ18O and δD) also respond to gradients in elevation and humidity, but these influences remain poorly understood. In this study, we measured grasshopper body water and local vegetation isotopic compositions along an elevation gradient in Colorado to evaluate three hypotheses: 1) Insect body water isotopic composition is directly related to food source water composition 2) Water vapor transport alters body water isotopic compositions relative to original diet sources, and 3) Elevation gradients influence isotopic compositions in insect body water. Thirty-five species of grasshopper were collected from 14 locations in Colorado grasslands, ranging in elevation from 450 to 800 meters (n=131). Body water was distilled from previously frozen grasshopper specimens using a vacuum extraction line, furnaces (90 °C), and liquid nitrogen traps. Water samples were then analyzed for δ18O and δD on an LGR Liquid Water Isotope Analyzer, housed in the Department of Geosciences, Boise State University. Grasshopper body water isotopic compositions show wide variation, with values ranging between -76.64‰ to +42.82‰ in δD and -3.06‰ to +26.78‰ in δ18O. Precipitation δ18O values over the entire Earth excluding the poles vary by approximately 30‰, comparable to the total range measured in our single study area. Most grasshopper values deviate from the global meteoric water line relating δ18O and δD in precipitation, consistent with evaporative enrichment in food (plants) due to plant transpiration. However, grasshopper body water from any given location is further enriched in 18O and D relative to food. Isotopic values decrease slightly with increasing elevation, but some specific grasshopper species appear more sensitive to elevation. Overall, evaporative enrichment of 18O and D in this relatively dry environment appears the strongest factors influencing grasshopper compositions.

Potassium isotopic evidence for a high-energy giant impact origin of the Moon.

PubMed

Wang, Kun; Jacobsen, Stein B

2016-10-27

The Earth-Moon system has unique chemical and isotopic signatures compared with other planetary bodies; any successful model for the origin of this system therefore has to satisfy these chemical and isotopic constraints. The Moon is substantially depleted in volatile elements such as potassium compared with the Earth and the bulk solar composition, and it has long been thought to be the result of a catastrophic Moon-forming giant impact event. Volatile-element-depleted bodies such as the Moon were expected to be enriched in heavy potassium isotopes during the loss of volatiles; however such enrichment was never found. Here we report new high-precision potassium isotope data for the Earth, the Moon and chondritic meteorites. We found that the lunar rocks are significantly (>2σ) enriched in the heavy isotopes of potassium compared to the Earth and chondrites (by around 0.4 parts per thousand). The enrichment of the heavy isotope of potassium in lunar rocks compared with those of the Earth and chondrites can be best explained as the result of the incomplete condensation of a bulk silicate Earth vapour at an ambient pressure that is higher than 10 bar. We used these coupled constraints of the chemical loss and isotopic fractionation of K to compare two recent dynamic models that were used to explain the identical non-mass-dependent isotope composition of the Earth and the Moon. Our K isotope result is inconsistent with the low-energy disk equilibration model, but supports the high-energy, high-angular-momentum giant impact model for the origin of the Moon. High-precision potassium isotope data can also be used as a 'palaeo-barometer' to reveal the physical conditions during the Moon-forming event.

The Chlorine Isotopic Composition Of Lunar UrKREEP

NASA Technical Reports Server (NTRS)

Barnes, J. J.; Tartese, R.; Anand, M.; McCubbin, F. M.; Neal, C. R.; Franchi, I. A.

2016-01-01

Since the long standing paradigm of an anhydrous Moon was challenged there has been a renewed focus on investigating volatiles in a variety of lunar samples. However, the current models for the Moon’s formation have yet to fully account for its thermal evolution in the presence of H2O and other volatiles. When compared to chondritic meteorites and terrestrial rocks, lunar samples have exotic chlorine isotope compositions, which are difficult to explain in light of the abundance and isotopic composition of other volatile species, especially H, and the current estimates for chlorine and H2O in the bulk silicate Moon. In order to better understand the processes involved in giving rise to the heavy chlorine isotope compositions of lunar samples, we have performed a comprehensive in situ high precision study of chlorine isotopes, using NanoSIMS (Nanoscale Secondary Ion Mass Spectrometry) of lunar apatite from a suite of Apollo samples covering a range of geochemical characteristics and petrologic types.

Forest Canopy Water Cycling Responses to an Intermediate Disturbance Revealed Through Stable Water Vapor Isotopes

NASA Astrophysics Data System (ADS)

Fiorella, R.; Poulsen, C. J.; Matheny, A. M.; Rey Sanchez, C.; Fotis, A. T.; Morin, T. H.; Vogel, C. S.; Gough, C. M.; Aron, P.; Bohrer, G.

2016-12-01

Forest structure, age, and species composition modulate fluxes of carbon and water between the land surface and the atmosphere. The response of forests to intermediate disturbances such as ecological succession, species-specific insect invasion, or selective logging that disrupt the canopy but do not promote complete stand replacement, shape how these fluxes evolve through time. We investigate the impact of an intermediate disturbance to water cycling processes by comparing vertical profiles of stable water isotopes in two closely located forest canopies in the northern lower peninsula of Michigan using cavity ring-down spectroscopy. In one of the canopies, an intermediate disturbance was prescribed in 2008 by inducing mortality in all canopy-dominant early successional species. Isotopic compositions of atmospheric water vapor are measured at six heights during two time periods (summer and early fall) at two flux towers and compared with local meteorology and calculated atmospheric back-trajectories. Disturbance has little impact on low-frequency changes in isotopic composition (e.g., >1 day); at these timescales, isotopic composition is strongly related to large-scale moisture transport. In contrast, disturbance has substantial impacts on the vertical distribution of water isotopes throughout the canopy when transpiration rates are high during the summer, but impact is muted during early fall. Sub-diurnal differences in canopy water vapor cycling are likely related to differences in species composition and response to disturbance and changes in canopy structure. Predictions of transpiration fluxes by land-surface models that do not account species-specific relationships and canopy structure are unlikely to capture these relationships, but addition of stable isotopes to land surface models may provide a useful parameter to improve these predictions.

The earliest Lunar Magma Ocean differentiation recorded in Fe isotopes

NASA Astrophysics Data System (ADS)

Wang, Kun; Jacobsen, Stein B.; Sedaghatpour, Fatemeh; Chen, Heng; Korotev, Randy L.

2015-11-01

Recent high-precision isotopic measurements show that the isotopic similarity of Earth and Moon is unique among all known planetary bodies in our Solar System. These observations provide fundamental constraints on the origin of Earth-Moon system, likely a catastrophic Giant Impact event. However, in contrast to the isotopic composition of many elements (e.g., O, Mg, Si, K, Ti, Cr, and W), the Fe isotopic compositions of all lunar samples are significantly different from those of the bulk silicate Earth. Such a global Fe isotopic difference between the Moon and Earth provides an important constraint on the lunar formation - such as the amount of Fe evaporation as a result of a Giant Impact origin of the Moon. Here, we show through high-precision Fe isotopic measurements of one of the oldest lunar rocks (4.51 ± 0.10 Gyr dunite 72 415), compared with Fe isotope results of other lunar samples from the Apollo program, and lunar meteorites, that the lunar dunite is enriched in light Fe isotopes, complementing the heavy Fe isotope enrichment in other lunar samples. Thus, the earliest olivine accumulation in the Lunar Magma Ocean may have been enriched in light Fe isotopes. This new observation allows the Fe isotopic composition of the bulk silicate Moon to be identical to that of the bulk silicate Earth, by balancing light Fe in the deep Moon with heavy Fe in the shallow Moon rather than the Moon having a heavier Fe isotope composition than Earth as a result of Giant Impact vaporization.

Latitudinal change in precipitation and water vapor isotopes over Southern ocean

NASA Astrophysics Data System (ADS)

Rahul, P.

2015-12-01

The evaporation process over ocean is primary source of water vapor in the hydrological cycle. The Global Network of Isotopes in Precipitation (GNIP) dataset of rainwater and water vapor isotopes are predominantly based on continental observations, with very limited observation available from the oceanic area. Stable isotope ratios in precipitation provide valuable means to understand the process of evaporation and transport of water vapor. This is further extended in the study of past changes in climate from the isotopic composition of ice core. In this study we present latitudinal variability of water vapor and rainwater isotopic composition and compared it with factors like physical condition of sea surface water from near equator (1°S) to the polar front (56°S) during the summer time expedition of the year 2013. The water vapor and rainwater isotopes showed a sharp depletion in isotopes while progressively move southward from the tropical regions (i.e. >30°S), which follows the pattern recorded in the surface ocean water isotopic composition. From the tropics to the southern latitudes, the water vapor d18O varied between -11.8‰ to -14.7‰ while dD variation ranges between -77.7‰ to -122.2‰. Using the data we estimated the expected water vapor isotopic composition under kinetic as well as equilibrium process. Our observation suggests that the water vapor isotopic compositions are in equilibrium with the sea water in majority of cases. At one point of observation, where trajectory of air parcel originated from the continental region, we observed a large deviation from the existing trend of latitudinal variability. The deduced rainwater composition adopting equilibrium model showed a consistent pattern with observed values at the tropical region, while role of kinetic process become dominant on progressive shift towards the southern latitudes. We will draw comparison of our observation with other data available in the literature together with isotope model data during the presentation.

Boron Isotopic Composition Correlates with Ultra-Structure in a - Sea Coral Lophelia Pertusa: Implications for Biomineralization and - PH

NASA Astrophysics Data System (ADS)

Blamart, D.; Rollion-Bard, C.; Meibom, A.; Cuif, J.; Juillet-Leclerc, A.; Dauphin, Y.; Douarin, M.

2007-12-01

The geochemistry (stable isotopes and trace elements) of biogenic carbonates has been widely used for more than fifty years to reconstruct past climatic variability. During this time, the studies were mainly based on bulk sampling limiting sometimes the interpretations of the geochemical data as paleoclimatic proxies. Recently, high spatial resolution sampling techniques, such as micro-mill and SIMS, have been employed in the study of C, O and B isotopic compositions and trace elements (Mg, Sr) in the skeletons of a variety of (deep-sea) coral species. These studies have documented dramatic 'vital effects' and uncovered a systematic relationship between skeletal ultra-structure and stable isotopic composition. The formation of skeleton corals follows a universal two-step growth process. At the tips of the skeletal structures, the mineralizing cell layer produces centers of calcification (COC) or, equivalently, Early Mineralization Zone (EMZ). These EMZ are subsequently overgrown by fibrous aragonite(FA) consisting of cyclically added layers. The EMZ are characterized by systematically lighter C and O isotopic compositions compared with the adjacent FA. A number of geochemical models have been proposed, in which this systematic stable isotopic difference between EMZ and FA is ascribed to a biologically induced variation in the pH of a proposed Extra-cytoplasmic Calcifying Fluid (ECF) reservoir. In these models, relatively high pH conditions during the formation of EMZ result in relatively light C and O isotopic compositions compared with FA, which form under generally lower pH conditions. A direct test of such models would be possible if the Boron isotopic composition, which is pH sensitive, of EMZ and FA could be measured. We performed ion microprobe d11B measurements for EMZ and FA in Lophelia pertusa, a deep-sea coral common in the North-East Atlantic Ocean. We observe a systematic difference in B isotopic composition between the EMZ and FA skeleton. In EMZ, the measured δ11B values are consistently low. Fibrous aragonite is characterized by systematically higher d11B values, but also display B isotopic heterogeneity associated with specific growth bands in the calyx wall. The magnitude of the observed B isotopic variations cannot be explained by changes in environmental conditions and are likely caused by biological processes involved in the biomineralization of new skeleton; i.e. 'vital' effects. The observed B isotopic variations are opposite to the predictions of geochemical models for vital effects. Our data indicate that pH variations are not responsible for the observed stable isotopic fractionations. Geochemical models therefore do not provide an adequate framework within which to understand coral skeletal formation. Without a better understanding of these processes, which require experiments, the use of B isotopic composition to reconstruct paleo-pH variations in the oceans must be considered problematic - at least as far as Lophelia pertusa is concerned.

The fate of moderately volatile elements during planetary formation in the inner Solar System

NASA Astrophysics Data System (ADS)

Pringle, E. A.; Moynier, F.

2017-12-01

Moderately volatile element abundances are variable among inner Solar System bodies, with differing degrees of depletion compared to chondrites. These variations are a consequence of the processes of planetary formation. The conditions and the specific mechanisms of planetary accretion and differentiation can be investigated by analyzing the stable isotope compositions of terrestrial and extraterrestrial samples. The moderately volatile lithophile elements are particularly useful to distinguish between the effects of accretion and those of core formation. Recent work has shown isotope variations in inner Solar System bodies for the moderately volatile elements Zn and K. The purely lithophile nature of Rb (in contrast to Zn) and the higher volatility of Rb compared to K make Rb an ideal element with which to further study moderately volatile element depletion. We have developed a new method for the high-precision measurement of Rb isotope ratios by MC-ICP-MS. Terrestrial rocks define a narrow range in Rb isotope composition, indicating that Rb isotope fractionation during igneous differentiation is limited (<30 ppm/amu). Larger Rb isotope variations are observed in extraterrestrial materials. Carbonaceous chondrites display a trend toward lighter Rb isotope composition coupled with decreasing Rb/Sr, opposite to the effect expected if their volatile element variations were caused by evaporative loss of Rb. This relationship indicates that the volatile element abundance variations in carbonaceous chondrites are not due to evaporation or condensation, but rather are due to the mixing of chemically and isotopically distinct primordial reservoirs. In contrast, there is a clear signature of Rb loss during evaporation in volatile-depleted achondrites and lunar rocks. Significant heavy isotope enrichments (up to several per mil for 87Rb/85Rb) are found for volatile-depleted planetesimals, including eucrites. In addition, lunar rocks also display heavy Rb isotope enrichments compared to the BSE. The most likely cause of these variations is Rb isotope fractionation due to evaporation during accretion.

Using Redwood Tree Ring Chronologies to Obtain the Long-View on California's Coastal Climate

NASA Astrophysics Data System (ADS)

Dawson, T. E.; Roden, J. S.; Voelker, S. L.; Johnstone, J. A.; Ambrose, A.

2014-12-01

Coast redwood (Sequoia sempervirens) occupies a long and narrow range at the land-sea interface from the southern Big Bur region to the California-Oregon boarder. Since mature trees can live in excess of 2000 years, using the interannual variability in the oxygen and carbon stable isotope composition of tree rings obtained from trees growing in different parts of the redwood range holds the potential for obtaining a long-term record of California's coastal climate, including the history of temperatures, low cloud / fog, rainfall and associated climatic drivers of their variation. We analyzed the oxygen and carbon stable isotope composition of tree ring cellulose from both tree cores and whole cross-sectional slabs and compared these data to several regional climate indicies and to published growth chronologies to obtain the long-view on California's coastal climate. Several highlights will be presented and discussed. These include: (1) redwoods faithfully record water sources they use in the oxygen stable isotope composition of their tree ring cellulose; (2) these is both strong watershed- and regional-scale coherence; (3) redwood tree ring carbon isotope composition shows its strongest correlations to tree water status, stand-scale humidity, and at the regional scale to what we term "summer precipitation" anomalies (lack of rain with presence of fog); also (4) that carbon stable isotope composition is very sensitive to within tree and stand microclimate while oxygen stable isotope composition seems to be sensitive to topographic site factors like slope position and proximity to riparian / gully habitats; (5) multivariate climatic analyses reveal that summertime drought recorded in the isotope excursions are most strongly linked to atmospheric circulation anomalies; and (6) that redwood tree rings and their isotope composition provide great potential for reconstructing high-resolution paleo-climate along the California coast.

Verification of the isotopic composition of precipitation simulated by a regional isotope circulation model over Japan.

PubMed

Tanoue, Masahiro; Ichiyanagi, Kimpei; Yoshimura, Kei

2016-01-01

The isotopic composition (δ(18)O and δ(2)H) of precipitation simulated by a regional isotope circulation model with a horizontal resolution of 10, 30 and 50 km was compared with observations at 56 sites over Japan in 2013. All simulations produced reasonable spatio-temporal variations in δ(18)O in precipitation over Japan, except in January. In January, simulated δ(18)O values in precipitation were higher than observed values on the Pacific side of Japan, especially during an explosively developing extratropical cyclone event. This caused a parameterisation of precipitation formulation about the large fraction of precipitated water to liquid detrained water in the lower troposphere. As a result, most water vapour that transported from the Sea of Japan precipitated on the Sea of Japan side. The isotopic composition of precipitation was a useful verification tool for the parameterisation of precipitation formulation as well as large-scale moisture transport processes in the regional isotope circulation model.

Comparing isotope signatures of prey fish: does gut removal affect δ13C or δ15N?

USGS Publications Warehouse

Chipps, Steven R.; Fincel, Mark J.; VanDeHey, Justin A.; Wuestewald, Andrew

2011-01-01

Stable isotope analysis is a quick and inexpensive method to monitor the effects of food web changes on aquatic communities. Traditionally, whole specimens have been used when determining isotope composition of prey fish or age-0 recreational fishes. However, gut contents of prey fish could potentially alter isotope composition of the specimen, especially when recent foraging has taken place or when the gut contains non-assimilated material that would normally pass through fishes undigested. To assess the impacts of gut content on prey fish isotope signatures, we examined the differences in isotopic variation of five prey fish species using whole fish, whole fish with the gut contents removed, and dorsal muscle only. We found significant differences in both δ15N and δ13C between the three tissue treatments. In most cases, muscle tissue was enriched compared to whole specimens or gut-removed specimens. Moreover, differences in mean δ15N within a species were up to 2‰ among treatments. This would result in a change of over half a trophic position (TP) based on a 3.4‰ increase per trophic level. However, there were no apparent relationships between tissue isotope values in fish with increased gut fullness (more prey tissue present). We suggest that muscle tissue should be used as the standard tissue for determining isotope composition of prey fish or age-0 recreational fishes, especially when determining enrichment for mixing models, calculating TP, or constructing aquatic food webs.

Copper and Zinc isotope composition of CR, CB and CH-like meteorites.

NASA Astrophysics Data System (ADS)

Russell, S.; Zhu, X.; Guo, Y.; Mullane, E.; Gounelle, M.; Mason, T.; Coles, B.

2003-04-01

Copper and zinc isotopes have recently been shown to be variable in isotopic composi-tion among terrestrial and extraterrestrial materials [1-3]. For this study, we have se-lected samples (bulk meteorite and chondrule separates) from the CR meteorite clan: Bencubbin (CB), Renazzo (CR2), NWA 801 (CR2), and HaH237 (CH-like). These meteorites were selected because meteorites from this clan have experienced very little alteration since their initial formation [4] and for their extremely high refrac-tory/volatile element ratios. The latter characteristic may allow a test of the correlation observed by [2] between element ratios and Cu isotope composition. Measurements were performed on NHM/IC Micromass Isoprobe and Oxford Nu MC-ICP-MS using techniques described elsewhere [1,5]. Each of the meteorites measured so far for Cu and Zn are isotopically light compared to the terrestrial mantle. This suggests that the terrestrial value may have been altered from the pristine solar system value, or else there were multiple early solar system components. Zinc isotopic com-positions lie on a fractionation line and range from δ66ZnNIST = -1.4±0.1ppm (bulk NWA801) to -1.9±0.1ppm (separated chondrule, NWA 801). Copper isotope compositions vary from δ65CuNIST976 = -1.5±0.1ppm (bulk Renazzo) to -3.1±0.1ppm (separated chondrule, NWA 801). Two chondrules from NWA 801 have differing Cu isotope values (-3.1±0.1 and -2.0±0.1ppm) and both are lighter than the bulk meteorite (-1.9±0.1ppm), suggesting a lack of equilibration with respect to Cu in this meteorite. The light values for the two separated chondrules, compared the bulk meteorite, hints that chondrules may be isotopically lighter than co-existing matrix, metal and sulphides with respect to Cu. The copper isotope compositions are not as isotopically light as expected for the high refractory/volatile element ratio observed in these chondrites. Thus a model to account for the Cu isotopes in chondrites may require greater com-plexity than one involving simple mixing of two primordial components. References: [1] Zhu et al., Chem. Geol. 163,139-149 (2000). [2] Luck et al., GCA 67 143 (2002). [3] Luck et al., MAPS 35 A100 (2000) [4] Krot et al., MAPS 37 1451-1490 (2002) [5] Mason et al. EOS Trans. AGU abstract V21A-0966 82 (2001)

Modeling the influence of a reduced equator-to-pole sea surface temperature gradient on the distribution of water isotopes in the Early/Middle Eocene

NASA Astrophysics Data System (ADS)

Speelman, Eveline N.; Sewall, Jacob O.; Noone, David; Huber, Matthew; von der Heydt, Anna; Damsté, Jaap Sinninghe; Reichart, Gert-Jan

2010-09-01

Proxy-based climate reconstructions suggest the existence of a strongly reduced equator-to-pole temperature gradient during the Azolla interval in the Early/Middle Eocene, compared to modern. Changes in the hydrological cycle, as a consequence of a reduced temperature gradient, are expected to be reflected in the isotopic composition of precipitation (δD, δ 18O). The interpretation of water isotopic records to quantitatively reconstruct past precipitation patterns is, however, hampered by a lack of detailed information on changes in their spatial and temporal distribution. Using the isotope-enabled version of the National Center for Atmospheric Research (NCAR) atmospheric general circulation model, Community Atmosphere Model v.3 (isoCAM3), relationships between water isotopes and past climates can be simulated. Here we examine the influence of an imposed reduced meridional sea surface temperature gradient on the spatial distribution of precipitation and its isotopic composition in an Early/Middle Eocene setting. As a result of the applied forcings, the Eocene simulation predicts the occurrence of less depleted high latitude precipitation, with δD values ranging only between 0 and -140‰ (compared to Present-day 0 to -300‰). Comparison with Early/Middle Eocene-age isotopic proxy data shows that the simulation accurately captures the main features of the spatial distribution of the isotopic composition of Early/Middle Eocene precipitation over land in conjunction with the aspects of the modeled Early/Middle Eocene climate. Hence, the included stable isotope module quantitatively supports the existence of a reduced meridional temperature gradient during this interval.

Triple oxygen isotope composition of photosynthetic oxygen

NASA Astrophysics Data System (ADS)

van der Meer, Anne; Kaiser, Jan

2013-04-01

The measurement of biological production rates is essential for our understanding how marine ecosystems are sustained and how much CO2 is taken up through aquatic photosynthesis. Traditional techniques to measure marine production are laborious and subject to systematic errors. A biogeochemical approach based on triple oxygen isotope measurements in dissolved oxygen (O2) has been developed over the last few years, which allows the derivation of gross productivity integrated over the depth of the mixed layer and the time-scale of O2 gas exchange (Luz and Barkan, 2000). This approach exploits the relative 17O/16O and 18O/16O isotope ratio differences of dissolved O2 compared to atmospheric O2 to work out the rate of biological production. Two parameters are key for this calculation: the isotopic composition of dissolved O2 in equilibrium with air and the isotopic composition of photosynthetic oxygen. Recently, a controversy has emerged in the literature over these parameters (Kaiser, 2011) and one of the goals of this research is to provide additional data to resolve this controversy. In order to obtain more information on the isotopic signature of biological oxygen, laboratory experiments have been conducted to determine the isotopic composition of oxygen produced by different phytoplankton cultures.

[Effect of microorganisms and seasonal factors on the isotope composition of organic carbon from Black Sea suspensions].

PubMed

Ivanov, M V; Lein, A Iu; Miller, Iu M; Iusunov, S K; Pimenov, N V; Wehrli, B; Rusanov, I I; Zehnder, A

2000-01-01

The isotopic composition of particulate organic carbon (POC) from the Black Sea deep-water zone was studied during a Russian-Swiss expedition in May 1998. POC from the upper part of the hydrogen sulfide zone (the C-layer) was found to be considerably enriched with the 12C isotope, as compared to the POC of the oxycline and anaerobic zone. In the C-layer waters, the concurrent presence of dissolved oxygen and hydrogen sulfide and an increased rate of dark CO2 fixation were recorded, suggesting that the change in the POC isotopic composition occurs at the expense of newly formed isotopically light organic matter of the biomass of autotrophic bacteria involved in the sulfur cycle. In the anaerobic waters below the C-layer, the organic matter of the biomass of autotrophs is consumed by the community of heterotrophic microorganisms; this results in weighting of the POC isotopic composition. Analysis of the data obtained and data available in the literature allows an inference to be made about the considerable seasonable variability of the POC delta 13C value, which depends on the ratio of terrigenic and planktonogenic components in the particulate organic matter.

Ti Isotopes: Echoes of Grain-Scale Heterogenaity in the Protoplanetary Disk

NASA Technical Reports Server (NTRS)

Jordan, M. K.; Kohl, I. E.; McCain, K. A.; Simon, J. I.; Young, E. D.

2017-01-01

Calcium-aluminum-rich inclusions (CAIs) are the oldest surviving solids to have formed in the Solar System. Their chemical and isotopic compositions provide a record of the conditions present in the protoplanetary disk where they formed and can aid our understanding of how solids formed in the solar nebula, an important step in the eventual process of planet building. The isotopic compositions of CAIs are primarily controlled by volatility. Evaporation/sublimation are well understood through both theory and experimental work to produce an enrichment in the heavy isotopes of an element, but less is understood about the effects of condensation. Mass-dependent fractionation can potentially provide a record of nebular condensation. Ti is not likely to experience evaporation due to its refractory nature, making it a useful tool for assessing the effects of condensation. We have undertaken a study of the stable isotope fractionation of Ti isotopes as a tracer of processes that predate the last evaporation events affecting CAIs. We compare the 49Ti/47Ti stable isotope ratio with excess 50Ti common in CAIs. We have collected Ti, Mg, Si, and Ca isotope data for a suite of CAIs in order to search for heterogeneity in each of these isotope systems, and for potential correlations among them. We compare our results to expectations for condensation.

Sr isotopic composition of Afar volcanics and its implication for mantle evolution

NASA Astrophysics Data System (ADS)

Barberi, F.; Civetta, L.; Varet, J.

1980-10-01

Investigations of Rb-Sr systematics of basalts from the Afar depression (Ethiopia) indicate the presence of a heterogeneous mantle source region. The Sr isotopic compositions of the basalts from the Afar axial and transverse ranges identify source regions which are enriched in LIL elements and radiogenic Sr (axial ranges) and others which are relatively depleted (transverse ranges). Sr isotopic composition of basalts from the Red Sea, Gulf of Aden and Gulf of Tadjoura, which range from 0.70300 to 0.70340 are also reported and compared with the more radiogenic Afar region, which is characterized by 87Sr/ 86Sr ranging from 0.70328 to 0.70410. Available geochemical and isotopic data suggest that a relation exists between magma composition and the advancement of the rifting process through progressive lithosphere attenuation leading to continental break-up. However, the petrogenetic process is not simple and probably implies a vertically zoned mantle beneath the Afar region. Sr isotopic evidence suggests that the vertically zoned mantle is more radiogenic and enriched in LIL elements in its upper part.

Predictive isotopic biogeochemistry: hydrocarbons from anoxic marine basins

NASA Technical Reports Server (NTRS)

Freeman, K. H.; Wakeham, S. G.; Hayes, J. M.

1994-01-01

Carbon isotopic compositions were determined for individual hydrocarbons in water column and sediment samples from the Cariaco Trench and Black Sea. In order to identify hydrocarbons derived from phytoplankton, the isotopic compositions expected for biomass of autotrophic organisms living in surface waters of both localities were calculated based on the concentrations of CO2(aq) and the isotopic compositions of dissolved inorganic carbon. These calculated values are compared to measured delta values for particulate organic carbon and for individual hydrocarbon compounds. Specifically, we find that lycopane is probably derived from phytoplankton and that diploptene is derived from the lipids of chemoautotrophs living above the oxic/anoxic boundary. Three acyclic isoprenoids that have been considered markers for methanogens, pentamethyleicosane and two hydrogenated squalenes, have different delta values and apparently do not derive from a common source. Based on the concentration profiles and isotopic compositions, the C31 and C33 n-alkanes and n-alkenes have a similar source, and both may have a planktonic origin. If so, previously assigned terrestrial origins of organic matter in some Black Sea sediments may be erroneous.

Overview and Brief History of the Boron Isotope Proxy for Past Seawater pH

NASA Astrophysics Data System (ADS)

Hoenisch, B.; Hemming, G.

2007-05-01

In 1992 Hemming and Hanson (GCA, vol. 56, p. 537-543) showed that a variety of modern marine carbonates revealed a boron isotopic composition close to the isotopic composition of dissolved borate at modern seawater pH, suggesting this was the boron species preferentially adsorbed and incorporated into marine carbonates. With a constant offset between the trigonal and tetrahedrally coordinated boron species and a pH-dependent variation in their fractions, it appeared that this system would be sensitive to pH changes in the natural range of seawater. Accordingly, it was suggested that the boron isotope composition of marine carbonates is a proxy for past seawater pH. Subsequent culture studies with living planktic foraminifers and corals, as well as synthetic precipitation experiments confirmed that the boron isotopic composition follows the isotopic composition of borate across a wide range of seawater pH. In order to use the proxy with confidence, however, all other controls apart from pH need to be thoroughly understood. Recent laboratory and sediment experiments have demonstrated that vital effects and partial shell dissolution have the potential to modify the primary seawater pH signal recorded in the boron isotopic composition of planktic foraminifers. However it has also been shown that careful sample selection allows for avoiding these potential complications. A record of reconstructed surface seawater pH and estimated aqueous PCO2 shows a remarkable match between boron isotope based atmospheric pCO2 estimates and the Vostok ice core CO2 record. This convincingly demonstrates that boron isotopes in planktic foraminifers allow quantitative estimates of atmospheric pCO2 in the past, and confirms that glacial surface ocean pH was ~0.2 units higher compared to interglacial periods. We are going to review and discuss the achievements generated in Gil Hanson's lab over the past 15 years in the light of recent empirical measurements of the boron isotope fractionation between boric acid and borate in seawater.

Isotopic Effects in Nuclear Fragmentation and GCR Transport Problems

NASA Technical Reports Server (NTRS)

Cucinotta, Francis A.

2002-01-01

Improving the accuracy of the galactic cosmic ray (GCR) environment and transport models is an important goal in preparing for studies of the projected risks and the efficiency of potential mitigations methods for space exploration. In this paper we consider the effects of the isotopic composition of the primary cosmic rays and the isotopic dependence of nuclear fragmentation cross sections on GCR transport models. Measurements are used to describe the isotopic composition of the GCR including their modulation throughout the solar cycle. The quantum multiple-scattering approach to nuclear fragmentation (QMSFRG) is used as the data base generator in order to accurately describe the odd-even effect in fragment production. Using the Badhwar and O'Neill GCR model, the QMSFRG model and the HZETRN transport code, the effects of the isotopic dependence of the primary GCR composition and on fragment production for transport problems is described for a complete GCR isotopic-grid. The principle finding of this study is that large errors ( 100%) will occur in the mass-flux spectra when comparing the complete isotopic-grid (141 ions) to a reduced isotopic-grid (59 ions), however less significant errors 30%) occur in the elemental-flux spectra. Because the full isotopic-grid is readily handled on small computer work-stations, it is recommended that they be used for future GCR studies.

Non-destructive measurement of carbonic anhydrase activity and the oxygen isotope composition of soil water

NASA Astrophysics Data System (ADS)

Jones, Sam; Sauze, Joana; Ogée, Jérôme; Wohl, Steven; Bosc, Alexandre; Wingate, Lisa

2016-04-01

Carbonic anhydrases are a group of metalloenzymes that catalyse the hydration of aqueous carbon dioxide (CO2). The expression of carbonic anhydrase by bacteria, archaea and eukarya has been linked to a variety of important biological processes including pH regulation, substrate supply and biomineralisation. As oxygen isotopes are exchanged between CO2 and water during hydration, the presence of carbonic anhydrase in plants and soil organisms also influences the oxygen isotope budget of atmospheric CO2. Leaf and soil water pools have distinct oxygen isotope compositions, owing to differences in pool sizes and evaporation rates, which are imparted on CO2during hydration. These differences in the isotopic signature of CO2 interacting with leaves and soil can be used to partition the contribution of photosynthesis and soil respiration to net terrestrial CO2 exchange. However, this relies on our knowledge of soil carbonic anhydrase activity and currently, the prevalence and function of these enzymes in soils is poorly understood. Isotopic approaches used to estimate soil carbonic anhydrase activity typically involve the inversion of models describing the oxygen isotope composition of CO2 fluxes to solve for the apparent, potentially catalysed, rate of oxygen exchange during hydration. This requires information about the composition of CO2 in isotopic equilibrium with soil water obtained from destructive, depth-resolved soil water sampling. This can represent a significant challenge in data collection given the considerable potential for spatial and temporal variability in the isotopic composition of soil water and limited a priori information with respect to the appropriate sampling resolution and depth. We investigated whether we could circumvent this requirement by constraining carbonic anhydrase activity and the composition of soil water in isotopic equilibrium with CO2 by solving simultaneously the mass balance for two soil CO2 steady states differing only in the oxygen isotope composition of ambient CO2. This non-destructive approach was tested through laboratory incubations of air-dried soils that were re-wetted with water of known isotopic composition. Performance was assessed by comparing estimates of the soil water oxygen isotope composition derived from open chamber flux measurements with those measured in the irrigation water and soil water extracted following incubations. The influence of soil pH and bovine carbonic anhydrase additions on these estimates was also investigated. Coherent values were found between the soil water composition estimates obtained from the dual steady state approach and those measured for irrigation waters. Estimates of carbonic anhydrase activity made using this approach also reflected well artificial increases to the concentration of carbonic anhydrase and indicated that this activity was sensitive to soil pH.

Silurian shale origin for light oil, condensate, and gas in Algeria and the Middle East

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zumberge, J.E.; Macko, S.

1996-01-01

Two of the largest gas fields in the world, Hasi R'Mel, Algeria and North Dome, Qatar, also contain substantial condensate and light oil reserves. Gas to source rock geochemical correlation is difficult due to the paucity of molecular parameters in the former although stable isotope composition is invaluable. However, by correlating source rocks with light oils and condensates associated with gas production using traditional geochemical parameters such as biomarkers and isotopes, a better understanding of the origin of the gas is achieved. Much of the crude oil in the Ghadames/Illizi Basins of Algeria has long been thought to have beenmore » generated from Silurian shales. New light oil discoveries in Saudi Arabia have also been shown to originate in basal euxinic Silurian shales. Key sterane and terpane biomarkers as well as the stable carbon isotopic compositions of the C15+ saturate and aromatic hydrocarbon fractions allow for the typing of Silurian-sourced, thermally mature light oils in Algeria and the Middle East. Even though biomarkers are often absent due to advanced thermal maturity, condensates can be correlated to the light oils using (1) carbon isotopes of the residual heavy hydrocarbon fractions, (2) light hydrocarbon distributions (e.g., C7 composition), and (3) compound specific carbon isotopic composition of the light hydrocarbons. The carbon isotopes of the C2-C4 gas components ran then be compared to the associated condensate and light oil isotopic composition.« less

Silurian shale origin for light oil, condensate, and gas in Algeria and the Middle East

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zumberge, J.E.; Macko, S.

Two of the largest gas fields in the world, Hasi R`Mel, Algeria and North Dome, Qatar, also contain substantial condensate and light oil reserves. Gas to source rock geochemical correlation is difficult due to the paucity of molecular parameters in the former although stable isotope composition is invaluable. However, by correlating source rocks with light oils and condensates associated with gas production using traditional geochemical parameters such as biomarkers and isotopes, a better understanding of the origin of the gas is achieved. Much of the crude oil in the Ghadames/Illizi Basins of Algeria has long been thought to have beenmore » generated from Silurian shales. New light oil discoveries in Saudi Arabia have also been shown to originate in basal euxinic Silurian shales. Key sterane and terpane biomarkers as well as the stable carbon isotopic compositions of the C15+ saturate and aromatic hydrocarbon fractions allow for the typing of Silurian-sourced, thermally mature light oils in Algeria and the Middle East. Even though biomarkers are often absent due to advanced thermal maturity, condensates can be correlated to the light oils using (1) carbon isotopes of the residual heavy hydrocarbon fractions, (2) light hydrocarbon distributions (e.g., C7 composition), and (3) compound specific carbon isotopic composition of the light hydrocarbons. The carbon isotopes of the C2-C4 gas components ran then be compared to the associated condensate and light oil isotopic composition.« less

In Situ Carbon Isotope Analysis by Laser Ablation MC-ICP-MS.

PubMed

Chen, Wei; Lu, Jue; Jiang, Shao-Yong; Zhao, Kui-Dong; Duan, Deng-Fei

2017-12-19

Carbon isotopes have been widely used in tracing a wide variety of geological and environmental processes. The carbon isotope composition of bulk rocks and minerals was conventionally analyzed by isotope ratio mass spectrometry (IRMS), and, more recently, secondary ionization mass spectrometry (SIMS) has been widely used to determine carbon isotope composition of carbon-bearing solid materials with good spatial resolution. Here, we present a new method that couples a RESOlution S155 193 nm laser ablation system with a Nu Plasma II MC-ICP-MS, with the aim of measuring carbon isotopes in situ in carbonate minerals (i.e., calcite and aragonite). Under routine operating conditions for δ 13 C analysis, instrumental bias generally drifts by 0.8‰-2.0‰ in a typical analytical session of 2-3 h. Using a magmatic calcite as the standard, the carbon isotopic composition was determined for a suite of calcite samples with δ 13 C values in the range of -6.94‰ to 1.48‰. The obtained δ 13 C data are comparable to IRMS values. The combined standard uncertainty for magmatic calcite is <0.3‰ (1s). No significant matrix effects have been identified in calcite with the amplitude of chemical composition variation (i.e., MnO, SrO, MgO, or FeO) up to 2.5 wt %. Two modern corals were investigated using magmatic calcite as the calibration standard, and the average δ 13 C values for both corals are similar to the bulk IRMS values. Moreover, coral exhibits significant heterogeneity in carbon isotope compositions, with differences up to 4.85‰ within an individual coral. This study indicates that LA-MC-ICP-MS can serve as an appropriate method to analyze carbon isotopes of carbonate minerals in situ.

Behaviour of Structural Carbonate Stable Carbon and Oxygen Isotope Compositions in Bioapatite During Burning of Bone

NASA Astrophysics Data System (ADS)

Munro, L. E.; Longstaffe, F. J.; White, C. D.

2003-12-01

Bioapatite, the principal inorganic phase comprising bone, commonly contains a small fraction of carbonate, which has been substituted into the phosphate structure during bone formation. The isotopic compositions of both the phosphate oxygen and the structural carbonate oxygen are now commonly used in palaeoclimatological and bioarchaeological investigations. The potential for post-mortem alteration of these isotopic compositions, therefore, is of interest, with the behaviour of structural carbonate being of most concern. In bioarchaeological studies, alteration of bone isotopic compositions has the potential to occur not only during low-temperature processes associated with burial but also during food preparation involving heating (burning, boiling). Here, we examine the stable isotopic behaviour of structural carbonate oxygen and carbon, and coexisting phosphate oxygen during the burning of bone. Freshly deceased (6<8 months) white-tailed deer leg bones (Odocoileus virginianus) were collected from Pinery Provincial Park, Ontario, Canada. Each long bone was sectioned and incrementally heated from 25 to 900° C, in 25° intervals. The samples were then ground to a standardized grain-size (45<63μ m), and changes in bioapatite crystallinity (CI) were determined using powder X-ray diffraction (pXRD), and Fourier transform infra-red spectroscopy (FTIR). Combined differential thermal and thermogravimetric analyses (DTA/TG) were used to evaluate weight loss and associated reactions during heating. Stable carbon isotope compositions of the bioapatite remain relatively constant (+/-1‰ ) during heating to 650° C. A 4‰ increase in stable carbon isotopic composition then occurs between 650-750° C, accompanied by an increase in CI, followed by a 10‰ decline at temperatures above 800° C, as carbonate carbon is lost. Carbonate and phosphate oxygen isotopic compositions are correlated over the entire heating range, with carbonate being enriched relative to phosphate by about 8-10‰ below 500° C, 5-6‰ between 500-700° C, and 8-10‰ above 700° C. CI and oxygen isotopic compositions of carbonate and phosphate are not well correlated. Only modest CI changes are recorded from 25-675° C, compared with much larger changes in oxygen isotopic composition, especially above 300° C. On average, original isotopic compositions are largely preserved for both phosphate (+/-1‰ ) and carbonate (+/-2‰ ) oxygen at <300° C. At higher temperatures, however, both phosphate and carbonate oxygen in the bioapatite are systematically depleted of oxygen-18 relative to original values.

Development of particle induced gamma-ray emission methods for nondestructive determination of isotopic composition of boron and its total concentration in natural and enriched samples.

PubMed

Chhillar, Sumit; Acharya, Raghunath; Sodaye, Suparna; Pujari, Pradeep K

2014-11-18

We report simple particle induced gamma-ray emission (PIGE) methods using a 4 MeV proton beam for simultaneous and nondestructive determination of the isotopic composition of boron ((10)B/(11)B atom ratio) and total boron concentrations in various solid samples with natural isotopic composition and enriched with (10)B. It involves measurement of prompt gamma-rays at 429, 718, and 2125 keV from (10)B(p,αγ)(7)Be, (10)B(p, p'γ)(10)B, and (11)B(p, p'γ)(11)B reactions, respectively. The isotopic composition of boron in natural and enriched samples was determined by comparing peak area ratios corresponding to (10)B and (11)B of samples to natural boric acid standard. An in situ current normalized PIGE method, using F or Al, was standardized for total B concentration determination. The methods were validated by analyzing stoichiometric boron compounds and applied to samples such as boron carbide, boric acid, carborane, and borosilicate glass. Isotopic compositions of boron in the range of 0.247-2.0 corresponding to (10)B in the range of 19.8-67.0 atom % and total B concentrations in the range of 5-78 wt % were determined. It has been demonstrated that PIGE offers a simple and alternate method for total boron as well as isotopic composition determination in boron based solid samples, including neutron absorbers that are important in nuclear technology.

Geochemistry of oceanic carbonatites compared with continental carbonatites: mantle recycling of oceanic crustal carbonate

NASA Astrophysics Data System (ADS)

Hoernle, Kaj; Tilton, George; Le Bas, Mike; Duggen, Svend; Garbe-Schönberg, Dieter

Major and trace element and Sr-Nd-Pb-O-C isotopic compositions are presented for carbonatites from the Cape Verde (Brava, Fogo, Sáo Tiago, Maio and Sáo Vicente) and Canary (Fuerteventura) Islands. Carbonatites show pronounced enrichment in Ba, Th, REE, Sr and Pb in comparison to most silicate volcanic rocks and relative depletion in Ti, Zr, Hf, K and Rb. Calcio (calcitic)-carbonatites have primary (mantle-like) stable isotopic compositions and radiogenic isotopic compositions similar to HIMU-type ocean island basalts. Cape Verde carbonatites, however, have more radiogenic Pb isotope ratios (e.g. 206Pb/204Pb=19.3-20.4) than reported for silicate volcanic rocks from these islands (18.7-19.9 Gerlach et al. 1988; Kokfelt 1998). We interpret calcio-carbonatites to be derived from the melting of recycled carbonated oceanic crust (eclogite) with a recycling age of 1.6 Ga. Because of the degree of recrystallization, replacement of calcite by secondary dolomite and elevated ∂13C and ∂18O, the major and trace element compositions of the magnesio (dolomitic)-carbonatites are likely to reflect secondary processes. Compared with Cape Verde calcio-carbonatites, the less radiogenic Nd and Pb isotopic ratios and the negative Δ7/4 of the magnesio-carbonatites (also observed in silicate volcanic rocks from the Canary and Cape Verde Islands) cannot be explained through secondary processes or through the assimilation of Cape Verde crust. These isotopic characteristics require the involvement of a mantle component that has thus far only been found in the Smoky Butte lamproites from Montana, which are believed to be derived from subcontinental lithospheric sources. Continental carbonatites show much greater variation in radiogenic isotopic composition than oceanic carbonatites, requiring a HIMU-like component similar to that observed in the oceanic carbonatites and enriched components. We interpret the enriched components to be Phanerozoic through Proterozoic marine carbonate (e.g. limestone) recycled through shallow, subcontinental-lithospheric-mantle and deep, lower-mantle sources.

Geochemistry of oceanic carbonatites compared with continental carbonatites: mantle recycling of oceanic crustal carbonate

NASA Astrophysics Data System (ADS)

Hoernle, Kaj; Tilton, George; Le Bas, Mike; Duggen, Svend; Garbe-Schönberg, Dieter

2001-11-01

Major and trace element and Sr-Nd-Pb-O-C isotopic compositions are presented for carbonatites from the Cape Verde (Brava, Fogo, Sáo Tiago, Maio and Sáo Vicente) and Canary (Fuerteventura) Islands. Carbonatites show pronounced enrichment in Ba, Th, REE, Sr and Pb in comparison to most silicate volcanic rocks and relative depletion in Ti, Zr, Hf, K and Rb. Calcio (calcitic)-carbonatites have primary (mantle-like) stable isotopic compositions and radiogenic isotopic compositions similar to HIMU-type ocean island basalts. Cape Verde carbonatites, however, have more radiogenic Pb isotope ratios (e.g. 206Pb/204Pb=19.3-20.4) than reported for silicate volcanic rocks from these islands (18.7-19.9 Gerlach et al. 1988; Kokfelt 1998). We interpret calcio-carbonatites to be derived from the melting of recycled carbonated oceanic crust (eclogite) with a recycling age of 1.6 Ga. Because of the degree of recrystallization, replacement of calcite by secondary dolomite and elevated ∂13C and ∂18O, the major and trace element compositions of the magnesio (dolomitic)-carbonatites are likely to reflect secondary processes. Compared with Cape Verde calcio-carbonatites, the less radiogenic Nd and Pb isotopic ratios and the negative Δ7/4 of the magnesio-carbonatites (also observed in silicate volcanic rocks from the Canary and Cape Verde Islands) cannot be explained through secondary processes or through the assimilation of Cape Verde crust. These isotopic characteristics require the involvement of a mantle component that has thus far only been found in the Smoky Butte lamproites from Montana, which are believed to be derived from subcontinental lithospheric sources. Continental carbonatites show much greater variation in radiogenic isotopic composition than oceanic carbonatites, requiring a HIMU-like component similar to that observed in the oceanic carbonatites and enriched components. We interpret the enriched components to be Phanerozoic through Proterozoic marine carbonate (e.g. limestone) recycled through shallow, subcontinental-lithospheric-mantle and deep, lower-mantle sources.

Mn-53-Cr-53 Systematics of R-Chondrite NWA 753

NASA Technical Reports Server (NTRS)

Jogo, K.; Shih, C-Y.; Reese, Y. D.; Nyquist, L. E.

2006-01-01

Chondrules and chondrites are interpreted as objects formed in the early solar system, and it is important to study them in order to elucidate its evolution. Here, we report the study of the Mn-Cr systematics of the R-Chondrite NWA753 and compare the results to other chondrite data. The goal was to determine Cr isotopic and age variations among chondrite groups with different O-isotope signatures. The Mn-53-Cr-53 method as applied to individual chondrules [1] or bulk chondrites [2] is based on the assumption that 53Mn was initially homogeneously distributed in that portion the solar nebula where the chondrules and/or chondrites formed. However, different groups of chondrites formed from regions of different O-isotope compositions. So, different types of chondrites also may have had different initial Mn-53 abundances and/or Cr isotopic compositions. Thus, it is important to determine the Cr isotopic systematics among chondrites from various chondrite groups. We are studying CO-chondrite ALH83108 and Tagish Lake in addition to R-Chondrite NWA753. These meteorites have very distinct O-isotope compositions (Figure 1).

Isotope composition and volume of Earth's early oceans.

PubMed

Pope, Emily C; Bird, Dennis K; Rosing, Minik T

2012-03-20

Oxygen and hydrogen isotope compositions of Earth's seawater are controlled by volatile fluxes among mantle, lithospheric (oceanic and continental crust), and atmospheric reservoirs. Throughout geologic time the oxygen mass budget was likely conserved within these Earth system reservoirs, but hydrogen's was not, as it can escape to space. Isotopic properties of serpentine from the approximately 3.8 Ga Isua Supracrustal Belt in West Greenland are used to characterize hydrogen and oxygen isotope compositions of ancient seawater. Archaean oceans were depleted in deuterium [expressed as δD relative to Vienna standard mean ocean water (VSMOW)] by at most 25 ± 5‰, but oxygen isotope ratios were comparable to modern oceans. Mass balance of the global hydrogen budget constrains the contribution of continental growth and planetary hydrogen loss to the secular evolution of hydrogen isotope ratios in Earth's oceans. Our calculations predict that the oceans of early Earth were up to 26% more voluminous, and atmospheric CH(4) and CO(2) concentrations determined from limits on hydrogen escape to space are consistent with clement conditions on Archaean Earth.

Isotope composition and volume of Earth’s early oceans

PubMed Central

Pope, Emily C.; Bird, Dennis K.; Rosing, Minik T.

2012-01-01

Oxygen and hydrogen isotope compositions of Earth’s seawater are controlled by volatile fluxes among mantle, lithospheric (oceanic and continental crust), and atmospheric reservoirs. Throughout geologic time the oxygen mass budget was likely conserved within these Earth system reservoirs, but hydrogen’s was not, as it can escape to space. Isotopic properties of serpentine from the approximately 3.8 Ga Isua Supracrustal Belt in West Greenland are used to characterize hydrogen and oxygen isotope compositions of ancient seawater. Archaean oceans were depleted in deuterium [expressed as δD relative to Vienna standard mean ocean water (VSMOW)] by at most 25 ± 5‰, but oxygen isotope ratios were comparable to modern oceans. Mass balance of the global hydrogen budget constrains the contribution of continental growth and planetary hydrogen loss to the secular evolution of hydrogen isotope ratios in Earth’s oceans. Our calculations predict that the oceans of early Earth were up to 26% more voluminous, and atmospheric CH4 and CO2 concentrations determined from limits on hydrogen escape to space are consistent with clement conditions on Archaean Earth. PMID:22392985

Influence of the balance of the intertropical front on seasonal variations of the isotopic composition in rainfall at Kisiba Masoko (Rungwe Volcanic Province, SW, Tanzania).

PubMed

Nivet, Fantine; Bergonzini, Laurent; Mathé, Pierre-Etienne; Noret, Aurélie; Monvoisin, Gaël; Majule, Amos; Williamson, David

2018-08-01

Tropical rainfall isotopic composition results from complex processes. The climatological and environmental variability in East Africa increases this complexity. Long rainfall isotope datasets are needed to fill the lack of observations in this region. At Kisiba Masoko, Tanzania, rainfall and rain isotopic composition have been monitored during 6 years. Mean year profiles allow to analyse the seasonal variations. The mean annual rainfall is 2099 mm with a rain-weighted mean composition of -3.2 ‰ for δ 18 O and -11.7 ‰ for δ 2 H. The results are consistent with available data although they present their own specificity. Thus, if the local meteoric water line is δ 2 H = 8.6 δ 18 O + 14.8, two seasonal lines are observed. The seasonality of the isotopic composition in rain and deuterium excess has been compared with precipitating air masses backtracking trajectories to characterize a simple scheme of vapour histories. The three major oceanic sources have two moisture signatures with their own trajectory histories: one originated from the tropical Indian Ocean at the beginning of the rainy season and one from the Austral Ocean at its end. The presented isotopic seasonality depends on the balance of the intertropical front and provides a useful dataset to improve the knowledge about local processes.

SIMSISH Technique Does Not Alter the Apparent Isotopic Composition of Bacterial Cells

PubMed Central

Chapleur, Olivier; Wu, Ting-Di; Guerquin-Kern, Jean-Luc; Mazéas, Laurent; Bouchez, Théodore

2013-01-01

In order to identify the function of uncultured microorganisms in their environment, the SIMSISH method, combining in situ hybridization (ISH) and nanoscale secondary ion mass spectrometry (nanoSIMS) imaging, has been proposed to determine the quantitative uptake of specific labelled substrates by uncultured microbes at the single cell level. This technique requires the hybridization of rRNA targeted halogenated DNA probes on fixed and permeabilized microorganisms. Exogenous atoms are introduced into cells and endogenous atoms removed during the experimental procedures. Consequently differences between the original and the apparent isotopic composition of cells may occur. In the present study, the influence of the experimental procedures of SIMSISH on the isotopic composition of carbon in E. coli cells was evaluated with nanoSIMS and compared to elemental analyser-isotopic ratio mass spectrometer (EA-IRMS) measurements. Our results show that fixation and hybridization have a very limited, reproducible and homogeneous influence on the isotopic composition of cells. Thereby, the SIMSISH procedure minimizes the contamination of the sample by exogenous atoms, thus providing a means to detect the phylogenetic identity and to measure precisely the carbon isotopic composition at the single cell level. This technique was successfully applied to a complex sample with double bromine – iodine labelling targeting a large group of bacteria and a specific archaea to evaluate their specific 13C uptake during labelled methanol anaerobic degradation. PMID:24204855

Stable isotope compositions of waters in the Great Basin, United States 3. Comparison of groundwaters with modern precipitation

USGS Publications Warehouse

Smith, G.I.; Friedman, I.; Veronda, G.; Johnson, C.A.

2002-01-01

Groundwater samples from wells and springs, scattered over most of the Great Basin province, were collected and analyzed for their isotopic makeup. They were augmented by previously published isotopic data on groundwaters from southeast California and by several hundred unpublished isotopic analyses. The ratio of 2H (deuterium, D) to 1H, in water samples from valleys in parts of California, Idaho, Nevada, Oregon, and Utah, are here compared with the winter, summer, and annual isotopic compositions of precipitation falling in or near the sampled areas. The main goal of this study was to identify basins where the groundwaters have isotopic compositions that are "lighter" (depleted in the heavier isotope, D) relative to modern winter precipitation. Where these basins do not adjoin substantially higher terrain, we consider those light groundwaters to be of Pleistocene age and thus more than 10,000 years old. Where the groundwater is 10 to 19??? lighter than local winter precipitation, we consider it to be possibly an indication of Pleistocene water; where the ??D makeup is >20??? lighter, we consider it to be probably Pleistocene water. More than 80 sites underlain by waters of possible or probable Pleistocene age were identified.

Origin of isotopically light Zn in lunar samples through vaporization and the Zn isotope composition of the Moon

NASA Astrophysics Data System (ADS)

Kato, C.; Valdes, M. C.; Dhaliwal, J.; Day, J. M.; Moynier, F.

2013-12-01

The origin of the volatile element depletion of the Moon compared to Earth remains a key question in planetary science. It has recently been shown that both high-Ti and low-Ti lunar basalts are enriched in the heavier isotopes of Zn compared to Earth with an effect of ~1.3 permil on the 66Zn/64Zn ratio (Paniello et al., Nature, 2012). In order to obtain a better understanding of Zn behavior in and on the Moon, we present new measurements of lunar basalts, pyroclastic green glass 15426, highland anorthosites, cataclastic dunite 77215, cataclastic norite 72415 and some lunar soils. Samples were analyzed using a Thermo-Fisher Neptune Plus multi collector inductively coupled plasma mass spectrometer (MC-ICP-MS) at Washington University in St Louis. The data presented below are reported as the permil deviation of the 66Zn/64Zn ratio from the JMC-Lyon standard (δ66Zn). Four new high Ti basalts and three low Ti basalts confirm the observations of Paniello et al. (2012), that there is an enrichment in the heavier isotopes of Zn compared with chondrites and terrestrial samples. Combining these data together with Paniello et al. (2012) and Herzog et al. (GCA, 2009) we calculate a new average for lunar basalts of δ66Zn= 1.4×0.4 (1sd, n = 27). A few exceptions (5 samples out of 32) are isotopically light and probably represent addition of isotopically light Zn condensed onto the lunar surface from Zn isotopic fractionation during meteoritic impact, creating correspondingly isotopically heavy soils. In contrast to the homogeneity of mare basalts, highland samples show large Zn isotopic variability (δ66Zn -11.4 up to +4.24 permil) which encompasses the entire Zn isotopic variability measured so far in the Solar System. These δ66Zn variations are negatively correlated with the Zn abundance, with the isotopically light samples having the highest Zn concentrations. We interpret these results as the consequence of meteoritic bombardment and volatilization/condensation of Zn at the surface of the Moon. This represents secondary effects and mixing with exogenous Zn, explaining the higher abundance of Zn in highland rocks, relative to mare basalts. The pyroclastic green glass (15426) has a higher measured Zn concentration (~50ppm) compared with mare basalts, but is still depleted in Zn relative to most terrestrial basalts (typically >50 to 100 ppm). 15426 is also isotopically light (δ66Zn= -0.98), which is similar to previous measurements of Zn composition made for high-Ti pyroclastic glass beads (74220). We interpret the composition of the lunar pyroclastic glasses to reflect lava fountaining and coating of the surface of the beads by a volatile rich and isotopically light vapor. Thus, we conclude that mare basalts, which are isotopically heavier than the Earth, best represent the lunar silicate composition.

Stable calcium isotope composition of a pedogenic carbonate in forested ecosystem: the case of the needle fibre calcite (NFC).

NASA Astrophysics Data System (ADS)

Milliere, Laure; Verrecchia, Eric; Gussone, Nikolaus

2014-05-01

Calcium (Ca), carbon (C) and oxygen (O) are important elements in terrestrial environment, as their biogeochemical cycles are directly related to the storage of atmospheric carbon. Nevertheless, contrarily to C and O, Ca isotope composition has been only poorly studied in the terrestrial carbonates. Needle Fibre Calcite (NFC) is one of the most common pedogenic carbonates, unless its origin is still under debate. Recent studies explain its formation by precipitation inside fungal hyphae. Due to this possible biogenic origin, NFC can be considered as a potential bridge between the biochemistry (precipitation inside organic structure) and geochemistry (pedogenic carbonate related to soil conditions) of the Ca. Thus, the study of the Ca isotope composition of NFC seem to be of first interest in order to shed light on the behaviour of Ca in terrestrial environment, especially when precipitation of secondary carbonates is involved. The sampling site is situated in the Swiss Jura Mountains and has been chosen due to a previous complete study of the C and O isotope composition of NFC in relation to the ecosystem, which represent a good precondition for the understanding of the NFC Ca isotope signatures in this context. In this study, the implication of the fungi in the origin of NFC is investigated, by comparing the Ca isotope composition of NFC and a purely physicochemical calcite cement (LCC), both precipitated in the same environment. The δ44Ca signature of NFC and LCC crystals were used to determine possible differences of the precipitation rate during their formation. NFC and LCC have similar δ18O composition and are supposed to precipitate at the same temperature (Milliere et al., 2011a). Thus the study of Ca isotope composition of NFC seems to demonstrate that the elongated shape of the calcite needle can be explained by different precipitation processes than the rhombohedric calcite crystals precipitated in the same environment; and more precisely, the specific shape of NFC could be ascribed to a growth related to fungal organic molecules or potentially inside fungal hyphae. Three microscopic morphologies of NFC, previously defined (Milliere et al., 2011a), have been also examined in order to trace the evolution of the NFC inside the soil porosity. The Ca isotope composition of the simple needles, which are supposed to be the original form of NFC are the less fractionated compared to the soil solution, whereas the Ca isotope composition of the two other microscopic morphologies, namely the simple needle with nanofibres and the simple needle with overgrowths, are more fractionated, like the LCC, indicating potentially the influence of biogenic processes in the formation of the simple needles. Milliere L, Hasinger O, Bindschedler S, Cailleau G, Spangenberg JE, Verrecchia EP. 2011a. Stable carbon and oxygen isotopic signatures of pedogenic needle fibre calcite. Geoderma 161, 74-87.

Compound-specific isotopes of fatty acids as indicators of trophic interactions in the East China Sea ecosystem

NASA Astrophysics Data System (ADS)

Wu, Ying; Wang, Na; Zhang, Jing; Wan, Ruijing; Dai, Fangqun; Jin, Xianshi

2016-09-01

The composition and compound-specific isotopes of fatty acids were studied within food webs in the East China Sea. Lipid-normalized stable carbon isotopes of total organic carbon had a good correlation with trophic level. Variations in fatty acid compositions among diff erent species were observed but were unclear. Diff erent dietary structures could be traced from molecular isotopes of selected fatty acids in the Shiba shrimp ( Matapenaeus joyneri), the coastal mud shrimp ( Solenocera crassicornis) and the northern Maoxia shrimp ( Acetes chinensis). Both M. joyneri and S. crassicornis are mainly benthos feeders, while A. chinensis is a pelagic species, although they have a similar fatty acid composition. There was a good correlation for isotopes of arachidonic acid (C20:4n6; ARA) and docosahexaenoic acid (C22:6n3; DHA) among pelagic species from higher trophic levels. The isotopic compositions of DHA in benthic species were more negative than those of pelagic species at the same trophic level. The fact that the diet of benthic species contains more degraded items, the carbon isotopes of which are derived from a large biochemical fraction, may be the reason for this variation. A comparative study of benthic and pelagic species demonstrated the diff erent carbon sources in potential food items and the presence of a more complex system at the water-sediment interface.

Authentication and traceability of Italian extra-virgin olive oils by means of stable isotopes techniques.

PubMed

Portarena, S; Gavrichkova, O; Lauteri, M; Brugnoli, E

2014-12-01

Authentication of food origin is relevant to avoid food fraud. This work aimed to explore the variation of isotopic compositions (δ(13)C, δ(18)O) of extra-virgin olive oils from Italy growing in different environmental conditions. A total of 387 oil samples from nine different regions (from North to South), produced on 2009, 2010 and 2011, were analysed. Statistical analysis showed correlations among oil isotope compositions and latitude, mean annual temperature, mean annual precipitation and xerothermic index. No correlation was found comparing isotope compositions with elevation and longitude. An observed shift of the oil δ(18)O per centigrade degree of the mean annual temperature is congruent with literature. The year effect was significant for both δ(18)O and δ(13)C. Samples from Sicilia and Sardegna were higher in (13)C and (18)O than oils from northern regions. Copyright © 2014 Elsevier Ltd. All rights reserved.

Constraints on Galactic Cosmic-Ray Origins from Elemental and Isotopic Composition Measurements

NASA Technical Reports Server (NTRS)

Binns, W. R.; Christian, E. R.; Cummings, A. C.; deNolfo, G. A.; Israel, M. H.; Leske, R. A.; Mewaldt, R. A,; Stone, E. C.; vonRosevinge, T. T.; Wiedenbeck, M. E.

2013-01-01

The most recent measurements by the Cosmic Ray Isotope Spectrometer (CRIS) aboard the Advanced Composition Explorer (ACE) satellite of ultra-heavy cosmic ray isotopic and elemental abundances will be presented. A range of isotope and element ratios, most importantly Ne-22/Ne-20, Fe-58/Fe-56, and Ga-31/Ge -32 show that the composition is consistent with source material that is a mix of approx 80% ISM (with Solar System abundances) and 20% outflow/ejecta from massive stars. In addition, our data show that the ordering of refractory and volatile elements with atomic mass is greatly improved when compared to an approx 80%/20% mix rather than pure ISM, that the refractory and volatile elements have similar slopes, and that refractory elements are preferentially accelerated by a factor of approx 4. We conclude that these data are consistent with an OB association origin of GCRs.

Combined simulation of carbon and water isotopes in a global ocean model

NASA Astrophysics Data System (ADS)

Paul, André; Krandick, Annegret; Gebbie, Jake; Marchal, Olivier; Dutkiewicz, Stephanie; Losch, Martin; Kurahashi-Nakamura, Takasumi; Tharammal, Thejna

2013-04-01

Carbon and water isotopes are included as passive tracers in the MIT general circulation model (MITgcm). The implementation of the carbon isotopes is based on the existing MITgcm carbon cycle component and involves the fractionation processes during photosynthesis and air-sea gas exchange. Special care is given to the use of a real freshwater flux boundary condition in conjunction with the nonlinear free surface of the ocean model. The isotopic content of precipitation and water vapor is obtained from an atmospheric GCM (the NCAR CAM3) and mapped onto the MITgcm grid system, but the kinetic fractionation during evaporation is treated explicitly in the ocean model. In a number of simulations, we test the sensitivity of the carbon isotope distributions to the formulation of fractionation during photosynthesis and compare the results to modern observations of δ13C and Δ14C from GEOSECS, WOCE and CLIVAR. Similarly, we compare the resulting distribution of oxygen isotopes to modern δ18O data from the NASA GISS Global Seawater Oxygen-18 Database. The overall agreement is good, but there are discrepancies in the carbon isotope composition of the surface water and the oxygen isotope composition of the intermediate and deep waters. The combined simulation of carbon and water isotopes in a global ocean model will provide a framework for studying present and past states of ocean circulation such as postulated from deep-sea sediment records.

On the origin and composition of Theia: Constraints from new models of the Giant Impact

NASA Astrophysics Data System (ADS)

Meier, M. M. M.; Reufer, A.; Wieler, R.

2014-11-01

Knowing the isotopic composition of Theia, the proto-planet which collided with the Earth in the Giant Impact that formed the Moon, could provide interesting insights on the state of homogenization of the inner Solar System at the late stages of terrestrial planet formation. We use the known isotopic and modeled chemical compositions of the bulk silicate mantles of Earth and Moon and combine them with different Giant Impact models, to calculate the possible ranges of isotopic composition of Theia in O, Si, Ti, Cr, Zr and W in each model. We compare these ranges to the isotopic composition of carbonaceous chondrites, Mars, and other Solar System materials. In the absence of post-impact isotopic re-equilibration, the recently proposed high angular momentum models of the Giant Impact ("impact-fission", Cúk, M., Stewart, S.T. [2012]. Science 338, 1047; and "merger", Canup, R.M. [2012]. Science 338, 1052) allow - by a narrow margin - for a Theia similar to CI-chondrites, and Mars. The "hit-and-run" model (Reufer, A., Meier, M.M.M., Benz, W., Wieler, R. [2012]. Icarus 221, 296-299) allows for a Theia similar to enstatite-chondrites and other Earth-like materials. If the Earth and Moon inherited their different mantle FeO contents from the bulk mantles of the proto-Earth and Theia, the high angular momentum models cannot explain the observed difference. However, both the hit-and-run as well as the classical or "canonical" Giant Impact model naturally explain this difference as the consequence of a simple mixture of two mantles with different FeO. Therefore, the simplest way to reconcile the isotopic similarity, and FeO dissimilarity, of Earth and Moon is a Theia with an Earth-like isotopic composition and a higher (∼20%) mantle FeO content.

Stable Isotopes as Indicators of Groundwater Recharge Mechanisms in Arid and Semi-arid Australia

NASA Astrophysics Data System (ADS)

Harrington, G. A.; Herczeg, A. L.

2001-05-01

The isotopic compositions of soil water and groundwaters in arid and semi-arid zones are always different from the mean composition of rainfall. Although evaporative processes always remove the lighter isotopes (1H and 16O) to the vapour phase, arid zone groundwaters are invariably depleted in the heavy isotopes (2H and 18O) relative to mean present day rainfall. We compare two sites, one in semi-arid South Australia and the other in arid Central Australia that have a similar mean annual rainfall (250 to 300 mm/a), very high potential evapotranspiration (2500 and 3500 mm/a respectively) but very different rainfall patterns (winter dominated versus summer monsoonal). We aim to evaluate whether inferences from groundwater \\delta2H and \\delta18O reveal information about palaeorecharge, or recharge mechanisms or a combination of both. Recharge to the unconfined limestone aquifer in the Mallee area of South Australia occurs annually via widespread (diffuse) infiltration of winter dominant rainfall. This process is reflected in soil and groundwater isotopic compositions that plot relatively close to both the Local Meteoric Water Line and the volume-weighted mean composition of winter rainfall, and have a deuterium excess (\\delta2H-8.\\delta18O) of between +2 and +8 for the freshest samples. Groundwater recharge to the arid Ti-Tree Basin occurs predominantly by inputs of partially-evaporated surface water from ephemeral rivers and flood-plains following rare, high-intensity storms that are derived from monsoonal activity to the north of Australia. These extreme events result in groundwater and soil water stable isotope compositions being significantly depleted in the heavy isotopes relative to the mean composition of rainfall and a deuterium excess of between minus 8 and +3 in the freshest groundwaters.

Large-scale drivers of Caucasus climate variability in meteorological records and Mt El'brus ice cores

NASA Astrophysics Data System (ADS)

Kozachek, Anna; Mikhalenko, Vladimir; Masson-Delmotte, Valérie; Ekaykin, Alexey; Ginot, Patrick; Kutuzov, Stanislav; Legrand, Michel; Lipenkov, Vladimir; Preunkert, Susanne

2017-05-01

A 181.8 m ice core was recovered from a borehole drilled into bedrock on the western plateau of Mt El'brus (43°20'53.9'' N, 42°25'36.0'' E; 5115 m a.s.l.) in the Caucasus, Russia, in 2009 (Mikhalenko et al., 2015). Here, we report on the results of the water stable isotope composition from this ice core with additional data from the shallow cores. The distinct seasonal cycle of the isotopic composition allows dating by annual layer counting. Dating has been performed for the upper 126 m of the deep core combined with 20 m from the shallow cores. The whole record covers 100 years, from 2013 back to 1914. Due to the high accumulation rate (1380 mm w.e. year-1) and limited melting, we obtained isotopic composition and accumulation rate records with seasonal resolution. These values were compared with available meteorological data from 13 weather stations in the region and also with atmosphere circulation indices, back-trajectory calculations, and Global Network of Isotopes in Precipitation (GNIP) data in order to decipher the drivers of accumulation and ice core isotopic composition in the Caucasus region. In the warm season (May-October) the isotopic composition depends on local temperatures, but the correlation is not persistent over time, while in the cold season (November-April), atmospheric circulation is the predominant driver of the ice core's isotopic composition. The snow accumulation rate correlates well with the precipitation rate in the region all year round, which made it possible to reconstruct and expand the precipitation record at the Caucasus highlands from 1914 until 1966, when reliable meteorological observations of precipitation at high elevation began.

Forest Fires as a Possible Source of Isotopically Light Marine Fe Aerosols

NASA Astrophysics Data System (ADS)

Tegler, L. A.; Sherry, A. M.; Romaniello, S. J.; Anbar, A. D.

2016-12-01

Iron (Fe) is an important limiting micronutrient for primary productivity in many high-nutrient, low-chlorophyll (HNLC) regions of the ocean. These marine systems receive a significant fraction of their Fe from atmospheric deposition, which is thought to be dominated by mineral dust with an Fe isotopic composition at or above 0‰. However, Mead et al. (2013) observed isotopically light Fe in marine aerosols smaller than 2.5 μm, which is difficult to reconcile with known sources of marine aerosols. Based on previous experimental work, we hypothesize that biomass burning is the source of isotopically light Fe in atmospheric particles and suggest that biomass burning might represent an underappreciated source of Fe to marine ecosystems. While Guelke et al (2007) demonstrated that Fe in agricultural plants is isotopically light, few studies have examined the Fe isotope composition of naturally occurring forests likely to be a significant source of Fe during forest fires. To address this question, we measured the isotopic composition of Ponderosa pine growing in northern Arizona. Ponderosa pine is one the most common forest types in the western US and thus representative of an important North American fire region. Pine needles were chosen because they are susceptible to complete combustion during biomass burning events. To determine the Fe isotopic composition of pine trees, pine needles were sampled at various tree heights. We found that these samples had δ56Fe values between -1.5 and 0‰, indicating that pine needles can be isotopically light compared to local grasses and soil. These results support the hypothesis that biomass burning may contribute isotopically light Fe to marine aerosols.

Carbon, nitrogen, magnesium, silicon, and titanium isotopic compositions of single interstellar silicon carbide grains from the Murchison carbonaceous chondrite

NASA Technical Reports Server (NTRS)

Hoppe, Peter; Amari, Sachiko; Zinner, Ernst; Ireland, Trevor; Lewis, Roy S.

1994-01-01

Seven hundred and twenty SiC grains from the Murchison CM2 chondrite, ranging in size from 1 to 10 micrometers, were analyzed by ion microprobe mass spectrometry for their C-isotopic compositions. Subsets of the grains were also analyzed for N (450 grains), Si (183 grains), Mg (179 grains), and Ti (28 grains) isotopes. These results are compared with previous measurements on 41 larger SiC grains (up to 15 x 26 micrometers) from a different sample of Murchison analyzed by Virag et al. (1992) and Ireland, Zinner, & Amari (1991a). All grains of the present study are isotopically anomalous with C-12/C-13 ratios ranging from 0.022 to 28.4 x solar, N-14/N-15 ratios from 0.046 to 30 x solar, Si-29/Si-28 from 0.54 to 1.20 x solar, Si-30/Si-28 from 0.42 to 1.14 x solar, Ti-49/Ti-48 from 0.96 to 1.95 x solar, and Ti-50/Ti-48 from 0.94 to 1.39 x solar. Many grains have large Mg-26 excesses from the decay of Al-26 with inferred Al-26/Al-27 ratios ranging up to 0.61, or 12,200 x the ratio of 5 x 10(exp -5) inferred for the early solar system. Several groups can be distinguished among the SiC grains. Most of the grains have C-13 and N-14 excesses, and their Si isotopic compositions (mostly excesses in Si-29 and Si-30) plot close to a slope 1.34 line on a Delta Si-29/Si-28 versus Delta Si-30/Si-28 three-isotope plot. Grains with small C-12/C-13 ratios (less than 10) tend to have smaller or no N-14 excesses and high Al-26/Al-27 ratios (up to 0.01). Grains with C-12/C-13 greater than 150 fall into two groups: grains X have N-15 excesses and Si-29 and Si-30 deficits and the highest (0.1 to 0.6) Al-26/Al-27 ratios; grains Y have N-14 excesses and plot on a slope 0.35 line on a Si three-isotope plot. In addition, large SiC grains of the Virag et al. (1992) study fall into three-distinct clusters according to their C-, Si-, and Ti-isotopic compositions. The isotopic diversity of the grains and the clustering of their isotopic compositions imply distinct and multiple stellar sources. The C- and N-isotopic compositions of most grains are consistent with H-burning in the CNO cycle. These and s-process Kr, Xe, Ba, and Nd suggest asymptotic giant branch (AGB) or Wolf-Rayet stars as likely sources for the grains, but existing models of nucleosynthesis in these stellar sites fail to account in detail for all the observed isotopic compositions. Special problems are posed by grains with C-12/C-13 less than 10 and almost normal and heavy N-isotopic compositions. Also the Si- and Ti-isotopic compositions, with excesses in Si-29 and Si-30 relative to Si-28 and excesses in all Ti isotopes relative to Ti-48, do not precisely conform with the compositions predicted for slow neutron capture. Additional theoretical efforts are needed to achieve an understanding of the isotopic composition of the SiC grains and their stellar sources.

The stable Cr isotopic compositions of chondrites and silicate planetary reservoirs

NASA Astrophysics Data System (ADS)

Schoenberg, Ronny; Merdian, Alexandra; Holmden, Chris; Kleinhanns, Ilka C.; Haßler, Kathrin; Wille, Martin; Reitter, Elmar

2016-06-01

The depletion of chromium in Earth's mantle (∼2700 ppm) in comparison to chondrites (∼4400 ppm) indicates significant incorporation of chromium into the core during our planet's metal-silicate differentiation, assuming that there was no significant escape of the moderately volatile element chromium during the accretionary phase of Earth. Stable Cr isotope compositions - expressed as the ‰-difference in 53Cr/52Cr from the terrestrial reference material SRM979 (δ53/52CrSRM979 values) - of planetary silicate reservoirs might thus yield information about the conditions of planetary metal segregation processes when compared to chondrites. The stable Cr isotopic compositions of 7 carbonaceous chondrites, 11 ordinary chondrites, 5 HED achondrites and 2 martian meteorites determined by a double spike MC-ICP-MS method are within uncertainties indistinguishable from each other and from the previously determined δ53/52CrSRM979 value of -0.124 ± 0.101‰ for the igneous silicate Earth. Extensive quality tests support the accuracy of the stable Cr isotope determinations of various meteorites and terrestrial silicates reported here. The uniformity in stable Cr isotope compositions of samples from planetary silicate mantles and undifferentiated meteorites indicates that metal-silicate differentiation of Earth, Mars and the HED parent body did not cause measurable stable Cr isotope fractionation between these two reservoirs. Our results also imply that the accretionary disc, at least in the inner solar system, was homogeneous in its stable Cr isotopic composition and that potential volatility loss of chromium during accretion of the terrestrial planets was not accompanied by measurable stable isotopic fractionation. Small but reproducible variations in δ53/52CrSRM979 values of terrestrial magmatic rocks point to natural stable Cr isotope variations within Earth's silicate reservoirs. Further and more detailed studies are required to investigate whether silicate differentiation processes, such as partial mantle melting and crystal fractionation, can cause stable Cr isotopic fractionation on Earth and other planetary bodies.

The mineralogy, petrology, and composition of anomalous eucrite Emmaville

NASA Astrophysics Data System (ADS)

Barrett, T. J.; Mittlefehldt, D. W.; Greenwood, R. C.; Charlier, B. L. A.; Hammond, S. J.; Ross, D. K.; Anand, M.; Franchi, I. A.; Abernethy, F. A. J.; Grady, M. M.

2017-04-01

The Emmaville eucrite is a relatively poorly studied basaltic achondrite with an anomalous oxygen isotope signature. In this study, we report comprehensive mineralogical, petrographic, and geochemical data from Emmaville in order to understand its petrogenesis and relationship with the basaltic eucrites. Emmaville is an unusually fine-grained, hornfelsic-textured metabasalt with pervasive impact melt veins and mineral compositions similar to those of typical basaltic eucrites. The major and trace element bulk composition of Emmaville is also typical of a basaltic eucrite. Three separated individual lithologies were also analyzed for O isotopes; a dark gray fraction (E1), a shocked lithology (E2), and a lighter gray portion (E3). Fractions E1 and E2 shared similar O isotope compositions to the bulk sample (E-B), whereas the lighter gray portion (E3) is slightly elevated in Δ17O and significantly elevated in δ18O compared to bulk. No evidence for any exogenous material is observed in the thin sections, coupled with the striking compositional similarity to typical basaltic eucrites, appears to preclude a simple impact-mixing hypothesis. The O-isotopes of Emmaville are similar to those of Bunburra Rockhole, A-881394, and EET 92023, and thus distinct from the majority of the HEDs, despite having similarities in petrology, mineral, and bulk compositions. It would, therefore, seem plausible that all four of these samples are derived from a single HED-like parent body that is isotopically distinct from that of the HEDs (Vesta) but similar in composition.

The record of mantle heterogeneity preserved in Earth's oceanic crust

NASA Astrophysics Data System (ADS)

Burton, K. W.; Parkinson, I. J.; Schiano, P.; Gannoun, A.; Laubier, M.

2017-12-01

Earth's oceanic crust is produced by melting of the upper mantle where it upwells beneath mid-ocean ridges, and provides a geographically widespread elemental and isotopic `sample' of Earth's mantle. The chemistry of mid-ocean ridge basalts (MORB), therefore, holds key information on the compositional diversity of the upper mantle, but the problem remains that mixing and reaction during melt ascent acts to homogenise the chemical variations they acquire. Nearly all isotope and elemental data obtained thus far are for measurements of MORB glass, and this represents the final melt to crystallise, evolving in an open system. However, the crystals that are present are often not in equilibrium with their glass host. Melts trapped in these minerals indicate that they crystallised from primitive magmas that possess diverse compositions compared to the glass. Therefore, these melt inclusions preserve information on the true extent of the mantle that sources MORB, but are rarely amenable to precise isotope measurement. An alternative approach is to measure the isotope composition of the primitive minerals themselves. Our new isotope data indicates that these minerals crystallised from melts with significantly different isotope compositions to their glass host, pointing to a mantle source that has experienced extreme melt depletion. These primitive minerals largely crystallised in the lower oceanic crust, and our preliminary data for lower crustal rocks and minerals shows that they preserve a remarkable range of isotope compositions. Taken together, these results indicate that the upper mantle sampled by MORB is extremely heterogeneous, reflecting depletion and enrichment over much of Earth's geological history.

Detecting intraannual dietary variability in wild mountain gorillas by stable isotope analysis of feces

PubMed Central

Blumenthal, Scott A.; Chritz, Kendra L.; Rothman, Jessica M.; Cerling, Thure E.

2012-01-01

We use stable isotope ratios in feces of wild mountain gorillas (Gorilla beringei) to test the hypothesis that diet shifts within a single year, as measured by dry mass intake, can be recovered. Isotopic separation of staple foods indicates that intraannual changes in the isotopic composition of feces reflect shifts in diet. Fruits are isotopically distinct compared with other staple foods, and peaks in fecal δ13C values are interpreted as periods of increased fruit feeding. Bayesian mixing model results demonstrate that, although the timing of these diet shifts match observational data, the modeled increase in proportional fruit feeding does not capture the full shift. Variation in the isotopic and nutritional composition of gorilla foods is largely independent, highlighting the difficulty for estimating nutritional intake with stable isotopes. Our results demonstrate the potential value of fecal sampling for quantifying short-term, intraindividual dietary variability in primates and other animals with high temporal resolution even when the diet is composed of C3 plants. PMID:23236160

A comparison of chemical compositions of reported altered oceanic crusts and global MORB data set: implication for isotopic heterogeneity of recycled materials

NASA Astrophysics Data System (ADS)

Shimoda, G.; Kogiso, T.

2017-12-01

Chemical composition of altered oceanic crust is one of important constraints to delineate chemical heterogeneity of the mantle. Accordingly, many researchers have been studied to determine bulk chemical composition of altered oceanic crust mainly based on chemical compositions of old oceanic crusts at Site 801 and Site 417/418, and young crust at Site 504 (e.g., Staudigel et al., 1996; Bach et al. 2003; Kuo et al., 2016). Their careful estimation provided reliable bulk chemical compositions of these Sites and revealed common geochemical feature of alteration. To assess effect of recycling of altered oceanic crust on chemical evolution of the mantle, it might be meaningful to discuss whether the reported chemical compositions of altered oceanic crusts can represent chemical composition of globally subducted oceanic crusts. Reported chemical compositions of fresh glass or less altered samples from Site 801, 417/418 and 504 were highly depleted compared to that of global MORB reported by Gale et al. (2013), suggesting that there might be sampling bias. Hence, it could be important to consider chemical difference between oceanic crusts of these three Sites and global MORB to discuss effect of recycling of oceanic crust on isotopic heterogeneity of the mantle. It has been suggested that one of controlling factors of chemical variation of oceanic crust is crustal spreading rate because different degree of partial melting affects chemical composition of magmas produced at a mid-ocean ridge. Crustal spreading rate could also affect intensity of alteration. Namely, oceanic crusts produced at slow-spreading ridges may prone to be altered due to existence of larger displacement faults compared to fast spreading ridges which have relatively smooth topography. Thus, it might be significant to evaluate isotopic evolution of oceanic crusts those were produced at different spreading rates. In this presentation, we will provide a possible chemical variation of altered oceanic crusts based on reported bulk chemical compositions of altered oceanic crusts and global data sets of MORB. On the basis of the chemical variation, we will discuss isotopic evolution of altered oceanic crusts to delineate isotopic variation of recycled oceanic crusts.

Carbon and hydrogen isotopic effects of stomatal density in Arabidopsis thaliana

NASA Astrophysics Data System (ADS)

Lee, Hyejung; Feakins, Sarah J.; Sternberg, Leonel da S. L.

2016-04-01

Stomata are key gateways mediating carbon uptake and water loss from plants. Varied stomatal densities in fossil leaves raise the possibility that isotope effects associated with the openness of exchange may have mediated plant wax biomarker isotopic proxies for paleovegetation and paleoclimate in the geological record. Here we use Arabidopsis thaliana, a widely used model organism, to provide the first controlled tests of stomatal density on carbon and hydrogen isotopic compositions of cuticular waxes. Laboratory grown wildtype and mutants with suppressed and overexpressed stomatal densities allow us to directly test the isotope effects of stomatal densities independent of most other environmental or biological variables. Hydrogen isotope (D/H) measurements of both plant waters and plant wax n-alkanes allow us to directly constrain the isotopic effects of leaf water isotopic enrichment via transpiration and biosynthetic fractionations, which together determine the net fractionation between irrigation water and n-alkane hydrogen isotopic composition. We also measure carbon isotopic fractionations of n-alkanes and bulk leaf tissue associated with different stomatal densities. We find offsets of +15‰ for δD and -3‰ for δ13C for the overexpressed mutant compared to the suppressed mutant. Since the range of stomatal densities expressed is comparable to that found in extant plants and the Cenozoic fossil record, the results allow us to consider the magnitude of isotope effects that may be incurred by these plant adaptive responses. This study highlights the potential of genetic mutants to isolate individual isotope effects and add to our fundamental understanding of how genetics and physiology influence plant biochemicals including plant wax biomarkers.

Cu isotope fractionation response to oxidative stress in a hepatic cell line studied using multi-collector ICP-mass spectrometry.

PubMed

Flórez, María R; Costas-Rodríguez, Marta; Grootaert, Charlotte; Van Camp, John; Vanhaecke, Frank

2018-03-01

Reactive oxygen species (ROS) are generated in biological processes involving electron transfer reactions and can act in a beneficial or deleterious way. When intracellular ROS levels exceed the cell's anti-oxidant capacity, oxidative stress occurs. In this work, Cu isotope fractionation was evaluated in HepG2 cells under oxidative stress conditions attained in various ways. HepG2 is a well-characterised human hepatoblastoma cell line adapted to grow under high oxidative stress conditions. During a pre-incubation stage, cells were exposed to a non-toxic concentration of Cu for 24 h. Subsequently, the medium was replaced and cells were exposed to one of three different external stressors: H 2 O 2 , tumour necrosis factor α (TNFα) or UV radiation. The isotopic composition of the intracellular Cu was determined by multi-collector ICP-mass spectrometry to evaluate the isotope fractionation accompanying Cu fluxes between cells and culture medium. For half of these setups, the pre-incubation solution also contained N-acetyl-cysteine (NAC) as an anti-oxidant to evaluate its protective effect against oxidative stress via its influence on the extent of Cu isotope fractionation. Oxidative stress caused the intracellular Cu isotopic composition to be heavier compared to that in untreated control cells. The H 2 O 2 and TNFα exposures rendered similar results, comparable to those obtained after mild UV exposure. The heaviest Cu isotopic composition was observed under the strongest oxidative conditions tested, i.e., when the cell surfaces were directly exposed to UV radiation without apical medium and in absence of NAC. NAC mitigated the extent of isotope fractionation in all cases.

Isotopic constraints on ice age fluids in active geothermal systems: Reykjanes, Iceland

NASA Astrophysics Data System (ADS)

Pope, Emily C.; Bird, Dennis K.; Arnórsson, Stefán; Fridriksson, Thráinn; Elders, Wilfred A.; Fridleifsson, Gudmundur Ó.

2009-08-01

The Reykjanes geothermal system is located on the landward extension of the Mid-Atlantic Ridge in southwest Iceland, and provides an on-land proxy to high-temperature hydrothermal systems of oceanic spreading centers. Previous studies of elemental composition and salinity have shown that Reykjanes geothermal fluids are likely hydrothermally modified seawater. However, δD values of these fluids are as low as -23‰, which is indicative of a meteoric water component. Here we constrain the origin of Reykjanes hydrothermal solutions by analysis of hydrogen and oxygen isotope compositions of hydrothermal epidote from geothermal drillholes at depths between 1 and 3 km. δDEPIDOTE values from wells RN-8, -9, -10 and -17 collectively range from -60 to -78‰, and δ18OEPIDOTE in these wells are between -3.0 and 2.3‰. The δD values of epidote generally increase along a NE trend through the geothermal field, whereas δ18O values generally decrease, suggesting a southwest to northeast migration of the geothermal upflow zone with time that is consistent with present-day temperatures and observed hydrothermal mineral zones. For comparative analysis, the meteoric-water dominated Nesjavellir and Krafla geothermal systems, which have a δDFLUID of ˜ -79‰ and -89‰, respectively, show δDEPIDOTE values of -115‰ and -125‰. In contrast, δDEPIDOTE from the mixed meteoric-seawater Svartsengi geothermal system is -68‰; comparable to δDEPIDOTE from well RN-10 at Reykjanes. Stable isotope compositions of geothermal fluids in isotopic equilibrium with the epidotes at Reykjanes are computed using published temperature dependent hydrogen and oxygen isotope fractionation curves for epidote-water, measured isotope composition of the epidotes and temperatures approximated from the boiling point curve with depth. Calculated δD and δ18O of geothermal fluids are less than 0‰, suggesting that fluids of meteoric or glacial origin are a significant component of the geothermal solutions. Additionally, δDFLUID values in equilibrium with geothermal epidote are lower than those of modern-day fluids, whereas calculated δ18OFLUID values are within range of the observed fluid isotope composition. We propose that modern δDEPIDOTE and δDFLUID values are the result of diffusional exchange between hydrous alteration minerals that precipitated from glacially-derived fluids early in the evolution of the Reykjanes system and modern seawater-derived geothermal fluids. A simplified model of isotope exchange in the Reykjanes geothermal system, in which the average starting δDROCK value is -125‰ and the water to rock mass ratio is 0.25, predicts a δDFLUID composition within 1‰ of average measured values. This model resolves the discrepancy between fluid salinity and isotope composition of Reykjanes geothermal fluids, explains the observed disequilibrium between modern fluids and hydrothermal epidote, and suggests that rock-fluid interaction is the dominant control over the evolution of fluid isotope composition in the hydrothermal system.

About Tagish Lake as a Potential Parent Body for Polar Micrometeorites; Clues from their Hydrogen Isotopic Compositions

NASA Technical Reports Server (NTRS)

Engrand, C.; Gounelle, M.; Zolensky, M. E.; Duprat, J.

2003-01-01

The origin of the Antarctic micrometeorites (AMMs) is still a matter of debate. Their closest meteoritic counterparts are the C2 chondrites, but the match is not perfect, and the parent body(ies) of the AMMs is(are) still to be identified. Tagish Lake is a new meteorite fall which bears similarity with CI1 and CM2 chondrites, but is distinct from both. Based on the mineralogy of phyllosilicates, Noguchi et al. proposed that the phyllosilicate-rich AMMs and the Tagish Lake meteorites could derive from similar asteroids. The hydrogen isotopic compositions of extra-terrestrial samples can be used to get some insight on their origin. The D/H ratios of AMMs and of Tagish Lake have been measured, but using different analytical techniques. They are therefore not directly comparable. We performed additional hydrogen isotopic analyses of fragments of Tagish Lake using the same experimental setup previously used for the measurement of the hydrogen isotopic composition of AMMs. In this work, we could also analyze separately both lithologies of Tagish Lake (carbonate-poor and -rich). The distributions of delta D values measured in the two lithologies of Tagish Lake are very similar, indicating that fluids with similar hydrogen isotopic compositions altered the meteorite on the parent body for the two lithologies. Yet, the hydrogen isotopic composition of Tagish Lake is different from that of AMMs, suggesting that they do not derive from the same parent body.

Isotopic modeling of the sub-cloud evaporation effect in precipitation.

PubMed

Salamalikis, V; Argiriou, A A; Dotsika, E

2016-02-15

In dry and warm environments sub-cloud evaporation influences the falling raindrops modifying their final stable isotopic content. During their descent from the cloud base towards the ground surface, through the unsaturated atmosphere, hydrometeors are subjected to evaporation whereas the kinetic fractionation results to less depleted or enriched isotopic signatures compared to the initial isotopic composition of the raindrops at cloud base. Nowadays the development of Generalized Climate Models (GCMs) that include isotopic content calculation modules are of great interest for the isotopic tracing of the global hydrological cycle. Therefore the accurate description of the underlying processes affecting stable isotopic content can improve the performance of iso-GCMs. The aim of this study is to model the sub-cloud evaporation effect using a) mixing and b) numerical isotope evaporation models. The isotope-mixing evaporation model simulates the isotopic enrichment (difference between the ground and the cloud base isotopic composition of raindrops) in terms of raindrop size, ambient temperature and relative humidity (RH) at ground level. The isotopic enrichment (Δδ) varies linearly with the evaporated raindrops mass fraction of the raindrop resulting to higher values at drier atmospheres and for smaller raindrops. The relationship between Δδ and RH is described by a 'heat capacity' model providing high correlation coefficients for both isotopes (R(2)>80%) indicating that RH is an ideal indicator of the sub-cloud evaporation effect. Vertical distribution of stable isotopes in falling raindrops is also investigated using a numerical isotope-evaporation model. Temperature and humidity dependence of the vertical isotopic variation is clearly described by the numerical isotopic model showing an increase in the isotopic values with increasing temperature and decreasing RH. At an almost saturated atmosphere (RH=95%) sub-cloud evaporation is negligible and the isotopic composition hardly changes even at high temperatures while at drier and warm conditions the enrichment of (18)Ο reaches up to 20‰, depending on the raindrop size and the initial meteorological conditions. Copyright © 2015 Elsevier B.V. All rights reserved.

[Research advances in identifying nitrate pollution sources of water environment by using nitrogen and oxygen stable isotopes].

PubMed

Mao, Wei; Liang, Zhi-wei; Li, Wei; Zhu, Yao; Yanng, Mu-yi; Jia, Chao-jie

2013-04-01

Water body' s nitrate pollution has become a common and severe environmental problem. In order to ensure human health and water environment benign evolution, it is of great importance to effectively identify the nitrate pollution sources of water body. Because of the discrepant composition of nitrogen and oxygen stable isotopes in different sources of nitrate in water body, nitrogen and oxygen stable isotopes can be used to identify the nitrate pollution sources of water environment. This paper introduced the fractionation factors of nitrogen and oxygen stable isotopes in the main processes of nitrogen cycling and the composition of these stable isotopes in main nitrate sources, compared the advantages and disadvantages of five pre-treatment methods for analyzing the nitrogen and oxygen isotopes in nitrate, and summarized the research advances in this aspect into three stages, i. e. , using nitrogen stable isotope alone, using nitrogen and oxygen stable isotopes simultaneously, and combining with mathematical models. The future research directions regarding the nitrate pollution sources identification of water environment were also discussed.

Paleoclimate Reconstruction at Lamanai, Belize Using Oxygen-Isotope Tropical Dendrochronology

NASA Astrophysics Data System (ADS)

Prentice, A.; Webb, E. A.; White, C. D.; Graham, E.

2009-05-01

Tropical dendrochronology can be complicated because many trees growing in these areas lack distinct visible annual rings. However, the oxygen-isotope composition of wood growing in tropical regions can provide a record of seasonal fluctuations in the amount of precipitation even when visible rings are absent. Variations in the oxygen-isotope compositions of cellulose as the trees grow can be related to the relative timing of wet and dry seasons and used to identify periods of drought. In this study, the oxygen-isotope composition was determined for cellulose extracted from living trees at the site of Lamanai, Belize to assess the variation in oxygen-isotope values that result from heterogeneity within individual tree rings and seasonal fluctuations in amount of precipitation. In temperate regions, the latewood rings that form during periods of reduced growth are traditionally selected for oxygen-isotope analysis of cellulose because their oxygen-isotope compositions are more directly influenced by climate and precipitation during the growing season. However, in tropical isotope dendrochronology, when visible rings are present, detailed sampling of both the light coloured earlywood and the denser latewood is required. At Lamanai, a seasonal signal was evident in the oxygen- isotope composition of the cellulose when tree rings were sectioned in very small increments (approximately every mm), sub-sampling both earlywood and latewood. However, the visible rings did not always correspond with minimum or maximum oxygen-isotope values. As a result, the amplitude of the oxygen-isotope signal obtained by considering only latewood samples is smaller than that obtained from fine-increment sampling. Hence, the oxygen-isotope values of latewood samples alone did not provide accurate data for climate reconstruction. Multiple series of latewood samples extracted from different cross-sections of the same tree did not consistently show the same trends in oxygen isotope values, which can differ by up to 2 permil around the circumference of the same ring. This indicates that even when visible rings are present in tropical trees, the rings may not be annual or continuous. However, the amplitude of variation in the oxygen-isotope values of cellulose from both early and latewood can be related to seasonal signals across the modern tree rings. These signals will be compared to the oxygen-isotope composition of tree ring cellulose extracted from a wood sample excavated from an ancient tomb at the site of Lamanai to assess the preservation of the cellulose- isotope signal in this artefact. If similar oxygen-isotope patterns are preserved in ancient cellulose they can be used as a proxy to determine past climate conditions, such as those experienced by the ancient Maya populations in Belize.

Estimates of lake trout (Salvelinus namaycush) diet in Lake Ontario using two and three isotope mixing models

USGS Publications Warehouse

Colborne, Scott F.; Rush, Scott A.; Paterson, Gordon; Johnson, Timothy B.; Lantry, Brian F.; Fisk, Aaron T.

2016-01-01

Recent development of multi-dimensional stable isotope models for estimating both foraging patterns and niches have presented the analytical tools to further assess the food webs of freshwater populations. One approach to refine predictions from these analyses is to include a third isotope to the more common two-isotope carbon and nitrogen mixing models to increase the power to resolve different prey sources. We compared predictions made with two-isotope carbon and nitrogen mixing models and three-isotope models that also included sulphur (δ34S) for the diets of Lake Ontario lake trout (Salvelinus namaycush). We determined the isotopic compositions of lake trout and potential prey fishes sampled from Lake Ontario and then used quantitative estimates of resource use generated by two- and three-isotope Bayesian mixing models (SIAR) to infer feeding patterns of lake trout. Both two- and three-isotope models indicated that alewife (Alosa pseudoharengus) and round goby (Neogobius melanostomus) were the primary prey items, but the three-isotope models were more consistent with recent measures of prey fish abundances and lake trout diets. The lake trout sampled directly from the hatcheries had isotopic compositions derived from the hatchery food which were distinctively different from those derived from the natural prey sources. Those hatchery signals were retained for months after release, raising the possibility to distinguish hatchery-reared yearlings and similarly sized naturally reproduced lake trout based on isotopic compositions. Addition of a third-isotope resulted in mixing model results that confirmed round goby have become an important component of lake trout diet and may be overtaking alewife as a prey resource.

Relationship between the trajectory of mid-latitude cyclones in the eastern Pacific Ocean and the isotopic composition of snowfall in the Sierra Nevada, California

NASA Astrophysics Data System (ADS)

Vasquez, K. T.; Sickman, J. O.; Lucero, D. M.; Heard, A. M.

2014-12-01

Climate change has caused a change in the Sierra Nevada snowpack and the timing of its snowmelt, threatening a valuable water resource that provides for 25 million people and 5 million hectares of irrigated land. Understanding past and future variations in the snowpack is crucial in order to plan future water management. Of particular importance would be an archive of the variability of past snowfall, which can be recorded through the isotopic records found in local paleoproxies (e.g., diatoms). We propose to quantify the relationship between sources of atmospheric moisture in the Sierra Nevada and the isotopic composition of its snowpack to uncover whether isotopic variations recorded in paloearchives are a result of the isotopic composition of the precipitation, thereby showing whether these archives could serve as a reliable source of atmospheric moisture. Preliminary analysis conducted from December 2012 to March 2013 at Sequoia National Park resulted in statistically significant correlations between the isotopic composition of the winter snowfall and storm track trajectories. It was observed that storms originating from more northern latitudes had predominantly lighter isotopes (more negative δ 2H and δ18O) and sub-tropical/tropical Pacific storms showed more positive δ 2H and δ18O. This pattern reflects the isotopic gradient of the Pacific Ocean and can prove useful when interpreting the climatic significance of the δ2H and δ18O values in analyzed proxies. While our initial investigation was promising, the winter of 2012 -2013 was abnormally dry compared to long-term averages. Before directing our investigation to known paleoproxies, we aim to determine if the correlation between storm tracks and isotopic composition of precipitation holds in years with average and above average precipitation through analysis of archived samples from calendar years 2007 - 2011 from Giant Forest in Sequoia National Park (southern sierra) and Manzanita Lake in Lassen Volcanic National Park (northern sierra).

Stable isotope fractionation of tungsten during adsorption on Fe and Mn (oxyhydr)oxides

NASA Astrophysics Data System (ADS)

Kashiwabara, Teruhiko; Kubo, Sayuri; Tanaka, Masato; Senda, Ryoko; Iizuka, Tsuyoshi; Tanimizu, Masaharu; Takahashi, Yoshio

2017-05-01

The similar, but not identical chemical properties of W compared with Mo suggest that the stable isotope system of W could be a novel proxy to explore the modern and ancient ocean as is the case in the well-established utility of Mo isotopes. We experimentally investigated the isotopic fractionation of W during adsorption on Fe and Mn (oxyhydr)oxides (ferrihydrite and δ-MnO2), a key process in the global ocean budget of this element. Our adsorption experiments confirmed that W isotopes fractionate substantially on both ferrihydrite and δ-MnO2: lighter W isotopes are preferentially adsorbed on both oxides as a result of equilibrium isotopic exchange between dissolved and adsorbed species, and the obtained values of Δ186/183Wliquid-solid (= δ186Wdissolved - δ186Wadsorbed) are 0.76 ± 0.09‰ for ferrihydrite and 0.88 ± 0.21‰ for δ-MnO2 (2σ, n = 6). Compared with the case of Mo isotopes, fractionation of W isotopes is (i) of comparable magnitude between ferrihydrite and δ-MnO2, and (ii) much smaller than that of Mo on δ-MnO2. Our previous XAFS observations and newly-performed DFT calculations both indicate that the observed W isotopic fractionations are caused by the symmetry change from Td (tetrahedral) WO42- to distorted Oh (octahedral) monomeric W species via formation of inner-sphere complexes on both ferrihydrite and δ-MnO2. The similar isotopic fractionations between the two oxides relate to the strong tendency for W to form inner-sphere complexes, which causes the symmetry change, in contrast to the outer-sphere complex of Mo on ferrihydrite. The smaller isotopic fractionation of W compared with Mo on δ-MnO2 despite their similar molecular symmetry seems to be due to their different degrees of distortion of Oh species. Our findings imply that the isotopic composition of W in modern oxic seawater is likely to become heavier relative to the input by removal of lighter W isotopes via adsorption on ferromanganese oxides in analogy with the Mo isotope budget. In contrast, the isotopic composition of W in ancient seawater should have evolved in response to the extent of deposition of both Fe and Mn oxides; this is likely to be different compared with that of the Mo isotopes, which is strongly associated with the occurrence of Mn oxides relative to Fe oxides.

Mechanisms controlling the silicon isotopic compositions of river waters

NASA Astrophysics Data System (ADS)

Georg, R. B.; Reynolds, B. C.; Frank, M.; Halliday, A. N.

2006-09-01

It has been proposed that silicon (Si) isotopes are fractionated during weathering and biological activity leading to heavy dissolved riverine compositions. In this study, the first seasonal variations of stable isotope compositions of dissolved riverine Si are reported and compared with concomitant changes in water chemistry. Four different rivers in Switzerland were sampled between March 2004 and July 2005. The unique high-resolution multi-collector ICP-MS Nu1700, has been used to provide simultaneous interference-free measurements of 28Si, 29Si and 30Si abundances with an average limiting precision of ± 0.04‰ on δ 30Si. This precision facilitates the clarification of small temporal variations in isotope composition. The average of all the data for the 40 samples is δ 30Si = + 0.84 ± 0.19‰ (± 1σ SD). Despite significant differences in catchment lithologies, biomass, climate, total dissolved solids and weathering fluxes the averaged isotopic composition of dissolved Si in each river is strikingly similar with means of + 0.70 ± 0.12‰ for the Birs,+ 0.95 ± 0.22‰ for the Saane,+ 0.93 ± 0.12‰ for the Ticino and + 0.79 ± 0.19‰ for the Verzasca. However, the δ 30Si undergoes seasonal variations of up to 0.6‰. Comparisons between δ 30Si and physico-chemical parameters, such as the concentration of dissolved Si and other cations, the discharge of the rivers, and the resulting weathering fluxes, permits an understanding of the processes that control the Si budget and the fate of dissolved Si within these rivers. The main mechanism controlling the Si isotope composition of the mountainous Verzasca River appears to be a two component mixing between the seepage of soil/ground waters, with heavier Si produced by clay formation and superficial runoff associated with lighter Si during high discharge events. A biologically-mediated fractionation can be excluded in this particular river system. The other rivers display increasing complexity with increases in the proportion of forested and cultivated landscapes as well as carbonate rocks in the catchment. In these instances it is impossible to resolve the extent of the isotopic fractionation and contributed flux of Si contributed by biological processes as opposed to abiotic weathering. The presence of seasonal variations in Si isotope composition in mountainous rivers provides evidence that extreme changes in climate affect the overall composition of dissolved Si delivered to the oceans. The oceanic Si isotope composition is very sensitive to even small changes in the riverine Si isotope composition and this parameter appears to be more critical than plausible changes in the Si flux. Therefore, concurrent changes in weathering style may need to be considered when using the Si isotopic compositions of diatoms, sponges and radiolaria as paleoproductivity proxies.

Organic and inorganic components of aerosols over the central Himalayas: winter and summer variations in stable carbon and nitrogen isotopic composition.

PubMed

Hegde, Prashant; Kawamura, Kimitaka; Joshi, H; Naja, M

2016-04-01

The aerosol samples were collected from a high elevation mountain site, Nainital, in India (1958 m asl) during September 2006 to June 2007 and were analyzed for water-soluble inorganic species, total carbon, nitrogen, and their isotopic composition (δ(13)C and δ(15)N, respectively). The chemical and isotopic composition of aerosols revealed significant anthropogenic influence over this remote free-troposphere site. The amount of total carbon and nitrogen and their isotopic composition suggest a considerable contribution of biomass burning to the aerosols during winter. On the other hand, fossil fuel combustion sources are found to be dominant during summer. The carbon aerosol in winter is characterized by greater isotope ratios (av. -24.0‰), mostly originated from biomass burning of C4 plants. On the contrary, the aerosols in summer showed smaller δ(13)C values (-26.0‰), indicating that they are originated from vascular plants (mostly of C3 plants). The secondary ions (i.e., SO4 (2-), NH4 (+), and NO3 (-)) were abundant due to the atmospheric reactions during long-range transport in both seasons. The water-soluble organic and inorganic compositions revealed that they are aged in winter but comparatively fresh in summer. This study validates that the pollutants generated from far distant sources could reach high altitudes over the Himalayan region under favorable meteorological conditions.

Variability of Fe isotope compositions of hydrothermal sulfides and oxidation products at mid-ocean ridges

NASA Astrophysics Data System (ADS)

Li, Xiaohu; Wang, Jianqiang; Chu, Fengyou; Wang, Hao; Li, Zhenggang; Yu, Xing; Bi, Dongwei; He, Yongsheng

2018-04-01

Significant Fe isotopic fractionation occurs during the precipitation and oxidative weathering of modern seafloor hydrothermal sulfides, which has an important impact on the cycling of Fe isotopes in the ocean. This study reports the Fe-isotope compositions of whole-rock sulfides and single-mineral pyrite collected from hydrothermal fields at the South Mid-Atlantic Ridge (SMAR) and the East Pacific Rise (EPR) and discusses the impacts of precipitation and late-stage oxidative weathering of sulfide minerals on Fe isotopic fractionation. The results show large variation in the Fe-isotope compositions of the sulfides from the different hydrothermal fields on the mid-oceanic ridges, indicating that relatively significant isotope fractionation occurs during the sulfide precipitation and oxidative weathering processes. The Fe-isotope compositions of the sulfides from the study area at the SMAR vary across a relatively small range, with an average value of 0.01‰. This Fe-isotope composition is similar to the Fe-isotope composition of mid-oceanic ridge basalt, which suggests that Fe was mainly leached from basalt. In contrast, the Fe-isotope composition of the sulfides from the study area at the EPR are significantly enriched in light Fe isotopes (average value - 1.63‰), mainly due to the kinetic fractionation during the rapid precipitation process of hydrothermal sulfide. In addition, the pyrite from different hydrothermal fields is enriched in light Fe isotopes, which is consistent with the phenomenon in which light Fe isotopes are preferentially enriched during the precipitation of pyrite. The red oxides have the heaviest Fe-isotope compositions (up to 0.80‰), indicating that heavy Fe isotopes are preferentially enriched in the oxidation product during the late-stage oxidation process. The data obtained from this study and previous studies show a significant difference between the Fe-isotope compositions of the sulfides from the SMAR and EPR. The relatively heavy Fe isotopes compositions of the sulfides from the SMAR may suggest the equilibrium fractionation process under high temperature conditions. The red Fe oxides are enriched in heavy Fe isotopes, indicating that the oxidative weathering processes result in the occurrence of significant Fe-isotope fractionation and the preferential enrichment of heavy Fe isotopes in the oxidation product.

Isotopy of the hydrosphere

NASA Astrophysics Data System (ADS)

Ferronskii, V. I.; Poliakov, V. A.

This book is concerned with the natural relations regarding the distribution of the stable isotopes of hydrogen and oxygen in the hydrosphere, taking into account the most important problems with respect to the dynamics and the origin of waters. The solution of these problems on an isotopic basis is considered. The physicochemical principles of isotope separation are discussed along with the isotopic composition of atmospheric moisture, the isotopic composition of surface continental waters, the hydrogen and oxygen isotopic composition of minerals of magmatic and metamorphic rocks and fluid inclusions, the isotopic composition of groundwaters of modern volcanic regions, and the origin of the earth's hydrosphere in the light of isotopic, cosmochemical, and theoretical studies. Attention is also given to the separation of hydrogen and oxygen isotopes of waters in the underground cycle, the isotopic composition of the deep-formation waters of sedimentary basins, the relationship between surface and ground waters, and the groundwater residence time in an aquifer.

Intracellular Cadmium Isotope Fractionation

NASA Astrophysics Data System (ADS)

Horner, T. J.; Lee, R. B.; Henderson, G. M.; Rickaby, R. E.

2011-12-01

Recent stable isotope studies into the biological utilization of transition metals (e.g. Cu, Fe, Zn, Cd) suggest several stepwise cellular processes can fractionate isotopes in both culture and nature. However, the determination of fractionation factors is often unsatisfactory, as significant variability can exist - even between different organisms with the same cellular functions. Thus, it has not been possible to adequately understand the source and mechanisms of metal isotopic fractionation. In order to address this problem, we investigated the biological fractionation of Cd isotopes within genetically-modified bacteria (E. coli). There is currently only one known biological use or requirement of Cd, a Cd/Zn carbonic anhydrase (CdCA, from the marine diatom T. weissfloggii), which we introduce into the E. coli genome. We have also developed a cleaning procedure that allows for the treating of bacteria so as to study the isotopic composition of different cellular components. We find that whole cells always exhibit a preference for uptake of the lighter isotopes of Cd. Notably, whole cells appear to have a similar Cd isotopic composition regardless of the expression of CdCA within the E. coli. However, isotopic fractionation can occur within the genetically modified E. coli during Cd use, such that Cd bound in CdCA can display a distinct isotopic composition compared to the cell as a whole. Thus, the externally observed fractionation is independent of the internal uses of Cd, with the largest Cd isotope fractionation occurring during cross-membrane transport. A general implication of these experiments is that trace metal isotopic fractionation most likely reflects metal transport into biological cells (either actively or passively), rather than relating to expression of specific physiological function and genetic expression of different metalloenzymes.

Identification of energy consumption and nutritional stress by isotopic and elemental analysis of urine in bonobos (Pan paniscus).

PubMed

Deschner, Tobias; Fuller, Benjamin T; Oelze, Vicky M; Boesch, Christophe; Hublin, Jean-Jacques; Mundry, Roger; Richards, Michael P; Ortmann, Sylvia; Hohmann, Gottfried

2012-01-15

A mounting body of evidence suggests that changes in energetic conditions like prolonged starvation can be monitored using stable isotope ratios of tissues such as bone, muscle, hair, and blood. However, it is unclear if urinary stable isotope ratios reflect a variation in energetic condition, especially if these changes in energetic condition are accompanied by shifts in dietary composition. In a feeding experiment conducted on captive bonobos (Pan paniscus), we monitored urinary δ(13)C, δ(15)N, total C (carbon), total N (nitrogen), and C/N ratios and compared these results with glucocorticoid levels under gradually changing energy availability and dietary composition. Measurements of daily collected urine samples over a period of 31 days showed that while shifts in urinary isotope signatures of δ(13)C and δ(15)N as well as total C were best explained by changes in energy consumption, urinary total N excretion as well as the C/N ratios matched the variation in dietary composition. Furthermore, when correcting for fluctuations in dietary composition, the isotope signatures of δ(13)C and δ(15)N as well as total C correlated with urinary glucocorticoid levels; however, the urinary total N and the C/N ratio did not. These results indicate for the first time that it is possible to non-invasively explore specific longitudinal records on animal energetic conditions and dietary compositions with urinary stable isotope ratios and elemental compositions, and this research provides a strong foundation for investigating how ecological factors and social dynamics affect feeding habits in wild animal populations such as primates. Copyright © 2011 John Wiley & Sons, Ltd.

Use of Zn isotopes as a probe of anthropogenic contamination and biogeochemical processes in the Seine River, France

NASA Astrophysics Data System (ADS)

Chen, J.; Gaillardet, J.; Louvat, P.; Birck, J.

2009-05-01

Metal contamination is a major issue of human impact on the aqueous environment. River water is particularly susceptible to contamination for both dissolved and particulate loads, displaying a major challenge in understanding the dominant sources and pathways of metals in polluted drainage basins. Recent improvements in mass spectrometry allow isotopic measurements of "non-traditional" metals (Zn, Cu, Fe, etc.), making their isotopes a new potential device to investigate contamination of metals under dissolved and particulate forms in rivers. We focus here on Zn isotope geochemistry in the largely anthropized Seine River (France). A new protocol of two-column separation of Zn from dilute aqueous solution has been developed and proven to be reproducible and satisfactory for accurate measurement of Zn isotopic ratios in water samples by MC-ICP-MS (2σ = 0.04‰). Preliminary results show a total variation of 0.65‰ for δ66Zn in dissolved phases of the Seine basin, and a light isotope enrichment in anthropogenic sources compared to other water samples. The determined conservative behavior of Zn in river water makes its isotopes an effective probe of anthropogenic contamination. The natural and anthropogenic inputs were clearly identified and calculated based on Zn isotope compositions for dissolved loads. Suspended particular matters (SPM) display different Zn isotope compositions compared to dissolved loads, with a total δ66Zn variation of 0.22‰. Zn concentrations and its isotope compositions in SPM reveal inverse relationships as function of the distance from the headwater and the SPM content for geographical and temporal samples, respectively. The δ66Zn data in SPM are interpreted as reflecting the mixture of natural and anthropogenic particles. The correlation between dissolved and particulate δ66Zn shows that adsorption processes are not the dominant process making Zn enrichment in SPM. We report here for the first time systematic δ66Zn data in waters of a whole river basin, showing Zn isotopes a powerful probe to trace contamination sources and biogeochemical processes in hydrologic systems.

Lithium contents and isotopic compositions of ferromanganese deposits from the global ocean

USGS Publications Warehouse

Chan, L.-H.; Hein, J.R.

2007-01-01

To test the feasibility of using lithium isotopes in marine ferromanganese deposits as an indicator of paleoceanographic conditions and seawater composition, we analyzed samples from a variety of tectonic environments in the global ocean. Hydrogenetic, hydrothermal, mixed hydrogenetic–hydrothermal, and hydrogenetic–diagenetic samples were subjected to a two-step leaching and dissolution procedure to extract first the loosely bound Li and then the more tightly bound Li in the Mn oxide and Fe oxyhydroxide. Total leachable Li contents vary from 2 by coulombic force. Hence, the abundant Li in hydrothermal deposits is mainly associated with the dominant phase, MnO2. The surface of amorphous FeOOH holds a slightly positive charge and attracts little Li, as demonstrated by data for hydrothermal Fe oxyhydroxide. Loosely sorbed Li in both hydrogenetic crusts and hydrothermal deposits exhibit Li isotopic compositions that resemble that of modern seawater. We infer that the hydrothermally derived Li scavenged onto the surface of MnO2 freely exchanged with ambient seawater, thereby losing its original isotopic signature. Li in the tightly bound sites is always isotopically lighter than that in the loosely bound fraction, suggesting that the isotopic fractionation occurred during formation of chemical bonds in the oxide and oxyhydroxide structures. Sr isotopes also show evidence of re-equilibration with seawater after deposition. Because of their mobility, Li and Sr in the ferromanganese crusts do not faithfully record secular variations in the isotopic compositions of seawater. However, Li content can be a useful proxy for the hydrothermal history of ocean basins. Based on the Li concentrations of the globally distributed hydrogenetic and hydrothermal samples, we estimate a scavenging flux of Li that is insignificant compared to the hydrothermal flux and river input to the ocean.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Campbell, Keri; Judge, Elizabeth J.; Dirmyer, Matthew R.

Surrogate nuclear explosive debris was synthesized and characterized for major, minor, and trace elemental composition as well as uranium isotopics. The samples consisted of an urban glass matrix, equal masses soda lime and cement, doped with 500 ppm uranium with varying enrichments. The surface and cross section morphology were measured with SEM, and the major elemental composition was determined by XPS. LA-ICP-MS was used to measure the uranium isotopic abundance comparing different sampling techniques. Furthermore, the results provide an example of the utility of LA-ICP-MS for forensics applications.

Titanium and Oxygen Isotopic Compositions of Sub-Micrometer TiC Crystals Within Presolar Graphite

NASA Astrophysics Data System (ADS)

Stadermann, F. J.; Bernatowicz, T.; Croat, T. K.; Zinner, E.; Messenger, S.; Amari, S.

2003-03-01

We have used the NanoSIMS to study Ti isotopes of individual TiC crystals inside a presolar graphite spherule. These measurements were made directly in TEM sections and the results can be compared to previous O measurements in the same subgrains.

The effects of magmatic processes and crustal recycling on the molybdenum stable isotopic composition of Mid-Ocean Ridge Basalts

NASA Astrophysics Data System (ADS)

Bezard, Rachel; Fischer-Gödde, Mario; Hamelin, Cédric; Brennecka, Gregory A.; Kleine, Thorsten

2016-11-01

Molybdenum (Mo) stable isotopes hold great potential to investigate the processes involved in planetary formation and differentiation. However their use is currently hampered by the lack of understanding of the dominant controls driving mass-dependent fractionations at high temperature. Here we investigate the role of magmatic processes and mantle source heterogeneities on the Mo isotope composition of Mid-Ocean Ridges Basalts (MORBs) using samples from two contrasting ridge segments: (1) the extremely fast spreading Pacific-Antarctic (66-41°S) section devoid of plume influence and; (2) the slow spreading Mohns-Knipovich segment (77-71°N) intercepted by the Jan Mayen Plume (71°N). We show that significant variations in Mo stable isotope composition exist in MORBs with δ98/95Mo ranging from - 0.24 ‰ to + 0.15 ‰ (relative to NIST SRM3134). The absence of correlation between δ98/95Mo and indices of magma differentiation or partial melting suggests a negligible impact of these processes on the isotopic variations observed. On the other hand, the δ98/95Mo variations seem to be associated with changes in radiogenic isotope signatures and rare earth element ratios (e.g., (La/Sm)N), suggesting mantle source heterogeneities as a dominant factor for the δ98/95Mo variations amongst MORBs. The heaviest Mo isotope compositions correspond to the most enriched signatures, suggesting that recycled crustal components are isotopically heavy compared to the uncontaminated depleted mantle. The uncontaminated depleted mantle shows slightly sub-chondritic δ98/95Mo, which cannot be produced by core formation and, therefore, more likely result from extensive anterior partial melting of the mantle. Consequently, the primitive δ98/95Mo composition of the depleted mantle appears overprinted by the effects of both partial melting and crustal recycling.

Tracing alteration of mantle peridotite in the Samail ophiolite using Mg isotopes

NASA Astrophysics Data System (ADS)

de Obeso, J. C.; Kelemen, P. B.; Higgins, J. A.

2017-12-01

Magnesium is one of the main constituents of mantle peridotite ( 22.8 wt%), which has a homogeneous Mg isotopic composition (d26Mg = -0.25 ± 0.04 ‰ (2 sd) DSM3, Teng et al 2010 GCA). Mg isotopes are used as tracers of continental and oceanic weathering as they exhibit variable degrees of fractionation during alteration depending on the lithology. Here we report some of the first Mg isotopic compositions of the mantle section of the Samail ophiolite in Oman and its alteration products. The mantle section of the ophiolite is composed mainly of depleted harzburgites and dunites with mantle-like d26Mg (-0.25, -0.21 ‰). Mantle peridotite is far from equilibrium in near surface conditions leading to rapid, extensive serpentinization, carbonation and oxidation, as well as other geochemical changes. Our analyzed samples encompass most of the alteration of peridotite products observed in Oman including listvenites (completely carbonated peridotite) near the basal thrust of the ophiolite, massive magnesite veins within peridotite outcrops, and heavily altered harzburgites. Magnesite listvenites have d26Mg slightly below mantle values (-0.33, -0.33‰) while dolomite listvenites are significantly lighter (-1.46, -0.89‰). This suggests that heavy Mg isotopes were removed from the listvenites during ophiolite emplacement. Heavily altered peridotite from Wadi Fins exhibit alteration halos with drastic changes in composition. The most oxidized areas are enriched in Fe and depleted in Mg compared to the cores of the samples. These variations in Mg concentrations are complemented by a shift to heavy Mg isotopic compositions (0.74, 0.86‰), among the heaviest d26Mg values that have been reported in altered peridotite. Potential sinks for light isotopes removed from such alteration zones are massive magnesite veins with very light compositions (-3.39, -3.14‰). The fractionation of Mg isotopes observed in the mantle section of the ophiolite spans more than 50% of the known terrestrial fractionation.

Chromium isotopic homogeneity between the Moon, the Earth, and enstatite chondrites

NASA Astrophysics Data System (ADS)

Mougel, Bérengère; Moynier, Frédéric; Göpel, Christa

2018-01-01

Among the elements exhibiting non-mass dependent isotopic variations in meteorites, chromium (Cr) has been central in arguing for an isotopic homogeneity between the Earth and the Moon, thus questioning physical models of Moon formation. However, the Cr isotopic composition of the Moon relies on two samples only, which define an average value that is slightly different from the terrestrial standard. Here, by determining the Cr isotopic composition of 17 lunar, 9 terrestrial and 5 enstatite chondrite samples, we re-assess the isotopic similarity between these different planetary bodies, and provide the first robust estimate for the Moon. In average, terrestrial and enstatite samples show similar ε54Cr. On the other hand, lunar samples show variables excesses of 53Cr and 54Cr compared to terrestrial and enstatite chondrites samples with correlated ε53Cr and ε54Cr (per 10,000 deviation of the 53Cr/52Cr and 54Cr/52Cr ratios normalized to the 50Cr/52Cr ratio from the NIST SRM 3112a Cr standard). Unlike previous suggestions, we show for the first time that cosmic irradiation can affect significantly the Cr isotopic composition of lunar materials. Moreover, we also suggest that rather than spallation reactions, neutron capture effects are the dominant process controlling the Cr isotope composition of lunar igneous rocks. This is supported by the correlation between ε53Cr and ε54Cr, and 150Sm/152Sm ratios. After correction of these effects, the average ε54Cr of the Moon is indistinguishable from the terrestrial and enstatite chondrite materials reinforcing the idea of an Earth-Moon-enstatite chondrite system homogeneity. This is compatible with the most recent scenarios of Moon formation suggesting an efficient physical homogenization after a high-energy impact on a fast spinning Earth, and/or with an impactor originating from the same reservoir in the inner proto-planetary disk as the Earth and enstatite chondrites and having similar composition.

Variations in Urine Calcium Isotope: Composition Reflect Changes in Bone Mineral Balance in Humans

NASA Technical Reports Server (NTRS)

Skulan, Joseph; Anbar, Ariel; Bullen, Thomas; Puzas, J. Edward; Shackelford, Linda; Smith, Scott M.

2004-01-01

Changes in bone mineral balance cause rapid and systematic changes in the calcium isotope composition of human urine. Urine from subjects in a 17 week bed rest study was analyzed for calcium isotopic composition. Comparison of isotopic data with measurements of bone mineral density and metabolic markers of bone metabolism indicates the calcium isotope composition of urine reflects changes in bone mineral balance. Urine calcium isotope composition probably is affected by both bone metabolism and renal processes. Calcium isotope. analysis of urine and other tissues may provide information on bone mineral balance that is in important respects better than that available from other techniques, and illustrates the usefulness of applying geochemical techniques to biomedical problems.

Distribution and geochemical characterization of coalbed gases at excavation fields at natural analogue site area Velenje Basin, Slovenia

NASA Astrophysics Data System (ADS)

Kanduč, Tjaša; Žigon, Stojan; Grassa, Fausto; Sedlar, Jerneja; Zadnik, Ivo; Zavšek, Simon

2016-04-01

Unconventional gas resources, including coal bed methane and shale gas, are a growing part of the global energy mix, which has changed the economic and strategic picture for gas consuming and producing countries, including the USA, China and Australia that, together are responsible for around half the currently recoverable unconventional gas resources. However, CBM production was often hindered by low permeability and mineralization in cleats and fractures, necessitating the development of cost effective horizontal drilling and completion techniques. Geochemical and isotopic monitoring of coalbed gases at excavation fields in Velenje Basin started in year 2000, with the aim to obtain better insights into the origin of coalbed gases. Results from active excavation fields in the mining areas Pesje and Preloge in the year period 2014-2015 are presented in this study. Composition and isotopic composition of coalbed gases were determined with mass - spectrometric methods. The chemical (methane, carbon dioxide, nitrogen) and isotopic composition of carbon in methane and carbon dioxide in the Velenje Basin vary and depend on the composition of the source of coalbed gas before excavation, advancement of the working face, depth of the longwall face, pre-mining activity and newly mined activity. The basic gas components determined in excavation fields are carbon dioxide and methane. Knowledge of the stable isotope geochemistry of coal bed and shale gas and the related production water is essential to determine not only gas origins but also the dominant methanogenic pathway in the case of microbial gas. Concentrations of methane at active excavation fields are changing from 1.8 to 63.9 %, concentrations of carbon dioxide are changing from 36.1 to 98.2% and CDMI (Carbon Dioxide Methane Index) index from 0.2 to 100 %. Isotopic composition of carbon dioxide is changing from -11.0 to -1.9‰ , isotopic composition of methane from -71.8 to -43.3‰ , isotopic composition of deuterium in methane from -343.9 to -223.1‰ , respectively. Further, these characteristics of methane have been compared with those observed in other coal sedimentary basins worldwide. The isotopic compositions of carbon and hydrogen in methane in the excavation fields show its biogenic origin, while a high Carbon Dioxide Methane Index (CDMI index) indicates the bacterial and endogenic origin of carbon dioxide.

Stable Isotopic Constraints on Abiogenic Hydrocarbon gas Contributions to Thermogenic Natural gas Resources in the Northern Appalachian Basin, USA

NASA Astrophysics Data System (ADS)

Burruss, R. C.; Laughrey, C. D.

2006-05-01

The generation of abiogenic methane by serpentinization or by graphite-water reactions in high-grade metamorphic rocks is well documented by isotopic, fluid inclusion, and petrographic studies. However, geochemical evidence is equivocal for abiogenic generation of higher hydrocarbon gases (ethane through pentane) in economic resources. Thermogenic hydrocarbon gases, generated by thermal cracking of sedimentary organic matter of biological origin, are progressively enriched in 13C as a function of increasing number of carbon atoms in the molecule. The isotopic composition is controlled by the kinetic isotope effect (KIE) during carbon-carbon bond breaking with the largest KIE for methane. Published work on gases in Precambrian rocks in Canada and South Africa suggest that some were generated by abiogenic Fischer-Tropsch type reactions that produced gases with carbon isotopic compositions that are reversed from the thermogenic trend. We have documented reversed isotopic compositions in natural gas accumulations in lower Paleozoic reservoirs of the Appalachian basin regionally from West Virginia and eastern Ohio through Pennsylvania to central New York. The regional accumulation in lower Silurian age strata shows progressive enhancement of the isotopic reversal with increasing depth in the basin. Multivariate analysis of the molecular and isotopic data define an end-member in the deep basin with an approximate composition of 98 mol % CH4, 1-2 mol % C2H6, << 1 mol % C3H8, and δ13C (CH4) = -27 ‰, δ13C (C2H6) = -40 ‰, δ13C (C3H8) = - 41‰. The nominal similarity of isotopic reversals in the gases from Precambrian rocks to those in the lower Paleozoic rocks of the Appalachian basin suggests that abiogenic F-T reactions may have generated some fraction of the gases in the deep basin. Comparison of molecular and hydrogen isotopic compositions show that the gases of putative abiogenic F-T origin are significantly different from Appalachian basin gases. All the Precambrian gases have extremely light hydrogen isotopic compositions of CH4 (δ2H < -300‰) and are depleted in CH4 (Canada gases C1/C2+ < 10, S. Africa gases C1/C2+ < 60) compared to gases in lower Paleozoic reservoirs of the Appalachian basin (δ2H (CH4) > -150‰, C1/C2+ up to 220). New isotopic studies of gas accumulations, gases in fluid inclusions, and of sedimentary organic matter in the Appalachian basin are in progress to constrain the possible contribution of abiogenic hydrocarbon generation to gas accumulations in this basin.

X-ray diffraction characterization of epitaxial CVD diamond films with natural and isotopically modified compositions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Prokhorov, I. A., E-mail: igor.prokhorov@mail.ru; Voloshin, A. E.; Ralchenko, V. G.

2016-11-15

Comparative investigations of homoepitaxial diamond films with natural and modified isotopic compositions, grown by chemical vapor deposition (CVD) on type-Ib diamond substrates, are carried out using double-crystal X-ray diffractometry and topography. The lattice mismatch between the substrate and film is precisely measured. A decrease in the lattice constant on the order of (Δa/a){sub relax} ∼ (1.1–1.2) × 10{sup –4} is recorded in isotopically modified {sup 13}C (99.96%) films. The critical thicknesses of pseudomorphic diamond films is calculated. A significant increase in the dislocation density due to the elastic stress relaxation is revealed by X-ray topography.

Mantle End-Members: The Trace Element Perspective

NASA Astrophysics Data System (ADS)

Willbold, M.; Stracke, A.; Hofmann, A. W.

2004-12-01

On the basis of their isotopic composition, ocean island basalts (OIB) have been classified into three to four end-members; HIMU with the most radiogenic Pb isotope ratios of OIB and Enriched Mantle 1 and 2 (EM1, EM2) with less radiogenic but variable Pb isotope and highly radiogenic Sr isotope signatures. It has also been argued that each of these isotopic families has common trace element characteristics that distinguish them from one another and so substantiated this classification. Here, we present new high-precision trace element data for samples from St. Helena, Tristan da Cunha and Gough in the Atlantic Ocean. The overall data-set is augmented by OIB data from the GEOROC database and includes data from all major isotopic families (HIMU: St. Helena, Mangaia, Tubuai, and Rururtu; EM1: Tristan da Cunha, Gough, Pitcairn; and EM2: Samoa, Marquesas, and Society). For each locality we use only islands defining the most extreme isotopic compositions. The entire data-set has been screened to exclude altered and highly differentiated samples. HIMU basalts have a very uniform trace element composition. Compared to HIMU-type basalts, EM-type basalts are enriched in Rb, Ba, and K, and depleted in U, Nb, and Ta, relative to La. Different EM-type OIBs from the same isotopic family (EM1 or EM2), have distinct trace element characteristics that can ultimately only be caused by different source compositions. For example, Ba/Th ratios in samples from both Tristan da Cunha (EM1) and Samoa (EM2) are similarly high (ca. 110) whereas Ba/Th ratios in samples from Pitcairn (EM1) and Society (EM2) samples are consistently lower (ca. 70). Thus on the basis of their trace element composition, EM-type OIB cannot be classified into EM1 and EM2 type basalts, nor can any other grouping be identified. The remarkably uniform isotopic and trace element composition of HIMU-type basalts suggests derivation from a single common source reservoir, most likely subduction-modified oceanic crust. Although there are some trace element characteristics common to all EM-type basalts, which distinguish them from HIMU-type basalts (e.g. uniformly high Th/U ratios of 4.7 ± 0.3, and enrichment in Cs-U), each suite of EM-type basalts has unique trace element signatures that distinguish them from any other suite of EM-type basalts. This is especially obvious when comparing the trace element composition of EM basalts from one isotopic family, for example EM1-type basalts from Tristan, Gough and Pitcairn. Consequently, the trace element systematics of EM-type basalts suggest that there are many different EM-type sources, whereas the isotopic composition of EM-type basalts suggest derivation from two broadly similar sources, i.e. EM1 and EM2. The large variability in subducting sediments with respect to both parent-daughter (e.g. Rb/Sr, Sm/Nd, U/Pb, Th/Pb,...) and other trace element ratios makes it unlikely that there are reproducible mixtures of sediments leading to two different isotopic evolution paths (EM1 and EM2) while preserving a range of incompatible element contents for each isotopic family, as would be required to reconcile the isotopic and trace element characteristics of EM-type basalts. Although this does not a priori argue against sediments as possible source components for OIB, it does argue against two distinct groups of sediments as EM1 and EM2 sources. Further characterization of sources with the same general origin (e.g. a certain type of crust or lithosphere) or identification of processes leading to reservoirs with similar parent-daughter ratio characteristics but different incompatible trace element contents could resolve the apparent conundrum.

Possible solar noble-gas component in Hawaiian basalts

USGS Publications Warehouse

Honda, M.; McDougall, I.; Patterson, D.B.; Doulgeris, A.; Clague, D.A.

1991-01-01

THE noble-gas elemental and isotopic composition in the Earth is significantly different from that of the present atmosphere, and provides an important clue to the origin and history of the Earth and its atmosphere. Possible candidates for the noble-gas composition of the primordial Earth include a solar-like component, a planetary-like component (as observed in primitive meteorites) and a component similar in composition to the present atmosphere. In an attempt to identify the contributions of such components, we have measured isotope ratios of helium and neon in fresh basaltic glasses dredged from Loihi seamount and the East Rift Zone of Kilauea1-3. We find a systematic enrichment in 20Ne and 21Ne relative to 22Ne, compared with atmospheric neon. The helium and neon isotope signatures observed in our samples can be explained by mixing of solar, present atmospheric, radiogenic and nucleogenic components. These data suggest that the noble-gas isotopic composition of the mantle source of the Hawaiian plume is different from that of the present atmosphere, and that it includes a significant solar-like component. We infer that this component was acquired during the formation of the Earth.

Determination of the isotopic composition of evapotranspiration in a mature oil palm plantation in Jambi province, Indonesia.

NASA Astrophysics Data System (ADS)

Bonazza, Mattia; Meijide, Ana; Knohl, Alexander

2017-04-01

Evapotranspiration (ET) is defined as the sum of the water vapor fluxes from evaporation (E) and transpiration (T). The relative proportion between these two quantities depends on the species, on their age and on the structure of the stand and canopy. Evaporation represents the fraction of water that doesn't contribute to plants growth hence it often considered as "unused" water by the plants root system. For this reason, in a fast changing environment like Indonesia where, since almost 30 years, tropical rainforests are gradually converted into extensive oil palm plantation, it is important to quantify the amount of evaporated water to improve agricultural practices and water quality. As powerful tracers of the hydrological cycle, water stable isotopes represent an important tool to estimate the isotopic composition of the evapotranspiration flux and they can be used as a starting point for the determination of the T/ET ratio, which can be considered as a plant water uptake efficiency indicator. The isotopic composition (δDvand δ18Ov) and the mixing ratio (qv) of water vapor measured in a stand is the result of the isotopic mixing between two members; ecosystem evapotranspiration (δET) and background air (δa). With the implementation of laser-based isotopic analysers we are now able to improve the measurement frequency of δDvand δ18Ov that leads us to an improved estimation of δET. Here we present the results of a measurement campaign, performed with a Picarro L-2120i and conducted in a mature oil palm plantation in the province of Jambi, Indonesia. We measured the atmospheric water vapor mixing ratio and isotopic composition at 5 sampling heights (21 m, 16 m, 9 m, 3.5 and 0.3 m) along a flux tower throughout the oil palm canopy (average height 10 m). The range of the water vapor isotopic composition was between -19 and -11 and -134 and -82 ‰ for δ18Ov and δDvrespectively. A fairly open canopy structure resulted in small mixing ratio gradients along the vertical profile. We collected and analysed all rain event and estimated the variability of the water vapor isotopic composition. Micrometeorological measurements, provided by the tower's sensors, were used to calculate ET using the Bowen ratio energy balance. To determine the isotopic composition of the evapotranspiration flux we used and compared two different methods: Keeling plot and flux gradient approach.

Sulfur Isotope Composition of Putative Primary Troilite in Chondrules

NASA Technical Reports Server (NTRS)

Tachibana, Shogo; Huss, Gary R.

2002-01-01

Sulfur isotope compositions of putative primary troilites in chondrules from Bishunpur were measured by ion probe. These primary troilites have the same S isotope compositions as matrix troilites and thus appear to be isotopically unfractionated. Additional information is contained in the original extended abstract.

EasyDelta: A spreadsheet for kinetic modeling of the stable carbon isotope composition of natural gases

NASA Astrophysics Data System (ADS)

Zou, Yan-Rong; Wang, Lianyuan; Shuai, Yanhua; Peng, Ping'an

2005-08-01

A new kinetic model and an Excel © spreadsheet program for modeling the stable carbon isotope composition of natural gases is provided in this paper. The model and spreadsheet could be used to describe and predict the variances in stable carbon isotope of natural gases under both experimental and geological conditions with heating temperature or geological time. It is a user-friendly convenient tool for the modeling of isotope variation with time under experimental and geological conditions. The spreadsheet, based on experimental data, requires the input of the kinetic parameters of gaseous hydrocarbons generation. Some assumptions are made in this model: the conventional (non-isotope species) kinetic parameters represent the light isotope species; the initial isotopic value is the same for all parallel chemical reaction of gaseous hydrocarbons generation for simplicity, the re-exponential factor ratio, 13A/ 12A, is a constant, and both heavy and light isotope species have similar activation energy distribution. These assumptions are common in modeling of isotope ratios. The spreadsheet is used for searching the best kinetic parameters of the heavy isotope species to reach the minimum errors compared with experimental data, and then extrapolating isotopic changes to the thermal history of sedimentary basins. A short calculation example on the variation in δ13C values of methane is provided in this paper to show application to geological conditions.

Atomic Weights and Isotopic Compositions

National Institute of Standards and Technology Data Gateway

SRD 144 Atomic Weights and Isotopic Compositions (Web, free access)   The atomic weights are available for elements 1 through 111, and isotopic compositions or abundances are given when appropriate.

Magnesium isotopic composition of the Earth and chondrites

NASA Astrophysics Data System (ADS)

Teng, Fang-Zhen; Li, Wang-Ye; Ke, Shan; Marty, Bernard; Dauphas, Nicolas; Huang, Shichun; Wu, Fu-Yuan; Pourmand, Ali

2010-07-01

To constrain further the Mg isotopic composition of the Earth and chondrites, and investigate the behavior of Mg isotopes during planetary formation and magmatic processes, we report high-precision (±0.06‰ on δ 25Mg and ±0.07‰ on δ 26Mg, 2SD) analyses of Mg isotopes for (1) 47 mid-ocean ridge basalts covering global major ridge segments and spanning a broad range in latitudes, geochemical and radiogenic isotopic compositions; (2) 63 ocean island basalts from Hawaii (Kilauea, Koolau and Loihi) and French Polynesia (Society Island and Cook-Austral chain); (3) 29 peridotite xenoliths from Australia, China, France, Tanzania and USA; and (4) 38 carbonaceous, ordinary and enstatite chondrites including 9 chondrite groups (CI, CM, CO, CV, L, LL, H, EH and EL). Oceanic basalts and peridotite xenoliths have similar Mg isotopic compositions, with average values of δ 25Mg = -0.13 ± 0.05 (2SD) and δ 26Mg = -0.26 ± 0.07 (2SD) for global oceanic basalts ( n = 110) and δ 25Mg = -0.13 ± 0.03 (2SD) and δ 26Mg = -0.25 ± 0.04 (2SD) for global peridotite xenoliths ( n = 29). The identical Mg isotopic compositions in oceanic basalts and peridotites suggest that equilibrium Mg isotope fractionation during partial melting of peridotite mantle and magmatic differentiation of basaltic magma is negligible. Thirty-eight chondrites have indistinguishable Mg isotopic compositions, with δ 25Mg = -0.15 ± 0.04 (2SD) and δ 26Mg = -0.28 ± 0.06 (2SD). The constancy of Mg isotopic compositions in all major types of chondrites suggest that primary and secondary processes that affected the chemical and oxygen isotopic compositions of chondrites did not significantly fractionate Mg isotopes. Collectively, the Mg isotopic composition of the Earth's mantle, based on oceanic basalts and peridotites, is estimated to be -0.13 ± 0.04 for δ 25Mg and -0.25 ± 0.07 for δ 26Mg (2SD, n = 139). The Mg isotopic composition of the Earth, as represented by the mantle, is similar to chondrites. The chondritic composition of the Earth implies that Mg isotopes were well mixed during accretion of the inner solar system.

The Chlorine Isotopic Composition Of Lunar UrKREEP

NASA Technical Reports Server (NTRS)

Barnes, J. J.; Tartese, R.; Anand, M.; McCubbin, F. M.; Neal, C. R.; Franchi, I. A.

2016-01-01

Since the long standing paradigm of an anhydrous Moon was challenged there has been a renewed focus on investigating volatiles in a variety of lunar samples. Numerous studies have examined the abundances and isotopic compositions of volatiles in lunar apatite, Ca5(PO4)3(F,Cl,OH). In particular, apatite has been used as a tool for assessing the sources of H2O in the lunar interior. However, current models for the Moon's formation have yet to fully account for its thermal evolution in the presence of H2O and other volatiles. For ex-ample, in the context of the lunar magma ocean (LMO) model, it is anticipated that chlorine (and other volatiles) should have been concentrated in the late-stage LMO residual melts (i.e., the dregs enriched in incompatible elements such as K, REEs (Rare Earth Elements), and P, collectively called KREEP, and in its primitive form - urKREEP, given its incompatibility in mafic minerals like olivine and pyroxene, which were the dominant phases that crystallized early in the cumulate pile of the LMO. When compared to chondritic meteorites and terrestrial rocks, lunar samples have exotic chlorine isotope compositions, which are difficult to explain in light of the abundance and isotopic composition of other volatile species, especially H, and the current estimates for chlorine and H2O in the bulk silicate Moon (BSM). In order to better understand the processes involved in giving rise to the heavy chlorine isotope compositions of lunar samples, we have performed a comprehensive in situ high precision study of chlorine isotopes in lunar apatite from a suite of Apollo samples covering a range of geochemical characteristics and petrologic types.

High-precision isotopic characterization of USGS reference materials by TIMS and MC-ICP-MS

NASA Astrophysics Data System (ADS)

Weis, Dominique; Kieffer, Bruno; Maerschalk, Claude; Barling, Jane; de Jong, Jeroen; Williams, Gwen A.; Hanano, Diane; Pretorius, Wilma; Mattielli, Nadine; Scoates, James S.; Goolaerts, Arnaud; Friedman, Richard M.; Mahoney, J. Brian

2006-08-01

The Pacific Centre for Isotopic and Geochemical Research (PCIGR) at the University of British Columbia has undertaken a systematic analysis of the isotopic (Sr, Nd, and Pb) compositions and concentrations of a broad compositional range of U.S. Geological Survey (USGS) reference materials, including basalt (BCR-1, 2; BHVO-1, 2), andesite (AGV-1, 2), rhyolite (RGM-1, 2), syenite (STM-1, 2), granodiorite (GSP-2), and granite (G-2, 3). USGS rock reference materials are geochemically well characterized, but there is neither a systematic methodology nor a database for radiogenic isotopic compositions, even for the widely used BCR-1. This investigation represents the first comprehensive, systematic analysis of the isotopic composition and concentration of USGS reference materials and provides an important database for the isotopic community. In addition, the range of equipment at the PCIGR, including a Nu Instruments Plasma MC-ICP-MS, a Thermo Finnigan Triton TIMS, and a Thermo Finnigan Element2 HR-ICP-MS, permits an assessment and comparison of the precision and accuracy of isotopic analyses determined by both the TIMS and MC-ICP-MS methods (e.g., Nd isotopic compositions). For each of the reference materials, 5 to 10 complete replicate analyses provide coherent isotopic results, all with external precision below 30 ppm (2 SD) for Sr and Nd isotopic compositions (27 and 24 ppm for TIMS and MC-ICP-MS, respectively). Our results also show that the first- and second-generation USGS reference materials have homogeneous Sr and Nd isotopic compositions. Nd isotopic compositions by MC-ICP-MS and TIMS agree to within 15 ppm for all reference materials. Interlaboratory MC-ICP-MS comparisons show excellent agreement for Pb isotopic compositions; however, the reproducibility is not as good as for Sr and Nd. A careful, sequential leaching experiment of three first- and second-generation reference materials (BCR, BHVO, AGV) indicates that the heterogeneity in Pb isotopic compositions, and concentrations, could be directly related to contamination by the steel (mortar/pestle) used to process the materials. Contamination also accounts for the high concentrations of certain other trace elements (e.g., Li, Mo, Cd, Sn, Sb, W) in various USGS reference materials.

A Stable U Isotopic Perspective on the U Budget and Global Extent of Modern Anoxia in the Ocean.

NASA Astrophysics Data System (ADS)

Tissot, F.; Dauphas, N.

2015-12-01

Isotopic fractionation between U4+ and U6+makes U stable isotopes potential tracers of global paleoredox conditions. In this work [1], we put the U-proxy up to a test against a highly constrained system: the modern ocean. We measured a large number of seawater samples from geographically diverse locations and found that the open ocean has a homogenous isotopic composition at δ238USW= -0.392 ± 0.005 ‰ (rel. to CRM-112a). From our measurement of rock samples (n=64) and compilations of literature data (n=380), we then estimated the U isotopic compositions of the various reservoirs involved in the modern oceanic U budget, as well as the fractionation factors associated with U incorporation into those reservoirs. Using a steady-state model, we compared the isotopic composition of the seawater predicted by the four most recent U oceanic budgets [2-5] to the modern seawater value we measured. Three of these budgets [2-4] predict a seawater isotopic composition in very good agreement with the observed δ238USW, which strengthens our confidence in the isotopic fractionation factors associated with each deposition environment and the fact that U is at steady-state in the modern ocean. The U oceanic budget of Henderson and Anderson (2003) does not reproduce the observed seawater composition because the U flux to anoxic/euxinic sediments relative to the total U flux out of the ocean is high in their model, which our analysis shows cannot be correct. The U isotopic composition of seawater is used to constrain the extent of anoxia in the modern ocean (% of seafloor covered by anoxic/euxinic sediments), which is 0.21 ± 0.09 %. This work demonstrates that stable isotopes of U can indeed trace the extent of anoxia in the modern global ocean, thereby validating the application of U isotope measurements to paleoredox reconstructions. Based on the above work, we will present the best estimate of the modern oceanic U budget. [1] Tissot F.L.H., Dauphas N. (2015) Geochim Cosmochim Ac 167, 113-143 [2] Barnes C. E., Cochran J. K. (1990) Earth Planet Sc Lett 97, 94-101 [3] Morford J. L., Emerson S. (1999) Geochim Cosmochim Ac 63, 1735-1750 [4] Dunk R. M., Mills R. A., Jenkins W. J. (2002) Chemical Geology 190, 45-67 [5] Henderson G. M., Anderson R. F. (2003) Rev Mineral Geochem 52, 493-531

Isotopic composition of cosmic ray nitrogen at 1.5 GeV/amu

NASA Technical Reports Server (NTRS)

Dwyer, R.; Meyer, P.

1975-01-01

For any location, the earth's magnetic field acts as a filter for incoming cosmic rays, allowing only particles above a certain rigidity. The relative isotopic composition of abundant elements can be measured with a detector sensitive to the velocity of particles in the penumbra of the earth's magnetic field. In this paper, the nitrogen velocity spectrum is compared with that of carbon plus oxygen as a reference, since in this case Z-dependent effects are minimal. The form of the energy spectrum of carbon, nitrogen, and oxygen, needed for proper correction, was measured in the same experiment. The results were obtained using a scintillator-Cerenkov counter telescope with a geometric factor of 0.25 sq in sr, flown twice on high-altitude balloons from Palestine, Texas, obtaining an exposure factor of 20 sq m sr hr. Results are presented on the isotopic composition of nitrogen at about 1.5GeV/amu.

Chemical Imaging and Stable Isotope Analysis of Atmospheric Particles by NanoSIMS (Invited)

NASA Astrophysics Data System (ADS)

Sinha, B.; Harris, E. J.; Pöhlker, C.; Wiedemann, K. T.; van Pinxteren, D.; Tilgner, A.; Fomba, K. W.; Schneider, J.; Roth, A.; Gnauk, T.; Fahlbusch, B.; Mertes, S.; Lee, T.; Collett, J. L.; Shiraiwa, M.; Gunthe, S. S.; Smith, M.; Artaxo, P. P.; Gilles, M.; Kilcoyne, A. L.; Moffet, R.; Weigand, M.; Martin, S. T.; Poeschl, U.; Andreae, M. O.; Hoppe, P.; Herrmann, H.; Borrmann, S.

2013-12-01

Chemical imaging analysis of the internal distribution of chemical compounds by a combination of SEM-EDX, and NanoSIMS allows investigating the physico-chemical properties and isotopic composition of individual aerosol particles. Stable sulphur isotope analysis provides insight into the sources, sinks and oxidation pathways of SO2 in the environment. Oxidation by OH radicals, O3 and H2O2 enriches the heavier isotope in the product sulphate, whereas oxidation by transition metal ions (TMI), hypohalites and hypohalous acids depletes the heavier isotope in the product sulphate. The isotope fractionation during SO2 oxidation by stabilized Criegee Intermediate radicals is unknown. We studied the relationship between aerosol chemical composition and predominant sulphate formation pathways in continental clouds in Central Europe and during the wet season in the Amazon rain forest. Sulphate formation in continental clouds in Central Europe was studied during HCCT-2010, a lagrangian-type field experiment, during which an orographic cloud was used as a natural flow-through reactor to study in-cloud aerosol processing (Harris et al. 2013). Sulphur isotopic compositions in SO2 and H2SO4 gas and particulate sulphate were measured and changes in the sulphur isotope composition of SO2 between the upwind and downwind measurement sites were used to determine the dominant SO2 chemical removal process occurring in the cloud. Changes in the isotopic composition of particulate sulphate revealed that transition metal catalysis pathway was the dominant SO2 oxidation pathway. This reaction occurred primarily on coarse mineral dust particles. Thus, sulphate produced due to in-cloud SO2 oxidation is removed relatively quickly from the atmosphere and has a minor climatic effect. The aerosol samples from the Amazonian rainforest, a pristine tropical environment, were collected during the rainy season. The samples were found to be dominated by SOA particles in the fine mode and primary biological aerosol particles in the coarse mode (Pöhlker et al. 2012). We applied STXM-NEXAFS analysis, SEM-EDX analysis and NanoSIMS analysis to investigate the morphology, chemical composition and isotopic composition of aerosol samples. Biogenic salt particles emitted from active biota in the rainforest were found to be enriched in the heavier sulphur isotope, whereas particles with a high organic mass fraction modified by condensation of VOC oxidation products and/or cloud processing were significantly depleted in the heavier sulphur isotope compared to the seed particles. This indicates either a depleted gas phase source of sulphur dioxide contributed to the sulphate formation via the H2O2, O3 or OH oxidation pathway or an unaccounted reaction pathway which depletes the heavier isotope in the product sulphate contributes to the secondary sulphate formation in the pristine Amazon rainforest. Harris, E., et al., Science 340, 727-730, 2013 Pöhlker, C., Science 337, 1075-1078, 2012

Converting isotope ratios to diet composition - the use of mixing models - June 2010

EPA Science Inventory

One application of stable isotope analysis is to reconstruct diet composition based on isotopic mass balance. The isotopic value of a consumer’s tissue reflects the isotopic values of its food sources proportional to their dietary contributions. Isotopic mixing models are used ...

A critical examination of the possible application of zinc stable isotope ratios in bivalve mollusks and suspended particulate matter to trace zinc pollution in a tropical estuary.

PubMed

Araújo, Daniel; Machado, Wilson; Weiss, Dominik; Mulholland, Daniel S; Boaventura, Geraldo R; Viers, Jerome; Garnier, Jeremie; Dantas, Elton L; Babinski, Marly

2017-07-01

The application of zinc (Zn) isotopes in bivalve tissues to identify zinc sources in estuaries was critically assessed. We determined the zinc isotope composition of mollusks (Crassostrea brasiliana and Perna perna) and suspended particulate matter (SPM) in a tropical estuary (Sepetiba Bay, Brazil) historically impacted by metallurgical activities. The zinc isotope systematics of the SPM was in line with mixing of zinc derived from fluvial material and from metallurgical activities. In contrast, source mixing alone cannot account for the isotope ratios observed in the bivalves, which are significantly lighter in the contaminated metallurgical zone (δ 66 Zn JMC  = +0.49 ± 0.06‰, 2σ, n = 3) compared to sampling locations outside (δ 66 Zn JMC  = +0.83 ± 0.10‰, 2σ, n = 22). This observation suggests that additional factors such as speciation, bioavailability and bioaccumulation pathways (via solution or particulate matter) influence the zinc isotope composition of bivalves. Copyright © 2017 Elsevier Ltd. All rights reserved.

Magma mixing and the generation of isotopically juvenile silicic magma at Yellowstone caldera inferred from coupling 238U–230Th ages with trace elements and Hf and O isotopes in zircon and Pb isotopes in sanidine

USGS Publications Warehouse

Stelten, Mark E.; Cooper, Kari M.; Vazquez, Jorge A.; Reid, Mary R.; Barfod, Gry H.; Wimpenny, Josh; Yin, Qing-Zhu

2013-01-01

The nature of compositional heterogeneity within large silicic magma bodies has important implications for how silicic reservoirs are assembled and evolve through time. We examine compositional heterogeneity in the youngest (~170 to 70 ka) post-caldera volcanism at Yellowstone caldera, the Central Plateau Member (CPM) rhyolites, as a case study. We compare 238U–230Th age, trace-element, and Hf isotopic data from zircons, and major-element, Ba, and Pb isotopic data from sanidines hosted in two CPM rhyolites (Hayden Valley and Solfatara Plateau flows) and one extracaldera rhyolite (Gibbon River flow), all of which erupted near the caldera margin ca. 100 ka. The Hayden Valley flow hosts two zircon populations and one sanidine population that are consistent with residence in the CPM reservoir. The Gibbon River flow hosts one zircon population that is compositionally distinct from Hayden Valley flow zircons. The Solfatara Plateau flow contains multiple sanidine populations and all three zircon populations found in the Hayden Valley and Gibbon River flows, demonstrating that the Solfatara Plateau flow formed by mixing extracaldera magma with the margin of the CPM reservoir. This process highlights the dynamic nature of magmatic interactions at the margins of large silicic reservoirs. More generally, Hf isotopic data from the CPM zircons provide the first direct evidence for isotopically juvenile magmas contributing mass to the youngest post-caldera magmatic system and demonstrate that the sources contributing magma to the CPM reservoir were heterogeneous in 176Hf/177Hf at ca. 100 ka. Thus, the limited compositional variability of CPM glasses reflects homogenization occurring within the CPM reservoir, not a homogeneous source.

A 120 ka record of reconstructed paleoprecipitation signals at Lake El'gygytgyn, NE Russia derived from compound-specific δD analysis of terrestrial biomarkers

NASA Astrophysics Data System (ADS)

Wilkie, K. M.; Chapligin, B.; Burns, S. J.; Petsch, S.; Meyer, H.; Brigham-Grette, J.

2011-12-01

Sediment cores recovered from Lake El'gygytgyn, NE Russia extend back to 3.6Ma, representing the longest time-continuous sediment record of past climate change in the terrestrial Arctic. Comparison of the stable isotope composition of modern precipitation and compound-specific isotopic analyses of modern vegetation and sedimentary lipids from the last 120ka allows reconstruction of past hydrological conditions, thereby providing a powerful tool for reconstructing past Arctic climate changes. The stable isotopic composition of modern precipitation, streams, and lake water are presented and used to constrain isotope systematics of the Lake El'gygytgyn Basin hydrology. The hydrogen isotopic compositions (δD) of alkanoic acids from modern vegetation are compared with modern precipitation and lake core top sediments. Multi-species net fractionation values between source water and leaf wax lipid δD values (-113 ± 13%) agree with previous results in arid environments and provide a basis for applying this proxy further downcore. δD measurements of sedimentary alkanoic acids representing terrestrial sources (e.g. δDTER: nC30) show significant variation (up to 70%) over the past 120 ka. Interglacial periods are characterized by isotopic enrichment while the most negative δDTER values occur during glacial conditions (i.e. the Last Glacial Maximum and MIS 4). Preliminary reconstruction of the isotopic composition of past precipitation from the δDTER record correlates strongly with the δ18Ocalcite record from Sanbao and Hulu caves1 (China) and the δDvostok record2 (Antarctica) suggesting global teleconnections and 'circum-Pacific' coherence to paleo-precipitation archives. 1 Wang et al. (2005), Science 308, 854-857. 2 Petit et al. (1999), Nature 399, 429-436.

Carbon and nitrogen isotope composition of core catcher samples from the ICDP deep drilling at Laguna Potrok Aike (Patagonia, Argentina)

NASA Astrophysics Data System (ADS)

Luecke, Andreas; Wissel, Holger; Mayr*, Christoph; Oehlerich, Markus; Ohlendorf, Christian; Zolitschka, Bernd; Pasado Science Team

2010-05-01

The ICDP project PASADO aims to develop a detailed paleoclimatic record for the southern part of the South American continent from sediments of Laguna Potrok Aike (51°58'S, 70°23'W), situated in the Patagonian steppe east of the Andean cordillera and north of the Street of Magellan. The precursor project SALSA recovered the Holocene and Late Glacial sediment infill of Laguna Potrok Aike and developed the environmental history of the semi-arid Patagonian steppe by a consequent interdisciplinary multi-proxy approach (e.g. Haberzettl et al., 2007). From September to November 2008 the ICDP deep drilling took place and successfully recovered in total 510 m of sediments from two sites resulting in a composite depth of 106 m for the selected main study Site 2. A preliminary age model places the record within the last 50.000 years. During the drilling campaign, the core catcher content of each drilled core run (3 m) was taken as separate sample to be shared and distributed between involved laboratories long before the main sampling party. A total of 70 core catcher samples describe the sediments of Site 2 and will form the base for more detailed investigations on the palaeoclimatic history of Patagonia. We here report on the organic carbon and nitrogen isotope composition of bulk sediment and plant debris of the core catcher samples. Similar investigations were performed for Holocene and Late Glacial sediments of Laguna Potrok Aike revealing insights into the organic matter dynamics of the lake and its catchment as well as into climatically induced hydrological variations with related lake level fluctuations (Mayr et al., 2009). The carbon and nitrogen content of the core catcher fine sediment fraction (<200 µm) is low to very low (around 1 % and 0.1 %, respectively) and requires particular attention in isotope analysis. The carbon isotope composition shows comparably little variation around a value of -26.0 per mil. The positive values of the Holocene and the Late Glacial (up to 22.0 per mil) are only sporadically reached down core. Compared to this, separated moss debris is remarkably 13C depleted with a minimum at 31.5 per mil. The nitrogen isotope ratios of glacial Laguna Potrok Aike sediments are lower (2.5 per mil) than those of the younger part of the record. The core catcher samples indicate several oscillations between 0.5 and 3.5 per mil. Data suggest a correlation between nitrogen isotopes and C/N ratios, but no linear relation between carbon isotopes and carbon content and an only weak relationship between carbon and nitrogen isotopes. Increasing nitrogen isotope values from 8000 cm downwards could probably be related to changed environmental conditions of Marine Isotope Stage 3 (MIS 3) compared to Marine Isotope Stage 2 (MIS 2). This will be further evaluated with higher resolution from the composite profile including a detailed study of discrete plant debris layers. References Haberzettl, T. et al. (2007). Lateglacial and Holocene wet-dry cycles in southern Patagonia: chronology, sedimentology and geochemistry of a lacustrine record from Laguna Potrok Aike, Argentina. The Holocene, 17: 297-310. Mayr, C. et al. (2009). Isotopic and geochemical fingerprints of environmental changes during the last 16,000 years on lacustrine organic matter from Laguna Potrok Aike (southern Patagonia, Argentina). Journal of Paleolimnology, 42: 81-102.

Sulphur and oxygen isotopic composition of sulphates in springs feeding the Wieprz river and other springs of Lublin Upland and Roztocze.

PubMed

Trembaczowski, A; Swieca, A

2002-12-01

Springs on Roztocze and Lublin Upland have been studied. Isotopic data are compared with data of chemical analyses. The results of studies allow us to distinguish five types of groundwaters. The differentiation is based upon different lithology; opokas, gaizes, sandy-silty-clay deposits, sands with shell sandstones, marly opokas, marly limestones and 'soft limestones of chalk type. A correlation can be observed between delta34S and the concentration of Ca or Mg ions also a correlation between HCO3- ion concentration and delta18O in sulphates. Probably these correlations are the result of some simultaneous processes, which occur in groundwater. The seasonal variations of the isotopic composition and sulphate concentration were observed in four springs feeding the upper Wieprz. The variations were simultaneous and often similar in these springs. Probably, these variations are caused by the admixture of sulphates coming from shallow water layers (or leached from soil); however the variations of the groundwater level may also change chemical and isotopic composition in groundwater.

Isotopic Dependence of GCR Fluence behind Shielding

NASA Technical Reports Server (NTRS)

Cucinotta, Francis A.; Wilson, John W.; Saganti, Premkumar; Kim, Myung-Hee Y.; Cleghorn, Timothy; Zeitlin, Cary; Tripathi, Ram K.

2006-01-01

In this paper we consider the effects of the isotopic composition of the primary galactic cosmic rays (GCR), nuclear fragmentation cross-sections, and isotopic-grid on the solution to transport models used for shielding studies. Satellite measurements are used to describe the isotopic composition of the GCR. For the nuclear interaction data-base and transport solution, we use the quantum multiple-scattering theory of nuclear fragmentation (QMSFRG) and high-charge and energy (HZETRN) transport code, respectively. The QMSFRG model is shown to accurately describe existing fragmentation data including proper description of the odd-even effects as function of the iso-spin dependence on the projectile nucleus. The principle finding of this study is that large errors (+/-100%) will occur in the mass-fluence spectra when comparing transport models that use a complete isotopic-grid (approx.170 ions) to ones that use a reduced isotopic-grid, for example the 59 ion-grid used in the HZETRN code in the past, however less significant errors (<+/-20%) occur in the elemental-fluence spectra. Because a complete isotopic-grid is readily handled on small computer workstations and is needed for several applications studying GCR propagation and scattering, it is recommended that they be used for future GCR studies.

Evaluation of stable isotope fingerprinting techniques for the assessment of the predominant methanogenic pathways in anaerobic digesters.

PubMed

Nikolausz, M; Walter, R F H; Sträuber, H; Liebetrau, J; Schmidt, T; Kleinsteuber, S; Bratfisch, F; Günther, U; Richnow, H H

2013-03-01

Laboratory biogas reactors were operated under various conditions using maize silage, chicken manure, or distillers grains as substrate. In addition to the standard process parameters, the hydrogen and carbon stable isotopic composition of biogas was analyzed to estimate the predominant methanogenic pathways as a potential process control tool. The isotopic fingerprinting technique was evaluated by parallel analysis of mcrA genes and their transcripts to study the diversity and activity of methanogens. The dominant hydrogenotrophs were Methanomicrobiales, while aceticlastic methanogens were represented by Methanosaeta and Methanosarcina at low and high organic loading rates, respectively. Major changes in the relative abundance of mcrA transcripts were observed compared to the results obtained from DNA level. In agreement with the molecular results, the isotope data suggested the predominance of the hydrogenotrophic pathway in one reactor fed with chicken manure, while both pathways were important in the other reactors. Short-term changes in the isotopic composition were followed, and a significant change in isotope values was observed after feeding a reactor digesting maize silage. This ability of stable isotope fingerprinting to follow short-term activity changes shows potential for indicating process failures and makes it a promising technology for process control.

Synthesis and characterization of surrogate nuclear explosion debris: urban glass matrix

DOE PAGES

Campbell, Keri; Judge, Elizabeth J.; Dirmyer, Matthew R.; ...

2017-07-26

Surrogate nuclear explosive debris was synthesized and characterized for major, minor, and trace elemental composition as well as uranium isotopics. The samples consisted of an urban glass matrix, equal masses soda lime and cement, doped with 500 ppm uranium with varying enrichments. The surface and cross section morphology were measured with SEM, and the major elemental composition was determined by XPS. LA-ICP-MS was used to measure the uranium isotopic abundance comparing different sampling techniques. Furthermore, the results provide an example of the utility of LA-ICP-MS for forensics applications.

Non-zero Δ33S preserved in rocks from the Basal Ultramafic Sequence indicate crustal contamination in the most primitive magma of the Rustenburg Layered Suite (Bushveld Complex, South Africa)

NASA Astrophysics Data System (ADS)

Magalhaes, N.; Wilson, A.; Penniston-Dorland, S.; Farquhar, J.

2017-12-01

The sulfur isotope composition of the Rustenburg Layered Suite (RLS) of the Bushveld Complex is different than expected from a magma sourced from the mantle (Δ33S=0), as measurements indicate the presence of an Archean surface-derived sulfur component. The Basal Ultramafic Sequence (BUS) is thought to be the most primitive magma of the RLS, as it is the lowest in the stratigraphy, has the highest Mg# (>0.92) for primary phases (olivine and orthopyroxene), and is in direct contact with the Magaliesberg quartzite of the Pretoria Group.We have measured the composition of sulfides in rocks from the Lower Zone, Marginal Zone, and the BUS, which were sampled in a 2300m drill core from the Clapham area, in the eastern Bushveld Complex. While the rocks of the Lower Zone have a relatively homogeneous non-zero Δ33S of 0.065‰, comparable to previous findings, there is an abrupt increase in the value of Δ33S (up to +0.301‰) in the Marginal Zone, which may be consistent with the observation in hand sample of assimilation of country rocks. The BUS also shows a surface-derived signal (average of 0.040‰), which is the lowest measured for any zone of the RLS.The non-zero Δ33S found in the Basal Ultramafic Sequence is evidence of the contamination of the magma with surface-derived material. In the upper parts of the intrusion, the Δ33S signature relates to whole-rock Sr and Nd isotopes, and their relationship suggests multiple sources of contamination. However, the relationship between sulfur and in-situ strontium isotope compositions (plagioclase) in this section of the RLS is not as clear as it is further up in the stratigraphy. This might reflect small-scale processes during the magmatic chamber stage, different compositions of local wall rock compared to deeper contaminants, or the presence of decoupled behavior between the isotope systems.These differences in the sulfur isotope composition between the different stratigraphic layers have been preserved regardless of any late magmatic processes that may have occurred, which further supports that the sulfur isotope composition of the RLS was not fully homogenized at a later stage by fluid migration.

Does Oxygen Isotopic Heterogeneity in Refractory Inclusions and Their Wark-Lovering Rims Record Nebular Repressing?

NASA Technical Reports Server (NTRS)

Simon, J. I.; Matzel, J. E. P.; Simon, S. B.; Weber, P. K.; Grossman, L.; Ross, D. K.; Hutcheon, I. D.

2013-01-01

Large systematic variations in O-isotopic compositions found within individual mineral layers of rims surrounding Ca-, Al-rich inclusions (CAIs) and at the margins of some CAIs imply formation from distinct environments [e.g., 1-3]. The O-isotope compositions of many CAIs preserve a record of the Solar nebula gas believed to initially be O-16-rich (delta O-17 less than or equal to -25%0) [4-5]. Data from a recent study of the compact Type A Allende CAI, A37, preserve a diffusion profile in the outermost 70 micrometers of the inclusion and show greater than 25%0 variations in delta O-17 within its 100 micrometer-thick Wark-Lovering rim (WL-rim) [3]. This and comparable heterogeneity measured in several other CAIs have been explained by isotopic mixing between the O-16-rich Solar reservoir and a second O-16-poor reservoir (probably nebular gas) with a planetary-like isotopic composition, e.g., [1,2,3,6]. However, there is mineralogical and isotopic evidence from the interiors of CAIs, in particular those from Allende, for parent body alteration. At issue is how to distinguish the record of secondary reprocessing in the nebula from that which occurred on the parent body. We have undertaken the task to study a range of CAI types with varying mineralogies, in part, to address this problem.

Intra-trophic isotopic discrimination of 15N/14N for amino acids in autotrophs: Implications for nitrogen dynamics in ecological studies

USDA-ARS?s Scientific Manuscript database

Metabolic reactions within heterotrophs cause discrimination in their stable nitrogen isotopic composition of amino acids (d15NAA) compared to their diets. Ecologists have exploited this measurable inter-trophic discrimination in the d15NAA value to estimate the trophic positions of heterotrophic an...

Effects of climatic seasonality on the isotopic composition of evaporating soil waters

NASA Astrophysics Data System (ADS)

Benettin, Paolo; Volkmann, Till H. M.; von Freyberg, Jana; Frentress, Jay; Penna, Daniele; Dawson, Todd E.; Kirchner, James W.

2018-05-01

Stable water isotopes are widely used in ecohydrology to trace the transport, storage, and mixing of water on its journey through landscapes and ecosystems. Evaporation leaves a characteristic signature on the isotopic composition of the water that is left behind, such that in dual-isotope space, evaporated waters plot below the local meteoric water line (LMWL) that characterizes precipitation. Soil and xylem water samples can often plot below the LMWL as well, suggesting that they have also been influenced by evaporation. These soil and xylem water samples frequently plot along linear trends in dual-isotope space. These trend lines are often termed "evaporation lines" and their intersection with the LMWL is often interpreted as the isotopic composition of the precipitation source water. Here we use numerical experiments based on established isotope fractionation theory to show that these trend lines are often by-products of the seasonality in evaporative fractionation and in the isotopic composition of precipitation. Thus, they are often not true evaporation lines, and, if interpreted as such, can yield highly biased estimates of the isotopic composition of the source water.

Baseline shifts in coral skeletal oxygen isotopic composition: a signature of symbiont shuffling?

NASA Astrophysics Data System (ADS)

Carilli, J. E.; Charles, C. D.; Garren, M.; McField, M.; Norris, R. D.

2013-06-01

Decades-long records of the stable isotopic composition of coral skeletal cores were analyzed from four sites on the Mesoamerican Reef. Two of the sites exhibited baseline shifts in oxygen isotopic composition after known coral bleaching events. Changes in pH at the calcification site caused by a change in the associated symbiont community are invoked to explain the observed shift in the isotopic composition. To test the hypothesis that changes in symbiont clade could affect skeletal chemistry, additional coral samples were collected from Belize for paired Symbiodinium identification and skeletal stable isotopic analysis. We found some evidence that skeletal stable isotopic composition may be affected by symbiont clade and suggest this is an important topic for future investigation. If different Symbiodinium clades leave consistent signatures in skeletal geochemical composition, the signature will provide a method to quantify past symbiont shuffling events, important for understanding how corals are likely to respond to climate change.

Supernova graphite in the NanoSIMS: Carbon, oxygen and titanium isotopic compositions of a spherule and its TiC sub-components

NASA Astrophysics Data System (ADS)

Stadermann, F. J.; Croat, T. K.; Bernatowicz, T. J.; Amari, S.; Messenger, S.; Walker, R. M.; Zinner, E.

2005-01-01

Presolar graphite spherules from the Murchison low-density separate KE3 contain a large number of internal TiC crystals that range in size from 15 to 500 nm. We have studied one such graphite grain in great detail by successive analyses with SEM, ims3f SIMS, TEM and NanoSIMS. Isotopic measurements of the 'bulk' particle in the ims3f indicate a supernova origin for this graphite spherule. The NanoSIMS measurements of C, N, O and Ti isotopes were performed directly on TEM ultramicrotome sections of the spherule, allowing correlated studies of the isotopic and mineralogical properties of the graphite grain and its internal crystals. We found isotopic gradients in 12C/ 13C and 16O/ 18O from the core of the graphite spherule to its perimeter, with the most anomalous compositions being present in the center. These gradients may be the result of isotopic exchange with isotopically normal material, either in the laboratory or during the particle's history. No similar isotopic gradients were found in the 16O/ 17O and 14N/ 15N ratios, which are normal within analytical uncertainty throughout the graphite spherule. Due to an unusually high O signal, internal TiC crystals were easily located during NanoSIMS imaging measurements. It was thus possible to determine isotopic compositions of several internal TiC grains independent of the surrounding graphite matrix. These TiC crystals are significantly more anomalous in their O isotopes than the graphite, with 16O/ 18O ratios ranging from 14 to 250 (compared to a terrestrial value of 499). Even the most centrally located TiC grains show significant variations in their O isotopic compositions from crystal to crystal. Measurement of the Ti isotopes in three TiC grains found no variations among them and no large differences between the compositions of the different crystals and the 'bulk' graphite spherule. However, the same three TiC crystals vary by a factor of 3 in their 16O/ 18O ratios. It is not clear in what form the O is associated with the TiC grains and whether it is cogenetic or the result of surface reactions on the TiC grains before they accreted onto the growing graphite spherule. The presence of 44Ca from short-lived 44Ti (t 1/2 = 60y) in one of the TiC subgrains confirms the identification of this graphite spherule as a supernova condensate.

Investigating the effects of abyssal peridotite alteration on Si, Mg and Zn isotopes

NASA Astrophysics Data System (ADS)

Savage, P. S.; Wimpenny, J.; Harvey, J.; Yin, Q.; Moynier, F.

2013-12-01

Around 1/3 of Earth's divergent ridge system is now classified as "slow" spreading [1], exposing ultramafic rocks (abyssal peridotites) at the seafloor. Such material is often highly altered by serpentinisation and steatisation (talc formation). It is crucial to understand such processes in order to access the original composition of the mantle, and to quantify any impact on ocean composition. Here we examine the effect of both serpentinisation and steatisation on Si, Mg and Zn isotopes. Hydrothermal alteration and seafloor weathering are both sources of oceanic Si [2] and weathering of abyssal peridotites is a source of oceanic Mg [3]; hence isotopic fractionation as a result of seafloor alteration could affect oceanic Si and Mg isotope composition. Zinc isotopes can provide complimentary information; the magnitude and direction of fractionation is highly dependent on complexing ligand [4] and can provide compositional information on the fluids driving metasomatism. For this study, two cores from the well-characterised abyssal peridotites recovered on ODP Leg 209 were examined [5]. Hole 1274a peridotites exhibit variable serpentinisation at ~200°C, whereas samples from Hole 1268a have been comprehensively serpentinised and then subsequently steatised to talc facies at ~350°C, by a low Mg/Si, low pH fluid. The Si, Mg and Zn isotope compositions of 1274a samples are extremely homogeneous, identical to that of pristine mantle rocks (BSE) i.e., serpentinisation at this locality was predominantly isochemical [5]. In contrast, samples from 1268a show greater isotopic variability. In all samples, Mg is enriched in the heavier isotopes relative to BSE, consistent with formation of isotopically heavy secondary phases [6]. For Si, serpentinised samples are slightly enriched in the lighter isotopes compared to BSE, again consistent with the behaviour of Si during formation of secondary phases [7]. Within the steatised samples, some exhibit enrichments in the lighter Si isotopes (similar to the serpentinites), however, some are isotopically heavy, relative to BSE. Such samples were found to have abundant chlorite, whose formation requires fluid with high Al activity, likely sourced from late-emplaced gabbroic dykes. The Zn of all 1268a samples are enriched in the lighter isotopes, implying the involvement of isotopically light sulfide precipitation during metasomatism [4]. The consistently heavy Mg isotope data suggest that seafloor alteration of peridotites can input an isotopically light Mg-bearing fluid to the ocean. Fluid composition is less easy to determine from the more complex behaviour observed in Si isotopes, although it is unlikely to substantially deviate from BSE, consistent with previous observations [8]. Finally, the strong enrichment in the lighter isotopes of Zn confirms that this isotope system could be used as a tracer of recycled serpentinised material at arc settings, as suggested in [4]. [1] Dick et al. (2003) Nature 426, 405-412; [2] Treguer and De La Rocha (2013) Ann. Rev. Mar. Sci. 5, 477-501; [3] Snow & Dick (1995) GCA, 59, 4219-4235; [4] Pons et al. (2011) PNAS 108(43) 17639-17643; [5] Bach et al., (2004) G3 5; [6] Tipper et al. (2006) EPSL 247, 267-279; [7] Opfergelt et al. (2012) Chem. Geol. 326, 113-122; [8] De La Rocha et al. (2000) GCA 64, 2467-2477.

Compound-specific isotopic analyses: a novel tool for reconstruction of ancient biogeochemical processes

NASA Technical Reports Server (NTRS)

Hayes, J. M.; Freeman, K. H.; Popp, B. N.; Hoham, C. H.

1990-01-01

Patterns of isotopic fractionation in biogeochemical processes are reviewed and it is suggested that isotopic fractionations will be small when substrates are large. If so, isotopic compositions of biomarkers will reflect those of their biosynthetic precursors. This prediction is tested by consideration of results of analyses of geoporphyrins and geolipids from the Greenhorn Formation (Cretaceous, Western Interior Seaway of North America) and the Messel Shale (Eocene, lacustrine, southern Germany). It is shown (i) that isotopic compositions of porphyrins that are related to a common source, but which have been altered structurally, cluster tightly and (ii) that isotopic differences between geolipids and porphyrins related to a common source are equal to those observed in modern biosynthetic products. Both of these observations are consistent with preservation of biologically controlled isotopic compositions during diagenesis. Isotopic compositions of individual compounds can thus be interpreted in terms of biogeochemical processes in ancient depositional environments. In the Cretaceous samples, isotopic compositions of n-alkanes are covariant with those of total organic carbon, while delta values for pristane and phytane are covariant with those of porphyrins. In this unit representing an open marine environment, the preserved acyclic polyisoprenoids apparently derive mainly from primary material, while the extractable, n-alkanes derive mainly from lower levels of the food chain. In the Messel Shale, isotopic compositions of individual biomarkers range from -20.9 to -73.4% vs PDB. Isotopic compositions of specific compounds can be interpreted in terms of origin from methylotrophic, chemautotrophic, and chemolithotrophic microorganisms as well as from primary producers that lived in the water column and sediments of this ancient lake.

Seasonality of Oxygen isotope composition in cow (Bos taurus) hair and its model interpretation

NASA Astrophysics Data System (ADS)

Chen, Guo; Schnyder, Hans; Auerswald, Karl

2017-04-01

Oxygen isotopes in animal and human tissues are expected to be good recorders of geographical origin and migration histories based on the isotopic relationship between hair oxygen and annual precipitation and the well-known spatial pattern of oxygen isotope composition in meteoric water. However, seasonal variation of oxygen isotope composition may diminish the origin information in the tissues. Here the seasonality of oxygen isotope composition in tail hair was investigated in a domestic suckler cow (Bos taurus) that underwent different ambient conditions, physiological states, and keeping and feeding strategies during five years. A detailed mechanistic model involving in ambient conditions, soil properties and animal physiology was built to explain this variation. The measured oxygen isotope composition in hair was significantly related (p<0.05) to the isotope composition in meteoric water in a regression analysis. Modelling suggested that this relation was only partly derived from the direct influence of feed moisture. Ambient conditions (temperature, moisture) did not only influence the isotopic signal of precipitation but also affected the animal itself (drinking water demand, transcutaneous vapor etc.). The clear temporal variation thus resulted from complex interactions with multiple influences. The twofold influence of ambient conditions via the feed and via the animal itself is advantageous for tracing the geographic origin because the oxygen isotope composition is then less influenced by variations in moisture uptake; however, it is unfavorable for indicating the production system, e.g. to distinguish between milk produced from fresh grass or from silage.

Investigating the behaviour of Mg isotopes during the formation of clay minerals

NASA Astrophysics Data System (ADS)

Wimpenny, Joshua; Colla, Christopher A.; Yin, Qing-Zhu; Rustad, James R.; Casey, William H.

2014-03-01

We present elemental and isotopic data detailing how the Mg isotope system behaves in natural and experimentally synthesized clay minerals. We show that the bulk Mg isotopic composition (δ26Mg) of a set of natural illite, montmorillonite and kaolinite spans a 2‰ range, and that their isotopic composition depends strongly on a balance between the relative proportions of structural and exchangeable Mg. After acid leaching, these natural clays become relatively enriched in isotopically heavy Mg by between 0.2‰ and 1.6‰. Results of exchange experiments indicate that the Mg that has adsorbed to interlayer spaces and surface charged sites is relatively enriched in isotopically light Mg compared to the residual clay. The isotopic composition of this exchangeable Mg (-1.49‰ to -2.03‰) is characteristic of the isotopic composition of Mg found in many natural waters. Further experiments with an isotopically characterized MgCl2 solution shows that the clay minerals adsorb this exchangeable Mg with little or no isotopic fractionation, although we cannot discount the possibility that the uptake of exchangeable Mg does so with a slight preference for 24Mg. To characterize the behaviour of Mg isotopes during clay mineral formation we synthesized brucite (Mg(OH)2), which we consider to be a good analogue for the incorporation of Mg into the octahedral sheet of Mg-rich clay minerals or into the brucitic layer of clays such as chlorite. In our experiment the brucite mineral becomes enriched in the heavy isotopes of Mg while the corresponding solution is always relatively enriched in isotopically light Mg. The system reaches a steady state after 10 days with a final fractionation factor (αsolid-solution) of 1.0005 at near-neutral pH. This result is consistent with the general consensus that secondary clay minerals preferentially take up isotopically heavy Mg during their formation. However our results also show that exchangeable Mg is an important component within bulk clay minerals and can have an important influence over the bulk clay δ26Mg value. Modeling shows that in certain soils or sediments where the percentage of exchangeable Mg is >30% and the isotopic composition of the exchangeable Mg is around -2‰, the generation of bulk δ26Mg values of <-0.5‰ is likely. On a broader scale, Mg-rich minerals such as smectite and illite are likely to impart a stronger control over the Mg budget in clay rich sediments, and their high structural Mg component is likely to result in bulk sediment δ26Mg values that are closer in composition to the UCC. Despite this, results of modeling, together with experimental observation suggests that the uptake of exchangeable Mg into these clay rich sediments could cause a decrease in the bulk δ26Mg value by up to ˜0.3-0.4‰. This should be accounted for when assessing the δ26Mg value of sediments on a crustal scale.

Linking the isotopic composition of monthly precipitation, cave drip water and tree ring cellulose - 15 years of monitoring and data-model comparison

NASA Astrophysics Data System (ADS)

Labuhn, Inga; Genty, Dominique; Daux, Valérie; Bourges, François; Hoffmann, Georg

2013-04-01

The isotopic composition of proxies used for palaeoclimate reconstruction, like tree ring cellulose or speleothem calcite, is controlled to a large extent by the isotopic composition of precipitation. In order to calibrate and interpret these proxies in terms of climate, it is necessary to study water isotopes in rainfall and their link with the proxies' source water. We present 10 to 15-year series of stable hydrogen and oxygen isotopes in monthly precipitation from three sites in the south of France, along with corresponding REMOiso model simulations, a monitoring of cave drip water from two of these sites (Villars cave in the south-west and Chauvet cave in the south-east), as well as measurements of oxygen isotopes in tree ring cellulose from oak trees growing in the same area. The isotopic composition of monthly precipitation at the three sites displays a typical annual cycle. At the south-west sites, under Atlantic influence, the interannual variability is much more pronounced during the winter months than during the summer, whereas the south-eastern Mediterranean site shows the same variability throughout the year. The model simulations are able to reproduce the annual cycle of monthly precipitation δ18O as well as the intra-seasonal variability. Compared to the data, however, the modelled average isotopic values and the seasonal amplitude are overestimated. Correlations between temperature and precipitation δ18O are generally weak at all our sites, on both the monthly and the annual scale, even when using temperature averages weighted by the amount of precipitation. Consequently, a proxy which is controlled by the δ18O of precipitation cannot be directly interpreted in terms of temperature in this region. The isotopic composition of cave drip water in both caves remains stable throughout the monitoring period. By calculating different weighted averages of precipitation δ18O for time periods ranging from months to years, we demonstrate that the cave drip water isotopic composition is the result of several years of rainfall mixing. The precipitation of every month must be considered in order to attain the drip water values, which means that rain water infiltrates throughout the year. There is no modification of the soil water isotopic composition by evaporation and no seasonal bias introduced by transpiring plants; they use water from reserves which represents several months or years of mixing. For the interpretation of tree ring cellulose δ18O, this implies that - at least for the monitoring period of 15 years - the source water signal is more or less constant. Therefore, the variability of cellulose δ18O must be mainly due to evaporation at the leaf level, which is strongly dependent on summer temperature. Insights on the variability and temperature correlations of stable isotopes in precipitation and on the origin and composition of cave drip water are important for the interpretation of proxies. Long-term monitoring is needed for model validation, and the locally validated and corrected model can provide longer time series for a reliable proxy calibration.

Using in-situ observations of atmospheric water vapor isotopes to benchmark and isotope-enabled General Circulation Models and improve ice core paleo-climate reconstruction

NASA Astrophysics Data System (ADS)

Steen-Larsen, Hans Christian; Sveinbjörnsdottir, Arny; Masson-Delmotte, Valerie; Werner, Martin; Risi, Camille; Yoshimura, Kei

2016-04-01

We have since 2010 carried out in-situ continuous water vapor isotope observations on top of the Greenland Ice Sheet (3 seasons at NEEM), in Svalbard (1 year), in Iceland (4 years), in Bermuda (4 years). The expansive dataset containing high accuracy and precision measurements of δ18O, δD, and the d-excess allow us to validate and benchmark the treatment of the atmospheric hydrological cycle's processes in General Circulation Models using simulations nudged to reanalysis products. Recent findings from both Antarctica and Greenland have documented strong interaction between the snow surface isotopes and the near surface atmospheric water vapor isotopes on diurnal to synoptic time scales. In fact, it has been shown that the snow surface isotopes take up the synoptic driven atmospheric water vapor isotopic signal in-between precipitation events, erasing the precipitation isotope signal in the surface snow. This highlights the importance of using General or Regional Climate Models, which accurately are able to simulate the atmospheric water vapor isotopic composition, to understand and interpret the ice core isotope signal. With this in mind we have used three isotope-enabled General Circulation Models (isoGSM, ECHAM5-wiso, and LMDZiso) nudged to reanalysis products. We have compared the simulations of daily mean isotope values directly with our in-situ observations. This has allowed us to characterize the variability of the isotopic composition in the models and compared it to our observations. We have specifically focused on the d-excess in order to characterize why both the mean and the variability is significantly lower than our observations. We argue that using water vapor isotopes to benchmark General Circulation Models offers an excellent tool for improving the treatment and parameterization of the atmospheric hydrological cycle. Recent studies have documented a very large inter-model dispersion in the treatment of the Arctic water cycle under a future global warming and greenhouse gas emission scenario. Our results call for action to create an international pan-Arctic monitoring water vapor isotope network in order to improve future projections of Arctic climate.

Stable isotopic variation in tropical forest plants for applications in primatology.

PubMed

Blumenthal, Scott A; Rothman, Jessica M; Chritz, Kendra L; Cerling, Thure E

2016-10-01

Stable isotope analysis is a promising tool for investigating primate ecology although nuanced ecological applications remain challenging, in part due to the complex nature of isotopic variability in plant-animal systems. The aim of this study is to investigate sources of carbon and nitrogen isotopic variation at the base of primate food webs that reflect aspects of primate ecology. The majority of primates inhabit tropical forest ecosystems, which are dominated by C3 vegetation. We used stable isotope ratios in plants from Kibale National Park, Uganda, a well-studied closed-canopy tropical forest, to investigate sources of isotopic variation among C3 plants related to canopy stratification, leaf age, and plant part. Unpredictably, our results demonstrate that vertical stratification within the canopy does not explain carbon or nitrogen isotopic variation in leaves. Leaf age can be a significant source of isotopic variation, although the direction and magnitude of this difference is not consistent across tree species. Some plant parts are clearly differentiated in carbon and nitrogen isotopic composition, particularly leaves compared to non-photosynthetic parts such as reproductive parts and woody stem parts. Overall, variation in the isotopic composition of floral communities, plant species, and plant parts demonstrates that stable isotope studies must include analysis of local plant species and parts consumed by the primates under study from within the study area. Am. J. Primatol. 78:1041-1054, 2016. © 2015 Wiley Periodicals, Inc. © 2015 Wiley Periodicals, Inc.

Stable iron isotopes and microbial mediation in red pigmentation of the Rosso Ammonitico (mid-late Jurassic, Verona area, Italy).

PubMed

Préat, Alain R; de Jong, Jeroen T M; Mamet, Bernard L; Mattielli, Nadine

2008-08-01

The iron (Fe) isotopic composition of 17 Jurassic limestones from the Rosso Ammonitico of Verona (Italy) have been analyzed by Multiple-Collector Inductively Coupled Plasma Mass Spectrometry (MC-ICP-MS). Such analysis allowed for the recognition of a clear iron isotopic fractionation (mean -0.8 per thousand, ranging between -1.52 to -0.06 per thousand) on a millimeter-centimeter scale between the red and grey facies of the studied formation. After gentle acid leaching, measurements of the Fe isotopic compositions gave delta(56)Fe values that were systematically lower in the red facies residues (median: -0.84 per thousand, range: -1.46 to +0.26 per thousand) compared to the grey facies residues (median: -0.08 per thousand, range: -0.34 to +0.23 per thousand). In addition, the red facies residues were characterized by a lighter delta(56)Fe signal relative to their corresponding leachates. These Fe isotopic fractionations could be a sensitive fingerprint of a biotic process; systematic isotopic differences between the red and grey facies residues, which consist of hematite and X-ray amorphous iron hydroxides, respectively, are hypothesized to have resulted from the oxidizing activity of iron bacteria and fungi in the red facies. The grey Fe isotopic data match the Fe isotopic signature of the terrestrial baseline established for igneous rocks and low-C(org) clastic sedimentary rocks. The Fe isotopic compositions of the grey laminations are consistent with the influx of detrital iron minerals and lack of microbial redox processes at the water-interface during deposition. Total Fe concentration measurements were performed by Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES) (confirmed by concentration estimations obtained by MC-ICP-MS analyses of microdrilled samples) on five samples, and resultant values range between 0.30% (mean) in the grey facies and 1.31% (mean) in the red facies. No correlation was observed between bulk Fe content and pigmentation or between bulk Fe content and Fe isotopic compositions. The rapid transformation of the original iron oxyhydroxides to hematite could have preserved the original isotopic composition if it had occurred at about the same temperature. This paper supports the use of Fe isotopes as sensitive tracers of biological activities recorded in old sedimentary sequences that contain microfossils of iron bacteria and fungi. However, a careful interpretation of the iron isotopic fractionation in terms of biotic versus abiotic processes requires supporting data or direct observations to characterize the biological, (geo)chemical, or physical context in relation to the geologic setting. This will become even more pertinent when Fe isotopic studies are expanded to the interplanetary realm.

Magnesium isotopic composition of the mantle

NASA Astrophysics Data System (ADS)

Teng, F.; Li, W.; Ke, S.; Marty, B.; Huang, S.; Dauphas, N.; Wu, F.; Helz, R. L.

2009-12-01

Studies of Mg isotopic composition of the Earth not only are important for understanding its geochemistry but also can shed light on the accretion history of the Earth as well as the evolution of the Earth-Moon system. However, to date, the Mg isotopic composition of the Earth is still poorly constrained and highly debated. There is uncertainty in the magnitude of Mg isotope fractionation at mantle temperatures and whether the Earth has a chondritic Mg isotopic composition or not. To constrain further the Mg isotopic composition of the mantle and investigate the behavior of Mg isotopes during igneous differentiation, we report >200 high-precision (δ26Mg < 0.1‰, 2SD) analyses of Mg isotopes on 1) global mid-ocean ridge basalts covering major ridge segments of the world and spanning a broad range in latitudes, chemical and radiogenic isotopic compositions; 2) ocean island basalts from Hawaiian (Koolau, Kilauea and Loihi) and French Polynesian volcanoes (Society island and Cook Austral chain); 3) olivine grains from Hawaiian volcanoes (Kilauea, Koolau and Loihi) and 4) peridotite xenoliths from Australia, China, France, Tanzania and USA. Global oceanic basalts and peridotite xenoliths have a limited (<0.2 ‰) variation in Mg isotopic composition, with an average δ26Mg = -0.25 relative to DSM3. Olivines from Hawaiian lavas have δ26Mg ranging from -0.43 to +0.03, with most having compositions identical to basalts and peridotites. Therefore, the mantle’s δ26Mg value is estimated to be ~ -0.25 ± 0.1 (2SD), different from that reported by Wiechert and Halliday (2007; δ26Mg = ~ 0) but similar to more recent studies (δ26Mg = -0.27 to -0.33) (Teng et al. 2007; Handler et al. 2009; Yang et al., 2009). Moreover, we suggest the Earth, as represented by the mantle, has a Mg isotopic composition similar to chondrites (δ26Mg = ~-0.33). The need for a model such as that of Wiechert and Halliday (2007) that involves sorting of chondrules and calcium-aluminum-rich inclusions in the proto planetary disc is thus not required to explain the Mg isotopic composition of the Earth.

Carbon Isotope Characterization of Organic Intermediaries in Hydrothermal Hydrocarbon Synthesis by Pyrolysis-GC-MS-C-IRMS

NASA Technical Reports Server (NTRS)

Socki, Richard A.; Fu, Qi; Niles, Paul B.

2010-01-01

We report results of experiments designed to characterize the carbon isotope composition of intermediate organic compounds produced as a result of mineral surface catalyzed reactions. The impetus for this work stems from recently reported detection of methane in the Martian atmosphere coupled with evidence showing extensive water-rock interaction during Martian history. Abiotic formation by Fischer-Tropsch-type (FTT) synthesis during serpentinization reactions may be one possible process responsible for methane generation on Mars, and measurement of carbon and hydrogen isotopes of intermediary organic compounds can help constrain the origin of this methane. Of particular interest within the context of this work is the isotopic composition of organic intermediaries produced on the surfaces of mineral catalysts (i.e. magnetite) during hydrothermal experiments, and the ability to make meaningful and reproducible isotope measurements. Our isotope measurements utilize a unique analytical technique combining Pyrolysis-Gas Chromatograph-Mass Spectrometry-Combustion-Isotope Ratio Mass Specrometry (Py-GC-MS-C-IRMS). Others have conducted similar pyrolysis-IRMS experiments on low molecular weight organic acids (Dias, et al, Organic Geochemistry, 33 [2002]). Our technique differs in that it carries a split of the pyrolyzed GC-separated product to a Thermo DSQ-II quadrupole mass spectrometer as a means of making qualitative and semi-quantitative compositional measurements of the organic compounds. A sample of carboxylic acid (mixture of C1 through C6) was pyrolyzed at 100 XC and passed through the GC-MS-C-IRMS (combusted at 940 XC). In order to test the reliability of our technique we compared the _13C composition of different molecular weight organic acids (from C1 through C6) extracted individually by the traditional sealed-tube cupric oxide combustion (940 XC) method with the _13C produced by our pyrolysis technique. Our data indicate that an average 4.3. +/-0.5. (V-PDB) apparent isotopic fractionation accompanies the pyrolysis extractions. We postulate that this isotope offset could be the result of incomplete thermal desorption during pyrolysis. We are continuing to investigate the reliability of this pyrolysis technique for correcting carbon isotope measurements of mineral surface catalyzed organic compounds.

Neodymium Isotope associated with planktonic foraminifera as a proxy of deglacial changes in Pacific ocean circulation

NASA Astrophysics Data System (ADS)

Hu, R.

2015-12-01

Neodymium isotopes of ferromanganese oxide coatings precipitated on planktonic foraminifera have been intensively used as a proxy for water mass reconstruction in the deep Atlantic and Indian Ocean, but their suitability is not well constrained in the Pacific and may be affected by enhanced inputs and scavenging relative to advection. In this study, Nd isotopes and Rare Earth Element (REE) concentrations of planktonic foraminifera from ~60 sites widely distributed throughout the Pacific are presented. We found that the REE pattern associated with planktonic foraminifera in our study and Fe-Mn oxides/coatings in the global ocean have a common heavy REE depleted pattern when normalized to their ambient seawater due to preferential removal of light REEs onto particles relative to heavy REEs during scavenging. The core-top ɛNd results agree with the proximal seawater compositions, indicating that planktonic foraminiferal coatings can give a reliable record of past changes in bottom water Nd isotopes in the Pacific. A good correlation between foraminifera Nd isotopes and seawater phosphate suggests that Nd with a predominantly radiogenic isotopic composition was probably added gradually along continental boundaries so that the Nd isotopic composition change paralleled the accumulation of nutrients in the deep Pacific. By confirming Nd isotopes as a reliable water mass tracer in the Pacific Ocean, this proxy is then applied to reconstruct how the water mass circulation changes during the Last Glacial Maximum (LGM). Most of the cores in deep North Pacific show essentially invariant Nd isotopic compositions during the LGM compared with core-top values, suggesting that Nd isotope of Pacific end-member did not change during glacial times. However, the LGM Southwest Pacific cores have more radiogenic ɛNd than core-tops corroborating the previous findings of reduced inflow of North Atlantic Deep Water. The Eastern Equatorial Pacific cores above ~2 km showed consistently lower LGM ɛNd values, which might suggest a reduced influence of more radiogenic North Pacific Deep Water return flow. Taken together, our results indicate a slower Pacific overturning circulation during the glacial times, and the inflow and return flow of the Pacific meridional overturning were closely linked in the glacial-interglacial cycles.

ISOTOPE CONVERSION DEVICE

DOEpatents

Wigner, E.P.; Young, G.J.; Ohlinger, L.A.

1957-12-01

This patent relates to nuclear reactors of tbe type utilizing a liquid fuel and designed to convert a non-thermally fissionable isotope to a thermally fissionable isotope by neutron absorption. A tank containing a reactive composition of a thermally fissionable isotope dispersed in a liquid moderator is disposed within an outer tank containing a slurry of a non-thermally fissionable isotope convertible to a thermally fissionable isotope by neutron absorption. A control rod is used to control the chain reaction in the reactive composition and means are provided for circulating and cooling the reactive composition and slurry in separate circuits.

Oxygen isotope exchange between refractory inclusion in Allende and solar nebula gas.

PubMed

Yurimoto, H; Ito, M; Nagasawa, H

1998-12-04

A calcium-aluminum-rich inclusion (CAI) from the Allende meteorite was analyzed and found to contain melilite crystals with extreme oxygen-isotope composition (approximately 5 percent oxygen-16 enrichment relative to terrestrial oxygen-16). Some of the melilite is also anomalously enriched in oxygen-16 compared with oxygen isotopes measured in other CAIs. The oxygen isotopic variation measured among the minerals (melilite, spinel, and fassaite) indicates that crystallization of the CAI started from oxygen-16-rich materials that were probably liquid droplets in the solar nebula, and oxygen isotope exchange with the surrounding oxygen-16-poor nebular gas progressed through the crystallization of the CAI. Additional oxygen isotope exchange also occurred during subsequent reheating events in the solar nebula.

Oxygen isotope exchange between refractory inclusion in allende and solar nebula Gas

PubMed

Yurimoto; Ito; Nagasawa

1998-12-04

A calcium-aluminum-rich inclusion (CAI) from the Allende meteorite was analyzed and found to contain melilite crystals with extreme oxygen-isotope compositions ( approximately 5 percent oxygen-16 enrichment relative to terrestrial oxygen-16). Some of the melilite is also anomalously enriched in oxygen-16 compared with oxygen isotopes measured in other CAIs. The oxygen isotopic variation measured among the minerals (melilite, spinel, and fassaite) indicates that crystallization of the CAI started from oxygen-16-rich materials that were probably liquid droplets in the solar nebula, and oxygen isotope exchange with the surrounding oxygen-16-poor nebular gas progressed through the crystallization of the CAI. Additional oxygen isotope exchange also occurred during subsequent reheating events in the solar nebula.

In-Situ Oxygen Isotopic Composition of Tagish Lake: An Ungrouped Type 2 Carbonaceous Chondrite

NASA Technical Reports Server (NTRS)

Zolensky, Michael E.; Engrand, Cecile; Gounelle, Matthieu; Zolensky, Mike E.

2001-01-01

We have measured the oxygen isotopic composition of several components of Tagish Lake by ion microprobe. This meteorite constitutes the best preserved sample of C2 matter presently available for study. It presents two different lithologies (carbonate-poor and -rich) which have fairly comparable oxygen isotopic composition, with regard to both the primary or secondary minerals. For the olivine and pyroxene grains, their delta O-18 values range from - 10.5% to + 7.4% in the carbonate-poor lithology, with a mean Delta O-17 value of - 3.7 2.4%. In the carbonate-rich lithology, delta O-18 varies from - 7.9% to + 3.3%, and the mean Delta O-17 value is - 4.7 +/- 1.4%. Olivine inclusions (Fo(sub >99)) with extreme O-16-enrichment were found in both lithologies: delta O-18 = - 46.1 %, delta O-187= - 48.3% and delta O-18 = - 40.6%, delta O-17 = - 41.2% in the carbonate-rich lithology; delta O-18 = - 41.5%, delta O-17 = -43.4%0 in the carbonate-poor lithology. Anhydrous minerals in the carbonate-poor lithology are slightly more O-16-rich than in the carbonate-rich one. Four low-iron manganese-rich (LIME) olivine grains do not have an oxygen isotopic composition distinct from the other "normal" olivines. The phyllosilicate matrix presents the same range of oxygen isotopic compositions in both lithologies: delta O-18 from approximately 11 % to approximately 6%, with an average Delta. O-17 approximately 0%. Because the bulk Tagish Lake oxygen isotopic composition given by Brown et al. is on the high end of our matrix analyses, we assume that this "bulk Tagish Lake" composition probably only represents that of the carbonate-rich lithology. Calcium carbonates have delta O-18 values up to 35%, with Delta O-17 approximately 0.5%0. Magnetite grains present very high Delta O-17 values approximately + 3.4%0 +/- 1.2%. Given our analytical uncertainties and our limited carbonate data, the matrix and the carbonate seem to have formed in isotopic equilibrium. In that case, their large isotopic fractionation would argue for a low temperature (CM-like, T approximately 0 deg) formation. Magnetite probably formed during a separate event. Tagish Lake magnetite data is surprisingly compatible with that of R-chondrites and unequilibrated ordinary (LL3) chondrites. Our oxygen isotope data strongly supports the hypothesis of a single precursor for both lithologies. Drastic mineralogical changes between the two lithologies not being accompanied with isotopic fractionation seem compatible with the alteration model presented by Young et aI. Tagish Lake probably represents the first well preserved large sample of the C2 matter that dominates interplanetary matter since the formation of the solar system.

MAST - A mass spectrometer telescope for studies of the isotopic composition of solar, anomalous, and galactic cosmic ray nuclei

NASA Technical Reports Server (NTRS)

Cook, Walter R.; Cummings, Alan C.; Cummings, Jay R.; Garrard, Thomas L.; Kecman, Branislav; Mewaldt, Richard A.; Selesnick, Richard S.; Stone, Edward C.; Von Rosenvinge, T. T.

1993-01-01

The Mass Spectrometer Telescope (MAST) on SAMPEX is designed to provide high resolution measurements of the isotopic composition of energetic nuclei from He to Ni (Z = 2 to 28) over the energy range from about 10 to several hundred MeV/nuc. During large solar flares MAST will measure the isotopic abundances of solar energetic particles to determine directly the composition of the solar corona, while during solar quiet times MAST will study the isotopic composition of galactic cosmic rays. In addition, MAST will measure the isotopic composition of both interplanetary and trapped fluxes of anomalous cosmic rays, believed to be a sample of the nearby interstellar medium.

Lithium and boron in late-orogenic granites - Isotopic fingerprints for the source of crustal melts?

NASA Astrophysics Data System (ADS)

Romer, Rolf L.; Meixner, Anette; Förster, Hans-Jürgen

2014-04-01

Geochemically diverse late- and post-Variscan granites of the Erzgebirge-Vogtland, the Saxon Granulite Massif, and Thuringia (Germany) formed by anatectic melting of Palaeozoic sedimentary successions and associated mafic to felsic volcanic rocks. The compositional diversity of the least evolved of these granites is largely inherited from the protoliths. We present Li and B-isotopic data of these granites and compare them with the isotopic composition of their protoliths, to investigate whether (i) there exist systematic differences in the Li and B-isotopic composition among different granite types and (ii) Li and B-isotopic compositions provide information on the granite sources complementary to information from the isotopic composition of Sr, Nd, and Pb and the trace-element signatures. Low-F biotite and two-mica granite types have flat upper continental crust (UCC)-normalized trace-element pattern with variable enrichments in Li, Rb, Cs, Sn, and W and depletions in Sr, Ba, and Eu. These signatures are least pronounced for the Niederbobritzsch biotite granite, which has the largest contribution of mafic material, and most pronounced for the two-mica granites. The granites show a relatively narrow range of δ7Li values (-3.0 to -0.5) and a broad range of δ11B values (-13.4 to +20.1). The δ11B values are lower in rocks with distinctly higher contents of Li, Rb, Cs, and Sn. The high δ11B of the Niederbobritzsch granite may be explained by the melting of former altered oceanic crust in its source. Relative to UCC, intermediate-F to high-F low-P granites show strong depletions in Sr, Ba, Eu as well as Zr and Hf, strong enrichments in Li, Rb, and Cs as well as Nb, Sn, Ta, and W, and REE pattern with stronger enrichments for HREE than for LREE. These granites show narrow ranges of δ7Li (-2.0 to +1.6) and δ11B values (-14.7 to -9.1), reflecting the smaller variability of the Li and B-isotopic composition in their source lithologies. The anomalously high δ7Li value (14.7) of one granite sample (Burgberg), which is similar to δ7Li values of its wall rocks (up to 14.5), may indicate late-magmatic fluid-rock interaction with external, wall rock-derived fluids. Because of the small compositional range of most source lithologies, the Li and B-isotopic variation in the granites is also small indicating that the isotopic composition of Li and B does not represent a particularly sensitive source tracer, with the exception of source lithologies characterized by extreme δ7Li or δ11B values.

In situ observations of the isotopic composition of methane at the Cabauw tall tower site

NASA Astrophysics Data System (ADS)

Röckmann, Thomas; Eyer, Simon; van der Veen, Carina; Popa, Maria E.; Tuzson, Béla; Monteil, Guillaume; Houweling, Sander; Harris, Eliza; Brunner, Dominik; Fischer, Hubertus; Zazzeri, Giulia; Lowry, David; Nisbet, Euan G.; Brand, Willi A.; Necki, Jaroslav M.; Emmenegger, Lukas; Mohn, Joachim

2016-08-01

High-precision analyses of the isotopic composition of methane in ambient air can potentially be used to discriminate between different source categories. Due to the complexity of isotope ratio measurements, such analyses have generally been performed in the laboratory on air samples collected in the field. This poses a limitation on the temporal resolution at which the isotopic composition can be monitored with reasonable logistical effort. Here we present the performance of a dual isotope ratio mass spectrometric system (IRMS) and a quantum cascade laser absorption spectroscopy (QCLAS)-based technique for in situ analysis of the isotopic composition of methane under field conditions. Both systems were deployed at the Cabauw Experimental Site for Atmospheric Research (CESAR) in the Netherlands and performed in situ, high-frequency (approx. hourly) measurements for a period of more than 5 months. The IRMS and QCLAS instruments were in excellent agreement with a slight systematic offset of (+0.25 ± 0.04) ‰ for δ13C and (-4.3 ± 0.4) ‰ for δD. This was corrected for, yielding a combined dataset with more than 2500 measurements of both δ13C and δD. The high-precision and high-temporal-resolution dataset not only reveals the overwhelming contribution of isotopically depleted agricultural CH4 emissions from ruminants at the Cabauw site but also allows the identification of specific events with elevated contributions from more enriched sources such as natural gas and landfills. The final dataset was compared to model calculations using the global model TM5 and the mesoscale model FLEXPART-COSMO. The results of both models agree better with the measurements when the TNO-MACC emission inventory is used in the models than when the EDGAR inventory is used. This suggests that high-resolution isotope measurements have the potential to further constrain the methane budget when they are performed at multiple sites that are representative for the entire European domain.

In-situ observations of the isotopic composition of methane at the Cabauw tall tower site

NASA Astrophysics Data System (ADS)

Röckmann, Thomas; Eyer, Simon; van der Veen, Carina; E Popa, Maria; Tuzson, Béla; Monteil, Guillaume; Houweling, Sander; Harris, Eliza; Brunner, Dominik; Fischer, Hubertus; Zazzeri, Giulia; Lowry, David; Nisbet, Euan G.; Brand, Willi A.; Necki, Jaroslav M.; Emmenegger, Lukas; Mohn, Joachim

2017-04-01

High precision analyses of the isotopic composition of methane in ambient air can potentially be used to discriminate between different source categories. Due to the complexity of isotope ratio measurements, such analyses have generally been performed in the laboratory on air samples collected in the field. This poses a limitation on the temporal resolution at which the isotopic composition can be monitored with reasonable logistical effort. Here we present the performance of a dual isotope ratio mass spectrometric system (IRMS) and a quantum cascade laser absorption spectroscopy (QCLAS) based technique for in-situ analysis of the isotopic composition of methane under field conditions. Both systems were deployed at the Cabauw experimental site for atmospheric research (CESAR) in the Netherlands and performed in-situ, high-frequency (approx. hourly) measurements for a period of more than 5 months. The IRMS and QCLAS instruments were in excellent agreement with a slight systematic offset of +0.05 ± 0.03 ‰ for δ13C-CH4 and -3.6 ± 0.4 ‰ for δD-CH4. This was corrected for, yielding a combined dataset with more than 2500 measurements of both δ13C and δD. The high precision and temporal resolution dataset does not only reveal the overwhelming contribution of isotopically depleted agricultural CH4 emissions from ruminants at the Cabauw site, but also allows the identification of specific events with elevated contributions from more enriched sources such as natural gas and landfills. The final dataset was compared to model calculations using the global model TM5 and the mesoscale model FLEXPART-COSMO. The results of both models agree better with the measurements when the TNO-MACC emission inventory is used in the models than when the EDGAR inventory is used. This suggests that high-resolution isotope measurements have the potential to further constrain the methane budget, when they are performed at multiple sites that are representative for the entire European domain.

Magnesium Isotopic Composition of Kamchatka Sub-Arc Mantle Peridotites

NASA Astrophysics Data System (ADS)

Hu, Y.; Teng, F. Z.; Ionov, D. A.

2016-12-01

Subduction of the oceanic slab may add a crustal isotopic signal to the mantle wedge. The highly variable Mg isotopic compositions (δ26Mg) of the subducted oceanic crust input[1] and arc lava output[2] imply a distinctive Mg isotopic signature of the mantle wedge. Magnesium isotopic data on samples from the sub-arc mantle are still limited, however. To characterize the Mg isotopic composition of typical sub-arc mantle, 17 large and fresh spinel harzburgite xenoliths from Avacha volcano were analyzed. The harzburgites were formed by 30% melt extraction at ≤ 1 2 GPa and fluid fluxing condition, and underwent possible fluid metasomatism as suggested by distinctively high orthopyroxene mode in some samples, the presence of accessory amphibole and highly variable Ba/La ratios[3]. However, their δ26Mg values display limited variation from -0.32 to -0.21, which are comparable to the mantle average at -0.25 ± 0.07[4]. The overall mantle-like and homogenous δ26Mg of Avacha sub-arc peridotites are consistent with their similar chemical compositions and high MgO contents (> 44 wt%) relative to likely crustal fluids. Furthermore, clinopyroxene (-0.24 ± 0.10, 2SD, n = 5), a late-stage mineral exsolved from high-temperature, Ca-rich residual orthopyroxene, is in broad Mg isotopic equilibrium with olivine (-0.27 ± 0.04, 2SD, n = 17) and orthopyroxene (-0.22 ± 0.06, 2SD, n = 17). Collectively, this study finds that the Kamchatka mantle wedge, as represented by the Avacha peridotites, has a mantle-like δ26Mg, and low-degree fluid-mantle interaction does not cause significant Mg isotope fractionation in sub-arc mantle peridotites. [1] Wang et al., EPSL, 2012 [2] Teng et al., PNAS, 2016 [3] Ionov, J. Petrol., 2010, [4] Teng et al., GCA, 2010.

Cadmium cycling in the water column of the Kuroshio-Oyashio Extension region: Insights from dissolved and particulate isotopic composition

NASA Astrophysics Data System (ADS)

Yang, Shun-Chung; Zhang, Jing; Sohrin, Yoshiki; Ho, Tung-Yuan

2018-07-01

We measured dissolved and particulate Cd isotopic composition in the water column of a meridional transect across the Kuroshio-Oyashio Extension region in a Japanese GEOTRACES cruise to investigate the relative influence of physical and biogeochemical processes on Cd cycling in the Northwestern Pacific Ocean. Located at 30-50°N along 165°E, the transect across the extension region possesses dramatic hydrographic contrast. Cold surface water and a relatively narrow and shallow thermocline characterizes the Oyashio Extension region in contrast to a relatively warm and highly stratified surface water and thermocline in the Kuroshio Extension region. The contrasting hydrographic distinction at the study site provides us with an ideal platform to investigate the spatial variations of Cd isotope fractionation systems in the ocean. Particulate samples demonstrated biologically preferential uptake of light Cd isotopes, and the fractionation effect varied dramatically in the surface water of the two regions, with relatively large fractionation factors in the Oyashio region. Based on the relationship of dissolved Cd concentrations and isotopic composition, we found that a closed system fractionation model can reasonably explain the relationship in the Kuroshio region. However, using dissolved Cd isotopic data, either a closed system or steady-state open system fractionation model may explain the relationship in the surface water of the Oyashio region. Particulate δ114/110Cd data further supports that the surface water of the Oyashio region matches a steady-state open system model more closely. Contrary to the surface water, the distribution of potential density exhibits comparable patterns with Cd elemental and isotopic composition in the thermocline and deep water in the two extension regions, showing that physical processes are the dominant forcing controlling Cd cycling in the deep waters. The results demonstrate that Cd isotope fractionation can match either a closed or open system Rayleigh fractionation model, depending on the relative contribution of physical and biogeochemical processes on its cycling.

The stable isotope amount effect: New insights from NEXRAD echo tops, Luquillo Mountains, Puerto Rico

USGS Publications Warehouse

Scholl, Martha A.; Shanley, James B.; Zegarra, Jan Paul; Coplen, Tyler B.

2009-01-01

The stable isotope amount effect has often been invoked to explain patterns of isotopic composition of rainfall in the tropics. This paper describes a new approach, correlating the isotopic composition of precipitation with cloud height and atmospheric temperature using NEXRAD radar echo tops, which are a measure of the maximum altitude of rainfall within the clouds. The seasonal differences in echo top altitudes and their corresponding temperatures are correlated with the isotopic composition of rainfall. These results offer another factor to consider in interpretation of the seasonal variation in isotopic composition of tropical rainfall, which has previously been linked to amount or rainout effects and not to temperature effects. Rain and cloud water isotope collectors in the Luquillo Mountains in northeastern Puerto Rico were sampled monthly for three years and precipitation was analyzed for δ18O and δ2H. Precipitation enriched in 18O and 2H occurred during the winter dry season (approximately December–May) and was associated with a weather pattern of trade wind showers and frontal systems. During the summer rainy season (approximately June–November), precipitation was depleted in 18O and 2H and originated in low pressure systems and convection associated with waves embedded in the prevailing easterly airflow. Rain substantially depleted in 18O and 2H compared to the aforementioned weather patterns occurred during large low pressure systems. Weather analysis showed that 29% of rain input to the Luquillo Mountains was trade wind orographic rainfall, and 30% of rainfall could be attributed to easterly waves and low pressure systems. Isotopic signatures associated with these major climate patterns can be used to determine their influence on streamflow and groundwater recharge and to monitor possible effects of climate change on regional water resources.

Biogeochemical cycling in an organic-rich coastal marine basin. 8. A sulfur isotopic budget balanced by differential diffusion across the sediment-water interface

USGS Publications Warehouse

Chanton, J.P.; Martens, C.S.; Goldhaber, M.B.

1987-01-01

The sulfur isotopic composition of the sulfur fluxes occurring in the anoxic marine sediments of Cape Lookout Bight, N.C., U.S.A., was determined, and the result of isotopic mass balance was obtained via the differential diffusion model. Seasonal pore water sulfate ??34S measurements yielded a calculated sulfate input of 0.6%.. Sulfate transported into the sediments via diffusion appeared to be enriched in the lighter isotope because its concentration gradient was steeper, due to the increase in the measured isotopic composition of sulfate with depth. Similarly, the back diffusion of dissolved sulfide towards the sediment-water interface appeared enriched in the heavier isotope. The isotopic composition of this flux was calculated from measurements of the ??34S of dissolved sulfide and was determined to be 15.9%.. The isotopic composition of buried sulfide was determined to be -5.2%. and the detrital sulfur input was estimated to be -6.2%.. An isotope mass balance equation based upon the fluxes at the sediment-water interface successfully predicted the isotopic composition of the buried sulfur flux within 0.5%., thus confirming that isotopes diffuse in response to their individual concentration gradients. ?? 1987.

Molybdenum Isotopic Composition of Iron Meteorites, Chondrites and Refractory Inclusions

NASA Technical Reports Server (NTRS)

Becker, H.; Walker, R. J.

2003-01-01

Recent Mo isotopic studies of meteorites reported evidence for differences in isotopic compositions for whole rocks of some primitive and differentiated meteorites relative to terrestrial materials. Enrichments of r- and p-process isotopes of up to 3-4 units (e unit = parts in 10(exp 4) over s-process dominated isotopes are the most prominent features. Certain types of presolar grains show large enrichments in s-process isotopes, however, it was concluded on grounds of mass balance that incomplete digestion of such grains cannot explain the enrichments of r- and p-process isotopes in whole rocks of primitive chondrites. If the reported variability in r- and p-process isotope enrichments reflects the true isotopic characteristics of the whole rocks, the implications are quite profound. It would suggest the presence of large scale Mo isotopic heterogeneity within the solar accretion disk with likely collateral effects for other elements. However, such effects were not found for Ru isotopes, nor for Zr isotopes. Another recent Mo isotopic study by multi collector ICP-MS could not confirm the reported deviations in Allende, Murchison or iron meteorites. Here, we present new results for the Mo isotopic composition of iron meteorites, chondrites and CAIs obtained by negative thermal ionization mass spectrometry (NTIMS). We discuss analytical aspects and the homogeneity of Mo isotopic compositions in solar system materials.

Transgenerational isotopic marking of carp Cyprinus carpio, L. using a 86Sr /84Sr double spike

NASA Astrophysics Data System (ADS)

Zitek, Andreas; Cervicek, Magdalena; Irrgeher, Johanna; Horsky, Monika; Kletzl, Manfred; Weismann, Thomas; Prohaska, Thomas

2013-04-01

Transgenerational isotopic marking has been recognized recently as an effective tool for mass marking and tracking of individual fish to their original source. Compared to other conventional marking techniques, transgenerational marking offers several advantages. Most importantly, it is possible to mark all offspring of one individual female without the necessity of handling eggs or larval fish. Furthermore it is possible to vary the concentrations of individual isotopes to obtain specific marks for individual female fish. An enriched isotopic spike solution is usually applied to gravid female spawners by injection into the body cavity for transgenerational marking. The isotope is then incorporated into the central otolith region of the offspring which is known to be built up by maternally derived material. Within this study transgenerational marking of a typical cyprinid fish species, Cyprinus carpio, L., was tested using a 86Sr /84Sr double spike. Buffered solutions with different isotopic composition and concentrations were administered to 4 female individuals by intraperitoneal injection 5 days before spawning, while one female was injected a blank solution. After spawning, otoliths (Lapilli) from juvenile fish were sampled at the age of about 5 months at fish sizes between 3 and 4 cm and analyzed for their isotopic composition by LA-ICPMS applying cross sectional line scans. Central otolith regions of the progeny showed a shift in the natural isotope ratios for the administered isotopes. Deconvolution of the blank corrected measurement data of the Sr isotopes was done to trace back the original spike ratio. The different spike ratios could be well distinguished reflecting the original composition of the spike solution. This study proved that it is possible to create batch-specific unique transgenerational marks in otolith cores by varying the concentrations of two naturally occurring Sr isotopes. This method has high potential to reduce the marking effort for any application in aquaculture and ecological research and management where the tracking of high numbers of offspring is needed.

The GENESIS Mission: Solar Wind Isotopic and Elemental Compositions and Their Implications

NASA Astrophysics Data System (ADS)

Wiens, R. C.; Burnett, D. S.; McKeegan, K. D.; Kallio, A. P.; Mao, P. H.; Heber, V. S.; Wieler, R.; Meshik, A.; Hohenberg, C. M.; Mabry, J. C.; Gilmour, J.; Crowther, S. A.; Reisenfeld, D. B.; Jurewicz, A.; Marty, B.; Pepin, R. O.; Barraclough, B. L.; Nordholt, J. E.; Olinger, C. T.; Steinberg, J. T.

2008-12-01

The GENESIS mission was a novel NASA experiment to collect solar wind at the Earth's L1 point for two years and return it for analysis. The capsule crashed upon re-entry in 2004, but many of the solar-wind collectors were recovered, including separate samples of coronal hole, interstream, and CME material. Laboratory analyses of these materials have allowed higher isotopic precision than possible with current in-situ detectors. To date GENESIS results have been obtained on isotopes of O, He, Ne, Ar, Kr, and Xe on the order of 1% accuracy and precision, with poorer uncertainty on Xe isotopes and significantly better uncertainties on the lighter noble gases. Elemental abundances are available for the above elements as well as Mg, Si, and Fe. When elemental abundances are compared with other in situ solar wind measurements, agreement is generally quite good. One exception is the Ne elemental abundance, which agrees with Ulysses and Apollo SWC results, but not with ACE. Neon is of particular interest because of the uncertainty in the solar Ne abundance, which has significant implications for the standard solar model. Helium isotopic results of material from the different solar wind regimes collected by GENESIS is consistent with isotopic fractionation predictions of the Coulomb drag model, suggesting that isotopic fractionation corrections need to be applied to heavier elements as well when extrapolating solar wind to solar compositions. Noble gas isotopic compositions from GENESIS are consistent with those obtained for solar wind trapped in lunar grains, but have for the first time yielded a very precise Ar isotopic result. Most interesting for cosmochemistry is a preliminary oxygen isotopic result from GENESIS which indicates a solar enrichment of ~4% in 16O relative to the planets, consistent with a photolytic self-shielding phenomenon during solar system formation. Analyses of solar wind N and C isotopes may further elucidate this phenomenon. Preliminary results from GENESIS have been reported for N, and results are still pending for C.

Iron speciation and isotope fractionation during silicate weathering and soil formation in an alpine glacier forefield chronosequence

NASA Astrophysics Data System (ADS)

Kiczka, Mirjam; Wiederhold, Jan G.; Frommer, Jakob; Voegelin, Andreas; Kraemer, Stephan M.; Bourdon, Bernard; Kretzschmar, Ruben

2011-10-01

The chemical weathering of primary Fe-bearing minerals, such as biotite and chlorite, is a key step of soil formation and an important nutrient source for the establishment of plant and microbial life. The understanding of the relevant processes and the associated Fe isotope fractionation is therefore of major importance for the further development of stable Fe isotopes as a tracer of the biogeochemical Fe cycle in terrestrial environments. We investigated the Fe mineral transformations and associated Fe isotope fractionation in a soil chronosequence of the Swiss Alps covering 150 years of soil formation on granite. For this purpose, we combined for the first time stable Fe isotope analyses with synchrotron-based Fe-EXAFS spectroscopy, which allowed us to interpret changes in Fe isotopic composition of bulk soils, size fractions, and chemically separated Fe pools over time in terms of weathering processes. Bulk soils and rocks exhibited constant isotopic compositions along the chronosequence, whereas soil Fe pools in grain size fractions spanned a range of 0.4‰ in δ 56Fe. The clay fractions (<2 μm), in which newly formed Fe(III)-(hydr)oxides contributed up to 50% of the total Fe, were significantly enriched in light Fe isotopes, whereas the isotopic composition of silt and sand fractions, containing most of the soil Fe, remained in the range described by biotite/chlorite samples and bulk soils. Iron pools separated by a sequential extraction procedure covered a range of 0.8‰ in δ 56Fe. For all soils the lightest isotopic composition was observed in a 1 M NH 2OH-HCl-25% acetic acid extract, targeting poorly-crystalline Fe(III)-(hydr)oxides, compared with easily leachable Fe in primary phyllosilicates (0.5 M HCl extract) and Fe in residual silicates. The combination of the Fe isotope measurements with the speciation data obtained by Fe-EXAFS spectroscopy permitted to quantitatively relate the different isotope pools forming in the soils to the mineral weathering reactions which have taken place at the field site. A kinetic isotope effect during the Fe detachment from the phyllosilicates was identified as the dominant fractionation mechanism in young weathering environments, controlling not only the light isotope signature of secondary Fe(III)-(hydr)oxides but also significantly contributing to the isotope signature of plants. The present study further revealed that this kinetic fractionation effect can persist over considerable reaction advance during chemical weathering in field systems and is not only an initial transient phenomenon.

Do Hf isotopes in magmatic zircons represent those of their host rocks?

NASA Astrophysics Data System (ADS)

Wang, Di; Wang, Xiao-Lei; Cai, Yue; Goldstein, Steven L.; Yang, Tao

2018-04-01

Lu-Hf isotopic system in zircon is a powerful and widely used geochemical tracer in studying petrogenesis of magmatic rocks and crustal evolution, assuming that zircon Hf isotopes can represent initial Hf isotopes of their parental whole rock. However, this assumption may not always be valid. Disequilibrium partial melting of continental crust would preferentially melt out non-zircon minerals with high time-integrated Lu/Hf ratios and generate partial melts with Hf isotope compositions that are more radiogenic than those of its magma source. Dissolution experiments (with hotplate, bomb and sintering procedures) of zircon-bearing samples demonstrate this disequilibrium effect where partial dissolution yielded variable and more radiogenic Hf isotope compositions than fully dissolved samples. A case study from the Neoproterozoic Jiuling batholith in southern China shows that about half of the investigated samples show decoupled Hf isotopes between zircons and the bulk rocks. This decoupling could reflect complex and prolonged magmatic processes, such as crustal assimilation, magma mixing, and disequilibrium melting, which are consistent with the wide temperature spectrum from ∼630 °C to ∼900 °C by Ti-in-zircon thermometer. We suggest that magmatic zircons may only record the Hf isotopic composition of their surrounding melt during crystallization and it is uncertain whether their Hf isotopic compositions can represent the primary Hf isotopic compositions of the bulk magmas. In this regard, using zircon Hf isotopic compositions to trace crustal evolution may be biased since most of these could be originally from disequilibrium partial melts.

What controls the stable isotope composition of precipitation in the Mekong Delta? A model-based statistical approach

NASA Astrophysics Data System (ADS)

Le Duy, Nguyen; Heidbüchel, Ingo; Meyer, Hanno; Merz, Bruno; Apel, Heiko

2018-02-01

This study analyzes the influence of local and regional climatic factors on the stable isotopic composition of rainfall in the Vietnamese Mekong Delta (VMD) as part of the Asian monsoon region. It is based on 1.5 years of weekly rainfall samples. In the first step, the isotopic composition of the samples is analyzed by local meteoric water lines (LMWLs) and single-factor linear correlations. Additionally, the contribution of several regional and local factors is quantified by multiple linear regression (MLR) of all possible factor combinations and by relative importance analysis. This approach is novel for the interpretation of isotopic records and enables an objective quantification of the explained variance in isotopic records for individual factors. In this study, the local factors are extracted from local climate records, while the regional factors are derived from atmospheric backward trajectories of water particles. The regional factors, i.e., precipitation, temperature, relative humidity and the length of backward trajectories, are combined with equivalent local climatic parameters to explain the response variables δ18O, δ2H, and d-excess of precipitation at the station of measurement. The results indicate that (i) MLR can better explain the isotopic variation in precipitation (R2 = 0.8) compared to single-factor linear regression (R2 = 0.3); (ii) the isotopic variation in precipitation is controlled dominantly by regional moisture regimes (˜ 70 %) compared to local climatic conditions (˜ 30 %); (iii) the most important climatic parameter during the rainy season is the precipitation amount along the trajectories of air mass movement; (iv) the influence of local precipitation amount and temperature is not significant during the rainy season, unlike the regional precipitation amount effect; (v) secondary fractionation processes (e.g., sub-cloud evaporation) can be identified through the d-excess and take place mainly in the dry season, either locally for δ18O and δ2H, or along the air mass trajectories for d-excess. The analysis shows that regional and local factors vary in importance over the seasons and that the source regions and transport pathways, and particularly the climatic conditions along the pathways, have a large influence on the isotopic composition of rainfall. Although the general results have been reported qualitatively in previous studies (proving the validity of the approach), the proposed method provides quantitative estimates of the controlling factors, both for the whole data set and for distinct seasons. Therefore, it is argued that the approach constitutes an advancement in the statistical analysis of isotopic records in rainfall that can supplement or precede more complex studies utilizing atmospheric models. Due to its relative simplicity, the method can be easily transferred to other regions, or extended with other factors. The results illustrate that the interpretation of the isotopic composition of precipitation as a recorder of local climatic conditions, as for example performed for paleorecords of water isotopes, may not be adequate in the southern part of the Indochinese Peninsula, and likely neither in other regions affected by monsoon processes. However, the presented approach could open a pathway towards better and seasonally differentiated reconstruction of paleoclimates based on isotopic records.

Zn isotopes in hydrothermal sulfides and their oxidation products along the south mid-Atlantic ridge: evidence of hydrothermal fluid deposition

NASA Astrophysics Data System (ADS)

Li, Xiaohu; Wang, Jianqiang; Chu, Fengyou; Lei, Jijiang; Wang, Hao; Li, Zhenggang

2018-04-01

Significant Zn isotope fractionation occurs during seafloor hydrothermal activities. Therefore, exploring variations in Zn isotope composition affected by hydrothermal fluids and oxidative processes would help to better understand hydrothermal fluid cycling and sulfide deposition on mid-ocean ridges. In this paper, the Zn isotope compositions of different types of sulfides and their oxidation products obtained from hydrothermal fields on the South Mid-Atlantic Ridge (13-15°S) were analyzed using a Neptune plus MC-ICP-MS. The δ66Zn ratios range from -0.14‰ to +0.38‰, and the average δ66Zn ratio is +0.12±0.06‰ ( n=21, 2 SD) for all the studied sulfides and oxidation products. The Cu-rich sulfides have a slightly heavier Zn isotope composition (average δ66Zn=+0.19±0.07‰, n=6) than the Zn-rich sulfides (average δ66Zn=-0.02±0.06‰, n=5). The Zn isotope compositions of the oxidation products are similar to those of the Cu-rich sulfides, with an average δ66Zn ratio of 0.14±0.06‰ ( n=10, 2 SD). The Zn isotope compositions of all the samples are generally within the ranges of sulfides from hydrothermal fields on other mid-ocean ridges, such as the East Pacific Rise (9°N, 21°N) and the Trans-Atlantic Geotraverse. However, the average Zn isotope composition indicates the presence of significantly lighter Zn isotopes relative to those reported in the literature (average δ66Zn=+0.39‰). The significant enrichment of the Zn-rich sulfides with light Zn isotopes reveals that kinetic fractionation likely occurs during mineral deposition. Furthermore, the Zn isotope compositions of the sulfides and their oxidation products (average δ66Zn=+0.12‰) are significantly lighter than the average Zn isotope composition of the ocean (δ66Zn=+0.5‰), which could further constrain the modern Zn isotope cycle in the ocean by serving as a sink for light Zn isotopes.

Variability in magnesium, carbon and oxygen isotope compositions, and trace element contents of brachiopod shells: implications for paleoceanographic studies

NASA Astrophysics Data System (ADS)

Rollion-Bard, Claire; Saulnier, Ségolène; Vigier, Nathalie; Schumacher, Aimryc; Chaussidon, Marc; Lécuyer, Christophe

2016-04-01

Magnesium content in the ocean is ≈ 1290 ppm and is one of the most abundant elements. It is involved in the carbon cycle via the dissolution and precipitation of carbonates, especially Mg-rich carbonates as dolomites. The Mg/Ca ratio of the ocean is believed to have changed through time. The causes of these variations, i.e. hydrothermal activity change or enhanced precipitation of dolomite, could be constrained using the magnesium isotope composition (δ26Mg) of carbonates. Brachiopods, as marine environmental proxies, have the advantage to occur worldwide in a depth range from intertidal to abyssal, and have been found in the geological record since the Cambrian. Moreover, as their shell is in low-Mg calcite, they are quite resistant to diagenetic processes. Here we report δ26Mg, δ18O, δ13C values along with trace element contents of one modern brachiopod specimen (Terebratalia transversa) and one fossil specimen (Terebratula scillae, 2.3 Ma). We combined δ26Mg values with oxygen and carbon isotope compositions and trace element contents to look for possible shell geochemical heterogeneities in order to investigate the processes that control the Mg isotope composition of brachiopod shells. We also evaluate the potential of brachiopods as a proxy of past seawater δ26Mg values. The two investigated brachiopod shells present the same range of δ26Mg variation (up to 2 ‰)). This variation cannot be ascribed to changes in environmental parameters, i.e. temperature or pH. As previously observed, the primary layer of calcite shows the largest degree of oxygen and carbon isotope disequilibrium relative to seawater. In contrast, the δ26Mg value of this layer is comparable to that of the secondary calcite layer value. In both T. scillae and T. transversa, negative trends are observable between magnesium isotopic compositions and oxygen and carbon isotopic compositions. These trends, combined to linear relationships between δ26Mg values and REE contents, are best explained by kinetic effects linked to changes in growth rate during the brachiopod life. The innermost calcite layer of T. transversa is in isotopic equilibrium for both oxygen and magnesium and could therefore be the best target for reconstructing past δ26Mg values of seawater.

Multi-stage metasomatism revealed by trace element and Li isotope distributions in minerals of peridotite xenoliths from Allègre volcano (French Massif Central)

NASA Astrophysics Data System (ADS)

Gu, Xiaoyan; Deloule, Etienne; France, Lydéric; Ingrin, Jannick

2016-11-01

The modal, chemical, and isotopic compositions of mantle peridotite are largely modified by metasomatic processes, which may affect them repeatedly. Xenoliths are commonly used to characterize those metasomatic processes along with the structure, and chemical and isotopic compositions of mantle domains. Nevertheless, the original mantle signatures born by mantle xenoliths are potentially obscured by the interactions occurring between the host magma and the xenolith itself. Here we attempt to identify to which degree the original Li content and isotopic composition, as well as other trace element contents of mantle xenoliths, can be modified by interaction with the host magma. Peridotite xenoliths that have suffered extensive exchange with the entraining magma were sampled in the solidified lava lake of Allègre, Southern French Massif Central, in order to decipher the signature related to peridotite-melt interaction, and to further unravel the evolution of the sub-continental lithospheric mantle. In-situ trace element analyses of clinopyroxene (Cpx) were performed via LA-ICP-MS, and the Li content and isotopic composition of pyroxene and olivine (Ol) via SIMS. Negative HFSE anomalies (Ti/Eu ratios as low as 437) and markedly high LREE/HREE ratios ((La/Yb)N as high as 79) are characteristic of mantle metasomatism at depth. Lithium isotope systematics indicates that at least two different metasomatic events affected the peridotite. Exceptionally high Li contents in Cpx (up to 50 ppm) and slight Li enrichment of Ol rims are ascribed to diffusive Li influx with a positive δ7Li value (+ 3.2‰) from the host magma after entrainment. Conversely, Ol cores preserve extremely light Li isotopic compositions (δ7Li as low as - 25‰) with high Li contents (up to 4.4 ppm) compared to normal mantle, indicating a metasomatic event that occurred before xenolith entrainment. The negative δ7Li signature of this early metasomatism may be related to subduction-related fluids released during the Variscan orogeny. Trace element distributions in minerals reveal that the HFSE and REE composition of Cpx and the negative δ7Li signature in Ol cores were not acquired simultaneously. Therefore at least three successive metasomatic events affected the Allegre peridotites, as revealed through the use of detailed in-situ Li isotopic analyses to trace melt-rock interactions.

Magnesium isotopic evidence for chemical disequilibrium among cumulus minerals in layered mafic intrusion

NASA Astrophysics Data System (ADS)

Chen, Lie-Meng; Teng, Fang-Zhen; Song, Xie-Yan; Hu, Rui-Zhong; Yu, Song-Yue; Zhu, Dan; Kang, Jian

2018-04-01

Magnesium isotopic compositions of olivine, clinopyroxene, and ilmenite from the Baima intrusion, SW China, for the first time, are investigated to constrain the magnitude and mechanisms of Mg isotope fractionation among cumulus minerals in layered mafic intrusions and to evaluate their geological implications. Olivine and clinopyroxene have limited Mg isotope variations, with δ26Mg ranging from -0.33 to +0.05‰ and from -0.29 to -0.13‰, respectively, similar to those of mantle xenolithic peridotites. By contrast, ilmenites display extremely large Mg isotopic variation, with δ26Mg ranging from -0.50 to +1.90‰. The large inter-mineral fractionations of Mg isotopes between ilmenite and silicates may reflect both equilibrium and kinetic processes. A few ilmenites have lighter Mg isotopic compositions than coexisting silicates and contain high MgO contents without compositional zoning, indicating equilibrium fractionation. The implication is that the light Mg isotopic compositions of lunar high-Ti basalts may result from an isotopically light source enriched in cumulate ilmenites. On the other hand, most ilmenites have heavy Mg isotopic compositions, coupled with high MgO concentration and chemical zoning, which can be quantitatively modeled by kinetic Mg isotope fractionations induced by subsolidus Mg-Fe exchange between ilmenite and ferromagnesian silicates during the cooling of the Baima intrusion. The extensive occurrence of kinetic Mg isotope fractionation in ilmenites implies the possibility of widespread compositional disequilibrium among igneous minerals in magma chambers. Consequently, disequilibrium effects need to be considered in studies of basaltic magma evolution, magma chamber processes, and magmatic Fe-Ti oxide ore genesis.

Tracing subducted crustal materials in the mantle by using magnesium isotopes

NASA Astrophysics Data System (ADS)

Teng, F. Z.

2016-12-01

Recent studies show that some continental basalt, mantle-metasomatised peridotite and cratonic eclogite have heterogeneous Mg isotopic compositions. These isotopically distinct Mg isotopic compositions have been explained by the incorporation of subducted materials in their mantle sources though the detailed mechanisms are still not well understood. In particular, how Mg-poor crustal materials can modify Mg isotopic systematics of Mg-rich mantle is unknown. Subduction zones are the most efficient sites for crust and mantle interactions, hence should be where the most prominent Mg isotopic variation occurs. However, to date, little is known on Mg isotope systematics in the subduction factory. Here I first review and report new Mg isotopic data for arc lava, subarc peridotite and the subducted slab (marine sediment, altered basalt and abyssal peridotite), then use them to constrain the origins of mantle Mg isotopic heterogeneity and lay the foundation for using Mg isotopes as new tools for tracing crust-mantle interactions. The main conclusions are 1) fluid-rock interactions can modify Mg isotopic systematics of abyssal peridotites; 2) island arc lavas have non-MORB Mg isotopic compositions, reflecting distinct surbarc mantle Mg isotopic signature; 3) continental arcs have non-MORB Mg isotopic compositions, likely resulting from crustal contamination and 4) the isotopically heterogeneous continental basalts are mainly produced by mixing of isotopically distinct magmas instead of being partial melting products of metasomatised mantle peridotites.

Constraints on post-depositional isotope modifications in East Antarctic firn from analysing temporal changes of isotope profiles

NASA Astrophysics Data System (ADS)

Münch, Thomas; Kipfstuhl, Sepp; Freitag, Johannes; Meyer, Hanno; Laepple, Thomas

2017-09-01

The isotopic composition of water in ice sheets is extensively used to infer past climate changes. In low-accumulation regions their interpretation is, however, challenged by poorly constrained effects that may influence the initial isotope signal during and after deposition of the snow. This is reflected in snow-pit isotope data from Kohnen Station, Antarctica, which exhibit a seasonal cycle but also strong interannual variations that contradict local temperature observations. These inconsistencies persist even after averaging many profiles and are thus not explained by local stratigraphic noise. Previous studies have suggested that post-depositional processes may significantly influence the isotopic composition of East Antarctic firn. Here, we investigate the importance of post-depositional processes within the open-porous firn (≳ 10 cm depth) at Kohnen Station by separating spatial from temporal variability. To this end, we analyse 22 isotope profiles obtained from two snow trenches and examine the temporal isotope modifications by comparing the new data with published trench data extracted 2 years earlier. The initial isotope profiles undergo changes over time due to downward advection, firn diffusion and densification in magnitudes consistent with independent estimates. Beyond that, we find further modifications of the original isotope record to be unlikely or small in magnitude (≪ 1 ‰ RMSD). These results show that the discrepancy between local temperatures and isotopes most likely originates from spatially coherent processes prior to or during deposition, such as precipitation intermittency or systematic isotope modifications acting on drifting or loose surface snow.

Correcting speleothem oxygen isotopic variations for growth-rate controlled kinetic fractionation effects

NASA Astrophysics Data System (ADS)

Stoll, Heather; Moreno, Ana; Cacho, Isabel; Mendez Vicence, Ana; Gonzalez Lemos, Saul; Pirla Casasayas, Gemma; Cheng, Hai; Wang, Xianfeng; Edwards, R. Lawrence

2015-04-01

The oxygen isotopic signature may be the most widely used climate indicator in stalagmites, but recent experimental and theoretical studies indicate the potential for kinetic fractionation effects which may be significant, especially in situations where the primary signal from rainfall isotopic composition and cave temperature is limited to a few permil. Here we use a natural set of stalagmites to illustrate the magnitude of such effects and the potential for deconvolving kinetic signals from the primary temperature and rainfall signals. We compare isotopic records from 6 coeval stalagmites covering the interval 140 to 70 ka, from two proximal caves in NW Spain which experienced the same primary variations in temperature and rainfall d18O, but exhibit a large range in growth rates and temporal trends in growth rate. Stalagmites growing at faster rates near 50 microns/year have oxygen isotopic ratios more than 1 permil more negative than coeval stalagmites with very slow (5 micron/year) growth rates. Because growth rate variations also occur over time within any given stalagmite, the measured oxygen isotopic time series for a given stalagmite includes both climatic and kinetic components. Removal of the kinetic component of variation in each stalagmite, based on the dependence of the kinetic component on growth rate, is effective at distilling a common temporal evolution among the oxygen isotopic records of the multiple stalagmites. However, this approach is limited by the quality of the age model. For time periods characterized by very slow growth and long durations between dates, the presence of crypto-hiatus may result in average growth rates which underestimate the instantaneous speleothem deposition rates and which therefore underestimate the magnitude of kinetic effects. We compare the composite corrected oxygen isotopic record with other records of the timing of glacial inception in the North Atlantic realm.

The role of mantle-hybridization and crustal contamination in the petrogenesis of lithospheric mantle-derived alkaline rocks: constraints from Os and Hf isotopes

NASA Astrophysics Data System (ADS)

Mayer, B.; Jung, S.; Brauns, M.; Münker, C.

2018-06-01

The Rhön area as part of the Central European Volcanic Province (CEVP) hosts an unusual suite of Tertiary 24-Ma old hornblende-bearing alkaline basalts that provide insights into melting and fractionation processes within the lithospheric mantle. These chemically primitive to slightly evolved and isotopically (Sr, Nd, Pb) depleted basalts have slightly lower Hf isotopic compositions than respective other CEVP basalts and Os isotope compositions more radiogenic than commonly observed for continental intraplate alkaline basalts. These highly radiogenic initial 187Os/188Os ratios (0.268-0.892) together with their respective Sr-Nd-Pb isotopic compositions are unlikely to result from crustal contamination alone, although a lack of Os data for lower crustal rocks from the area and limited data for CEVP basalts or mantle xenoliths preclude a detailed evaluation. Similarly, melting of the same metasomatized subcontinental lithospheric mantle as inferred for other CEVP basalts alone is also unlikely, based on only moderately radiogenic Os isotope compositions obtained for upper mantle xenoliths from elsewhere in the province. Another explanation for the combined Nd, Sr and Os isotope data is that the lavas gained their highly radiogenic Os isotope composition through a mantle "hybridization", metasomatism process. This model involves a mafic lithospheric component, such as an intrusion of a sublithospheric primary alkaline melt or a melt derived from subducted oceanic material, sometime in the past into the lithospheric mantle where it metasomatized the ambient mantle. Later at 24 Ma, thermal perturbations during rifting forced the isotopically evolved parts of the mantle together with the peridotitic ambient mantle to melt. This yielded a package of melts with highly correlated Re/Os ratios and radiogenic Os isotope compositions. Subsequent movement through the crust may have further altered the Os isotope composition although this effect is probably minor for the majority of the samples based on radiogenic Nd and unradiogenic Sr isotope composition of the lavas. If the radiogenic Os isotope composition can be explained by a mantle-hybridization and metasomatism model, the isotopic compositions of the hornblende basalts can be satisfied by ca. 5-25% addition of the mafic lithospheric component to an asthenospheric alkaline magma. Although a lack of isotope data for all required endmembers make this model somewhat speculative, the results show that the Re-Os isotope system in continental basalts is able to distinguish between crustal contamination and derivation of continental alkaline lavas from isotopically evolved peridotitic lithosphere that was contaminated by mafic material in the past and later remelted during rifting. The Hf isotopic compositions are slightly less radiogenic than in other alkaline basalts from the province and indicate the derivation of the lavas from low Lu-Hf parts of the lithospheric mantle. The new Os and Hf isotope data constrain a new light of the nature of such metasomatizing agents, at least for these particular rocks, which represent within the particular volcanic complex the first product of the volcanism.

The silicon isotope composition of the upper continental crust

NASA Astrophysics Data System (ADS)

Savage, Paul S.; Georg, R. Bastian; Williams, Helen M.; Halliday, Alex N.

2013-05-01

The upper continental crust (UCC) is the major source of silicon (Si) to the oceans and yet its isotopic composition is not well constrained. In an effort to investigate the degree of heterogeneity and provide a robust estimate for the average Si isotopic composition of the UCC, a representative selection of well-characterised, continentally-derived clastic sediments have been analysed using high-precision MC-ICPMS. Analyses of loess samples define a narrow range of Si isotopic compositions (δ30Si = -0.28‰ to -0.15‰). This is thought to reflect the primary igneous mineralogy and predominance of mechanical weathering in the formation of such samples. The average loess δ30Si is -0.22 ± 0.07‰ (2 s.d.), identical to average granite and felsic igneous compositions. Therefore, minor chemical weathering does not resolvably affect bulk rock δ30Si, and loess is a good proxy for the Si isotopic composition of unweathered, crystalline, continental crust. The Si isotopic compositions of shales display much more variability (δ30Si = -0.82‰ to 0.00‰). Shale Si isotope compositions do not correlate well with canonical proxies for chemical weathering, such as CIA values, but do correlate negatively with insoluble element concentrations and Al/Si ratios. This implies that more intensive or prolonged chemical weathering of a sedimentary source, with attendant desilicification, is required before resolvable negative Si isotopic fractionation occurs. Shale δ30Si values that are more positive than those of felsic igneous rocks most likely indicate the presence of marine-derived silica in such samples. Using the data gathered in this study, combined with already published granite Si isotope analyses, a weighted average composition of δ30Si = -0.25 ± 0.16‰ (2 s.d.) for the UCC has been calculated.

Breeding of 233U in the thorium-uranium fuel cycle in VVER reactors using heavy water

NASA Astrophysics Data System (ADS)

Marshalkin, V. E.; Povyshev, V. M.

2015-12-01

A method is proposed for achieving optimal neutron kinetics and efficient isotope transmutation in the 233U-232Th oxide fuel of water-moderated reactors with variable water composition (D2O, H2O) that ensures breeding of the 233U and 235U isotopes. The method is comparatively simple to implement.

Controls on the barium isotope compositions of marine sediments

NASA Astrophysics Data System (ADS)

Bridgestock, Luke; Hsieh, Yu-Te; Porcelli, Donald; Homoky, William B.; Bryan, Allison; Henderson, Gideon M.

2018-01-01

The accumulation of barium (Ba) in marine sediments is considered to be a robust proxy for export production, although this application can be limited by uncertainty in BaSO4 preservation and sediment mass accumulation rates. The Ba isotope compositions of marine sediments could potentially record insights into past changes in the marine Ba cycle, which should be insensitive to these limitations, enabling more robust interpretation of sedimentary Ba as a proxy. To investigate the controls on the Ba isotope compositions of marine sediments and their potential for paleo-oceanographic applications, we present the first Ba isotope compositions results for sediments, as well as overlying seawater depth profiles collected in the South Atlantic. Variations in Ba isotope compositions of the sediments predominantly reflect changes in the relative contributions of detrital and authigenic Ba sources, with open-ocean sediments constraining the isotope composition of authigenic Ba to be δ 138/134Ba ≈ + 0.1 ‰. This value is consistent with the average isotope composition inferred for sinking particulate Ba using simple mass balance models of Ba in the overlying water column and is hypothesized to reflect the removal of Ba from the upper water column with an associated isotopic fractionation of Δ diss-part 138/134Ba ≈ + 0.4 to +0.5. Perturbations to upper ocean Ba cycling, due to changes in export production and the supply of Ba via upwelling, should therefore be recorded by the isotope compositions of sedimentary authigenic Ba. Such insights will help to improve the reliable application of Ba accumulation rates in marine sediments as a proxy for past changes in export production.

Isotopic signals of denitrification in a northern hardwood forested catchment

NASA Astrophysics Data System (ADS)

Wexler, Sarah; Goodale, Christine

2013-04-01

Water samples from streams, groundwater and precipitation were collected during summer from the hydrologic reference watershed (W3) at Hubbard Brook Experimental Forest in the White Mountains, New Hampshire, and analysed for d15N-NO3 and d18O-NO3. Despite very low nitrate concentrations (<0.5 to 8.8 uM NO3-) dual-isotopic signals of sources and processes were clearly distinguishable. The isotopic composition of nitrate from shallow groundwater showed evidence of dual isotopic fractionation in line with denitrification, with a positive relationship between nitrogen and oxygen isotopic composition, a regression line slope of 0.76 (r2 = 0.68), and an empirical isotope enrichment factor of ɛP-S 15N-NO3 -12.7%. The isotopic composition of riparian groundwater nitrate from time-series samples showed variation in processes over a small spatial scale. The expected isotopic composition of nitrate sources in the watershed was used to distinguish nitrate in rain and nitrate from nitrification of both rainfall ammonium and ammonium from mineralised soil organic nitrogen. Evidence of oxygen exchange with water during nitrification was seen in the isotopic composition of stream and shallow groundwater nitrate. The isotopic composition of streamwater nitrate following a period of storms indicated that 25% of nitrate in the streamwater was of atmospheric origin. This suggests rapid infiltration of rainfall via vertical bypass flow to the saturated zone, enabling transport of atmospheric nitrate to the stream channels. Across the Hubbard Brook basin, the isotopic composition of nitrate from paired samples from watersheds 4-7 indicated a switch between a nitrification and assimilation dominated system, to a system influenced by rainfall nitrogen inputs and denitrification. The dual isotope approach has revealed evidence of denitrification of nitrate from different sources at low concentrations at Hubbard Brook during summer. This isotopic evidence deepens our understanding of the significance and spatial variability of denitrification in environments with low levels of nitrate, represented by this northern hardwood forested catchment.

Barium isotopes in cold-water corals

NASA Astrophysics Data System (ADS)

Hemsing, Freya; Hsieh, Yu-Te; Bridgestock, Luke; Spooner, Peter T.; Robinson, Laura F.; Frank, Norbert; Henderson, Gideon M.

2018-06-01

Recent studies have introduced stable Ba isotopes (δ 138 / 134Ba) as a novel tracer for ocean processes. Ba isotopes could potentially provide insight into the oceanic Ba cycle, the ocean's biological pump, water-mass provenance in the deep ocean, changes in activity of hydrothermal vents, and land-sea interactions including tracing riverine inputs. Here, we show that aragonite skeletons of various colonial and solitary cold-water coral (CWC) taxa record the seawater (SW) Ba isotope composition. Thirty-six corals of eight different taxa from three oceanic regions were analysed and compared to δ 138 / 134Ba measurements of co-located seawater samples. Sites were chosen to cover a wide range of temperature, salinity, Ba concentrations and Ba isotope compositions. Seawater samples at the three sites exhibit the well-established anti-correlation between Ba concentration and δ 138 / 134Ba. Furthermore, our data set suggests that Ba/Ca values in CWCs are linearly correlated with dissolved [Ba] in ambient seawater, with an average partition coefficient of DCWC/SW = 1.8 ± 0.4 (2SD). The mean isotope fractionation of Ba between seawater and CWCs Δ138/134BaCWC-SW is -0.21 ± 0.08‰ (2SD), indicating that CWC aragonite preferentially incorporates the lighter isotopes. This fractionation likely does not depend on temperature or other environmental variables, suggesting that aragonite CWCs could be used to trace the Ba isotope composition in ambient seawater. Coupled [Ba] and δ 138 / 134Ba analysis on fossil CWCs has the potential to provide new information about past changes in the local and global relationship between [Ba] and δ 138 / 134Ba and hence about the operation of the past global oceanic Ba cycle in different climate regimes.

Physics of the Isotopic Dependence of Galactic Cosmic Ray Fluence Behind Shielding

NASA Technical Reports Server (NTRS)

Cucinotta, Francis A.; Saganti, Premkumar B.; Hu, Xiao-Dong; Kim, Myung-Hee Y.; Cleghorn, Timothy F.; Wilson, John W.; Tripathi, Ram K.; Zeitlin, Cary J.

2003-01-01

For over 25 years, NASA has supported the development of space radiation transport models for shielding applications. The NASA space radiation transport model now predicts dose and dose equivalent in Earth and Mars orbit to an accuracy of plus or minus 20%. However, because larger errors may occur in particle fluence predictions, there is interest in further assessments and improvements in NASA's space radiation transport model. In this paper, we consider the effects of the isotopic composition of the primary galactic cosmic rays (GCR) and the isotopic dependence of nuclear fragmentation cross-sections on the solution to transport models used for shielding studies. Satellite measurements are used to describe the isotopic composition of the GCR. Using NASA's quantum multiple-scattering theory of nuclear fragmentation (QMSFRG) and high-charge and energy (HZETRN) transport code, we study the effect of the isotopic dependence of the primary GCR composition and secondary nuclei on shielding calculations. The QMSFRG is shown to accurately describe the iso-spin dependence of nuclear fragmentation. The principal finding of this study is that large errors (plus or minus 100%) will occur in the mass-fluence spectra when comparing transport models that use a complete isotope grid (approximately 170 ions) to ones that use a reduced isotope grid, for example the 59 ion-grid used in the HZETRN code in the past, however less significant errors (less than 20%) occur in the elemental-fluence spectra. Because a complete isotope grid is readily handled on small computer workstations and is needed for several applications studying GCR propagation and scattering, it is recommended that they be used for future GCR studies.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Valysaev, B.M.; Erokhin, V.E.; Grinchenko, Y.I.

A study has been made of the isotopic composition of the carbon in methane and carbon dioxide, as well as hydrogen in the methane, in the gases of mud volcanoes, for all main mud volcano areas in the USSR. The isotopic composition of carbon and hydrogen in methane shows that the gases resemble those of oil and gas deposits, while carbon dioxide of these volcanoes has a heavier isotopic composition with a greater presence of ''ultraheavy'' carbon dioxide. By the chemical and isotopic composition of gases, Azerbaidzhan and South Sakhalin types of mud volcano gases have been identified, as wellmore » as Bulganak subtypes and Akhtala and Kobystan varieties. Correlations are seen between the isotopic composition of gases and the geological build of mud volcano areas.« less

Compound Specific Isotope Analysis of Fatty Acids in Southern African Aerosols

NASA Astrophysics Data System (ADS)

Billmark, K. A.; Macko, S. A.; Swap, R. J.

2003-12-01

This study, conducted as a part of the Southern African Regional Science Initiative (SAFARI 2000), applied compound specific isotope analysis to describe aerosols at source regions and rural locations. Stable carbon isotopic compositions of individual fatty acids were determined for aerosol samples collected at four sites throughout southern Africa. Mongu, Zambia and Skukuza, South Africa were chosen for their location within intense seasonal Miombo woodland savanna and bushveld savanna biomass burning source regions, respectively. Urban aerosols were collected at Johannesburg, South Africa and rural samples were collected at Sua Pan, Botswana. Fatty acid isotopic compositions varied temporally. Urban aerosols showed significant isotopic enrichment of selected short chain fatty acids (C < 20) compared to aerosols produced during biomass combustion. Sua Pan short chain fatty acid signatures were significantly different from the other non-urban sites, which suggests that sources other than biomass combustion products, such as organic eolian material, impact the Sua Pan aerosol profile. However, a high degree of correlation between Sua Pan and Skukuza long chain fatty acid δ 13C values confirm atmospheric linkages between the two areas and that isotopic signatures of combusted fatty acids are unaltered during atmospheric transport highlighting their potential for use as a conservative tracer.

Stable isotopic composition of perchlorate and nitrate accumulated in plants: Hydroponic experiments and field data.

PubMed

Estrada, Nubia Luz; Böhlke, J K; Sturchio, Neil C; Gu, Baohua; Harvey, Greg; Burkey, Kent O; Grantz, David A; McGrath, Margaret T; Anderson, Todd A; Rao, Balaji; Sevanthi, Ritesh; Hatzinger, Paul B; Jackson, W Andrew

2017-10-01

Natural perchlorate (ClO 4 - ) in soil and groundwater exhibits a wide range in stable isotopic compositions (δ 37 Cl, δ 18 O, and Δ 17 O), indicating that ClO 4 - may be formed through more than one pathway and/or undergoes post-depositional isotopic alteration. Plants are known to accumulate ClO 4 - , but little is known about their ability to alter its isotopic composition. We examined the potential for plants to alter the isotopic composition of ClO 4 - in hydroponic and field experiments conducted with snap beans (Phaseolus vulgaris L.). In hydroponic studies, anion ratios indicated that ClO 4 - was transported from solutions into plants similarly to NO 3 - but preferentially to Cl - (4-fold). The ClO 4 - isotopic compositions of initial ClO 4 - reagents, final growth solutions, and aqueous extracts from plant tissues were essentially indistinguishable, indicating no significant isotope effects during ClO 4 - uptake or accumulation. The ClO 4 - isotopic composition of field-grown snap beans was also consistent with that of ClO 4 - in varying proportions from irrigation water and precipitation. NO 3 - uptake had little or no effect on NO 3 - isotopic compositions in hydroponic solutions. However, a large fractionation effect with an apparent ε ( 15 N/ 18 O) ratio of 1.05 was observed between NO 3 - in hydroponic solutions and leaf extracts, consistent with partial NO 3 - reduction during assimilation within plant tissue. We also explored the feasibility of evaluating sources of ClO 4 - in commercial produce, as illustrated by spinach, for which the ClO 4 - isotopic composition was similar to that of indigenous natural ClO 4 - . Our results indicate that some types of plants can accumulate and (presumably) release ClO 4 - to soil and groundwater without altering its isotopic characteristics. Concentrations and isotopic compositions of ClO 4 - and NO 3 - in plants may be useful for determining sources of fertilizers and sources of ClO 4 - in their growth environments and consequently in food supplies. Copyright © 2017 Elsevier B.V. All rights reserved.

Stable isotopic composition of perchlorate and nitrate accumulated in plants: Hydroponic experiments and field data

USGS Publications Warehouse

Estrada, Nubia Luz; Böhlke, John Karl; Sturchio, Neil C.; Gu, Baohua; Harvey, Greg; Burkey, Kent O.; Grantz, David A.; McGrath, Margaret T.; Anderson, Todd A.; Rao, Balaji; Sevanthi, Ritesh; Hatzinger, Paul B.; Jackson, W. Andrew

2017-01-01

Natural perchlorate (ClO4−) in soil and groundwater exhibits a wide range in stable isotopic compositions (δ37Cl, δ18O, and Δ17O), indicating that ClO4− may be formed through more than one pathway and/or undergoes post-depositional isotopic alteration. Plants are known to accumulate ClO4−, but little is known about their ability to alter its isotopic composition. We examined the potential for plants to alter the isotopic composition of ClO4− in hydroponic and field experiments conducted with snap beans (Phaseolus vulgaris L.). In hydroponic studies, anion ratios indicated that ClO4− was transported from solutions into plants similarly to NO3− but preferentially to Cl− (4-fold). The ClO4− isotopic compositions of initial ClO4− reagents, final growth solutions, and aqueous extracts from plant tissues were essentially indistinguishable, indicating no significant isotope effects during ClO4− uptake or accumulation. The ClO4− isotopic composition of field-grown snap beans was also consistent with that of ClO4− in varying proportions from irrigation water and precipitation. NO3− uptake had little or no effect on NO3− isotopic compositions in hydroponic solutions. However, a large fractionation effect with an apparent ε (15N/18O) ratio of 1.05 was observed between NO3− in hydroponic solutions and leaf extracts, consistent with partial NO3− reduction during assimilation within plant tissue. We also explored the feasibility of evaluating sources of ClO4− in commercial produce, as illustrated by spinach, for which the ClO4− isotopic composition was similar to that of indigenous natural ClO4−. Our results indicate that some types of plants can accumulate and (presumably) release ClO4− to soil and groundwater without altering its isotopic characteristics. Concentrations and isotopic compositions of ClO4−and NO3− in plants may be useful for determining sources of fertilizers and sources of ClO4− in their growth environments and consequently in food supplies.

Plume versus plate origin for the Shatsky Rise oceanic plateau (NW Pacific): Insights from Nd, Pb and Hf isotopes

NASA Astrophysics Data System (ADS)

Heydolph, Ken; Murphy, David T.; Geldmacher, Jörg; Romanova, Irina V.; Greene, Andrew; Hoernle, Kaj; Weis, Dominique; Mahoney, John

2014-07-01

Shatsky Rise, an early Cretaceous igneous oceanic plateau in the NW Pacific, comprises characteristics that could be attributed to either formation by shallow, plate tectonic-controlled processes or to an origin by a mantle plume (head). The plateau was drilled during Integrated Ocean Drilling Program (IODP) Expedition 324. Complementary to a recent trace element study (Sano et al., 2012) this work presents Nd, Pb and Hf isotope data of recovered lava samples cored from the three major volcanic edifices of the Shatsky Rise. Whereas lavas from the oldest edifice yield fairly uniform compositions, a wider isotopic spread is found for lavas erupted on the younger parts of the plateau, suggesting that the Shatsky magma source became more heterogeneous with time. At least three isotopically distinct components can be identified in the magma source: 1) a volumetrically and spatially most common, moderately depleted component of similar composition to modern East Pacific Ridge basalt but with low 3He/4He, 2) an isotopically very depleted component which could represent local, early Cretaceous (entrained) depleted upper mantle, and 3) an isotopically enriched component, indicating the presence of (recycled) continental material in the magma source. The majority of analyzed Shatsky lavas, however, possess Nd-Hf-Pb isotope compositions consistent with a derivation from an early depleted, non-chondritic reservoir. By comparing these results with petrological and trace element data of mafic volcanic rock samples from all three massifs (Tamu, Ori, Shirshov), we discuss the origin of Shatsky Rise magmatism and evaluate the possible involvement of a mantle plume (head).

Isotopic measurements of the cosmic ray nuclei at 1.7 GeV/n and 0.5 GeV/n

NASA Technical Reports Server (NTRS)

Juliusson, E.

1975-01-01

Results are presented on the mean isotopic composition of cosmic ray nuclei, or the average neutron excess for the elements Be to Si. At 1.7 GeV/nucleon they have been obtained by comparing the abundances measured above a rigidity threshold at Palestine, Texas, with abundances measured above an equivalent velocity threshold at Cape Girardeau Missouri. At 0.5 GeV/nucleon the results are obtained by analysing the variation in the chemical composition with energy in the energy region around the geomagnetic cut-off.

What Hf isotopes in zircon tell us about crust-mantle evolution

NASA Astrophysics Data System (ADS)

Iizuka, Tsuyoshi; Yamaguchi, Takao; Itano, Keita; Hibiya, Yuki; Suzuki, Kazue

2017-03-01

The 176Lu-176Hf radioactive decay system has been widely used to study planetary crust-mantle differentiation. Of considerable utility in this regard is zircon, a resistant mineral that can be precisely dated by the U-Pb chronometer and record its initial Hf isotope composition due to having low Lu/Hf. Here we review zircon U-Pb age and Hf isotopic data mainly obtained over the last two decades and discuss their contributions to our current understanding of crust-mantle evolution, with emphasis on the Lu-Hf isotope composition of the bulk silicate Earth (BSE), early differentiation of the silicate Earth, and the evolution of the continental crust over geologic history. Meteorite zircon encapsulates the most primitive Hf isotope composition of our solar system, which was used to identify chondritic meteorites best representative of the BSE (176Hf/177Hf = 0.282793 ± 0.000011; 176Lu/177Hf = 0.0338 ± 0.0001). Hadean-Eoarchean detrital zircons yield highly unradiogenic Hf isotope compositions relative to the BSE, providing evidence for the development of a geochemically enriched silicate reservoir as early as 4.5 Ga. By combining the Hf and O isotope systematics, we propose that the early enriched silicate reservoir has resided at depth within the Earth rather than near the surface and may represent a fractionated residuum of a magma ocean underlying the proto-crust, like urKREEP beneath the anorthositic crust on the Moon. Detrital zircons from world major rivers potentially provide the most robust Hf isotope record of the preserved granitoid crust on a continental scale, whereas mafic rocks with various emplacement ages offer an opportunity to trace the Hf isotope evolution of juvenile continental crust (from εHf[4.5 Ga] = 0 to εHf[present] = + 13). The river zircon data as compared to the juvenile crust composition highlight that the supercontinent cycle has controlled the evolution of the continental crust by regulating the rates of crustal generation and intra-crustal reworking processes and the preservation potential of granitoid crust. We use the data to explore the timing of generation of the preserved continental crust. Taking into account the crustal residence times of continental crust recycled back into the mantle, we further propose a model of net continental growth that stable continental crust was firstly established in the Paleo- and Mesoarchean and significantly grew in the Paleoproterozoic.

Tracing Cd, Zn and Pb pollution sources in bivalves using isotopes

NASA Astrophysics Data System (ADS)

Shiel, A. E.; Weis, D. A.; Orians, K. J.

2010-12-01

In a multi-tracer study, Cd, Zn and Pb isotopes (MC-ICP-MS) and elemental concentrations (HR-ICP-MS) are evaluated as tools to distinguish between natural and anthropogenic sources of these metals in bivalves from western Canada (British Columbia), the eastern USA, Hawaii and France. High Cd concentrations found in BC oysters have elicited economic and health concerns. The source of these high Cd levels is unknown but thought to be largely natural. High Cd levels in BC oysters are largely attributed to the natural upwelling of Cd-rich intermediate waters in the North Pacific as the δ114/110Cd (-0.69 to -0.09‰) and δ66/64Zn (0.28 to 0.36‰) values of BC oysters fall within the range reported for North Pacific seawater. Different contributions from anthropogenic sources account for the variability of Cd isotopic compositions of BC oysters; the lightest of these oysters are from the BC mainland. These oysters also have Pb isotopic compositions that reflect primarily anthropogenic sources (e.g., leaded and unleaded automotive gasoline and smelting of Pb ores, potentially historical). On the contrary, USA East Coast bivalves exhibit relatively light Cd isotopic compositions (δ114/110Cd = -1.20 to -0.54‰; lighter than reported for North Atlantic seawater) due to the high prevalence of industry on this coast. The Pb isotopic compositions of these bivalves indicate contributions from the combustion of coal. The large variability of environmental health among coastal areas in France is reflected in the broad range of Cd isotopic compositions exhibited by French bivalves (δ114/110Cd = -1.08 to -0.20‰). Oysters and mussels from the Marennes-Oléron basin and Gironde estuary have the lightest Cd isotopic compositions of the French oysters consistent with significant historical Cd emissions from the now-closed proximal Zn smelter. In these bivalves, significant declines in the Cd levels between 1984/7 and 2004/5 are not accompanied by a significant shift in the Cd isotopic composition toward natural values. The Mediterranean samples have isotopic compositions within error of the lighter end of the range reported for Mediterranean seawater. The Zn isotopic compositions of French oysters and mussels (δ66/64Zn = 0.39 to 0.46‰) are identical to those reported for North Atlantic seawater, with the exception of the much heavier compositions of oysters (δ66/64Zn = 1.03 to 1.15‰) from the polluted Gironde estuary. In agreement with Cd and Zn isotopic compositions, the Pb isotopic compositions of the French bivalves indicate primarily industrial (as opposed to automotive) sources; this is consistent with the collection of most of the French bivalve samples in 2004, after the complete phase-out of leaded gasoline in France. This study demonstrates the effective use of Cd and Zn isotopes to trace anthropogenic sources in the environment and the benefit of combining these tools with Pb isotope “fingerprinting” techniques to identify processes contributing metals. Use of these new geochemical tools requires site-specific knowledge of potential metal sources and their isotopic compositions.

Alteration of the Carbon and Nitrogen Isotopic Composition in the Martian Surface Rocks Due to Cosmic Ray Exposure

NASA Technical Reports Server (NTRS)

Pavlov, A. A.; Pavlov, A. K.; Ostryakov, V. M.; Vasilyev, G. I.; Mahaffy, P.; Steele, A.

2014-01-01

C-13/C-12 and N-15/N-14 isotopic ratios are pivotal for our understanding of the Martian carbon cycle, history of the Martian atmospheric escape, and origin of the organic compounds on Mars. Here we demonstrate that the carbon and nitrogen isotopic composition of the surface rocks on Mars can be significantly altered by the continuous exposure of Martian surface to cosmic rays. Cosmic rays can effectively produce C-13 and N-15 isotopes via spallation nuclear reactions on oxygen atoms in various Martian rocks. We calculate that in the top meter of the Martian rocks, the rates of production of both C-13 and N-15 due to galactic cosmic rays (GCRs) exposure can vary within 1.5-6 atoms/cm3/s depending on rocks' depth and chemical composition. We also find that the average solar cosmic rays can produce carbon and nitrogen isotopes at a rate comparable to GCRs in the top 5-10 cm of the Martian rocks. We demonstrate that if the total carbon content in a surface Martian rock is <10 ppm, then the "light," potentially "biological" C-13/C-12 ratio would be effectively erased by cosmic rays over 3.5 billion years of exposure. We found that for the rocks with relatively short exposure ages (e.g., 100 million years), cosmogenic changes in N-15/N-14 ratio are still very significant. We also show that a short exposure to cosmic rays of Allan Hills 84001 while on Mars can explain its high-temperature heavy nitrogen isotopic composition (N-15/N-14). Applications to Martian meteorites and the current Mars Science Laboratory mission are discussed.

Effects of euthanasia method on stable-carbon and stable-nitrogen isotope analysis for an ectothermic vertebrate.

PubMed

Atwood, Meredith A

2013-04-30

Stable isotope analysis is a critical tool for understanding ecological food webs; however, results can be sensitive to sample preparation methods. To limit the possibility of sample contamination, freezing is commonly used to euthanize invertebrates and preserve non-lethal samples from vertebrates. For destructive sampling of vertebrates, more humane euthanasia methods are preferred to freezing and it is essential to evaluate how these euthanasia methods affect stable isotope results. Stable isotope ratios and elemental composition of carbon and nitrogen were used to evaluate whether the euthanasia method compromised the integrity of the sample for analysis. Specifically, the stable isotope and C:N ratios were compared for larval wood frogs (Rana sylvatica  =  Lithobates sylvaticus), an ectothermic vertebrate, that had been euthanized by freezing with four different humane euthanasia methods: CO2, benzocaine, MS-222 (tricaine methanesulfonate), and 70% ethanol. The euthanasia method was not related to the δ(13)C or δ(15)N values and the comparisons revealed no differences between freezing and any of the other treatments. However, there were slight (non-significant) differences in the isotope ratios of benzocaine and CO2 when each was compared with freezing. The elemental composition was altered by the euthanasia method employed. The percentage nitrogen was higher in CO2 treatments than in freezing, and similar (non-significant) trends were seen for ethanol treatments relative to freezing. The resulting C:N ratios were higher for benzocaine treatments than for both CO2 and ethanol. Similar (non-significant) trends suggested that the C:N ratios were also higher for animals euthanized by freezing than for both CO2 and ethanol euthanasia methods. The euthanasia method had a larger effect on elemental composition than stable isotope ratios. The percentage nitrogen and the subsequent C:N ratios were most affected by the CO2 and ethanol euthanasia methods, whereas non-significant trends suggested that benzocaine and CO2 altered the stable isotope ratios. It appears that the use of MS-222 and freezing with dry ice are the most appropriate euthanasia methods for ectothermic vertebrates. Copyright © 2013 John Wiley & Sons, Ltd.

Red deer bone and antler collagen are not isotopically equivalent in carbon and nitrogen.

PubMed

Stevens, Rhiannon E; O'Connell, Tamsin C

2016-09-15

Bone and antler collagen δ(13) C and δ(15) N values are often assumed to be equivalent when measured in palaeodietary, palaeoclimate and palaeocological studies. Although compositionally similar, bone grows slowly and is remodelled whereas antler growth is rapid and remodelling does not occur. These different patterns of growth could result in isotopic difference within antler and between the two tissue types. Here we test whether red deer (Cervus elaphus) bone and antler δ(13) C and δ(15) N values are equivalent, and whether intra-antler isotopic values are uniform. Bone and antler were isotopically analysed from six stags that lived in a temperate maritime climate on the Isle of Rum, Scotland. Multiple antlers from different years were sampled per individual, together with a single bone sample per individual. Up to 12 samples were taken along the length of each antler (total of 25 antlers, 259 samples) so that a chronological record of the isotopic composition during antler growth could be obtained. Collagen was extracted and its δ(13) C and δ(15) N values were measured by continuous-flow isotope ratio mass spectrometry. Intra-antler collagen isotope signatures vary, and show that not all antlers from an individual or a growth year are equivalent in carbon and nitrogen isotopic ratios. δ(15) N values typically increase with distance along antler length, but no overall trend is observed in δ(13) C values. An isotopic offset is visible between bone and antler, with bone δ(13) C and δ(15) N values being higher in most cases. Bone and antler collagen δ(13) C and δ(15) N values are not isotopically equivalent and are therefore not directly comparable in palaeodietary, palaeoclimate and palaeocological studies. Bone and antler collagen isotopic differences probably relate to differential metabolic processes during the formation of the two tissues. Intra- and inter-antler isotopic variations probably reflect the isotopic composition of an individual's diet rather than physiological parameters, and may have the potential to provide high-resolution individual-specific information in modern and ancient cervid populations. Copyright © 2016 John Wiley & Sons, Ltd. Copyright © 2016 John Wiley & Sons, Ltd.

Hadean Oceanography: Experimental Constraints on the Development of the Terrestrial Hydrosphere and the Origin of Life on Earth

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ryerson, F J

The oxygen isotopic compositions of the world's oldest mineral grains, zircon, have recently been used to infer the compositions of the rocks from which they crystallized. The results appear to require a source that had once experienced isotopic fractionation between clay minerals and liquid water, thereby implying the presence of liquid water at the Earth's surface prior to 4.4 billion years ago, less than 2 million years after accretion. This observation has important implications for the development of the Earth's continental crust. The inferred composition of the zircon source rock is directly dependent upon the oxygen isotopic fractionation between zirconmore » and melt, and zircon and water. These fractionation factors have not been determined experimentally, however, constituting the weak link in this argument. A series of experiments to measure these fractionation factors has been conducted. The experiments consist of finely powdered quartz, a polished single crystal of zircon and isotopically-enriched or isotopically normal water to provide a range of isotopic compositions. The experiments will be run until quartz is in isotopic equilibrium with water. Zircon was expected to partially equilibrate producing an oxygen isotopic diffusion profile perpendicular to the surface. Ion probe spot analysis of quartz and depth profiling of zircon will determine the bulk and surface isotopic compositions of the phases, respectively. The well-known quartz-water isotopic fractionation factors can be used to calculate the oxygen isotopic composition of the fluid, and with the zircon surface composition, the zircon-water fractionation factor. Run at temperatures up to 1000 C for as long as 500 hours have not produced diffusion profiles longer than 50 nm. The steep isotopic gradient at the samples surface precludes use of the diffusion profile for estimation on the surface isotopic composition. The short profiles may be the result of surface dissolution, although such dissolution cannot be resolved in SEM images. The sluggish nature of diffusion in zircon may require that fractionation factors be determined by direct hydrothermal synthesis of zircon rather than by mineral-fluid exchange.« less

Iron isotope biogeochemistry of Neoproterozoic marine shales

NASA Astrophysics Data System (ADS)

Kunzmann, Marcus; Gibson, Timothy M.; Halverson, Galen P.; Hodgskiss, Malcolm S. W.; Bui, Thi Hao; Carozza, David A.; Sperling, Erik A.; Poirier, André; Cox, Grant M.; Wing, Boswell A.

2017-07-01

Iron isotopes have been widely applied to investigate the redox evolution of Earth's surface environments. However, it is still unclear whether iron cycling in the water column or during diagenesis represents the major control on the iron isotope composition of sediments and sedimentary rocks. Interpretation of isotopic data in terms of oceanic redox conditions is only possible if water column processes dominate the isotopic composition, whereas redox interpretations are less straightforward if diagenetic iron cycling controls the isotopic composition. In the latter scenario, iron isotope data is more directly related to microbial processes such as dissimilatory iron reduction. Here we present bulk rock iron isotope data from late Proterozoic marine shales from Svalbard, northwestern Canada, and Siberia, to better understand the controls on iron isotope fractionation in late Proterozoic marine environments. Bulk shales span a δ 56Fe range from -0.45 ‰ to +1.04 ‰ . Although δ 56Fe values show significant variation within individual stratigraphic units, their mean value is closer to that of bulk crust and hydrothermal iron in samples post-dating the ca. 717-660 Ma Sturtian glaciation compared to older samples. After correcting for the highly reactive iron content in our samples based on iron speciation data, more than 90% of the calculated δ 56Fe compositions of highly reactive iron falls in the range from ca. -0.8 ‰ to +3 ‰ . An isotope mass-balance model indicates that diagenetic iron cycling can only change the isotopic composition of highly reactive iron by < 1 ‰ , suggesting that water column processes, namely the degree of oxidation of the ferrous seawater iron reservoir, control the isotopic composition of highly reactive iron. Considering a long-term decrease in the isotopic composition of the iron source to the dissolved seawater Fe(II) reservoir to be unlikely, we offer two possible explanations for the Neoproterozoic δ 56Fe trend. First, a decreasing supply of Fe(II) to the ferrous seawater iron reservoir could have caused the reservoir to decrease in size, allowing a higher degree of partial oxidation, irrespective of increasing environmental oxygen levels. Alternatively, increasing oxygen levels would have led to a higher proportion of Fe(II) being oxidized, without decreasing the initial size of the ferrous seawater iron pool. We consider the latter explanation as the most likely. According to this hypothesis, the δ 56Fe record reflects the redox evolution of Earth's surface environments. δ 56Fe values in pre-Sturtian samples significantly heavier than bulk crust and hydrothermal iron imply partial oxidation of a ferrous seawater iron reservoir. In contrast, mean δ 56Fe values closer to that of hydrothermal iron in post-Sturtian shales reflects oxidation of a larger proportion of the ferrous seawater iron reservoir, and by inference, higher environmental oxygen levels. Nevertheless, significant iron isotopic variation in post-Sturtian shales suggest redox heterogeneity and possibly a dominantly anoxic deep ocean, consistent with results from recent studies using iron speciation and redox sensitive trace metals. However, the interpretation of generally increasing environmental oxygen levels after the Sturtian glaciation highlights the need to better understand the sensitivity of different redox proxies to incremental changes in oxygen levels to enable us to reconcile results from different paleoredox proxies.

Variable Isotopic Compositions of Host Plant Populations Preclude Assessment of Aphid Overwintering Sites

PubMed Central

Voegtlin, David J.; Hamilton, Krista L.; Hogg, David B.

2017-01-01

Soybean aphid (Aphis glycines Matsumura) is a pest of soybean in the northern Midwest whose migratory patterns have been difficult to quantify. Improved knowledge of soybean aphid overwintering sites could facilitate the development of control efforts with exponential impacts on aphid densities on a regional scale. In this preliminary study, we explored the utility of variation in stable isotopes of carbon and nitrogen to distinguish soybean aphid overwintering origins. We compared variation in bulk 13C and 15N content in buckthorn (Rhamnus cathartica L.) and soybean aphids in Wisconsin, among known overwintering locations in the northern Midwest. Specifically, we looked for associations between buckthorn and environmental variables that could aid in identifying overwintering habitats. We detected significant evidence of correlation between the bulk 13C and 15N signals of soybean aphids and buckthorn, despite high variability in stable isotope composition within and among buckthorn plants. Further, the 15N signal in buckthorn varied predictably with soil composition. However, lack of sufficient differentiation of geographic areas along axes of isotopic and environmental variation appears to preclude the use of carbon and nitrogen isotopic signals as effective predictors of likely aphid overwintering sites. These preliminary data suggest the need for future work that can further account for variability in 13C and 15N within/among buckthorn plants, and that explores the utility of other stable isotopes in assessing likely aphid overwintering sites. PMID:29206134

Stable-Carbon Isotopic Composition of Maple Sap and Foliage 1

PubMed Central

Leavitt, Steven W.; Long, Austin

1985-01-01

The 13C/12C ratios of Acer grandidentatum sap sugar collected during the dormant period are compared to those of buds, leaves, and wood developed over the following growing season. As the primary carbon source for cellulose manufacture at initiation of annual growth in deciduous trees, sap sucrose would be expected to have an isotopic composition similar to first-formed cellulose. Although constancy in concentration and 13C/12C ratios of the maple sap sugar suggests any gains or losses (e.g. to maintenance metabolism) do not appreciably alter composition, the 13C/12C ratios of cellulose of the enlarging buds in the spring are quite distinct from those of the sap sugar, seemingly precluding a simple direct biochemical pathway of sap sucrose→glucose→cellulose in favor of a more complex pathway with greater likelihood of isotopic fractionation. The 13C/12C ratios of the leaves and in the growth ring were initially similar to the sap sugar but decreased steadily over the growing season. PMID:16664259

Stable-carbon isotopic composition of maple sap and foliage.

PubMed

Leavitt, S W; Long, A

1985-06-01

The (13)C/(12)C ratios of Acer grandidentatum sap sugar collected during the dormant period are compared to those of buds, leaves, and wood developed over the following growing season. As the primary carbon source for cellulose manufacture at initiation of annual growth in deciduous trees, sap sucrose would be expected to have an isotopic composition similar to first-formed cellulose. Although constancy in concentration and (13)C/(12)C ratios of the maple sap sugar suggests any gains or losses (e.g. to maintenance metabolism) do not appreciably alter composition, the (13)C/(12)C ratios of cellulose of the enlarging buds in the spring are quite distinct from those of the sap sugar, seemingly precluding a simple direct biochemical pathway of sap sucrose-->glucose-->cellulose in favor of a more complex pathway with greater likelihood of isotopic fractionation. The (13)C/(12)C ratios of the leaves and in the growth ring were initially similar to the sap sugar but decreased steadily over the growing season.

Affordable measurement of human total energy expenditure and body composition using one-tenth dose doubly labelled water.

PubMed

Mann, D V; Ho, C S; Critchley, L; Fok, B S P; Pang, E W H; Lam, C W K; Hjelm, N M

2007-05-01

The doubly labelled water (DLW) method is the technique of choice for measurement of free-living total energy expenditure (TEE) in humans. A major constraint on the clinical applicability of the method has been the expense of the (18)O isotope. We have used a reduced-dose (one-tenth of the currently recommended standard dose) of DLW for the measurement of TEE and body composition in nine healthy adult male volunteers. TEE measured by reduced-dose DLW was positively correlated with resting energy expenditure measured by metabolic cart (r=0.87, P<0.01). Isotope-derived fat mass and body mass index were strongly correlated (r=0.86, P<0.01). In four subjects in whom we performed a complementary evaluation using standard-dose isotope enrichment, the TEE measurements were satisfactorily comparable (mean+/-s.d.: reduced dose 2586+/-155 kcal/day vs standard dose 2843+/-321 kcal/day; mean difference 257+/-265 kcal/day). These data indicate that DLW measurements of human energy expenditure and body composition can be performed at a substantially reduced dose (and cost) of isotope enrichment than is currently employed.

Deuterium values from volcanic glass: A paleoelevation proxy for Oregon's Cascade Range

NASA Astrophysics Data System (ADS)

Carlson, T. B.; Bershaw, J. T.

2016-12-01

Hydrated volcanic glass has been used as a proxy to constrain Cenozoic paleoclimate across many of the world's mountain ranges. However, there are concerns that volcanic glass may not preserve the isotopic composition of syndepositional meteoric water. The Cascades are an excellent location to study the validity of hydrated volcanic glass as a paleoenvironmental proxy for several reasons. Moisture is derived from a single oceanic source and falls as orographic precipitation in the Cascades, leading to a characteristic altitude effect, or inverse relationship between elevation and the isotopic composition of meteoric water (δD). In addition, past studies have inferred uplift of the Cascades and an increase in the rain shadow effect since the Eocene through independent methods such as changing fossil assemblages, and other isotopic proxies including carbonates and fossil teeth. In this study, δD values of two hydrated tuff samples are compared: one prior to ( 29 Ma) and one following ( 5 Ma) the onset of High Cascade volcanism. The isotopic composition of these samples are interpreted in the context of modern water across the range to understand the potential of volcanic glass as a proxy for paleoelevation in the Pacific Northwest.

Gas geochemistry of Sierra Negra volcano, Galapagos hot spot

NASA Astrophysics Data System (ADS)

Taran, Y.; Christenson, B.; Sumino, H.; Kennedy, B.

2010-12-01

We report chemical and isotopic compositions of gases from the Mina Azufral fumarolic field of Sierra Negra volcano, Isabela Island, Galápagos, collected in 2004 and compare our data with the data by Giggenbach (unpublished) collected in 1990 and Goff et al. (2000) collected in 1995. New results include the noble gas elemental and isotope abundances and nitrogen isotope ratios for the discharges. Maximum fumarole temperatures and ratios of major components (C/S/Cl/N) changed very little between 1995 and 2004, but the water fraction varied significantly over this period (39 mol% in 1990; 77% in 1995 and 52% in 2004). Carbon and helium isotopic compositions were stable (-3 to -4‰ and 16-18Ra, respectively), and water isotopic composition showed a notable negative oxygen shift from the local meteoric water value depending on the relative water content and thus controlled by the H2O-CO2 oxygen isotope fractionation. In terms of the noble gas abundances and isotopic ratios, heavy noble gases (Kr and Xe) are mainly of the atmospheric origin. Ne isotopic ratios also show strong meteoric signatures, but fall along the 20Ne/22Ne - 21Ne/22Ne air-deep mantle mixing trend for Fernandina glasses (Kurz et al., 2009). 40Ar/36Ar ratios up to 400 show a notable contribution of radiogenic Ar, and 40Ar*/4He ~ 0.3 ratios are consistent with un-degassed upper mantle values. Despite the high He/Ne ratios in gases collected in 2004, and only trace air contamination attributable to sampling, the nitrogen isotope ratios (~ -1 ‰) show a high fraction of the air-saturated water in the volcanic vapor. The chemical composition of the parent magmatic gas is difficult to characterise due to significant interaction between magmatic and hydrothermal system fluids beneath the Sierra Negra caldera. Never-the-less, some important indicators can be estimated: CO2/3He ≈ 3.5x10^9; N2/He <30; CO2/N2 >500. The last value is much higher than the accepted value of ~ 100 for the upper mantle.

Thallium isotope evidence for a permanent increase in marine organic carbon export in the early Eocene

USGS Publications Warehouse

Nielsen, S.G.; Mar-Gerrison, S.; Gannoun, A.; LaRowe, D.; Klemm, V.; Halliday, A.N.; Burton, K.W.; Hein, J.R.

2009-01-01

The first high resolution thallium (Tl) isotope records in two ferromanganese crusts (Fe-Mn crusts), CD29 and D11 from the Pacific Ocean are presented. The crusts record pronounced but systematic changes in 205Tl/203Tl that are unlikely to reflect diagenetic overprinting or changes in isotope fractionation between seawater and Fe-Mn crusts. It appears more likely that the Fe-Mn crusts track the Tl isotope composition of seawater over time. The present-day oceanic residence time of Tl is estimated to be about 20,000??yr, such that the isotopic composition should reflect ocean-wide events. New and published Os isotope data are used to construct age models for these crusts that are consistent with each other and significantly different from previous age models. Application of these age models reveals that the Tl isotope composition of seawater changed systematically between ~ 55??Ma and ~ 45??Ma. Using a simple box model it is shown that the present day Tl isotope composition of seawater depends almost exclusively on the ratio between the two principal output fluxes of marine Tl. These fluxes are the rate of removal of Tl from seawater via scavenging by authigenic Fe-Mn oxyhydroxide precipitation and the uptake rate of Tl during low temperature alteration of oceanic crust. It is highly unlikely that the latter has changed greatly. Therefore, assuming that the marine Tl budget has also not changed significantly during the Cenozoic, the low 205Tl/203Tl during the Paleocene is best explained by a more than four-fold higher sequestration of Tl by Fe-Mn oxyhydroxides compared with at the present day. The calculated Cenozoic Tl isotopic seawater curve displays a striking similarity to that of S, providing evidence that both systems may have responded to the same change in the marine environment. A plausible explanation is a marked and permanent increase in organic carbon export from ~ 55??Ma to ~ 45??Ma, which led to higher pyrite burial rates and a significantly reduced flux of Fe-Mn oxide removal as a result of increased biological uptake of Fe and Mn. ?? 2008 Elsevier B.V. All rights reserved.

Reconstruction of the Nd isotope composition of seawater on epicontinental seas: Testing the potential of Fe-Mn oxyhydroxide coatings on foraminifera tests for deep-time investigations

NASA Astrophysics Data System (ADS)

Charbonnier, Guillaume; Pucéat, Emmanuelle; Bayon, Germain; Desmares, Delphine; Dera, Guillaume; Durlet, Christophe; Deconinck, Jean-François; Amédro, Francis; Gourlan, Alexandra T.; Pellenard, Pierre; Bomou, Brahimsamba

2012-12-01

The Fe-Mn oxide fraction leached from deep-sea sediments has been increasingly used to reconstruct the Nd isotope composition of deep water masses, that can be used to track changes in oceanic circulation with a high temporal resolution. Application of this archive to reconstruct the Nd isotope composition of bottom seawater in shallow shelf environments remained however to be tested. Yet as the Nd isotope composition of seawater on continental margins is particularly sensitive to changes in erosional inputs, establishment of neritic seawater Nd isotope evolution around areas of deep water formation would be useful to discriminate the influence of changes in oceanic circulation and in isotopic composition of erosional inputs on the Nd isotope record of deep waters. The purpose of this study is to test the potential of Fe-Mn coatings leached from foraminifera tests to reconstruct the Nd isotope composition of seawater in shelf environments for deep-time intervals. Albian to Turonian samples from two different outcrops have been recovered, from the Paris Basin (Wissant section, northern France) and from the Western Interior Seaway (Hot Spring, South Dakota, USA), that were deposited in epicontinental seas. Rare Earth Element (REE) spectra enriched in middle REEs in the foraminifera leach at Wissant highlight the presence of Fe-Mn oxides. The similarity of the Nd isotopic signal of the Fe-Mn oxide fraction leached from foraminifera tests with that of fish teeth suggests that Fe-Mn oxides coating foraminifera can be good archives of shelf bottom seawater Nd isotopic composition. Inferred bottom shelf water Nd isotope compositions at Wissant range from -8.5 to -9.7 ɛ-units, about 1.5-2 ɛ-units higher than that of the contemporaneous local detrital fraction. At Hot Spring, linear REE spectra characterizing foraminifera leach may point to an absence of authigenic marine Fe-Mn oxide formation in this area during the Late Cenomanian-Early Turonian, consistent with dysoxic to anoxic conditions at Hot Spring, contemporaneous to an Oceanic Anoxic Event. The similarity of the Nd isotopic signal of the carbonate matrix of foraminifera with that of fish teeth suggests that it records the Nd isotope composition of bottom shelf seawater as well. Inferred bottom shelf water Nd isotope compositions at Hot Spring are quite radiogenic, between -7 and -6 ɛ-units, about 2.5-4 ɛ-units higher than that of the contemporaneous local detrital fraction. In contrast, in both sections Fe-Mn oxides leached directly from the decarbonated sediment tend to yield a less radiogenic Nd isotopic composition, typically between 0.2 and 0.8 ɛ-units lower, that is intermediate between that of fish teeth and of the detrital fraction. This suggests the contribution of pre-formed continental Fe-Mn oxides to the Nd isotopic signal, along with authigenic marine oxides, or a detrital contamination during leaching.

Hydrogen and oxygen in brine shrimp chitin reflect environmental water and dietary isotopic composition

NASA Astrophysics Data System (ADS)

Nielson, Kristine E.; Bowen, Gabriel J.

2010-03-01

Hydrogen and oxygen isotope ratios of the common structural biopolymer chitin are a potential recorder of ecological and environmental information, but our understanding of the mechanisms of incorporation of H and O from environmental substrates into chitin is limited. We report the results of a set of experiments in which the isotopic compositions of environmental water and diet were varied independently in order to assess the contribution of these variables to the H and O isotopic composition of Artemia franciscana chitin. Hydrogen isotope ratios of chitin were strongly linearly correlated with both food and water, with approximately 26% of the hydrogen signal reflecting food and approximately 38% reflecting water. Oxygen isotopes were also strongly correlated with the isotopic composition of water and food, but whereas 69% of oxygen in chitin exchanged with environmental water, only 10% was derived from food. We propose that these observations reflect the position-specific, partial exchange of H and O atoms with brine shrimp body water during the processes of digestion and chitin biosynthesis. Comparison of culture experiments with a set of natural samples collected from the Great Salt Lake, UT in 2006 shows that, with some exceptions, oxygen isotope compositions of chitin track those of water, whereas hydrogen isotopes vary inversely with those of lake water. The different behavior of the two isotopic systems can be explained in terms of a dietary shift from allochthonous particulate matter with relatively higher δ 2H values in the early spring to autochthonous particulate matter with significantly lower δ 2H values in the late summer to autumn. These results suggest oxygen in chitin may be a valuable proxy for the oxygen isotopic composition of environmental water, whereas hydrogen isotope values from the same molecule may reveal ecological and biogeochemical changes within lakes.

Isotopologue Distributions of Peptide Product Ions by Tandem Mass Spectrometry: Quantitation of Low Levels of Deuterium Incorporation1

PubMed Central

Wang, Benlian; Sun, Gang; Anderson, David R.; Jia, Minghong; Previs, Stephen; Anderson, Vernon E.

2007-01-01

Protonated molecular peptide ions and their product ions generated by tandem mass spectrometry appear as isotopologue clusters due to the natural isotopic variations of carbon, hydrogen, nitrogen, oxygen and sulfur. Quantitation of the isotopic composition of peptides can be employed in experiments involving isotope effects, isotope exchange, isotopic labeling by chemical reactions, and studies of metabolism by stable isotope incorporation. Both ion trap and quadrupole-time of flight mass spectrometry are shown to be capable of determining the isotopic composition of peptide product ions obtained by tandem mass spectrometry with both precision and accuracy. Tandem mass spectra obtained in profile-mode of clusters of isotopologue ions are fit by non-linear least squares to a series of Gaussian peaks (described in the accompanying manuscript) which quantify the Mn/M0 values which define the isotopologue distribution (ID). To determine the isotopic composition of product ions from their ID, a new algorithm that predicts the Mn/M0 ratios is developed which obviates the need to determine the intensity of all of the ions of an ID. Consequently a precise and accurate determination of the isotopic composition a product ion may be obtained from only the initial values of the ID, however the entire isotopologue cluster must be isolated prior to fragmentation. Following optimization of the molecular ion isolation width, fragmentation energy and detector sensitivity, the presence of isotopic excess (2H, 13C, 15N, 18O) is readily determined within 1%. The ability to determine the isotopic composition of sequential product ions permits the isotopic composition of individual amino acid residues in the precursor ion to be determined. PMID:17559791

Nucleosynthetic Heterogeneity Controls Vanadium Isotope Variations in Bulk Chondrites

NASA Technical Reports Server (NTRS)

Nielsen, S. G.; Righter, K.; Wu, F.; Owens, J. D.; Prytulak, J.; Burton, K.; Parkinson, I.; Davis, D.

2018-01-01

The vanadium (V) isotope composition of early solar system materials have been hypothesized to be sensitive to high energy irradiation that originated from the young Sun. Vanadium has two isotopes with masses 50 and 51 that have (51)V/(50)V ratio of approximately 410. High energy irradiation produces (50)V from various target isotopes of Ti, Cr and Fe, which would result in light V isotope compositions (expressed as delta (51)V in per mille = 1000 x (((51)V/(50)V(sub sample)/(51)V/(50)V(sub AlfaAesar)) - 1)) relative to a presumably chondritic starting composition. Recently published V isotope data for calcium aluminium inclusions (CAIs) has revealed some very negative values relative to chondrites (by almost -4 per mille) that were indeed interpreted to reflect irradiation processes despite the fact that the studied CAIs all exhibited significant initial abundances of (10)Be, while only a few CAIs displayed light V isotope compositions. It is difficult to relate V isotope variations directly to a singular process because V only possesses two isotopes. Therefore, V isotope variations can principally be produced both mass dependent and independent processes. Mass dependent kinetic stable isotope fractionation is common in CAIs for refractory elements due to partial condensation/evaporation processes. The element strontium (Sr) has an almost identical condensation temperature to V and studies of stable Sr isotope compositions in CAIs reveal both heavy and light values relative to chondrites of several permil. These variations are similar in magnitude to those reported for V isotopes in CAIs, which suggests it is possible that some of the V isotope variation in CAIs could be due to kinetic stable isotope fractionation during condensation/evaporation processes.

The Mg isotopic systematics of granitoids in continental arcs and implications for the role of chemical weathering in crust formation

PubMed Central

Shen, Bing; Jacobsen, Benjamin; Lee, Cin-Ty A.; Yin, Qing-Zhu; Morton, Douglas M.

2009-01-01

Continental crust is too Si-rich and Mg-poor to derive directly from mantle melting, which generates basaltic rather than felsic magmas. Converting basalt to more felsic compositions requires a second step involving Mg loss, which is thought to be dominated by internal igneous differentiation. However, igneous differentiation alone may not be able to generate granites, the most silicic endmember making up the upper continental crust. Here, we show that granites from the eastern Peninsular Ranges Batholith (PRB) in southern California are isotopically heavy in Mg compared with PRB granodiorites and canonical mantle. Specifically, Mg isotopes correlate positively with Si content and O, Sr, and Pb isotopes and negatively with Mg content. The elevated Sr and Pb isotopes require that a component in the source of the granitic magmas to be ancient preexisting crust making up the prebatholithic crustal basement, but the accompanying O and Mg isotope fractionations suggest that this prebatholithic crust preserved a signature of low-temperature alteration. The protolith of this basement rock may have been the residue of chemical weathering, which progressively leached Mg from the residue, leaving the remaining Mg highly fractionated in terms of its isotopic signature. Our observations indicate that ancient continental crust preserves the isotopic signature of compositional modification by chemical weathering. PMID:19920171

Seasonality of Leaf Carbon Isotopic Composition and Leaf Water Isotopic Enrichment in a Mixed Evergreen Forest in Southern California

NASA Astrophysics Data System (ADS)

Santiago, L. S.; Sickman, J. O.; Goulden, M.; DeVan, C.; Pasquini, S. C.; Pivovaroff, A. L.

2011-12-01

Leaf carbon isotopic composition and leaf water isotopic enrichment reflect physiological processes and are important for linking local and regional scale processes to global patterns. We investigated how seasonality affects the isotopic composition of bulk leaf carbon, leaf sugar carbon, and leaf water hydrogen under a Mediterranean climate. Leaf and stem samples were collected monthly from four tree species (Calocedrus decurrens, Pinus lambertiana, Pinus ponderosa, and Quercus chrysolepis) at the James San Jacinto Mountain Reserve in southern California. Mean monthly bulk leaf carbon isotopic composition varied from -34.5 % in P. ponderosa to -24.7 % in P. lambertiana and became more depleted in 13C from the spring to the summer. Mean monthly leaf sugar varied from -29.3 % in P. ponderosa to -21.8 % in P. lambertiana and was enriched in 13C during the winter, spring and autumn, but depleted during the mid-summer. Leaf water hydrogen isotopic composition was 28.4 to 68.8 % more enriched in deuterium than source water and this enrichment was greater as seasonal drought progressed. These data indicate that leaf carbon and leaf water hydrogen isotopic composition provide sensitive measures that connect plant physiological processes to short-term climatic variability.

Sr, Nd and Pb isotopes in Proterozoic intrusives astride the Grenville Front in Labrador: Implications for crustal contamination and basement mapping

USGS Publications Warehouse

Ashwal, L.D.; Wooden, J.L.; Emslie, R.F.

1986-01-01

We report Sr, Nd and Pb isotopic compositions of mid-Proterozoic anorthosites and related rocks (1.45-1.65 Ga) and of younger olivine diabase dikes (1.4 Ga) from two complexes on either side of the Grenville Front in Labrador. Anorthositic or diabasic samples from the Mealy Mountains (Grenville Province) and Harp Lake (Nain-Churchill Provinces) complexes have very similar major, minor and trace element compositions, but distinctly different isotopic signatures. All Mealy Mountains samples have ISr = 0.7025-0.7033, ??{lunate}Nd = +0.6 to +5.6 and Pb isotopic compositions consistent with derivation from a mantle source depleted with respect to Nd/Sm and Rb/Sr. Pb isotopic compositions for the Mealy Mountains samples are slightly more radiogenic than model mantle compositions. All Harp Lake samples have ISr = 0.7032-0.7066, ??{lunate}Nd = -0.3 to -4.4 and variable, but generally unradiogenic 207Pb 204Pb and 206Pb 204Pb compared to model mantle, suggesting mixing between a mantle-derived component and a U-depleted crustal contaminant. Crustal contaminants are probably a variety of Archean high-grade quartzofeldspathic gneisses with low U/Pb ratios and include a component that must be isotopically similar to the early Archean (>3.6 Ga) Uivak gneisses of Labrador or the Amitsoq gneisses of west Greenland. This would imply that the ancient gneiss complex of coastal Labrador and Greenland is larger than indicated by present surface exposure and may extend in the subsurface as far west as the Labrador Trough. If Harp Lake and Mealy Mountains samples were subjected to the same degree of contamination, as suggested by their chemical similarities, then the Mealy contaminants must be much younger, probably early or middle Proterozoic in age. The Labrador segment of the Grenville Front, therefore, appears to coincide with the southern margin of the Archean North Atlantic craton and may represent a pre mid-Proterozoic suture. ?? 1986.

Revisiting streamside trees that do not use stream water: can the two water worlds hypothesis and snowpack isotopic effects explain a missing water source?: Riparian tree water sources

DOE PAGES

Bowling, David R.; Schulze, Emily S.; Hall, Steven J.

2016-10-14

We revisit a classic ecohydrological study that showed streamside riparian trees in a semiarid mountain catchment did not use perennial stream water. The original study suggested that mature individuals of Acer negundo, Acer grandidentatum, and other species were dependent on water from “deeper strata,” possibly groundwater. We used a dual stable isotope approach (δ 18O and δ 2H) to further examine the water sources of these trees. We tested the hypothesis that groundwater was the main tree water source, but found that neither groundwater nor stream water matched the isotope composition of xylem water during two growing seasons. Soil watermore » (0–1 m depth) was closest to and periodically overlapped with xylem water isotope composition, but overall, xylem water was isotopically enriched compared to all measured water sources. The “two water worlds” hypothesis postulates that soil water comprises isotopically distinct mobile and less mobile pools that do not mix, potentially explaining this disparity. We further hypothesized that isotopic effects during snowpack metamorphosis impart a distinct isotope signature to the less mobile soil water that supplies summer transpiration. Depth trends in water isotopes following snowmelt were consistent with the two water worlds hypothesis, but snow metamorphic isotope effects could not explain the highly enriched xylem water. Thus, the dual isotope approach did not unambiguously determine the water source(s) of these riparian trees. Further exploration of physical, geochemical, and biological mechanisms of water isotope fractionation and partitioning is necessary to resolve these data, highlighting critical challenges in the isotopic determination of plant water sources.« less

Revisiting streamside trees that do not use stream water: can the two water worlds hypothesis and snowpack isotopic effects explain a missing water source?: Riparian tree water sources

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bowling, David R.; Schulze, Emily S.; Hall, Steven J.

We revisit a classic ecohydrological study that showed streamside riparian trees in a semiarid mountain catchment did not use perennial stream water. The original study suggested that mature individuals of Acer negundo, Acer grandidentatum, and other species were dependent on water from “deeper strata,” possibly groundwater. We used a dual stable isotope approach (δ 18O and δ 2H) to further examine the water sources of these trees. We tested the hypothesis that groundwater was the main tree water source, but found that neither groundwater nor stream water matched the isotope composition of xylem water during two growing seasons. Soil watermore » (0–1 m depth) was closest to and periodically overlapped with xylem water isotope composition, but overall, xylem water was isotopically enriched compared to all measured water sources. The “two water worlds” hypothesis postulates that soil water comprises isotopically distinct mobile and less mobile pools that do not mix, potentially explaining this disparity. We further hypothesized that isotopic effects during snowpack metamorphosis impart a distinct isotope signature to the less mobile soil water that supplies summer transpiration. Depth trends in water isotopes following snowmelt were consistent with the two water worlds hypothesis, but snow metamorphic isotope effects could not explain the highly enriched xylem water. Thus, the dual isotope approach did not unambiguously determine the water source(s) of these riparian trees. Further exploration of physical, geochemical, and biological mechanisms of water isotope fractionation and partitioning is necessary to resolve these data, highlighting critical challenges in the isotopic determination of plant water sources.« less

Nitrogen Isotope Evidence for a Shift in Eastern Beringian Nitrogen Cycle after the Terminal Pleistocene

NASA Astrophysics Data System (ADS)

Tahmasebi, F.; Longstaffe, F. J.; Zazula, G.

2016-12-01

The loess deposits of eastern Beringia, a region in North America between 60° and 70°N latitude and bounded by Chukchi Sea to the west and the Mackenzie River to the east, are a magnificent repository of Late Pleistocene megafauna fossils. The stable carbon and nitrogen isotope compositions of these fossils are measured to determine the paleodiet of these animals, and hence the paleoenvironment of this ecosystem during the Quaternary. For this approach to be most successful, however, requires consideration of possible changes in nutrient cycling and hence the carbon and nitrogen isotopic compositions of vegetation in this ecosystem. To test for such a shift following the terminal Pleistocene, we analyzed the stable carbon and nitrogen isotope compositions of modern plants and bone collagen of Arctic ground squirrels from Yukon Territory, and fossil plants and bones recovered from Late Pleistocene fossil Arctic ground squirrel nests. The data for modern samples provided a measure of the isotopic fractionation between ground squirrel bone collagen and their diet. The over-wintering isotopic effect of decay on typical forage grasses was also measured to evaluate its role in determining fossil plant isotopic compositions. The grasses showed only a minor change ( 0-1 ‰) in carbon isotope composition, but a major change ( 2-10 ‰) in nitrogen isotope composition over the 317-day experiment. Based on the modern carbon isotope fractionation between ground squirrel bone collagen and their diet, the modern vegetation carbon isotopic baseline provides a suitable proxy for the Late Pleistocene of eastern Beringia, after accounting for the Suess effect. However, the predicted nitrogen isotope composition of vegetation comprising the diet of fossil ground squirrels remains 2.5 ‰ higher than modern grasslands in this area, even after accounting for possible N-15 enrichment during decay. This result suggests a change in N cycling in this region since the Late Pleistocene.

Thallium isotope composition of the upper continental crust and rivers - An investigation of the continental sources of dissolved marine thallium

USGS Publications Warehouse

Nielsen, S.G.; Rehkamper, M.; Porcelli, D.; Andersson, P.; Halliday, A.N.; Swarzenski, P.W.; Latkoczy, C.; Gunther, D.

2005-01-01

The thallium (Tl) concentrations and isotope compositions of various river and estuarine waters, suspended riverine particulates and loess have been determined. These data are used to evaluate whether weathering reactions are associated with significant Tl isotope fractionation and to estimate the average Tl isotope composition of the upper continental crust as well as the mean Tl concentration and isotope composition of river water. Such parameters provide key constraints on the dissolved Tl fluxes to the oceans from rivers and mineral aerosols. The Tl isotope data for loess and suspended riverine detritus are relatively uniform with a mean of ??205Tl = -2.0 ?? 0.3 (??205Tl represents the deviation of the 205Tl/203Tl isotope ratio of a sample from NIST SRM 997 Tl in parts per 104). For waters from four major and eight smaller rivers, the majority were found to have Tl concentrations between 1 and 7 ng/kg. Most have Tl isotope compositions very similar (within ??1.5 ??205Tl) to that deduced for the upper continental crust, which indicates that no significant Tl isotope fractionation occurs during weathering. Based on these results, it is estimated that rivers have a mean natural Tl concentration and isotope composition of 6 ?? 4 ng/kg and ??205Tl = -2.5 ?? 1.0, respectively. In the Amazon estuary, both additions and losses of Tl were observed, and these correlate with variations in Fe and Mn contents. The changes in Tl concentrations have much lower amplitudes, however, and are not associated with significant Tl isotope effects. In the Kalix estuary, the Tl concentrations and isotope compositions can be explained by two-component mixing between river water and a high-salinity end member that is enriched in Tl relative to seawater. These results indicate that Tl can display variable behavior in estuarine systems but large additions and losses of Tl were not observed in the present study. Copyright ?? 2005 Elsevier Ltd.

Deciphering the iron isotope message of the human body

NASA Astrophysics Data System (ADS)

Walczyk, Thomas; von Blanckenburg, Friedhelm

2005-04-01

Mass-dependent variations in isotopic composition are known since decades for the light elements such as hydrogen, carbon or oxygen. Multicollector-inductively coupled plasma mass spectrometry (MC-ICP-MS) and double-spike thermal ionization mass spectrometry (TIMS) permit us now to resolve small variations in isotopic composition even for the heavier elements such as iron. Recent studies on the iron isotopic composition of human blood and dietary iron sources have shown that lighter iron isotopes are enriched along the food chain and that each individual bears a certain iron isotopic signature in blood. To make use of this finding in biomedical research, underlying mechanisms of isotope fractionation by the human body need to be understood. In this paper available iron isotope data for biological samples are discussed within the context of isotope fractionation concepts and fundamental aspects of human iron metabolism. This includes evaluation of new data for body tissues which show that blood and muscle tissue have a similar iron isotopic composition while heavier iron isotopes are concentrated in the liver. This new observation is in agreement with our earlier hypothesis of a preferential absorption of lighter iron isotopes by the human body. Possible mechanisms for inducing an iron isotope effect at the cellular and molecular level during iron uptake are presented and the potential of iron isotope effects in human blood as a long-term measure of dietary iron absorption is discussed.

Tooth enamel maturation reequilibrates oxygen isotope compositions and supports simple sampling methods

NASA Astrophysics Data System (ADS)

Trayler, Robin B.; Kohn, Matthew J.

2017-02-01

Oxygen isotope and major element zoning patterns of several disparate ungulate teeth were collected to evaluate the timing and geometry of enamel formation, records of isotope zoning, and tooth enamel sampling strategies. Isotopic zoning in mammalian tooth enamel encodes a sub-annual time series of isotopic variation of an animal's body water composition, with a damping factor that depends on the specifics of how enamel mineralizes. Enamel formation comprises two stages: precipitation of appositional enamel with a high CO3:PO4 ratio, followed by precipitation of maturational enamel with a lower CO3:PO4. If appositional and maturational enamel both contribute to isotope compositions (but with different CO3:PO4), and if isotope compositions vary seasonally, paired δ18O values from CO3 and PO4 profiles should show a spatial separation. CO3 isotope patterns should be shifted earlier seasonally than PO4 isotope patterns. Such paired profiles for new and published data show no resolvable shifts, i.e. CO3 and PO4 δ18O profiles show coincident maxima and minima. This coincidence suggests that enamel maturation reequilibrates appositional isotope compositions. If enamel maturation establishes enamel isotope compositions, the geometry of maturation, not apposition, should be considered when devising sampling protocols. X-ray maps of Ca zoning show that the majority of enamel (inner and middle layers) mineralizes heavily at a high angle to the external tooth surface and the enamel-dentine junction over length scales of 2-4 mm, while the outer enamel surface mineralizes more slowly. These data suggest that isotopic sampling strategies should parallel maturational geometry and focus on interior enamel to improve data fidelity. The magnitude of isotopic damping is also smaller than implied in previous studies, so tooth enamel zoning more closely reflects original body water isotopic variations than previously assumed.

Lead isotope compositions of Late Cretaceous and early Tertiary igneous rocks and sulfide minerals in Arizona: Implications for the sources of plutons and metals in porphyry copper deposits

USGS Publications Warehouse

Bouse, R.M.; Ruiz, J.; Titley, S.R.; Tosdal, R.M.; Wooden, J.L.

1999-01-01

Porphyry copper deposits in Arizona are genetically associated with Late Cretaceous and early Tertiary igneous complexes that consist of older intermediate volcanic rocks and younger intermediate to felsic intrusions. The igneous complexes and their associated porphyry copper deposits were emplaced into an Early Proterozoic basement characterized by different rocks, geologic histories, and isotopic compositions. Lead isotope compositions of the Proterozoic basement rocks define, from northwest to southeast, the Mojave, central Arizona, and southeastern Arizona provinces. Porphyry copper deposits are present in each Pb isotope province. Lead isotope compositions of Late Cretaceous and early Tertiary plutons, together with those of sulfide minerals in porphyry copper deposits and of Proterozoic country rocks, place important constraints on genesis of the magmatic suites and the porphyry copper deposits themselves. The range of age-corrected Pb isotope compositions of plutons in 12 Late Cretaceous and early Tertiary igneous complexes is 206Pb/204Pb = 17.34 to 22.66, 207Pb/204Pb = 15.43 to 15.96, and 208Pb/204Pb = 37.19 to 40.33. These Pb isotope compositions and calculated model Th/U are similar to those of the Proterozoic rocks in which the plutons were emplaced, thereby indicating that Pb in the younger rocks and ore deposits was inherited from the basement rocks and their sources. No Pb isotope differences distinguish Late Cretaceous and early Tertiary igneous complexes that contain large economic porphyry copper deposits from less rich or smaller deposits that have not been considered economic for mining. Lead isotope compositions of Late Cretaceous and early Tertiary plutons and sulfide minerals from 30 metallic mineral districts, furthermore, require that the southeastern Arizona Pb province be divided into two subprovinces. The northern subprovince has generally lower 206Pb/204Pb and higher model Th/U, and the southern subprovince has higher 206Pb/204Pb and lower model Th/U. These Pb isotope differences are inferred to result from differences in their respective post-1.7 Ga magmatic histories. Throughout Arizona, Pb isotope compositions of Late Cretaceous and early Tertiary plutons and associated sulfide minerals are distinct from those of Jurassic plutons and also middle Tertiary igneous rocks and sulfide minerals. These differences most likely reflect changes in tectonic setting and magmatic sources. Within Late Cretaceous and early Tertiary igneous complexes that host economic porphyry copper deposits, there is commonly a decrease in Pb isotope composition from older to younger plutons. This decrease in Pb isotope values with time suggests an increasing involvement of crust with lower U/Pb than average crust in the source(s) of Late Cretaceous and early Tertiary magmas. Lead isotope compositions of the youngest porphyries in the igneous complexes are similar to those in most sulfide minerals within the associated porphyry copper deposit. This Pb isotope similarity argues for a genetic link between them. However, not all Pb in the sulfide minerals in porphyry copper deposits is magmatically derived. Some sulfide minerals, particularly those that are late stage, or distal to the main orebody, or in Proterozoic or Paleozoic rocks, have elevated Pb isotope compositions displaced toward the gross average Pb isotope composition of the local country rocks. The more radiogenic isotopic compositions argue for a contribution of Pb from those rocks at the site of ore deposition. Combining the Pb isotope data with available geochemical, isotopic, and petrologic data suggests derivation of the young porphyry copper-related plutons, most of their Pb, and other metals from a hybridized lower continental crustal source. Because of the likely involvement of subduction-related mantle-derived basaltic magma in the hybridized lower crustal source, an indiscernible mantle contribution is probable in the porphyry magmas. Clearly, in addition

Diel variations in carbon isotopic composition and concentration of organic acids and their impact on plant dark respiration in different species.

PubMed

Lehmann, M M; Wegener, F; Werner, R A; Werner, C

2016-09-01

Leaf respiration in the dark and its C isotopic composition (δ(13) CR ) contain information about internal metabolic processes and respiratory substrates. δ(13) CR is known to be less negative compared to potential respiratory substrates, in particular shortly after darkening during light enhanced dark respiration (LEDR). This phenomenon might be driven by respiration of accumulated (13) C-enriched organic acids, however, studies simultaneously measuring δ(13) CR during LEDR and potential respiratory substrates are rare. We determined δ(13) CR and respiration rates (R) during LEDR, as well as δ(13) C and concentrations of potential respiratory substrates using compound-specific isotope analyses. The measurements were conducted throughout the diel cycle in several plant species under different environmental conditions. δ(13) CR and R patterns during LEDR were strongly species-specific and showed an initial peak, which was followed by a progressive decrease in both values. The species-specific differences in δ(13) CR and R during LEDR may be partially explained by the isotopic composition of organic acids (e.g., oxalate, isocitrate, quinate, shikimate, malate), which were (13) C-enriched compared to other respiratory substrates (e.g., sugars and amino acids). However, the diel variations in both δ(13) C and concentrations of the organic acids were generally low. Thus, additional factors such as the heterogeneous isotope distribution in organic acids and the relative contribution of the organic acids to respiration are required to explain the strong (13) C enrichment in leaf dark-respired CO2 . © 2016 German Botanical Society and The Royal Botanical Society of the Netherlands.

Ecological differences in three autochthonous equid species in Mongolian Gobi inferred from stable isotopes in tail hair

NASA Astrophysics Data System (ADS)

Burnik Šturm, Martina; Voigt, Christian C.; Oyunsaikhan, Ganbaatar; Kaczensky, Petra

2014-05-01

In the Dzungarian Gobi of Mongolia three equid species, Asiatic wild ass (Equus hemionus), domestic horse (Equus caballus), and re-introduced Przewalski's horse (Equus ferus przewalskii) share the same habitat and thus provide a unique opportunity for comparative ecological studies. In our project we use the stable isotope analysis of tail hair as a tool to study feeding ecology, water use and movement pattern of the three extant sympatric equid species to reveal species specific differences and thus strengthen our understanding of the ecological adaptations of the three species to the harsh environment of the Gobi desert. Since tail hair grow continuously and is isotopically inert after formation, when sampled and analysed longitudinally, provides temporary explicit information on dietary regime and movement pattern. We use the carbon isotopes in the tail hair to determine the quantitative dependence of each animal on isotopically distinct C3 (grasses) and C4 (multitude of annuals and perennials) diet. Nitrogen isotopes reflect the isotopic composition of the diet and hydrogen isotopes reflect the isotopic composition of the water that animals utilize, while both elements have been reported to also give information on the physical status of the animal. Combined isotope data will be used to describe the movement patterns and habitat use of the three equid species. We will present the methodology and first preliminary results of carbon and nitrogen isotope analysis of potential forage plants of the study area and of the tail hair analysis. Among the analysed plants, collected in the pilot sampling campaign in 2012 (n = 192), we identified 14 C3 and two C4species and found no general trend that could explain the effect of altitude on carbon isotopic composition in C3 plants and no correlation between carbon isotopic composition and longitude or latitude. We performed additional, more detailed plant sampling in 2013. The first results obtained from the tail hair analysis indicate differences in feeding preferences between extant wild asses (n = 6) and Przewalski's (n = 6) and domestic horses (n = 6). While wild asses switch regularly between periods with predominantly feeding on C3 diet with low incorporation of C4 diet (wet season) and periods with high incorporation of C4 (dry season) diet, Przewalski's and domestic horses predominantly feed on C3 plant diet but seem to also include C4plants in their diet during extreme conditions (i.e. extremely harsh winters).

COORDINATED ANALYSES OF PRESOLAR GRAINS IN THE ALLAN HILLS 77307 AND QUEEN ELIZABETH RANGE 99177 METEORITES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nguyen, Ann N.; Nittler, Larry R.; Alexander, Conel M. O'D.

2010-08-10

We report the identification of presolar silicates ({approx}177 ppm), presolar oxides ({approx}11 ppm), and one presolar SiO{sub 2} grain in the Allan Hills (ALHA) 77307 chondrite. Three grains having Si-isotopic compositions similar to SiC X and Z grains were also identified, though the mineral phases are unconfirmed. Similar abundances of presolar silicates ({approx}152 ppm) and oxides ({approx}8 ppm) were also uncovered in the primitive CR chondrite Queen Elizabeth Range (QUE) 99177, along with 13 presolar SiC grains and one presolar silicon nitride. The O-isotopic compositions of the presolar silicates and oxides indicate that most of the grains condensed in low-massmore » red giant and asymptotic giant branch stars. Interestingly, unlike presolar oxides, few presolar silicate grains have isotopic compositions pointing to low-metallicity, low-mass stars (Group 3). The {sup 18}O-rich (Group 4) silicates, along with the few Group 3 silicates that were identified, likely have origins in supernova outflows. This is supported by their O- and Si-isotopic compositions. Elemental compositions for 74 presolar silicate grains were determined by scanning Auger spectroscopy. Most of the grains have non-stoichiometric elemental compositions inconsistent with pyroxene or olivine, the phases commonly used to fit astronomical spectra, and have comparable Mg and Fe contents. Non-equilibrium condensation and/or secondary alteration could produce the high Fe contents. Transmission electron microscopic analysis of three silicate grains also reveals non-stoichiometric compositions, attributable to non-equilibrium or multistep condensation, and very fine scale elemental heterogeneity, possibly due to subsequent annealing. The mineralogies of presolar silicates identified in meteorites thus far seem to differ from those in interplanetary dust particles.« less

Isotopic Compositions of the Elements, 2001

NASA Astrophysics Data System (ADS)

Böhlke, J. K.; de Laeter, J. R.; De Bièvre, P.; Hidaka, H.; Peiser, H. S.; Rosman, K. J. R.; Taylor, P. D. P.

2005-03-01

The Commission on Atomic Weights and Isotopic Abundances of the International Union of Pure and Applied Chemistry completed its last review of the isotopic compositions of the elements as determined by isotope-ratio mass spectrometry in 2001. That review involved a critical evaluation of the published literature, element by element, and forms the basis of the table of the isotopic compositions of the elements (TICE) presented here. For each element, TICE includes evaluated data from the "best measurement" of the isotope abundances in a single sample, along with a set of representative isotope abundances and uncertainties that accommodate known variations in normal terrestrial materials. The representative isotope abundances and uncertainties generally are consistent with the standard atomic weight of the element Ar(E) and its uncertainty U[Ar(E)] recommended by CAWIA in 2001.

Gas exchange parameters inferred from {delta}{sup 13}C of conifer annual rings throughout the 20th century

DOE Office of Scientific and Technical Information (OSTI.GOV)

Marshall, J.D.; Monserud, R.A.

1995-12-31

In this study the stable isotopes of carbon in plant tissue provided a means of inferring the proportional decrease in carbon dioxide concentration across the stomata, which is closely related to photosynthetic water-use efficiency. The authors analyzed the stable carbon isotope composition of tree rings laid down over the past 80 years to determine whether the proportional decrease in CO{sub 2} concentration across the stomata had increased. Dominant and codominant trees of western white pine (Pinus monticola), ponderosa pine (P. ponderosa), and Douglas-fir (Pseudotsuga menziesii var. glauca) growing at the Priest River Experimental Forest, in northern Idaho, were analyzed. Tomore » avoid confounding age and year, the authors compared the innermost rings of mature trees to trees of intermediate age and to saplings. The isotopic data were corrected for changes in isotopic composition and carbon dioxide concentration using published data from ice cores.« less

Provenance of cryoconite deposited on the glaciers of the Tibetan Plateau: New insights from Nd-Sr isotopic composition and size distribution

NASA Astrophysics Data System (ADS)

Dong, Zhiwen; Kang, Shichang; Qin, Dahe; Li, Yang; Wang, Xuejia; Ren, Jiawen; Li, Xiaofei; Yang, Jiao; Qin, Xiang

2016-06-01

This study presents the Nd-Sr isotopic compositions and size distributions of cryoconite deposited on the glaciers at different locations on the Tibetan Plateau, in order to trace its source areas and the provenance of long-range transported (LRT) Asian dust on the Tibetan Plateau. The result of scanning electron microscope-energy dispersive X-ray spectrometer analysis indicated that mineral dust particles were dominant in the cryoconite. Most of the cryoconite samples from the Tibetan Plateau indicated different Sr and Nd isotopic composition compared with sand from large deserts (e.g., the Taklimakan and Qaidam deserts). Some cryoconite samples showed very similar Nd-Sr isotopic ratios compared with those of nearby glacier basins (e.g., at Laohugou Glacier No.12, Dongkemadi Glacier, and Shiyi Glacier), indicating the potential input of local crustal dust to cryoconite. The volume-size distribution for the cryoconite particles also indicated bimodal distribution graphs with volume median diameters ranging from 0.57 to 20 µm and from 20 to 100 µm, demonstrating the contribution of both LRT Asian dust and local dust inputs to cryoconite. Based on the particle size distribution, we calculated a mean number ratio of local dust contribution to cryoconite ranging from 0.7% (Baishui Glacier No.1) to 17.6% (Shiyi Glacier) on the Tibetan Plateau. In general, the marked difference in the Nd-Sr isotopic ratios of cryoconite compared with those of large deserts probably indicates that materials from the western deserts have not been easily transported to the hinterland of Tibetan Plateau by the Westerlies under the current climatic conditions, and the arid deserts on the Tibetan Plateau are the most likely sources for cryoconite deposition. The resistance of the Tibetan Plateau to the Westerlies may have caused such phenomena, especially for LRT eolian dust transported over the Tibetan Plateau. Thus, this work is of great importance in understanding the large-scale eolian dust transport and climate over the Tibetan Plateau.

Provenance of cryoconite deposited on the glaciers of the Tibetan Plateau: new insights from Nd-Sr isotopic composition and size distribution

NASA Astrophysics Data System (ADS)

Dong, Z.

2016-12-01

This study presents the Nd-Sr isotopic compositions and size distributions of cryoconite deposited on the glaciers at different locations on the Tibetan Plateau, in order to trace its source areas and the provenance of long-range transported (LRT) Asian dust on the Tibetan Plateau. The result of SEM-EDS analysis indicated that mineral dust particles were dominant in the cryoconite. Most of the cryoconite samples from the Tibetan Plateau indicated different Sr and Nd isotopic composition compared with sand from large deserts (e.g., the Taklimakan and Qaidam deserts). Some cryoconite samples showed very similar Nd-Sr isotopic ratios compared with those of nearby glacier basins (e.g., at Laohugou Glacier No.12, Dongkemadi Glacier and Shiyi Glacier), indicating the potential input of local crustal dust to cryoconite. The volume-size distribution for the cryoconite particles also indicated bi-modal distribution graphs with volume median diameters ranging from 0.57 to 20 μm and from 20 to 100 μm, demonstrating the contribution of both LRT Asian dust and local dust inputs to cryoconite. Based on the particle size distribution, we calculated a mean number ratio of local dust contribution to cryoconite ranging from 0.7% (Baishui Glacier No.1) to 17.6% (Shiyi Glacier) on the Tibetan Plateau. In general, the marked difference in the Nd-Sr isotopic ratios of cryoconite compared with those of large deserts probably indicates that, materials from the western deserts have not been easily transported to the hinterland of Tibetan Plateau by the Westerlies under the current climatic conditions, and the arid deserts on the Tibetan Plateau are the most likely sources for cryoconite deposition. The resistance of the Tibetan Plateau to the Westerlies may have caused such phenomena, especially for LRT eolian dust transported over the Tibetan Plateau. Thus, this work is of great importance in understanding the large scale eolian dust transport and climate over the Tibetan Plateau.

The origin of volatile element depletion in early solar system material: Clues from Zn isotopes in chondrules

NASA Astrophysics Data System (ADS)

Pringle, Emily A.; Moynier, Frédéric; Beck, Pierre; Paniello, Randal; Hezel, Dominik C.

2017-06-01

Volatile lithophile elements are depleted in the different planetary materials to various degrees, but the origin of these depletions is still debated. Stable isotopes of moderately volatile elements such as Zn can be used to understand the origin of volatile element depletions. Samples with significant volatile element depletions, including the Moon and terrestrial tektites, display heavy Zn isotope compositions (i.e. enrichment of 66Zn vs. 64Zn), consistent with kinetic Zn isotope fractionation during evaporation. However, Luck et al. (2005) found a negative correlation between δ66Zn and 1/[Zn] between CI, CM, CO, and CV chondrites, opposite to what would be expected if evaporation caused the Zn abundance variations among chondrite groups. We have analyzed the Zn isotope composition of multiple samples of the major carbonaceous chondrite classes: CI (1), CM (4), CV (2), CO (4), CB (2), CH (2), CK (4), and CK/CR (1). The bulk chondrites define a negative correlation in a plot of δ66Zn vs 1/[Zn], confirming earlier results that Zn abundance variations among carbonaceous chondrites cannot be explained by evaporation. Exceptions are CB and CH chondrites, which display Zn systematics consistent with a collisional formation mechanism that created enrichment in heavy Zn isotopes relative to the trend defined by CI-CK. We further report Zn isotope analyses of chondrite components, including chondrules from Allende (CV3) and Mokoia (CV3), as well as an aliquot of Allende matrix. All chondrules are enriched in light Zn isotopes (∼500 ppm on 66Zn/64Zn) relative to the bulk, contrary to what would be expected if Zn were depleted during evaporation, on the other hand the matrix has a complementary heavy isotope composition. We report sequential leaching experiments in un-equilibrated ordinary chondrites, which show sulfides are isotopically heavy compared to silicates and the bulk meteorite by ca. +0.65 per mil on 66Zn/64Zn. We suggest isotopically heavy sulfides were removed from either chondrules or their precursors, thereby producing the light Zn isotope enrichments in chondrules.

Spatial and mineralogic variation of Na-Ca alteration in Laramide porphyry systems of Arizona

NASA Astrophysics Data System (ADS)

Runyon, S.; Seedorff, E.; Barton, M. D.; Mazdab, F. K.; Lecumberri-Sanchez, P.; Steele-MacInnis, M.

2017-12-01

Na-Ca alteration is characterized by the metasomatic addition of Ca ± Na and the loss of K. Minor volumes of Na-Ca alteration in Laramide porphyry systems develops from 3 to 8 km paleodepth. Mineral assemblages, mineral compositions, hydrogen isotopes, whole-rock analyses, and reconnaissance fluid inclusion characteristics have been documented for Na-Ca alteration in Laramide porphyry systems such as Tea Cup and Sierrita. Volumetrically minor Na-Ca alteration in Laramide porphyry systems documented in this study commonly takes the form of one of three mineral assemblages: albite-epidote-chlorite, Na-plagioclase-actinolite ± epidote, and garnet- or diopside-stable Na-plagioclase-actinolite ± epidote. These different Na-Ca mineral assemblages have broad spatial relationships, from shallow albite-chlorite-epidote to deeper Na-plagioclase-actinolite within a given district. Hydrogen isotope data on Na-Ca alteration minerals shows consistently distinct δD compositions of Na-Ca alteration minerals compared to igneous minerals in a given district. Further, calculated hydrogen isotope composition of fluids in equilibrium with Na-Ca alteration minerals are consistently enriched in δD compared to magmatic-hydrothermal fluids. Whole-rock analyses show consistent losses of K and variable addition of Na and Ca across different Na-Ca alteration assemblages. Na-Ca alteration has been well documented associated with the Jurassic arc. Previous studies demonstrated through mass balance, timing and spatial relationships, isotopic, and fluid inclusion studies that Na-Ca alteration associated with the Jurassic arc likely formed from the circulation of external, highly saline, non-magmatic fluids (e.g., Battles and Barton, 1995; Dilles et al., 1995). Na-Ca alteration documented in Laramide systems is generally similar to Na-Ca alteration documented along the Jurassic arc in mineral assemblages, compositions, and timing, but the volume of Na-Ca alteration in the Laramide systems is small as compared to the voluminous Na-Ca alteration documented in systems associated with the Jurassic arc.

Stable isotopes in water vapor and rainwater over Indian sector of Southern Ocean and estimation of fraction of recycled moisture.

PubMed

Rahul, P; Prasanna, K; Ghosh, Prosenjit; Anilkumar, N; Yoshimura, Kei

2018-05-15

Stable Hydrogen and Oxygen isotopic composition of water vapor, rainwater and surface seawater show a distinct trend across the latitude over the Southern Indian Ocean. Our observations on isotopic composition of surface seawater, water vapor and rainwater across a transect covering the tropical Indian Ocean to the regions of the Southern Ocean showed a strong latitudinal dependency; characterized by the zonal process of evaporation and precipitation. The sampling points were spread across diverse zones of SST, wind speed and rainfall regimes. The observed physical parameters such as sea surface temperature, wind speed and relative humidity over the oceanic regions were used in a box model calculation across the latitudes to predict the isotopic composition of water vapor under equilibrium and kinetic conditions, and compared with results from isotope enabled global spectral model. Further, we obtained the average fraction of recycled moisture across the oceanic transect latitudes as 13.4 ± 7.7%. The values of recycled fraction were maximum at the vicinity of the Inter Tropical Convergence Zone (ITCZ), while the minimum values were recorded over the region of subsidence and evaporation, at the Northern and Southern latitudes of the ITCZ. These estimates are consistent with the earlier reported recyling values.

[High-precision in situ analysis of the lead isotopic composition in copper using femtosecond laser ablation MC-ICP-MS and the application in ancient coins].

PubMed

Chen, Kai-Yun; Fan, Chao; Yuan, Hong-Lin; Bao, Zhi-An; Zong, Chun-Lei; Dai, Meng-Ning; Ling, Xue; Yang, Ying

2013-05-01

In the present study we set up a femtosecond laser ablation MC-ICP-MS method for lead isotopic analysis. Pb isotopic composition of fifteen copper (brass, bronze) standard samples from the National Institute of Standards Material were analyzed using the solution method (MC-ICP-MS) and laser method (fLA-MC-ICPMS) respectively, the results showed that the Pb isotopic composition in CuPb12 (GBW02137) is very homogeneous, and can be used as external reference material for Pb isotopic in situ analysis. On CuPb12 112 fLA-MC-ICPMS Pb isotope analysis, the weighted average values of the Pb isotopic ratio are in good agreement with the results analyzed by bulk solution method within 2sigma error, the internal precision RSEs of the 208 Pb/204 Pb ratio and 207 Pb/206 Pb ratio are less than 90 and 40 ppm respectively, and the external precision RSDs of them are less than 60 and 30 ppm respectively. Pb isotope of thirteen ancient bronze coins was analyzed via fLA-MC-ICPMS, the results showed that the Pb isotopic composition of ancient coins of different dynasties is significantly different, and not all the Pb isotopic compositions in the coins even from the same dynasty are in agreement with each other.

Oxygen and strontium isotope tracing of human migration at the Bell Beaker site Le Tumulus des Sables, France.

NASA Astrophysics Data System (ADS)

Willmes, Malte; James, Hannah; Boel, Ceridwen; Courtaud, Patrice; Chancerel, Antoine; McMorrow, Linda; Armstrong, Richard; Kinsley, Les; Aubert, Maxime; Eggins, Stephen; Moffat, Ian; Grün, Rainer

2014-05-01

Oxygen (δ18O) and strontium (87Sr/86Sr) isotopes were used as tools to investigate human migration at the early Bell Beaker site (2500-2000 BC) Le Tumulus des Sables, Saint-Laurent-Médoc, south-west France. The O and Sr isotope ratios measured in tooth enamel record the average dietary isotope signature ingested by that individual during their childhood. When this data is compared to the isotope signature of the burial site it can be used to indicate if the individual migrated into this area during their lifetime. The O isotopic composition of meteoric water changes depending on climate, temperature and quantity of precipitation. O isotope ratios in skeletal and dental remains are related to body water, which in turn is influenced by diet, physiology and climate. Most of the water consumed by large mammals comes from drinking water, typically sourced locally. Sr isotope ratios on the other hand vary between different geologic regions, depending on their age and composition. Sr is released through weathering and transported into the soil, ground and surface water, where it becomes available for uptake by plants, enters the food cycle and eventually ends up in skeletal and dental tissue where it substitutes for calcium. We analysed the teeth of 18 adult and 8 juvenile disarticulated skeletons from Le Tumulus des Sables. O isotopes were analysed in-situ by Sensitive High Resolution Ion Micro Probe (SHRIMP).The Sr isotope analysis involved drilling a 0.2-0.5 mg sample of enamel from the tooth. The Sr was then chemically separated and analysed by Thermal Ionization Mass Spectrometry (TIMS). These results were then compared to the O isoscape of Europe and bioavailable Sr isotope data (fauna, plants, soils) from the IRHUM database. We found that most of the individuals at Le Tumulus des Sables show O and Sr isotope ratios corresponding to the local environmental signal and we interpret these as part of the local population. 3 adults however show slightly higher 87Sr/86Sr ratios, which correspond to a clay and limestone unit in close proximity (

Human drinking water compared with river waters throughout the United States with respect to their stable hydrogen and oxygen isotopic composition

NASA Astrophysics Data System (ADS)

Landwehr, J. M.; Coplen, T. B.; Qi, H.

2009-04-01

The composition of stable isotopes of hydrogen (^2H) and oxygen (^18O) in animal tissues, such as hair, nail, teeth and bone, has been used to trace migrations and geographic origin of individuals. Variations of these isotopic ratios in tissue are known to show significant correlations with the isotopic composition of ingested water, as well as with diet and other oxygen sources. Drinking water in natural ecosystems is defined by what is locally available for animal consumption, primarily surface waters such as streams, ponds, lakes, seeps, springs, etc. Tap water provides the drinking water in many human ecosystems. It may derive from local sources but can also draw on more diverse sources, such as large rivers with watersheds larger than those of local creeks, deep ground waters or even imported supplies, which may be isotopically distinct from local ecosystem supplies. Because of the potentially complex hydrologic pathways of water sources available in either animal or human ecosystems, the stable isotopic composition of these supplies may differ significantly from that of the (weighted average) local precipitation which is sometimes used to represent local water supplies. For example, water samples taken from three different taps in Washington, D.C., USA, on August 15, 2007, had measured ^2H and ^18O values of -41.7 per mill and -6.13 per mill, -41.7 per mill and -6.06 per mill, and -42.2 per mill and -6.22 per mill, respectively. A water sample taken on the same day from the Potomac River, which is the source of the D.C. water supply, had ^2H and ^18O values of -41.7 per mill and -6.06 per mill, respectively, consistent with that of the urban tap water. However, precipitation samples collected locally in Reston, Virginia, USA, had ^2H and ^18O values of -16.1 per mill and -3.13 per mill, respectively, for the week ending on August 15, 2007; -17.5 per mill and -3.40 per mill, respectively, for the month preceding August 15, 2007; and -13.6 per mill and -3.39 per mill, respectively, for the average values for the month of August over three years. The isotopic composition of local precipitation was significantly more positive than that for the concurrently available tap water and the river water from which it was drawn. Thus, in order to allow valid geographic inferences for forensic purposes, it is necessary to have available the measured isotopic composition of drinking waters or of their appropriate sources. We have now collected tap water samples concurrently at 345 sites throughout the United States and measured ^2H and ^18O during both summer (2007) and winter (2008) seasons. Since large rivers are frequently the source of urban water supplies, we compare this information with data published for rivers and streams throughout the United States (Coplen and Kendall, 2000). These data and analyses should inform the use of stable isotopes of water for forensic determinations.

A Comparison of Anorthositic Lunar Lithologies: Variation on the FAN Theme

NASA Technical Reports Server (NTRS)

Nyquist, L. E.; Shih, C-Y.; Yamaguchi, A.; Mittlefehldt, D. W.; Peng, Z. X.; Park, J.; Herzog, G. F.; Shirai, N.

2014-01-01

Certain anorthositic rocks that are rare in the returned lunar samples have been identified among lunar meteorites. The variety of anorthosites in the Apollo collection also is more varied than is widely recognized. James eta. identified three lithologies in a composite clast o ferroan anorthosite (FAN)-suite rocks in lunar breccia 64435. They further divided all FANs into four subgroups: anorthositic ferroan (AF), mafic magnesian (MM), mafic ferroan (MF), and anorthositic sodic (AS, absent in the 64435 clast). Here we report Sm-Nd isotopic studies of the lithologies present in the 64435 composite clast and compare the new data to our previous data for lunar anorthosites incuding lunar anorthositic meteorites. Mineralogy-petrography, in situ trace element studies, Sr-isotope studies, and Ar-Ar chronology are included, but only the Nd-isotopic studies are currently complete.

Statistical clumped isotope signatures

PubMed Central

Röckmann, T.; Popa, M. E.; Krol, M. C.; Hofmann, M. E. G.

2016-01-01

High precision measurements of molecules containing more than one heavy isotope may provide novel constraints on element cycles in nature. These so-called clumped isotope signatures are reported relative to the random (stochastic) distribution of heavy isotopes over all available isotopocules of a molecule, which is the conventional reference. When multiple indistinguishable atoms of the same element are present in a molecule, this reference is calculated from the bulk (≈average) isotopic composition of the involved atoms. We show here that this referencing convention leads to apparent negative clumped isotope anomalies (anti-clumping) when the indistinguishable atoms originate from isotopically different populations. Such statistical clumped isotope anomalies must occur in any system where two or more indistinguishable atoms of the same element, but with different isotopic composition, combine in a molecule. The size of the anti-clumping signal is closely related to the difference of the initial isotope ratios of the indistinguishable atoms that have combined. Therefore, a measured statistical clumped isotope anomaly, relative to an expected (e.g. thermodynamical) clumped isotope composition, may allow assessment of the heterogeneity of the isotopic pools of atoms that are the substrate for formation of molecules. PMID:27535168

Spatial patterns of throughfall isotopic composition at the event and seasonal timescales

Treesearch

Scott T. Allen; Richard F. Keim; Jeffrey J. McDonnell

2015-01-01

Spatial variability of throughfall isotopic composition in forests is indicative of complex processes occurring in the canopy and remains insufficiently understood to properly characterize precipitation inputs to the catchment water balance. Here we investigate variability of throughfall isotopic composition with the objectives: (1) to quantify the spatial variability...

The effect of bonding environment on iron isotope fractionation between minerals at high temperature

NASA Astrophysics Data System (ADS)

Sossi, Paolo A.; O'Neill, Hugh St. C.

2017-01-01

Central to understanding the processes that drive stable isotope fractionation in nature is their quantification under controlled experimental conditions. The polyvalent element iron, given its abundance in terrestrial rocks, exerts controls on the structural and chemical properties of minerals and melts. The iron isotope compositions of typical high temperature minerals are, however, poorly constrained and their dependence on intensive (e.g. fO2) and extensive (e.g. compositional) variables is unknown. In this work, experiments involving a reference phase, 2 M FeCl2·4H2O(l), together with an oxide mix corresponding to the bulk composition of the chosen mineral were performed in a piston cylinder in Ag capsules. The oxide mix crystallised in situ at 1073 K and 1 GPa, in equilibrium with the iron chloride, and was held for 72 h. In order to characterise the effect of co-ordination and oxidation state on the isotope composition independently, exclusively Fe2+ minerals were substituted in: VIII-fold almandine, VI-fold ilmenite, fayalite and IV-fold chromite and hercynite. Δ57FeMin-FeCl2 increases in the order VIII < VI < IV, consistent with a decrease in the mean Fe-O bond length. Magnetite, which has mixed VI- and IV-fold co-ordination, has the heaviest Δ57Fe by virtue of 2/3 of its iron being the smaller, ferric ion. The composition of the VIFe2+-bearing minerals is similar to that of the aqueous FeCl2 fluid. To the degree that this represents the speciation of iron in fluids exsolving from magmas, the fractionation between them should be small, unless the iron is hosted in magnetite. By contrast, predominantly Fe2+-bearing mantle garnets should preserve a much lighter δ57Fe than their lower pressure spinel counterparts, a signature that may be reflected in partial melts from these lithologies. As the Fe-O bond lengths in fayalite and ilmenite are comparable, their isotope compositions overlap, suggesting that high Ti mare basalts acquired their heavy isotopic signature from ilmenite that crystallised late during lunar magma ocean solidification.

The Effects of Core Composition on Iron Isotope Fractionation During Planetary Differentiation

NASA Astrophysics Data System (ADS)

Elardo, S. M.; Shahar, A.; Caracas, R.; Mock, T. D.; Sio, C. K. I.

2018-05-01

High pressure and temperature isotope exchange experiments and density functional theory calculations show how the composition of planetary cores affects the fractionation of iron isotopes during planetary differentiation.

Influences on the stable oxygen and carbon isotopes in gerbillid rodent teeth in semi-arid and arid environments: Implications for past climate and environmental reconstruction

NASA Astrophysics Data System (ADS)

Jeffrey, Amy; Denys, Christiane; Stoetzel, Emmanuelle; Lee-Thorp, Julia A.

2015-10-01

The stable isotope composition of small mammal tissues has the potential to provide detailed information about terrestrial palaeoclimate and environments, because their remains are abundant in palaeontological and archaeological sites, and they have restricted home ranges. Applications to the Quaternary record, however, have been sparse and limited by an acute lack of understanding of small mammal isotope ecology, particularly in arid and semi-arid environments. Here we document the oxygen and carbon isotope composition of Gerbillinae (gerbil) tooth apatite across a rainfall gradient in northwestern Africa, in order to test the relative influences of the 18O/16O in precipitation or moisture availability on gerbil teeth values, the sensitivity of tooth apatite 13C/12C to plant responses to moisture availability, and the influence of developmental period on the isotopic composition of gerbil molars and incisors. The results show that the isotopic composition of molars and incisors from the same individuals differs consistent with the different temporal periods reflected by the teeth; molar teeth are permanently rooted and form around the time of birth, whereas incisors grow continuously. The results indicate that tooth choice is an important consideration for applications as proxy Quaternary records, but also highlights a new potential means to distinguish seasonal contexts. The oxygen isotope composition of gerbil tooth apatite is strongly correlated with mean annual precipitation (MAP) below 600 mm, but above 600 mm the teeth reflect the oxygen isotope composition of local meteoric water instead. Predictably, the carbon isotope composition of the gerbil teeth reflected C3 and C4 dietary inputs, however arid and mesic sites could not be distinguished because of the high variability displayed in the carbon isotope composition of the teeth due to the microhabitat and short temporal period reflected by the gerbil. We show that the oxygen isotope composition of small mammal teeth strongly reflects moisture availability in semi-arid and arid environments and would provide an excellent record of palaeo-aridity in a terrestrial setting. The results illustrate that an understanding of an animal's physiology is essential for interpreting the animal's isotopic responses to external contexts, especially in arid zones.

Stable lead isotopic analyses of historic and contemporary lead contamination of San Francisco Bay estuary

USGS Publications Warehouse

Ritson, P.I.; Bouse, R.M.; Flegal, A.R.; Luoma, S.N.

1999-01-01

Variations in stable lead isotopic composition (240Pb, 206Pb, 207Pb, 208Pb) in three sediment cores from the San Francisco Bay estuary document temporal changes in sources of lead during the past two centuries. Sediment, with lead from natural geologic sources, and relatively homogeneous lead isotopic compositions are overlain by sediments whose isotopic compositions indicate change in the sources of lead associated with anthropogenic modification of the estuary. The first perturbations of lead isotopic composition in the cores occur in the late 1800s concordant with the beginning of industrialization around the estuary. Large isotopic shifts, toward lower 206Pb/207Pb, occur after the turn of the century in both Richardson and San Pablo Bays. A similar relationship among lead isotopic compositions and lead concentrations in both Bays suggest contamination from the same source (a lead smelter). The uppermost sediments (post 1980) of all cores also have a relatively homogenous lead isotopic composition distinct from pre-anthropogenic and recent aerosol signatures. Lead isotopic compositions of leachates from fourteen surface sediments and five marsh samples from the estuary were also analyzed. These analyses suggest that the lead isotopic signature identified in the upper horizons of the cores is spatially homogeneous among recently deposited sediments throughout the estuary. Current aerosol lead isotopic compositions [Smith, D.R., Niemeyer, S., Flegal, A.R., 1992. Lead sources to California sea otters: industrial inputs circumvent natural lead biodepletion mechanisms. Environmental Research 57, 163-175] are distinct from the isotopic compositions of the surface sediments, suggesting that the major source of lead is cycling of historically contaminated sediments back through the water column. Both the upper core sediments and surface sediments apparently derive their lead predominantly from sources internal to the estuary. These results support the idea that geochemical cycling of lead between sediments and water accounts for persistently elevated lead concentrations in the water column despite 10-fold reduction of external source inputs to San Francisco Bay [Flegal, A.R., Rivera-Duarte, I., Ritson, P.I., Scelfo, G., Smith, G.J., Gordon, M., Sanudo-Wilhelmy, S.A., 1996. Metal contamination in San Francisco Waters: historic perturbations, contemporary concentrations, and future considerations in San Francisco Bay. In: Hollobaugh, J.T. (Ed.), The Ecosystem. AAAS, pp. 173-188].

Experimental identification of Ca isotopic fractionations in higher plants

NASA Astrophysics Data System (ADS)

Cobert, Florian; Schmitt, Anne-Désirée; Bourgeade, Pascale; Labolle, François; Badot, Pierre-Marie; Chabaux, François; Stille, Peter

2011-10-01

Hydroponic experiments have been performed in order to identify the co-occurring geochemical and biological processes affecting the Ca isotopic compositions within plants. To test the influence of the Ca concentration and pH of the nutritive solution on the Ca isotopic composition of the different plant organs, four experimental conditions were chosen combining two different Ca concentrations (5 and 60 ppm) and two pHs (4 and 6). The study was performed on rapid growing bean plants in order to have a complete growth cycle. Several organs (root, stem, leaf, reproductive) were sampled at two different growth stages (10 days and 6 weeks of culture) and prepared for Ca isotopic measurements. The results allow to identify three Ca isotopic fractionation levels. The first one takes place when Ca enters the lateral roots, during Ca adsorption on cation-exchange binding sites in the apoplasm. The second one takes place when Ca is bound to the polygalacturonic acids (pectins) of the middle lamella of the xylem cell wall. Finally, the last fractionation occurs in the reproductive organs, also caused by cation-exchange processes with pectins. However, the cell wall structures of these organs and/or number of available exchange sites seem to be different to those of the xylem wall. These three physico-chemical fractionation mechanisms allow to enrich the organs in the light 40Ca isotope. The amplitude of the Ca isotopic fractionation within plant organs is highly dependent on the composition of the nutritive solution: low pH (4) and Ca concentrations (5 ppm) have no effect on the biomass increase of the plants but induce smaller fractionation amplitudes compared to those obtained from other experimental conditions. Thus, Ca isotopic signatures of bean plants are controlled by the external nutritive medium. This study highlights the potential of Ca isotopes to be applied in plant physiology (to identify Ca uptake, circulation and storage mechanisms within plants) and in biogeochemistry (to identify Ca recycling, Ca content and pH evolutions in soil solutions through time).

Ba isotopic compositions in stardust SiC grains from the Murchison meteorite: Insights into the stellar origins of large SiC grains

NASA Astrophysics Data System (ADS)

Ávila, Janaína N.; Ireland, Trevor R.; Gyngard, Frank; Zinner, Ernst; Mallmann, Guilherme; Lugaro, Maria; Holden, Peter; Amari, Sachiko

2013-11-01

We report barium isotopic measurements in 12 large (7-58 μm) stardust silicon carbide grains recovered from the Murchison carbonaceous chondrite. The C-, N-, and Si-isotopic compositions indicate that all 12 grains belong to the mainstream population and, as such, are interpreted to have condensed in the outflows of low-mass carbon-rich asymptotic giant branch (AGB) stars with close-to-solar metallicity. Barium isotopic analyses were carried out on the Sensitive High Resolution Ion Microprobe - Reverse Geometry (SHRIMP-RG) with combined high mass resolution and energy filtering to eliminate isobaric interferences from molecular ions. Contrary to previous measurements in small (<5 μm) mainstream grains, the analyzed large SiC grains do not show the classical s-process enrichment, having near solar Ba isotopic compositions. While contamination with solar material is a common explanation for the lack of large isotopic anomalies in stardust SiC grains, particularly for these large grains which have low trace element abundances, our results are consistent with previous observations that Ba isotopic ratios are dependent on grain size. We have compared the SiC data with theoretical predictions of the evolution of Ba isotopic ratios in the envelopes of low-mass AGB stars with a range of stellar masses and metallicities. The Ba isotopic measurements obtained for large SiC grains from the LS + LU fractions are consistent with grain condensation in the envelope of very low-mass AGB stars (1.25 M⊙) with close-to-solar metallicity, which suggests that conditions for growth of large SiC might be more favorable in very low-mass AGB stars during the early C-rich stages of AGB evolution or in stable structures around AGB stars whose evolution was cut short due to binary interaction, before the AGB envelope had already been largely enriched with the products of s-process nucleosynthesis.

Stable Carbon Fractionation In Size Segregated Aerosol Particles Produced By Controlled Biomass Burning

NASA Astrophysics Data System (ADS)

Masalaite, Agne; Garbaras, Andrius; Garbariene, Inga; Ceburnis, Darius; Martuzevicius, Dainius; Puida, Egidijus; Kvietkus, Kestutis; Remeikis, Vidmantas

2014-05-01

Biomass burning is the largest source of primary fine fraction carbonaceous particles and the second largest source of trace gases in the global atmosphere with a strong effect not only on the regional scale but also in areas distant from the source . Many studies have often assumed no significant carbon isotope fractionation occurring between black carbon and the original vegetation during combustion. However, other studies suggested that stable carbon isotope ratios of char or BC may not reliably reflect carbon isotopic signatures of the source vegetation. Overall, the apparently conflicting results throughout the literature regarding the observed fractionation suggest that combustion conditions may be responsible for the observed effects. The purpose of the present study was to gather more quantitative information on carbonaceous aerosols produced in controlled biomass burning, thereby having a potential impact on interpreting ambient atmospheric observations. Seven different biomass fuel types were burned under controlled conditions to determine the effect of the biomass type on the emitted particulate matter mass and stable carbon isotope composition of bulk and size segregated particles. Size segregated aerosol particles were collected using the total suspended particle (TSP) sampler and a micro-orifice uniform deposit impactor (MOUDI). The results demonstrated that particle emissions were dominated by the submicron particles in all biomass types. However, significant differences in emissions of submicron particles and their dominant sizes were found between different biomass fuels. The largest negative fractionation was obtained for the wood pellet fuel type while the largest positive isotopic fractionation was observed during the buckwheat shells combustion. The carbon isotope composition of MOUDI samples compared very well with isotope composition of TSP samples indicating consistency of the results. The measurements of the stable carbon isotope ratio in size segregated aerosol particles suggested that combustion processes could strongly affect isotopic fractionation in aerosol particles of different sizes thereby potentially affecting an interpretation of ambient atmospheric observations.

A 1400 km geochemical transect along the Central American Arc: Summary of mafic Holocene volcanism from Guatemala to Panama

NASA Astrophysics Data System (ADS)

Geldmacher, J.; Hoernle, K.; Gill, J. B.; Hauff, F.; Heydolph, K.

2016-12-01

It is generally accepted that subducted oceanic crust and sediments contribute to the composition of arc magmas. Systematic variations of input parameters (including age, subduction angle, and chemical composition of the subducting material) make the Central American Volcanic Arc (CAVA), which extends from Guatemala in the northwest through El Salvador, Honduras, Nicaragua, Costa Rica and Panama to the southeast, a prime study object. We present a comprehensive (major and trace element and Sr-Nd-Pb-Hf isotope data) and consistent (all data generated in the same labs using the same methods and data reduction procedures) compilation of published and unpublished Holocene mafic volcanic rocks sampled along the entire arc. New data include Sr and, for the first time, Hf isotope data from the entire CAVA as well as major and trace element data for 43 samples from southern Nicaragua and central Costa Rica from which only isotopic compositions were previously published. The combined elemental and isotopic data confirm the influence of distinct subduction components on the composition of CAVA magmas. Along-arc geochemical variations (especially delta 208Pb/204Pb) of volcanic front magmas in Costa Rica and Panama have been explained by the different compositions of seamounts/ridges of the isotopically zoned Galápagos hotspot track that covers the subducting Cocos Plate in this sector of the arc (Hoernle et al. 2008, Nature 451). Our new data confirm this relationship with arc lavas from Costa Rica having higher 87Sr/86Sr ratios than those from western Panama reflecting a similar spatial-compositional distinction in the subducting hotspot track beneath them. In contrast, 176Hf/177Hf shows no comparable variations in this sector of the arc, indicating that the Hf is primarily derived from the mantle wedge rather than the subducting slab. Although small degree hydrous melts are believed to fertilize the mantle wedge beneath Costa Rica, residual zircon may hold back the Hf.

Silicon isotope amount ratios and molar masses for two silicon isotope reference materials: IRMM-018a and NBS28

NASA Astrophysics Data System (ADS)

Valkiers, S.; Ding, T.; Inkret, M.; Ruße, K.; Taylor, P.

2005-04-01

A new 2 kg batch of SiO2 crystals, IRMM-018a as well as the existing NBS28 silica sand (or RM 8546, obtained by I. Friedman from U.S. Geological Survey) have been characterised for their "absolute" silicon isotope composition and molar mass. The amount-of-substance measurements needed for that purpose were performed on the IRMM amount comparator (Avogadro II) on samples from these batches, which were converted to gaseous silicon tetra-fluoride (SiF4). The isotope amount ratio measurements were calibrated by means of synthesized isotope amount ratios realized in the form of synthetic Si isotope mixtures, the measurement procedure of which makes them SI-traceable. IRMM-018a is intended to be used as Isotope Reference Material for isotope amount measurements in geochemical and other isotope abundance studies of silicon. It is distributed in samples of about 0.1 mol and will replace IRMM-018 (exhausted).

Isotopic compositions of the elements, 2001

USGS Publications Warehouse

Böhlke, J.K.; De Laeter, J. R.; De Bievre, P.; Hidaka, H.; Peiser, H.S.; Rosman, K.J.R.; Taylor, P.D.P.

2005-01-01

The Commission on Atomic Weights and Isotopic Abundances of the International Union of Pure and Applied Chemistry completed its last review of the isotopic compositions of the elements as determined by isotope-ratio mass spectrometry in 2001. That review involved a critical evaluation of the published literature, element by element, and forms the basis of the table of the isotopic compositions of the elements (TICE) presented here. For each element, TICE includes evaluated data from the “best measurement” of the isotope abundances in a single sample, along with a set of representative isotope abundances and uncertainties that accommodate known variations in normal terrestrial materials. The representative isotope abundances and uncertainties generally are consistent with the standard atomic weight of the element Ar(E)">Ar(E)Ar(E) and its uncertainty U[Ar(E)]">U[Ar(E)]U[Ar(E)] recommended by CAWIA in 2001.

Calcium Isotopic Compositions of Forearc Sediments from DSDP Site 144

NASA Astrophysics Data System (ADS)

Zhang, Z.; Zhu, H.; Nan, X.; Li, X.; Huang, F.

2016-12-01

It is important to investigate calcium isotopic compositions of reservoirs of the Earth for better application of Ca isotopes into studies of a variety of geochemical problems. Because Ca isotopic compositions for igneous rocks and carbonates are increasingly reported, this maybe bring new requirements on carefully understanding the isotopic compositions of subducted marine sediments. Marine sediments mainly contains carbonates and clays, controlling the compositions of slab-derived materials which are added to the mantle wedge. Obviously, it could have different elemental and calcium isotopic compositions with marine carbonate. Thus, it could also put biases on calcium isotopic signatures of basalts resulted from recycling oceanic carbonate into the mantle. Here, we report calcium isotopic compositions of 17 sediment samples from Deep Sea Drilling Project (DSDP) site 144 (09°27.23' N, 54°20.52' W) which is located about 400 km north of Surinam on the northern flank of the Demerara Rise with a water depth of 2957 meters. These samples have CaO contents ranging from 14.56 wt.% to 41.46 wt.% with an average of 29.61 ± 18.21 (2SD), δ44/40Ca ranges from 0.19 to 0.58 (relative to SRM915a) with an average of 0.40 ± 0.22 (2SD). These carbonate-rich sediments can be used to represent an endmember with high CaO content and low δ44/40Ca, which could modify chemical composition of the upper mantle and subduction zone lavas if they are recycled to the convective mantle during subduction. The positive linear correlation between CaO and δ44/40Ca in the sediments cannot be explained by a simple mixing between marine carbonate and clay. Instead, δ44/40Ca of these samples roughly increase from the Upper Cretaceous to the Early Oligocene, which might reflect the evolution of calcium isotopic compositions of seawater through time.

Lignin methoxyl hydrogen isotope ratios in a coastal ecosystem

NASA Astrophysics Data System (ADS)

Feakins, Sarah J.; Ellsworth, Patricia V.; Sternberg, Leonel da Silveira Lobo

2013-11-01

Stable hydrogen isotope ratios of plant lignin methoxyl groups have recently been shown to record the hydrogen isotopic composition of meteoric water. Here we extend this technique towards tracing water source variations across a saltwater to freshwater gradient in a coastal, subtropical forest ecosystem. We measure the hydrogen isotopic composition of xylem water (δDxw) and methoxyl hydrogen (δDmethoxyl) to calculate fractionations for coastal mangrove, buttonwood and hammock tree species in Sugarloaf Key, as well as buttonwoods from Miami, both in Florida, USA. Prior studies of the isotopic composition of cellulose and plant leaf waxes in coastal ecosystems have yielded only a weak correlation to source waters, attributed to leaf water effects. Here we find δDmethoxyl values range from -230‰ to -130‰, across a 40‰ range in δDxw with a regression equation of δDmethoxyl ‰ = 1.8 * δDxw - 178‰ (R2 = 0.48, p < 0.0001, n = 74). This is comparable within error to the earlier published relationship for terrestrial trees which was defined across a much larger 125‰ isotopic range in precipitation. Analytical precision for measurements of δD values of pure CH3I by gas chromatography-pyrolysis-isotope ratio mass spectrometry (GC-P-IRMS) is σ = 6‰ (n = 31), which is considerably better than for CH3I liberated through cleavage with HI from lignin with σ = 18‰ (n = 26). Our results establish that δDmethoxyl can record water sources and salinity incursion in coastal ecosystems, where variations sufficiently exceed method uncertainties (i.e., applications with δD excursions >50‰). For the first time, we also report yields of propyl iodide, which may indicate lignin synthesis of propoxyl groups under salt-stress.

Re — Os isotopic constraints on the origin of volcanic rocks, Gorgona Island, Colombia: Os isotopic evidence for ancient heterogeneities in the mantle

NASA Astrophysics Data System (ADS)

Walker, R. J.; Echeverria, L. M.; Shirey, S. B.; Horan, M. F.

1991-04-01

The Re — Os isotopic systematics of komatiites and spatially associated basalts from Gorgona Island, Colombia, indicate that they were produced at 155±43 Ma. Subsequent episodes of volcanism produced basalts at 88.1±3.8 Ma and picritic and basaltic lavas at ca. 58 Ma. The age for the ultramafic rocks is important because it coincides with the late-Jurassic, early-Cretaceous disassembly of Pangea, when the North- and South-American plates began to pull apart. Deep-seated mantle upwelling possibly precipitated the break-up of these continental plates and caused a tear in the subducting slab west of Gorgona, providing a rare, late-Phanerozoic conduit for the komatiitic melts. Mantle sources for the komatiites were heterogeneous with respect to Os and Pb isotopic compositions, but had homogeneous Nd isotopic compositions (ɛNd+9±1). Initial 187Os/186Os normalized to carbonaceous chondrites at 155 Ma (γOs) ranged from 0 to +22, and model-initial μ values ranged from 8.17 to 8.39. The excess radiogenic Os, compared with an assumed bulk-mantle evolution similar to carbonaceous chondrites, was likely produced in portions of the mantle with long-term elevated Re concentrations. The Os, Pb and Nd isotopic compositions, together with major-element constraints, suggest that the sources of the komatiites were enriched more than 1 Ga ago by low (<20%) and variable amounts of a basalt or komatiite component. This component was added as either subducted oceanic crust or melt derived from greater depths in the mantle. These results suggest that the Re — Os isotope system may be a highly sensitive indicator of the presence of ancient subducted oceanic crust in mantle-source regions.

Re - Os isotopic constraints on the origin of volcanic rocks, Gorgona Island, Colombia: Os isotopic evidence for ancient heterogeneities in the mantle

USGS Publications Warehouse

Walker, R.J.; Echeverria, L.M.; Shirey, S.B.; Horan, M.F.

1991-01-01

The Re - Os isotopic systematics of komatiites and spatially associated basalts from Gorgona Island, Colombia, indicate that they were produced at 155??43 Ma. Subsequent episodes of volcanism produced basalts at 88.1??3.8 Ma and picritic and basaltic lavas at ca. 58 Ma. The age for the ultramafic rocks is important because it coincides with the late-Jurassic, early-Cretaceous disassembly of Pangea, when the North- and South-American plates began to pull apart. Deep-seated mantle upwelling possibly precipitated the break-up of these continental plates and caused a tear in the subducting slab west of Gorgona, providing a rare, late-Phanerozoic conduit for the komatiitic melts. Mantle sources for the komatiites were heterogeneous with respect to Os and Pb isotopic compositions, but had homogeneous Nd isotopic compositions (??Nd+9??1). Initial 187Os/186Os normalized to carbonaceous chondrites at 155 Ma (??Os) ranged from 0 to +22, and model-initial ?? values ranged from 8.17 to 8.39. The excess radiogenic Os, compared with an assumed bulk-mantle evolution similar to carbonaceous chondrites, was likely produced in portions of the mantle with long-term elevated Re concentrations. The Os, Pb and Nd isotopic compositions, together with major-element constraints, suggest that the sources of the komatiites were enriched more than 1 Ga ago by low (<20%) and variable amounts of a basalt or komatiite component. This component was added as either subducted oceanic crust or melt derived from greater depths in the mantle. These results suggest that the Re - Os isotope system may be a highly sensitive indicator of the presence of ancient subducted oceanic crust in mantle-source regions. ?? 1991 Springer-Verlag.

Barium isotope fractionation during witherite (BaCO3) dissolution, precipitation and at equilibrium

NASA Astrophysics Data System (ADS)

Mavromatis, Vasileios; van Zuilen, Kirsten; Purgstaller, Bettina; Baldermann, Andre; Nägler, Thomas F.; Dietzel, Martin

2016-10-01

This study examines the behavior of Ba isotope fractionation between witherite and fluid during mineral dissolution, precipitation and at chemical equilibrium. Experiments were performed in batch reactors at 25 °C in 10-2 M NaCl solution where the pH was adjusted by continuous bubbling of a water saturated gas phase of CO2 or atmospheric air. During witherite dissolution no Ba isotope fractionation was observed between solid and fluid. In contrast, during witherite precipitation, caused by a pH increase, a preferential uptake of the lighter 134Ba isotopomer in the solid phase was observed. In this case, the isotope fractionation factor αwitherite-fluid is calculated to be 0.99993 ± 0.00004 (or Δ137/134Bawitherite-fluid ≈ -0.07 ± 0.04‰, 2 sd). The most interesting feature of this study, however, is that after the attainment of chemical equilibrium, the Ba isotope composition of the aqueous phase is progressively becoming lighter, indicating a continuous exchange of Ba2+ ions between witherite and fluid. Mass balance calculations indicate that the detachment of Ba from the solid is not only restricted to the outer surface layer of the solid, but affects several (∼7 unit cells) subsurface layers of the crystal. This observation comes in excellent agreement with the concept of a dynamic system at chemical equilibrium in a mineral-fluid system, denoting that the time required for the achievement of isotopic equilibrium in the witherite-fluid system is longer compared to that observed for chemical equilibrium. Overall, these results indicate that the isotopic composition of Ba bearing carbonates in natural environments may be altered due to changes in fluid composition without a net dissolution/precipitation to be observed.

Isotopic compositions of carbonates and organic carbon from upper Proterozoic successions in Namibia: stratigraphic variation and the effects of diagenesis and metamorphism

NASA Technical Reports Server (NTRS)

Kaufman, A. J.; Hayes, J. M.; Knoll, A. H.; Germs, G. J.

1991-01-01

The carbon isotope geochemistry of carbonates and organic carbon in the late Proterozoic Damara Supergroup of Namibia, including the Nama, Witvlei, and Gariep groups on the Kalahari Craton and the Mulden and Otavi groups on the Congo Craton, has been investigated as an extension of previous studies of secular variations in the isotopic composition of late Proterozoic seawater. Subsamples of microspar and dolomicrospar were determined, through petrographic and cathodoluminescence examination, to represent the "least-altered" portions of the rock. Carbon-isotopic abundances in these phases are nearly equal to those in total carbonate, suggesting that 13C abundances of late Proterozoic fine-grained carbonates have not been significantly altered by meteoric diagenesis, although 18O abundances often differ significantly. Reduced and variable carbon-isotopic differences between carbonates and organic carbon in these sediments indicate that isotopic compositions of organic carbon have been altered significantly by thermal and deformational processes, likely associated with the Pan-African Orogeny. Distinctive stratigraphic patterns of secular variation, similar to those noted in other, widely separated late Proterozoic basins, are found in carbon-isotopic compositions of carbonates from the Nama and Otavi groups. For example, in Nama Group carbonates delta 13C values rise dramatically from -4 to +5% within a short stratigraphic interval. This excursion suggests correlation with similar excursions noted in Ediacaran-aged successions of Siberia, India, and China. Enrichment of 13C (delta 13C> +5%) in Otavi Group carbonates reflects those in Upper Riphean successions of the Akademikerbreen Group, Svalbard, its correlatives in East Greenland, and the Shaler Group, northwest Canada. The widespread distribution of successions with comparable isotopic signatures supports hypotheses that variations in delta 13C reflect global changes in the isotopic composition of late Proterozoic seawater. Within the Damara basin, carbon-isotopic compositions of carbonates provide a potentially useful tool for the correlation of units between the Kalahari and Congo cratons. Carbonates depleted in 13C were deposited during and immediately following three separate glacial episodes in Namibia. The correspondence between ice ages and negative delta 13C excursions may reflect the effects of lowered sea levels; enhanced circulation of deep, cold, O2-rich seawater; and/or the upwelling of 13C-depleted deep water. Iron-formation is additionally associated with one of the glacial horizons, the Chuos tillite. Carbon-13 enriched isotopic abundances in immediately pre-glacial carbonates suggest that oceanographic conditions favored high rates of organic burial. It is likely that marine waters were stratified, with deep waters anoxic. A prolonged period of ocean stratification would permit the build-up of ferrous iron, probably from hydrothermal sources. At the onset of glaciation, upwelling would have brought 13C-depleted and iron-rich deep water onto shallow shelves where contact with cold, oxygenated surface waters led to the precipitation of ferric iron.

A petrologic comparison of Triassic plutonism in the San Gabriel and Mule Mountains, southern California

NASA Astrophysics Data System (ADS)

Barth, Andrew P.; Tosdal, R. M.; Wooden, J. L.

1990-11-01

Triassic magmatism in the southwest U.S. Cordillera forms a semicontinuous magmatic arc extending from northwestern Nevada to southeastern California. Quartz monzodioritic and quartz monzonitic rocks and associated diorites and granites are widespread in southeastern California, and we suggest that these rocks represent exposure of a structurally deeper part of the Triassic arc, where it was emplaced into comparatively thick Proterozoic crust. Elemental and isotopic data suggest that Triassic quartz monzodiorites and quartz monzonites in the Mule and San Gabriel Mountains were derived from a relatively undepleted, nonradiogenic mafic lithospheric source, with virtually no upper crustal interaction. Very limited data for associated Triassic(?) diorites indicate a wide range in composition and a surprisingly radiogenic isotopic signature. Younger Triassic(?) granites record a strong geochemical signature of interaction with continental crust, including inherited zircon and high initial Sr ratios but comparatively less radiogenic Pb isotopic compositions. The major and trace element geochemistry of Late Triassic plutonic rocks in southeastern California is similar in many respects to alkalic components of the Triassic arc in the Mojave Desert. However, contemporaneous rocks farther north have a calc-alkalic signature, perhaps reflecting the variation in age and composition of lithosphere across which the Triassic arc was constructed.

A petrologic comparison of Triassic plutonism in the San Gabriel and Mule Mountains, southern California

DOE Office of Scientific and Technical Information (OSTI.GOV)

Barth, A.P.; Tosdal, R.M.; Wooden, J.L.

1990-11-10

Triassic magmatism in the southwest US Cordillera forms a semicontinuous magmatic arc extending from northwestern Nevada to southeastern California. Quartz monzodioritic and quartz monzonitic rocks and associated diorites and granites are widespread in southeastern California, and the authors suggest that these rocks represent exposure of a structurally deeper part of the Triassic arc, where it was emplaced into comparatively thick Proterozoic crust. Elemental and isotopic data suggest that Triassic quartz monzodiorites and quartz monzonites in the Mule and San Gabriel Mountains were derived from a relatively undepleted, nonradiogenic mafic lithospheric source, with virtually no upper crustal interaction. Very limited datamore » for associated Triassic ( ) diorites indicate a wide range in composition and a surprisingly radiogenic isotopic signature. Younger Triassic( ) granites record a strong geochemical signature of interaction with continental crust, including inherited zircon and high initial Sr ratios but comparatively less radiogenic Pb isotopic compositions. The major and trace element geochemistry of Late Triassic plutonic rocks in southeastern California is similar in many respects to akalic components of the Triassic arc in the Mojave Desert. However, contemporaneous rocks farther north have a calc-alkalic signature, perhaps reflecting the variation in age and composition of lithosphere across which the Triassic arc was constructed.« less

Paleogene Seawater Osmium Isotope Records

NASA Astrophysics Data System (ADS)

Rolewicz, Z.; Thomas, D. J.; Marcantonio, F.

2012-12-01

Paleoceanographic reconstructions of the Late Cretaceous and early Cenozoic require enhanced geographic coverage, particularly in the Pacific, in order to better constrain meridional variations in environmental conditions. The challenge with the existing inventory of Pacific deep-sea cores is that they consist almost exclusively of pelagic clay with little existing age control. Pelagic clay sequences are useful for reconstructions of dust accumulation and water mass composition, but accurate correlation of these records to other sites requires improved age control. Recent work indicates that seawater Os isotope analyses provide useful age control for red clay sequences. The residence time of Os in seawater is relatively long compared to oceanic mixing, therefore the global seawater 187Os/188Os composition is practically homogeneous. A growing body of Late Cretaceous and Cenozoic data has constrained the evolution of the seawater Os isotopic composition and this curve is now a viable stratigraphic tool, employed in dating layers of Fe-Mn crusts (e.g., Klemm et al., 2005). Ravizza (2007) also demonstrated that the seawater Os isotopic composition can be extracted reliably from pelagic red clay sediments by analyzing the leached oxide minerals. The drawback to using seawater Os isotope stratigraphy to date Paleogene age sediments is that the compilation of existing data has some significant temporal gaps, notably between ~38 and 55 Ma. To improve the temporal resolution of the seawater Os isotope curve, we present new data from Ocean Drilling Program (ODP) Site 865 in the equatorial Pacific. Site 865 has excellent biostratigraphic age control over the interval ~38-55Ma. Preliminary data indicate an increase in the seawater composition from 0.427 at 53.4 Ma to 0.499 by 43 Ma, consistent with the apparent trend in the few existing data points. We also analyzed the Os isotopic composition recorded by oxide minerals at Integrated Ocean Drilling Program (IODP) Site U1370 to construct an age model for this predominantly pelagic clay section. The 187Os/188Os values generally increase from 0.312 at 64.46 mbsf to 0.531 at 28.26 mbsf. The low value recorded at 64.46 likely reflects the Os isotope minimum recorded across the K/Pg boundary, while the uppermost value likely correlates to the E/O interval. Comparison of the Os-derived ages with a crude linearly interpolated sedimentation rate age model reveals variations in sediment accumulation rate between 0.86 and 1.5 m/Myr.

Natural variations of copper and sulfur stable isotopes in blood of hepatocellular carcinoma patients

NASA Astrophysics Data System (ADS)

Balter, Vincent; Nogueira da Costa, Andre; Paky Bondanese, Victor; Jaouen, Klervia; Lamboux, Aline; Sangrajrang, Suleeporn; Vincent, Nicolas; Fourel, François; Télouk, Philippe; Gigou, Michelle; Lécuyer, Christophe; Srivatanakul, Petcharin; Bréchot, Christian; Albarède, Francis; Hainaut, Pierre

2015-01-01

The widespread hypoxic conditions of the tumor microenvironment can impair the metabolism of bioessential elements such as copper and sulfur, notably by changing their redox state and, as a consequence, their ability to bind specific molecules. Because competing redox state is known to drive isotopic fractionation, we have used here the stable isotope compositions of copper (65Cu/63Cu) and sulfur (34S/32S) in the blood of patients with hepatocellular carcinoma (HCC) as a tool to explore the cancer-driven copper and sulfur imbalances. We report that copper is 63Cu-enriched by ∼0.4‰ and sulfur is 32S-enriched by ∼1.5‰ in the blood of patients compared with that of control subjects. As expected, HCC patients have more copper in red blood cells and serum compared with control subjects. However, the isotopic signature of this blood extra copper burden is not in favor of a dietary origin but rather suggests a reallocation in the body of copper bound to cysteine-rich proteins such as metallothioneins. The magnitude of the sulfur isotope effect is similar in red blood cells and serum of HCC patients, implying that sulfur fractionation is systemic. The 32S-enrichment of sulfur in the blood of HCC patients is compatible with the notion that sulfur partly originates from tumor-derived sulfides. The measurement of natural variations of stable isotope compositions, using techniques developed in the field of Earth sciences, can provide new means to detect and quantify cancer metabolic changes and provide insights into underlying mechanisms.

Isotopic Resonance Hypothesis: Experimental Verification by Escherichia coli Growth Measurements

NASA Astrophysics Data System (ADS)

Xie, Xueshu; Zubarev, Roman A.

2015-03-01

Isotopic composition of reactants affects the rates of chemical and biochemical reactions. As a rule, enrichment of heavy stable isotopes leads to progressively slower reactions. But the recent isotopic resonance hypothesis suggests that the dependence of the reaction rate upon the enrichment degree is not monotonous. Instead, at some ``resonance'' isotopic compositions, the kinetics increases, while at ``off-resonance'' compositions the same reactions progress slower. To test the predictions of this hypothesis for the elements C, H, N and O, we designed a precise (standard error +/-0.05%) experiment that measures the parameters of bacterial growth in minimal media with varying isotopic composition. A number of predicted resonance conditions were tested, with significant enhancements in kinetics discovered at these conditions. The combined statistics extremely strongly supports the validity of the isotopic resonance phenomenon (p << 10-15). This phenomenon has numerous implications for the origin of life studies and astrobiology, and possible applications in agriculture, biotechnology, medicine, chemistry and other areas.

[Sources of Methane in the Boreal Region

NASA Technical Reports Server (NTRS)

1998-01-01

In determining the global methane budget the sources of methane must be balanced with the sinks and atmospheric inventory. The approximate contribution of the different methane sources to the budget has been establish showing the major terrestrial inputs as rice, wetlands, bogs, fens, and tundra. Measurements and modeling of production in these sources suggest that temperature, water table height and saturation along with substratum composition are important in controlling methane production and emission. The isotopic budget of 13 C and D/H in methane can be used as a tool to clarify the global budget. This approach has achieved success at constraining the inputs. Studies using the isotopic approach place constraints on global methane production from different sources. Also, the relation between the two biogenic production pathways, acetate fermentation and CO2 reduction, and the effect of substratum composition can be made using isotope measurements shows the relation between the different biogenic, thermogenic and anthropogenic sources of methane as a function of the carbon and hydrogen isotope values for each source and the atmosphere, tropospheric composition. Methane emissions from ponds and fens are a significant source in the methane budget of the boreal region. An initial study in 1993 and 1994 on the isotopic composition of this methane source and the isotopic composition in relation to oxidation of methane at the sediment surface of the ponds or fen was conducted as part of our BOREAS project. The isotopic composition of methane emitted by saturated anoxic sediment is dependent on the sediment composition and geochemistry, but will be influenced by in situ oxidation, in part, a function of rooted plant activity. The influence of oxidation mediated by rooted plant activities on the isotopic composition of methane is not well known and will depend on the plant type, sediment temperature, and numerous other variables. Information on this isotopic composition is important in both understanding the bio-geochemistry of the system and also in determining the regional and global inputs for the methane isotope budget. In determining the destruction of methane for balancing the atmospheric methane budget soil oxidation must be considered.

Iron isotopic composition of blood serum in anemia of chronic kidney disease.

PubMed

Anoshkina, Yulia; Costas-Rodríguez, Marta; Speeckaert, Marijn; Van Biesen, Wim; Delanghe, Joris; Vanhaecke, Frank

2017-05-24

Chronic kidney disease (CKD) is a general term for disorders that affect the structure and function of the kidneys. Iron deficiency (ID) and anemia occur in the vast majority of CKD patients, most of whom are elderly. However, establishing the cause of anemia in CKD, and therefore making an informed decision concerning the corresponding therapeutic treatment, is still a challenge. High-precision Fe isotopic analysis of blood serum samples of CKD patients with and without ID/anemia was performed via multi-collector inductively coupled plasma-mass spectrometry (MC-ICP-MS) for such a purpose. Patients with CKD and/or iron disorders showed a heavier serum Fe isotopic composition than controls. Many clinical parameters used for the diagnosis and follow-up of anemia correlated significantly with the serum Fe isotopic composition. In contrast, no relation was observed between the serum Fe isotopic composition and the estimated glomerular filtration rate as a measure of kidney function. Among the CKD patients, the serum Fe isotopic composition was substantially heavier in the occurrence of ID anemia, while erythropoietin-related anemia did not exert this effect. The Fe isotopic composition can thus be useful for distinguishing these different types of anemias in CKD patients, i.e. ID anemia vs. erythropoietin-related anemia.

Oxygen and carbon stable isotopes in coast redwood tree rings respond to spring and summer climate signals

NASA Astrophysics Data System (ADS)

Johnstone, James A.; Roden, John S.; Dawson, Todd E.

2013-12-01

variability in the oxygen and carbon isotope composition of tree ring cellulose was investigated in coast redwood (Sequoia sempervirens) from three sites in coastal Northern California. Middle and late wood samples from annual tree rings were compared to regional climate indices and gridded ocean-atmosphere fields for the years 1952-2003. The strongest climate-isotope relationship (r = 0.72) was found with summer (June-September) daily maximum temperature and middle wood δ13, which also responds positively to coastal sea surface temperature and negatively to summer low cloud frequency. Late wood δ18O reflects a balance between 18O-enriched summer fog drip and depleted summer rainwater, while a combined analysis of late wood δ18O and δ13C revealed sensitivity to the sign of summer precipitation anomalies. Empirical orthogonal function analysis of regional summer climate indices and coast redwood stable isotopes identified multivariate isotopic responses to summer fog and drought that correspond to atmospheric circulation anomalies over the NE Pacific and NW U.S. The presence of regional climate signals in coast redwood stable isotope composition, consistent with known mechanistic processes and prior studies, offers the potential for high-resolution paleoclimate reconstructions of the California current system from this long-lived tree species.

High-precision measurement of variations in calcium isotope ratios in urine by multiple collector inductively coupled plasma mass spectrometry

USGS Publications Warehouse

Morgan, J.L.L.; Gordon, G.W.; Arrua, R.C.; Skulan, J.L.; Anbar, A.D.; Bullen, T.D.

2011-01-01

We describe a new chemical separation method to isolate Ca from other matrix elements in biological samples, developed with the long-term goal of making high-precision measurement of natural stable Ca isotope variations a clinically applicable tool to assess bone mineral balance. A new two-column procedure utilizing HBr achieves the purity required to accurately and precisely measure two Ca isotope ratios (44Ca/42Ca and 44Ca/43Ca) on a Neptune multiple collector inductively coupled plasma mass spectrometer (MC-ICPMS) in urine. Purification requirements for Sr, Ti, and K (Ca/Sr > 10000; Ca/Ti > 10000000; and Ca/K > 10) were determined by addition of these elements to Ca standards of known isotopic composition. Accuracy was determined by (1) comparing Ca isotope results for samples and standards to published data obtained using thermal ionization mass spectrometry (TIMS), (2) adding a Ca standard of known isotopic composition to a urine sample purified of Ca, and (3) analyzing mixtures of urine samples and standards in varying proportions. The accuracy and precision of δ44/42Ca measurements of purified samples containing 25 μg of Ca can be determined with typical errors less than ±0.2‰ (2σ).

Comparison of IRMS and NMR spectrometry for the determination of intramolecular 13C isotope composition: application to ethanol.

PubMed

Gilbert, Alexis; Hattori, Ryota; Silvestre, Virginie; Wasano, Nariaki; Akoka, Serge; Hirano, Satoshi; Yamada, Keita; Yoshida, Naohiro; Remaud, Gérald S

2012-09-15

Isotopic (13)C NMR is a relatively recent technique which allows the determination of intramolecular (13)C isotope composition at natural abundance. It has been used in various scientific fields such as authentication, counterfeiting or plant metabolism. Although its precision has already been evaluated, the determination of its trueness remains still challenging. To deal with that issue, a comparison with another normalized technique must be achieved. In this work, we compare the intramolecular (13)C isotope distribution of ethanol from different origins obtained using both Isotope Ratio Mass Spectrometry (IRMS) and Nuclear Magnetic Resonance (NMR) spectrometry techniques. The IRMS approach consists of the oxidation of ethanol to acetic acid followed by the degradation of the latter for the analysis of each fragments formed. We show here that the oxidation of ethanol to acetic acid does not bring any significant error on the determination of the site-specific δ(13)C (δ(13)C(i)) of ethanol using the IRMS approach. The difference between the data obtained for 16 samples from different origins using IRMS and NMR approaches is not statistically significant and remains below 0.3‰. These results are encouraging for the future studies using isotopic NMR, especially in combination with the IRMS approach. Copyright © 2012. Published by Elsevier B.V.

Fast chemical and isotopic exchange of nitrogen during reaction with hot molybdenum

NASA Astrophysics Data System (ADS)

Yokochi, Reika; Marty, Bernard

2006-07-01

Molybdenum crucibles are commonly used to extract nitrogen from geological samples by induction heating. Because nitrogen is known to be reactive with certain metals (e.g., Ti and Fe), we have tested the reactivity of gaseous nitrogen with a Mo crucible held at 1800°C. The consumption of nitrogen, determined by monitoring the N2/40Ar ratio of the gas phase, varied between 25 and 100%, depending on the reaction duration. Nitrogen of the reacted gas was found to be systematically enriched in 15N relative to 14N by 10‰ compared to the initial isotopic composition, without any correlation with nitrogen consumption. We propose that a rapid isotopic exchange occurs between nitrogen originally trapped in the crucible and nitrogen from the gas phase, which modifies the isotopic composition of the reacted gas. This process can significantly bias the isotopic determination of nitrogen in rocks and minerals when a Mo furnace is used for gas extraction. Meanwhile, the rate of N-Mo chemical bonding may be controlled by the formation of nitride (rather than solid solution), a process slower than the isotopic exchange. The use of a Mo furnace for the extraction of trace nitrogen from rocks and minerals should therefore be avoided.

Xenon isotopic composition of the Mid Ocean Ridge Basalt (MORB) source

NASA Astrophysics Data System (ADS)

Peto, M. K.; Mukhopadhyay, S.

2012-12-01

Although convection models do not preclude preservation of smaller mantle regions with more pristine composition throughout Earth's history, it has been widely assumed that the moon forming giant impact likely homogenizes the whole mantle following a magma ocean that extended all the way to the bottom of the mantle. Recent findings of tungsten and xenon heterogeneities in the mantle [1,2,3,4], however, imply that i) the moon forming giant impact may not have homogenized the whole mantle and ii) plate tectonics was inefficient in erasing early formed compositional differences, particularly for the xenon isotopes. Therefore, the xenon isotope composition in the present day mantle still preserves a memory of early Earth processes. However, determination of the xenon isotopic composition of the mantle source is still scarce, since the mantle composition is overprinted by post-eruptive atmospheric contamination in basalts erupted at ocean islands and mid ocean ridges. The xenon composition of the depleted upper mantle has been defined by the gas rich sample, 2πD43 (also known as "popping rock"), from the North Atlantic (13° 469`N). However, the composition of a single sample is not likely to define the composition of the upper mantle, especially since popping rock has an "enriched" trace element composition. We will present Ne, Ar and Xe isotope data on MORB glass samples with "normal" helium isotope composition (8±1 Ra) from the Southeast Indian Ridge, the South Atlantic Ridge, the Sojourn Ridge, the Juan de Fuca, the East Pacific Rise, and the Gakkel Ridge. Following the approach of [1], we correct for syn- and post-eruptive atmosphere contamination, and determine the variation of Ar and Xe isotope composition of the "normal" MORB source. We investigate the effect of atmospheric recycling in the variation of MORB mantle 40Ar/36Ar and 129Xe/130Xe ratios, and attempt to constrain the average upper mantle argon and xenon isotopic compositions. [1] Mukhopadhyay, Nature 2012; [2] Tucker et al., EPSL (in review); [3] Moreira et al., Nature 1998 [4] Touboul et al., Science 2012.

SrNdPb isotopic and trace element evidence for crustal contamination of plume-derived flood basalts: Oligocene flood volcanism in western Yemen

NASA Astrophysics Data System (ADS)

Baker, J. A.; Thirlwall, M. F.; Menzies, M. A.

1996-07-01

Oligocene flood basalts from western Yemen have a relatively limited range in initial isotopic composition compared with other continental flood basalts: 87Sr/86Sr = 0.70365-0.70555 ; 143Nd/144Nd = 0.5129-0.51248 ( ɛNd = +6.0 to -2.4) ; 206pb/204Pb = 17.9-19.3 . Most compositions lie outside the isotopic ranges of temporally and spatially appropriate mantle source compositions observed in this area, i.e., Red Sea/Gulf of Aden MORB mantle, the Afar plume, and Pan-African lithospheric mantle Correlations between indices of fractionation, silica, and isotope ratios suggest that crustal contamination has substantially modified the primary isotopic and incompatible trace element characteristics of the flood basalts. However, significant scatter in these correlations was produced by: (a) the heterogeneous isotopic composition of Pan-African crust; (b) the difference in susceptibility of magmas to contamination as a result of variable incompatible trace element contents in primary melts produced by differing degrees of partial melting; (c) the presence or absence of plagioclase as a fractionating phase generating complex contamination trajectories for Sr; (d) sampling over a wide area not representing a single coherent magmatic system; and (e) variation in contamination mechanisms from assimilation associated with fractionation (AFC) to assimilation by hot mafic magmas with little concomitant fractionation. The presence of plagioclase as a fractionating phase in some suites that were undergoing AFC requires assimilation to have taken place within the crust and, coupled with the limited LREE-enrichment accompanying isotopic variations, excludes the possibility that an AFC-type process took place during magma transfer through the lithospheric mantle. Isotopic compositions of some of the inferred crustal assimilants are similar to those postulated by other workers for an enriched lithospheric mantle source of many flood basalts in southwestern Yemen, Ethiopia, and Djibouti. The western Yemen flood basalts contain 0-30% crust which largely swamps their primary lead isotopic signature, but the primary SrNd isotopic signature is close to that of the least contaminated and isotopically most depleted flood basalts. LREE/HFSE and LILE/HFSE ratios also correlate with isotopic data as a result of crustal contamination. However, Nb/La and K/Nb ratios of >1.1 and <150, respectively, in least contaminated samples require an OIB-like source. The pre-contamination isotopic signature is estimated to be: 87Sr/86Sr ˜ 0.7036; 143Nd/144Nd ˜ 0.51292 ; 206Pb/204Pb ˜ 18.4-19.0 . This, coupled with low LILE/HFSE ratios, suggest the source has characteristics akin to the Afar plume. A mantle source isotopically more depleted than Bulk Earth, but not as depleted as MORB, coupled with LILE depletion, also characterises other examples of plume-derived flood volcanism. This mantle reservoir is responsible for the second largest outbursts of volcanism on Earth and has radiogenic isotopic characteristics akin to PREMA mantle, but the incompatible trace element signature of HIMU mantle.

Moss stable isotopes (carbon-13, oxygen-18) and testate amoebae reflect environmental inputs and microclimate along a latitudinal gradient on the Antarctic Peninsula.

PubMed

Royles, Jessica; Amesbury, Matthew J; Roland, Thomas P; Jones, Glyn D; Convey, Peter; Griffiths, Howard; Hodgson, Dominic A; Charman, Dan J

2016-07-01

The stable isotope compositions of moss tissue water (δ(2)H and δ(18)O) and cellulose (δ(13)C and δ(18)O), and testate amoebae populations were sampled from 61 contemporary surface samples along a 600-km latitudinal gradient of the Antarctic Peninsula (AP) to provide a spatial record of environmental change. The isotopic composition of moss tissue water represented an annually integrated precipitation signal with the expected isotopic depletion with increasing latitude. There was a weak, but significant, relationship between cellulose δ(18)O and latitude, with predicted source water inputs isotopically enriched compared to measured precipitation. Cellulose δ(13)C values were dependent on moss species and water content, and may reflect site exposure to strong winds. Testate amoebae assemblages were characterised by low concentrations and taxonomic diversity, with Corythion dubium and Microcorycia radiata types the most cosmopolitan taxa. The similarity between the intra- and inter-site ranges measured in all proxies suggests that microclimate and micro-topographical conditions around the moss surface were important determinants of proxy values. Isotope and testate amoebae analyses have proven value as palaeoclimatic, temporal proxies of climate change, whereas this study demonstrates that variations in isotopic and amoeboid proxies between microsites can be beyond the bounds of the current spatial variability in AP climate.

Flotsam samples can help explain the δ13C and δ15N values of invertebrate resting stages in lake sediment

NASA Astrophysics Data System (ADS)

van Hardenbroek, Maarten; Rinta, Päivi; Wooller, Matthew J.; Schilder, Jos; Stötter, Tabea; Heiri, Oliver

2018-06-01

The stable isotopic composition of chitinous remains of Cladocera (water fleas) and freshwater Bryozoa (moss animals) preserved in lake sediment records can provide supporting insights into past environmental and ecosystem changes in lakes. Here we explore whether analyses of these remains isolated from lake flotsam can provide information on the driving variables affecting the isotopic composition of these remains. We collected flotsam in 53 lakes and found enough material in 33 lakes to measure the stable carbon and nitrogen isotope ratios (expressed as δ13C and δ15N values, respectively) of resting stages. These values were compared with lake characteristics, water chemistry measurements, and the isotopic composition of sedimentary organic matter (SOM) in the lakes. Mean δ13C values of cladoceran ephippia and SOM were correlated and both were also negatively correlated with deep water methane concentrations and indicators of lake stratification. This supports the findings of previous studies that methane-derived carbon can provide a significant proportion of carbon entering planktonic food webs. Mean δ15N values of bryozoan statoblasts and SOM were correlated, suggesting that both reflect the δ15N values of phytoplankton. Our results provide information on how environmental variables in lakes can influence the δ13C and δ15N values in resting stages, but flotsam samples can also potentially be used to assess seasonal stable isotope variability of resting stages. Both types of information are important to improve palaeoenvironmental interpretations of stable isotope records based on these remains in lake sediments.

A stable isotope study of fossil mammal remains from the Paglicci cave, Southern Italy. N and C as palaeoenvironmental indicators

NASA Astrophysics Data System (ADS)

Iacumin, P.; Bocherens, H.; Delgado Huertas, A.; Mariotti, A.; Longinelli, A.

1997-04-01

A set of 102 tooth and bone samples of Pleistocene age (32,600-13,300 yr BP) belonging to the species Cervus elaphus, Bos primigenius and Equus caballus and coming from the Paglicci cave (Southern Italy) was studied for the carbon (δ 13C) and nitrogen (δ 15N) isotopic composition of bone and dentine collage and for the carbon (δ 13C c) isotopic composition of tooth enamel carbonate. The amount of collagen extracted from bone and tooth samples (mg/g) was rather variable, representing approximately only 0.5-15% of the collagen present in a fresh bone. However, the loss of an important fraction of the original collagen during diagenesis did not change the in vivo isotopic composition. In general, when the δ 13C of both collagen and carbonate and the δ 15N of collagen obtained from each level for the three species are compared, wild ox shows the most increased values, deer the most decreased values and horse shows intermediate results. These differences are probably related to distinct diets or to differences in their physiological behaviour. However, the isotopic results suggest that the three species considered lived in an open environment with a diet based on C 3 plants. The stratigraphic sequence of light and heavy nitrogen isotope values between 19,000 and 15,000 may be related to shifts from arid to humid conditions, while the overall trend shown by δ 13C toward lighter values may be related to a progressive development of a forest habitat.

A molecular stable carbon isotope study of organic matter in immature Miocene Monterey sediments, Pismo basin

NASA Astrophysics Data System (ADS)

Schouten, Stefan; Schoell, Martin; Rijpstra, W. Irene C.; Sinninghe Damsté, Jaap S.; de Leeuw, Jan W.

1997-05-01

The 300 m section of the Miocene Monterey Formation outcropping at Shell Beach (Pismo basin; ca. 15-11 Ma) is composed of calcareous phosphatic (15.1-14.5 Ma) and siliceous facies (14.5-11.0 Ma). An objective of this paper is to document lateral paleoenvironmental changes in the Miocene Moneterey Formation by comparing the Shell Beach (SB) profile with the Naples Beach (NB) section in the Santa Barbara-Ventura basin (Schouten et al., 1997) which is ˜80 km to the south. Eight samples (one sample representing, on average, a time period of ca. 2000 y) from this section were analyzed for variations of extractable biomarkers and their carbon isotopic signatures as indicators for paleoenvironmental change during the Miocene. Saturated hydrocarbons present include 28,30-dinorhopane, phytane, n-alkanes (C 17sbnd C 31), lycopane, and 17β,21β(H)-homohopane. The biomarkers released after desulfurization of the polar fractions predominantly consist of phytane, 2,6,10,14-tetramethyl-7-(3-methylpentyl)pentadecane, C 17sbnd C 31n-alkanes, regular 5α- and 5β-steranes, dinosteranes, and (22R)-17β,21β(H)-pentakishomohopane. Steranes have similar carbon isotopic compositions (-25 to -27‰) throughout the section and are isotopically similar at both sites, indicating laterally similar and vertically stable environmental conditions for algae living in the upper part of the photic zone. Free and S-bound n-alkanes at SB mainly originate from marine organisms and not from terrestrial sources as in the NB section. S-bound pentakishomohopane is ca. 1-4‰ depleted compared to the steranes and is thought to be derived from the deeper water dwelling cyanobacteria. These findings are consistent with stable carbon isotopic data obtained for these compounds from Middle Miocene Monterey sediments at Naples Beach and indicates similar environmental conditions in the depositional environments of the Santa Barbara-Ventura and the Pismo basin. S-bound highly branched isoprenoids have, at both sites, different isotopic compositions indicating the presence of different diatom species, special growth conditions, or different bloom periods in the Pismo basin. The carbon isotopic composition of 28,30-dinorhopane shifts to more depleted values up section, suggesting that the dinorhopane-synthesizing organism or organisms live on CO 2, which is isotopically influenced by methane production and oxidation. The C 31 hopane is enriched by 1-4‰ in 13C compared to other hopanes and steranes. Specific bacteria, possibly heterotrophs, may have been the organisms producing this compound.

Breeding of {sup 233}U in the thorium–uranium fuel cycle in VVER reactors using heavy water

DOE Office of Scientific and Technical Information (OSTI.GOV)

Marshalkin, V. E., E-mail: marshalkin@vniief.ru; Povyshev, V. M.

A method is proposed for achieving optimal neutron kinetics and efficient isotope transmutation in the {sup 233}U–{sup 232}Th oxide fuel of water-moderated reactors with variable water composition (D{sub 2}O, H{sub 2}O) that ensures breeding of the {sup 233}U and {sup 235}U isotopes. The method is comparatively simple to implement.

Modelling and intepreting the isotopic composition of water vapour in convective updrafts

NASA Astrophysics Data System (ADS)

Bolot, M.; Legras, B.; Moyer, E. J.

2012-08-01

The isotopic compositions of water vapour and its condensates have long been used as tracers of the global hydrological cycle, but may also be useful for understanding processes within individual convective clouds. We review here the representation of processes that alter water isotopic compositions during processing of air in convective updrafts and present a unified model for water vapour isotopic evolution within undiluted deep convective cores, with a special focus on the out-of-equilibrium conditions of mixed phase zones where metastable liquid water and ice coexist. We use our model to show that a combination of water isotopologue measurements can constrain critical convective parameters including degree of supersaturation, supercooled water content and glaciation temperature. Important isotopic processes in updrafts include kinetic effects that are a consequence of diffusive growth or decay of cloud particles within a supersaturated or subsaturated environment; isotopic re-equilibration between vapour and supercooled droplets, which buffers isotopic distillation; and differing mechanisms of glaciation (droplet freezing vs. the Wegener-Bergeron-Findeisen process). As all of these processes are related to updraft strength, droplet size distribution and the retention of supercooled water, isotopic measurements can serve as a probe of in-cloud conditions of importance to convective processes. We study the sensitivity of the profile of water vapour isotopic composition to differing model assumptions and show how measurements of isotopic composition at cloud base and cloud top alone may be sufficient to retrieve key cloud parameters.

Modelling and interpreting the isotopic composition of water vapour in convective updrafts

NASA Astrophysics Data System (ADS)

Bolot, M.; Legras, B.; Moyer, E. J.

2013-08-01

The isotopic compositions of water vapour and its condensates have long been used as tracers of the global hydrological cycle, but may also be useful for understanding processes within individual convective clouds. We review here the representation of processes that alter water isotopic compositions during processing of air in convective updrafts and present a unified model for water vapour isotopic evolution within undiluted deep convective cores, with a special focus on the out-of-equilibrium conditions of mixed-phase zones where metastable liquid water and ice coexist. We use our model to show that a combination of water isotopologue measurements can constrain critical convective parameters, including degree of supersaturation, supercooled water content and glaciation temperature. Important isotopic processes in updrafts include kinetic effects that are a consequence of diffusive growth or decay of cloud particles within a supersaturated or subsaturated environment; isotopic re-equilibration between vapour and supercooled droplets, which buffers isotopic distillation; and differing mechanisms of glaciation (droplet freezing vs. the Wegener-Bergeron-Findeisen process). As all of these processes are related to updraft strength, particle size distribution and the retention of supercooled water, isotopic measurements can serve as a probe of in-cloud conditions of importance to convective processes. We study the sensitivity of the profile of water vapour isotopic composition to differing model assumptions and show how measurements of isotopic composition at cloud base and cloud top alone may be sufficient to retrieve key cloud parameters.

Isotope effects on the optical spectra of semiconductors

NASA Astrophysics Data System (ADS)

Cardona, Manuel; Thewalt, M. L. W.

2005-10-01

Since the end of the cold war, macroscopic amounts of separated stable isotopes of most elements have been available “off the shelf” at affordable prices. Using these materials, single crystals of many semiconductors have been grown and the dependence of their physical properties on isotopic composition has been investigated. The most conspicuous effects observed have to do with the dependence of phonon frequencies and linewidths on isotopic composition. These affect the electronic properties of solids through the mechanism of electron-phonon interaction, in particular, in the corresponding optical excitation spectra and energy gaps. This review contains a brief introduction to the history, availability, and characterization of stable isotopes, including their many applications in science and technology. It is followed by a concise discussion of the effects of isotopic composition on the vibrational spectra, including the influence of average isotopic masses and isotopic disorder on the phonons. The final sections deal with the effects of electron-phonon interaction on energy gaps, the concomitant effects on the luminescence spectra of free and bound excitons, with particular emphasis on silicon, and the effects of isotopic composition of the host material on the optical transitions between the bound states of hydrogenic impurities.

Determination of lithium isotopes at natural abundance levels by atomic absorption spectrometry

USGS Publications Warehouse

Meier, A.L.

1982-01-01

The relationships of the absorption of 6Li and 7Li hollow cathode lamp emissions are used to determine lithium isotopic composition in the natural abundance range of geologic materials. Absorption was found to have a nonlinear dependence upon total lithium concentration and isotopic composition. A method using nonlinear equations to describe the relationship of the absorption of 6Li and 7Li lamp radiation is proposed as a means of calculating isotopic composition that is independent of total lithium concentration.

Thermal Diffusion Fractionation of Cr and V Isotope in Silicate Melt

NASA Astrophysics Data System (ADS)

Lin, X.; Lundstrom, C.

2017-12-01

Earth's mantle is isotopically heavy relative to chondrites for V, Cr and some other siderophile elements. A possible solution is that isotopic fractionation by thermal diffusion occurs in a thermal boundary layer between solid mantle and an underlying basal magma ocean (BMO:Labrosse et al.,2007). If so, isotopically light composition might partition into the core, resulting in a complimentary isotopically heavy solid mantle. To verify how much fractionation could happen in this process, piston cylinder experiment were conducted to investigate the fractionation of Cr and V isotope ratios in partially molten silicate under an imposed temperature gradient from 1650 °C to 1350 °C at 1 GPa for 10 to 50 hours to reach a steady state isotopic profile. The temperature profile for experiments was determined by the spinel-growth method at the same pressure and temperature. Experimental runs result in 100% glass at the hot end progressing to nearly 100 % olivine at the cold end. Major and minor element concentrations of run products show systematic changes with temperature. Glass MgO contents increase and Al2O3 and CaO contents decrease by several weight percent as temperature increases across the charge. These are well modeled using IRIDIUM (Boudreau 2003) to simulate the experiments. Isotopic composition measurements of Cr and V at different temperatures are in progress, providing the first determinations of thermal diffusion isotopic sensitivity, Ω (permil isotopic fractionation per temperature offset per mass unit) for these elements. These results will be compared with previously determined Ω for network formers and modifiers and used in a BMO-based thermal diffusion model for formation of Earth's isotopically heavy mantle.

Stable Isotope Anatomy of Tropical Cyclone Ita, North-Eastern Australia, April 2014

PubMed Central

Munksgaard, Niels C.; Zwart, Costijn; Kurita, Naoyuki; Bass, Adrian; Nott, Jon; Bird, Michael I.

2015-01-01

The isotope signatures registered in speleothems during tropical cyclones (TC) provides information about the frequency and intensity of past TCs but the precise relationship between isotopic composition and the meteorology of TCs remain uncertain. Here we present continuous δ18O and δ2H data in rainfall and water vapour, as well as in discrete rainfall samples, during the passage of TC Ita and relate the evolution in isotopic compositions to local and synoptic scale meteorological observations. High-resolution data revealed a close relationship between isotopic compositions and cyclonic features such as spiral rainbands, periods of stratiform rainfall and the arrival of subtropical and tropical air masses with changing oceanic and continental moisture sources. The isotopic compositions in discrete rainfall samples were remarkably constant along the ~450 km overland path of the cyclone when taking into account the direction and distance to the eye of the cyclone at each sampling time. Near simultaneous variations in δ18O and δ2H values in rainfall and vapour and a near-equilibrium rainfall-vapour isotope fractionation indicates strong isotopic exchange between rainfall and surface inflow of vapour during the approach of the cyclone. In contrast, after the passage of spiral rainbands close to the eye of the cyclone, different moisture sources for rainfall and vapour are reflected in diverging d-excess values. High-resolution isotope studies of modern TCs refine the interpretation of stable isotope signatures found in speleothems and other paleo archives and should aim to further investigate the influence of cyclone intensity and longevity on the isotopic composition of associated rainfall. PMID:25742628

The genesis solar-wind sample return mission

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wiens, Roger C

2009-01-01

The compositions of the Earth's crust and mantle, and those of the Moon and Mars, are relatively well known both isotopically and elementally. The same is true of our knowledge of the asteroid belt composition, based on meteorite analyses. Remote measurements of Venus, the Jovian atmosphere, and the outer planet moons, have provided some estimates of their compositions. The Sun constitutes a large majority, > 99%, of all the matter in the solar system. The elemental composition of the photosphere, the visible 'surface' of the Sun, is constrained by absorption lines produced by particles above the surface. Abundances for manymore » elements are reported to the {+-}10 or 20% accuracy level. However, the abundances of other important elements, such as neon, cannot be determined in this way due to a relative lack of atomic states at low excitation energies. Additionally and most importantly, the isotopic composition of the Sun cannot be determined astronomically except for a few species which form molecules above sunspots, and estimates derived from these sources lack the accuracy desired for comparison with meteoritic and planetary surface samples measured on the Earth. The solar wind spreads a sample of solar particles throughout the heliosphere, though the sample is very rarified: collecting a nanogram of oxygen, the third most abundant element, in a square centimeter cross section at the Earth's distance from the Sun takes five years. Nevertheless, foil collectors exposed to the solar wind for periods of hours on the surface of the Moon during the Apollo missions were used to determine the helium and neon solar-wind compositions sufficiently to show that the Earth's atmospheric neon was significantly evolved relative to the Sun. Spacecraft instruments developed subsequently have provided many insights into the composition of the solar wind, mostly in terms of elemental composition. These instruments have the advantage of observing a number of parameters simultaneously, including charge state distributions, velocities, and densities, all of which have been instrumental in characterizing the nature of the solar wind. However, these instruments have lacked the ability to make large dynamic range measurements of adjacent isotopes (i.e., {sup 17}O/{sup 16}O {approx} 2500) or provide the permil (tenths of percent) accuracy desirable for comparison with geochemical isotopic measurements. An accurate knowledge of the solar and solar-wind compositions helps to answer important questions across a number of disciplines. It aids in understanding the acceleration mechanisms of the solar wind, gives an improved picture of the charged particle environment near the photosphere, it constrains processes within the Sun over its history, and it provides a database by which to compare differences among planetary systems with the solar system's starting composition, providing key information on planetary evolution. For example, precise knowledge of solar isotopic and elemental compositions of volatile species in the Sun provides a baseline for models of atmospheric evolution over time for Earth, Venus, and Mars. Additionally, volatile and chemically active elements such as C, H, O, N, and S can tell us about processes active during the evolution of the solar nebula. A classic example of this is the oxygen isotope system. In the 1970s it was determined that the oxygen isotopic ratio in refractory inclusions in primitive meteorites was enriched {approx}4% in {sup 16}O relative to the average terrestrial, lunar, and thermally processed meteorite materials. In addition, all processed solar-system materials appeared to each have a unique oxygen isotopic composition (except the Moon and Earth, which are thought to be formed from the same materials), though differences are in the fraction of a percent range, much smaller than the refractory material {sup 16}O enrichment. Several theories were developed over the years to account for the oxygen isotope heterogeneity, each theory predicting a different solar isotopic composition and each invoking a different early solar-system process to produce the heterogeneity. Other volatiles such as C, N, and H may also have experienced similar effects, but with only two isotopes it is often impossible to distinguish with these elements between mass-dependent fractionation and other effects such as mixing or mass-independent fractionation. Table 1 provides a summary of the major measurement objectives of the Genesis mission. Determining the solar oxygen isotopic composition is at the top of the list. Volatile element and isotope ratios constitute six of the top seven priorities. A number of disciplines stand to gain from information from the Genesis mission, as will be discussed later. Based on the Apollo solar-wind foil experiment, the Genesis mission was designed to capture solar wind over orders of magnitude longer duration and in a potentially much cleaner environment than the lunar surface.« less

Elemental and iron isotopic composition of aerosols collected in a parking structure.

PubMed

Majestic, Brian J; Anbar, Ariel D; Herckes, Pierre

2009-09-01

The trace metal contents and iron isotope composition of size-resolved aerosols were determined in a parking structure in Tempe, AZ, USA. Particulate matter (PM)<2.5 microm in diameter (the fine fraction) and PM>2.5 microm were collected. Several air toxics (e.g., arsenic, cadmium, and antimony) were enriched above the crustal average, implicating automobiles as an important source. Extremely high levels of fine copper (up to 1000 ng m(-3)) were also observed in the parking garage, likely from brake wear. The iron isotope composition of the aerosols were found to be +0.15+/-0.03 per thousand and +0.18+/-0.03 per thousand for the PM<2.5 microm and PM>2.5 microm fractions, respectively. The similarity of isotope composition indicates a common source for each size fraction. To better understand the source of iron in the parking garage, the elemental composition in four brake pads (two semi-metallic and two ceramic), two tire tread samples, and two waste oil samples were determined. Striking differences in the metallic and ceramic brake pads were observed. The ceramic brake pads contained 10-20% copper by mass, while the metallic brake pads contained about 70% iron, with very little copper. Both waste oil samples contained significant amounts of calcium, phosphorous, and zinc, consistent with the composition of some engine oil additives. Differences in iron isotope composition were observed between the source materials; most notably between the tire tread (average=+0.02 per thousand) and the ceramic brake linings (average=+0.65 per thousand). Differences in isotopic composition were also observed between the metallic (average=+0.18 per thousand) and ceramic brake pads, implying that iron isotope composition may be used to resolve these sources. The iron isotope composition of the metallic brake pads was found to be identical to the aerosols, implying that brake dust is the dominant source of iron in a parking garage.

Long-term changes in solar wind elemental and isotopic ratios - A comparison of two lunar ilmenites of different antiquities

NASA Technical Reports Server (NTRS)

Becker, Richard H.; Pepin, Robert O.

1989-01-01

The solar wind components in two lunar ilmenites are examined. The noble gas and nitrogen elemental and isotopic abundances of lunar regolith breccia sample 79035, assumed to have been exposed to solar winds more than 2 Ga ago, are analyzed using stepwise oxidation and pyrolysis. This sample is compared with the data of Frick et al. (1988) for soil sample 71501, recently exposed to solar winds. It is observed that the two elements differ in terms of xenon abundance, helium and neon isotopic rates, and He/Ar elemental ratios. It is concluded that there have been isotopic and elemental abundance changes in solar wind composition over time.

Intramolecular Isotopic Studies: Chemical Enhancements and Alternatives

NASA Astrophysics Data System (ADS)

Hayes, J. M.

2016-12-01

As mass spectroscopic and NMR-based methods now appropriately flourish, chemical techniques should not be forgotten. First, the methods developed by pioneering intramolecular analysts can be reapplied to new samples. Second, they can be extended. The synthesis of intramolecular isotopic standards is particularly important and straightforward. It requires only that a chemical reaction has no secondary products. An example is provided by the addition of carbon dioxide to a Grignard reagent. The reaction proceeds with an isotope effect. The isotopic composition of the carboxyl group in the acid which is produced is thus not equal to that of the starting carbon dioxide but the unconsumed CO2 can be recovered and analyzed. A simple titration can show that all the rest of the CO2 is in the product acid. The isotopic composition of the carboxyl group can then be calculated by difference. The product is an intramolecular isotopic standard, an organic molecule in which the isotopic composition of a specific carbon position is known accurately. Both analysts and reviewers can thus gain invaluable confidence in the accuracy of instrumental results. A second example: the haloform reaction quantitatively degrades methyl ketones, producing a carboxylic acid which can be decarboxylated to determine the isotopic composition of the parent carbonyl and a haloform (CHI3, for example) that can be combusted to determine the isotopic composition of the methyl group. Ketones thus analyzed can be combined with Grignard reagents to yield carbon skeletons in which the isotopic compositions of internal and terminal -CH2- and -CH3 groups are known accurately. In general, analysts accustomed to demanding quantitative reactions should remember the power of mass balances and recognize that many organic-chemical reactions, while not quantitative, lack side products and can be driven to the total consumption of at least one reactant.

Multiple stable isotope fronts during non-isothermal fluid flow

NASA Astrophysics Data System (ADS)

Fekete, Szandra; Weis, Philipp; Scott, Samuel; Driesner, Thomas

2018-02-01

Stable isotope signatures of oxygen, hydrogen and other elements in minerals from hydrothermal veins and metasomatized host rocks are widely used to investigate fluid sources and paths. Previous theoretical studies mostly focused on analyzing stable isotope fronts developing during single-phase, isothermal fluid flow. In this study, numerical simulations were performed to assess how temperature changes, transport phenomena, kinetic vs. equilibrium isotope exchange, and isotopic source signals determine mineral oxygen isotopic compositions during fluid-rock interaction. The simulations focus on one-dimensional scenarios, with non-isothermal single- and two-phase fluid flow, and include the effects of quartz precipitation and dissolution. If isotope exchange between fluid and mineral is fast, a previously unrecognized, significant enrichment in heavy oxygen isotopes of fluids and minerals occurs at the thermal front. The maximum enrichment depends on the initial isotopic composition of fluid and mineral, the fluid-rock ratio and the maximum change in temperature, but is independent of the isotopic composition of the incoming fluid. This thermally induced isotope front propagates faster than the signal related to the initial isotopic composition of the incoming fluid, which forms a trailing front behind the zone of transient heavy oxygen isotope enrichment. Temperature-dependent kinetic rates of isotope exchange between fluid and rock strongly influence the degree of enrichment at the thermal front. In systems where initial isotope values of fluids and rocks are far from equilibrium and isotope fractionation is controlled by kinetics, the temperature increase accelerates the approach of the fluid to equilibrium conditions with the host rock. Consequently, the increase at the thermal front can be less dominant and can even generate fluid values below the initial isotopic composition of the input fluid. As kinetics limit the degree of isotope exchange, a third front may develop in kinetically limited systems, which propagates with the advection speed of the incoming fluid and is, therefore, traveling fastest. The results show that oxygen isotope signatures at thermal fronts recorded in rocks and veins that experienced isotope exchange with fluids can easily be misinterpreted, namely if bulk analytical techniques are applied. However, stable isotope microanalysis on precipitated minerals may - if later isotope exchange is kinetically limited - provide a valuable archive of the transient thermal and hydrological evolution of a system.

Nuclear forensic analysis of an unknown uranium ore concentrate sample seized in a criminal investigation in Australia

DOE PAGES

Keegan, Elizabeth; Kristo, Michael J.; Colella, Michael; ...

2014-04-13

In early 2009, a state policing agency raided a clandestine drug laboratory in a suburb of a major city in Australia. While searching the laboratory, they discovered a small glass jar labelled “Gamma Source” and containing a green powder. The powder was radioactive. This paper documents the detailed nuclear forensic analysis undertaken to characterize and identify the material and determine its provenance. Isotopic and impurity content, phase composition, microstructure and other characteristics were measured on the seized sample, and the results were compared with similar material obtained from the suspected source (ore and ore concentrate material). While an extensive rangemore » of parameters were measured, the key ‘nuclear forensic signatures’ used to identify the material were the U isotopic composition, Pb and Sr isotope ratios, and the rare earth element pattern. These measurements, in combination with statistical analysis of the elemental and isotopic content of the material against a database of uranium ore concentrates sourced from mines located worldwide, led to the conclusion that the seized material (a uranium ore concentrate of natural isotopic abundance) most likely originated from Mary Kathleen, a former Australian uranium mine.« less

Intercomparison of Lab-Based Soil Water Extraction Methods for Stable Water Isotope Analysis

NASA Astrophysics Data System (ADS)

Pratt, D.; Orlowski, N.; McDonnell, J.

2016-12-01

The effect of pore water extraction technique on resultant isotopic signature is poorly understood. Here we present results of an intercomparison of five common lab-based soil water extraction techniques: high pressure mechanical squeezing, centrifugation, direct vapor equilibration, microwave extraction, and cryogenic extraction. We applied five extraction methods to two physicochemically different standard soil types (silty sand and clayey loam) that were oven-dried and rewetted with water of known isotopic composition at three different gravimetric water contents (8, 20, and 30%). We tested the null hypothisis that all extraction techniques would provide the same isotopic result independent from soil type and water content. Our results showed that the extraction technique had a significant effect on the soil water isotopic composition. Each method exhibited deviations from spiked reference water, with soil type and water content showing a secondary effect. Cryogenic extraction showed the largest deviations from the reference water, whereas mechanical squeezing and centrifugation provided the closest match to the reference water for both soil types. We also compared results for each extraction technique that produced liquid water on both an OA-ICOS and IRMS; differences between them were negligible.

Nuclear forensic analysis of an unknown uranium ore concentrate sample seized in a criminal investigation in Australia.

PubMed

Keegan, Elizabeth; Kristo, Michael J; Colella, Michael; Robel, Martin; Williams, Ross; Lindvall, Rachel; Eppich, Gary; Roberts, Sarah; Borg, Lars; Gaffney, Amy; Plaue, Jonathan; Wong, Henri; Davis, Joel; Loi, Elaine; Reinhard, Mark; Hutcheon, Ian

2014-07-01

Early in 2009, a state policing agency raided a clandestine drug laboratory in a suburb of a major city in Australia. During the search of the laboratory, a small glass jar labelled "Gamma Source" and containing a green powder was discovered. The powder was radioactive. This paper documents the detailed nuclear forensic analysis undertaken to characterise and identify the material and determine its provenance. Isotopic and impurity content, phase composition, microstructure and other characteristics were measured on the seized sample, and the results were compared with similar material obtained from the suspected source (ore and ore concentrate material). While an extensive range of parameters were measured, the key 'nuclear forensic signatures' used to identify the material were the U isotopic composition, Pb and Sr isotope ratios, and the rare earth element pattern. These measurements, in combination with statistical analysis of the elemental and isotopic content of the material against a database of uranium ore concentrates sourced from mines located worldwide, led to the conclusion that the seized material (a uranium ore concentrate of natural isotopic abundance) most likely originated from Mary Kathleen, a former Australian uranium mine. Copyright © 2014 Elsevier Ireland Ltd. All rights reserved.

Nuclear forensic analysis of an unknown uranium ore concentrate sample seized in a criminal investigation in Australia

DOE Office of Scientific and Technical Information (OSTI.GOV)

Keegan, Elizabeth; Kristo, Michael J.; Colella, Michael

In early 2009, a state policing agency raided a clandestine drug laboratory in a suburb of a major city in Australia. While searching the laboratory, they discovered a small glass jar labelled “Gamma Source” and containing a green powder. The powder was radioactive. This paper documents the detailed nuclear forensic analysis undertaken to characterize and identify the material and determine its provenance. Isotopic and impurity content, phase composition, microstructure and other characteristics were measured on the seized sample, and the results were compared with similar material obtained from the suspected source (ore and ore concentrate material). While an extensive rangemore » of parameters were measured, the key ‘nuclear forensic signatures’ used to identify the material were the U isotopic composition, Pb and Sr isotope ratios, and the rare earth element pattern. These measurements, in combination with statistical analysis of the elemental and isotopic content of the material against a database of uranium ore concentrates sourced from mines located worldwide, led to the conclusion that the seized material (a uranium ore concentrate of natural isotopic abundance) most likely originated from Mary Kathleen, a former Australian uranium mine.« less

Using multiple isotopes to understand the source of ingredients used in golden beverages

NASA Astrophysics Data System (ADS)

Wynn, J. G.

2011-12-01

Traditionally, beer contains 4 simple ingredients: water, barley, hops and yeast. Each of these ingredients used in the brewing process contributes some combination of a number of "traditional" stable isotopes (i.e., isotopes of H, C, O, N and S) to the final product. As an educational exercise in an "Analytical Techniques in Geology" course, a group of students analyzed the isotopic composition of the gas, liquid and solid phases of a variety of beer samples collected from throughout the world (including other beverages). The hydrogen and oxygen isotopic composition of the water followed closely the isotopic composition of local meteoric water at the source of the brewery, although there is a systematic offset from the global meteoric water line that may be due to the effects of CO2-H2O equilibration. The carbon isotopic composition of the CO2 reflected that of the solid residue (the source of carbon used as a fermentation substrate), but may potentially be modified by addition of gas-phase CO2 from an inorganic source. The carbon isotopic composition of the solid residue similarly tracks that of the fermentation substrate, and may indicate some alcohol fermented from added sugars in some cases. The nitrogen isotopic composition of the solid residue was relatively constant, and may track the source of nitrogen in the barley, hops and yeast. Each of the analytical methods used is a relatively standard technique used in geological applications, making this a "fun" exercise for those involved, and gives the students hands-on experience with a variety of analytes from a non-traditional sample material.

The influence of diet on the δ 13C of shell carbon in the pulmonate snail Helix aspersa

NASA Astrophysics Data System (ADS)

Stott, Lowell D.

2002-02-01

The influence of diet and atmospheric CO 2 on the carbon isotope composition of shell aragonite and shell-bound organic carbon in the pulmonate snail Helix aspersa raised in the laboratory was investigated. Three separate groups of snails were raised on romaine lettuce (C3 plant, δ 13C=-25.8‰), corn (C4 plant, δ 13C=-10.5‰), and sour orange ( 12C-enriched C3 plant, δ 13C=-39.1‰). The isotopic composition of body tissues closely tracked the isotopic composition of the snail diet as demonstrated previously. However, the isotopic composition of the acid insoluble organic matrix extracted from the aragonite shells does not track diet in all groups. In snails that were fed corn the isotopic composition of the organic matrix was more negative than the body by as much as 5‰ whereas the matrix was approximately 1‰ heavier than the body tissues in snails fed a diet of C3 plant material. These results indicate that isotopic composition of the organic matrix carbon cannot be used as an isotopic substrate for paleodietary reconstructions without first determining the source of the carbon and any associated fractionations. The isotopic composition of the shell aragonite is offset from the body tissues by 12.3‰ in each of the culture groups. This offset was not influenced by the consumption of carbonate and is not attributable to the diffusion of atmospheric CO 2 into the hemolymph. The carbon isotopic composition of shell aragonite is best explained in terms of equilibrium fractionations associated with exchange between metabolic CO 2 and HCO 3 in the hemolymph and the fractionation associated with carbonate precipitation. These results differ from previous studies, based primarily on samples collected in the field, that have suggested atmospheric carbon dioxide contributes significantly to the shell δ 13C. The culture results indicate that the δ 13C of aragonite is a good recorder of the isotopic composition of the snail body tissue, and therefore a better recorder of diet than is the insoluble shell organic carbon. Because the systematic fractionation of carbon isotopes within the snail is temperature dependent, the δ 13C of the shell could provide an independent technique for estimating paleotemperature changes.

Measurement of natural carbon isotopic composition of acetone in human urine.

PubMed

Yamada, Keita; Ohishi, Kazuki; Gilbert, Alexis; Akasaka, Mai; Yoshida, Naohiro; Yoshimura, Ryoko

2016-02-01

The natural carbon isotopic composition of acetone in urine was measured in healthy subjects using gas chromatography-combustion-isotope ratio mass spectrometry combined with headspace solid-phase microextraction (HS-SPME-GC-C-IRMS). Before applying the technique to a urine sample, we optimized the measurement conditions of HS-SPME-GC-C-IRMS using aqueous solutions of commercial acetone reagents. The optimization enabled us to determine the carbon isotopic compositions within ±0.2 ‰ of precision and ±0.3‰ of error using 0.05 or 0.2 mL of aqueous solutions with acetone concentrations of 0.3-121 mg/L. For several days, we monitored the carbon isotopic compositions and concentrations of acetone in urine from three subjects who lived a daily life with no restrictions. We also monitored one subject for 3 days including a fasting period of 24 h. These results suggest that changes in the availability of glucose in the liver are reflected in changes in the carbon isotopic compositions of urine acetone. Results demonstrate that carbon isotopic measurement of metabolites in human biological samples at natural abundance levels has great potential as a tool for detecting metabolic changes caused by changes in physiological states and disease.

Estimates of groundwater recharge rates and sources in the East Mountain area, Eastern Bernalillo County, New Mexico, 2005-12

USGS Publications Warehouse

Rice, Steven E.; Crilley, Dianna M.

2014-01-01

Stable isotope data from springs and snowpacks sampled in the East Mountain area were compared with local, regional, and global meteoric water lines and were analyzed along with values representing the stable isotope composition of winter precipitation and summer monsoonal rains. Results of the stable isotope analysis from springs in this study suggested that winter precipitation is the primary source of groundwater recharge to the aquifers supplying the springs, but there is a component of more isotopically enriched precipitation being recharged as well, likely from summer monsoonal rains. Specific conductance, groundwater-level hydrographs, snowpack chemistry, and snow-water equivalent data were used to inform the analyses and corroborate the findings of the CMB and stable isotope results.

Lead isotopes in iron and manganese oxide coatings and their use as an exploration guide for concealed mineralization

USGS Publications Warehouse

Gulson, B.L.; Church, S.E.; Mizon, K.J.; Meier, A.L.

1992-01-01

Lead isotopes from Fe and Mn oxides that coat stream pebbles from around the Mount Emmons porphyry molybdenum deposit in Colorado were studied to assess the feasibility of using Pb isotopes to detect concealed mineral deposits. The Fe/Mn oxide coatings were analyzed to determine their elemental concentrations using ICP-AES. The Pb isotope compositions of solutions from a selected suite of samples were measured, using both thermal ionization and ICP mass spectrometry, to compare results determined by the two analytical methods. Heavy mineral concentrates from the same sites were also analyzed to compare the Pb isotope compositions of the Fe/Mn coatings with those found in panned concentrates. The Fe/Mn and 206Pb/204Pb ratios of the oxide coatings are related to the lithology of the host rocks; Fe/Mn oxide coatings on pebbles of black shale have higher Fe/Mn values than do the coatings on either sandstone or igneous rocks. The shale host rocks have a more radiogenic signature (e.g. higher 206Pb/ 204Pb) than the sandstone or igneous host rocks. The Pb isotope data from sandstone and igneous hosts can detect concealed mineralized rock on both a regional and local scale, even though there are contributions from: (1) metals from the main-stage molybdenite ore deposit; (2) metals from the phyllic alteration zone which has a more radiogenic Pb isotope signature reflecting hydrothermal leaching of Pb from the Mancos Shale; (3) Pb-rich base metal veins with a highly variable Pb isotope signature; and (4) sedimentary country rocks which have a more radiogenic Pb isotope signature. An investigation of within-stream variation shows that the Pb isotope signature of the molybdenite ore zone is retained in the Fe/Mn oxide coatings and is not camouflaged by contributions from Pb-rich base-metal veins that crop out upstream. In another traverse, the Pb isotope data from Fe/Mn oxide coatings reflect a complex mixing of Pb from the molybdenite ore zone and its hornfels margin, Pb-rich base-metal veins, and sedimentary country rocks. Stream-sediment anomalies detected using oxalic acid leaches can be evaluated using Pb isotope analysesof selected geochemical anomalies. Such an evaluation procedure, given regional target Pb isotope signatures for concealed mineralization, can greatly reduce the cost of exploration for undiscovered ore deposits concealed beneath barren overburden. Lead isotope measurements on aliquots of the same solutions showed that ICP-MS determinations are of low precision and vary non-systematically when compared with the Pb isotope values of the higher precision thermal ionization method. These variations and lower precision of the ICP-MS measurements are attributed to matrix effects. ?? 1992.

Sr isotopic tracer study of the Samail ophiolite, Oman.

USGS Publications Warehouse

Lanphere, M.A.; Coleman, R.G.; Hopson, C.A.

1981-01-01

Rb and Sr concentrations and Sr-isotopic compositions were measured in 41 whole-rock samples and 12 mineral separates from units of the Samail ophiolite, including peridotite, gabbro, plagiogranite, diabase dykes, and gabbro and websterite dykes within the metamorphic peridotite. Ten samples of cumulate gabbro from the Wadir Kadir section and nine samples from the Wadi Khafifah section have 87Sr/86Sr ratios of 0.70314 + or - 0.00030 and 0.70306 + or - 0.00034, respectively. The dispersion in Sr- isotopic composition may reflect real heterogeneities in the magma source region. The average Sr-isotopic composition of cumulate gabbro falls in the range of isotopic compositions of modern MORB. The 87Sr/86Sr ratios of noncumulate gabbro, plagiogranite, and diabase dykes range 0.7034-0.7047, 0.7038-0.7046 and 0.7037- 0.7061, respectively. These higher 87Sr/86Sr ratios are due to alteration of initial magmatic compositions by hydrothermal exchange with sea-water. Mineral separates from dykes that cut harzburgite tectonite have Sr-isotopic compositions which agree with that of cumulate gabbro. These data indicate that the cumulate gabbro and the different dykes were derived from partial melting of source regions that had similar long-term histories and chemical compositions.-T.R.

Rare earth element transport in the western North Atlantic inferred from Nd isotopic observations

NASA Technical Reports Server (NTRS)

Piepgras, D. J.; Wasserburg, G. J.

1987-01-01

The relationship between the Nd isotopic composition in the Atlantic waters and the origin and circulation of the water masses was investigated. Samples were collected in the western North Atlantic between 7 and 54 deg N. The isotopic composition (Nd-143/Nd-144 ratios) showed extensive vertical structure at all locations. In regions where a thermocline was well-developed, large isotopic shifts were observed across the base of the thermocline, while regions without a thermocline were characterized by much more gradual shifts in isotopic composition with depth. The data reveal an excellent correlation between the Nd isotopic distribution in the western North Atlantic water column and the distribution of water masses identified from temperature and salinity measurements.

Sm-Nd in marine carbonates and phosphates - Implications for Nd isotopes in seawater and crustal ages

NASA Technical Reports Server (NTRS)

Shaw, H. F.; Wasserburg, G. J.

1985-01-01

The possibility of establishing a record of variations in the isotopic composition of Nd in seawater over geologic time is explored. To construct such a record, a phase must be identified which incorporated Nd with the same isotopic composition as seawater at the time of its formation, preserves that composition, and which is relatively common in sediments. To evaluate the suitability of carbonates and phosphates, the Rb, Sr, Sm, and Nd concentrations and the Nd and Sr isotopic composition of a variety of modern and ancient marine calcite, aragonite, and apatite samples have been measured and the results are presented and discussed.

Fingerprints of carbon, nitrogen, and silicon isotopes in small interstellar SiC grains from the Murchison meteorite

NASA Technical Reports Server (NTRS)

Hoppe, Peter; Geiss, Johannes; Buehler, Fritz; Neuenschwander, Juerg; Amari, Sachiko; Lewis, Roy S.

1993-01-01

We report ion microprobe determinations of the carbon, nitrogen, and silicon isotopic compositions of small SiC grains from the Murchison CM2 chondrite. Analyses were made on samples containing variable numbers of grains and on 14 individual grains. In some cases the multiple-grain sample compositions were probably dominated by only one or two grains. Total ranges observed are given. Only a few grains show values near the range limits. Both the total ranges of carbon and nitrogen isotopic compositions, and even the narrower ranges typical for the majority of the grains, are similar to those observed for larger SiC grains. Two rare components appear to be present in the smaller-size fraction, one characterized by C-12/C-13 about 12-16 and the other by very heavy nitrogen. The carbon and nitrogen isotopic compositions qualitatively may reflect hydrostatic H-burning via the CNO cycle and He-burning in red giants, as well as explosive H-burning in novae. The silicon isotopic compositions of most grains qualitatively show what is the signature of He-burning. The silicon isotopic composition of one grain, however, suggests a different process.

Geochemistry of Precambrian carbonates. IV - Early Paleoproterozoic (2.25 +/- 0.25 Ga) seawater

NASA Technical Reports Server (NTRS)

Veizer, Jan; Clayton, R. N.; Hinton, R. W.

1992-01-01

The mineralogy, chemistry, and isotopic composition of the Malmani Dolomite, Duck Creek Dolomite, and Bruce 'Limestone' Member of the Espanola Formation are studied in an effort to restrict the first- and second-order variations in isotopic composition of Early Paleoproterozoic seawater. The diagenetic rank is found to increase in the order Duck Creek less than Bruce less than Malmani. The interpolation of alteration trends to 'best' value yields an estimate of 0.70550 for Sr-87/Sr-86. For delta C-13, the measured range of 0 +/- 1.5 percent PDB is similar to that observed for Phanerozoic marine carbonates, while the 'best' delta O-18 value for dolostones is -5 percent PDB, depleted in O-18 relative to Phanerozoic counterparts but comparable to estimates obtained for Archean facies. The isotope geochemistry and mineralogy of Bruce 'Limestone' Member is consistent with the proposition that the sequence was deposited in a lacustrine environment.

Common Occurrence of Explosive Hydrogen Burning in Type II Supernovae

NASA Astrophysics Data System (ADS)

Liu, Nan; Stephan, Thomas; Boehnke, Patrick; Nittler, Larry R.; Meyer, Bradley S.; O’D. Alexander, Conel M.; Davis, Andrew M.; Trappitsch, Reto; Pellin, Michael J.

2018-03-01

We report Mo isotopic data for 16 15N-rich presolar SiC grains of type AB (14N/15N < solar, AB1) and their correlated Sr and Ba isotope ratios when available. Of the 16 AB1 grains, 8 show s-process Mo isotopic compositions, together with s-process Ba and/or Sr isotopic compositions. We found that a higher percentage of AB1 grains show anomalous isotopic compositions than that of AB2 grains (14N/15N > solar), thus providing further support to the division of the two AB subgroups recently proposed by Liu et al., who showed that AB1 grains most likely originated from Type II supernovae (SNe) with explosive H burning. Comparison of the Sr, Mo, and Ba isotopic compositions of the AB1 grains with SN model predictions indicates that the s-process isotopic compositions of AB1 grains resulted from neutron-capture processes occurring during the progenitor massive stars’ pre-SN evolution rather than from an explosive neutron-capture process. In addition, the observations of (1) explosive H burning occurring in the C-rich regions of the progenitor SNe of X grains as suggested by the isotopic compositions of X grains, and (2) explosive H burning occurring both at the bottom of the He/C zone and at the top of the He/N zone as suggested by model simulations, imply that explosive H burning is a common phenomenon in outer SN zones.

Common Occurrence of Explosive Hydrogen Burning in Type II Supernovae

DOE PAGES

Liu, Nan; Stephan, Thomas; Boehnke, Patrick; ...

2018-03-16

In this paper, we report Mo isotopic data for 16 15N-rich presolar SiC grains of type AB ( 14N/ 15N < solar, AB1) and their correlated Sr and Ba isotope ratios when available. Of the 16 AB1 grains, 8 show s-process Mo isotopic compositions, together with s-process Ba and/or Sr isotopic compositions. We found that a higher percentage of AB1 grains show anomalous isotopic compositions than that of AB2 grains ( 14N/ 15N > solar), thus providing further support to the division of the two AB subgroups recently proposed by Liu et al., who showed that AB1 grains most likelymore » originated from Type II supernovae (SNe) with explosive H burning. Comparison of the Sr, Mo, and Ba isotopic compositions of the AB1 grains with SN model predictions indicates that the s-process isotopic compositions of AB1 grains resulted from neutron-capture processes occurring during the progenitor massive stars' pre-SN evolution rather than from an explosive neutron-capture process. Finally, in addition, the observations of (1) explosive H burning occurring in the C-rich regions of the progenitor SNe of X grains as suggested by the isotopic compositions of X grains, and (2) explosive H burning occurring both at the bottom of the He/C zone and at the top of the He/N zone as suggested by model simulations, imply that explosive H burning is a common phenomenon in outer SN zones.« less

Common Occurrence of Explosive Hydrogen Burning in Type II Supernovae

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Nan; Stephan, Thomas; Boehnke, Patrick

In this paper, we report Mo isotopic data for 16 15N-rich presolar SiC grains of type AB ( 14N/ 15N < solar, AB1) and their correlated Sr and Ba isotope ratios when available. Of the 16 AB1 grains, 8 show s-process Mo isotopic compositions, together with s-process Ba and/or Sr isotopic compositions. We found that a higher percentage of AB1 grains show anomalous isotopic compositions than that of AB2 grains ( 14N/ 15N > solar), thus providing further support to the division of the two AB subgroups recently proposed by Liu et al., who showed that AB1 grains most likelymore » originated from Type II supernovae (SNe) with explosive H burning. Comparison of the Sr, Mo, and Ba isotopic compositions of the AB1 grains with SN model predictions indicates that the s-process isotopic compositions of AB1 grains resulted from neutron-capture processes occurring during the progenitor massive stars' pre-SN evolution rather than from an explosive neutron-capture process. Finally, in addition, the observations of (1) explosive H burning occurring in the C-rich regions of the progenitor SNe of X grains as suggested by the isotopic compositions of X grains, and (2) explosive H burning occurring both at the bottom of the He/C zone and at the top of the He/N zone as suggested by model simulations, imply that explosive H burning is a common phenomenon in outer SN zones.« less

Low-temperature, non-stoichiometric oxygen isotope exchange coupled to Fe(II)-goethite interactions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Frierdich, Andrew J.; Beard, Brian L.; Rosso, Kevin M.

2015-07-01

The oxygen isotope composition of natural iron oxide minerals has been widely used as a paleoclimate proxy. Interpretation of their stable isotope compositions, however, requires accurate knowledge of isotopic fractionation factors and an understanding of their isotopic exchange kinetics, the latter of which informs us how diagenetic processes may alter their isotopic compositions. Prior work has demonstrated that crystalline iron oxides do not significantly exchange oxygen isotopes with pure water at low temperature, which has restricted studies of isotopic fractionation factors to precipitation experiments or theoretical calculations. Using a double three-isotope method (¹⁸O-¹⁷O-¹⁶O and ⁵⁷Fe-⁵⁶Fe-⁵⁴Fe) we compare O and Femore » isotope exchange kinetics, and demonstrate, for the first time, that O isotope exchange between structural O in crystalline goethite and water occurs in the presence of aqueous Fe(II) (Fe(II) aq) at ambient temperature (i.e., 22–50 °C). The three-isotope method was used to extrapolate partial exchange results to infer the equilibrium, mass-dependent isotope fractionations between goethite and water. In addition, this was combined with a reversal approach to equilibrium by reacting goethite in two unique waters that vary in composition by about 16‰ in ¹⁸O/¹⁶O ratios. Our results show that interactions between Fe(II) aq and goethite catalyzes O isotope exchange between the mineral and bulk fluid; no exchange (within error) is observed when goethite is suspended in ¹⁷O-enriched water in the absence of Fe(II) aq. In contrast, Fe(II)-catalyzed O isotope exchange is accompanied by significant changes in ¹⁸O/¹⁶O ratios. Despite significant O exchange, however, we observed disproportionate amounts of Fe versus O exchange, where Fe isotope exchange in goethite was roughly three times that of O. This disparity provides novel insight into the reactivity of oxide minerals in aqueous solutions, but presents a challenge for utilizing such an approach to determine equilibrium isotope fractionation factors. Despite the uncertainty from extrapolation, there is consistency in goethite-water fractionation factors for our reversal approach to equilibrium, with final weighted average fractionation factor values of Δ¹⁸O Gth-wate r = 0.2 (±0.9‰) and 3.0 (±2.5‰) at 22 °C and -1.6 (±0.8‰) and 1.9 (±1.5‰) at 50 °C for micron-sized and nano-particulate goethite, respectively (errors at 2σ level). Reaction of ferrihydrite with Fe(II) aq in two distinct waters resulted in a quantitative conversion to goethite and complete O isotope exchange in each case, and similar fractionation factors were observed for experiments using the two waters. Comparison of our results with previous studies of O isotope fractionation between goethite and water suggests that particle size may be a contributing factor to the disparity among experimental studies.« less

Rb-Sr and Sm-Nd Ages of Zagami DML and SR Isotopic Heterogeneity in Zagami

NASA Technical Reports Server (NTRS)

Nyquist, L.aurenceE.; Shih, C.-Y.; Reese, Y. D.

2010-01-01

Zagami contains lithologic heterogeneity suggesting that it did not form in a homogeneous, thick lava flow [1]. We have previously investigated the Sr and Nd isotopic systematics of Coarse-Grained (CG) and Fine-Grained (FG) lithologies described by [2]. Both appear to belong to Normal Zagami (NZ) [1,3], but their initial Sr-isotopic compositions differ [4,5]. Here we report new analyses of the Dark Mottled Lithology (DML, [3]) that show its age and initial Sr and Nd isotopic compositions to be identical within error limits with those of CG, but Sr initial isotopic compositions differ from those of FG.

The O and H stable isotope composition of freshwaters in the British Isles. 2. Surface waters and groundwater

NASA Astrophysics Data System (ADS)

Darling, W. G.; Bath, A. H.; Talbot, J. C.

The utility of stable isotopes as tracers of the water molecule has a long pedigree. The study reported here is part of an attempt to establish a comprehensive isotopic "baseline" for the British Isles as background data for a range of applications. Part 1 of this study (Darling and Talbot, 2003) considered the isotopic composition of rainfall in Britain and Ireland. The present paper is concerned with the composition of surface waters and groundwater. In isotopic terms, surface waters (other than some upland streams) are poorly characterised in the British Isles; their potential variability has yet to be widely used as an aid in hydrological research. In what may be the first study of a major British river, a monthly isotopic record of the upper River Thames during 1998 was obtained. This shows high damping of the isotopic variation compared to that in rainfall over most of the year, though significant fluctuations were seen for the autumn months. Smaller rivers such as the Stour and Darent show a more subdued response to the balance between runoff and baseflow. The relationship between the isotopic composition of rainfall and groundwater is also considered. From a limited database, it appears that whereas Chalk groundwater is a representative mixture of weighted average annual rainfall, for Triassic sandstone groundwater there is a seasonal selection of rainfall biased towards isotopically-depleted winter recharge. This may be primarily the result of physical differences between the infiltration characteristics of rock types, though other factors (vegetation, glacial history) could be involved. In the main, however, groundwaters appear to be representative of bulk rainfall within an error band of 0.5‰ δ18O. Contour maps of the δ18O and δ2H content of recent groundwaters in the British Isles show a fundamental SW-NE depletion effect modified by topography. The range of measured values, while much smaller than those for rainfall, still covers some ‰ for δ18O and 30‰ for δ2H. Over lowland areas the "altitude effect" is of little significance, but in upland areas is consistent with a range of -0.2 to -0.3‰ per 100 m increase in altitude. Groundwaters dating from the late Pleistocene are usually modified in δ18O and δ2H owing to the effects of climate change on the isotopic composition of rainfall and thus of recharge. Contour maps of isotopic variability prior to 10 ka BP, based on the relatively limited information available from the British Isles, allow a first comparison between groundwaters now and at the end of the last Ice Age. The position of the British Isles in the context of the stable isotope systematics of NW Europe is reviewed briefly.

Molecular controls on Cu and Zn isotopic fractionation in Fe-Mn crusts

NASA Astrophysics Data System (ADS)

Little, S. H.; Sherman, D. M.; Vance, D.; Hein, J. R.

2014-06-01

The isotopic systems of the transition metals are increasingly being developed as oceanic tracers, due to their tendency to be fractionated by biological and/or redox-related processes. However, for many of these promising isotope systems the molecular level controls on their isotopic fractionations are only just beginning to be explored. Here we investigate the relative roles of abiotic and biotic fractionation processes in controlling modern seawater Cu and Zn isotopic compositions. Scavenging to Fe-Mn oxides represents the principal output for Cu and Zn to sediments deposited under normal marine (oxic) conditions. Using Fe-Mn crusts as an analogue for these dispersed phases, we investigate the phase association and crystal chemistry of Cu and Zn in such sediments. We present the results of an EXAFS study that demonstrate unequivocally that Cu and Zn are predominantly associated with the birnessite (δ-MnO2) phase in Fe-Mn crusts, as previously predicted from sequential leaching experiments (e.g., Koschinsky and Hein, 2003). The crystal chemistry of Cu and Zn in the crusts implies a reduction in coordination number in the sorbed phase relative to the free metal ion in seawater. Thus, theory would predict equilibrium fractionations that enrich the heavy isotope in the sorbed phase (e.g., Schauble, 2004). In natural samples, Fe-Mn crusts and nodules are indeed isotopically heavy in Zn isotopes (at ∼1‰) compared to deep seawater (at ∼0.5‰), consistent with the predicted direction of equilibrium isotopic fractionation based on our observations of the coordination environment of sorbed Zn. Further, ∼50% of inorganic Zn‧ is chloro-complexed (the other ∼50% is present as the free Zn2+ ion), and complexation by Cl- is also predicted to favour equilibrium partitioning of light Zn isotopes into the dissolved phase. The heavy Zn isotopic composition of Fe-Mn crusts and nodules relative to seawater can therefore be explained by an inorganic fractionation during uptake. However, Cu in Fe-Mn crusts is isotopically light (at ∼0.3 to 0.5‰) compared to the dissolved phase in seawater (at ∼0.9‰). We suggest that this is because dissolved Cu in the oceans is overwhelmingly complexed to strong organic ligands, which are better competitors for the heavy isotope.

Investigation of thallium fluxes from subaerial volcanism-Implications for the present and past mass balance of thallium in the oceans

USGS Publications Warehouse

Baker, R.G.A.; Rehkamper, M.; Hinkley, T.K.; Nielsen, S.G.; Toutain, J.P.

2009-01-01

A suite of 34 volcanic gas condensates and particulates from Kilauea (Hawaii), Mt. Etna and Vulcano (Italy), Mt. Merapi (Indonesia), White Island and Mt. Nguaruhoe (New Zealand) were analysed for both Tl isotope compositions and Tl/Pb ratios. When considered together with published Tl-Pb abundance data, the measurements provide globally representative best estimates of Tl/Pb = 0.46 ?? 0.25 and ??205Tl = -1.7 ?? 2.0 for the emissions of subaerial volcanism to the atmosphere and oceans (??205Tl is the deviation of the 205Tl/203Tl isotope ratio from NIST SRM 997 isotope standard in parts per 10,000). Compared to igneous rocks of the crust and mantle, volcanic gases were found to have (i) Tl/Pb ratios that are typically about an order of magnitude higher, and (ii) significantly more variable Tl isotope compositions but a mean ??205Tl value that is indistinguishable from estimates for the Earth's mantle and continental crust. The first observation can be explained by the more volatile nature of Tl compared to Pb during the production of volcanic gases, whilst the second reflects the contrasting and approximately balanced isotope fractionation effects that are generated by partial evaporation of Tl during magma degassing and partial Tl condensation as a result of the cooling and differentiation of volcanic gases. Mass balance calculations, based on results from this and other recent Tl isotope studies, were carried out to investigate whether temporal changes in the volcanic Tl fluxes could be responsible for the dramatic shift in the ??205Tl value of the oceans at ???55 Ma, which has been inferred from Tl isotope time series data for ferromanganese crusts. The calculations demonstrate that even large changes in the marine Tl input fluxes from volcanism and other sources are unable to significantly alter the Tl isotope composition of the oceans. Based on modelling, it is shown that the large inferred change in the ??205Tl value of seawater is best explained if the oceans of the early Cenozoic featured significantly larger Tl output fluxes to oxic pelagic sediments, whilst the sink fluxes to altered ocean crust remained approximately constant. ?? 2009 Elsevier Ltd.

Isotopic Composition of Trapped and Cosmogenic Noble Gases in Several Martian Meteorites

NASA Technical Reports Server (NTRS)

Garrison, Daniel H.; Bogard, Donald D.

1997-01-01

Isotopic abundances of the noble gases were measured in the following Martian meteorites: two shock glass inclusions from EET79001, shock vein glass from Shergotty and Y793605, and whole rock samples of ALH84001 and QUE94201. These glass samples, when combined with literature data on a separate single glass inclusion from EET79001 and a glass vein from Zagami, permit examination of the isotopic composition of Ne, Ar, Kr, and Xe trapped from the Martian atmosphere in greater detail. The isotopic composition of Martian Ne, if actually present in these glasses, remains poorly defined. The Ar-40/Ar-36 ratio of Martian atmospheric Ar may be much less than the ratio measured by Viking and possibly as low as approx. 1900. The atmospheric Ar-36/Ar-38 ratio is less than or equal to 4.0. Martian atmospheric Kr appears to be enriched in lighter isotopes by approx. 0.4%/amu compared to both solar wind Kr and to the Martian composition previously reported. The Martian atmospheric Ar-36/Xe-132 and Kr-84/Xe-132 Xe elemental ratios are higher than those reported by Viking by factors of approx. 3.3 and approx. 2.5, respectively. Cosmogenic gases indicate space exposure ages of 13.9 +/- 1 Myr for ALH84001 and 2.7 +/- 0.6 Myr for QUE94201. Small amounts of Ne-21 produced by energetic solar protons may be present in QUE94201, but are not present in ALH84001 or Y793605. The space exposure age for Y793605 is 4.9 +/- 0.6 Myr and appears to be distinctly older than the ages for basaltic shergottites.

A Carbon Source Apportionment Shift in Mexico City Atmospheric Particles During 2003-2004 as Determined with Stable Carbon Isotopes

NASA Astrophysics Data System (ADS)

Lopez-Veneroni, D. G.; Vega, E.

2013-05-01

The stable carbon isotope composition of atmospheric particles (PM2.5) was measured at La Merced (MER), a commercial site in the eastern sector, and at Xalostoc (XAL) an industrial site in the NE sector of Mexico City, during three sampling periods in autumn 2003, and spring and autumn 2004. At each site and sampling campaign particle samples were collected daily with minivol samplers during two week periods. Ancillary data included organic and elemental carbon, trace elements and ionic species. This data base was complement with air quality data from the RAMA (Automatic Atmospheric Monitoring Network). In general, particle concentrations, ionic species and some air quality species showed higher concentrations in autumn and lowest values in spring. Moreover, the concentrations of these chemical species were highest at XAL compared to MER. The stable carbon isotope composition of PM2.5 during autumn 2003 and spring 2004 had and average value of -26.04 (± 1.54) ‰ vs. PDB. Differences in the isotopic composition between the two sites were non significant. The average δ13C during these seasons were 1 ‰ lighter relative to data collected previously at these sites during 2000 and 2001, and is consistent with a predominant source of hydrocarbon combustion. In autumn 2004, however, average δ13C at XAL and MER increased to -22.8 (± 0.9) and -20.6 (± 3.1) ‰, respectively. Organic carbon concentrations during this period increased concomitantly at these sites. The shift in the isotopic composition in ambient particles suggests a predominance of soil-derived carbon during this period. The possible causes and implications of this are discussed.

Tracing the distribution of erosion in the Brahmaputra watershed from isotopic compositions of stream sediments

NASA Astrophysics Data System (ADS)

Singh, Sunil K.; France-Lanord, Christian

2002-09-01

Bank sediments and suspended loads of the Brahmaputra River and its important tributaries were collected from the Himalayan front to Bangladesh along with most of the important tributaries. Chemical and isotopic compositions of the sediments are used to trace sediment provenance and to understand erosion patterns in the basin. Overall isotopic compositions range from 0.7053 to 0.8250 for Sr and ɛNd from -20.5 to -6.9. This large range derives from the variable proportions of sediments from Himalayan formations with high Sr isotopic ratios and low ɛNd, and Transhimalayan plutonic belt with lower Sr isotopic ratios and higher ɛNd. The latter are exposed to erosion in the Tsangpo and in the eastern tributary drainages. Overall erosion of the Himalayan rocks is dominant, representing ca 70% of the detrital influx. Compositions of the Brahmaputra main channel are rather stable between 0.7177 and 0.7284 for Sr and between -14.4 and -12.5 for ɛNd throughout its course in the plain from the Siang-Tsangpo at the foot of the Himalayan range down to the delta. This stability, despite the input of large Himalayan rivers suggests that the Siang-Tsangpo River represents the major source of sediment to the whole Brahmaputra. Geochemical budget implies that erosion of the Namche Barwa zone represents about 45% of the total flux at its outflow before confluence with the Ganga from only 20% of the mountain area. Higher erosion rates in the eastern syntaxis compared to the other Himalayan ranges is related to the rapid exhumation rates of this region, possibly triggered by higher precipitation over the far-eastern Himalaya and the high incision potential of the Tsangpo River due to its very high water discharge.

Gallium isotopic evidence for extensive volatile loss from the Moon during its formation

PubMed Central

Kato, Chizu; Moynier, Frédéric

2017-01-01

The distribution and isotopic composition of volatile elements in planetary materials holds a key to the characterization of the early solar system and the Moon’s formation. The Moon and Earth are chemically and isotopically very similar. However, the Moon is highly depleted in volatile elements and the origin of this depletion is still debated. We present gallium isotopic and elemental measurements in a large set of lunar samples to constrain the origin of this volatile depletion. We show that while Ga has a geochemical behavior different from zinc, both elements show a systematic enrichment in the heavier isotopes in lunar mare basalts and Mg-suite rocks compared to the silicate Earth, pointing to a global-scale depletion event. On the other hand, the ferroan anorthosites are isotopically heterogeneous, suggesting a secondary distribution of Ga at the surface of the Moon by volatilization and condensation. The isotopic difference of Ga between Earth and the Moon and the isotopic heterogeneity of the crustal ferroan anorthosites suggest that the volatile depletion occurred following the giant impact and during the lunar magma ocean phase. These results point toward a Moon that has lost its volatile elements during a whole-scale evaporation event and that is now relatively dry compared to Earth. PMID:28782027

Analysis of High Frequency Site-Specific Nitrogen and Oxygen Isotopic Composition of Atmospheric Nitrous Oxide at Mace Head, Ireland

NASA Astrophysics Data System (ADS)

McClellan, M. J.; Harris, E. J.; Olszewski, W.; Ono, S.; Prinn, R. G.

2014-12-01

Atmospheric nitrous oxide (N2O) significantly impacts Earth's climate due to its dual role as an inert potent greenhouse gas in the troposphere and as a reactive source of ozone-destroying nitrogen oxides in the stratosphere. However, there remain significant uncertainties in the global budget of this gas. The marked spatial divide in its reactivity means that all stages in the N2O life cycle—emission, transport, and destruction—must be examined to understand the overall effect of N2O on climate. Source and sink processes of N2O lead to varying concentrations of N2O isotopologues (14N14N16O, 14N15N16O, 15N14N16O, and 14N14N18O being measured) due to preferential isotopic production and elimination in different environments. Estimation of source and sink fluxes can be improved by combining isotopically resolved N2O observations with simulations using a chemical transport model with reanalysis meteorology and treatments of isotopic signatures of specific surface sources and stratospheric intrusions. We present the first few months of site-specific nitrogen and oxygen isotopic composition data from the Stheno-TILDAS instrument (Harris et al, 2013) at Mace Head, Ireland and compare these to results from MOZART-4 (Model for Ozone and Related Chemical Tracers, version 4) chemical transport model runs including N2O isotopic fractionation processes and reanalysis meterological fields (NCEP/NCAR, MERRA, and GEOS-5). This study forms the basis for future inverse modeling experiments that will improve the accuracy of isotopically differentiated N2O emission and loss estimates. Ref: Harris, E., D. Nelson, W. Olszewski, M. Zahniser, K. Potter, B. McManus, A. Whitehill, R. Prinn, and S. Ono, Development of a spectroscopic technique for continuous online monitoring of oxygen and site-specific nitrogen isotopic composition of atmospheric nitrous oxide, Analytical Chemistry, 2013; DOI: 10.1021/ac403606u.

Water vapor isotopes measurements at Mauna Loa, Hawaii: Comparison of laser spectroscopy and remote sensing with traditional methods, and the need for ongoing monitoring

NASA Astrophysics Data System (ADS)

Noone, D.; Galewsky, J.; Sharp, Z.; Worden, J.

2008-12-01

The isotopic composition of water vapor (2H/1H and 18O/16 ratios) provides unique information on the transport pathways that link the water sources to regional sinks, and thus proves useful in understanding the large scale humidity budgets. Recent advances in measurement technology allow the monitoring of water vapor isotope composition in ways which has can revolutionize investigations of atmospheric hydrology. Traditional measurement of isotopic composition requires trapping of samples with either large volume vacuum flasks or by trapping liquid samples with cryogens for later analyses using mass spectrometry, and are laborious and seldom span more than just short dedicated observational periods. On the other hand, laser absorption spectroscopy can provide almost continuous and autonomous in situ measurements of isotope abundances with precision almost that of traditional mass spectrometry, and observations from spacecraft can make almost daily maps of the global isotope distributions. In October of 2008 three laser based spectrometers were deployed at the Mauna Loa Laboratory in Hawaii to make continuous measurement of the 2H and 18O abundance of free tropospheric water vapor. These results are compared with traditional measurements and with measurements from two satellite platforms. While providing field validation of the new methodologies, the data show variability which captures the transport processes in the region. The data are used to characterize the role of large scale mixing of dry air, the influence of the boundary layer and the importance of moist convection in controlling the low humidity of subtropical air near Hawaii. Although the record is short, it demonstrates the usefulness of using robust isotope measurements to understand the budgets of the most important greenhouse gas. This work motivates establishing a continuous record of isotopes measurement at baseline sites, like Mauna Loa, such that the changes in water cycle can be understood and monitored as climate changes.

Water vapor isotopes measurements at Mauna Loa, Hawaii: Comparison of laser spectroscopy and remote sensing with traditional methods, and the need for ongoing monitoring

NASA Astrophysics Data System (ADS)

Galewsky, J.; Noone, D.; Sharp, Z.; Worden, J.

2009-04-01

The isotopic composition of water vapor (2H/1H and 18O/16 ratios) provides unique information on the transport pathways that link water sources to regional sinks, and thus proves useful in understanding large scale atmospheric humidity budgets. Recent advances in measurement technology allow the monitoring of water vapor isotope composition in ways which has can revolutionize investigations of atmospheric hydrology. Traditional measurement of isotopic composition requires trapping of samples with either large volume vacuum flasks or by trapping liquid samples with cryogens for later analyses using mass spectrometry, and are laborious and seldom span more than just short dedicated observational periods. On the other hand, laser absorption spectroscopy can provide almost continuous and autonomous in situ measurements of isotope abundances with precision almost that of traditional mass spectrometry, and observations from spacecraft can make almost daily maps of the global isotope distributions. In October of 2008 three laser based spectrometers were deployed at the Mauna Loa Laboratory in Hawaii to make continuous measurement of the 2H and 18O abundance of free tropospheric water vapor. These results are compared with traditional measurements and with measurements from two satellite platforms. While providing field validation of the new methodologies, the data show variability which captures the transport processes in the region. The data are used to characterize the role of large scale mixing of dry air, the influence of the boundary layer and the importance of moist convection in controlling the low humidity of subtropical air near Hawaii. Although the record is short, it demonstrates the usefulness of using robust isotope measurements to understand the budgets of the most important greenhouse gas. This work motivates establishing a continuous record of isotopes measurement at baseline sites, like Mauna Loa, such that the changes in water cycle can be understood and monitored as climate changes.

Calcium Isotopic Compositions of Normal Mid-Ocean Ridge Basalts From the Southern Juan de Fuca Ridge

NASA Astrophysics Data System (ADS)

Zhu, Hongli; Liu, Fang; Li, Xin; Wang, Guiqin; Zhang, Zhaofeng; Sun, Weidong

2018-02-01

Mantle peridotites show that Ca is isotopically heterogeneous in Earth's mantle, but the mechanism for such heterogeneity remains obscure. To investigate the effect of partial melting on Ca isotopic fractionation and the mechanism for Ca isotopic heterogeneity in the mantle, we report high-precision Ca isotopic compositions of the normal Mid-Ocean Ridge Basalts (N-MORB) from the southern Juan de Fuca Ridge. δ44/40Ca of these N-MORB samples display a small variation ranging from 0.75 ± 0.05 to 0.86 ± 0.03‰ (relative to NIST SRM 915a, a standard reference material produced by the National Institute of Standards and Technology), which are slightly lower than the estimated Upper Mantle value of 1.05 ± 0.04‰ and the Bulk Silicate Earth (BSE) value of 0.94 ± 0.05‰. This phenomenon cannot be explained by fractional crystallization, because olivine and orthopyroxene fractional crystallization has limited influence on δ44/40Ca of N-MORB due to their low CaO contents, while plagioclase fractional crystallization cannot lead to light Ca isotopic compositions of the residue magma. Instead, the lower δ44/40Ca of N-MORB samples compared to their mantle source is most likely caused by partial melting. The offset in δ44/40Ca between N-MORB and BSE indicates that at least 0.1-0.2‰ fractionation would occur during partial melting and light Ca isotopes are preferred to be enriched in magma melt, which is in accordance with the fact that δ44/40Ca of melt-depleted peridotites are higher than fertile peridotites in literature. Therefore, partial melting is an important process that can decrease δ44/40Ca in basalts and induce Ca isotopic heterogeneity in Earth's mantle.

Oxygen isotope analysis of fossil organic matter by secondary ion mass spectrometry

NASA Astrophysics Data System (ADS)

Tartèse, Romain; Chaussidon, Marc; Gurenko, Andrey; Delarue, Frédéric; Robert, François

2016-06-01

We have developed an analytical procedure for the measurement of oxygen isotope composition of fossil organic matter by secondary ion mass spectrometry (SIMS) at the sub-per mill level, with a spatial resolution of 20-30 μm. The oxygen isotope composition of coal and kerogen samples determined by SIMS are on average consistent with the bulk oxygen isotope compositions determined by temperature conversion elemental analysis - isotope ratio mass spectrometry (TC/EA-IRMS), but display large spreads of δ18O of ∼5-10‰, attributed to mixing of remnants of organic compounds with distinct δ18O signatures. Most of the δ18O values obtained on two kerogen residues extracted from the Eocene Clarno and Early Devonian Rhynie continental chert samples and on two immature coal samples range between ∼10‰ and ∼25‰. Based on the average δ18O values of these samples, and on the O isotope composition of water processed by plants that now constitute the Eocene Clarno kerogen, we estimated δ18Owater values ranging between around -11‰ and -1‰, which overall correspond well within the range of O isotope compositions for present-day continental waters. SIMS analyses of cyanobacteria-derived organic matter from the Silurian Zdanow chert sample yielded δ18O values in the range 12-20‰. Based on the O isotope composition measured on recent cyanobacteria from the hypersaline Lake Natron (Tanzania), and on the O isotope composition of the lake waters in which they lived, we propose that δ18O values of cyanobacteria remnants are enriched by about ∼18 ± 2‰ to 22 ± 2‰ relative to coeval waters. This relationship suggests that deep ocean waters in which the Zdanow cyanobacteria lived during Early Silurian times were characterised by δ18O values of around -5 ± 4‰. This study, establishing the feasibility of micro-analysis of Phanerozoic fossil organic matter samples by SIMS, opens the way for future investigations of kerogens preserved in Archean cherts and of the O isotopic composition of ocean water at that period in time.

Isotope Geochemistry of Possible Terrestrial Analogue for Martian Meteorite ALH84001

NASA Technical Reports Server (NTRS)

Mojzsis, Stephen J.

2000-01-01

We have studied the microdomain oxygen and carbon isotopic compositions by SIMS of complex carbonate rosettes from spinel therzolite xenoliths, hosted by nepheline basanite, from the island of Spitsbergen (Norway). The Quaternary volcanic rocks containing the xenoliths erupted into a high Arctic environment and through relatively thick continental crust containing carbonate rocks. We have attempted to constrain the sources of the carbonates in these rocks by combined O-18/O-16 and C-13/C-12 ratio measurements in 25 micron diameter spots of the carbonate and compare them to previous work based primarily on trace-element distributions. The origin of these carbonates can be interpreted in terms of either contamination by carbonate country rock during ascent of the xenoliths in the host basalt, or more probably by hydrothermal processes after emplacement. The isotopic composition of these carbonates from a combined delta.18O(sub SMOW) and delta.13C(sub PDB) standpoint precludes a primary origin of these minerals from the mantle. Here a description is given of the analysis procedure, standardization of the carbonates, major element compositions of the carbonates measured by electron microprobe, and their correlated C and O isotope compositions as measured by ion microprobe. Since these carbonate rosettes may represent a terrestrial analogue to the carbonate "globules" found in the martian meteorite ALH84001 interpretations for the origin of the features found in the Spitsbergen may be of interest in constraining the origin of these carbonate minerals on Mars.

Migration of sharks into freshwater systems during the Miocene and implications for Alpine paleoelevation

NASA Astrophysics Data System (ADS)

Kocsis, László; Vennemann, Torsten W.; Fontignie, Denis

2007-05-01

Trace-element and isotopic compositions of fossilized shark teeth sampled from Miocene marine sediments of the north Alpine Molasse Basin, the Vienna Basin, and the Pannonian Basin generally show evidence of formation in a marine environment under conditions geochemically equivalent to the open ocean. In contrast, two of eight shark teeth from the Swiss Upper Marine Molasse locality of La Molière have extremely low δ18O values (10.3‰ and 11.3‰) and low 87Sr/86Sr ratios (0.707840 and 0.707812) compared to other teeth from this locality (21.1‰ 22.4‰ and 0.708421 0.708630). The rare earth element (REE) abundances and patterns from La Molière not only differ between dentine and enameloid of the same tooth, but also between different teeth, supporting variable conditions of diagenesis at this site. However, the REE patterns of enameloid from the “exotic” teeth analyzed for O and Sr isotopic compositions are similar to those of teeth that have O and Sr isotopic compositions typical of a marine setting at this site. Collectively, this suggests that the two “exotic” teeth were formed while the sharks frequented a freshwater environment with very low 18O-content and Sr isotopic composition controlled by Mesozoic calcareous rocks. This is consistent with a paleogeography of high-elevation (˜2300 m) Miocene Alps adjacent to a marginal sea.

Silicon Isotopic Fractionation of CAI-like Vacuum Evaporation Residues

DOE Office of Scientific and Technical Information (OSTI.GOV)

Knight, K; Kita, N; Mendybaev, R

2009-06-18

Calcium-, aluminum-rich inclusions (CAIs) are often enriched in the heavy isotopes of magnesium and silicon relative to bulk solar system materials. It is likely that these isotopic enrichments resulted from evaporative mass loss of magnesium and silicon from early solar system condensates while they were molten during one or more high-temperature reheating events. Quantitative interpretation of these enrichments requires laboratory determinations of the evaporation kinetics and associated isotopic fractionation effects for these elements. The experimental data for the kinetics of evaporation of magnesium and silicon and the evaporative isotopic fractionation of magnesium is reasonably complete for Type B CAI liquidsmore » (Richter et al., 2002, 2007a). However, the isotopic fractionation factor for silicon evaporating from such liquids has not been as extensively studied. Here we report new ion microprobe silicon isotopic measurements of residual glass from partial evaporation of Type B CAI liquids into vacuum. The silicon isotopic fractionation is reported as a kinetic fractionation factor, {alpha}{sub Si}, corresponding to the ratio of the silicon isotopic composition of the evaporation flux to that of the residual silicate liquid. For CAI-like melts, we find that {alpha}{sub Si} = 0.98985 {+-} 0.00044 (2{sigma}) for {sup 29}Si/{sup 28}Si with no resolvable variation with temperature over the temperature range of the experiments, 1600-1900 C. This value is different from what has been reported for evaporation of liquid Mg{sub 2}SiO{sub 4} (Davis et al., 1990) and of a melt with CI chondritic proportions of the major elements (Wang et al., 2001). There appears to be some compositional control on {alpha}{sub Si}, whereas no compositional effects have been reported for {alpha}{sub Mg}. We use the values of {alpha}Si and {alpha}Mg, to calculate the chemical compositions of the unevaporated precursors of a number of isotopically fractionated CAIs from CV chondrites whose chemical compositions and magnesium and silicon isotopic compositions have been previously measured.« less

Re-assessing the Molybdenum Isotope Composition of Pre-GOE Seawater: Evidence for Dynamic Ocean Redox

NASA Astrophysics Data System (ADS)

Ostrander, C. M.; Kendall, B.; Roy, M.; Romaniello, S. J.; Nunn, S. J.; Gordon, G. W.; Olson, S. L.; Lyons, T. W.; Zheng, W.; Anbar, A. D.

2016-12-01

Molybdenum (Mo) isotope compositions of Archean shales can provide important insights into ocean and atmosphere redox dynamics prior to the Great Oxidation Event (GOE). Unfortunately, the relatively limited Mo isotope database and small number of sample sets for Archean shales do not allow for in-depth reconstructions and specifically make it difficult to differentiate global from local effects. To accurately estimate the Mo isotope composition of Archean seawater and better investigate the systematics of local and global redox, more complete sample sets are needed. We carried out a Mo isotope analysis of the euxinic 2.65 Ga Roy Hill Shale sampled in two stratigraphically correlated cores, and revisited the well-studied euxinic 2.5 Ga Mt. McRae Shale in higher resolution. Our data show contrasting Mo isotope values in the 2.65 Ga Roy Hill Shale between near- and offshore depositional environments, with systematically heavier isotope values in the near-shore environment. High-resolution analysis of the Mt. McRae Shale yields oscillating Mo concentrations and isotope values at the cm- to dm-scale during the well-characterized "whiff of O2" interval, with the heaviest isotope values measured during euxinic deposition. Variations in the measured isotope values within each section are primarily associated with redox changes in the local depositional environment and amount of detrital content. Both non-quantitative removal of Mo associated with incorporation into non-euxinic sediments and large detrital Mo contributions shift some measured isotopic compositions toward lighter values. This is readily apparent in the near-shore Roy Hill Shale section and the Mt. McRae Shale, but may not fully explain variations observed in the offshore Roy Hill Shale deposit. Here, euxinic deposition is not accompanied by Mo enrichments or isotopic compositions as heavy as the near-shore equivalent, even after detrital correction. This disparity between the near- and offshore environment could signify spatial variation in the Mo isotope composition of 2.65 Ga seawater and highlights the need for multi-site and high-resolution studies in order to best assess paleoenvironmental conditions.

Pb-, Sr- and Nd-Isotopic systematics and chemical characteristics of cenozoic basalts, Eastern China

USGS Publications Warehouse

Peng, Z.C.; Zartman, R.E.; Futa, K.; Chen, D.G.

1986-01-01

Forty-eight Paleogene, Neogene and Quaternary basaltic rocks from northeastern and east-central China have been analyzed for major-element composition, selected trace-element contents, and Pb, Sr and Nd isotopic systematics. The study area lies entirely within the marginal Pacific tectonic domain. Proceeding east to west from the continental margin to the interior, the basalts reveal an isotopic transition in mantle source material and/or degree of crustal interaction. In the east, many of the rocks are found to merge both chemically and isotopically with those previously reported from the Japanese and Taiwan island-arc terrains. In the west, clear evidence exists for component(s) of Late Archean continental lithosphere to be present in some samples. A major crustal structure, the Tan-Lu fault, marks the approximate boundary between continental margin and interior isotopic behaviors. Although the isotopic signature of the western basalts has characteristics of lower-crustal contamination, a subcrustal lithosphere, i.e. an attached mantle keel, is probably more likely to be the major contributor of their continental "flavor". The transition from continental margin to interior is very pronounced for Pb isotopes, although Sr and Nd isotopes also combine to yield correlated patterns that deviate strikingly from the mid-ocean ridge basalt (MORB) and oceanic-island trends. The most distinctive chemical attribute of this continental lithosphere component is its diminished U Pb as reflected in the Pb isotopic composition when compared to sources of MORB, oceanic-island and island-arc volcanic rocks. Somewhat diminished Sm Nd and elevated Rb Sr, especially in comparison to the depleted asthenospheric mantle, are also apparent from the Nd- and Sr-isotopic ratios. ?? 1986.

High-precision measurement of (186)Os/(188)Os and (187)Os/(188)Os: isobaric oxide corrections with in-run measured oxygen isotope ratios.

PubMed

Chu, Zhu-Yin; Li, Chao-Feng; Chen, Zhi; Xu, Jun-Jie; Di, Yan-Kun; Guo, Jing-Hui

2015-09-01

We present a novel method for high precision measurement of (186)Os/(188)Os and (187)Os/(188)Os ratios, applying isobaric oxide interference correction based on in-run measurements of oxygen isotopic ratios. For this purpose, we set up a static data collection routine to measure the main Os(16)O3(-) ion beams with Faraday cups connected to conventional 10(11) amplifiers, and (192)Os(16)O2(17)O(-) and (192)Os(16)O2(18)O(-) ion beams with Faraday cups connected to 10(12) amplifiers. Because of the limited number of Faraday cups, we did not measure (184)Os(16)O3(-) and (189)Os(16)O3(-) simultaneously in-run, but the analytical setup had no significant influence on final (186)Os/(188)Os and (187)Os/(188)Os data. By analyzing UMd, DROsS, an in-house Os solution standard, and several rock reference materials, including WPR-1, WMS-1a, and Gpt-5, the in-run measured oxygen isotopic ratios were proven to present accurate Os isotopic data. However, (186)Os/(188)Os and (187)Os/(188)Os data obtained with in-run O isotopic compositions for the solution standards and rock reference materials show minimal improvement in internal and external precision, compared to the conventional oxygen correction method. We concluded that, the small variations of oxygen isotopes during OsO3(-) analytical sessions are probably not the main source of error for high precision Os isotopic analysis. Nevertheless, use of run-specific O isotopic compositions is still a better choice for Os isotopic data reduction and eliminates the requirement of extra measurements of the oxygen isotopic ratios.

Cryogenic Calcite: A Morphologic and Isotopic Analog to the ALH84001 Carbonates

NASA Technical Reports Server (NTRS)

Niles, P. B.; Leshin, L. A.; Socki, R. A.; Guan, Y.; Ming, D. W.; Gibson, E. K.

2004-01-01

Martian meteorite ALH84001 carbonates preserve large and variable microscale isotopic compositions, which in some way reflect their formation environment. These measurements show large variations (>20%) in the carbon and oxygen isotopic compositions of the carbonates on a 10-20 micron scale that are correlated with chemical composition. However, the utilization of these data sets for interpreting the formation conditions of the carbonates is complex due to lack of suitable terrestrial analogs and the difficulty of modeling under non-equilibrium conditions. Thus, the mechanisms and processes are largely unknown that create and preserve large microscale isotopic variations in carbonate minerals. Experimental tests of the possible environments and mechanisms that lead to large microscale isotopic variations can help address these concerns. One possible mechanism for creating large carbon isotopic variations in carbonates involves the freezing of water. Carbonates precipitate during extensive CO2 degassing that occurs during the freezing process as the fluid s decreasing volume drives CO2 out. This rapid CO2 degassing results in a kinetic isotopic fractionation where the CO2 gas has a much lighter isotopic composition causing an enrichment of 13C in the remaining dissolved bicarbonate. This study seeks to determine the suitability of cryogenically formed carbonates as analogs to ALH84001 carbonates. Specifically, our objective is to determine how accurately models using equilibrium fractionation factors approximate the isotopic compositions of cryogenically precipitated carbonates. This includes determining the accuracy of applying equilibrium fractionation factors during a kinetic process, and determining how isotopic variations in the fluid are preserved in microscale variations in the precipitated carbonates.

The temporal evolution of magnesium isotope fractionation during hydromagnesite dissolution, precipitation, and at equilibrium

NASA Astrophysics Data System (ADS)

Oelkers, Eric H.; Berninger, Ulf-Niklas; Pérez-Fernàndez, Andrea; Chmeleff, Jérôme; Mavromatis, Vasileios

2018-04-01

This study provides experimental evidence of the resetting of the magnesium (Mg) isotope signatures of hydromagnesite in the presence of an aqueous fluid during its congruent dissolution, precipitation, and at equilibrium at ambient temperatures over month-long timescales. All experiments were performed in batch reactors in aqueous sodium carbonate buffer solutions having a pH from 7.8 to 9.2. The fluid phase in all experiments attained bulk chemical equilibrium within analytical uncertainty with hydromagnesite within several days, but the experiments were allowed to continue for up to 575 days. During congruent hydromagnesite dissolution, the fluid first became enriched in isotopically light Mg compared to the dissolving hydromagnesite, but this Mg isotope composition became heavier after the fluid attained chemical equilibrium with the mineral. The δ26Mg composition of the fluid was up to ∼0.35‰ heavier than the initial dissolving hydromagnesite at the end of the dissolution experiments. Hydromagnesite precipitation was provoked during one experiment by increasing the reaction temperature from 4 to 50 °C. The δ26Mg composition of the fluid increased as hydromagnesite precipitated and continued to increase after the fluid attained bulk equilibrium with this phase. These observations are consistent with the hypothesis that mineral-fluid equilibrium is dynamic (i.e. dissolution and precipitation occur at equal, non-zero rates at equilibrium). Moreover the results presented in this study confirm (1) that the transfer of material from the solid to the fluid phase may not be conservative during stoichiometric dissolution, and (2) that the isotopic compositions of carbonate minerals can evolve even when the mineral is in bulk chemical equilibrium with its coexisting fluid. This latter observation suggests that the preservation of isotopic signatures of carbonate minerals in the geological record may require a combination of the isolation of fluid-mineral system from external chemical input and/or the existence of a yet to be defined dissolution/precipitation inhibition mechanism.

The role of stable isotopes in understanding rainfall interception processes: a review

EPA Science Inventory

The isotopic composition of water transmitted by the canopy as throughfall or stemflow reflects important hydrologic processes occurring in the canopy. A synthesis of the literature shows that complex spatiotemporal variations of isotopic composition are created by canopy interce...

Metal stable isotopes in weathering and hydrology: Chapter 10

USGS Publications Warehouse

Bullen, Thomas D.; Holland, Heinrich; Turekian, K.

2014-01-01

This chapter highlights some of the major developments in the understanding of the causes of metal stable isotope compositional variability in and isotope fractionation between natural materials and provides numerous examples of how that understanding is providing new insights into weathering and hydrology. At this stage, our knowledge of causes of stable isotope compositional variability among natural materials is greatest for the metals lithium, magnesium, calcium, and iron, the isotopes of which have already provided important information on weathering and hydrological processes. Stable isotope compositional variability for other metals such as strontium, copper, zinc, chromium, barium, molybdenum, mercury, cadmium, and nickel has been demonstrated but is only beginning to be applied to questions related to weathering and hydrology, and several research groups are currently exploring the potential. And then there are other metals such as titanium, vanadium, rhenium, and tungsten that have yet to be explored for variability of stable isotope composition in natural materials, but which may hold untold surprises in their utility. This impressive list of metals having either demonstrated or potential stable isotope signals that could be used to address important unsolved questions related to weathering and hydrology, constitutes a powerful toolbox that will be increasingly utilized in the coming decades.

Quality assurance and quality control in light stable isotope laboratories: A case study of Rio Grande, Texas, water samples

USGS Publications Warehouse

Coplen, T.B.; Qi, H.

2009-01-01

New isotope laboratories can achieve the goal of reporting the same isotopic composition within analytical uncertainty for the same material analysed decades apart by (1) writing their own acceptance testing procedures and putting them into their mass spectrometric or laser-based isotope-ratio equipment procurement contract, (2) requiring a manufacturer to demonstrate acceptable performance using all sample ports provided with the instrumentation, (3) for each medium to be analysed, prepare two local reference materials substantially different in isotopic composition to encompass the range in isotopic composition expected in the laboratory and calibrated them with isotopic reference materials available from the International Atomic Energy Agency (IAEA) or the US National Institute of Standards and Technology (NIST), (4) using the optimum storage containers (for water samples, sealing in glass ampoules that are sterilised after sealing is satisfactory), (5) interspersing among sample unknowns local laboratory isotopic reference materials daily (internationally distributed isotopic reference materials can be ordered at three-year intervals, and can be used for elemental analyser analyses and other analyses that consume less than 1 mg of material) - this process applies to H, C, N, O, and S isotope ratios, (6) calculating isotopic compositions of unknowns by normalising isotopic data to that of local reference materials, which have been calibrated to internationally distributed isotopic reference materials, (7) reporting results on scales normalised to internationally distributed isotopic reference materials (where they are available) and providing to sample submitters the isotopic compositions of internationally distributed isotopic reference materials of the same substance had they been analysed with unknowns, (8) providing an audit trail in the laboratory for analytical results - this trail commonly will be in electronic format and might include a laboratory information management system, (9) making at regular intervals a complete backup of laboratory analytical data (both of samples logged into the laboratory and of mass spectrometric analyses), being sure to store one copy of this backup offsite, and (10) participating in interlaboratory comparison exercises sponsored by the IAEA and other agencies at regular intervals. ?? Taylor & Francis.

The energy dependence of the neon-22 excess in the cosmic radiation

NASA Technical Reports Server (NTRS)

Herrstroem, N. Y.; Lund, N.

1985-01-01

It has been recognized now for some time that the heavy neon isotope, neon-22, is overabundant by a factor of 3 to 4 with respect to neon-22 in the cosmic ray source compared to the ratio of these isotopes in the Solar System. In view of the otherwise remarkable similarity of the chemical composition of the cosmic ray source and the composition of the Solar Energetic Particles, the anomaly regarding the neon isotopes is so much more striking. The observed excess of neon-22 is too large to be explained as a result of the chemical evolution of the Galaxy since the formation of the Solar System. Further information on the origin of the neon-22 excess may come from a comparison of the energy spectra of the two neon isotopes. If the cosmic radiation in the solar neighborhood is a mixture of material from several sources, one of which has an excess of neon-22, then the source energy spectra of neon-20 and neon-22 may differ significantly.

Titanium stable isotope investigation of magmatic processes on the Earth and Moon

NASA Astrophysics Data System (ADS)

Millet, Marc-Alban; Dauphas, Nicolas; Greber, Nicolas D.; Burton, Kevin W.; Dale, Chris W.; Debret, Baptiste; Macpherson, Colin G.; Nowell, Geoffrey M.; Williams, Helen M.

2016-09-01

We present titanium stable isotope measurements of terrestrial magmatic samples and lunar mare basalts with the aims of constraining the composition of the lunar and terrestrial mantles and evaluating the potential of Ti stable isotopes for understanding magmatic processes. Relative to the OL-Ti isotope standard, the δ49Ti values of terrestrial samples vary from -0.05 to +0.55‰, whereas those of lunar mare basalts vary from -0.01 to +0.03‰ (the precisions of the double spike Ti isotope measurements are ca. ±0.02‰ at 95% confidence). The Ti stable isotope compositions of differentiated terrestrial magmas define a well-defined positive correlation with SiO2 content, which appears to result from the fractional crystallisation of Ti-bearing oxides with an inferred isotope fractionation factor of ΔTi49oxide-melt = - 0.23 ‰ ×106 /T2. Primitive terrestrial basalts show no resolvable Ti isotope variations and display similar values to mantle-derived samples (peridotite and serpentinites), indicating that partial melting does not fractionate Ti stable isotopes and that the Earth's mantle has a homogeneous δ49Ti composition of +0.005 ± 0.005 (95% c.i., n = 29). Eclogites also display similar Ti stable isotope compositions, suggesting that Ti is immobile during dehydration of subducted oceanic lithosphere. Lunar basalts have variable δ49Ti values; low-Ti mare basalts have δ49Ti values similar to that of the bulk silicate Earth (BSE) while high-Ti lunar basalts display small enrichment in the heavy Ti isotopes. This is best interpreted in terms of source heterogeneity resulting from Ti stable isotope fractionation associated with ilmenite-melt equilibrium during the generation of the mantle source of high-Ti lunar mare basalts. The similarity in δ49Ti between terrestrial samples and low-Ti lunar basalts provides strong evidence that the Earth and Moon have identical stable Ti isotope compositions.

Low-temperature aqueous alteration on the CR chondrite parent body: Implications from in situ oxygen-isotope analyses

NASA Astrophysics Data System (ADS)

Jilly-Rehak, Christine E.; Huss, Gary R.; Nagashima, Kazu; Schrader, Devin L.

2018-02-01

The presence of hydrated minerals in chondrites indicates that water played an important role in the geologic evolution of the early Solar System; however, the process of aqueous alteration is still poorly understood. Renazzo-like carbonaceous (CR) chondrites are particularly well-suited for the study of aqueous alteration. Samples range from being nearly anhydrous to fully altered, essentially representing snapshots of the alteration process through time. We studied oxygen isotopes in secondary-minerals from six CR chondrites of varying hydration states to determine how aqueous fluid conditions (including composition and temperature) evolved on the parent body. Secondary minerals analyzed included calcite, dolomite, and magnetite. The O-isotope composition of calcites ranged from δ18O ≈ 9 to 35‰, dolomites from δ18O ≈ 23 to 27‰, and magnetites from δ18O ≈ -18 to 5‰. Calcite in less-altered samples showed more evidence of fluid evolution compared to heavily altered samples, likely reflecting lower water/rock ratios. Most magnetite plotted on a single trend, with the exception of grains from the extensively hydrated chondrite MIL 090292. The MIL 090292 magnetite diverges from this trend, possibly indicating an anomalous origin for the meteorite. If magnetite and calcite formed in equilibrium, then the relative 18O fractionation between them can be used to extract the temperature of co-precipitation. Isotopic fractionation in Al Rais carbonate-magnetite assemblages revealed low precipitation temperatures (∼60 °C). Assuming that the CR parent body experienced closed-system alteration, a similar exercise for parallel calcite and magnetite O-isotope arrays yields "global" alteration temperatures of ∼55 to 88 °C. These secondary mineral arrays indicate that the O-isotopic composition of the altering fluid evolved upon progressive alteration, beginning near the Al Rais water composition of Δ17O ∼ 1‰ and δ18O ∼ 10‰, and becoming increasingly 16O-enriched toward a final fluid composition of Δ17O ∼ -1.2‰ and δ18O ∼ -15‰.

Garnet Pyroxenites from Kaula, Hawaii: Implications for Plume-Lithosphere Interaction

NASA Astrophysics Data System (ADS)

Bizimis, M.; Garcia, M. O.; Norman, M. D.

2006-12-01

The presence of garnet pyroxenite xenoliths on Oahu and Kaula Islands, Hawaii, provides the rare opportunity to investigate the composition of the deeper oceanic mantle lithosphere and the nature of plume-lithosphere interaction in two dimensions, downstream from the center of the Hawaiian plume. Kaula (60 miles SW of Kauai) is on the same bathymetric shallow as Kauai and the Kaula-Niihau-Kauai islands form a cross-trend relationship to the Hawaiian Island ridge. Here, we present the first Sr-Nd isotope data on clinopyroxenes (cpx) from Kaula pyroxenites, and we compare them with the Salt Lake Crater (SLC) pyroxenites from Oahu. The Kaula cpx major element compositions overlap those of the (more variable) SLC pyroxenites (e.g. Mg# = 0.79-0.83), except for their higher Al2O3 contents (9% vs. 5-8%) than the SLC. The Kaula cpx are LREE enriched with elevated Dy/Yb ratios, similar to the SLC pyroxenites and characteristic of the presence of garnet that preferentially incorporates the HREE. In Sr-Nd isotope space, the Kaula pyroxenite compositions (87Sr/86Sr= 0.70312-0.70326, ɛNd= 7.2-8.6) overlap those of both the Oahu-Kauai post erosional lavas and the SLC pyroxenites, falling at the isotopically depleted end of the Hawaiian lava compositions. The depleted Sr-Nd isotope compositions of the Kaula pyroxenites suggest that they are not related to the isotopically enriched shield stage Hawaiian lavas, either as a source material (i.e. recycled eclogite) or as cumulates. Their elevated 87Sr/86Sr ratios relative to MORB also suggests that they are not likely MORB-related cumulates. The similarities between the Oahu and Kaula pyroxenites, some 200 km apart, suggest the widespread presence of pyroxenitic material in the deeper (>60km) Pacific lithosphere between Oahu and Kaula-Kauai, as high pressure cumulates from melts isotopically similar to the secondary Hawaiian volcanism. The presence of this material within the lower lithosphere is consistent with seismic observations suggesting erosion and replacement of the deeper Pacific lithosphere by plume material, downstream from the center of the plume.

Effect of 3-nitrooxypropanol on methane and hydrogen emissions, methane isotopic signature, and ruminal fermentation in dairy cows.

PubMed

Lopes, J C; de Matos, L F; Harper, M T; Giallongo, F; Oh, J; Gruen, D; Ono, S; Kindermann, M; Duval, S; Hristov, A N

2016-07-01

The objective of this crossover experiment was to investigate the effect of a methane inhibitor, 3-nitrooxypropanol (3NOP), on enteric methane emission, methane isotopic composition, and rumen fermentation and microbial profile in lactating dairy cows. The experiment involved 6 ruminally cannulated late-lactation Holstein cows assigned to 2 treatments: control and 3NOP (60 mg/kg of feed dry matter). Compared with the control, 3NOP decreased methane emission by 31% and increased hydrogen emission from undetectable to 1.33 g/d. Methane emissions per kilogram of dry matter intake and milk yield were also decreased 34% by 3NOP. Milk production and composition were not affected by 3NOP, except milk fat concentration was increased compared with the control. Concentrations of total VFA and propionate in ruminal fluid were not affected by treatment, but acetate concentration tended to be lower and acetate-to-propionate ratio was lower for 3NOP compared with the control. The 3NOP decreased the molar proportion of acetate and increase those of propionate, butyrate, valerate, and isovalerate. Deuterium-to-hydrogen ratios of methane and the abundance of (13)CH3D were similar between treatments. Compared with the control, minor (4‰) depletion in the (13)C/(12)C ratio was observed for 3NOP. Genus composition of methanogenic archaea (Methanobrevibacter, Methanosphaera, and Methanomicrobium) was not affected by 3NOP, but the proportion of methanogens in the total cell counts tended to be decreased by 3NOP. Prevotella spp., the predominant bacterial genus in ruminal contents in this experiment, was also not affected by 3NOP. Compared with the control, Ruminococcus and Clostridium spp. were decreased and Butyrivibrio spp. was increased by 3NOP. This experiment demonstrated that a substantial inhibition of enteric methane emission by 3NOP in dairy cows was accompanied with increased hydrogen emission and decreased acetate-to-propionate ratio; however, neither an effect on rumen archaeal community composition nor a significant change in the isotope composition of methane was observed. Copyright © 2016 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.

Sr, Nd and Pb Isotope Geochemistry of Near-ridge Seamounts in Eastern Pacific: Implications for Upper Mantle Composition and EPR Magmatic Segmentation

NASA Astrophysics Data System (ADS)

Castillo, P. R.; White, W. M.; Batiza, R.

2005-12-01

Near-ridge seamount lavas tend to reflect the true composition of the upper mantle source of MORB because these are generated by relatively smaller degrees of melting of smaller volumes of the mantle compared to nearby axial lavas; they also by-pass the axial chamber mixing and fractionation processes that are responsible for the relatively more uniform chemical and isotopic composition of normal-MORB. New Sr, Nd and Pb isotope data combined with published data for lavas from near-ridge seamounts on either side of the EPR segment between the 11o45' OSC and Orozco Transform at 15o00' show latitudinal isotopic variation very similar to that shown by the rise axial lavas (Castillo et al., G3 1, 1999). Seamount and axial lavas at both ends of the rise segment have on average slightly higher and more limited range of 143Nd/144Nd, but slightly lower 206Pb/204Pb and 87Sr/86Sr ratios than lavas at the center of the segment. Some of the seamounts are located on ~8 Ma rise flank crust although most of the seamount lavas are fairly young (e.g., lavas from Seamount 6 on ~3 Ma crust are only 3 to 900 kyr - Graham et al., Nature 326, 1987). Thus near-ridge seamount isotope data provide the first documentation for a large-scale (~350 km long x ~720 km wide), systematic compositional variation of the upper mantle source of EPR MORB. Such a scale of variation is larger and longer than the size and <1 myr life span of the majority of non-transform offsets, which are supposed to be responsible for the along-axis compositional variations of EPR MORB according to the "bottoms up" model of magmatic segmentation.

Isotopic Composition of Molybdenum and Barium in Single Presolar Silicon Carbide Grains of Type A+B

NASA Technical Reports Server (NTRS)

Savina, M. R.; Tripa, C. E.; Pellin, M. J.; Davis, A. M.; Clayton, R. N.; Lewis, R. S.; Amari, S.

2003-01-01

Presolar SiC grains fall into several groups based on C, N, and Si isotopic compositions. Approximately 93% are defined as mainstream, having 10 less than C-12/C-13 less than 100 and N-14/N-15 ranging from 50 to 20,000. A number of studies have shown that the most likely sources of mainstream grains are low mass asymptotic giant branch stars. Models of nucleosynthesis in AGB stars reproduce the s-process enhancements seen in the heavy elements in mainstream SiC grains. Among the less common grains, A+B grains, which comprise approximately 3-4% of presolar SiC, are perhaps the least well understood. Recent studies by Amari et al. show that A+B grains can be divided into at least 4 groups based on their trace element concentration patterns. Of 20 grains studied, 7 showed trace element patterns consistent with condensation from a gas of solar system composition, while the rest had varying degrees of process enhancements. Our previous measurements on 3 A+B grains showed Mo of solar isotopic composition, but Zr with a strong enhancement in 96Zr, which is an r-process isotope but can be made in an sprocess if the neutron density is high enough to bridge the unstable Zr-95 (T(sub 1/2)= 64 d). The observation of Mo with solar system isotopic composition in the same grains is puzzling however. Meyer et al. have recently shown that a neutron burst mechanism can produce a high Zr-96/Zr-94 without enhancing Mo-100, however this model leads to enhancements in Mo-95 and Mo-97 not observed in A+B grains. We report here results of Mo measurements on 7 additional A+B grains, and Ba measurements on 2 A+B grains, and compare these to the previous studies.

The post-Paleozoic chronology and mechanism of 13C depletion in primary marine organic matter

NASA Technical Reports Server (NTRS)

Popp, B. N.; Takigiku, R.; Hayes, J. M.; Louda, J. W.; Baker, E. W.

1989-01-01

Carbon-isotopic compositions of geoporphyrins have been measured from marine sediments of Mesozoic and Cenozoic age in order to elucidate the timing and extent of depletion of 13C in marine primary producers. These results indicate that the difference in isotopic composition of coeval marine carbonates and marine primary photosynthate was approximately 5 to 7 permil greater during the Mesozoic and early Cenozoic than at present. In contrast to the isotopic record of marine primary producers, isotopic compositions of terrestrial organic materials have remained approximately constant for this same interval of time. This difference in the isotopic records of marine and terrestrial organic matter is considered in terms of the mechanisms controlling the isotopic fractionation associated with photosynthetic fixation of carbon. We show that the decreased isotopic fractionation between marine carbonates and organic matter from the Early to mid-Cenozoic may record variations in the abundance of atmospheric CO2.

Isotopic compositions of cometary matter returned by Stardust.

PubMed

McKeegan, Kevin D; Aléon, Jerome; Bradley, John; Brownlee, Donald; Busemann, Henner; Butterworth, Anna; Chaussidon, Marc; Fallon, Stewart; Floss, Christine; Gilmour, Jamie; Gounelle, Matthieu; Graham, Giles; Guan, Yunbin; Heck, Philipp R; Hoppe, Peter; Hutcheon, Ian D; Huth, Joachim; Ishii, Hope; Ito, Motoo; Jacobsen, Stein B; Kearsley, Anton; Leshin, Laurie A; Liu, Ming-Chang; Lyon, Ian; Marhas, Kuljeet; Marty, Bernard; Matrajt, Graciela; Meibom, Anders; Messenger, Scott; Mostefaoui, Smail; Mukhopadhyay, Sujoy; Nakamura-Messenger, Keiko; Nittler, Larry; Palma, Russ; Pepin, Robert O; Papanastassiou, Dimitri A; Robert, François; Schlutter, Dennis; Snead, Christopher J; Stadermann, Frank J; Stroud, Rhonda; Tsou, Peter; Westphal, Andrew; Young, Edward D; Ziegler, Karen; Zimmermann, Laurent; Zinner, Ernst

2006-12-15

Hydrogen, carbon, nitrogen, and oxygen isotopic compositions are heterogeneous among comet 81P/Wild 2 particle fragments; however, extreme isotopic anomalies are rare, indicating that the comet is not a pristine aggregate of presolar materials. Nonterrestrial nitrogen and neon isotope ratios suggest that indigenous organic matter and highly volatile materials were successfully collected. Except for a single (17)O-enriched circumstellar stardust grain, silicate and oxide minerals have oxygen isotopic compositions consistent with solar system origin. One refractory grain is (16)O-enriched, like refractory inclusions in meteorites, suggesting that Wild 2 contains material formed at high temperature in the inner solar system and transported to the Kuiper belt before comet accretion.

Isotopic Analysis and Evolved Gases

NASA Technical Reports Server (NTRS)

Swindle, Timothy D.; Boynton, William V.; Chutjian, Ara; Hoffman, John H.; Jordan, Jim L.; Kargel, Jeffrey S.; McEntire, Richard W.; Nyquist, Larry

1996-01-01

Precise measurements of the chemical, elemental, and isotopic composition of planetary surface material and gases, and observed variations in these compositions, can contribute significantly to our knowledge of the source(s), ages, and evolution of solar system materials. The analyses discussed in this paper are mostly made by mass spectrometers or some other type of mass analyzer, and address three broad areas of interest: (1) atmospheric composition - isotopic, elemental, and molecular, (2) gases evolved from solids, and (3) solids. Current isotopic data on nine elements, mostly from in situ analysis, but also from meteorites and telescopic observations are summarized. Potential instruments for isotopic analysis of lunar, Martian, Venusian, Mercury, and Pluto surfaces, along with asteroid, cometary and icy satellites, surfaces are discussed.

Approaches to Plant Hydrogen and Oxygen Isoscapes Generation

DOE Office of Scientific and Technical Information (OSTI.GOV)

West, Jason B.; Kreuzer-Martin, Helen W.; Ehleringer, James

2009-12-01

Plant hydrogen and oxygen isoscapes have been utilized to address important and somewhat disparate research goals. The isotopic composition of leaf water affects the isotopic composition of atmospheric CO2 and O2 and is a logical starting point for understanding the isotopic composition of plant organic compounds since photosynthesis occurs in the leaf water environment. Leaf water isoscapes have been produced largely as part of efforts to understand atmospheric gas isotopic composition. The isotopic composition of plant organic matter has also been targeted for its potential to serve as a proxy for past environmental conditions. Spatially distributed sampling and modeling ofmore » modern plant H & O isoscapes can improve our understanding of the controls of the isotope ratios of compounds such as cellulose or n-alkanes from plants and therefore their utility for paleoreconstructions. Spatially varying plant hydrogen and oxygen isotopes have promise for yielding geographic origin information for a variety of plant products, including objects of criminal forensic interest or food products. The future has rich opportunities for the continued development of mechanistic models, methodologies for the generation of hydrogen and oxygen isoscapes, and cross-disciplinary interactions as these tools for understanding are developed, shared, and utilized to answer large-scale questions.« less

Using Stable Isotope Geochemistry to Determine Changing Paleohydrology and Diagenetic Alteration in the Late Cretaceous Kaiparowits Formation, UT USA

NASA Astrophysics Data System (ADS)

Yamamura, Daigo

The Western Interior Basin of the North America preserves one of the best sedimentary and paleontological records of the Cretaceous in the world. The Upper Cretaceous Kaiparowits Formation is a rapidly deposited fluvial sequence and preserves one of the most complete terrestrial fossil record of the North America. Such a unique deposit provides an opportunity to investigate the interaction between the physical environment and ecology. In an effort to decipher such interaction, stable isotope composition of cements in sedimentary rocks, concretions and vertebrate fossils were analyzed. Despite the difference in facies and sedimentary architecture, the isotope composition does not change significantly at 110 m from the base of the formation. Among the well-preserved cement samples, stable isotope composition indicates a significant hydrologic change within the informal Middle unit; a 6.37‰ depletion in delta13C and 3.30‰ enrichment in delta 18O occurs at 300 m above the base of the formation. The isotope values indicate that the sandstone cements below 300 m were precipitated in a mixing zone between marine and terrestrial groundwater, whereas the cements in upper units were precipitated in a terrestrial groundwater. Despite the difference in physical appearance (i.e. color and shape), the isotopic compositions of cements in concretions are similar to well-cemented sandstone bodies in similar stratigraphic positions. Isotope compositions of the host rock are similar to that of mudrock and weathered sandstone, suggesting the origin of cementing fluids for the sandstone and concretions were the same indicating that: 1) the concretions were formed in shallow groundwater and not related to the groundwater migration, or 2) all cements in upper Kaiparowits Formation are precipitated or altered during later stage groundwater migration. Average delta18Oc from each taxon show the same trend as the delta18Op stratigraphic change, suggesting delta18Oc is still useful as a paleoclimatic proxy. Compared to other Campanian formations, fossil delta18O p are depleted for their paleolatitude, suggesting the Kaiparowits Plateau had higher input from high-elevation runoff, consistent with other paleoclimatic studies. Estimated delta18Ow ranged between vadose influenced dry season values of -8.88‰ to high elevation runoff values of -13.76‰ suggesting dynamic hydrologic interactions.

Stable Chlorine Isotope Study: Application to Early Solar System Materials

NASA Technical Reports Server (NTRS)

Mala,ira. M/; Nyquist, L. E.; Reese, Y.; Shih, C-Y; Fujitani, T.; Okano, O.

2010-01-01

A significantly large mass fractionation between two stable chlorine isotopes is expected during planetary processes In addition, in view of the isotopic heterogeneity of other light elements, the chlorine isotopes can potentially be used as a tracer for the origins and evolutionary processes of early solar system materials. Due to analytical difficulties, however, current chlorine isotope studies on planetary materials are quite controversial among IRMS (gas source mass spectrometry) and/or TIMS (Thermal Ionization Mass Spectrometry) groups [i.e. 1-3]. Although a cross-calibration of IRMS and TIMS indicates that both techniques are sufficiently consistent with each other [4], some authors have claimed that the Cl-37/Cl-35 ratio of geological samples obtained by TIMS technique are, in general, misleadingly too high and variable compared to those of IRMS [3]. For example, almost no differences of Cl isotope composition were observed among mantle materials and carbonaceous meteorites by [3]. On the other hand, according to more recent IRMS work [2], significant Cl isotope variations are confirmed for mantle materials. Therefore, additional careful investigation of Cl isotope analyses are now required to confirm real chlorine isotope variations for planetary materials including carbonaceous chondrites [5]. A significantly large mass fractionation between two stable chlorine isotopes is expected during planetary processes In addition, in view of the isotopic heterogeneity of other light elements, the chlorine isotopes can potentially be used as a tracer for the origins and evolutionary processes of early solar system materials. Due to analytical difficulties, however, current chlorine isotope studies on planetary materials are quite controversial among IRMS (gas source mass spectrometry) and/or TIMS (Thermal Ionization Mass Spectrometry) groups [i.e. 1-3]. Although a cross-calibration of IRMS and TIMS indicates that both techniques are sufficiently consistent with each other [4], some authors have claimed that the 37Cl/35Cl ratio of geological samples obtained by TIMS technique are, in general, misleadingly too high and variable compared to those of IRMS [3]. For eample, almost no differences of Cl isotope composition were observed among mantle materials and carbonaceous meteorites by [3]. On the other hand, according to more recent IRMS work [2], significant Cl isotope variations are confirmed for mantle materials. Therefore, additional careful investigation of Cl isotope analyses are now required to confirm real chlorine isotope variations for planetary materials including carbonaceous chondrites [5]. In order to clarify the stable chlorine isotope features of early solar system materials, we have initiated development of the TIMS technique at NASA JSC applicable to analysis of small amounts of meteoritic and planetary materials. We report here the current status of chlorine isotope analysis at NASA JSC.

The evolution of 13C and 18O isotope composition of DIC in a calcite depositing film of water with isotope exchange between the DIC and a CO2 containing atmosphere, and simultaneous evaporation of the water. Implication to climate proxies from stalagmites: A theoretical model

NASA Astrophysics Data System (ADS)

Dreybrodt, Wolfgang; Romanov, Douchko

2016-12-01

The most widely applied climate proxies in speleothems are the isotope compositions of carbon and oxygen expressed by δ13C and δ18O values. However, mechanisms, which are not related to climate changes, overlay the climate signal. One is the temporal increase of both, δ13C and δ18O values by kinetic processes during precipitation of calcite. Isotope exchange between DIC in the water and the CO2 in the surrounding cave atmosphere can also change isotope composition. Here we present a theoretical model of the temporal isotope evolution of DIC in a thin water layer during precipitation of calcite and simultaneous isotope exchange with the cave atmosphere, and simultaneous evaporation of water. The exchange of oxygen isotopes in the DIC with those in the water is also considered.

Stable isotope dilution analysis of hydrologic samples by inductively coupled plasma mass spectrometry

USGS Publications Warehouse

Garbarino, John R.; Taylor, Howard E.

1987-01-01

Inductively coupled plasma mass spectrometry is employed in the determination of Ni, Cu, Sr, Cd, Ba, Ti, and Pb in nonsaline, natural water samples by stable isotope dilution analysis. Hydrologic samples were directly analyzed without any unusual pretreatment. Interference effects related to overlapping isobars, formation of metal oxide and multiply charged ions, and matrix composition were identified and suitable methods of correction evaluated. A comparability study snowed that single-element isotope dilution analysis was only marginally better than sequential multielement isotope dilution analysis. Accuracy and precision of the single-element method were determined on the basis of results obtained for standard reference materials. The instrumental technique was shown to be ideally suited for programs associated with certification of standard reference materials.

Compilation of minimum and maximum isotope ratios of selected elements in naturally occurring terrestrial materials and reagents

USGS Publications Warehouse

Coplen, T.B.; Hopple, J.A.; Böhlke, J.K.; Peiser, H.S.; Rieder, S.E.; Krouse, H.R.; Rosman, K.J.R.; Ding, T.; Vocke, R.D.; Revesz, K.M.; Lamberty, A.; Taylor, P.; De Bievre, P.

2002-01-01

Documented variations in the isotopic compositions of some chemical elements are responsible for expanded uncertainties in the standard atomic weights published by the Commission on Atomic Weights and Isotopic Abundances of the International Union of Pure and Applied Chemistry. This report summarizes reported variations in the isotopic compositions of 20 elements that are due to physical and chemical fractionation processes (not due to radioactive decay) and their effects on the standard atomic weight uncertainties. For 11 of those elements (hydrogen, lithium, boron, carbon, nitrogen, oxygen, silicon, sulfur, chlorine, copper, and selenium), standard atomic weight uncertainties have been assigned values that are substantially larger than analytical uncertainties because of common isotope abundance variations in materials of natural terrestrial origin. For 2 elements (chromium and thallium), recently reported isotope abundance variations potentially are large enough to result in future expansion of their atomic weight uncertainties. For 7 elements (magnesium, calcium, iron, zinc, molybdenum, palladium, and tellurium), documented isotope-abundance variations in materials of natural terrestrial origin are too small to have a significant effect on their standard atomic weight uncertainties. This compilation indicates the extent to which the atomic weight of an element in a given material may differ from the standard atomic weight of the element. For most elements given above, data are graphically illustrated by a diagram in which the materials are specified in the ordinate and the compositional ranges are plotted along the abscissa in scales of (1) atomic weight, (2) mole fraction of a selected isotope, and (3) delta value of a selected isotope ratio. There are no internationally distributed isotopic reference materials for the elements zinc, selenium, molybdenum, palladium, and tellurium. Preparation of such materials will help to make isotope ratio measurements among laboratories comparable. The minimum and maximum concentrations of a selected isotope in naturally occurring terrestrial materials for selected chemical elements reviewed in this report are given below: Isotope Minimum mole fraction Maximum mole fraction -------------------------------------------------------------------------------- 2H 0 .000 0255 0 .000 1838 7Li 0 .9227 0 .9278 11B 0 .7961 0 .8107 13C 0 .009 629 0 .011 466 15N 0 .003 462 0 .004 210 18O 0 .001 875 0 .002 218 26Mg 0 .1099 0 .1103 30Si 0 .030 816 0 .031 023 34S 0 .0398 0 .0473 37Cl 0 .240 77 0 .243 56 44Ca 0 .020 82 0 .020 92 53Cr 0 .095 01 0 .095 53 56Fe 0 .917 42 0 .917 60 65Cu 0 .3066 0 .3102 205Tl 0 .704 72 0 .705 06 The numerical values above have uncertainties that depend upon the uncertainties of the determinations of the absolute isotope-abundance variations of reference materials of the elements. Because reference materials used for absolute isotope-abundance measurements have not been included in relative isotope abundance investigations of zinc, selenium, molybdenum, palladium, and tellurium, ranges in isotopic composition are not listed for these elements, although such ranges may be measurable with state-of-the-art mass spectrometry. This report is available at the url: http://pubs.water.usgs.gov/wri014222.

Non-linear mixing effects on mass-47 CO2 clumped isotope thermometry: Patterns and implications.

PubMed

Defliese, William F; Lohmann, Kyger C

2015-05-15

Mass-47 CO(2) clumped isotope thermometry requires relatively large (~20 mg) samples of carbonate minerals due to detection limits and shot noise in gas source isotope ratio mass spectrometry (IRMS). However, it is unreasonable to assume that natural geologic materials are homogenous on the scale required for sampling. We show that sample heterogeneities can cause offsets from equilibrium Δ(47) values that are controlled solely by end member mixing and are independent of equilibrium temperatures. A numerical model was built to simulate and quantify the effects of end member mixing on Δ(47). The model was run in multiple possible configurations to produce a dataset of mixing effects. We verified that the model accurately simulated real phenomena by comparing two artificial laboratory mixtures measured using IRMS to model output. Mixing effects were found to be dependent on end member isotopic composition in δ(13)C and δ(18)O values, and independent of end member Δ(47) values. Both positive and negative offsets from equilibrium Δ(47) can occur, and the sign is dependent on the interaction between end member isotopic compositions. The overall magnitude of mixing offsets is controlled by the amount of variability within a sample; the larger the disparity between end member compositions, the larger the mixing offset. Samples varying by less than 2 ‰ in both δ(13)C and δ(18)O values have mixing offsets below current IRMS detection limits. We recommend the use of isotopic subsampling for δ(13)C and δ(18)O values to determine sample heterogeneity, and to evaluate any potential mixing effects in samples suspected of being heterogonous. Copyright © 2015 John Wiley & Sons, Ltd.

Seasonal isotope hydrology of a coffee agroforestry watershed in Costa Rica

NASA Astrophysics Data System (ADS)

Welsh Unwala, K.; Boll, J.; Roupsard, O.

2014-12-01

Improved information of seasonal variations in watershed hydrology in the tropics can strengthen models and understanding of hydrology of these areas. Seasonality in the tropics produces rainy seasons versus dry seasons, leading to different hydrologic and water quality processes throughout the year. We questioned whether stable isotopes in water can be used to trace the seasonality in this region, despite experiencing a "drier" season, such as in a Tropical Humid location. This study examines the fluctuations of stable isotope compositions (δ18O and δD) in water balance components in a small (<1 km2) coffee agroforestry watershed located in central Costa Rica on the Caribbean side. Samples were collected in precipitation, groundwater, and stream water for more than two years, across seasons and at an hourly frequency during storm events to better characterize spatial and temporal variations of the isotopic composition and of the respective contribution of surface and deeper groundwater to streamflow in the watershed. Isotope composition in precipitation ranged from -18.5 to -0.3‰ (∂18O) and -136.4 to 13.7‰ (∂D), and data indicate that atmospheric moisture cycling plays an important role in this region. A distinct seasonality was observed in monthly-averaged data between enriched dry season events as compared with the rainy season events. Streamflow data indicate that a deep groundwater system contributes significantly to baseflow, although a shallow, spring-driven system also contributes to stream water within the watershed. During storm events, precipitation contributes to stormflow in the short-term, confirming the role of superficial runoff. These results indicate that isotopes are helpful to partition the water balance even in a Tropical Humid situation where the rainfall seasonality is weak.

Light Isotopes and Trace Organics Analysis of Mars Samples with Mass Spectrometry

NASA Technical Reports Server (NTRS)

Mahaffy, P.; Niemann, Hasso (Technical Monitor)

2001-01-01

Precision measurement of light isotopes in Mars surface minerals and comparison of this isotopic composition with atmospheric gas and other, well-mixed reservoirs such as surface dust are necessary to understand the history of atmospheric evolution from a possibly warmer and wetter Martian surface to the present state. Atmospheric sources and sinks that set these ratios are volcanism, solar wind sputtering, photochemical processes, and weathering. Measurement of a range of trace organic species with a particular focus on species such as amino acids that are the building blocks of terrestrial life are likewise important to address the questions of prebiotic and present or past biological activity on Mars. The workshop topics "isotopic mineralogy" and "biology and pre-biotic chemistry" will be addressed from the point of view of the capabilities and limitations of insitu mass spectrometry (MS) techniques such as thermally evolved gas analysis (TEGA) and gas chromatography (GC) surface experiments using MS, in both cases, as a final chemical and isotopic composition detector. Insitu experiments using straightforward adaptations of existing space proven hardware can provide a substantial improvement in the precision and accuracy of our present knowledge of isotopic composition both in molecular and atomic species in the atmosphere and those chemically bound in rocks and soils. Likewise, detection of trace organic species with greatly improved sensitivity from the Viking GCMS experiment is possible using gas enrichment techniques. The limits to precision and accuracy of presently feasible insitu techniques compared to laboratory analysis of returned samples will be explored. The insitu techniques are sufficiently powerful that they can provide a high fidelity method of screening samples obtained from a diverse set of surface locations such as the subsurface or the interior of rocks for selection of those that are the most interesting for return to Earth.

Rainfall and cave water isotopic relationships in two South-France sites

NASA Astrophysics Data System (ADS)

Genty, D.; Labuhn, I.; Hoffmann, G.; Danis, P. A.; Mestre, O.; Bourges, F.; Wainer, K.; Massault, M.; Van Exter, S.; Régnier, E.; Orengo, Ph.; Falourd, S.; Minster, B.

2014-04-01

This article presents isotopic measurements (δ18O and δD) of precipitation and cave drip water from two sites in southern France in order to investigate the link between rainfall and seepage water, and to characterize regional rainfall isotopic variability. These data, which are among the longest series in France, come from two rainfall stations in south-west France (Le Mas 1996-2012, and Villars 1998-2012; typically under Atlantic influence), and from one station in the south-east (Orgnac 2000-2012; under both Mediterranean and Atlantic influence). Rainfall isotopic composition is compared to drip water collected under stalactites from the same sites: Villars Cave (four drip stations 1999-2012) in the south-west, and Chauvet Cave (two drip stations 2000-2012) in the south-east, near Orgnac. The study of these isotopic data sets allows the following conclusions to be drawn about the rainfall/drip water relationships and about rainfall variability: (1) the cave drip water isotopic composition does not show any significant changes since the beginning of measurements; in order to explain its isotopic signature it is necessary to integrate weighted rainfall δ18O of all months during several years, which demonstrates that, even at shallow depths (10-50 m), cave drip water is a mixture of rain water integrated over relatively long periods, which give an apparent time residence from several months to up to several years. These results have important consequences on the interpretation of proxies like speleothem fluid inclusions and tree-ring cellulose isotopic composition, which are used for paleoclimatic studies; (2) in the Villars Cave, where drip stations at two different depths were studied, lower δ18O values were observed in the lower galleries, which might be due to winter season overflows during infiltration and/or to older rain water with a different isotopic composition that reaches the lower galleries after years; (3) local precipitation is characterized by local meteoric water lines, LMWL, with δ18O/δD slopes close to 7 in both areas, and correlations between air temperature and precipitation δ18O are low at both monthly and annual scales, even with temperature weighted by the amount of precipitation; (4) the mesoscale climate model REMOiso, equipped with a water isotope module, allows the direct comparison of modeled and observed long term water isotope records. The model slightly overestimates rainfall δ18O at the respective sampling stations. However, it simulates very well not only the seasonal rainfall isotopic signal but also some intra-seasonal patterns such as a typical double-peak δ18O pattern in winter time.

Phosphorus dynamics in soils irrigated with reclaimed waste water or fresh water - A study using oxygen isotopic composition of phosphate

USGS Publications Warehouse

Zohar, I.; Shaviv, A.; Young, M.; Kendall, C.; Silva, S.; Paytan, A.

2010-01-01

Transformations of phosphate (Pi) in different soil fractions were tracked using the stable isotopic composition of oxygen in phosphate (??18Op) and Pi concentrations. Clay soil from Israel was treated with either reclaimed waste water (secondary, low grade) or with fresh water amended with a chemical fertilizer of a known isotopic signature. Changes of ??18Op and Pi within different soil fractions, during a month of incubation, elucidate biogeochemical processes in the soil, revealing the biological and the chemical transformation impacting the various P pools. P in the soil solution is affected primarily by enzymatic activity that yields isotopic equilibrium with the water molecules in the soil solution. The dissolved P interacts rapidly with the loosely bound P (extracted by bicarbonate). The oxides and mineral P fractions (extracted by NaOH and HCl, respectively), which are considered as relatively stable pools of P, also exhibited isotopic alterations in the first two weeks after P application, likely related to the activity of microbial populations associated with soil surfaces. Specifically, isotopic depletion which could result from organic P mineralization was followed by isotopic enrichment which could result from preferential biological uptake of depleted P from the mineralized pool. Similar transformations were observed in both soils although transformations related to biological activity were more pronounced in the soil treated with reclaimed waste water compared to the fertilizer treated soil. ?? 2010 Elsevier B.V.

Stable bromine isotopic composition of methyl bromide released from plant matter

NASA Astrophysics Data System (ADS)

Horst, Axel; Holmstrand, Henry; Andersson, Per; Thornton, Brett F.; Wishkerman, Asher; Keppler, Frank; Gustafsson, Örjan

2014-01-01

Methyl bromide (CH3Br) emitted from plants constitutes a natural source of bromine to the atmosphere, and is a component in the currently unbalanced global CH3Br budget. In the stratosphere, CH3Br contributes to ozone loss processes. Studies of stable isotope composition may reduce uncertainties in the atmospheric CH3Br budget, but require well-constrained isotope fingerprints of the source end members. Here we report the first measurements of stable bromine isotopes (δ81Br) in CH3Br from abiotic plant emissions. Incubations of both KBr-fortified pectin, a ubiquitous cell-stabilizing macromolecule, and of a natural halophyte (Salicornia fruticosa), yielded an enrichment factor (ε) of -2.00 ± 0.23‰ (1σ, n = 8) for pectin and -1.82 ± 0.02‰ (1σ, n = 4) for Salicornia (the relative amount of the heavier 81Br was decreased in CH3Br compared to the substrate salt). For short incubations, and up to 10% consumption of the salt substrate, this isotope effect was similar for temperatures from 30 up to 300 °C. For longer incubations of up to 90 h at 180 °C the δ81Br values increased from -2‰ to 0‰ for pectin and to -1‰ for Salicornia. These δ81Br source signatures of CH3Br formation from plant matter combine with similar data for carbon isotopes to facilitate multidimensional isotope diagnostics of the CH3Br budget.

Benthic iron cycling in a high-oxygen environment: Implications for interpreting the Archean sedimentary iron isotope record.

PubMed

McCoy, V E; Asael, D; Planavsky, N

2017-09-01

The most notable trend in the sedimentary iron isotope record is a shift at the end of the Archean from highly variable δ 56 Fe values with large negative excursions to less variable δ 56 Fe values with more limited negative values. The mechanistic explanation behind this trend has been extensively debated, with two main competing hypotheses: (i) a shift in marine redox conditions and the transition to quantitative iron oxidation; and (ii) a decrease in the signature of microbial iron reduction in the sedimentary record because of increased bacterial sulfate reduction (BSR). Here, we provide new insights into this debate and attempt to assess these two hypotheses by analyzing the iron isotope composition of siderite concretions from the Carboniferous Mazon Creek fossil site. These concretions precipitated in an environment with water column oxygenation, extensive sediment pile dissimilatory iron reduction (DIR) but limited bacterial sulfate reduction (BSR). Most of the concretions have slightly positive iron isotope values, with a mean of 0.15‰ and limited iron isotope variability compared to the Archean sedimentary record. This limited variability in an environment with high DIR and low BSR suggests that these conditions alone are insufficient to explain Archean iron isotope compositions. Therefore, these results support the idea that the unusually variable and negative iron isotope values in the Archean are due to dissimilatory iron reduction (DIR) coupled with extensive water column iron cycling. © 2017 John Wiley & Sons Ltd.

Heterogeneity of the Caribbean plateau mantle source: Sr, O and He isotopic compositions of olivine and clinopyroxene from Gorgona Island

NASA Astrophysics Data System (ADS)

Révillon, S.; Chauvel, C.; Arndt, N. T.; Pik, R.; Martineau, F.; Fourcade, S.; Marty, B.

2002-12-01

The composition of the mantle plumes that created large oceanic plateaus such as Ontong Java or the Caribbean is still poorly known. Geochemical and isotopic studies on accreted portions of the Caribbean plateau have shown that the plume source was heterogeneous and contained isotopically depleted and relatively enriched portions. A distinctive feature of samples from the Caribbean plateau is their unusual Sr isotopic compositions, which, at a given Nd isotopic ratio, are far higher than in samples from other oceanic plateaus. Sr, O and He isotopic compositions of whole rocks and magmatic minerals (clinopyroxene or olivine) separated from komatiites, gabbros and peridotites from Gorgona Island in Colombia were determined to investigate the origin of these anomalously radiogenic compositions. Sequentially leached clinopyroxenes have Sr isotopic compositions in the range 87Sr/ 86Sr=0.70271-0.70352, systematically lower than those of leached and unleached whole rocks. Oxygen isotopic ratios of clinopyroxene vary within the range δ 18O=5.18-5.35‰, similar to that recorded in oceanic island basalts. He isotopic ratios are high ( R/ Ra=8-19). The lower 87Sr/ 86Sr ratios of most of the clinopyroxenes shift the field of the Caribbean plateau in Nd-Sr isotope diagrams toward more 'normal' values, i.e. a position closer to the field defined by mid-ocean ridge basalts and oceanic-island basalts. Three clinopyroxenes have slightly higher 87Sr/ 86Sr ratios that cannot be explained by an assimilation model. The high 87Sr/ 86Sr and variations of 143Nd/ 144Nd are interpreted as a source characteristic. Trace-element ratios, however, are controlled mainly by fractionation during partial melting. We combine these isotopic data in a heterogeneous plume source model that accounts for the diversity of isotopic signatures recorded on Gorgona Island and throughout the Caribbean plateau. The heterogeneities are related to old recycled oceanic lithosphere in the plume source; the high 3He/ 4He ratios may indicate that the source material once resided in the lower mantle.

Nd Isotope and U-Th-Pb Age Mapping of Single Monazite Grains by Laser Ablation Split Stream Analysis

NASA Astrophysics Data System (ADS)

Fisher, C. M.; Hanchar, J. M.; Miller, C. F.; Phillips, S.; Vervoort, J. D.; Martin, W.

2015-12-01

Monazite is a common accessory mineral that occurs in medium to high grade metamorphic and Ca-poor felsic igneous rocks, and often controls the LREE budget (including Sm and Nd) of the host rock in which it crystallizes. Moreover, it contains appreciable U and Th, making it an ideal mineral for determining U-Th-Pb ages and Sm-Nd isotopic compositions, both of which are readily determined using in situ techniques with very high spatial resolution like LA-MC-ICPMS. Here, we present the results of laser ablation split stream analyses (LASS), which allows for simultaneous determination of the age and initial Nd isotopic composition in a single analysis. Analyses were done using a 20mm laser spot that allowed for detailed Nd isotope mapping of monazite grains (~30 analyses per ~250mm sized grain). Combined with LREE ratios (e.g., Sm/Nd, Ce/Gd, and Eu anomalies) these results yield important petrogenetic constraints on the evolution of peraluminous granites from the Old Woman-Piute batholith in southeastern California. Our findings also allow an improved understanding of the causes of isotope heterogeneity in granitic rocks. U-Th-Pb age mapping across the crystals reveals a single Cretaceous age for all grains with precision and accuracy typical of laser ablation analyses (~2%). In contrast, the concurrent Nd isotope mapping yields homogeneous initial Nd isotope compositions for some grains and large initial intra-grain variations of up to 8 epsilon units in others. The grains that yield homogeneous Nd isotope compositions have REE ratios suggesting that they crystallized in a fractionally crystallizing magma. Conversely, other grains, which also record fractional crystallization of both feldspar and LREE rich minerals, demonstrate a change in the Nd isotope composition of the magma during crystallization of monazite. Comparison of inter- and intra-grain Nd isotope compositions reveals further details on the potential mechanisms responsible for isotope heterogeneity present in single rock samples. This method highlights the potential of single grain isotope mapping of LREE phases such as monazite, allanite, and titanite for understanding both igneous and metamorphic petrogenesis.

Isotopic inferences of ancient biochemistries - Carbon, sulfur, hydrogen, and nitrogen

NASA Technical Reports Server (NTRS)

Schidlowski, M.; Hayes, J. M.; Kaplan, I. R.

1983-01-01

In processes of biological incorporation and subsequent biochemical processing sizable isotope effects occur as a result of both thermodynamic and kinetic fractionations which take place during metabolic and biosynthetic reactions. In this chapter a review is provided of earlier work and recent studies on isotope fractionations in the biogeochemical cycles of carbon, sulfur, hydrogen, and nitrogen. Attention is given to the biochemistry of carbon isotope fractionation, carbon isotope fractionation in extant plants and microorganisms, isotope fractionation in the terrestrial carbon cycle, the effects of diagenesis and metamorphism on the isotopic composition of sedimentary carbon, the isotopic composition of sedimentary carbon through time, implications of the sedimentary carbon isotope record, the biochemistry of sulfur isotope fractionation, pathways of the biogeochemical cycle of nitrogen, and the D/H ratio in naturally occurring materials.

Isotopic compositions of the elements 2013 (IUPAC Technical Report)

USGS Publications Warehouse

Meija, Juris; Coplen, Tyler B.; Berglund, Michael; Brand, Willi A.; De Bièvre, Paul; Gröning, Manfred; Holden, Norman E.; Irrgeher, Johanna; Loss, Robert D.; Walczyk, Thomas; Prohaska, Thomas

2016-01-01

The Commission on Isotopic Abundances and Atomic Weights (ciaaw.org) of the International Union of Pure and Applied Chemistry (iupac.org) has revised the Table of Isotopic Compositions of the Elements (TICE). The update involved a critical evaluation of the recent published literature. The new TICE 2013 includes evaluated data from the “best measurement” of the isotopic abundances in a single sample, along with a set of representative isotopic abundances and uncertainties that accommodate known variations in normal terrestrial materials.

Impact of moisture source regions on the isotopic composition of precipitation events at high-mountain continental site Kasprowy Wierch, southern Poland

NASA Astrophysics Data System (ADS)

Rozanski, Kazimierz; Chmura, Lukasz; Dulinski, Marek

2016-04-01

Five-year record of deuterium and oxygen-18 isotope composition of precipitation events collected on top of the Kasprowy Wierch mountain (49° 14'N, 19° 59'E, 1989 m a.s.l.) located in north-western High Tatra mountain ridge, southern Poland, is presented and discussed. In total 670 precipitation samples have been collected and analysed. Stable isotope composition of the analysed precipitation events varied in a wide range, from -2.9 to -26.6‰ for δ18O and from -7 to -195 ‰ for δ2H. The local meteoric water line (LMWL) defined by single events data (δ2H=(7.86±0.05)δ18O+(12.9±0.6) deviate significantly from the analogous line defined by monthly composite precipitation data available for IAEA/GNIP station Krakow-Balice (50o04'N, 19o55'E, 220 m a.s.l.), located ca. 100 km north of Kasprowy Wierch ((δ2H=(7.82±0.11)δ18O+(6.9±1.1). While slopes of those two LMWLs are statistically indistinguishable, the intercept of Kasprowy Wierch line is almost two times higher that that characterizing Krakow monthly precipitation. This is well-documented effect associated with much higher elevation of Kasprowy Wierch sampling site when compared to Krakow. The isotope data for Kasprowy Wierch correlate significantly with air temperature, with the slope of the regression line being equal 0.35±0.02 ‰oC for δ18O, whereas no significant correlation with precipitation amount could be established. The impact of moisture source regions on the isotopic composition of precipitation events collected at Kasprowy Wierch site was analysed using HYSPLITE back trajectory model. Five-days back trajectories were calculated for all analysed precipitation events and seasonal maps of trajectory distribution were produced. They illustrate changes in the prevailing transport patterns of air masses bringing precipitation to the sampling site. Back trajectories for the events yielding extreme isotopic composition of precipitation collected at Kasprowy Wierch were analyzed in detail. Acknowledgements. Financial support of this work through Ministry of Science and Higher Education (statutory funds of AGH University od Science and Technology, project No.11.11.220.01) is kindly acknowledged.

Relationship between the trajectory of mid-latitude cyclones in the eastern Pacific Ocean and the isotopic composition of snowfall in the Sierra Nevada, California

NASA Astrophysics Data System (ADS)

Vasquez, K. T.; Sickman, J. O.; Heard, A.; Lucero, D.

2013-12-01

Diatoms, preserved in lake sediments, provide a potential archive of snowfall variability in the Sierra Nevada through their sensitivity to changes in water chemistry (a proxy for runoff volume) and by recording the isotopic composition of snow-melt (potentially a proxy for sources of atmospheric moisture). In the Sierra Nevada, we hypothesize that the oxygen isotopic composition of diatom silica is principally controlled by snow and that the isotopic composition of snow varies as a function of the tracks of mid-latitude cyclonic storms in the eastern Pacific Ocean. Snow samples from discrete storms were collected from December 2012 to March 2013 at 2042 meters a.s.l. in Sequoia National Park. The δ18O and δ2H values of the snow samples were measured using a temperature-conversion elemental analyzer coupled to a Delta V isotope ratio mass spectrometer. The isotopic measurements were then coupled to 3, 5 and 7-day air mass back trajectories using the NOAA HYSPLIT model. The measured δ18O values ranged from -17.6 to -7.8 per mil and the δ2H ranged from -119.8 to -73.3 per mil. Both δ18O and δ2H were inversely related to the latitude of the storm origin (R^2 values of 0.67 and 0.57, respectively). Winter storms from the Gulf of Alaska were the most isotopically depleted while storms originating in the subtropical/tropical Pacific were the most isotopically enriched, reflecting the overall latitudinal pattern of ocean-water isotope composition in the Pacific Ocean. Our results suggest that the isotopic composition of Sierra Nevada snowfall is influenced by storm track trajectory and this relationship could be useful in interpreting the climatic significance of δ18O of diatom silica preserved in lake cores.

Calibrating NIST SRM 683 as A New International Reference Standard for Zn Isotopes

NASA Astrophysics Data System (ADS)

Yang, Y.; Zhang, X.; Yu, H.; Huang, F.

2017-12-01

Zinc isotopes have been widely applied in the cosmochemical, geochemical, and environmental studies (Moynier et al. 2017). Obtaining precise Zn isotopic data for inter-laboratory comparison is a prerequisite to these applications. Currently, the JMC3-0749L is the primary reference standard for Zn isotopes (Albarède 2004), but it is not commercially available now. Thus, it is necessary to calibrate a new international primary reference standard for Zn isotopic analysis. Chen et al. (2016) showed that NIST SRM 683 (a pure Zn metal nugget of 140 grams) has a δ66ZnJMC of 0.12‰, which is falling within the range of natural Zn isotopic compositions, and it may a good candidate for the next generation of international reference standard (Chen et al. 2016). In order to further examine whether NIST SRM 683 has a homogeneous Zn isotopic composition, we measured more NIST SRM 683 by double-spike methods using MC-ICPMS (Conway et al. 2013). The metal nuggets of NIST SRM 683 were intensively sampled by micro-drilling. Zinc isotope analyses for two nuggets show that they have δ66Zn of 0.14 ± 0.02‰ (2SD, N = 32) and 0.13 ± 0.02‰ (2SD, N = 33), respectively. These values are similar to those of two Zn metal nuggets (0.11 ± 0.02‰ vs. 0.12 ± 0.02‰) reported previously by Chen et al. (2016). We fully dissolved one nugget, producing pure Zn solution with identical Zn isotopic composition with the drilling samples. All results strongly support that NIST SRM 683 is homogeneous in Zn isotopic compositions which could be an ideal candidate for the next reference for Zn isotopes. Tests on more metal nuggets will be performed in a few months for further confirming the Zn isotope compositions and homogeneity. Reference: Albarède et al., 2004. 'The stable isotope geochemistry of copper and zinc', Reviews in Mineralogy and Geochemistry, 55: 409-27. Chen et al., 2016. 'Zinc Isotopic Compositions of NIST SRM 683 and Whole-Rock Reference Materials', Geostandards and Geoanalytical Research, 40: 417-32. Conway et al., 2013. 'A new method for precise determination of iron, zinc and cadmium stable isotope ratios in seawater by double-spike mass spectrometry', Analytica chimica acta, 793: 44-52. Moynier et al., 2017. 'The isotope geochemistry of zinc and copper', Reviews in Mineralogy and Geochemistry, 82: 543-600.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Conroy, Jessica L; Cobb, Kim M; Noone, David

The objective of this field campaign was to investigate climatic controls on the stable isotopic composition of water vapor, precipitation, and seawater in the western tropical Pacific. Simultaneous measurements of the stable isotopic composition of vapor and precipitation from April 28 to May 8, 2013, at the Manus Tropical Western Pacific Atmospheric Radiation Measurement site, provided several key insights into the nature of the climate signal archived in precipitation and vapor isotope ratios. We observed a large shift from lower to higher isotopic values in vapor and precipitation because of the passage of a mesoscale convective system west of themore » site and a transition from a regional stormy period into a more quiescent period. During the quiescent period, the stable isotopic composition of vapor and precipitation indicated the predominance of oceanic evaporation in determining the isotopic composition of boundary-layer vapor and local precipitation. There was not a consistent relationship between intra-event precipitation amount at the site and the stable isotopic composition of precipitation, thus challenging simplified assumptions about the isotopic “amount effect” in the tropics on the time scale of individual storms. However, some storms did show an amount effect, and deuterium excess values in precipitation had a significant relationship with several meteorological variables, including precipitation, temperature, relative humidity, and cloud base height across all measured storms. The direction of these relationships points to condensation controls on precipitation deuterium excess values on intra-event time scales. The relationship between simultaneous measurements of vapor and precipitation isotope ratios during precipitation events indicates the ratio of precipitation-to-vapor isotope ratios can diagnose precipitation originating from a vapor source unique from boundary-layer vapor and rain re-evaporation.« less

Origin of heavy Fe isotope compositions in high-silica igneous rocks: A rhyolite perspective

NASA Astrophysics Data System (ADS)

Du, De-Hong; Wang, Xiao-Lei; Yang, Tao; Chen, Xin; Li, Jun-Yong; Li, Weiqiang

2017-12-01

The origin of heavy Fe isotope compositions in high-silica (>70 wt% SiO2) igneous rocks remains a highly controversial topic. Considering that fluid exsolution in eruptive rocks is more straight-forward to constrain than in plutonic rocks, this study addresses the problem of Fe isotope fractionation in high-silica igneous rocks by measuring Fe isotope compositions of representative rhyolitic samples from the Neoproterozoic volcanic-sedimentary basins in southern China and the Triassic Tu Le Basin in northern Vietnam. The samples show remarkably varied δ56FeIRMM014 values ranging from 0.05 ± 0.05‰ to 0.55 ± 0.05‰, which is among the highest values reported from felsic rocks. The extensional tectonic setting and short melt residence time in magma chambers for the studied rhyolites rule out Soret diffusion and thermal migration processes as causes of the high δ56Fe values. Effects of volcanic degassing and fluid exsolution on bulk rock δ56Fe values for the rhyolites are also assessed using bulk rock geochemical indicators and Rayleigh fractionation models, and these processes are found to be insufficient to produce resolvable changes in Fe isotope compositions of the residual melt. The most probable mechanism accounting for heavy Fe isotope compositions in the high-silica rhyolites is narrowed down to fractional crystallization processes in the magma before rhyolite eruption. Removal of isotopically light Fe-bearing minerals (i.e. ulvöspinel-rich titanomagnetite, ilmenite and biotite) is proposed as the main cause of Fe isotope variation in silicic melts during magmatic evolution. This study implies that crystal fractionation is the dominant mechanism that controls Fe isotope fractionation in eruptive rocks and Fe isotopes could be used to study magmatic differentiation of high-silica magmas.

Effect Of Substrates On The Fractionation Of Hydrogen Isotopes During Lipid-Biosynthesis By Haloarcula marismortui

NASA Astrophysics Data System (ADS)

Dirghangi, S. S.; Pagani, M.

2010-12-01

Lipids form an important class of proxies for paleoclimatological research, and hydrogen isotope ratios of lipids are being increasingly used for understanding changes in the hydrological system. Proper understanding of hydrogen isotope fractionation during lipid biosynthesis is therefore important and attention has been directed toward understanding the magnitude of hydrogen isotope fractionation that occurs during lipid biosynthesis in various organisms. Hydrogen isotope ratios of lipids depend on the hydrogen isotopic composition of the ambient water, hydrogen isotopic composition of NADPH used during biosynthesis, growth conditions, pathways of lipid biosynthesis, and substrates in the case of heterotrophic organisms. Recently it has been observed that NADPH contributes a significant part of the hydrogen in fatty acids synthesized by bacteria during heterotrophic growth (Zhang et al, 2009). As NADPH is formed by reduction of NADP+ during metabolism of substrates, different metabolic pathways form NADPH with different D/H ratios, which in turn results in variation in D/H ratios of lipids (Zhang et al, 2009). Therefore, substrates play a significant role in hydrogen isotopic compositions of lipids. For this study, we are investigating the effects of substrates on hydrogen isotope fractionation during biosynthesis of isoprenoidal lipids by heterotrophically growing halophilic archaea. Haloarcula marismortui is a halophilic archaea which synthesizes Archaeol (a diether lipid) and other isoprenoidal lipids. We have grown Haloarcula marismortui in pure cultures on three different substrates and are in the process of evaluating isotopic variability of Archaeol and other lipids associated with substrate and the D/H composition of ambient water. Our results will be helpful for a better understanding of hydrogen isotope fractionations during lipid synthesis by archaea. Also, halophilic archaea are the only source of archaeol in hypersaline environments. Therefore, our results will also indicate whether archaeol can be used as a proxy of ambient water hydrogen isotopic compositions in hypersaline environments.

A carbon isotope mass balance for an anoxic marine sediment: Isotopic signatures of diagenesis

NASA Technical Reports Server (NTRS)

Boehme, Susan E.

1993-01-01

A carbon isotope mass balance was determined for the sediments of Cape Lookout Bight, NC to constrain the carbon budgets published previously. The diffusive, ebullitive and burial fluxes of sigma CO2 and CH4, as well as the carbon isotope signatures of these fluxes, were measured. The flux-weighted isotopic signature of the remineralized carbon (-18.9 plus or minus 2.7 per mil) agreed with the isotopic composition of the remineralized organic carbon determined from the particulate organic carbon (POC) delta(C-13) profiles (-19.2 plus or minus 0.2), verifying the flux and isotopic signature estimates. The measured delta(C-13) values of the sigma CO2 and CH4 diffusive fluxes were significantly different from those calculated from porewater gradients. The differences appear to be influenced by methane oxidation at the sediment-water interface, although other potential processes cannot be excluded. The isotope mass balance provides important information concerning the locations of potential diagenetic isotope effects. Specifically, the absence of downcore change in the delta(C-13) value of the POC fraction and the identical isotopic composition of the POC and the products of remineralization indicate that no isotopic fractionation is expressed during the initial breakdown of the POC, despite its isotopically heterogeneous composition.

Quantifying uncertainty in stable isotope mixing models

DOE PAGES

Davis, Paul; Syme, James; Heikoop, Jeffrey; ...

2015-05-19

Mixing models are powerful tools for identifying biogeochemical sources and determining mixing fractions in a sample. However, identification of actual source contributors is often not simple, and source compositions typically vary or even overlap, significantly increasing model uncertainty in calculated mixing fractions. This study compares three probabilistic methods, SIAR [ Parnell et al., 2010] a pure Monte Carlo technique (PMC), and Stable Isotope Reference Source (SIRS) mixing model, a new technique that estimates mixing in systems with more than three sources and/or uncertain source compositions. In this paper, we use nitrate stable isotope examples (δ 15N and δ 18O) butmore » all methods tested are applicable to other tracers. In Phase I of a three-phase blind test, we compared methods for a set of six-source nitrate problems. PMC was unable to find solutions for two of the target water samples. The Bayesian method, SIAR, experienced anchoring problems, and SIRS calculated mixing fractions that most closely approximated the known mixing fractions. For that reason, SIRS was the only approach used in the next phase of testing. In Phase II, the problem was broadened where any subset of the six sources could be a possible solution to the mixing problem. Results showed a high rate of Type I errors where solutions included sources that were not contributing to the sample. In Phase III some sources were eliminated based on assumed site knowledge and assumed nitrate concentrations, substantially reduced mixing fraction uncertainties and lowered the Type I error rate. These results demonstrate that valuable insights into stable isotope mixing problems result from probabilistic mixing model approaches like SIRS. The results also emphasize the importance of identifying a minimal set of potential sources and quantifying uncertainties in source isotopic composition as well as demonstrating the value of additional information in reducing the uncertainty in calculated mixing fractions.« less

The Role of Fog in Ecosystem Hydrology: Initial Results from Investigations Using Stable Isotopes of Water in Hawaiian Cloud Forests

NASA Astrophysics Data System (ADS)

Scholl, M. A.; Gingerich, S. B.; Giambelluca, T. W.; Nullet, M. A.; Loope, L. L.

2002-05-01

The role of fog drip in cloud forest ecosystems is being investigated at two sites, one each on the windward and leeward sides of East Maui, Hawaii. The study involves using the different isotopic signatures of fog (cloud water) and rain to trace fog through the forest water cycle, as well as comparing relative amounts of fog, rain, and throughfall. At each site, volume of rain, fog plus rain, and throughfall is recorded hourly. Stable isotope samples of rain, fog, soil water, stream water, and tree sap are collected monthly, and each site has a visibility sensor and weather station. The windward site, at 1950 m altitude, is enveloped by orographic clouds under trade wind conditions almost every day. This site is near the upper boundary of extensive forested mountain slopes that are a major watershed for the island. Volume data suggest that fog drip (compared to rain as measured by a standard gage) contributes substantially to the forest water budget on the windward side. Tree sap deuterium composition was consistently similar to fog composition for samples analyzed thus far, while soil water was isotopically lighter, possibly reflecting a mixture of fog with rain or shallow groundwater. The leeward site, at 1220 m, is often in a cloud bank under trade wind conditions. During the summer the major source of precipitation is cloud water; rainfall generally occurs during winter storms. Scattered cloud forest remnants persist at this site despite degradation of extensive native forest by ungulate browsing, plant invasion, and fire. Here, fog drip was a smaller proportion of the total precipitation than at the windward site, but exceeded rainfall for some precipitation events. Unlike the windward site, tree sap and soil water had similar isotopic composition. The information gained from this study underscores the importance of trees and shrubs in extracting cloud water that contributes to soil moisture, groundwater recharge, and stream flow in watersheds.

Spacecraft measurements of the elemental and isotopic composition of solar energetic particles

NASA Technical Reports Server (NTRS)

Mewaldt, R. A.

1980-01-01

Within the past few years, instruments flown on satellites and space probes have made significant progress in measuring the elemental and isotopic composition of energetic heavy nuclei accelerated in solar flares. These new observations are discussed, focusing on: (1) the energy dependence of the elemental composition at energies not greater than 1 MeV/nucleon; (2) flare to flare variations in the composition; and (3) comparisons of the average solar particle abundances (Z not less than 2 and not greater than 28) with other measures of the solar composition, including photospheric, coronal, and solar wind observations. These comparisons have led to the suggestion that solar flares sample the composition of the corona. Isotopic measurements of heavy solar flare nuclei have recently added a new dimension to these studies. In particular, the isotopic composition of solar flare neon has been found to be significantly different from that measured in the solar wind, but consistent with the meteoritic component neon-A.

High precision calcium isotope analysis using 42Ca-48Ca double-spike TIMS technique

NASA Astrophysics Data System (ADS)

Feng, L.; Zhou, L.; Gao, S.; Tong, S. Y.; Zhou, M. L.

2014-12-01

Double spike techniques are widely used for determining calcium isotopic compositions of natural samples. The most important factor controlling precision of the double spike technique is the choice of appropriate spike isotope pair, the composition of double spikes and the ratio of spike to sample（CSp/CN）. We propose an optimal 42Ca-48Ca double spike protocol which yields the best internal precision for calcium isotopic composition determinations among all kinds of spike pairs and various spike compositions and ratios of spike to sample, as predicted by linear error propagation method. It is suggested to use spike composition of 42Ca/(42Ca+48Ca) = 0.44 mol/mol and CSp/(CN+ CSp)= 0.12mol/mol because it takes both advantages of the largest mass dispersion between 42Ca and 48Ca (14%) and lowest spike cost. Spiked samples were purified by pass through homemade micro-column filled with Ca special resin. K, Ti and other interference elements were completely separated, while 100% calcium was recovered with negligible blank. Data collection includes integration time, idle time, focus and peakcenter frequency, which were all carefully designed for the highest internal precision and lowest analysis time. All beams were automatically measured in a sequence by Triton TIMS so as to eliminate difference of analytical conditions between samples and standards, and also to increase the analytical throughputs. The typical internal precision of 100 duty cycles for one beam is 0.012‒0.015 ‰ (2δSEM), which agrees well with the predicted internal precision of 0.0124 ‰ (2δSEM). Our methods improve internal precisions by a factor of 2‒10 compared to previous methods of determination of calcium isotopic compositions by double spike TIMS. We analyzed NIST SRM 915a, NIST SRM 915b and Pacific Seawater as well as interspersed geological samples during two months. The obtained average δ44/40Ca (all relative to NIST SRM 915a) is 0.02 ± 0.02 ‰ (n=28), 0.72±0.04 ‰ (n=10) and 1.93±0.03 ‰ (n=21) for NIST SRM 915a, NIST SRM 915b and Pacific Seawater, respectively. The long-term reproducibility is 0.10‰ (2 δSD), which is comparable to the best external precision of 0.04 ‰ (2 δSD) of previous methods, but our sample throughputs are doubled with significant reduction in amount of spike used for single samples.

New technique for study on isotopic fractionation between sea water and foraminiferal growing processes

NASA Astrophysics Data System (ADS)

Cang, Shuxi; Shackleton, N. J.

1990-12-01

The stable isotopic δ18O and δ13C composition of foraminiferal shell calcite varies as a function of many factors including temperature and salinity. In order to understand and interpret the variations in the isotopic composition of foraminiferal shell calcite, research has been recently focused on the role of the “vital effects”. Our examination of the lamella structure of several recent planktonic foraminifera indicates that the secretion of sequential lamellae results in multiple lamillae on earlier chambers and a single lamella on the final chamber. We used a very simple procedure to separate the individual whole test of foraminifera into several chambers and measured the isotopic composition of each growth stage chamber. The results indicate that the stable isotopic composition (carbon and oxygen), particularly that of the last two chambers, of the foraminiferal test varies as a function of the individual growing process.

Hafnium isotope stratigraphy of ferromanganese crusts

PubMed

Lee; Halliday; Hein; Burton; Christensen; Gunther

1999-08-13

A Cenozoic record of hafnium isotopic compositions of central Pacific deep water has been obtained from two ferromanganese crusts. The crusts are separated by more than 3000 kilometers but display similar secular variations. Significant fluctuations in hafnium isotopic composition occurred in the Eocene and Oligocene, possibly related to direct advection from the Indian and Atlantic oceans. Hafnium isotopic compositions have remained approximately uniform for the past 20 million years, probably reflecting increased isolation of the central Pacific. The mechanisms responsible for the increase in (87)Sr/(86)Sr in seawater through the Cenozoic apparently had no effect on central Pacific deep-water hafnium.

A Sr and Mg isotopic study of soil and stream waters along an erosional gradient, Sierra Nevada, California

NASA Astrophysics Data System (ADS)

Rosen, V. B.; Maher, K.; Kouba, C. M.; Weinman, B. A.; Yoo, K.; Mudd, S. M.

2012-12-01

Since chemical weathering rates are proposed to regulate atmospheric CO2 concentrations and by extension global temperature over geologic timescales, understanding the relationship between chemical weathering rates and physical erosion is crucial to accurately interpreting Earth's climate history. The rate of supply of fresh minerals to the weathering zone is known to be an important control on chemical weathering rates. However, the consequences of physical erosion on the isotopic composition of weathering-derived solutes are more difficult to assess. This study capitalizes on a series of granitic hillslope transects with different erosion rates but similar climate, vegetation, and bedrock, in order to assess the consequences of erosion on the Sr and Mg isotopic composition of solutes. Reactive transport model simulations of varying complexity have been used to complement the field measurements and to analyze the sensitivity of fluid isotopic compositions to changes in key parameters such as erosion rate, flow rate, and biological cycling. The three hillslopes in the Feather River Basin, California reflect different degrees of channel erosion at their bases—BRC is a hillslope with active channel incision (60% average slope, below the knickpoint), FTA is a hillslope reflecting the transition between the relict and modern-day incising areas (50% average slope, at the knickpoint), and POMD is a 30% average hillslope in the relict landscape above the knickpoint. We measured the major element compositions, as well as the Sr and Mg isotopic compositions of soil water leaches (deionized water leaches), lysimeters, stream waters, and groundwaters by multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS). The 87Sr/86Sr values of soil and stream waters show minimal variation (0.7042 to 0.7046) as a function of soil depth, erosion rate, or sampling season despite abundant radiogenic biotite in the profiles. These results agree with the reactive transport model predictions at high erosion rates, and suggest that soil residence times and isotopic equilibrium times are too short for biotite weathering to influence the solute isotopic composition. In contrast, model results for δ26Mg of the soil waters and minerals suggest that the Mg isotopic composition of the solute changes as a function of erosion rate because of shorter isotopic equilibrium length scales at higher erosion rates. The isotopic reactive transport modeling, combined with hillslope depth profiles and stream water analyses, provides a useful approach for linking the isotopic composition of solutes to erosion rates. This study may provide insights into past and present riverine isotopic compositions, and contribute to our understanding of how surface processes have influenced past atmospheric conditions.

Importance of depth and intensity of convection on the isotopic composition of water vapor as seen from IASI and TES δD observations

NASA Astrophysics Data System (ADS)

Lacour, Jean-Lionel; Risi, Camille; Worden, John; Clerbaux, Cathy; Coheur, Pierre-François

2018-01-01

We use tropical observations of the water vapor isotopic composition, derived from IASI and TES spaceborne measurements, to show that the isotopic composition of water vapor in the free troposphere is sensitive to both the depth and the intensity of convection. We find that for any given precipitation intensity, vapor associated with deep convection is isotopically depleted relative to vapor associated with shallow convection. The intensity of precipitation also plays a role as for any given depth of convection, the relative enrichment of water vapor decreases as the intensity of precipitation increases. Shallow convection, via the uplifting of enriched boundary layer air into the free troposphere and the convective detrainment, enriches the free troposphere. In contrast, deep convection is associated with processes that deplete the water vapor in the free troposphere, such as rain re-evaporation. The results of this study allow for a better identification of the parameters controlling the isotopic composition of the free troposphere and indicate that the isotopic composition of water vapor can be used to evaluate the relative contributions of shallow and deep convection in global models.

Stable isotopic comparison between loggerhead sea turtle tissues.

PubMed

Vander Zanden, Hannah B; Tucker, Anton D; Bolten, Alan B; Reich, Kimberly J; Bjorndal, Karen A

2014-10-15

Stable isotope analysis has been used extensively to provide ecological information about diet and foraging location of many species. The difference in isotopic composition between animal tissue and its diet, or the diet-tissue discrimination factor, varies with tissue type. Therefore, direct comparisons between isotopic values of tissues are inaccurate without an appropriate conversion factor. We focus on the loggerhead sea turtle (Caretta caretta), for which a variety of tissues have been used to examine diet, habitat use, and migratory origin through stable isotope analysis. We calculated tissue-to-tissue conversions between two commonly sampled tissues. Epidermis and scute (the keratin covering on the carapace) were sampled from 33 adult loggerheads nesting at two beaches in Florida (Casey Key and Canaveral National Seashore). Carbon and nitrogen stable isotope ratios were measured in the epidermis and the youngest portion of the scute tissue, which reflect the isotopic composition of the diet and habitat over similar time periods of the order of several months. Significant linear relationships were observed between the δ(13)C and δ(15)N values of these two tissues, indicating they can be converted reliably. Whereas both epidermis and scute samples are commonly sampled from nesting sea turtles to study trophic ecology and habitat use, the data from these studies have not been comparable without reliable tissue-to-tissue conversions. The equations provided here allow isotopic datasets using the two tissues to be combined in previously published and subsequent studies of sea turtle foraging ecology and migratory movement. In addition, we recommend that future isotopic comparisons between tissues of any organism utilize linear regressions to calculate tissue-to-tissue conversions. Copyright © 2014 John Wiley & Sons, Ltd.

Utilization of non-weapons-grade plutonium and highly enriched uranium with breeding of the 233U isotope in the VVER reactors using thorium and heavy water

NASA Astrophysics Data System (ADS)

Marshalkin, V. E.; Povyshev, V. M.

2015-12-01

A method for joint utilization of non-weapons-grade plutonium and highly enriched uranium in the thorium-uranium—plutonium oxide fuel of a water-moderated reactor with a varying water composition (D2O, H2O) is proposed. The method is characterized by efficient breeding of the 233U isotope and safe reactor operation and is comparatively simple to implement.

Osmium isotope variations in the Pacific mantle: implications for the distribution of heterogeneity in the convecting mantle

NASA Astrophysics Data System (ADS)

Ishikawa, A.; Senda, R.; Suzuki, K.; Tani, K.; Ishii, T.

2015-12-01

Recent accumulation of Os isotope data obtained either from abyssal peridotites or from ocean island peridotite xenoliths has clearly demonstrated that the modern convecting mantle is substantially heterogeneous in Os-isotope composition. Unlike other radiogenic isotope heterogeneities observed in oceanic basalts, largely controlled by incorporation of recycled crustal materials, it seems likely that the observed range of Os-isotope compositions in oceanic peridotites directly reflect varying degrees of ancient melt extraction from peridotitic mantle. Hence, global variations of Os-isotope compositions in oceanic peridotites may provide an important piece of information in unraveling the geochemical and geodynamic evolution of the convecting mantle. Here we present the Os-isotope variations in peridotite-serpentinite recovered from the Pacific area because the number of data available is yet scarce when compared with data from other oceans (Atlantic, Arctic and Indian Ocean). Our primary purpose is to test whether mantle domains underlying four major oceans are distinct in terms of Os isotope variations, reflecting the pattern of mantle convection or mixing efficiency. We examined 187Os/188Os ratios and highly siderophile element concentrations in serpentinized harzburgite recovered from Hess Deep in the East Pacific Rise, a mantle section in the Taitao ophiolite, Chile (Schulte et al., 2009), serpentinized harzburgite bodies in the Izu-Ogasawara and Tonga forearc (Parkinson et al., 1998), peridotite xenoliths from the Pali-Kaau vent in O'ahu island, Hawaii (Bizimis et al., 2007), and low-temperature type peridotite xenoliths from Malaita, Solomon Islands (Ishikawa et al., 2011). The results demonstrate that samples from each area display very similar Os-isotope variations with a pronounced peak in 187Os/188Os = 0.125-0.128. Moreover, the relatively larger datasets obtained from Hess Deep, Taitao and Malaita clearly exhibit the presence of secondary peak in 187Os/188Os=0.117-0.119 (Re-depletion ages ~1.5 Ga). These characteristics are almost identical to the global population mainly comprised of data from other oceans. This suggests that small-scale heterogeneities created by ancient melt extraction are homogeneously distributed over large scales within the convecting mantle.

Fractionation of silver isotopes in native silver explained by redox reactions

NASA Astrophysics Data System (ADS)

Mathur, Ryan; Arribas, Antonio; Megaw, Peter; Wilson, Marc; Stroup, Steven; Meyer-Arrivillaga, Danilo; Arribas, Isabel

2018-03-01

Scant data exist on the silver isotope composition of native silver specimens because of the relative newness of the technique. This study increases the published dataset by an order of magnitude and presents 80 silver new isotope analyses from native silver originating from a diverse set of worldwide deposits (8 deposit types, 33 mining districts in five continents). The measured isotopic range (defined as δ109Ag/107Ag in per mil units compared to NIST 978 Ag isotope standard) is +2.1 to -0.86‰ (2σ errors less than 0.015); with no apparent systematic correlations to date with deposit type or even within districts. Importantly, the data centering on 0‰ all come from high temperature hypogene/primary deposits whereas flanking and overlapping data represent secondary supergene deposits. To investigate the causes for the more fractionated values, several laboratory experiments involving oxidation of silver from natural specimens of Ag-rich sulfides and precipitation and adsorption of silver onto reagent grade MnO2 and FeOOH were conducted. Simple leach experiments demonstrate little Ag isotope fractionation occurred through oxidation of Ag from native Ag (Δsolution-native109Ag = 0.12‰). In contrast, significant fractionation occurred through precipitation of native Ag onto MnO2 (up to Δsolution-MnO2109Ag = 0.68‰, or 0.3amu). Adsorption of silver onto the MnO2 and FeOOH did not produce as large fractionation as precipitation (mean value of Δsolution-MnO2109Ag = 0.10‰). The most likely cause for the isotopic variations seen relates to redox effects such as the reduction of silver from Ag (I) to Ag° that occurs during precipitation onto the mineral surface. Since many Ag deposits have halos dominated by MnO2 and FeOOH phases, potential may exist for the silver isotope composition of ores and surrounding geochemical haloes to be used to better understand ore genesis and potential exploration applications. Aside from the Mn oxides, surface fluid silver isotope compositions might provide information about geochemical reactions relevant to both environmental and hydrometallurgical applications.

Spatial patterns of throughfall isotopic composition at the event and seasonal timescales

NASA Astrophysics Data System (ADS)

Allen, Scott T.; Keim, Richard F.; McDonnell, Jeffrey J.

2015-03-01

Spatial variability of throughfall isotopic composition in forests is indicative of complex processes occurring in the canopy and remains insufficiently understood to properly characterize precipitation inputs to the catchment water balance. Here we investigate variability of throughfall isotopic composition with the objectives: (1) to quantify the spatial variability in event-scale samples, (2) to determine if there are persistent controls over the variability and how these affect variability of seasonally accumulated throughfall, and (3) to analyze the distribution of measured throughfall isotopic composition associated with varying sampling regimes. We measured throughfall over two, three-month periods in western Oregon, USA under a Douglas-fir canopy. The mean spatial range of δ18O for each event was 1.6‰ and 1.2‰ through Fall 2009 (11 events) and Spring 2010 (7 events), respectively. However, the spatial pattern of isotopic composition was not temporally stable causing season-total throughfall to be less variable than event throughfall (1.0‰; range of cumulative δ18O for Fall 2009). Isotopic composition was not spatially autocorrelated and not explained by location relative to tree stems. Sampling error analysis for both field measurements and Monte-Carlo simulated datasets representing different sampling schemes revealed the standard deviation of differences from the true mean as high as 0.45‰ (δ18O) and 1.29‰ (d-excess). The magnitude of this isotopic variation suggests that small sample sizes are a source of substantial experimental error.

Source discrimination of atmospheric metal deposition by multi-metal isotopes in the Three Gorges Reservoir region, China.

PubMed

Liu, Jinling; Bi, Xiangyang; Li, Fanglin; Wang, Pengcong; Wu, Jin

2018-05-12

Concentrations of heavy metals, as well as isotopic compositions of mercury (Hg) and lead (Pb), in mosses (Bryum argenteum) from the Three Gorges Reservoir (TGR) region were investigated to decipher the sources of atmospheric metals in this region. Higher contents of metals (0.90 ± 0.65 mg/kg of Cd, 24.6 ± 27.4 mg/kg of Cu, and 36.1 ± 51.1 mg/kg of Pb) in the mosses from TGR were found compared with those from pollution-free regions. Principal component analysis (PCA) grouped the moss metals into four main components which were associated with both anthropogenic and natural sources. The ratios of Pb isotopes of the mosses (1.153-1.173 for 206 Pb/ 207 Pb and 2.094-2.129 for 208 Pb/ 206 Pb) fell between those of the traffic emissions and coals. Similarly, the compositions of δ 202 Hg (-4.29∼-2.33‰) and Δ 199 Hg (within ±0.2‰) were comparable to those of the coals and coal combustion emissions from China and India. These joined results of Pb and Hg isotope data give solid evidences that the coal combustion and traffic emissions are the main causes of metal accumulation in the TGR region. Copyright © 2018 Elsevier Ltd. All rights reserved.

What controls silicon isotope fractionation during dissolution of diatom opal?

NASA Astrophysics Data System (ADS)

Wetzel, F.; de Souza, G. F.; Reynolds, B. C.

2014-04-01

The silicon isotope composition of opal frustules from photosynthesising diatoms is a promising tool for studying past changes in the marine silicon cycle, and indirectly that of carbon. Dissolution of this opal may be accompanied by silicon isotope fractionation that could disturb the pristine silicon isotope composition of diatom opal acquired in the surface ocean. It has previously been shown that dissolution of fresh and sediment trap diatom opal in seawater does fractionate silicon isotopes. However, as the mechanism of silicon isotope fractionation remained elusive, it is uncertain whether opal dissolution in general is associated with silicon isotope fractionation considering that opal chemistry and surface properties are spatially and temporally (i.e. opal of different age) diverse. In this study we dissolved sediment core diatom opal in 5 mM NaOH and found that this process is not associated with significant silicon isotope fractionation. Since no variability of the isotope effect was observed over a wide range of dissolution rates, we can rule out the suggestion that back-reactions had a significant influence on the net isotope effect. Similarly, we did not observe an impact of temperature, specific surface area, or degree of undersaturation on silicon isotope partitioning during dissolution, such that these can most likely also be ruled out as controlling factors. We discuss the potential impacts of the chemical composition of the dissolution medium and age of diatom opal on silicon isotope fractionation during dissolution. It appears most likely that the controlling mechanism of silicon isotope fractionation during dissolution is related to the reactivity, or potentially, aluminium content of the opal. Such a dependency would imply that silicon isotope fractionation during dissolution of diatom opal is spatially and temporally variable. However, since the isotope effects during dissolution are small, the silicon isotope composition of diatom opal appears to be robust against dissolution in the deep sea sedimentary environment.

Characteristics of Martian Crustal Materials and Implications for Magmatic Assimilation: Preliminary Re-Os Isotope and Highly Siderophile Element Abundance Data for Nakhlites and Tissint

NASA Astrophysics Data System (ADS)

Mari, N.; Riches, A. J. V.; Hallis, L. J.; Lee, M. R.

2017-07-01

This project, for the first time, aims to integrate nakhlite Os-isotope compositions and HSE abundance data with S-isotope compositions for sample fractions for which textural information is constrained prior to destructive analyses.

Isotopic Composition of Barium in Single Presolar Silicon Carbide Grains

NASA Technical Reports Server (NTRS)

Savina, M. R.; Tripa, C. E.; Pellin, M. J.; Davis, A. M.; Clayton, R. N.; Lewis, R. S.; Amari, S.

2002-01-01

We have measured Ba isotope distributions in individual presolar SiC grains. We find that the Ba isotopic composition in mainstream SiC grains is consistent with models of nucleosynthesis in low to intermediate mass asymptotic giant branch (AGB) stars. Additional information is contained in the original extended abstract.

Soil drying effects on the carbon isotope composition of soil respiration

EPA Science Inventory

Stable isotopes are used widely as a tool for determining sources of carbon (C) fluxes in ecosystem C studies. Environmental factors that change over time, such as moisture, can create dynamic changes in the isotopic composition of C assimilated by plants, and offers a unique opp...

Iron isotope behavior during fluid/rock interaction in K-feldspar alteration zone - A model for pyrite in gold deposits from the Jiaodong Peninsula, East China

NASA Astrophysics Data System (ADS)

Zhu, Zhi-Yong; Jiang, Shao-Yong; Mathur, Ryan; Cook, Nigel J.; Yang, Tao; Wang, Meng; Ma, Liang; Ciobanu, Cristiana L.

2018-02-01

Mechanisms for Fe isotope fractionation in hydrothermal mineral deposits and in zones of associated K-feldspar alteration remain poorly constrained. We have analyzed a suite of bulk samples consisting of granite displaying K-feldspar alteration, Precambrian metamorphic rocks, and pyrite from gold deposits of the Jiaodong Peninsula, East China, by multi-collector inductively-coupled plasma mass spectrometry. Pyrites from disseminated (J-type) ores show a δ56Fe variation from +0.01 to +0.64‰, overlapping with the signature of the host granites (+0.08 to +0.39‰). In contrast, pyrites from quartz veins (L-type ores) show a wide range of Fe-isotopic composition from -0.78 to +0.79‰. Negative values are never seen in the J-type pyrites. The Fe isotope signature of the host granite with K-feldspar alteration is significantly heavier than that of the bulk silicate Earth. The Fe isotopic compositions of Precambrian metamorphic rocks across the district display a narrow range between -0.16‰ and +0.19‰, which is similar to most terrestrial rocks. Concentrations of major and trace elements in bulk samples were also determined, so as to evaluate any correlation between Fe isotope composition and degree of alteration. We note that during progressive K-feldspar alteration to rocks containing >70 wt% SiO2, >75 ppm Rb, and <1.2 wt% total Fe2O3, the Fe isotope composition of the granite changes systematically. The Fe isotope signature becomes heavier as the degree of alteration increases. The extremely light Fe isotopic compositions in L-type gold deposits may be explained by Rayleigh fractionation during pyrite precipitation in an open fracture system. We note that the sulfur isotopic compositions of pyrite in the two types of ores are also different. Pyrite from J-type ores has a systematically 3.5‰-higher δ34S value (11.2‰) than those of pyrite from the L-type ores (7.7‰). There is, however, no correlation between Fe and S isotope signatures. The isotopic fractionation of sulfur is used to constrain a change in the fO2 of the hydrothermal fluids from which pyrite precipitated. This work demonstrates that the Fe isotope composition of pyrite displays a significant response to the process of pyrite precipitation in hydrothermal systems, and that systematic fractionation of iron isotopes occurs during fluid/rock reaction in the K-feldspar alteration zone of the Linglong granite. The implications of the results are that processes of mineralization and associated fluid-rock interaction, which are ubiquitously observed in porphyry-style Cu-Au-Mo and other hydrothermal deposits, may be readily traceable using Fe isotopes.

Isotopic anomalies - Chemical memory of Galactic evolution

NASA Technical Reports Server (NTRS)

Clayton, Donald D.

1988-01-01

New mechanisms for the chemical memory of isotopic anomalies are proposed which are based on the temporal change during the chemical evolution of the Galaxy of the isotopic composition of the mean ejecta from stars. Because of the differing temporal evolution of primary and secondary products of nucleosynthesis, the isotopic composition of the bulk interstellar medium changes approximately linearly with time, and thus any dust component having an age different from that of average dust will be isotopically anomalous. Special attention is given to C, O, Mg, Si, and isotopically heavy average-stellar condensates of SiC.

Continental sedimentary processes decouple Nd and Hf isotopes

NASA Astrophysics Data System (ADS)

Garçon, Marion; Chauvel, Catherine; France-Lanord, Christian; Huyghe, Pascale; Lavé, Jérôme

2013-11-01

The neodymium and hafnium isotopic compositions of most crustal and mantle rocks correlate to form the "Terrestrial Array". However, it is now well established that whereas coarse detrital sediments follow this trend, fine-grained oceanic sediments have high Hf ratios relative to their Nd isotopic ratios. It remains uncertain whether this "decoupling" of the two isotopic systems only occurs in the oceanic environment or if it is induced by sedimentary processes in continental settings. In this study, the hafnium and neodymium isotopic compositions of sediments in large rivers is expressly used to constrain the behavior of the two isotopic systems during erosion and sediment transport from continent to ocean. We report major and trace element concentrations together with Nd and Hf isotopic compositions of bedloads, suspended loads and river banks from the Ganges River and its tributaries draining the Himalayan Range i.e. the Karnali, the Narayani, the Kosi and the Marsyandi Rivers. The sample set includes sediments sampled within the Himalayan Range in Nepal, at the Himalayan mountain front, and also downstream on the floodplain and at the outflow of the Ganges in Bangladesh. Results show that hydrodynamic sorting of minerals explains the entire Hf isotopic range, i.e. more than 10 εHf units, observed in the river sediments but does not affect the Nd isotopic composition. Bedloads and bank sediments have systematically lower εHf values than suspended loads sampled at the same location. Coarse-grained sediments lie below or on the Terrestrial Array in an εHf vs. εNd diagram. In contrast, fine-grained sediments, including most of the suspended loads, deviate from the Terrestrial Array toward higher εHf relative to their εNd, as is the case for oceanic terrigenous clays. The observed Nd-Hf decoupling is explained by mineralogical sorting processes that enrich bottom sediments in coarse and dense minerals, including unradiogenic zircons, while surface sediments are enriched in fine material with radiogenic Hf signatures. The data also show that Nd-Hf isotopic decoupling increases with sediment transport in the floodplain to reach its maximum at the river mouth. This implies that the Nd-Hf isotopic decoupling observed in worldwide oceanic clays and river sediments is likely to have the same origin. Finally, we estimated the Nd-Hf isotopic composition of the present-day mantle if oceanic sediments had never been subducted and conclude that the addition of oceanic sediments with their anomalous Nd-Hf isotopic compositions has slowly shifted the composition of the Earth's mantle towards more radiogenic Hf values through time.

On the Origin of GEMS

NASA Technical Reports Server (NTRS)

Keller, L. P.; Messenger, S.

2004-01-01

GEMS (glass with embedded metal and sulfides) are a major component of anhydrous interplanetary dust particles (IDPs) their physical and chemical characteristics show marked similarities to contemporary interstellar dust. Recent oxygen isotopic measurements confirm that at least a small fraction (less than 5%) of GEMS are demonstrably presolar, while the remainder have ratios that are indistinguishable from solar values. GEMS with solar oxygen isotopic compositions either (1) had their isotopic compositions homogenized through processing in the interstellar medium (ISM), or (2) formed in the early solar system. Isotopic homogenization necessarily implies chemical homogenization, so (interstellar) GEMS compositions should reflect the average composition of dust in the local ISM. We performed a systematic examination of the bulk chemistry of GEMS in primitive IDPs in order to test this hypothesis.

Cu isotopic signature in blood serum of liver transplant patients: a follow-up study

NASA Astrophysics Data System (ADS)

Lauwens, Sara; Costas-Rodríguez, Marta; van Vlierberghe, Hans; Vanhaecke, Frank

2016-07-01

End-stage liver disease (ESLD) is life-threatening and liver transplantation (LTx) is the definitive treatment with good outcomes. Given the essential role of hepatocytes in Cu homeostasis, the potential of the serum Cu isotopic composition for monitoring a patient’s condition post-LTx was evaluated. For this purpose, high-precision Cu isotopic analysis of blood serum of ESLD patients pre- and post-LTx was accomplished via multi-collector ICP-mass spectrometry (MC-ICP-MS). The Cu isotopic composition of the ESLD patients was fractionated in favour of the lighter isotope (by about -0.50‰). Post-LTx, a generalized normalization of the Cu isotopic composition was observed for the patients with normal liver function, while it remained light when this condition was not reached. A strong decrease in the δ65Cu value a longer term post-LTx seems to indicate the recurrence of liver failure or cancer. The observed trend in favour of the heavier Cu isotopic composition post-LTx seems to be related with the restored biosynthetic capacity of the liver, the restored hepatic metabolism and/or the restored biliary secretion pathways. Thus, Cu isotopic analysis could be a valuable tool for the follow-up of liver transplant patients and for establishing the potential recurrence of liver failure.

Cu isotopic signature in blood serum of liver transplant patients: a follow-up study

PubMed Central

Lauwens, Sara; Costas-Rodríguez, Marta; Van Vlierberghe, Hans; Vanhaecke, Frank

2016-01-01

End-stage liver disease (ESLD) is life-threatening and liver transplantation (LTx) is the definitive treatment with good outcomes. Given the essential role of hepatocytes in Cu homeostasis, the potential of the serum Cu isotopic composition for monitoring a patient’s condition post-LTx was evaluated. For this purpose, high-precision Cu isotopic analysis of blood serum of ESLD patients pre- and post-LTx was accomplished via multi-collector ICP-mass spectrometry (MC-ICP-MS). The Cu isotopic composition of the ESLD patients was fractionated in favour of the lighter isotope (by about −0.50‰). Post-LTx, a generalized normalization of the Cu isotopic composition was observed for the patients with normal liver function, while it remained light when this condition was not reached. A strong decrease in the δ65Cu value a longer term post-LTx seems to indicate the recurrence of liver failure or cancer. The observed trend in favour of the heavier Cu isotopic composition post-LTx seems to be related with the restored biosynthetic capacity of the liver, the restored hepatic metabolism and/or the restored biliary secretion pathways. Thus, Cu isotopic analysis could be a valuable tool for the follow-up of liver transplant patients and for establishing the potential recurrence of liver failure. PMID:27468898

Cu isotopic signature in blood serum of liver transplant patients: a follow-up study.

PubMed

Lauwens, Sara; Costas-Rodríguez, Marta; Van Vlierberghe, Hans; Vanhaecke, Frank

2016-07-29

End-stage liver disease (ESLD) is life-threatening and liver transplantation (LTx) is the definitive treatment with good outcomes. Given the essential role of hepatocytes in Cu homeostasis, the potential of the serum Cu isotopic composition for monitoring a patient's condition post-LTx was evaluated. For this purpose, high-precision Cu isotopic analysis of blood serum of ESLD patients pre- and post-LTx was accomplished via multi-collector ICP-mass spectrometry (MC-ICP-MS). The Cu isotopic composition of the ESLD patients was fractionated in favour of the lighter isotope (by about -0.50‰). Post-LTx, a generalized normalization of the Cu isotopic composition was observed for the patients with normal liver function, while it remained light when this condition was not reached. A strong decrease in the δ(65)Cu value a longer term post-LTx seems to indicate the recurrence of liver failure or cancer. The observed trend in favour of the heavier Cu isotopic composition post-LTx seems to be related with the restored biosynthetic capacity of the liver, the restored hepatic metabolism and/or the restored biliary secretion pathways. Thus, Cu isotopic analysis could be a valuable tool for the follow-up of liver transplant patients and for establishing the potential recurrence of liver failure.

Zinc isotope anomalies in Allende meteorite inclusions

NASA Technical Reports Server (NTRS)

Loss, R. D.; Lugmair, G. W.

1990-01-01

The isotopic compositions of Zn, Cr, Ti, and Ca have been measured in a number of CAIs from the Allende meteorite. The aim was to test astrophysical models which predict large excesses of Zn-66 to accompany excesses in the neutron-rich isotopes of Ca, Ti, Cr, and Ni. Some of the CAIs show clearly resolved but small excesses for Zn-66 which are at least an order of magnitude smaller than predicted. This result may simply reflect the volatility and chemical behavior of Zn as compared to the other (more refractory) anomalous elements found in these samples. Alternatively, revision of parameters and assumptions used for the model calculations may be required.

Clumped Isotope Composition of Cold-Water Corals: A Role for Vital Effects?

NASA Astrophysics Data System (ADS)

Spooner, P.; Guo, W.; Robinson, L. F.

2014-12-01

Measurements on a set of cold-water corals (mainly Desmophyllum dianthus) have suggested that their clumped isotope composition could serve as a promising proxy for reconstructing paleocean temperatures. Such measurements have also offered support for certain isotope models of coral calcification. However, there are differences in the clumped isotope compositions between warm-water and cold-water corals, suggesting that different kinds of corals could have differences in their biocalcification processes. In order to understand the systematics of clumped isotope variations in cold-water corals more fully, we present clumped isotope data from a range of cold-water coral species from the tropical Atlantic and the Southern Ocean.Our samples were either collected live or recently dead (14C ages < 1,000 yrs) with associated temperature data. They include a total of 11 solitary corals and 1 colonial coral from the Atlantic, and 8 solitary corals from the Southern Ocean. The data indicate that coral clumped isotope systematics may be more complicated than previously thought. For example, for the genus Caryophyllia we observe significant variations in clumped isotope compositions for corals which grew at the same temperature with an apparent negative correlation between Δ47 and δ18O, different to patterns previously observed in Desmophyllum. These results indicate that existing isotope models of biocalcification may not apply equally well to all corals. Clumped isotope vital effects may be present in certain cold-water corals as they are in warm-water corals, complicating the use of this paleoclimate proxy.

Factors Controlling the Stable Nitrogen Isotopic Composition (δ15N) of Lipids in Marine Animals

PubMed Central

Svensson, Elisabeth; Schouten, Stefan; Hopmans, Ellen C.; Middelburg, Jack J.; Sinninghe Damsté, Jaap S.

2016-01-01

Lipid extraction of biomass prior to stable isotope analysis is known to cause variable changes in the stable nitrogen isotopic composition (δ15N) of residual biomass. However, the underlying factors causing these changes are not yet clear. Here we address this issue by comparing the δ15N of bulk and residual biomass of several marine animal tissues (fish, crab, cockle, oyster, and polychaete), as well as the δ15N of the extracted lipids. As observed previously, lipid extraction led to a variable offset in δ15N of biomass (differences ranging from -2.3 to +1.8 ‰). Importantly, the total lipid extract (TLE) was highly depleted in 15N compared to bulk biomass, and also highly variable (differences ranging from -14 to +0.7 ‰). The TLE consisted mainly of phosphatidylcholines, a group of lipids with one nitrogen atom in the headgroup. To elucidate the cause for the 15N-depletion in the TLE, the δ15N of amino acids was determined, including serine because it is one of the main sources of nitrogen to N-containing lipids. Serine δ15N values differed by -7 to +2 ‰ from bulk biomass δ15N, and correlated well with the 15N depletion in TLEs. On average, serine was less depleted (-3‰) than the TLE (-7 ‰), possibly due to fractionation during biosynthesis of N-containing headgroups, or that other nitrogen-containing compounds, such as urea and choline, or recycled nitrogen contribute to the nitrogen isotopic composition of the TLE. The depletion in 15N of the TLE relative to biomass increased with the trophic level of the organisms. PMID:26731720

Cenozoic marine geochemistry of thallium deduced from isotopic studies of ferromanganese crusts and pelagic sediments

USGS Publications Warehouse

Rehkamper, M.; Frank, M.; Hein, J.R.; Halliday, A.

2004-01-01

Cenozoic records of Tl isotope compositions recorded by ferromanganese (Fe-Mn) crusts have been obtained. Such records are of interest because recent growth surfaces of Fe-Mn crusts display a nearly constant Tl isotope fractionation relative to seawater. The time-series data are complemented by results for bulk samples and leachates of various marine sediments. Oxic pelagic sediments and anoxic marine deposits can be distinguished by their Tl isotope compositions. Both pelagic clays and biogenic oozes are typically characterized by ??205Tl greater than +2.5, whereas anoxic sediments have ??205Tl of less than -1.5 (??205Tl is the deviation of the 205Tl/203Tl isotope ratio of a sample from NIST SRM 997 Tl in parts per 104). Leaching experiments indicate that the high ??205Tl values of oxic sediments probably reflect authigenic Fe-Mn oxyhydroxides. Time-resolved Tl isotope compositions were obtained from six Fe-Mn crusts from the Atlantic, Indian, and Pacific oceans and a number of observations indicate that these records were not biased by diagenetic alteration. Over the last 25 Myr, the data do not show isotopic variations that significantly exceed the range of Tl isotope compositions observed for surface layers of Fe-Mn crusts distributed globally (??205 Tl=+12.8??1.2). This indicates that variations in deep-ocean temperature were not recorded by Tl isotopes. The results most likely reflect a constant Tl isotope composition for seawater. The growth layers of three Fe-Mn crusts that are older than 25 Ma show a systematic increase of ??205Tl with decreasing age, from about +6 at 60-50 Ma to about +12 at 25 Ma. These trends are thought to be due to variations in the Tl isotope composition of seawater, which requires that the oceans of the early Cenozoic either had smaller output fluxes or received larger input fluxes of Tl with low ??205Tl. Larger inputs of isotopically light Tl may have been supplied by benthic fluxes from reducing sediments, rivers, and/or volcanic emanations. Alternatively, the Tl isotope trends may reflect the increasing importance of Tl fluxes to altered ocean crust through time. ?? 2004 Elsevier B.V. All rights reserved.

Assessment of shock effects on amphibole water contents and hydrogen isotope compositions: 1. Amphibolite experiments

NASA Astrophysics Data System (ADS)

Minitti, Michelle E.; Rutherford, Malcolm J.; Taylor, Bruce E.; Dyar, M. Darby; Schultz, Peter H.

2008-02-01

Kaersutitic amphiboles found within a subset of the Martian meteorites have low water contents and variably heavy hydrogen isotope compositions. In order to assess if impact shock-induced devolatilization and hydrogen isotope fractionation were determining factors in these water and isotopic characteristics of the Martian kaersutites, we conducted impact shock experiments on samples of Gore Mountain amphibolite in the Ames Vertical Gun Range (AVGR). A parallel shock experiment conducted on an anorthosite sample indicated that contamination of shocked samples by the AVGR hydrogen propellant was unlikely. Petrographic study of the experimental amphibolite shock products indicates that only ˜ 10% of the shock products experienced levels of damage equivalent to those found in the most highly shocked kaersutite-bearing Martian meteorites (30-35 GPa). Ion microprobe studies of highly shocked hornblende from the amphibolite exhibited elevated water contents (ΔH 2O ˜ 0.1 wt.%) and enriched hydrogen isotope compositions (Δ D ˜ + 10‰) relative to unshocked hornblende. Water and hydrogen isotope analyses of tens of milligrams of unshocked, moderately shocked, and highly shocked hornblende samples by vacuum extraction/uranium reduction and isotope ratio mass spectrometry (IRMS), respectively, are largely consistent with analyses of single grains from the ion microprobe. The mechanisms thought to have produced the excess water in most of the shocked hornblendes are shock-induced reduction of hornblende Fe and/or irreversible adsorption of hydrogen. Addition of the isotopically enriched Martian atmosphere to the Martian meteorite kaersutites via these mechanisms could explain their enriched and variable isotopic compositions. Alternatively, regrouping the water extraction and IRMS analyses on the basis of isotopic composition reveals a small, but consistent, degree of impact-induced devolatilization (˜ 0.1 wt.% H 2O) and H isotope enrichment (Δ D ˜ + 10‰). Extrapolating the shock signature of the regrouped data to grains that experienced Martian meteorite-like shock pressures suggests that shock-induced water losses and hydrogen isotope enrichments could approach 1 wt.% H 2O and Δ D = + 100‰, respectively. If these values are valid, then impact shock effects could explain a substantial fraction of the low water contents and variable hydrogen isotope compositions of the Martian meteorite kaersutites.

FE and MG Isotopic Analyses of Isotopically Unusual Presolar Silicate Grains

NASA Technical Reports Server (NTRS)

Nguyen, A. N.; Messenger, S.; Ito, M.; Rahman, Z.

2011-01-01

Interstellar and circumstellar silicate grains are thought to be Mg-rich and Fe-poor, based on astronomical observations and equilibrium condensation models of silicate dust formation in stellar outflows. On the other hand, presolar silicates isolated from meteorites have surprisingly high Fe contents and few Mg-rich grains are observed. The high Fe contents in meteoritic presolar silicates may indicate they formed by a non-equilibrium condensation process. Alternatively, the Fe in the stardust grains could have been acquired during parent body alteration. The origin of Fe in presolar silicates may be deduced from its isotopic composition. Thus far, Fe isotopic measurements of presolar silicates are limited to the Fe-54/Fe-56 ratios of 14 grains. Only two slight anomalies (albeit solar within error) were observed. However, these measurements suffered from contamination of Fe from the adjacent meteorite matrix, which diluted any isotopic anomalies. We have isolated four presolar silicates having unusual O isotopic compositions by focused ion beam (FIB) milling and obtained their undiluted Mg and Fe isotopic compositions. These compositions help to identify the grains stellar sources and to determine the source of Fe in the grains.

Isotopic composition of transpiration and rates of change in leaf water isotopologue storage in response to environmental variables.

PubMed

Simonin, Kevin A; Roddy, Adam B; Link, Percy; Apodaca, Randy; Tu, Kevin P; Hu, Jia; Dawson, Todd E; Barbour, Margaret M

2013-12-01

During daylight hours, the isotope composition of leaf water generally approximates steady-state leaf water isotope enrichment model predictions. However, until very recently there was little direct confirmation that isotopic steady-state (ISS) transpiration in fact exists. Using isotope ratio infrared spectroscopy (IRIS) and leaf gas exchange systems we evaluated the isotope composition of transpiration and the rate of change in leaf water isotopologue storage (isostorage) when leaves were exposed to variable environments. In doing so, we developed a method for controlling the absolute humidity entering the gas exchange cuvette for a wide range of concentrations without changing the isotope composition of water vapour. The measurement system allowed estimation of (18)O enrichment both at the evaporation site and for bulk leaf water, in the steady state and the non-steady state. We show that non-steady-state effects dominate the transpiration isoflux even when leaves are at physiological steady state. Our results suggest that a variable environment likely prevents ISS transpiration from being achieved and that this effect may be exacerbated by lengthy leaf water turnover times due to high leaf water contents. © 2013 John Wiley & Sons Ltd.

New Hafnium Isotope and Trace Element Constraints on the Role of a Plume in Genesis of the Eastern Snake River Plain Basalts, Idaho

NASA Astrophysics Data System (ADS)

Taylor, R. D.; Reid, M. R.; Blichert-Toft, J.

2009-12-01

Bimodal volcanism associated with the eastern Snake River Plain (ESRP)-Yellowstone Plateau province has persisted since approximately 16 Ma. A time-transgressive track of rhyolitic eruptions which young progressively to the east and parallel the motion of the North American plate are overlain by younger basalts with no age progression. Interpretations for the origin of these basalts range from a thermo-chemical mantle plume to incipient melting of the shallow upper mantle, and remain controversial. The enigmatic ESRP basalts are characterized by high 3He/4He, diagnostic of a plume source, but also by lithophile radiogenic isotope signatures that are more enriched than expected for plume-derived OIBs. These features could possibly be caused by isotopic decoupling associated with shallow melting of a hybridized upper mantle, or derivation from an atypical mantle plume, or both by way of mixing. New Hf isotope and trace element data further constrain potential sources for the ESRP basalts. Their Hf isotopic signatures (ɛHf = +0.1 to -5.8) are moderately enriched and consistently fall above or in the upper part of the field of OIBs, with similar Nd isotope signatures (ɛNd = -2.0 to -5.8), indicating a source with high time-integrated Lu/Hf compared with Sm/Nd. The isotopic compositions of the basalts lie between those of Archean SCML and a more depleted end-member source, suggestive of contributions from at least two sources. The grouping of isotopic characteristics is compact compared to other regional volcanism, implying that the hybridization process is highly reproducible within the ESRP. Minor localized differences in isotopic composition may signify local variations in the relative proportions of the end-members. Trace element patterns also support genesis of the ESRP basalts from an enriched source. Our data detect evidence of deeper contributions derived from the garnet-stability field, and a greater affinity of the trace element signatures to plume sources than to sources in the mantle lithosphere. The Hf isotope and trace element characteristics of the ESRP basalts thus support a model of derivation from a deep mantle plume with additional melt contributions and isotopic overprinting from SCML.

Petrological, geochemical and isotopic characteristics of lignite and calcified lignite from mining area Pesje, Velenje Basin, Slovenia

NASA Astrophysics Data System (ADS)

Vrabec, Mirijam; Markič, Miloš; Vrabec, Marko; Jaćimović, Radojko; Kanduč, Tjaša

2014-05-01

Lignite (organic rich) and calcified lignite (inorganic rich) samples from excavation field -50c mining area Pesje, Velenje Basin, Slovenia were investigated. During geological and structural mapping lignite and calcified lignite samples were systematically taken for determination of their petrological, geochemical and isotopic characteristics. Lignite is composed of fine detritical gelified matrix. At least five different types of calcified lignite were recognized forming laminations, calcifications after wood, petrified wood and complete replacements of lignite with carbonate. All measured parameters so far indicate geochemical processes during sedimentation of the Velenej Basin. After macroscopic description samples were split to organic and inorganic component (Ward, 1984) and powdered in an agate mortar for geochemical and isotopic analyses. Major and trace elements (As, B, Ba, Cd, Co, Cr, Cu, Hg, Mn, Mo, Sb, Se, Th, U, Zn) in these samples were determined by instrumental neutron activation analysis (INAA) using k-0 standardization method (Jaćimović et al, 2002). The isotopic composition of carbon and nitrogen was determined using a Europa 20-20 continuous flow IRMS ANCA-SL preparation module. A 1 mg amount of a sample was weighed in a tin capsule for carbon and 10 mg for nitrogen analysis. Samples for carbon analyses were pretreated with 1 M HCl to remove carbonates. Carbonate samples from carbonate-rich strata and calcified xylite were first roasted at 450 deg C (Krantz et al., 1987). Three miligrams of carbonate sample was transformed into CO2 by reaction with anhydrous H3PO4 at 55 deg C under vacuum (McCrea, 1950) and measured with GV 2003 isotope ratio mass spectrometer. Measured isotopic composition of oxygen as VPDB values was recalculated to the VSMOW reference standard to enable the comparison with data from other coal basins. SEM/EDXS of carbonate rich sediments was performed with JEOL JSM 5800 electron microanalyzer scanning electron microscope energy dispersive X-ray spectroscopy at the Department of Ceramics at the Jožef Stefan Institute. Geochemical characteristics of major and trace elements indicate that the values of major and trace elements are comparable to world average coal (Zhang et al., 2004). Isotopic composition of carbon and isotopic composition of nitrogen of investigated samples indicate values from to -29.4o to -23.7o and 1.8o to 5.9o respectively. Lower value of isotopic composition of carbon indicates higher gelification (values up to -29.4) and higher value of isotopic composition of nitrogen (values up to 5.9) indicate higher mineralization. The results of SEM/EDXS microscopy revealed that in calcified lignite chemical composition of calcite prevails. Traces of diagenetic pyrite were also found, indicating localized anoxic conditions during sedimentation. Values of isotopic composition of CCaCO3 range from -2 to +13 and indicate temperature of precipitation from 17.3 to 35 deg C, which is similar to results obtained in previous studies (Kanduč et al., 2012). References Krantz, D.E., Williams, D.F., Jones, D.S., 1987: Ecological and paleoenvironmental information using stable isotope profiles from living and fossil mollusks. Palaeogeography, Palaeoclimatology, Palaeoecology 58, 249-266. Kanduč T., Markič M., Zavšek S., McIntosh J. 2012: carbon cycling in the Pliocene Velenje Coal Basin, Slovenia, inferred from stable carbon isotopes. International Journal of Coal Geology 89, 70-83. Jaćimović, R., Lazaru, A., Mihajlović, D., Ilić, R., Stafilov, T., 2002: Determination of major and trace elements in some minerals by k0-instrumental neutron activation analysis. Journal of Radioanalytical Nuclear Chemistry, 253, 427-434. McCrea, JM., 1950. On the isotopic chemistry of carbonates and a paleotemperature scale. Journal of Chemical Physics 18, 849. Ward C.R. (Ed.), 1984: Coal Geology and Coal Technology. Black-well, Oxford, 345 pp. Zhang J.Y., Zheng C.G., Ren D.Y., Chou C.L., Zheng R.S., Wang Z.P., Zhao F. H., Ge Y.T. 2004: Distribution of potentially hazardous trace elements in coals from Shoxi provinces, China. Fuel 83: 129-135.

Modes of planetary-scale Fe isotope fractionation

NASA Astrophysics Data System (ADS)

Schoenberg, Ronny; von Blanckenburg, Friedhelm

2006-12-01

A comprehensive set of high-precision Fe isotope data for the principle meteorite types and silicate reservoirs of the Earth is used to investigate iron isotope fractionation at inter- and intra-planetary scales. 14 chondrite analyses yield a homogeneous Fe isotope composition with an average δ56Fe/ 54Fe value of - 0.015 ± 0.020‰ (2 SE) relative to the international iron standard IRMM-014. Eight non-cumulate and polymict eucrite meteorites that sample the silicate portion of the HED (howardite-eucrite-diogenite) parent body yield an average δ56Fe/ 54Fe value of - 0.001 ± 0.017‰, indistinguishable to the chondritic Fe isotope composition. Fe isotope ratios that are indistinguishable to the chondritic value have also been published for SNC meteorites. This inner-solar system homogeneity in Fe isotopes suggests that planetary accretion itself did not significantly fractionate iron. Nine mantle xenoliths yield a 2 σ envelope of - 0.13‰ to + 0.09‰ in δ56Fe/ 54Fe. Using this range as proxy for the bulk silicate Earth in a mass balance model places the Fe isotope composition of the outer liquid core that contains ca. 83% of Earth's total iron to within ± 0.020‰ of the chondritic δ56Fe/ 54Fe value. These calculations allow to interprete magmatic iron meteorites ( δ56Fe/ 54Fe = + 0.047 ± 0.016‰; N = 8) to be representative for the Earth's inner metallic core. Eight terrestrial basalt samples yield a homogeneous Fe isotope composition with an average δ56Fe/ 54Fe value of + 0.072 ± 0.016‰. The observation that terrestrial basalts appear to be slightly heavier than mantle xenoliths and that thus partial mantle melting preferentially transfers heavy iron into the melt [S. Weyer, A.D. Anbar, G.P. Brey, C. Munker, K. Mezger and A.B. Woodland, Iron isotope fractionation during planetary differentiation, Earth and Planetary Science Letters 240(2), 251-264, 2005.] is intriguing, but also raises some important questions: first it is questionable whether the Fe isotope composition of lithospheric mantle xenoliths are representative for an undisturbed melt source, and second, HED and SNC meteorites, representing melting products of 4Vesta and Mars silicate mantles would be expected to show a similar fractionation towards heavy isotope compositions. This is not observed. Four international granitoid standards with SiO 2 contents between 60 and 70 wt.% yield δ56Fe/ 54Fe values between 0.118‰ and 0.132‰. An investigation of the alpine Bergell igneous rock suite revealed a positive correlation between Fe isotope compositions and SiO 2 contents — from gabbros and tonalites ( δ56Fe/ 54Fe ≈ 0.03 to 0.09‰) to granodiorites and silicic dykes ( δ56Fe/ 54Fe ≈ 0.14 to 0.23‰). Although in this suite δ56Fe/ 54Fe correlates with δ18O values and radiogenic isotopes, open-system behavior to explain the heavy iron is not undisputed. This is because an obvious assimilant with the required heavy Fe isotope composition has so far not been identified. Alternatively, the relatively heavy granite compositions might be obtained by fractional crystallisation of the melt. Ultimately, further detailed studies on natural rocks and the experimental determination of mineral/melt fractionation factors at magmatic conditions are required to unravel whether or not iron isotope fractionation takes place during partial mantle melting and crystal fractionation.

Crystal growth and disequilibrium distribution of oxygen isotopes in an igneous Ca-Al-rich inclusion from the Allende carbonaceous chondrite

NASA Astrophysics Data System (ADS)

Kawasaki, Noriyuki; Simon, Steven B.; Grossman, Lawrence; Sakamoto, Naoya; Yurimoto, Hisayoshi

2018-01-01

TS34 is a Type B1 Ca-Al-rich inclusion (CAI) from the Allende CV3 chondrite, consisting of spinel, melilite, Ti-Al-rich clinopyroxene (fassaite) and minor anorthite in an igneous texture. Oxygen and magnesium isotopic compositions were measured by secondary ion mass spectrometry in spots of known chemical composition in all major minerals in TS34. Using the sequence of formation from dynamic crystallization experiments and from chemical compositions of melilite and fassaite, the oxygen isotopic evolution of the CAI melt was established. Oxygen isotopic compositions of the constituent minerals plot along the carbonaceous chondrite anhydrous mineral line. The spinel grains are uniformly 16O-rich (Δ17O = -22.7 ± 1.7‰, 2SD), while the melilite grains are uniformly 16O-poor (Δ17O = -2.8 ± 1.8‰) irrespective of their åkermanite content and thus their relative time of crystallization. The fassaite crystals exhibit growth zoning overprinting poorly-developed sector zoning; they generally grow from Ti-rich to Ti-poor compositions. The fassaite crystals also show continuous variations in Δ17O along the inferred directions of crystal growth, from 16O-poor (Δ17O ∼ -3‰) to 16O-rich (Δ17O ∼ -23‰), covering the full range of oxygen isotopic compositions observed in TS34. The early-crystallized 16O-poor fassaite and the melilite are in oxygen isotope equilibrium and formed simultaneously. The correlation of oxygen isotopic compositions with Ti content in the fassaite imply that the oxygen isotopic composition of the CAI melt evolved from 16O-poor to 16O-rich during fassaite crystallization, presumably due to oxygen isotope exchange with a surrounding 16O-rich nebular gas. Formation of spinel, the liquidus phase in melts of this composition, predates crystallization of all other phases, so its 16O-rich composition is a relic of an earlier stage. Anorthite exhibits oxygen isotopic compositions between Δ17O ∼ -2‰ and -9‰, within the range of those of fassaite, indicating co-crystallization of these two minerals during the earliest to intermediate stage of fassaite growth. The melilite and fassaite yield an 26Al-26Mg mineral isochron with an initial value of (26Al/27Al)0 = (5.003 ± 0.075) × 10-5, corresponding to a relative age of 0.05 ± 0.02 Myr from the canonical Al-Mg age of CAIs. These data demonstrate that both 16O-rich and 16O-poor reservoirs existed in the solar nebula at least ∼0.05 Myr after the birth of the Solar System.

Oxygen isotope corrections for online δ34S analysis

USGS Publications Warehouse

Fry, B.; Silva, S.R.; Kendall, C.; Anderson, R.K.

2002-01-01

Elemental analyzers have been successfully coupled to stable-isotope-ratio mass spectrometers for online measurements of the δ34S isotopic composition of plants, animals and soils. We found that the online technology for automated δ34S isotopic determinations did not yield reproducible oxygen isotopic compositions in the SO2 produced, and as a result calculated δ34S values were often 1–3‰ too high versus their correct values, particularly for plant and animal samples with high C/S ratio. Here we provide empirical and analytical methods for correcting the S isotope values for oxygen isotope variations, and further detail a new SO2-SiO2 buffering method that minimizes detrimental oxygen isotope variations in SO2.

Ion microprobe analysis of {sup 18}O/{sup 16}O in authigenic and detrital quartz in the St. Peter Sandstone, Michigan Basin and Wisconsin Arch, USA: Contrasting diagenetic histories

DOE Office of Scientific and Technical Information (OSTI.GOV)

Graham, C.M.; Valley, J.W.; Winter, B.L.

1996-12-01

The oxygen isotopic compositions of authigenic quartz cements in sandstones provide a monitor of the temperatures, compositions, and origins of pore-occluding fluids during diagenesis, but quartz overgrowths are too fine-grained to be amenable to conventional isotopic analysis. We have used a Cameca ims-4f ion microprobe to determine oxygen isotopic variations in authigenic and detrital quartz in four samples of the Ordovician St. Peter Sandstone from the Michigan Basin and Wisconsin Arch, midwestern USA. Ion microprobe isotopic analyses have been successfully accomplished with an internal precision of {+-}1{per_thousand} (1{sigma}) and a spatial resolution of 20-30 {mu}m at low mass resolution usingmore » a high voltage offset technique. Repeated analyses of the quartz standard demonstrate a reproducibility of close to {+-}1{per_thousand} (1 sd) in good agreement with that expected from counting statistics. Conventional and ion microprobe analyses are mutually consistent, supporting the accuracy of the ion microprobe analyses. Within-sample isotopic variations of up to 13{per_thousand} and micro-scale isotopic variations of at least 4{per_thousand} over a distance of 100 {mu}m have been measured within quartz overgrowths in a sandstone from the Wisconsin Arch. Overgrowths are uniformly higher in {delta}{sup 18}O than detrital grains, and gradients of up to 25% exist across a few microns. {sup 18}O-enriched quartz overgrowths in sandstones from the Wisconsin Arch show complex CL zonation and reflect one of two possible processes: (1) low-temperature quartz precipitation during mixing of meteoric waters with upwelling basinal fluids; (2) higher temperature quartz precipitation during episodic gravity-driven upwelling of warm basinal fluids (of comparable isotopic composition to Michigan Basin fluids) from the Illinois Basin, related to evolution of Mississippi Valley type Pb-Zn ore-forming fluids. 59 refs., 7 figs., 4 tabs.« less

Using the magmatic record to constrain the growth of continental crust-The Eoarchean zircon Hf record of Greenland

NASA Astrophysics Data System (ADS)

Fisher, Christopher M.; Vervoort, Jeffrey D.

2018-04-01

Southern West Greenland contains some of the best-studied and best-preserved magmatic Eoarchean rocks on Earth, and these provide an excellent vantage point from which to view long-standing questions regarding the growth of the earliest continental crust. In order to address the questions surrounding early crustal growth and complementary mantle depletion, we present Laser Ablation Split Stream (LASS) analyses of the U-Pb and Hf isotope compositions of zircon from eleven samples of the least-altered meta-igneous rocks from the Itsaq (Amîtsoq) Gneisses of the Isukasia and Nuuk regions of southern West Greenland. This analytical technique allows a less ambiguous approach to determining the age and Hf isotope composition of complicated zircon. Results corroborate previous findings that Eoarchean zircon from the Itsaq Gneiss (∼3.85 Ga to ∼3.63 Ga) were derived from a broadly chondritic source. In contrast to the Sm-Nd whole rock isotope record for southern West Greenland, the zircon Lu-Hf isotope record provides no evidence for early mantle depletion, nor does it suggest the presence of crust older than ∼3.85 Ga in Greenland. Utilizing LASS U-Pb and Hf data from the Greenland zircons studied here, we demonstrate the importance of focusing on the magmatic (rather than detrital) zircon record to more confidently understand early crustal growth and mantle depletion. We compare the Greenland Hf isotope data with other Eoarchean magmatic complexes such as the Acasta Gneiss Complex, Nuvvuagittuq greenstone belt, and the gneissic complexes of southern Africa, and all lack zircons with suprachondritic Hf isotope compositions. In total, these data suggest only a very modest volume of crust was produced during (or survived from) the Hadean and earliest Eoarchean. There remains no record of planet-scale early Earth mantle depletion in the Hf isotope record prior to 3.8 Ga.

Experimental Constraints on Reconstruction of Archean Seawater Ni Isotopic Composition from Banded Iron Formations

NASA Astrophysics Data System (ADS)

Wang, S.; Wasylenki, L.

2016-12-01

Ni isotope systematics in banded iron formations (BIFs) potentially recorded the Ni isotopic composition of ancient seawater during the Precambrian Eon[1]. The use of BIFs as seawater proxies requires knowing how Ni isotopes fractionated during initial incorporation into iron-rich sediments and during early diagenesis. We conducted experiments to investigate Ni isotope behavior during coprecipitation with ferrihydrite and transformation of ferrihydrite to hematite. Ferrihydrite synthesis at neutral pH demonstrated that dissolved Ni was variably heavier than coprecipitated Ni (Δ60/58Ni = +0.08 to +0.50 ‰), in contrast to the constant offset observed earlier during adsorption to pre-existing ferrihydrite[2]. Experiments at lower pH (<7) yielded negative values of Δ60/58Ni ( -0.18 ‰), suggesting enrichment in heavier isotopes of structurally incorporated Ni relative to dissolved and adsorbed Ni, possibly due to the presence of a small amount of highly fractionated tetrahedral Ni2+ in the ferrihydrite structure. We model our results as equilibrium fractionation among three pools of Ni with systematically varied proportions. We synthesized hematite by transforming Ni-bearing ferrihydrite in aqueous solution at 100 °C and observed significant Ni release from solids (up to 60 %) as pH dropped from 7 to 4.5 - 5.5 during phase transformation. Rinsing hematite with acetic acid released very little Ni (presumably surface-adsorbed) compared to the amounts remaining in solid residues (presumably incorporated). We infer that Δ60/58Ni values (-0.04 to +0.77 ‰) observed in hematite experiments likely reflect Rayleigh fractionation between incorporated and dissolved Ni. The final hematite was slightly lighter than the ferrihydrite had been (by 0.08 ‰), indicating that this phase transformation results in very limited change in Ni isotopic composition, given current analytical uncertainty of ± 0.09 ‰. [1] Wasylenki and Wang (2016) Goldschmidt; [2] Wasylenki et al. (2015) ChemGeol.

Cloud water in windward and leeward mountain forests: The stable isotope signature of orographic cloud water

USGS Publications Warehouse

Scholl, M.A.; Giambelluca, T.W.; Gingerich, S.B.; Nullet, M.A.; Loope, L.L.

2007-01-01

Cloud water can be a significant hydrologic input to mountain forests. Because it is a precipitation source that is vulnerable to climate change, it is important to quantify amounts of cloud water input at watershed and regional scales. During this study, cloud water and rain samples were collected monthly for 2 years at sites on windward and leeward East Maui. The difference in isotopic composition between volume‐weighted average cloud water and rain samples was 1.4‰ δ18O and 12‰ δ2H for the windward site and 2.8‰ δ18O and 25‰ δ2H for the leeward site, with the cloud water samples enriched in 18O and 2H relative to the rain samples. A summary of previous literature shows that fog and/or cloud water is enriched in 18O and 2H compared to rain at many locations around the world; this study documents cloud water and rain isotopic composition resulting from weather patterns common to montane environments in the trade wind latitudes. An end‐member isotopic composition for cloud water was identified for each site and was used in an isotopic mixing model to estimate the proportion of precipitation input from orographic clouds. Orographic cloud water input was 37% of the total precipitation at the windward site and 46% at the leeward site. This represents an estimate of water input to the forest that could be altered by changes in cloud base altitude resulting from global climate change or deforestation.

Fingerprints of lagoonal life: Migration of the marine flatfish Solea solea assessed by stable isotopes and otolith microchemistry

NASA Astrophysics Data System (ADS)

Dierking, Jan; Morat, Fabien; Letourneur, Yves; Harmelin-Vivien, Mireille

2012-06-01

The commercially important marine flatfish common sole (Solea solea) facultatively uses NW Mediterranean lagoons as nurseries. To assess the imprint left by the lagoonal passage, muscle carbon (C) and nitrogen (N) isotope values of S. solea juveniles caught in Mauguio lagoon in spring (shortly after arrival from the sea) and in autumn (before the return to the sea) were compared with values of juveniles from adjacent coastal marine nurseries. In addition, in the lagoon, sole otolith stable isotope (C and oxygen (O)) and elemental (11 elements) composition in spring and autumn, and the stable isotope composition (C and N) of organic matter sources in autumn, were determined. Overall, our data indicate that a distinct lagoonal signature existed. Specifically, lagoon soles showed a strong enrichment in muscle tissue 15N (>6‰) compared to their coastal relatives, likely linked to sewage inputs (see below), and a depletion in 13C (1-2‰), indicative of higher importance of 13C depleted terrestrial POM in the lagoon compared to coastal nurseries. In addition, over the time spent in the lagoon, sole otolith δ13C and δ18O values and otolith elemental composition changed significantly. Analysis of the lagoon sole foodweb based on C and N isotopes placed sediment particulate organic matter (POM) at the base. Seagrasses, formerly common but in decline in Mauguio lagoon, played a minor role in the detritus cycle. The very strong 15N enrichment of the entire foodweb (+7 to +11‰) compared to little impacted lagoons and coastal areas testified of important human sewage inputs. Regarding the S. solea migration, the analysis of higher turnover and fast growth muscle tissue and metabolically inert and slower growth otoliths indicated that soles arrived at least several weeks prior to capture in spring, and that no migrations took place in summer. In the autumn, the high muscle δ15N value acquired in Mauguio lagoon would be a good marker of recent return to the sea, whereas altered otolith δ18O values and elemental ratios hold promise as long-term markers. The combination of several complementary tracers from muscle and otoliths may present the chance to distinguish between fish from specific lagoons and coastal nurseries in the future.

Chromium isotope heterogeneity in the mantle

NASA Astrophysics Data System (ADS)

Xia, Jiuxing; Qin, Liping; Shen, Ji; Carlson, Richard W.; Ionov, Dmitri A.; Mock, Timothy D.

2017-04-01

To better constrain the Cr isotopic composition of the silicate Earth and to investigate potential Cr isotopic fractionation during high temperature geological processes, we analyzed the Cr isotopic composition of different types of mantle xenoliths from diverse geologic settings: fertile to refractory off-craton spinel and garnet peridotites, pyroxenite veins, metasomatised spinel lherzolites and associated basalts from central Mongolia, spinel lherzolites and harzburgites from North China, as well as cratonic spinel and garnet peridotites from Siberia and southern Africa. The δ53CrNIST 979 values of the peridotites range from - 0.51 ± 0.04 ‰ (2SD) to + 0.75 ± 0.05 ‰ (2SD). The results show a slight negative correlation between δ53Cr and Al2O3 and CaO contents for most mantle peridotites, which may imply Cr isotopic fractionation during partial melting of mantle peridotites. However, highly variable Cr isotopic compositions measured in Mongolian peridotites cannot be caused by partial melting alone. Instead, the wide range in Cr isotopic composition of these samples most likely reflects kinetic fractionation during melt percolation. Chemical diffusion during melt percolation resulted in light Cr isotopes preferably entering into the melt. Two spinel websterite veins from Mongolia have extremely light δ53Cr values of - 1.36 ± 0.04 ‰ and - 0.77 ± 0.06 ‰, respectively, which are the most negative Cr isotopic compositions yet reported for mantle-derived rocks. These two websterite veins may represent crystallization products from the isotopically light melt that may also metasomatize some peridotites in the area. The δ53Cr values of highly altered garnet peridotites from southern Africa vary from - 0.35 ± 0.04 ‰ (2SD) to + 0.12 ± 0.04 ‰ (2SD) and increase with increasing LOI (Loss on Ignition), reflecting a shift of δ53Cr to more positive values by secondary alteration. The Cr isotopic composition of the pristine, fertile upper mantle is estimated as δ53Cr = - 0.14 ± 0.12 ‰, after corrections for the effects of partial melting and metasomatism. This value is in line with that estimated for the BSE (- 0.12 ± 0.10 ‰) previously.

Reassessment of the NH4 NO3 thermal decomposition technique for calibration of the N2 O isotopic composition.

PubMed

Mohn, Joachim; Gutjahr, Wilhelm; Toyoda, Sakae; Harris, Eliza; Ibraim, Erkan; Geilmann, Heike; Schleppi, Patrick; Kuhn, Thomas; Lehmann, Moritz F; Decock, Charlotte; Werner, Roland A; Yoshida, Naohiro; Brand, Willi A

2016-09-08

In the last few years, the study of N 2 O site-specific nitrogen isotope composition has been established as a powerful technique to disentangle N 2 O emission pathways. This trend has been accelerated by significant analytical progress in the field of isotope-ratio mass-spectrometry (IRMS) and more recently quantum cascade laser absorption spectroscopy (QCLAS). Methods The ammonium nitrate (NH 4 NO 3 ) decomposition technique provides a strategy to scale the 15 N site-specific (SP ≡ δ 15 N α - δ 15 N β ) and bulk (δ 15 N bulk  = (δ 15 N α  + δ 15 N β )/2) isotopic composition of N 2 O against the international standard for the 15 N/ 14 N isotope ratio (AIR-N 2 ). Within the current project 15 N fractionation effects during thermal decomposition of NH 4 NO 3 on the N 2 O site preference were studied using static and dynamic decomposition techniques. The validity of the NH 4 NO 3 decomposition technique to link NH 4 + and NO 3 - moiety-specific δ 15 N analysis by IRMS to the site-specific nitrogen isotopic composition of N 2 O was confirmed. However, the accuracy of this approach for the calibration of δ 15 N α and δ 15 N β values was found to be limited by non-quantitative NH 4 NO 3 decomposition in combination with substantially different isotope enrichment factors for the conversion of the NO 3 - or NH 4 + nitrogen atom into the α or β position of the N 2 O molecule. The study reveals that the completeness and reproducibility of the NH 4 NO 3 decomposition reaction currently confine the anchoring of N 2 O site-specific isotopic composition to the international isotope ratio scale AIR-N 2 . The authors suggest establishing a set of N 2 O isotope reference materials with appropriate site-specific isotopic composition, as community standards, to improve inter-laboratory compatibility. This article is protected by copyright. All rights reserved.

Seasonality of bottom water temperature in the northern North Sea reconstructed from the oxygen isotope composition of the bivalve Arctica islandica

NASA Astrophysics Data System (ADS)

Trofimova, Tamara; Andersson, Carin; Bonitz, Fabian

2017-04-01

The seasonality of temperature changes is an important characteristic of climate. However, observational data for the ocean are only available for the last 150 year from a limited number of locations. Prior to 18th century information is only available from proxy reconstructions. The vast majority of such reconstructions depend on land-based archives, primarily from dendrochronology. Established marine proxy records for the ocean, especially at high latitudes, are both sparsely distributed and poorly resolved in time. Therefore, the identification and development of proxies for studying key ocean processes at sub-annual resolution that can extend the marine instrumental record is a clear priority in marine climate science. In this study, we have developed a record of early Holocene seasonal variability of bottom water temperature from the Viking Bank in the northern most North Sea. This area is of a particular interest since the hydrography is controlled by the inflow of Atlantic water. The reconstruction is based on the oxygen isotope composition of the growth increments in two sub-fossil shells of Arctica islandica (Bivalvia), dated to 9600-9335 cal. yr BP. By combining radiocarbon dating and sclerochronological techniques a floating chronology spanning over 200 years was constructed. Using the chronology as an age model, oxygen isotope measurements from 2 shells were combined into a 22-years long record. The results from this oxygen isotope record are compared with stable oxygen isotope profiles from modern shells to estimate changes in the mean state and seasonality between present and early Holocene. Shell-derived oxygen isotope values together with ice-volume corrected oxygen isotope values for the seawater were used to calculate bottom-water temperatures on a sub-annual time-scale. Preliminary results of the reconstructed early Holocene bottom water temperature indicate higher seasonality and lower minimum temperature compared to the present.

A preliminary study on isotopic evolution of ice by a melting experiment

NASA Astrophysics Data System (ADS)

Ham, J. Y.; Lee, J.; Lee, W. S.; Han, Y.; Hur, S. D.

2016-12-01

Evidences of melted snow at surface were found on some ice cores. Melted layers may generate a significant error when paleo-temperature was retrieved from ice cores using stable water isotopes. To resolve this problem, it is necessary to understand the isotopic changes of ice and its meltwater that is made during the ice and snow melting. Isotopic fractionations between liquid water and snow have been discussed by Taylor et al. (2002) and Lee et al. (2009). The goal of this work is to understand isotopic evolution of ice and its meltwater. Melting experiments in a cold room were designed and conducted with heat source (infrared lamp) to mimic solar radiation. Melting rates were calculated in terms of specific discharge (g/min). To control melting rates, distances between ice surface and heat source were adjusted in various conditions (1 cm, 10 cm and 20 cm). The experiments were conducted by three different melting rates, 1.6 g/min, 3.5 g/min and 5.8 g/min. We used cubic ice that has 3 cm in width, length and height in dimension with 1.5 kg or 2 kg of ice used totally. The total time spent melting the whole ice was 592, 783, and 1180 minutes, respectively. Cold room temperature was range of -1 to 1°C, which removes an effect of air temperature. Meltwater samples were collected and isotopic compositions of oxygen and hydrogen were determined by a cavity ring down spectrometer (Picarro L-1120) installed at the Korea Polar Research Institute. We also analyzed bulk water and bulk ice to make the ice used in the experiments (-8.20 ‰ and -58.73 ‰ for oxygen and hydrogen isotopes, respectively). The isotopic compositions of meltwater increased linearly or to a second degree polynomial. The isotopic variations were larger in the lower melting rates, compared to the higher melting rates (0.65 of lower melting rates vs. 0.35 higher melting rates for oxygen isotope). The slope of linear regression between oxygen and hydrogen ranged 6.2, 7.3 and 6.2, which is less than that of the Global Meteoric Water Line (8) and the sublimation (7.7) suggested by Earman et al. (2006). We believe that isotopic exchange between liquid water and ice plays a crucial role in the variations of isotopes for the ice and its meltwater. We will modify a physically based 1-D model used in the previous studies to better understand the isotopic compositions of ice and its meltwater.

Tracing mantle processes with Fe isotopes

NASA Astrophysics Data System (ADS)

Weyer, S.; Ionov, D.

2006-12-01

High precision Fe isotope measurements have been performed on various mantle peridotites (fertile lherzolites, harzburgites, metasomatised Fe-enriched rocks) and volcanic rocks (mainly oceanic basalts) from different localities and tectonic settings. Pimitive peridotites (Mg# = 0.894) yield delta56Fe = 0.02 and are significantly lighter than the basalts (average delta56Fe = 0.11). Furthermore, the peridotites display a negative correlation of iron isotopes with Mg#. Taken together, these findings imply that Fe isotopes fractionate during partial melting, with heavy isotopes preferentially entering the melt [1, 2]. A particularly good correlation of the Fe isotope composition and Mg# shown by poorly metasomatised spinel lherzolites of three localities (Horoman, Kamchatka and Lherz) was used to model Fe isotope fractionation during partial melting, resulting in alphamantle-melt = 1.0003. This value implies higher Fe isotope fractionation between residual mantle and mantle-derived melts (i.e. Delta56Femantle-melt = 0.2-0.3) than the observed difference between the peridotites and the basalts in this study. Our data on plagioclase lherzolites from Horoman and spinel lherzolites from other localities indicate that the difference in Fe isotope composition between mantle and basalts may be reduced by partial re-equilibration between the isotopically heavy basalts and the isotopically light depleted lithospheric mantle during melt ascent. Besides partial melting, the Fe isotope composition of mantle peridotites can also be significantly modified by metasomatic events. At two localities (Tok, Siberia and Tariat, Mongolia) Fe isotopes correlates with the Fe concentration of the peridotites, which was increased up to 14.5% FeO by melt percolation. Such processes can be accompanied by chromatographic effects and produce a range of Fe isotope compositions in the percolation columns, from extremely light to heavy (delta56Fe = -0.42 to +0.17). We propose that Fe isotopes can be used as a sensitive tracer to identify such metasomatic processes in the mantle. [1] Weyer et al. (2005) EPSL 240: 251-264 [2] Williams et al. (2005) EPSL 235 : 435-452

Osmium isotopes suggest fast and efficient mixing in the oceanic upper mantle.

NASA Astrophysics Data System (ADS)

Bizimis, Michael; Salters, Vincent

2010-05-01

The depleted upper mantle (DUM; the source of MORB) is thought to represent the complementary reservoir of continental crust extraction. Previous studies have calculated the "average" DUM composition based on the geochemistry of MORB. However the Nd isotope compositions of abyssal peridotites have been shown to extend to more depleted compositions than associated MORB. While this argues for the presence of both relatively depleted and enriched material within the upper mantle, the extent of compositional variability, length scales of heterogeneity and timescales of mixing in the upper mantle are not well constrained. Model calculations show that 2Ga is a reasonable mean age of depletion for DUM while Hf - Nd isotopes show the persistence of a depleted terrestrial reservoir by the early Archean (3.5-3.8Ga). U/Pb zircon ages of crustal rocks show three distinct peaks at 1.2, 1.9, and 2.7Ga and these are thought to represent the ages of three major crustal growth events. A fundamental question therefore is whether the present day upper mantle retains a memory of multiple ancient depletion events, or has been effectively homogenized. This has important implications for the nature of convection and time scales of survival of heterogeneities in the upper mantle. Here we compare published Os isotope data from abyssal peridotites and ophiolitic Os-Ir alloys with new data from Hawaiian spinel peridotite xenoliths. The Re-Os isotope system has been shown to yield useful depletion age information in peridotites, so we use it here to investigate the distribution of Re-depletion ages (TRD) in these mantle samples as a proxy for the variability of DUM. The probability density functions (PDF) of TRD from osmiridiums, abyssal and Hawaiian peridotites are all remarkably similar and show a distinct peak at 1.2-1.3 Ga (errors for TRD are set at 0.2Ga to suppress statistically spurious age peaks). The Hawaiian peridotites further show a distinct peak at 1.9-2Ga, but no oceanic mantle samples with TRD older than 2Ga have been reported. The TRD age peaks overlap with two major crustal building events recorded in the U/Pb crustal zircon ages. Therefore, peridotites from the convecting upper mantle can retain some memory of ancient depletion events, and these depletions are perhaps linked to major crustal building or large-scale mantle melting events. In the case of the Hawaiian peridotites, an ancient depletion event is further supported by some extremely radiogenic Hf isotope compositions. However, the vast majority of oceanic mantle samples show a narrow rage of Os isotope compositions (187Os/188Os = 0.123-0.126) with TRDs at 300-600 Ma. If the upper mantle has been produced continuously (or episodically) since at least the early Archean, it is then surprising that almost all oceanic mantle samples record such young depletion ages. We suggest that convective mixing in the mantle is rigorous enough that effectively re-homogenizes and resets the Os isotope composition of previously depleted peridotites within short time scales (<500Ma). Similarly recent ages have been derived from modeling the Sr, Nd, Hf, Pb isotopic composition of MORBs. This resetting and homogenization can be due to re-equilibration of depleted mantle with enriched components, e.g. recycled basaltic crust or more fertile mantle. Ancient depletion events are only effectively preserved in the sublithospheric mantle samples (e.g. Kaapval, Slave, Wyoming cratons) because they remain isolated from the convective mantle.

Isotopic composition of inorganic mercury and methylmercury downstream of a historical gold mining region

USGS Publications Warehouse

Donovan, Patrick M.; Blum, Joel D.; Singer, Michael B.; Marvin-DiPasquale, Mark C.; Tsui, Martin T.K.

2016-01-01

We measured total mercury (THg) and monomethyl mercury (MMHg) concentrations and mercury (Hg) isotopic compositions in sediment and aquatic organisms from the Yuba River (California, USA) to identify Hg sources and biogeochemical transformations downstream of a historical gold mining region. Sediment THg concentrations and δ202Hg decreased from the upper Yuba Fan to the lower Yuba Fan and the Feather River. These results are consistent with the release of Hg during gold mining followed by downstream mixing and dilution. The Hg isotopic composition of Yuba Fan sediment (δ202Hg = −0.38 ± 0.17‰ and Δ199Hg = 0.04 ± 0.03‰; mean ± 1 SD, n = 7) provides a fingerprint of inorganic Hg (IHg) that could be methylated locally or after transport downstream. The isotopic composition of MMHg in the Yuba River food web was estimated using biota with a range of %MMHg (the percent of THg present as MMHg) and compared to IHg in sediment, algae, and the food web. The estimated δ202Hg of MMHg prior to photodegradation (−1.29 to −1.07‰) was lower than that of IHg and we suggest this is due to mass-dependent fractionation (MDF) of up to −0.9‰ between IHg and MMHg. This result is in contrast to net positive MDF (+0.4 to +0.8‰) previously observed in lakes, estuaries, coastal oceans, and forests. We hypothesize that this unique relationship could be due to differences in the extent or pathway of biotic MMHg degradation in stream environments.

Isotopic Composition of Inorganic Mercury and Methylmercury Downstream of a Historical Gold Mining Region.

PubMed

Donovan, Patrick M; Blum, Joel D; Singer, Michael Bliss; Marvin-DiPasquale, Mark; Tsui, Martin T K

2016-02-16

We measured total mercury (THg) and monomethyl mercury (MMHg) concentrations and mercury (Hg) isotopic compositions in sediment and aquatic organisms from the Yuba River (California, USA) to identify Hg sources and biogeochemical transformations downstream of a historical gold mining region. Sediment THg concentrations and δ(202)Hg decreased from the upper Yuba Fan to the lower Yuba Fan and the Feather River. These results are consistent with the release of Hg during gold mining followed by downstream mixing and dilution. The Hg isotopic composition of Yuba Fan sediment (δ(202)Hg = -0.38 ± 0.17‰ and Δ(199)Hg = 0.04 ± 0.03‰; mean ± 1 SD, n = 7) provides a fingerprint of inorganic Hg (IHg) that could be methylated locally or after transport downstream. The isotopic composition of MMHg in the Yuba River food web was estimated using biota with a range of %MMHg (the percent of THg present as MMHg) and compared to IHg in sediment, algae, and the food web. The estimated δ(202)Hg of MMHg prior to photodegradation (-1.29 to -1.07‰) was lower than that of IHg and we suggest this is due to mass-dependent fractionation (MDF) of up to -0.9‰ between IHg and MMHg. This result is in contrast to net positive MDF (+0.4 to +0.8‰) previously observed in lakes, estuaries, coastal oceans, and forests. We hypothesize that this unique relationship could be due to differences in the extent or pathway of biotic MMHg degradation in stream environments.

The Molybdenum Isotope System as a Tracer of Slab Input in Subduction Zones: An Example From Martinique, Lesser Antilles Arc

NASA Astrophysics Data System (ADS)

Gaschnig, Richard M.; Reinhard, Christopher T.; Planavsky, Noah J.; Wang, Xiangli; Asael, Dan; Chauvel, Catherine

2017-12-01

Molybdenum isotopes are fractionated by Earth-surface processes and may provide a tracer for the recycling of crustal material into the mantle. Here, we examined the Mo isotope composition of arc lavas from Martinique in the Lesser Antilles arc, along with Cretaceous and Cenozoic Deep Sea Drilling Project sediments representing potential sedimentary inputs into the subduction zone. Mo stable isotope composition (defined as δ98Mo in ‰ deviation from the NIST 3134 standard) in lavas older than ˜7 million years (Ma) exhibits a narrow range similar to and slightly higher than MORB, whereas those younger than ˜7 Ma show a much greater range and extend to unusually low δ98Mo values. Sediments from DSDP Leg 78A, Site 543 have uniformly low δ98Mo values whereas Leg 14, Site 144 contains both sediments with isotopically light Mo and Mo-enriched black shales with isotopically heavy Mo. When coupled with published radiogenic isotope data, Mo isotope systematics of the lavas can be explained through binary mixing between a MORB-like end-member and different sedimentary compositions identified in the DSDP cores. The lavas older than ˜7 Ma were influenced by incorporation of isotopically heavy black shales into the mantle wedge. The younger lavas are the product of mixing isotopically light sedimentary material into the mantle wedge. The change in Mo isotope composition of the lavas at ˜7 Ma is interpreted to reflect the removal of the Cretaceous black shale component due to the arrival of younger ocean crust where the age-equivalent Cretaceous sediments were deposited in shallower oxic waters. Isotopic fractionation of Mo during its removal from the slab is not required to explain the observed systematics in this system.

Trihalomethanes formed from natural organic matter isolates: Using isotopic and compositional data to help understand sources

USGS Publications Warehouse

Bergamaschi, Brian A.; Fram, Miranda S.; Fujii, Roger; Aiken, George R.; Kendall, Carol; Silva, Steven R.

2000-01-01

Over 20 million people drink water from the Sacramento-San Joaquin Delta despite problematic levels of natural organic matter (NOM) and bromide in Delta water, which can form trihalomethanes (THMs) during the treatment process. It is widely believed that NOM released from Delta peat islands is a substantial contributor to the pool of THM precursors present in Delta waters. Dissolved NOM was isolated from samples collected at five channel sites within the Sacramento-San Joaquin Rivers and Delta, California, USA, and from a peat island agricultural drain. To help understand the sources of THM precursors, samples were analyzed to determine their chemical and isotopic composition, their propensity to form THMs, and the isotopic composition of the THMs.The chemical composition of the isolates was quite variable, as indicated by significant differences in carbon-13 nuclear magnetic resonance spectra and carbon-to-nitrogen concentration ratios. The lowest propensity to form THMs per unit of dissolved organic carbon was observed in the peat island agricultural drain isolate, even though it possessed the highest fraction of aromatic material and the highest specific ultraviolet absorbance. Changes in the chemical and isotopic composition of the isolates and the isotopic composition of the THMs suggest that the source of the THMs precursors was different between samples and between isolates. The pattern of variability in compositional and isotopic data for these samples was not consistent with simple mixing of river- and peat-derived organic material.

Coordinated Petrography and Oxygen Isotopic Compositions of Al-Rich Chondrules from CV3 Chondrites

NASA Astrophysics Data System (ADS)

Zhang, M. M.; Lin, Y. T.; Tang, G. Q.; Li, X. H.

2017-07-01

In this study, we coordinated the petrology, bulk compositions and oxygen isotope compositions of 12 ARCs from Allende and Leoville and Ningqiang chondrites in order to elucidate any potential genetic relationships between ARCs, CAIs and FMCs.

Chapter 16Tracing Nitrogen Sources and Cycling in Catchments

USGS Publications Warehouse

Kendall, Carol

1998-01-01

This chapter focuses on the uses of isotopes to understand water chemistry.I Isotopic compositions generally cannot be interpreted successfully in the absence of other chemical and hydrologic data. The chapter focusses on uses of isotopes in tracing sources and cycling of nitrogen in the water-component of forested catchment, and on dissolved nitrate in shallow waters, nutrient uptake studies in agricultural areas, large-scale tracer experiments, groundwater contamination studies, food-web investigations, and uses of compound-specific stable isotope techniques. Shallow waters moving along a flowpath through a relatively uniform material and reacting with minerals probably do not achieve equilibrium but gradually approach some steady-state composition. The chapter also discusses the use of isotopic techniques to assess impacts of changes in land-management practices and land use on water quality. The analysis of individual molecular components for isotopic composition has much potential as a method for tracing the source, biogeochemistry, and degradation of organic liquids and gases because different materials have characteristic isotope spectrums or biomarkers.

Protein retention assessment of four levels of poultry by-product substitution of fishmeal in rainbow trout (Oncorhynchus mykiss) diets using stable isotopes of nitrogen (δ15N) as natural tracers.

PubMed

Badillo, Daniel; Herzka, Sharon Z; Viana, Maria Teresa

2014-01-01

This is second part from an experiment where the nitrogen retention of poultry by-product meal (PBM) compared to fishmeal (FM) was evaluated using traditional indices. Here a quantitative method using stable isotope ratios of nitrogen (δ(15)N values) as natural tracers of nitrogen incorporation into fish biomass is assessed. Juvenile rainbow trout (Oncorhynchus mykiss) were fed for 80 days on isotopically distinct diets in which 0, 33, 66 and 100% of FM as main protein source was replaced by PBM. The diets were isonitrogenous, isolipidic and similar in gross energy content. Fish in all treatments reached isotopic equilibrium by the end of the experiment. Two-source isotope mixing models that incorporated the isotopic composition of FM and PBM as well as that of formulated feeds, empirically derived trophic discrimination factors and the isotopic composition of fish that had reached isotopic equilibrium to the diets were used to obtain a quantitative estimate of the retention of each source of nitrogen. Fish fed the diets with 33 and 66% replacement of FM by PBM retained poultry by-product meal roughly in proportion to its level of inclusion in the diets, whereas no differences were detected in the protein efficiency ratio. Coupled with the similar biomass gain of fishes fed the different diets, our results support the inclusion of PBM as replacement for fishmeal in aquaculture feeds. A re-feeding experiment in which all fish were fed a diet of 100% FM for 28 days indicated isotopic turnover occurred very fast, providing further support for the potential of isotopic ratios as tracers of the retention of specific protein sources into fish tissues. Stable isotope analysis is a useful tool for studies that seek to obtain quantitative estimates of the retention of different protein sources.

Protein Retention Assessment of Four Levels of Poultry By-Product Substitution of Fishmeal in Rainbow Trout (Oncorhynchus mykiss) Diets Using Stable Isotopes of Nitrogen (δ15N) as Natural Tracers

PubMed Central

Badillo, Daniel; Herzka, Sharon Z.; Viana, Maria Teresa

2014-01-01

This is second part from an experiment where the nitrogen retention of poultry by-product meal (PBM) compared to fishmeal (FM) was evaluated using traditional indices. Here a quantitative method using stable isotope ratios of nitrogen (δ15N values) as natural tracers of nitrogen incorporation into fish biomass is assessed. Juvenile rainbow trout (Oncorhynchus mykiss) were fed for 80 days on isotopically distinct diets in which 0, 33, 66 and 100% of FM as main protein source was replaced by PBM. The diets were isonitrogenous, isolipidic and similar in gross energy content. Fish in all treatments reached isotopic equilibrium by the end of the experiment. Two-source isotope mixing models that incorporated the isotopic composition of FM and PBM as well as that of formulated feeds, empirically derived trophic discrimination factors and the isotopic composition of fish that had reached isotopic equilibrium to the diets were used to obtain a quantitative estimate of the retention of each source of nitrogen. Fish fed the diets with 33 and 66% replacement of FM by PBM retained poultry by-product meal roughly in proportion to its level of inclusion in the diets, whereas no differences were detected in the protein efficiency ratio. Coupled with the similar biomass gain of fishes fed the different diets, our results support the inclusion of PBM as replacement for fishmeal in aquaculture feeds. A re-feeding experiment in which all fish were fed a diet of 100% FM for 28 days indicated isotopic turnover occurred very fast, providing further support for the potential of isotopic ratios as tracers of the retention of specific protein sources into fish tissues. Stable isotope analysis is a useful tool for studies that seek to obtain quantitative estimates of the retention of different protein sources. PMID:25226392

Tracing fluid transfer across subduction zones using iron and zinc stable isotopes

NASA Astrophysics Data System (ADS)

Williams, H. M.; Debret, B.; Pons, M. L.; Bouilhol, P.

2016-12-01

In subduction zones, serpentinite devolatilization within the downgoing slab and the fluids released play a fundamental role in volatile transfer as well as the redox evolution of the sub-arc mantle. Constraining subduction-related serpentinite devolatilisation is essential in order to better understand of the nature and composition of slab-derived fluids and fluid/rock interactions. Fe and Zn stable isotopes can trace fluid composition and speciation as isotope partitioning is driven by changes in oxidation state, coordination, and bonding environment. In the case of serpentinite devolatilisation, Fe isotope fractionation should reflect changes in Fe redox state and the formation of Fe-Cl- and SO42- complexes (Hill et al., GCA 2010); Zn isotope fractionation should be sensitive to complexation with CO32-, HS- and SO42- anions (Fujii et al., GCA 2011). We targeted samples from Western Alps ophiolite complexes, interpreted as remnants of serpentinized oceanic lithosphere metamorphosed and devolatilized during subduction (Hattori and Guillot, G3 2007; Debret et al., Chem. Geol. 2013). A striking negative correlation is present between bulk serpentinite Fe isotope composition and Fe3+/Fetot, with the highest grade samples displaying the heaviest Fe isotope compositions and lowest Fe3+/Fetot (Debret et al., Geology, 2016). The same samples also display a corresponding variation in Zn isotopes, with the highest grade samples displaying isotopically light compositions (Pons et al., in revision). The negative correlation between Fe and Zn isotopes and decrease in Fe3+/Fetot can explained by serpentinite sulfide breakdown and the release of fluids enriched in isotopically light Fe and heavy Zn sulphate complexes. The migration of these SOX-bearing fluids from the slab to the slab-mantle interface or mantle wedge has important implications for the redox evolution of the sub-arc mantle and the transport of metals from the subducting slab.

Online induction heating for determination of isotope composition of woody stem water with laser spectrometry: A methods assessment

USGS Publications Warehouse

Lazarus, Brynne E.; Germino, Matthew; Vander Veen, Jessica L.

2016-01-01

Application of stable isotopes of water to studies of plant–soil interactions often requires a substantial preparatory step of extracting water from samples without fractionating isotopes. Online heating is an emerging approach for this need, but is relatively untested and major questions of how to best deliver standards and assess interference by organics have not been evaluated. We examined these issues in our application of measuring woody stem xylem of sagebrush using a Picarro laser spectrometer with online induction heating. We determined (1) effects of cryogenic compared to induction-heating extraction, (2) effects of delivery of standards on filter media compared to on woody stem sections, and (3) spectral interference from organic compounds for these approaches (and developed a technique to do so). Our results suggest that matching sample and standard media improves accuracy, but that isotopic values differ with the extraction method in ways that are not due to spectral interference from organics.

Improvement of 2,4-dinitrophenylhydrazine derivatization method for carbon isotope analysis of atmospheric acetone.

PubMed

Wen, Sheng; Yu, Yingxin; Guo, Songjun; Feng, Yanli; Sheng, Guoying; Wang, Xinming; Bi, Xinhui; Fu, Jiamo; Jia, Wanglu

2006-01-01

Through simulation experiments of atmospheric sampling, a method via 2,4-dinitrophenylhydrazine (DNPH) derivatization was developed to measure the carbon isotopic composition of atmospheric acetone. Using acetone and a DNPH reagent of known carbon isotopic compositions, the simulation experiments were performed to show that no carbon isotope fractionation occurred during the processes: the differences between the predicted and measured data of acetone-DNPH derivatives were all less than 0.5 per thousand. The results permitted the calculation of the carbon isotopic compositions of atmospheric acetone using a mass balance equation. In this method, the atmospheric acetone was collected by a DNPH-coated silica cartridge, washed out as acetone-DNPH derivatives, and then analyzed by gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS). Using this method, the first available delta13C data of atmospheric acetone are presented. Copyright 2006 John Wiley & Sons, Ltd.

Determination of chemical purity and isotopic composition of natural and carbon-13-labeled arsenobetaine bromide standards by quantitative(1)H-NMR.

PubMed

Le, Phuong-Mai; Ding, Jianfu; Leek, Donald M; Mester, Zoltan; Robertson, Gilles; Windust, Anthony; Meija, Juris

2016-10-01

In this study, we report the characterization of three arsenobetaine-certified reference materials by quantitative NMR. We have synthesized an arsenobetaine bromide high-purity standard of natural isotopic composition (ABET-1) and two carbon-13-labeled isotopic standards (BBET-1 and CBET-1). Assignments of the chemical purity and isotopic composition are not trivial in the case of arsenobetaine, and in this study we utilized quantitative(1)H-NMR techniques for the determination of the mass fractions (chemical purity). The isotopic purity of all three standards was also assessed by NMR from the carbon-13 satellite signals. The standards are non-hygroscopic, high-purity (ca. 0.99 g/g), and the carbon-13 enrichment for both isotopic standards is x((13)C)≈0.99. These standards are designed for use as primary calibrators for mass spectrometric determination of arsenobetaine in environmental samples.

Isotopic Analysis of Fingernails as a USGS Open House Demonstration of the Use of Stable Isotopes in Foodweb Studies

NASA Astrophysics Data System (ADS)

Silva, S. R.; Kendall, C.; Young, M. B.; Choy, D.

2011-12-01

The USGS Isotope Tracers Project uses stable isotopes and tritium to add a unique dimension of chemical information to a wide range of environmental investigations. The use and application of isotopes is usually an unfamiliar and even esoteric topic to the general public. Therefore during three USGS open house events, as a public outreach effort, we demonstrated the use of stable isotopes by analyzing nitrogen and carbon isotopes from very small fragments of fingernail from willing participants. We titled the exhibit "You Are What You Eat". The results from all participants were plotted on a graph indicating the general influence of different food groups on the composition of body tissues as represented by fingernails. All participants were assigned a number and no personal-identification information was collected. A subset of participants provided us with an estimate of the number of days a week various foods were eaten and if they were vegetarians, vegans or non-vegetarians. Volunteers from our research group were on hand to explain and discuss fundamental concepts such as how foods attain their isotopic composition, the difference between C3 and C4 plants, the effects of assimilation, trophic enrichment, and the various uses of stable isotopes in environmental studies. The results of the fingernail analyses showed the variation of the range of isotopic compositions among about 400 people at each event, the distinct influence of C4 plants (mainly corn and cane sugar) on our carbon isotopic composition, and the isotopic differences between vegetarians and non vegetarians among other details (http://wwwrcamnl.wr.usgs.gov/isoig/projects/fingernails/). A poll of visitors attending the open house event in 2006 indicated that "You Are What You Eat" was among the most popular exhibits. Following the first two open house events we were contacted by a group of researchers from Brazil who had completed a very similar study. Our collaboration resulted in a publication in the American Journal of Physical Anthropology (Nardoto et al., 2006). This study found that despite global trends toward dietary homogenization, regional differences in food resources and dietary preferences were recorded in the carbon and nitrogen isotopic compositions of fingernails.

Sea surface salinity of the Eocene Arctic Azolla event using innovative isotope modeling

NASA Astrophysics Data System (ADS)

Speelman, E. N.; Sewall, J. O.; Noone, D.; Huber, M.; Sinninghe Damste, J. S.; Reichart, G. J.

2009-04-01

With the realization that the Eocene Arctic Ocean was covered with enormous quantities of the free floating freshwater fern Azolla, new questions regarding Eocene conditions facilitating these blooms arose. Our present research focuses on constraining the actual salinity of, and water sources for, the Eocene Arctic basin through the application of stable water isotope tracers. Precipitation pathways potentially strongly affect the final isotopic composition of water entering the Arctic Basin. Therefore we use the Community Atmosphere Model (CAM3), developed by NCAR, combined with a recently developed integrated isotope tracer code to reconstruct the isotopic composition of global Eocene precipitation and run-off patterns. We further addressed the sensitivity of the modeled hydrological cycle to changes in boundary conditions, such as pCO2, sea surface temperatures (SSTs) and sea ice formation. In this way it is possible to assess the effect of uncertainties in proxy estimates of these parameters. Overall, results of all runs with Eocene boundary conditions, including Eocene topography, bathymetry, vegetation patterns, TEX86 derived SSTs and pCO2 estimates, show the presence of an intensified hydrological cycle with precipitation exceeding evaporation in the Arctic region. Enriched, precipitation weighted, isotopic values of around -120‰ are reported for the Arctic region. Combining new results obtained from compound specific isotope analyses (δD) on terrestrially derived n-alkanes extracted from Eocene sediments, and model outcomes make it possible to verify climate reconstructions for the middle Eocene Arctic. Furthermore, recently, characteristic long-chain mid-chain ω20 hydroxy wax constituents of Azolla were found in ACEX sediments. δD values of these C32 - C36 diols provide insight into the isotopic composition of the Eocene Arctic surface water. As the isotopic signature of the runoff entering the Arctic is modelled, and the final isotopic composition of the surface waters can be deduced from the isotopic composition of the diols, we can calculate the degree of mixing between freshwater (isotopically light) and seawater (isotopically heavy) in the surface waters. This way we quantify Eocene Arctic surface water salinity, which in turn will shed light on the degree of (seasonal) mixing and stratification.

Tibetan Magmatism Database

NASA Astrophysics Data System (ADS)

Chapman, James B.; Kapp, Paul

2017-11-01

A database containing previously published geochronologic, geochemical, and isotopic data on Mesozoic to Quaternary igneous rocks in the Himalayan-Tibetan orogenic system are presented. The database is intended to serve as a repository for new and existing igneous rock data and is publicly accessible through a web-based platform that includes an interactive map and data table interface with search, filtering, and download options. To illustrate the utility of the database, the age, location, and ɛHft composition of magmatism from the central Gangdese batholith in the southern Lhasa terrane are compared. The data identify three high-flux events, which peak at 93, 50, and 15 Ma. They are characterized by inboard arc migration and a temporal and spatial shift to more evolved isotopic compositions.

The Diversity of Anomalous HEDs: Isotopic Constraints on the Connection of EET 92023, GRA 98098, and Dhofar 700 With Vesta

NASA Technical Reports Server (NTRS)

Sanborn, M. E.; Yin, Q.-Z.; Mittlefehldt, D. W.

2016-01-01

The possibility for multiple parent bodies, instead of a common parent body of Vesta, for eucrites has been suggested based on the variable oxygen isotopic composition observed in some eucrites.. Recently, we added an extra dimension to the discussion based on the (epsilon)54Cr composition of the same eucrites with known (delta)17O to compare with the normal eucrites. The combined (delta)17O and (epsilon)54Cr isotope systematics for Pasamonte, PCA 91007, A-881394, and Ibitira indicate their likely origin from multiple different parent bodies than the normal eucrites. Often the qualifier anomalous is used to identify HEDs with (delta)17O values that deviate significantly (>3(sigma)) from the mean HED (delta)17O. However, variations in eucrites and diogenites also include unique geochemical characteristics such as bulk composition, trace element abundances, or volatile concentrations, in addition to (delta)17O. Here, we investigate three such geochemically anomalous HEDs: Elephant Moraine (EET) 92023, Graves Nunataks (GRA) 98098, and Dhofar 700. In addition, to verify the homogeneity of (epsilon)54Cr observed for normal HEDs thus far, a set of seven eucrites and diogenites considered normal samples were also investigated.

δ2H and δ18O of human body water: a GIS model to distinguish residents from non-residents in the contiguous USA.

PubMed

Podlesak, David W; Bowen, Gabriel J; O'Grady, Shannon; Cerling, Thure E; Ehleringer, James R

2012-06-01

An understanding of the factors influencing the isotopic composition of body water is important to determine the isotopic composition of tissues that are used to reconstruct movement patterns of humans. The δ(2)H and δ(18)O values of body water (δ(2)H(bw) and δ(18)O(bw)) are related to the δ(2)H and δ(18)O values of drinking water (δ(2)H(dw) and δ(18)O(dw)), but clearly distinct because of other factors including the composition of food. Here, we develop a mechanistic geographical information system (GIS) model to produce spatial projections of δ(2)H(bw) and δ(18)O(bw) values for the USA. We investigate the influence of gender, food, and drinking water on the predicted values by comparing them with the published values. The strongest influence on the predicted values was related to the source of δ(2)H(dw) and δ(18)O(dw) values. We combine the model with equations that describe the rate of turnover to produce estimates for the time required for a non-resident to reach an isotopic equilibrium with a resident population.

[Determination of 235U/238U isotope ratios in camphor tree bark samples by MC-ICP-MS after separation of uranium from matrix elements].

PubMed

Wang, Xiao-Ping; Zhang, Ji-Long

2007-07-01

Twelve camphor (cinnamomum camphora) tree bark samples were collected from Hiroshima and Kyoto, and the matrix element composition and morphology of the outer surface of these camphor tree bark samples were studied by EDXS and SEM respectively. After a dry decomposition, DOWEX 1-X8 anion exchange resin was used to separate uranium from matrix elements in these camphor tree bark samples. Finally, 235U/238 U isotope ratios in purified uranium solutions were determined by MC-ICP-MS. It was demonstrated that the outer surface of these camphor tree bark samples is porous and rough, with Al, Ca, Fe, K, Mg, Si, C, O and S as its matrix element composition. Uranium in these camphor tree bark samples can be efficiently separated and quantitatively recovered from the matrix element composition. Compared with those collected from Kyoto, the camphor tree bark samples collected from Hiroshima have significantly higher uranium contents, which may be due to the increased aerosol mass concentration during the city reconstruction. Moreover, the 235 U/23.U isotope ratios in a few camphor tree bark samples collected from Hiroshima are slightly higher than 0.007 25.

Sr and Nd isotopes of suspended sediments from rivers of the Amazon basin

NASA Astrophysics Data System (ADS)

Hatting, Karina; Santos, Roberto V.; Sondag, Francis

2014-05-01

The Rb-Sr and Sm-Nd isotopic systems are important tools to constrain the provenance of sediment load in river systems. This study presents the isotopic composition of Sr and Nd isotopes and major and minor elements in suspended sediments from the Marañón-Solimões, Amazonas and Beni-Madeira rivers. The data were used to constrain the source region of the sediments and to better understand the main seasonal and spatial transport processes within the basin based on the variations of the chemical and isotopic signals. They also allow establishing a relationship between sediment concentrations and flow rate values. The study presents data collected during a hydrological year between 2009 and 2010. The Marañón-Solimões River presents low Sr isotopic values (0.7090-0.7186), broad EpslonNd(0) range (-15.17 to -8.09) and Nd model (TDM) ages varying from 0.99 to 1.81 Ga. Sources of sediments to the Marañón-Solimões River include recent volcanic rocks in northern Peru and Ecuador, as well as rocks with long crustal residence time and carbonates from the Marañón Basin, Peru. The Beni-Madeira River has more radiogenic Sr isotope values (0.7255-0.7403), more negative EpslonNd(0) values (-20.46 to -10.47), and older Nd isotope model ages (from 1.40 to 2.35 Ga) when compared to the Marañón-Solimões River. These isotope data were related to the erosion of Paleozoic and Cenozoic foreland basins that are filled with Precambrian sediments derived from the Amazonian Craton. These basins are located in Bolivian Subandina Zone. The Amazon River presents intermediate isotopic values when compared to those found in the Marañón-Solimões and Beni-Madeira rivers. Its Sr isotope ratios range between 0.7193 and 0.7290, and its EpslonNd(0) values varies between -11.09 and -9.51. The Nd isotope model ages of the suspended sediments vary between 1.28 and 1.77 Ga. Concentrations of soluble and insoluble elements indicate a more intense weathering activity in sediments of the Beni-Madeira River. This river has a larger difference in the Sr isotopic composition between the diluted and solid phases, which has been assigned to the high level of weathering of its sediment source area. In the Beni-Madeira River sub-basin dominates weathering of silicate rocks, while in the Marañón-Solimões River sub-basin there also weathering of carbonate and evaporitic rocks.

Return to the Strangelove Ocean?: Preliminary results of carbon and oxygenisotope compositions of post-impact sediments, IODP Expedition 364 "Chicxulub Impact Crater"

NASA Astrophysics Data System (ADS)

Yamaguchi, K. E.; Ikehara, M.; Hayama, H.; Takiguchi, S.; Masuda, S.; Ogura, C.; Fujita, S.; Kurihara, E.; Matsumoto, T.; Oshio, S.; Ishihata, K.; Fuchizawa, Y.; Noda, H.; Sakurai, U.; Yamane, T.; Morgan, J. V.; Gulick, S. P. S.

2017-12-01

The Chicxulub crater in the northern Yucatan Peninsula, Mexico was formed by the asteroid impact at the Cretaceous-Paleogene boundary (66.0 Ma). In early 2016 the IODP Exp. 364 successfully drilled the materials from the topographic peak ring within the crater that was previously identified by seismological observations. A continuous core was recovered. The 112m-thick uppermost part of the continuous core (505.7-1334.7 mbsf) is post-impact sediments, including the PETM, that are mainly composed of carbonate with intercalation of siliciclastics and variable contents of organic carbon. More than 300 samples from the post-impact section were finely powdered for a variety of geochemical analysis. Here we report their carbon and oxygen isotope compositions of the carbonate fraction (mostly in the lower part of the analyzed section) and carbon and nitrogen isotope compositions of organic matter (mostly in the middle-upper part of the analyzed section). Isotope mass spectrometer Isoprime was used for the former analysis, and EA-irMS (elemental analyzer - isotope ratio mass spectrometer) was used for the latter analysis, both at CMCR, Kochi Univ. Depth profile of oxygen isotope compositions of carbonate fraction is variable and somewhat similar to those of Zachos et al. (2001; Science). Carbon isotope compositions of carbonate and organic carbon in the lower part of the analyzed section exhibit some excursions that could correspond to the hyperthemals in the early Paleogene. Their variable nitrogen isotope compositions reflect temporal changes in the style of biogeochemical cycles involving denitrification and nitrogen fixation. Coupled temporal changes in the carbon isotope compositions of organic and carbonate carbon immediately after the K-Pg boundary might support a Strangelove ocean (Kump, 1991; Geology), however high export production (Ba/Ti, nannoplankton and calcisphere blooms, high planktic foram richness, and diverse and abundant micro- and macrobenthic organisms) at the base of the Danian limestone cored during Exp. 364 contradict a Strangelove Ocean.

Nickel isotopic composition of the mantle

NASA Astrophysics Data System (ADS)

Gall, Louise; Williams, Helen M.; Halliday, Alex N.; Kerr, Andrew C.

2017-02-01

This paper presents a detailed high-precision study of Ni isotope variations in mantle peridotites and their minerals, komatiites as well as chondritic and iron meteorites. Ultramafic rocks display a relatively large range in δ60 Ni (permil deviation in 60 Ni /58 Ni relative to the NIST SRM 986 Ni isotope standard) for this environment, from 0.15 ± 0.07‰ to 0.36 ± 0.08‰, with olivine-rich rocks such as dunite and olivine cumulates showing lighter isotope compositions than komatiite, lherzolite and pyroxenite samples. The data for the mineral separates shed light on the origin of these variations. Olivine and orthopyroxene display light δ60 Ni whereas clinopyroxene and garnet are isotopically heavy. This indicates that peridotite whole-rock δ60 Ni may be controlled by variations in modal mineralogy, with the prediction that mantle melts will display variable δ60 Ni values due to variations in residual mantle and cumulate mineralogy. Based on fertile peridotite xenoliths and Phanerozoic komatiite samples it is concluded that the upper mantle has a relatively homogeneous Ni isotope composition, with the best estimate of δ60Nimantle being 0.23 ± 0.06‰ (2 s.d.). Given that >99% of the Ni in the silicate Earth is located in the mantle, this also defines the Ni isotope composition of the Bulk Silicate Earth (BSE). This value is nearly identical to the results obtained for a suite of chondrites and iron meteorites (mean δ60 Ni 0.26 ± 0.12‰ and 0.29 ± 0.10‰, respectively) showing that the BSE is chondritic with respect to its Ni isotope composition, with little to no Ni mass-dependent isotope fractionation resulting from core formation.

Utilization of non-weapons-grade plutonium and highly enriched uranium with breeding of the {sup 233}U isotope in the VVER reactors using thorium and heavy water

DOE Office of Scientific and Technical Information (OSTI.GOV)

Marshalkin, V. E., E-mail: marshalkin@vniief.ru; Povyshev, V. M.

A method for joint utilization of non-weapons-grade plutonium and highly enriched uranium in the thorium–uranium—plutonium oxide fuel of a water-moderated reactor with a varying water composition (D{sub 2}O, H{sub 2}O) is proposed. The method is characterized by efficient breeding of the {sup 233}U isotope and safe reactor operation and is comparatively simple to implement.

[Changes of chlorine isotope composition characterize bacterial dehalogenation of dichloromethane].

PubMed

Ziakun, A M; Firsova, Iu E; Torgonskaia, M L; Doronina, N V; Trotsenko, Iu A

2007-01-01

Fractionation of dichloromethane (DCM) molecules with different chlorine isotopes by aerobic methylobacteria Methylobacterium dichloromethanicum DM4 and Albibacter nethylovorans DM10; cell-free extract of strain DM4; and transconjugant Methylobacterium evtorquens Al1/pME 8220, expressing the dcmA gene for DCM dehalogenase but unable to grow on DCM, was studied. Kinetic indices of DCM isotopomers for chlorine during bacterial dehalogenation and diffusion were compared. A two-step model is proposed, which suggests diffusional DCM transport to bacterial cells.

What is the iron isotope composition of the Moon?

NASA Astrophysics Data System (ADS)

Poitrasson, F.; Zambardi, T.; Magna, T.; Neal, C. R.

2016-12-01

It is difficult to estimate the bulk chemical and isotopic composition of the Moon because of severe limitations in our sampling. As a result, there is currently a debate on the bulk Fe isotope composition of the Moon despite the constraints on the lunar accretion modes or differentiation processes it may provide. For this, a proper mass balance estimation of essential planetary reservoirs is required. For instance, the dichotomy in δ57Fe between low- and high-Ti mare basalt varieties as a consequence of differences in degree of fractional crystallization of their respective lunar mantle sources should be rigorously tested. To investigate this, we performed new iron isotope measurements of 33 bulk lunar mare basalts and highland rocks, including KREEP-related materials. The new data show significant Fe isotope differences between high-Ti and low-Ti mare basalts, yielding mean δ57FeIRMM-014=0.277±0.020‰ and δ57FeIRMM-014=0.127±0.020‰, respectively. Assuming that lunar basalts mirror the iron isotope composition of their respective mantle protoliths, the estimated relative proportion of the low-Ti and high-Ti mantle source suggests that the lunar upper mantle should be close to δ57Fe=0.14±0.03‰. At present, it is unclear whether the bulk lunar Fe isotope composition is indistinguishable from that of the Earth (δ57FeIRMM-014=0.10±0.03‰), when estimated solely from mare basalts data, or if it is twice as heavy relative to chondrites, as initially proposed. A large scatter at δ57Fe=0.08±0.19‰ for ferroan anorthosites, Mg-suite rocks and a KREEP basalt imparts more complexities for global isotopic view of the Moon. A better understanding of the cause of Fe isotope heterogeneity among the lunar highland rocks will likely allow to better estimate the bulk Moon composition, and possibly to improve our knowledge about the genesis of the lunar crust itself.

Nicotine, acetanilide and urea multi-level2H-,13C- and15N-abundance reference materials for continuous-flow isotope ratio mass spectrometry

USGS Publications Warehouse

Schimmelmann, A.; Albertino, A.; Sauer, P.E.; Qi, H.; Molinie, R.; Mesnard, F.

2009-01-01

Accurate determinations of stable isotope ratios require a calibration using at least two reference materials with different isotopic compositions to anchor the isotopic scale and compensate for differences in machine slope. Ideally, the S values of these reference materials should bracket the isotopic range of samples with unknown S values. While the practice of analyzing two isotopically distinct reference materials is common for water (VSMOW-SLAP) and carbonates (NBS 19 and L-SVEC), the lack of widely available organic reference materials with distinct isotopic composition has hindered the practice when analyzing organic materials by elemental analysis/isotope ratio mass spectrometry (EA-IRMS). At present only L-glutamic acids USGS40 and USGS41 satisfy these requirements for ??13C and ??13N, with the limitation that L-glutamic acid is not suitable for analysis by gas chromatography (GC). We describe the development and quality testing of (i) four nicotine laboratory reference materials for on-line (i.e. continuous flow) hydrogen reductive gas chromatography-isotope ratio mass-spectrometry (GC-IRMS), (ii) five nicotines for oxidative C, N gas chromatography-combustion-isotope ratio mass-spectrometry (GC-C-IRMS, or GC-IRMS), and (iii) also three acetanilide and three urea reference materials for on-line oxidative EA-IRMS for C and N. Isotopic off-line calibration against international stable isotope measurement standards at Indiana University adhered to the 'principle of identical treatment'. The new reference materials cover the following isotopic ranges: ??2Hnicotine -162 to -45%o, ??13Cnicotine -30.05 to +7.72%, ?? 15Nnicotine -6.03 to +33.62%; ??15N acetanilide +1-18 to +40.57%; ??13Curea -34.13 to +11.71%, ??15Nurea +0.26 to +40.61% (recommended ?? values refer to calibration with NBS 19, L-SVEC, IAEA-N-1, and IAEA-N-2). Nicotines fill a gap as the first organic nitrogen stable isotope reference materials for GC-IRMS that are available with different ??13N values. Comparative ??13C and ??15N on-line EA-IRMS data from 14 volunteering laboratories document the usefulness and reliability of acetanilides and ureas as EA-IRMS reference materials.

Hercynian Pb-Zn mineralization types in the Alcudia Valley mining district (Spain) and their reflect in Pb isotopic signatures

NASA Astrophysics Data System (ADS)

García de Madinabeitia, S.; Santos Zalduegui, J. F.; Palero, F.; Gil Ibarguchi, J. I.; Carracedo, M.

2003-04-01

More than 450 ore deposits indexed within the Alcudia Valley of the Central-Iberian Zone (Spain) may be grouped by their tectonic and lithologic characteristics (1,2) as follows: type A of rare stratabound mineralizations, and types B, C, D and E represented by abundant Hercynian veins (post-Namurian). 86 new Pb isotope analyses of galenas from the four vein types reveal that types B and C have similar isotopic ratios with values of μ_2 = 10.07, ω_2 = 40.6 and a mean model age of 564 Ma. Types D and E have μ_2 and ω_2 values of 9.79 and 38.5, respectively, but differ each other with respect to their model ages, 600 Ma (type D) and 335 Ma (type E). The observed variations appear to be related to the geochemical features of the metasedimentary host-rocks of the mineralizations where two distinct types of Pb isotopic ratios have been reported (3): one with μ_2 and ω_2 comparable to those of the D and E types and another with a more radiogenic composition, close to those of the B and C types of galenas. Nägler et al. have suggested partial rehomogeneization of Pb isotopic composition within the metasediments at ca. 330 Ma, that is, prior to the mineralization events, but the extent of this process and its effects on the ore bodies isotopic features is not evident. The origin of the more abundant E type ore bodies has been related to the Hercynian granitic rocks in the area (2, and references therein). Other plutons within this sector of the Central Iberian Zone (e.g., Linares, etc.; cf. accompanying Abstract) associate ore bodies whose Pb isotopic composition is very similar to that of the E type galenas from the Alcudia Valley. The isotopic data obtained thus point to a related or common source material for the various types of granites within the area studied. Yet, the Pb isotopic composition of other mineralizations (B, C, D), likewise located in Hercynian veins, allow to consider different types of Pb-Zn ore bodies and point therefore to different sources of Pb at a regional scale. (1) Palero, F.J. Ph. D., University of Salamanca, Spain (1991). (2) Palero, F.; Both, R.A.; Arribas, A.; Boyce, A.J.; Mangas, J. &Martín-Izard, A. Economic Geology (in press). (3) Nägler, T. Ph. D., Diss ETH, Zurich N^o 9245 (1990).

Re-Os systematics of komatiites and komatiitic basalts at Dundonald Beach, Ontario, Canada: Evidence for a complex alteration history and implications of a late-Archean chondritic mantle source

NASA Astrophysics Data System (ADS)

Gangopadhyay, A.; Sproule, R. A.; Walker, R. J.; Lesher, C.

2004-12-01

Re-Os concentrations and isotopic compositions have been examined in one komatiite unit and one komatiitic basalt unit at Dundonald Beach, which is part of the spatially-extensive 2.7 Ga Kidd-Munro volcanic assemblage in the Abitibi greenstone belt, Ontario, Canada. The komatiitic rocks in this locality record at least three episodes of alteration of Re-Os elemental and isotope systematics. First, an average of 40% and as much as 75% Re was lost due to shallow degassing during eruption and/or hydrothermal leaching during or immediately after the lava emplacement. Second, the Re-Os isotope systematics of the rocks with 187Re/188Os ratios >1 were reset at ˜2.5 Ga, most likely due to a regional metamorphic event. Finally, there is evidence for relatively recent gain and loss of Re. The variations in Os concentrations in the Dundonald komatiites yield a relative bulk distribution coefficient for Os (DOs solid/liquid) of 2-4, consistent with those obtained for stratigraphically-equivalent komatiites in the nearby Alexo area and in Munro Township. This suggests that Os was moderately compatible during crystal-liquid fractionation of the magma parental to the Kidd-Munro komatiitic rocks. Furthermore, whole-rock samples and chromite separates with low 187Re/188Os ratios (<1) yield a precise chondritic average initial 187Os/188Os ratio of 0.1083 ± 0.0006 (\\gammaOs = 0.0 ± 0.6). The chondritic initial Os isotopic composition of the mantle source for the Dundonald rocks is consistent with that determined for komatiites in the Alexo area and in Munro Township. Our Os isotope results for the Dundonald komatiitic rocks, combined with those in the Alexo and Pyke Hill areas suggest that the mantle source region for the Kidd- Munro volcanic assemblage had evolved along a long-term chondritic Os isotopic trajectory until their eruption at ˜2.7 Ga. The chondritic initial Os isotopic composition of the Kidd-Munro komatiites is indistinguishable from that of the projected contemporaneous convective upper mantle. The uniform chondritic Os isotopic composition of the ˜2.7 Ga mantle source for the Kidd-Munro komatiites contrasts with the typical large-scale Os isotopic heterogeneity in the mantle sources for komatiites from the Gorgona Island, present-day ocean island basalts or arc-related lavas. This suggests a significantly more homogeneous mantle source in the Archean compared to the presentday mantle.

Reconstruction of Late Quaternary Climate in Central Europe - A Comparison of Stable Isotope and Trace Element Variations in Speleothems From Different Cave Systems in Germany.

NASA Astrophysics Data System (ADS)

Nordhoff, P.; Wiegand, B.; Simon, K.; Rosendahl, W.; Hansen, B. T.; Kempe, S.

2003-12-01

Speleothems (stalagmites, stalactites, flowstones) are important archives for Late Quaternary continental climatic and paleo-environmental reconstruction. Speleothems form when calcium carbonate precipitates from solutions seeping into caves hosted e.g. in limestone or dolomite complexes. Information of past climate variability and changes in local environmental conditions can be obtained from signatures of the stable isotopes of oxygen and carbon as well as trace element pattern recorded in speleothems. Reconstruction of paleo-temperature and past environmental conditions from stable isotopes, however, require isotopic equilibrium between the drip water and the precipitating calcium carbonate. Results from Dietzel et al. (1992) and Johnson and Ingram (2001) indicate that the formation of modern travertine and speleothem calcite occurs under isotopic equilibrium. Factors that influence the stable oxygen and carbon isotope composition during speleothem precipitation include e.g. the moisture source and precipitation, photosynthetic pathways, the bedrock proportion, and the drip rate. This often leads to a situation with several variables. However, a specific interpretation is possible when dealing with environments where only one of the factors is dominant, or specific settings are assumed to be invariant, or further proxies like trace element variations help to define the frame conditions during speleothem formation. Concentrations of trace elements (e.g. Sr, Mg) which are co-precipitated with calcite are related to changes in the composition of the solution and strongly depend on the dissolution/precipitation dynamics along drip water flow paths. In a multiproxy approach they are a valuable tool for the interpretation of the recorded stable isotope variations. We present first results from different cave systems located in the Swabian Alps and the Harz Mountains (Germany). Our study includes a high-resolution multiproxy approach, using U/Th-TIMS data, stable oxygen/carbon isotope data, and geochemical compositions of speleothems, covering ages from the Late Pleistocene to the Early Holocene. The results are compared to geochemical data from host rocks, soil zones, cave sediments, drip water compositions, and recent calcium carbonate precipitates. Understanding the response of a cave system to the actual climatic, hydrologic and environmental regimen is a main requirement for the interpretation of "paleo-information" conserved in speleothems in order to lead to a coherent picture of past continental climate dynamics. References: Dietzel M., Usdowski E., and Hoefs J., (1992): Applied Geochemistry 7: 177-184. Johnson, K.R. and Ingram, B.L. (2001): Abstract volume, 4th Internat. Symp. On Applied Isotope Geochemistry, Pacific Groove, USA: 70-72.

Isotope and trace element insights into heterogeneity of subridge mantle

NASA Astrophysics Data System (ADS)

Mallick, Soumen; Dick, Henry J. B.; Sachi-Kocher, Afi; Salters, Vincent J. M.

2014-06-01

Geochemical data for abyssal peridotites are used to determine the relationship to mid-ocean ridge basalts from several locations at ridge segments on the SW Indian Ridge (SWIR), the Mid-Cayman-Rise (MCR), and the Mid-Atlantic Ridge (MAR). Based on chemical and petrological criteria peridotites are categorized as being either dominantly impregnated with melt or being residual after recent melting. Those that are considered impregnated with melt also have isotopic compositions similar to the basalts indicating impregnation by an aggregate MORB melt. A SWIR and MCR residual peridotite Nd-isotopic compositions partly overlap the Nd-isotopic compositions of the basalts but extend to more radiogenic compositions. The differences between peridotite and basalt Nd-isotopic compositions can be explained by incorporating a low-solidus component with enriched isotopic signature in the subridge mantle: a component that is preferentially sampled by the basalts. At the MAR, peridotites and associated basalts have overlapping Nd-isotopic compositions, suggesting a more homogeneous MORB mantle. The combined chemistry and petrography indicates a complex history with several depletion and enrichment events. The MCR data indicate that a low-solidus component can be a ubiquitous component of the asthenosphere. Residual abyssal peridotites from limited geographic areas also show significant chemical variations that could be associated with initial mantle heterogeneities related to events predating the ridge-melting event. Sm-Nd model ages for possible earlier depletion events suggest these could be as old as 2.4 Ga. This article was corrected on 9 JULY 2014. See the end of the full text for details.

Correlated Si isotope anomalies and large C-13 enrichments in a family of exotic SiC grains

NASA Technical Reports Server (NTRS)

Stone, J.; Hutcheon, I. D.; Epstein, S.; Wasserburg, G. J.

1991-01-01

A hypothesis is presented to the effect that the distinctive morphological characteristics and comparatively simple Si isotope systematics identify the platy SiC crystals as a genetically related family, formed around a single isotopically heterogeneous presolar star on an association of related stars. The enrichments in C-13 and the Si isotope systematics of the platy SiC are broadly consistent with theoretical models of nucleosynthesis in low-mass, carbon stars on the ASG. The Si isotope array most plausibly reflects mixing between (Si-28)-rich material, inherited from a previous generation of stars, and material enriched in Si-29 and Si-30, produced in intershell regions by neutron capture during He-burning. The absence of a correlation between the Si and C isotopic compositions of the SiC suggests either episodic condensation of SiC, extending over several thermal pulses, in the atmosphere of a single star, or the derivation of the SiC from several stars characterized by different rates of C-13 production.

Triple Oxygen Isotope Constraints on Seawater δ18O and Temperature

NASA Astrophysics Data System (ADS)

Hayles, J.; Shen, B.; Homann, M.; Yeung, L.

2017-12-01

One point of contention among geoscientists is whether the 18O/16O ratio of seawater is roughly constant, or if it varies considerably throughout geologic time. On one hand, the oxygen isotope composition of the ocean is thought to be well buffered by high- and low-temperature interactions between seawater and seafloor rocks. If these interactions do not vary on billion-year timescales, the oxygen-isotope compositions of marine sedimentary rocks mostly relate to changes in seawater temperature and global ice volume. On the other hand, long-term cooling of the planetary interior would alter these water-rock interactions leading to a secular change in the oxygen isotope composition of seawater. Models suggest that this secular change would enrich seawater with heavy oxygen isotopes over time. In this study, we present new, high precision, triple-oxygen-isotope (18O/16O, 17O/16O) analyses of marine chert samples from 3.45 Ga to 460Ma. The results of these analyses are paired with a new theoretical quartz-water equilibrium curve and a simplified seawater model to provide possible pairings of δ'18O and Δ'17O for the water which these samples could have formed in equilibrium with. Analysis of the new sample data, in addition to published chert triple oxygen isotope compositions, shows a general trend of older chert samples being progressively incompatible with waters possessing a modern-like seawater triple oxygen isotope composition. Implications on constraining the secular evolution of seawater δ18O and temperature will be discussed.

Impact of topography, climate and moisture sources on isotopic composition (δ18O &δD) of rivers in the Pyrenees: Implications for topographic reconstructions in small orogens

NASA Astrophysics Data System (ADS)

Huyghe, Damien; Mouthereau, Frédéric; Sébilo, Mathieu; Vacherat, Arnaud; Ségalen, Loïc; Richard, Patricia; Biron, Philippe; Bariac, Thierry

2018-02-01

Understanding how orogenic topography controls the spatial distribution and isotopic composition of precipitation is critical for paleoaltitudinal reconstructions. Here, we determine the isotopic composition (δ18O and δD) of 82 small rivers and springs from small catchments in the Pyrenees. Calculation of the deuterium excess (d-excess) parameter allows the distinction of four distinct isotopic provinces with d-excess values of between 15 and 22‰ in the northwest, between 7 and 14‰ in the central northern Pyrenees and between 3 and 11‰ in the northeast. The southern Pyrenees have a homogenous d-excess signature ranging from 7 to 14‰. Our results show significant local moisture recycling and/or rain amount effect in the northwestern Pyrenees, and control by evaporation processes during rainfall events in the southern Pyrenees and for low elevated samples of the northeast of the range. Based on the distribution of d-excess values, we estimate contrasting isotope lapse rates of -2.9/-21.4‰/km (δ18O/δD) in the northwest, -2.7/-21.4‰/km (δ18O/δD) in the north central and -3.7/-31.7‰/km (δ18O/δD) in the northeastern Pyrenees. The southern Pyrenees show distinctly higher lapse rates of -9.5/-77.5‰/km (δ18O/δD), indicating that in this area the altitudinal effect in not the only parameter driving isotopic composition of rivers. Despite their relatively low topographic gradient, the Pyrenees exert a direct control on the isotopic composition of river waters, especially on their northern side. The variations in isotopic composition-elevation relationships documented along the strike of the range are interpreted to reflect an increasing continentality effect driven by wind trajectories parallel to the range, and mixing with Mediterranean air masses. Despite these effects, the measurable orographic effect on precipitation in the Pyrenees proves that the isotopic composition approach for reconstructing past topography is applicable to low-elevation orogens.

Hydrogen Isotope Measurements of Organic Acids and Alcohols by Pyrolysis-GC-MS-TC-IRMS

NASA Technical Reports Server (NTRS)

Socki, Richard A.; Fu, Qi; Niles, Paul B.

2011-01-01

One possible process responsible for methane generation on Mars is abiotic formation by Fischer-Tropsch-type (FTT) synthesis during serpentinization reactions. Measurement of carbon and hydrogen isotopes of intermediary organic compounds can help constrain the origin of this methane by tracing the geochemical pathway during formation. Of particular interest within the context of this work is the isotopic composition of organic intermediaries produced on the surfaces of mineral catalysts (i.e. magnetite) during hydrothermal experiments, and the ability to make meaningful and reproducible hydrogen isotope measurements. Reported here are results of experiments to characterize the hydrogen isotope composition of low molecular weight organic acids and alcohols. The presence of these organic compounds has been suggested by others as intermeadiary products made during mineral surface catalyzed reactions. This work compliments our previous study characterizing the carbon isotope composition of similar low molecular weight intermediary organic compounds (Socki, et al, American Geophysical Union Fall meeting, Abstr. #V51B-2189, Dec., 2010). Our hydrogen isotope measurements utilize a unique analytical technique combining Pyrolysis-Gas Chromatograph-Mass Spectrometry-High Temperature Conversion-Isotope Ratio Mass Spectrometry (Py-GC-MS-TC-IRMS). Our technique is unique in that it carries a split of the pyrolyzed GC-separated product to a Thermo DSQ-II? quadrupole mass spectrometer as a means of making qualitative and semi-quantitative compositional measurements of separated organic compounds, therefore both chemical and isotopic measurements can be carried out simultaneously on the same sample.

Isotopic coherence of refractory inclusions from CV and CK meteorites: Evidence from multiple isotope systems

NASA Astrophysics Data System (ADS)

Shollenberger, Quinn R.; Borg, Lars E.; Render, Jan; Ebert, Samuel; Bischoff, Addi; Russell, Sara S.; Brennecka, Gregory A.

2018-05-01

Calcium-aluminum-rich inclusions (CAIs) are the oldest dated materials in the Solar System and numerous previous studies have revealed nucleosynthetic anomalies relative to terrestrial rock standards in many isotopic systems. However, most of the isotopic data from CAIs has been limited to the Allende meteorite and a handful of other CV3 chondrites. To better constrain the isotopic composition of the CAI-forming region, we report the first Sr, Mo, Ba, Nd, and Sm isotopic compositions of two CAIs hosted in the CK3 desert meteorites NWA 4964 and NWA 6254 along with two CAIs from the CV3 desert meteorites NWA 6619 and NWA 6991. After consideration of neutron capture processes and the effects of hot-desert weathering, the Sr, Mo, Ba, Nd, and Sm stable isotopic compositions of the samples show clearly resolvable nucleosynthetic anomalies that are in agreement with previous results from Allende and other CV meteorites. The extent of neutron capture, as manifested by shifts in the observed 149Sm-150Sm isotopic composition of the CAIs is used to estimate the neutron fluence experienced by some of these samples and ranges from 8.40 × 1013 to 2.11 × 1015 n/cm2. Overall, regardless of CAI type or host meteorite, CAIs from CV and CK chondrites have similar nucleosynthetic anomalies within analytical uncertainty. We suggest the region that CV and CK CAIs formed was largely uniform with respect to Sr, Mo, Ba, Nd, and Sm isotopes when CAIs condensed and that CAIs hosted in CV and CK meteorites are derived from the same isotopic reservoir.

Large Carbonate Associated Sulfate isotopic variability between brachiopods, micrite, and other sedimentary components in Late Ordovician strata

NASA Astrophysics Data System (ADS)

Present, Theodore M.; Paris, Guillaume; Burke, Andrea; Fischer, Woodward W.; Adkins, Jess F.

2015-12-01

Carbonate Associated Sulfate (CAS) is trace sulfate incorporated into carbonate minerals during their precipitation. Its sulfur isotopic composition is often assumed to track that of seawater sulfate and inform global carbon and oxygen budgets through Earth's history. However, many CAS sulfur isotope records based on bulk-rock samples are noisy. To determine the source of bulk-rock CAS variability, we extracted CAS from different internal sedimentary components micro-drilled from well-preserved Late Ordovician and early Silurian-age limestones from Anticosti Island, Quebec, Canada. Mixtures of these components, whose sulfur isotopic compositions vary by nearly 25‰, can explain the bulk-rock CAS range. Large isotopic variability of sedimentary micrite CAS (34S-depleted from seawater by up to 15‰) is consistent with pore fluid sulfide oxidation during early diagenesis. Specimens recrystallized during burial diagenesis have CAS 34S-enriched by up to 9‰ from Hirnantian seawater, consistent with microbial sulfate reduction in a confined aquifer. In contrast to the other variable components, brachiopods with well-preserved secondary-layer fibrous calcite-a phase independently known to be the best-preserved sedimentary component in these strata-have a more homogeneous isotopic composition. These specimens indicate that seawater sulfate remained close to about 25‰ (V-CDT) through Hirnantian (end-Ordovician) events, including glaciation, mass extinction, carbon isotope excursion, and pyrite-sulfur isotope excursion. The textural relationships between our samples and their CAS isotope ratios highlight the role of diagenetic biogeochemical processes in setting the isotopic composition of CAS.

Nitrogen isotopes suggest a change in nitrogen dynamics between the Late Pleistocene and modern time in Yukon, Canada

PubMed Central

Longstaffe, Fred J.; Zazula, Grant

2018-01-01

A magnificent repository of Late Pleistocene terrestrial megafauna fossils is contained in ice-rich loess deposits of Alaska and Yukon, collectively eastern Beringia. The stable carbon (δ13C) and nitrogen (δ15N) isotope compositions of bone collagen from these fossils are routinely used to determine paleodiet and reconstruct the paleoecosystem. This approach requires consideration of changes in C- and N-isotope dynamics over time and their effects on the terrestrial vegetation isotopic baseline. To test for such changes between the Late Pleistocene and modern time, we compared δ13C and δ15N for vegetation and bone collagen and structural carbonate of some modern, Yukon, arctic ground squirrels with vegetation and bones from Late Pleistocene fossil arctic ground squirrel nests preserved in Yukon loess deposits. The isotopic discrimination between arctic ground squirrel bone collagen and their diet was measured using modern samples, as were isotopic changes during plant decomposition; Over-wintering decomposition of typical vegetation following senescence resulted in a minor change (~0–1 ‰) in δ13C of modern Yukon grasses. A major change (~2–10 ‰) in δ15N was measured for decomposing Yukon grasses thinly covered by loess. As expected, the collagen-diet C-isotope discrimination measured for modern samples confirms that modern vegetation δ13C is a suitable proxy for the Late Pleistocene vegetation in Yukon Territory, after correction for the Suess effect. The N-isotope composition of vegetation from the fossil arctic ground squirrel nests, however, is determined to be ~2.8 ‰ higher than modern grasslands in the region, after correction for decomposition effects. This result suggests a change in N dynamics in this region between the Late Pleistocene and modern time. PMID:29447202

Where does streamwater come from in low-relief forested watersheds? A dual-isotope approach

DOE Office of Scientific and Technical Information (OSTI.GOV)

Klaus, J.; McDonnell, J. J.; Jackson, C. R.

The time and geographic sources of streamwater in low-relief watersheds are poorly understood. This is partly due to the difficult combination of low runoff coefficients and often damped streamwater isotopic signals precluding traditional hydrograph separation and convolution integral approaches. Here we present a dual-isotope approach involving 18O and 2H of water in a low-angle forested watershed to determine streamwater source components and then build a conceptual model of streamflow generation. We focus on three headwater lowland sub-catchments draining the Savannah River Site in South Carolina, USA. Our results for a 3-year sampling period show that the slopes of the meteoricmore » water lines/evaporation water lines (MWLs/EWLs) of the catchment water sources can be used to extract information on runoff sources in ways not considered before. Our dual-isotope approach was able to identify unique hillslope, riparian and deep groundwater, and streamflow compositions. Thus, the streams showed strong evaporative enrichment compared to the local meteoric water line (δ 2H = 7.15 · δ 18O +9.28‰) with slopes of 2.52, 2.84, and 2.86. Based on the unique and unambiguous slopes of the EWLs of the different water cycle components and the isotopic time series of the individual components, we were able to show how the riparian zone controls baseflow in this system and how the riparian zone "resets" the stable isotope composition of the observed streams in our low-angle, forested watersheds. Although this approach is limited in terms of quantifying mixing percentages between different end-members, our dual-isotope approach enabled the extraction of hydrologically useful information in a region with little change in individual isotope time series.« less

Where does streamwater come from in low-relief forested watersheds? A dual-isotope approach

DOE PAGES

Klaus, J.; McDonnell, J. J.; Jackson, C. R.; ...

2015-01-08

The time and geographic sources of streamwater in low-relief watersheds are poorly understood. This is partly due to the difficult combination of low runoff coefficients and often damped streamwater isotopic signals precluding traditional hydrograph separation and convolution integral approaches. Here we present a dual-isotope approach involving 18O and 2H of water in a low-angle forested watershed to determine streamwater source components and then build a conceptual model of streamflow generation. We focus on three headwater lowland sub-catchments draining the Savannah River Site in South Carolina, USA. Our results for a 3-year sampling period show that the slopes of the meteoricmore » water lines/evaporation water lines (MWLs/EWLs) of the catchment water sources can be used to extract information on runoff sources in ways not considered before. Our dual-isotope approach was able to identify unique hillslope, riparian and deep groundwater, and streamflow compositions. Thus, the streams showed strong evaporative enrichment compared to the local meteoric water line (δ 2H = 7.15 · δ 18O +9.28‰) with slopes of 2.52, 2.84, and 2.86. Based on the unique and unambiguous slopes of the EWLs of the different water cycle components and the isotopic time series of the individual components, we were able to show how the riparian zone controls baseflow in this system and how the riparian zone "resets" the stable isotope composition of the observed streams in our low-angle, forested watersheds. Although this approach is limited in terms of quantifying mixing percentages between different end-members, our dual-isotope approach enabled the extraction of hydrologically useful information in a region with little change in individual isotope time series.« less

Nitrogen isotopes suggest a change in nitrogen dynamics between the Late Pleistocene and modern time in Yukon, Canada.

PubMed

Tahmasebi, Farnoush; Longstaffe, Fred J; Zazula, Grant

2018-01-01

A magnificent repository of Late Pleistocene terrestrial megafauna fossils is contained in ice-rich loess deposits of Alaska and Yukon, collectively eastern Beringia. The stable carbon (δ13C) and nitrogen (δ15N) isotope compositions of bone collagen from these fossils are routinely used to determine paleodiet and reconstruct the paleoecosystem. This approach requires consideration of changes in C- and N-isotope dynamics over time and their effects on the terrestrial vegetation isotopic baseline. To test for such changes between the Late Pleistocene and modern time, we compared δ13C and δ15N for vegetation and bone collagen and structural carbonate of some modern, Yukon, arctic ground squirrels with vegetation and bones from Late Pleistocene fossil arctic ground squirrel nests preserved in Yukon loess deposits. The isotopic discrimination between arctic ground squirrel bone collagen and their diet was measured using modern samples, as were isotopic changes during plant decomposition; Over-wintering decomposition of typical vegetation following senescence resulted in a minor change (~0-1 ‰) in δ13C of modern Yukon grasses. A major change (~2-10 ‰) in δ15N was measured for decomposing Yukon grasses thinly covered by loess. As expected, the collagen-diet C-isotope discrimination measured for modern samples confirms that modern vegetation δ13C is a suitable proxy for the Late Pleistocene vegetation in Yukon Territory, after correction for the Suess effect. The N-isotope composition of vegetation from the fossil arctic ground squirrel nests, however, is determined to be ~2.8 ‰ higher than modern grasslands in the region, after correction for decomposition effects. This result suggests a change in N dynamics in this region between the Late Pleistocene and modern time.

δ2H isotopic flux partitioning of evapotranspiration over a grass field following a water pulse and subsequent dry down

NASA Astrophysics Data System (ADS)

Good, Stephen P.; Soderberg, Keir; Guan, Kaiyu; King, Elizabeth G.; Scanlon, Todd M.; Caylor, Kelly K.

2014-02-01

The partitioning of surface vapor flux (FET) into evaporation (FE) and transpiration (FT) is theoretically possible because of distinct differences in end-member stable isotope composition. In this study, we combine high-frequency laser spectroscopy with eddy covariance techniques to critically evaluate isotope flux partitioning of FET over a grass field during a 15 day experiment. Following the application of a 30 mm water pulse, green grass coverage at the study site increased from 0 to 10% of ground surface area after 6 days and then began to senesce. Using isotope flux partitioning, transpiration increased as a fraction of total vapor flux from 0% to 40% during the green-up phase, after which this ratio decreased while exhibiting hysteresis with respect to green grass coverage. Daily daytime leaf-level gas exchange measurements compare well with daily isotope flux partitioning averages (RMSE = 0.0018 g m-2 s-1). Overall the average ratio of FT to FET was 29%, where uncertainties in Keeling plot intercepts and transpiration composition resulted in an average of uncertainty of ˜5% in our isotopic partitioning of FET. Flux-variance similarity partitioning was partially consistent with the isotope-based approach, with divergence occurring after rainfall and when the grass was stressed. Over the average diurnal cycle, local meteorological conditions, particularly net radiation and relative humidity, are shown to control partitioning. At longer time scales, green leaf area and available soil water control FT/FET. Finally, we demonstrate the feasibility of combining isotope flux partitioning and flux-variance similarity theory to estimate water use efficiency at the landscape scale.

Methylmercury degradation and exposure pathways in streams and wetlands impacted by historical mining.

PubMed

Donovan, Patrick M; Blum, Joel D; Singer, Michael Bliss; Marvin-DiPasquale, Mark; Tsui, Martin T K

2016-10-15

Monomethyl mercury (MMHg) and total mercury (THg) concentrations and Hg stable isotope ratios (δ(202)Hg and Δ(199)Hg) were measured in sediment and aquatic organisms from Cache Creek (California Coast Range) and Yolo Bypass (Sacramento Valley). Cache Creek sediment had a large range in THg (87 to 3870ng/g) and δ(202)Hg (-1.69 to -0.20‰) reflecting the heterogeneity of Hg mining sources in sediment. The δ(202)Hg of Yolo Bypass wetland sediment suggests a mixture of high and low THg sediment sources. Relationships between %MMHg (the percent ratio of MMHg to THg) and Hg isotope values (δ(202)Hg and Δ(199)Hg) in fish and macroinvertebrates were used to identify and estimate the isotopic composition of MMHg. Deviation from linear relationships was found between %MMHg and Hg isotope values, which is indicative of the bioaccumulation of isotopically distinct pools of MMHg. The isotopic composition of pre-photodegraded MMHg (i.e., subtracting fractionation from photochemical reactions) was estimated and contrasting relationships were observed between the estimated δ(202)Hg of pre-photodegraded MMHg and sediment IHg. Cache Creek had mass dependent fractionation (MDF; δ(202)Hg) of at least -0.4‰ whereas Yolo Bypass had MDF of +0.2 to +0.5‰. This result supports the hypothesis that Hg isotope fractionation between IHg and MMHg observed in rivers (-MDF) is unique compared to +MDF observed in non-flowing water environments such as wetlands, lakes, and the coastal ocean. Copyright © 2016 Elsevier B.V. All rights reserved.

Methylmercury degradation and exposure pathways in streams and wetlands impacted by historical mining

USGS Publications Warehouse

Donovan, Patrick M.; Blum, Joel D.; Singer, Michael B.; Marvin-DiPasquale, Mark C.; Tsui, Martin T.K.

2016-01-01

Monomethyl mercury (MMHg) and total mercury (THg) concentrations and Hg stable isotope ratios (δ202Hg and Δ199Hg) were measured in sediment and aquatic organisms from Cache Creek (California Coast Range) and Yolo Bypass (Sacramento Valley). Cache Creek sediment had a large range in THg (87 to 3870 ng/g) and δ202Hg (−1.69 to −0.20‰) reflecting the heterogeneity of Hg mining sources in sediment. The δ202Hg of Yolo Bypass wetland sediment suggests a mixture of high and low THg sediment sources. Relationships between %MMHg (the percent ratio of MMHg to THg) and Hg isotope values (δ202Hg and Δ199Hg) in fish and macroinvertebrates were used to identify and estimate the isotopic composition of MMHg. Deviation from linear relationships was found between %MMHg and Hg isotope values, which is indicative of the bioaccumulation of isotopically distinct pools of MMHg. The isotopic composition of pre-photodegraded MMHg (i.e., subtracting fractionation from photochemical reactions) was estimated and contrasting relationships were observed between the estimated δ202Hg of pre-photodegraded MMHg and sediment IHg. Cache Creek had mass dependent fractionation (MDF; δ202Hg) of at least −0.4‰ whereas Yolo Bypass had MDF of +0.2 to +0.5‰. This result supports the hypothesis that Hg isotope fractionation between IHg and MMHg observed in rivers (−MDF) is unique compared to +MDF observed in non-flowing water environments such as wetlands, lakes, and the coastal ocean.

Investigation of Chemical and Physical Changes to Bioapatite During Fossilization Using Trace Element Geochemistry, Infrared Spectroscopy and Stable Isotopes

NASA Astrophysics Data System (ADS)

Suarez, C. A.; Kohn, M. J.

2013-12-01

Bioapatite in the form of vertebrate bone can be used for a wide variety of paleo-proxies, from determination of ancient diet to the isotopic composition of meteoric water. Bioapatite alteration during diagenesis is a constant barrier to the use of fossil bone as a paleo-proxy. To elucidate the physical and chemical alteration of bone apatite during fossilization, we analyzed an assortment of fossil bones of different ages for trace elements, using LA-ICP-MS, stable isotopes, and reflected IR spectroscopy. One set of fossil bones from the Pleistocene of Idaho show a diffusion recrystallization profile, however, rare earth element (REE) profiles indicate diffusion adsorption. This suggests that REE diffusion is controlled by changing (namely decreasing) boundary conditions (i.e. decreasing concentration of REE in surrounding pore fluids). Reflected IR analysis along this concentration profile reveal that areas high in U have lost type A carbonate from the crystal structure in addition to water and organics. Stable isotopic analysis of carbon and oxygen will determine what, if any, change in the isotopic composition of the carbonate component of apatite has occurred do to the diffusion and recrystallization process. Analysis of much older bone from the Cretaceous of China reveal shallow REE and U concentration profiles and very uniform reflected IR spectra with a significant loss of type A carbonate throughout the entire bone cortex. Analysis of stable isotopes through the bone cortex will be compared to the stable isotopes collected from the Pleistocene of Idaho.

Bioconversion of Coal: Hydrologic indicators of the extent of coal biodegradation under different redox conditions and coal maturity, Velenje Basin case study, Slovenia

NASA Astrophysics Data System (ADS)

Kanduč, Tjaša; Grassa, Fausto; Lazar, Jerneja; Jamnikar, Sergej; Zavšek, Simon; McIntosh, Jennifer

2014-05-01

Underground mining of coal and coal combustion for energy has significant environmental impacts. In order to reduce greenhouse gas emissions, other lower -carbon energy sources must be utilized. Coalbed methane (CBM) is an important source of relatively low-carbon energy. Approximately 20% of world's coalbed methane is microbial in origin (Bates et al., 2011). Interest in microbial CBM has increased recently due to the possibility of stimulating methanogenesis. Despite increasing interest, the hydrogeochemical conditions and mechanisms for biodegradation of coal and microbial methane production are poorly understood. This project aims to examine geochemical characteristics of coalbed groundwater and coalbed gases in order to constrain biogeochemical processes to better understand the entire process of coal biodegradation of coal to coalbed gases. A better understanding of geochemical processes in CBM areas may potentially lead to sustainable stimulation of microbial methanogenesis at economical rates. Natural analogue studies of carbon dioxide occurring in the subsurface have the potential to yield insights into mechanisms of carbon dioxide storage over geological time scales (Li et al., 2013). In order to explore redox processes related to methanogenesis and determine ideal conditions under which microbial degradation of coal is likely to occur, this study utilizes groundwater and coalbed gas samples from Velenje Basin. Determination of the concentrations of methane, carbondioxide, nitrogen, oxygen, argon was performed with homemade NIER mass spectrometer. Isotopic composition of carbon dioxide, isotopic composition of methane, isotopic composition of deuterium in methane was determined with Europa-Scientific IRMS with an ANCA-TG preparation module and Thermo Delta XP GC-TC/CF-IRMS coupled to a TRACE GC analyzer. Total alkalinity of groundwater was measured by Gran titration. Major cations were analyzed by ICP-OES and anions by IC method. Isotopic composition of dissolved inorganic carbon was determined by MultiflowBio preparation module. The stable isotope composition of sulphur was determined with a Europa Scientific 20-20 continuous flow IRMS ANCA-SL preparation module. Concentrations of tritium were determined with the electrolytic enrichment method. PHREEQC for Windows was used to perform thermodynamic modelling. The average coalbed gas composition in the coalbed seam is approximately carbon dioxide: methane > 2:1, where a high proportion of CO2 is adsorbed on the lignite structure, while methane is present free in coal fractures. It can be concluded that isotopic composition of carbon in methane from -70.4‰ to -50.0‰ is generated via acetate fermentation and via reduction of carbon dioxide, while isotopic composition of carbon in methane values range from -50.0‰ to -18.8‰, thermogenic methane can be explained by secondary processes, causing enrichment of residual methane with the heavier carbon isotope. Isotopic composition of deuterium in methane range from -343.9‰ to -223.1‰. Isotopic composition of carbon in carbon dioxide values at excavation fields range from -11.0‰ to +5‰ and are endogenic and microbial in origin. The major ion chemistry, redox conditions, stable isotopes and tritium measured in groundwater from the Velenje Basin, suggest that the Pliocene and Triassic aquifers contain distinct water bodies. Groundwater in the Triassic aquifer is dominated by hydrogen carbonate, calcium, magnesium and isotopic composition of dissolved inorganic carbon indicating degradation of soil organic matter and dissolution of carbonate minerals, similar to surface waters. In addition, groundwater in the Triassic aquifer has isotopic composition of oxygen and isotopic composition of deuterium values which plot near surface waters on the local and global meteoric water lines and detectable tritium reflects recent recharge. In contrast, groundwater in the Pliocene aquifers is enriched in magnesium, sodium, calcium, potassium, and silica and has alkalinity and isotopic composition of dissolved inorganic carbon values with low sulphate and nitrate concentrations. These waters have likely been influenced by sulfate reduction and microbial methanogenesis associated with coal seams and dissolution of feldspars and magnesium-rich clay minerals. Pliocene aquifer waters are also depleted in heavier oxygen isotope and heavier deuterium isotope and have tritium concentrations near the detection limit, suggesting these waters are older. References Bates, B.L., McIntosh J.C., Lohse K.A., Brooks P.D. 2011: Influence of groundwater flowpaths, residence times, and nutrients on the extent of microbial methanogenesis in coal beds: Powder River Basin, USA, Chemical geology, 284, 45-61. Li, W., Cheng Y., Wang L., Zhou H., Wang H., Wang L. 2013: Evaluating the security of geological coalbed sequestration of supercritical CO2 reservoirs: The Haishiwan coalfield, China as a natural analogue, International Journal of Greenhouse Gas Control, 13, 102-111.

Real-time measurements of the concentration and isotope composition of atmospheric and volcanic CO2 at Mount Etna (Italy)

NASA Astrophysics Data System (ADS)

Rizzo, Andrea Luca; Jost, Hans-Jürg; Caracausi, Antonio; Paonita, Antonio; Liotta, Marcello; Martelli, Mauro

2014-04-01

We present unprecedented data of real-time measurements of the concentration and isotope composition of CO2 in air and in fumarole-plume gases collected in 2013 during two campaigns at Mount Etna volcano, which were made using a laser-based isotope ratio infrared spectrometer. We performed approximately 360 measurements/h, which allowed calculation of the δ13C values of volcanic CO2. The fumarole gases of Torre del Filosofo (2900 m above sea level) range from -3.24 ± 0.06‰ to -3.71 ± 0.09‰, comparable to isotope ratio mass spectrometry (IRMS) measurements of discrete samples collected on the same dates. Plume gases sampled more than 1 km from the craters show a δ13C = -2.2 ± 0.4‰, in agreement with the crater fumarole gases analyzed by IRMS. Measurements performed along ~17 km driving track from Catania to Mount Etna show more negative δ13C values when passing through populated centers due to anthropogenic-derived CO2 inputs (e.g., car exhaust). The reported results demonstrate that this technique may represent an important advancement for volcanic and environmental monitoring.

Atmospheric CO2 effect on stable carbon isotope composition of terrestrial fossil archives.

PubMed

Hare, Vincent J; Loftus, Emma; Jeffrey, Amy; Ramsey, Christopher Bronk

2018-01-17

The 13 C/ 12 C ratio of C 3 plant matter is thought to be controlled by the isotopic composition of atmospheric CO 2 and stomatal response to environmental conditions, particularly mean annual precipitation (MAP). The effect of CO 2 concentration on 13 C/ 12 C ratios is currently debated, yet crucial to reconstructing ancient environments and quantifying the carbon cycle. Here we compare high-resolution ice core measurements of atmospheric CO 2 with fossil plant and faunal isotope records. We show the effect of pCO 2 during the last deglaciation is stronger for gymnosperms (-1.4 ± 1.2‰) than angiosperms/fauna (-0.5 ± 1.5‰), while the contributions from changing MAP are -0.3 ± 0.6‰ and -0.4 ± 0.4‰, respectively. Previous studies have assumed that plant 13 C/ 12 C ratios are mostly determined by MAP, an assumption which is sometimes incorrect in geological time. Atmospheric effects must be taken into account when interpreting terrestrial stable carbon isotopes, with important implications for past environments and climates, and understanding plant responses to climate change.

Sulfur isotope analysis of cinnabar from Roman wall paintings by elemental analysis/isotope ratio mass spectrometry--tracking the origin of archaeological red pigments and their authenticity.

PubMed

Spangenberg, Jorge E; Lavric, Jost V; Meisser, Nicolas; Serneels, Vincent

2010-10-15

The most valuable pigment of the Roman wall paintings was the red color obtained from powdered cinnabar (Minium Cinnabaris pigment), the red mercury sulfide (HgS), which was brought from mercury (Hg) deposits in the Roman Empire. To address the question of whether sulfur isotope signatures can serve as a rapid method to establish the provenance of the red pigment in Roman frescoes, we have measured the sulfur isotope composition (δ(34)S value in ‰ VCDT) in samples of wall painting from the Roman city Aventicum (Avenches, Vaud, Switzerland) and compared them with values from cinnabar from European mercury deposits (Almadén in Spain, Idria in Slovenia, Monte Amiata in Italy, Moschellandsberg in Germany, and Genepy in France). Our study shows that the δ(34)S values of cinnabar from the studied Roman wall paintings fall within or near to the composition of Almadén cinnabar; thus, the provenance of the raw material may be deduced. This approach may provide information on provenance and authenticity in archaeological, restoration and forensic studies of Roman and Greek frescoes. Copyright © 2010 John Wiley & Sons, Ltd.

Noble gases in the moon

NASA Technical Reports Server (NTRS)

Manuel, O. K.; Srinivasan, B.; Hennecke, E. W.; Sinclair, D. E.

1972-01-01

The abundance and isotopic composition of helium, neon, argon, krypton, and xenon which were released by stepwise heating of lunar fines (15601.64) and (15271.65) were measured spectrometrically. The results of a composition of noble gases released from the lunar fines with noble gases in meteorites and in the earth are presented along with the isotopic composition of noble gases in lunar fines, in meteorites, and in the atmosphere. A study of two isotopically distinct components of trapped xenon in carbonaceous chondrites is also included.

Stable Isotope Characteristics of Jarosite: The Acidic Aqueous History of Mars

NASA Technical Reports Server (NTRS)

Earl, Lyndsey D.

2005-01-01

The Mars Rover Opportunity found jarosite (Na(+) or K(+))Fe3SO4(OH)6 at the Meridiani Planum site. This mineral forms from the evaporation of an aqueous acidic sulfate brine. Oxygen isotope compositions may characterize formation conditions but subsequent isotope exchange may have occurred between the sulfate and hydroxide of jarosite and water. The rate of oxygen isotope exchange depends on the acidity and temperature of the brine, but it has not been investigated in detail. We performed laboratory experiments to determine the rate of oxygen isotope exchange under varying acidities and temperatures to learn more about this process. Barium sulfate samples were precipitated weekly from acidic sodium sulfate brines. The oxygen isotope composition of the precipitated sulfate was obtained using a Finnigan MAT253 Isotope Ratio Mass-Spectrometer. The results show that water was trapped in barium sulfate during precipitation. Trapped water may exchange with sulfate when exposed to high temperatures, thus changing the isotope composition of sulfate and the observed fractionation factor of oxygen isotope exchange between sulfate and water. The results of our research will contribute to the understanding of oxygen isotope exchange rates between water and sulfate under acidic conditions and provide experimental knowledge for the dehydration of barium sulfate samples.

Experimental investigation on the carbon isotope fractionation of methane during gas migration by diffusion through sedimentary rocks at elevated temperature and pressure

NASA Astrophysics Data System (ADS)

Zhang, Tongwei; Krooss, Bernhard M.

2001-08-01

Molecular transport (diffusion) of methane in water-saturated sedimentary rocks results in carbon isotope fractionation. In order to quantify the diffusive isotope fractionation effect and its dependence on total organic carbon (TOC) content, experimental measurements have been performed on three natural shale samples with TOC values ranging from 0.3 to 5.74%. The experiments were conducted at 90°C and fluid pressures of 9 MPa (90 bar). Based on the instantaneous and cumulative composition of the diffused methane, effective diffusion coefficients of the 12CH4 and 13CH4 species, respectively, have been calculated. Compared with the carbon isotopic composition of the source methane (δ13C1 = -39.1‰), a significant depletion of the heavier carbon isotope (13C) in the diffused methane was observed for all three shales. The degree of depletion is highest during the initial non-steady state of the diffusion process. It then gradually decreases and reaches a constant difference (Δ δ = δ13Cdiff -δ13Csource) when approaching the steady-state. The degree of the isotopic fractionation of methane due to molecular diffusion increases with the TOC content of the shales. The carbon isotope fractionation of methane during molecular migration results practically exclusively from differences in molecular mobility (effective diffusion coefficients) of the 12CH4 and 13CH4 entities. No measurable solubility fractionation was observed. The experimental isotope-specific diffusion data were used in two hypothetical scenarios to illustrate the extent of isotopic fractionation to be expected as a result of molecular transport in geological systems with shales of different TOC contents. The first scenario considers the progression of a diffusion front from a constant source (gas reservoir) into a homogeneous ;semi-infinite; shale caprock over a period of 10 Ma. In the second example, gas diffusion across a 100 m caprock sequence is analyzed in terms of absolute quantities and isotope fractionation effects. The examples demonstrate that methane losses by molecular diffusion are small in comparison with the contents of commercial size gas accumulations. The degree of isotopic fractionation is related inversely to the quantity of diffused gas so that strong fractionation effects are only observed for relatively small portions of gas. The experimental data can be readily used in numerical basin analysis to examine the effects of diffusion-related isotopic fractionation on the composition of natural gas reservoirs.

Geochemical and iron isotopic insights into hydrothermal iron oxyhydroxide deposit formation at Loihi Seamount

NASA Astrophysics Data System (ADS)

Rouxel, Olivier; Toner, Brandy; Germain, Yoan; Glazer, Brian

2018-01-01

Low-temperature hydrothermal vents, such as those encountered at Loihi Seamount, harbor abundant microbial communities and provide ideal systems to test hypotheses on biotic versus abiotic formation of hydrous ferric oxide (FeOx) deposits at the seafloor. Hydrothermal activity at Loihi Seamount produces abundant microbial mats associated with rust-colored FeOx deposits and variably encrusted with Mn-oxyhydroxides. Here, we applied Fe isotope systematics together with major and trace element geochemistry to study the formation mechanisms and preservation of such mineralized microbial mats. Iron isotope composition of warm (<60 °C), Fe-rich and H2S-depleted hydrothermal fluids yielded δ56Fe values near +0.1‰, indistinguishable from basalt values. Suspended particles in the vent fluids and FeOx deposits recovered nearby active vents yielded systematically positive δ56Fe values. The enrichment in heavy Fe isotopes between +1.05‰ and +1.43‰ relative to Fe(II) in vent fluids suggest partial oxidation of Fe(II) during mixing of the hydrothermal fluid with seawater. By comparing the results with experimentally determined Fe isotope fractionation factors, we determined that less than 20% of Fe(II) is oxidized within active microbial mats, although this number may reach 80% in aged or less active deposits. These results are consistent with Fe(II) oxidation mediated by microbial processes considering the expected slow kinetics of abiotic Fe oxidation in low oxygen bottom water at Loihi Seamount. In contrast, FeOx deposits recovered at extinct sites have distinctly negative Fe-isotope values down to -1.77‰ together with significant enrichment in Mn and occurrence of negative Ce anomalies. These results are best explained by the near-complete oxidation of an isotopically light Fe(II) source produced during the waning stage of hydrothermal activity under more oxidizing conditions. Light Fe isotope values of FeOx are therefore generated by subsurface precipitation of isotopically heavy Fe-oxides rather than by the activity of dissimilatory Fe reduction in the subsurface. Overall, Fe-isotope compositions of microbial mats at Loihi Seamount display a remarkable range between -1.2‰ and +1.6‰ which indicate that Fe isotope compositions of hydrothermal Fe-oxide precipitates are particularly sensitive to local environmental conditions where they form, and are less sensitive to abiotic versus biotic origins. It follows that FeOx deposits at Loihi Seamount provides important modern analogues for ancient seafloor Fe-rich deposits allowing for testing hypotheses about the biogeochemical cycling of Fe isotopes on early Earth.

Thallium-isotopic compositions of euxinic sediments as a proxy for global manganese-oxide burial

NASA Astrophysics Data System (ADS)

Owens, Jeremy D.; Nielsen, Sune G.; Horner, Tristan J.; Ostrander, Chadlin M.; Peterson, Larry C.

2017-09-01

Thallium (Tl) isotopes are a new and potentially powerful paleoredox proxy that may track bottom water oxygen conditions based on the global burial flux of manganese oxides. Thallium has a residence time of ∼20 thousand years, which is longer than the ocean mixing time, and it has been inferred that modern oxic seawater is conservative with respect to both concentration and isotopes. Marine sources of Tl have nearly identical isotopic values. Therefore, the Tl sinks, adsorption onto manganese oxides and low temperature oceanic crust alteration (the dominant seawater output), are the primary controls of the seawater isotopic composition. For relatively short-term, ∼million years, redox events it is reasonable to assume that the dominant mechanism that alters the Tl isotopic composition of seawater is associated with manganese oxide burial because large variability in low temperature ocean crust alteration is controlled by long-term, multi-million years, average ocean crust production rates. This study presents new Tl isotope data for an open ocean transect in the South Atlantic, and depth transects for two euxinic basins (anoxic and free sulfide in the water column), the Cariaco Basin and Black Sea. The Tl isotopic signature of open ocean seawater in the South Atlantic was found to be homogeneous with ε205Tl = -6.0 ± 0.3 (±2 SD, n = 41) while oxic waters from Cariaco and the Black Sea are -5.6 and -2.2, respectively. Combined with existing data from the Pacific and Arctic Oceans, our Atlantic data establish the conservatism of Tl isotopes in the global ocean. In contrast, partially- and predominantly-restricted basins reveal Tl isotope differences that vary between open-ocean (-6) and continental material (-2) ε205Tl, scaling with the degree of restriction. Regardless of the differences between basins, Tl is quantitatively removed from their euxinic waters below the chemocline. The burial of Tl in euxinic sediments is estimated to be an order of magnitude less than each of the modern ocean outputs and imparts no isotopic fractionation. Thallium removal into pyrite appears to be associated with a small negative fractionation between -1 and -3 ε205Tl, which renders Tl-depleted waters below the chemocline enriched in isotopically-heavy Tl. Due to the quantitative removal of Tl from euxinic seawater, Tl isotope analyses of the authigenic fraction of underlying euxinic sediments from both the Black Sea and Cariaco Basin capture the Tl isotope value of the oxic portion of their respective water column with no net isotope fractionation. Since the Tl isotope composition of seawater is largely dictated by the relative fraction of Mn-oxide burial versus oceanic crust alteration, we contend that the Tl isotope composition of authigenic Tl in black shales, deposited under euxinic conditions but well-connected to the open ocean, can be utilized to reconstruct the Tl isotope composition of seawater, and thus to reconstruct the global history of Mn-oxide burial.

Iron isotope composition of particles produced by UV-femtosecond laser ablation of natural oxides, sulfides, and carbonates.

PubMed

d'Abzac, Francois-Xavier; Beard, Brian L; Czaja, Andrew D; Konishi, Hiromi; Schauer, James J; Johnson, Clark M

2013-12-17

The need for femtosecond laser ablation (fs-LA) systems coupled to MC-ICP-MS to accurately perform in situ stable isotope analyses remains an open question, because of the lack of knowledge concerning ablation-related isotopic fractionation in this regime. We report the first iron isotope analysis of size-resolved, laser-induced particles of natural magnetite, siderite, pyrrhotite, and pyrite, collected through cascade impaction, followed by analysis by solution nebulization MC-ICP-MS, as well as imaging using electron microscopy. Iron mass distributions are independent of mineralogy, and particle morphology includes both spheres and agglomerates for all ablated phases. X-ray spectroscopy shows elemental fractionation in siderite (C-rich agglomerates) and pyrrhotite/pyrite (S-rich spheres). We find an increase in (56)Fe/(54)Fe ratios of +2‰, +1.2‰, and +0.8‰ with increasing particle size for magnetite, siderite, and pyrrhotite, respectively. Fe isotope differences in size-sorted aerosols from pyrite ablation are not analytically resolvable. Experimental data are discussed using models of particles generation by Hergenröder and elemental/isotopic fractionation by Richter. We interpret the isotopic fractionation to be related to the iron condensation time scale, dependent on its saturation in the gas phase, as a function of mineral composition. Despite the isotopic variations across aerosol size fractions, total aerosol composition, as calculated from mass balance, confirms that fs-LA produces a stoichiometric sampling in terms of isotopic composition. Specifically, both elemental and isotopic fractionation are produced by particle generation processes and not by femtosecond laser-matter interactions. These results provide critical insights into the analytical requirements for laser-ablation-based stable isotope measurements of high-precision and accuracy in geological samples, including the importance of quantitative aerosol transport to the ICP.

On the equilibrium isotopic composition of the thorium-uranium-plutonium fuel cycle

NASA Astrophysics Data System (ADS)

Marshalkin, V. Ye.; Povyshev, V. M.

2016-12-01

The equilibrium isotopic compositions and the times to equilibrium in the process of thorium-uranium-plutonium oxide fuel recycling in VVER-type reactors using heavy water mixed with light water are estimated. It is demonstrated thEhfat such reactors have a capacity to operate with self-reproduction of active isotopes in the equilibrium mode.

On the equilibrium isotopic composition of the thorium–uranium–plutonium fuel cycle

DOE Office of Scientific and Technical Information (OSTI.GOV)

Marshalkin, V. Ye., E-mail: marshalkin@vniief.ru; Povyshev, V. M.

2016-12-15

The equilibrium isotopic compositions and the times to equilibrium in the process of thorium–uranium–plutonium oxide fuel recycling in VVER-type reactors using heavy water mixed with light water are estimated. It is demonstrated thEhfat such reactors have a capacity to operate with self-reproduction of active isotopes in the equilibrium mode.

Optimized slice-selective 1H NMR experiments combined with highly accurate quantitative 13C NMR using an internal reference method

NASA Astrophysics Data System (ADS)

Jézéquel, Tangi; Silvestre, Virginie; Dinis, Katy; Giraudeau, Patrick; Akoka, Serge

2018-04-01

Isotope ratio monitoring by 13C NMR spectrometry (irm-13C NMR) provides the complete 13C intramolecular position-specific composition at natural abundance. It represents a powerful tool to track the (bio)chemical pathway which has led to the synthesis of targeted molecules, since it allows Position-specific Isotope Analysis (PSIA). Due to the very small composition range (which represents the range of variation of the isotopic composition of a given nuclei) of 13C natural abundance values (50‰), irm-13C NMR requires a 1‰ accuracy and thus highly quantitative analysis by 13C NMR. Until now, the conventional strategy to determine the position-specific abundance xi relies on the combination of irm-MS (isotopic ratio monitoring Mass Spectrometry) and 13C quantitative NMR. However this approach presents a serious drawback since it relies on two different techniques and requires to measure separately the signal of all the carbons of the analyzed compound, which is not always possible. To circumvent this constraint, we recently proposed a new methodology to perform 13C isotopic analysis using an internal reference method and relying on NMR only. The method combines a highly quantitative 1H NMR pulse sequence (named DWET) with a 13C isotopic NMR measurement. However, the recently published DWET sequence is unsuited for samples with short T1, which forms a serious limitation for irm-13C NMR experiments where a relaxing agent is added. In this context, we suggest two variants of the DWET called Multi-WET and Profiled-WET, developed and optimized to reach the same accuracy of 1‰ with a better immunity towards T1 variations. Their performance is evaluated on the determination of the 13C isotopic profile of vanillin. Both pulse sequences show a 1‰ accuracy with an increased robustness to pulse miscalibrations compared to the initial DWET method. This constitutes a major advance in the context of irm-13C NMR since it is now possible to perform isotopic analysis with high relaxing agent concentrations, leading to a strong reduction of the overall experiment time.

Reinterpreting the Early Cretaceous Sulfur Isotope Records: Implications for the Evolution of Seawater Chemistry

NASA Astrophysics Data System (ADS)

Mills, J. V.; Gomes, M. L.; Sageman, B. B.; Jacobson, A. D.; Hurtgen, M. T.

2013-12-01

The geologic record of the Cretaceous is punctuated by several periods of high organic carbon burial interpreted to represent global Ocean Anoxic Events (OAEs). In addition to the short-term (<1-Myr) changes in carbon (C) cycling associated with OAEs, evidence from a number of geochemical proxies has been interpreted to represent large-scale changes in ocean chemistry during the period. Specifically, the sulfur (S) isotope composition of early Cretaceous seawater sulfate as recorded in marine barite exhibits an ~5 permil shift in d34Ssulfate that persists for ~15Myr before returning to pre-excursion values. Superimposed upon this long-term shift in S-isotopes is OAE1a, the second major anoxic event recognized in the Cretaceous. Two hypotheses have been proposed to explain this S isotope perturbation: (1) massive evaporite deposition associated with rifting during the opening of the South Atlantic and a corresponding decrease in pyrite burial rates and (2) increased inputs of volcanic-derived S due to extensive LIP-volcanism. While there is geologic evidence for both evaporite deposition and enhanced hydrothermal activity, the relative influence of these potential driving factors remains largely unconstrained. Variation in the strontium (Sr) isotope composition of marine carbonates provides a tool for distinguishing between these influences. We examine the S isotope composition of carbonate-associated sulfate (CAS) spanning the Barremian through Aptian from Resolution Guyot (ODP Site 866) and compare the S isotope record to time equivalent records of carbon and strontium isotopes. Correlative changes in the C, S, and Sr cycles are observed: an ~5 permil shift in d34Ssulfate, which begins at the onset of OAE1a and continues after the positive d13Ccarb excursion, is accompanied by a contemporaneous, parallel shift in 87Sr/86Sr to unradiogenic values. The tight coupling observed between S and Sr throughout the interval is highly suggestive of a common driving mechanism and suggests that changes in the S-cycle were dominantly driven by increases in volcanism and hydrothermal activity. Constraints on S-cycle fluxes and implications for seawater chemistry will be discussed in the context of coupled S-Sr geochemical models.

Multiple sources supply eolian mineral dust to the Atlantic sector of coastal Antarctica: Evidence from recent snow layers at the top of Berkner Island ice sheet

NASA Astrophysics Data System (ADS)

Bory, Aloys; Wolff, Eric; Mulvaney, Robert; Jagoutz, Emil; Wegner, Anna; Ruth, Urs; Elderfield, Harry

2010-03-01

The Sr and Nd isotopic composition of dust extracted from recent snow layers at the top of Berkner Island ice sheet (located within the Filchner-Ronne Ice Shelf at the southern end of the Weddell Sea) enables us, for the first time, to document dust provenance in Antarctica outside the East Antarctic Plateau (EAP) where all previous studies based on isotopic fingerprinting were carried out. Berkner dust displays an overall crust-like isotopic signature, characterized by more radiogenic 87Sr/ 86Sr and much less radiogenic 143Nd/ 144Nd compared to dust deposited on the EAP during glacial periods. Differences with EAP interglacial dust are not as marked but still significant, indicating that present-day Berkner dust provenance is distinct, at least to some extent, from that of the dust reaching the EAP. The fourteen snow-pit sub-seasonal samples that were obtained span a two-year period (2002-2003) and their dust Sr and Nd isotopic composition reveals that multiple sources are at play over a yearly time period. Southern South America, Patagonia in particular, likely accounts for part of the observed spring/summer dust deposition maxima, when isotopic composition is shifted towards "younger" isotopic signatures. In the spring, possible additional inputs from Australian sources would also be supported by the data. Most of the year, however, the measured isotopic signatures would be best explained by a sustained background supply from putative local sources in East Antarctica, which carry old-crust-like isotopic fingerprints. Whether the restricted East Antarctic ice-free areas produce sufficient eolian material has yet to be substantiated however. The fact that large (> 5 μm) particles represent a significant fraction of the samples throughout the entire time-series supports scenarios that involve contributions from proximal sources, either in Patagonia and/or Antarctica (possibly including snow-free areas in the Antarctic Peninsula and other areas as well). This also indicates that additional dust transport, which does not reach the EAP, must occur at low-tropospheric levels to this coastal sector of Antarctica.

Methane transport mechanisms and isotopic fractionation in emergent macrophytes of an Alaskan tundra lake

NASA Technical Reports Server (NTRS)

Chanton, Jeffrey P.; Martens, Christopher S.; Kelley, Cheryl A.; Crill, Patrick M.; Showers, William J.

1992-01-01

The stable carbon isotopic composition of methane associated with and emitted by the two dominant emergent macrophytes abundant in the many Alaskan tundra lakes, Carex rostrata and Arctophila fulva, is determined. The carbon isotopic composition of the methane was -58.6 +/- 0.5 (n=2) for Arctophila and -66.6 +/- 2.5 (n=6) for Carex. The methane emitted by these species is depleted in C-13 by 12 per mil for Arctophila and 18 per mil for Carex relative to methane withdrawn from plant stems 1-2 cm below the waterline. The results suggest more rapid transport of (C-12)H4 relative to (C-13)H4 through plants to the atmosphere. Plant stem methane concentrations ranged from 0.2 to 4.0 percent in Arctophila, with an isotopic composition of -46.1 +/- 4.3 percent (n=8). Carex stem methane concentrations ranged from 150 to 1200 ppm, with an isotopic composition of -48.3 +/- 1.4 per mil (n=3).

U-Pb systematics in iron meteorites - Uniformity of primordial lead

NASA Astrophysics Data System (ADS)

Gopel, C.; Manhes, G.; Allegre, C. J.

1985-08-01

Pb isotopic compositions and U-Pb abundances were determined in the metal phase of six iron meteorites: Canyon Diablo IA, Toluca IA, Odessa IA, Youndegin IA, Deport IA, and Mundrabilla An. Prior to complete dissolution, samples were subjected to a series of leachings and partial dissolutions. Isotopic compositions and abundances of the etched Pb indicate a contamination by terrestrial Pb which is attributable to previous cutting of the meteorite. Pb isotopic compositions measured in the decontaminated samples are identical within 0.2 percent and essentially confirm the primordial Pb value defined by Tatsumoto et al. (1973). These data invalidate more radiogenic Pb isotopic compositions published for iron meteorites, which are the result of terrestrial Pb contamination introduced mainly by analytical procedure. The results of this study support the idea of a solar nebula which was isotopically homogeneous for Pb 4.55 Ga ago. The new upper limit for U-abundance in iron meteorites, 0.001 ppb, is in agreement with its expected thermodynamic solubility in the metal phase.

Hydrogen isotope fractionation during lipid biosynthesis by Haloarcula marismortui

NASA Astrophysics Data System (ADS)

Dirghangi, Sitindra S.; Pagani, Mark

2013-10-01

We studied the controls on the fractionation of hydrogen isotopes during lipid biosynthesis by Haloarcula marismortui, a halophilic archaea, in pure culture experiments by varying organic substrate, the hydrogen isotope composition (D/H) of water, temperature, and salinity. Cultures were grown on three substrates: succinate, pyruvate and glycerol with known hydrogen isotope compositions, and in water with different hydrogen isotopic compositions. All culture series grown on a particular substrate show strong correlations between δDarchaeol and δDwater. However, correlations are distinctly different for cultures grown on different substrates. Our results indicate that the metabolic pathway of substrate exerts a fundamental influence on the δD value of lipids, likely by influencing the D/H composition of NADPH (nicotinamide adenine dinucleotide phosphate), the reducing agent that contributes hydrogen to carbon atoms during lipid biosynthesis. Temperature and salinity have smaller, but similar effects on δDlipid, primarily due to the way temperature and salinity influence growth rate, as well as temperature effects on the activity of enzymes.

Fe isotope composition of bulk chondrules from Murchison (CM2): Constraints for parent body alteration, nebula processes and chondrule-matrix complementarity

NASA Astrophysics Data System (ADS)

Hezel, Dominik C.; Wilden, Johanna S.; Becker, Daniel; Steinbach, Sonja; Wombacher, Frank; Harak, Markus

2018-05-01

Chondrules are a major constituent of primitive meteorites. The formation of chondrules is one of the most elusive problems in cosmochemistry. We use Fe isotope compositions of chondrules and bulk chondrites to constrain the conditions of chondrule formation. Iron isotope compositions of bulk chondrules are so far only known from few studies on CV and some ordinary chondrites. We studied 37 chondrules from the CM chondrite Murchison. This is particularly challenging, as CM chondrites contain the smallest chondrules of all chondrite groups, except for CH chondrites. Bulk chondrules have δ56Fe between -0.62 and +0.24‰ relative to the IRMM-014 standard. Bulk Murchison has as all chondrites a δ56Fe of 0.00‰ within error. The δ56Fe distribution of the Murchison chondrule population is continuous and close to normal. The width of the δ56Fe distribution is narrower than that of the Allende chondrule population. Opaque modal abundances in Murchison chondrules is in about 67% of the chondrules close to 0 vol.%, and in 33% typically up to 6.5 vol.%. Chondrule Al/Mg and Fe/Mg ratios are sub-chondritic, while bulk Murchison has chondritic ratios. We suggest that the variable bulk chondrule Fe isotope compositions were established during evaporation and recondensation prior to accretion in the Murchison parent body. This range in isotope composition was likely reduced during aqueous alteration on the parent body. Murchison has a chondritic Fe isotope composition and a number of chondritic element ratios. Chondrules, however, have variable Fe isotope compositions and chondrules and matrix have complementary Al/Mg and Fe/Mg ratios. In combination, this supports the idea that chondrules and matrix formed from a single reservoir and were then accreted in the parent body. The formation in a single region also explains the compositional distribution of the chondrule population in Murchison.

Sedimentary input into the source of Martinique lavas: a Li perspective

NASA Astrophysics Data System (ADS)

Tang, M.; Chauvel, C.; Rudnick, R. L.

2013-12-01

The Lesser Antilles arc is known for the prominent continental crustal signatures in its lavas. It thus provides an ideal target for studying crustal recycling in subduction zones. Martinique Island, located in the middle of the Lesser Antilles arc, has been well characterized for its elemental and radiogenic isotope geochemistry (Labanieh et al., 2012). We measured Li isotopes in the Martinique lavas as well as sediments cored at the southern (Site 144) and northern part (Site 543) of the subducting slab. The sediments show a large isotopic variation (δ7Li ~ -4.2‰ to +3.2‰) but the average δ7Li of -1.1 × 2.4‰ (1 σ, n = 15) is significantly lower than that of N-MORB (δ7Li = + 3.4 × 0.7‰, 1 σ, Tomascak et al., 2008), reflecting the influence of chemical weathering in the continental provenance. Although the subducting sediments display marked mineralogical and chemical shifts from south to north due to different deposition distances to the continental platform (Carpentier et al., 2009), their average Li isotopic compositions are indiscernible from each other. With a few exceptions, the Li isotopic compositions of the Martinique lavas are systematically lighter than MORB, giving an average δ7Li of 1.6 × 1.4‰ (1 σ, n = 25, 4 exceptions excluded). The δ7Li values show no correlation with any radiogenic isotope ratios (206Pb/204Pb, 87Sr/86Sr, 143Nd/144Nd and 176Hf/177Hf), Li/Y ratio, La/Sm ratio and SiO2 content. Therefore, the light Li isotopic composition likely reflects the source characteristics rather than contamination within the arc crust. Incorporation of the isotopically light sediments from Site 144 and 543 in the source may explain the depletion of 7Li in the Martinique lavas. A two-end-member mixing model requires 2-5% addition of the sediments into the depleted mantle source, compared with 1-10% sediments constrained by radiogenic isotopes (Carpentier et al., 2008). References Carpentier, M., Chauvel, C., & Mattielli, N., 2008. Pb-Nd isotopic constraints on sedimentary input into the Lesser Antilles arc system. Earth and Planetary Science Letters, 272(1), 199-211. Carpentier, M., Chauvel, C., Maury, R. C., & Mattielli, N., 2009. The 'zircon effect' as recorded by the chemical and Hf isotopic compositions of Lesser Antilles forearc sediments. Earth and Planetary Science Letters, 287(1), 86-99. Labanieh, S., Chauvel, C., Germa, A., & Quidelleur, X., 2012. Martinique: a Clear Case for Sediment Melting and Slab Dehydration as a Function of Distance to the Trench. Journal of Petrology, 53(12), 2441-2464. Tomascak, P. B., Langmuir, C. H., le Roux, P. J., & Shirey, S. B. (2008). Lithium isotopes in global mid-ocean ridge basalts. Geochimica et Cosmochimica Acta, 72(6), 1626-1637.

Re-Os isotopic evidence for an enriched-mantle source for the Noril'sk-type, ore-bearing intrusions, Siberia

USGS Publications Warehouse

Walker, R.J.; Morgan, J.W.; Horan, M.F.; Czamanske, G.K.; Krogstad, E.J.; Fedorenko, V.A.; Kunilov, V.E.

1994-01-01

Magmatic Cu-Ni sulfide ores and spatially associated ultramafic and mafic rocks from the Noril'sk I, Talnakh, and Kharaelakh intrusions are examined for Re-Os isotopic systematics. Neodymium and lead isotopic data also are reported for the ultramafic and mafic rocks. The Re-Os data for most samples indicate closed-system behavior since the ca. 250 Ma igneous crystallization age of the intrusions. There are small but significant differences in the initial osmium isotopic compositions of samples from the three intrusions. Ores from the Noril'sk I intrusion have ??Os values that vary from +0.4 to +8.8, but average +5.8. Ores from the Talnakh intrusion have ??Os values that range from +6.7 to +8.2, averaging +7.7. Ores from the Kharaelakh intrusion have ??Os values that range from +7.8 to +12.9, with an average value of +10.4. The osmium isotopic compositions of the ore samples from the Main Kharaelakh orebody exhibit minimal overlap with those for the Noril'sk I and Talnakh intrusions, indicating that these Kharaelakh ores were derived from a more radiogenic source of osmium than the other ores. Combined osmium and lead data for major orebodies in the three intrusions plot in three distinct fields, indicating derivation of osmium and lead from at least three isotopically distinct sources. Some of the variation in lead isotopic compositions may be the result of minor lower-crustal contamination. However, in contrast to most other isotopic and trace element data, Os-Pb variations are generally inconsistent with significant crustal contamination or interaction with the subcontinental lithosphere. Thus, the osmium and lead isotopic compositions of these intrusions probably reflect quite closely the compositions of their mantle source, and suggest that these two isotope systems were insensitive to lithospheric interaction. Ultramafic and mafic rocks have osmium and lead isotopic compositions that range only slightly beyond the compositions of the ores. These rocks also have relatively uniform ??{lunate}Nd values that range only from -0.8 to + 1.1. This limited variation in neodymium isotopic composition may reflect the characteristics of the mantle sources of the rocks, or it may indicate that somehow similar proportions of crust contaminated the parental melts. The osmium, lead, and neodymium isotopic data for these rocks most closely resemble the mantle sources of certain ocean island basalts (OIB), such as some Hawaiian basalts. Hence, these data are consistent with derivation of primary melts from a mantle source similar to that of some types of hotspot activity. The long-term Re/Os enrichment of this and similar mantle sources, relative to chondritic upper mantle, may reflect 1. (1) incorporation of recycled oceanic crust into the source more than 1 Ga ago, 2. (2) derivation from a mantle plume that originated at the outer core-lower mantle interface, or 3. (3) persistence of primordial stratification of rhenium and osmium in the mantle. ?? 1994.

Stable-isotope fingerprints of biological agents as forensic tools.

PubMed

Horita, Juske; Vass, Arpad A

2003-01-01

Naturally occurring stable isotopes of light elements in chemical and biological agents may possess unique "stable-isotope fingerprints" depending on their sources and manufacturing processes. To test this hypothesis, two strains of bacteria (Bacillus globigii and Erwinia agglomerans) were grown under controlled laboratory conditions. We observed that cultured bacteria cells faithfully inherited the isotopic composition (hydrogen, carbon, and nitrogen) of media waters and substrates in predictable manners in terms of bacterial metabolism and that even bacterial cells of the same strain, which grew in media water and substrates of different isotopic compositions, have readily distinguishable isotopic signatures. These "stable-isotopic fingerprints" of chemical and biological agents can be used as forensic tools in the event of biochemical terrorist attacks.

Magnesium isotope compositions of Solar System materials determined by double spiking

NASA Astrophysics Data System (ADS)

Hin, R.; Lai, Y. J.; Coath, C.; Elliott, T.

2015-12-01

As a major element, magnesium is of interest for investigating large scale processes governing the formation and evolution of rocky planetary bodies. Determining the Mg isotope composition of the Earth and other planetary bodies has hence been a topic of interest ever since mass-dependent fractionation of 'non-traditional' stable isotopes has been used to study high-temperature processes. Published results, however, suffer from disagreement on the Mg isotope compositions of the Earth and chondrites [1-5], which is attributed to residual matrix effects. Nonetheless, most recent studied have converged towards a homogeneous (chondritic) Mg isotope composition in the Solar System [2-5]. However, in several of the recent studies there is a hint of a systematic difference of about 0.02-0.06‰ in the 26Mg/24Mg isotope compositions of chondrites and Earth. Such difference, however, is only resolvable by taking standard errors, which assumes robust data for homogenous sample sets. The discrepancies between various studies unfortunately undermine the confidence in such robustness and homogeneity. The issues with matrix effects during isotopic analyses can be overcome by using a double spike approach. Such methodology generally requires three isotope ratios to solve for three unknowns, a requirement that cannot be met for Mg. However, using a newly developed approach, we present Mg isotope compositions obtained by critical mixture double spiking. This new approach should allow greater confidence in the robustness of the data and hence enable improvement of. Preliminary data indicate that chondrites have a resolvable ~0.04‰ lighter 26Mg/24Mg than (ultra)mafic rocks from Earth, Mars and the eucrite parent body, which appear indistinguishable from each other. It seems implausible that this difference is caused by magmatic process such as partial melting or crystallisation. More likely, Mg isotopes are fractionated by a non-magmatic process during the formation of planets, e.g. by vapour-condensate fractionation. [1] Wiechert and Halliday, 2007. EPSL 256, 360-371. [2] Bourdon et al., 2010. GCA 74, 5069-5083. [3] Teng et al., 2010. GCA 74, 4150-4166. [4] Chakrabarti and Jacobsen, 2010. EPSl 293, 349-358. [5] Von Strandmann, 2011. GCA 75, 5247-5268.

Equilibrium and non-equilibrium controls on the abundances of clumped isotopologues of methane during thermogenic formation in laboratory experiments: Implications for the chemistry of pyrolysis and the origins of natural gases

NASA Astrophysics Data System (ADS)

Shuai, Yanhua; Douglas, Peter M. J.; Zhang, Shuichang; Stolper, Daniel A.; Ellis, Geoffrey S.; Lawson, Michael; Lewan, Michael D.; Formolo, Michael; Mi, Jingkui; He, Kun; Hu, Guoyi; Eiler, John M.

2018-02-01

Multiply isotopically substituted molecules ('clumped' isotopologues) can be used as geothermometers because their proportions at isotopic equilibrium relative to a random distribution of isotopes amongst all isotopologues are functions of temperature. This has allowed measurements of clumped-isotope abundances to be used to constrain formation temperatures of several natural materials. However, kinetic processes during generation, modification, or transport of natural materials can also affect their clumped-isotope compositions. Herein, we show that methane generated experimentally by closed-system hydrous pyrolysis of shale or nonhydrous pyrolysis of coal yields clumped-isotope compositions consistent with an equilibrium distribution of isotopologues under some experimental conditions (temperature-time conditions corresponding to 'low,' 'mature,' and 'over-mature' stages of catagenesis), but can have non-equilibrium (i.e., kinetically controlled) distributions under other experimental conditions ('high' to 'over-mature' stages), particularly for pyrolysis of coal. Non-equilibrium compositions, when present, lead the measured proportions of clumped species to be lower than expected for equilibrium at the experimental temperature, and in some cases to be lower than a random distribution of isotopes (i.e., negative Δ18 values). We propose that the consistency with equilibrium for methane formed by relatively low temperature pyrolysis reflects local reversibility of isotope exchange reactions involving a reactant or transition state species during demethylation of one or more components of kerogen. Non-equilibrium clumped-isotope compositions occur under conditions where 'secondary' cracking of retained oil in shale or wet gas hydrocarbons (C2-5, especially ethane) in coal is prominent. We suggest these non-equilibrium isotopic compositions are the result of the expression of kinetic isotope effects during the irreversible generation of methane from an alkyl precursor. Other interpretations are also explored. These findings provide new insights into the chemistry of thermogenic methane generation, and may provide an explanation of the elevated apparent temperatures recorded by the methane clumped-isotope thermometer in some natural gases. However, it remains unknown if the laboratory experiments capture the processes that occur at the longer time and lower temperatures of natural gas formation.

Evaluating climate model performance in the tropics with retrievals of water isotopic composition from Aura TES

NASA Astrophysics Data System (ADS)

Field, Robert; Kim, Daehyun; Kelley, Max; LeGrande, Allegra; Worden, John; Schmidt, Gavin

2014-05-01

Observational and theoretical arguments suggest that satellite retrievals of the stable isotope composition of water vapor could be useful for climate model evaluation. The isotopic composition of water vapor is controlled by the same processes that control water vapor amount, but the observed distribution of isotopic composition is distinct from amount itself . This is due to the fractionation that occurs between the abundant H216O isotopes (isotopologues) and the rare and heavy H218O and HDO isotopes during evaporation and condensation. The fractionation physics are much simpler than the underlying moist physics; discrepancies between observed and modeled isotopic fields are more likely due to problems in the latter. Isotopic measurements therefore have the potential for identifying problems that might not be apparent from more conventional measurements. Isotopic tracers have existed in climate models since the 1980s but it is only since the mid 2000s that there have been enough data for meaningful model evaluation in this sense, in the troposphere at least. We have evaluated the NASA GISS ModelE2 general circulation model over the tropics against water isotope (HDO/H2O) retrievals from the Aura Tropospheric Emission Spectrometer (TES), alongside more conventional measurements. A small ensemble of experiments was performed with physics perturbations to the cumulus and planetary boundary layer schemes, done in the context of the normal model development process. We examined the degree to which model-data agreement could be used to constrain a select group of internal processes in the model, namely condensate evaporation, entrainment strength, and moist convective air mass flux. All are difficult to parameterize, but exert strong influence over model performance. We found that the water isotope composition was significantly more sensitive to physics changes than precipitation, temperature or relative humidity through the depth of the tropical troposphere. Among the processes considered, this was most closely, and fairly exclusively, related to mid-tropospheric entrainment strength. This demonstrates that water isotope retrievals have considerable potential alongside more conventional measurements for climate model evaluation and development.

Magnesium Isotopes as a Tracer of Crustal Materials in Volcanic Arc Magmas in the Northern Cascade Arc

NASA Astrophysics Data System (ADS)

Brewer, Aaron W.; Teng, Fang-Zhen; Mullen, Emily

2018-03-01

Fifteen North Cascade Arc basalts and andesites were analyzed for Mg isotopes to investigate the extent and manner of crustal contributions to this magmatic system. The δ26Mg of these samples vary from within the range of ocean island basalts (the lightest being -0.33 ± 0.07‰) to heavier compositions (as heavy as -0.15 ± 0.06‰). The observed range in chemical and isotopic composition is similar to that of other volcanic arcs that have been assessed to date in the circum-pacific subduction zones and in the Caribbean. The heavy Mg isotope compositions are best explained by assimilation and fractional crystallization within the deep continental crust with a possible minor contribution from the addition of subducting slab-derived fluids to the primitive magma. The bulk mixing of sediment into the primitive magma or mantle source and the partial melting of garnet-rich peridotite are unlikely to have produced the observed range of Mg isotope compositions. The results show that Mg isotopes may be a useful tracer of crustal input into a magma, supplementing traditional methods such as radiogenic isotopic and trace element data, particularly in cases in which a high fraction of crustal material has been added.

Stable Vanadium Isotopes as a Redox Proxy at High Temperatures?

NASA Astrophysics Data System (ADS)

Prytulak, J.; Sossi, P.; Halliday, A.; Plank, T. A.; Savage, P.; Woodhead, J. D.

2016-12-01

There is currently no consensus on the relative oxygen fugacity (fO2) of the mantle source of mid-ocean ridge basalts compared to the sub-arc mantle, the region that is central to the mediation of crust-mantle mass balances. Vanadium is a multivalent transition metal whose stable isotope fractionation may reflect oxygen fugacity (fO2). However, a direct link between V isotope composition and fO2 is currently far from convincingly demonstrated. Furthermore, differences in co-ordination environment also play a large role in causing stable isotope fractionation. Here we present V isotope measurements of two suites of co-genetic magmas from contrasting tectonic settings: the Mariana arc and Hekla volcano, Iceland. We use this data alongside the tightly constrained V isotope composition of MORB [1] to assess the effects of fO2 and crystal fractionation on stable vanadium isotopes. We show that, for a given MgO content, V isotopes are identical within analytical error between arc basalts from the Marianas, lavas from Hekla, and MORB. The most striking aspect of our igneous, high temperature V isotope data is the large isotope fractionation (on the order of 2 ‰) towards heavier values in magmatic suites from both Hekla and the Marianas with progressive differentiation. We use a self consistent model of fractionating cotectic phases in both igneous suites to match major, trace and V isotope data. Vanadium partition coefficients required for (titano)magnetite are significantly higher in Hekla (DVmag = 42) than Mariana lavas (DVmag = 32), consistent with a more oxidised source in the latter. Calculated Rayleigh fractionation factors are similar in both suites (Δ51Vmin-melt of -0.4 to -0.5‰) and strongly implicate co-ordination differences between oxides and melt are the dominant driving force for V isotope fractionation. Thus, although fO2likely has a second order effect on V isotopes, they are not a direct proxy for oxygen fugacity in magmatic systems. [1] Prytulak, et al. 2013. EPSL 365, 177-189

Planetary and meteoritic Mg/Si and δ30 Si variations inherited from solar nebula chemistry

NASA Astrophysics Data System (ADS)

Dauphas, Nicolas; Poitrasson, Franck; Burkhardt, Christoph; Kobayashi, Hiroshi; Kurosawa, Kosuke

2015-10-01

The bulk chemical compositions of planets are uncertain, even for major elements such as Mg and Si. This is due to the fact that the samples available for study all originate from relatively shallow depths. Comparison of the stable isotope compositions of planets and meteorites can help overcome this limitation. Specifically, the non-chondritic Si isotope composition of the Earth's mantle was interpreted to reflect the presence of Si in the core, which can also explain its low density relative to pure Fe-Ni alloy. However, we have found that angrite meteorites display a heavy Si isotope composition similar to the lunar and terrestrial mantles. Because core formation in the angrite parent-body (APB) occurred under oxidizing conditions at relatively low pressure and temperature, significant incorporation of Si in the core is ruled out as an explanation for this heavy Si isotope signature. Instead, we show that equilibrium isotopic fractionation between gaseous SiO and solid forsterite at ∼1370 K in the solar nebula could have produced the observed Si isotope variations. Nebular fractionation of forsterite should be accompanied by correlated variations between the Si isotopic composition and Mg/Si ratio following a slope of ∼1, which is observed in meteorites. Consideration of this nebular process leads to a revised Si concentration in the Earth's core of 3.6 (+ 6.0 / - 3.6) wt% and provides estimates of Mg/Si ratios of bulk planetary bodies.

Stable water isotopic composition of the Antarctic subglacial Lake Vostok: implications for understanding the lake's hydrology.

PubMed

Ekaykin, Alexey A; Lipenkov, Vladimir Y; Kozachek, Anna V; Vladimirova, Diana O

2016-01-01

We estimated the stable isotopic composition of water from the subglacial Lake Vostok using two different sets of samples: (1) water frozen on the drill bit immediately after the first lake unsealing and (2) water frozen in the borehole after the unsealing and re-drilled one year later. The most reliable values of the water isotopic composition are: -59.0 ± 0.3 ‰ for oxygen-18, -455 ± 1 ‰ for deuterium and 17 ± 1 ‰ for d-excess. This result is also confirmed by the modelling of isotopic transformations in the water which froze in the borehole, and by a laboratory experiment simulating this process. A comparison of the newly obtained water isotopic composition with that of the lake ice (-56.2 ‰ for oxygen-18, -442.4 ‰ for deuterium and 7.2 ‰ for d-excess) leads to the conclusion that the lake ice is very likely formed in isotopic equilibrium with water. In turn, this means that ice is formed by a slow freezing without formation of frazil ice crystals and/or water pockets. This conclusion agrees well with the observed physical and chemical properties of the lake's accreted ice. However, our estimate of the water's isotopic composition is only valid for the upper water layer and may not be representative for the deeper layers of the lake, so further investigations are required.

Interactions between surface waters in King George Island, Antarctica - a stable isotope perspective

NASA Astrophysics Data System (ADS)

Perşoiu, Aurel; Bădăluşă, Carmen

2017-04-01

In this paper we present a first study of the isotopic composition of surface waters in the southern peninsulas (Barton, Fildes, Weaver and Potter) of King George Island, Antarctica. We have collected > 200 samples of snow and snowmelt, water (lake, river and spring), ice (glacier ice and permafrost) from the four peninsulas in February 2016 and analyzed them for their oxygen and hydrogen stable isotopic composition. Samples from lake water (50+) indicate a clear west-east depletion trend, suggesting a rain-out process as air masses are moving westward (and are progressively depleted in heavy isotopes) from their origin in the Drake Passage. In both Fildes and Barton Peninsulas, permafrost samples have the heaviest isotopic composition, most probably due to preferential incorporation of heavy isotopes in the ice during freezing (and no fractionation during melting). As permafrost melts, the resulting water mixes with isotopically lighter infiltrated snowmelt, and thus the groundwater has a lower isotopic composition. Further, lake and river (the later fed by lakes) water has the lightest isotopic composition, being derived mostly from the melting of light snow and glacier ice. It seems feasible to separate isotopically water in lakes/rivers (largely fed by melting multi-year glaciers and snow) and water from melting of snow/ground ice This preliminary study suggests that it is possible to separate various water sources in the southern peninsulas of King George Island, and this separation could be used to study permafrost degradation, as well as feeding and migration patterns in the bird fauna, with implications for protection purposes. Acknowledgments. The National Institute of Research and Development for Biological Sciences (Bucharest, Romania) and the Korean polar institute financially supported fieldwork in King George Island. We thank the personal at King Sejong (South Korea), Belingshaussen (Russia) and Carlini (Argentina) stations in King George Island for logistic supports.

PALOMA : an isotope analyzer using static mass spectrometry, coupled with cryogenic and chemical trapping, for the MSL mission to Mars

NASA Astrophysics Data System (ADS)

Chassefiere, E.; Jambon, A.; Berthelier, J.-J.; Goulpeau, G.; Leblanc, F.; Montmessin, F.; Sarda, P.; Agrinier, P.; Fouchet, T.; Waite, H.

The technique of GCMS analysis has to be completed by static mass spectrometry for precise in-situ measurements of the isotopic composition of planetary atmospheres (noble gases, stable isotopes), and volatile outgassed products from solid sample pyrolysis. Static mass spectrometry, coupled with gas separation by cryo-separation and gettering, is commonly used in the laboratory to study volatiles extracted from terrestrial and meteoritic samples. Such an instrument (PALOMA) is presently developed in our laboratories, and it will be coupled with a Pyr-GCMS analyzer (MACE), built by a US consortium of science laboratories and industrials (University of Michigan, Southwest Research Institute, JPL, Ball Aerospace). The MACE/PALOMA experiment will be proposed on the NASA Mars Science Laboratory mission, planned to be launched in 2009. The scientific objectives of PALOMA, coupled with MACE, may be listed as follows : (i) search for isotopic signatures of past life in atmosphere, rock, dust and ice samples, with emphasis on carbon, nitrogen and hydrogen; (ii) accurately measure isotopic composition of atmospheric noble gases, and stable isotopes, in order to better constrain past escape, surface interaction, outgassing history and climate evolution; (iii) precisely measure diurnal/ seasonal variations of isotopic ratios of H2O, CO2, and N2, for improving our understanding of present and past climate, and of the role of water cycle. Main measurement objectives are : (i) C, H, O, N isotopic composition in both organic evolved samples (provided by MACE pyrolysis system) and atmosphere with high accuracy (a few per mil at 1-s level); (ii) noble gas (He, Ne, Ar, Kr, Xe) and stable (C, H, O, N) isotope composition in atmosphere with high accuracy (a few per mil at 1-s level); (iii) molecular and isotopic composition of inorganic evolved samples (salts, hydrates, nitrates, {ldots}), including ices; (iv) diurnal and seasonal monitoring of D/H in water vapor, and water ice.

Spatiotemporal patterns of plant water isotope values from a continental-scale sample network in Europe as a tool to improve hydroclimate proxies

NASA Astrophysics Data System (ADS)

Nelson, D. B.; Kahmen, A.

2016-12-01

The hydrogen and oxygen isotopic composition of water available for biosynthetic processes in vascular plants plays an important role in shaping the isotopic composition of organic compounds that these organisms produce, including leaf waxes and cellulose in leaves and tree rings. Characterizing changes in large scale spatial patterns of precipitation, soil water, stem water, and leaf water isotope values over time is therefore useful for evaluating how plants reflect changes in the isotopic composition of these source waters in different environments. This information can, in turn, provide improved calibration targets for understanding the environmental signals that plants preserve. The pathway of water through this continuum can include several isotopic fractionations, but the extent to which the isotopic composition of each of these water pools varies under normal field conditions and over space and time has not been systematically and concurrently evaluated at large spatial scales. Two season-long sampling campaigns were conducted at nineteen sites throughout Europe over the 2014 and 2015 growing seasons to track changes in the isotopic composition of plant-relevant waters. Samples of precipitation, soil water, stem water, and leaf water were collected over more than 200 field days and include more than 500 samples from each water pool. Measurements were used to validate continent-wide gridded estimates of leaf water isotope values derived from a combination of mechanistic and statistical modeling conducted with temperature, precipitation, and relative humidity data. Data-model comparison shows good agreement for summer leaf waters, and substantiates the incorporation of modeled leaf waters in evaluating how plants respond to hydroclimate changes at large spatial scales. These results also suggest that modeled leaf water isotope values might be used in future studies in similar ecosystems to improve the coverage density of spatial or temporal data.

Absolute Isotopic Abundance Ratios and the Accuracy of Δ47 Measurements

NASA Astrophysics Data System (ADS)

Daeron, M.; Blamart, D.; Peral, M.; Affek, H. P.

2016-12-01

Conversion from raw IRMS data to clumped isotope anomalies in CO2 (Δ47) relies on four external parameters: the (13C/12C) ratio of VPDB, the (17O/16O) and (18O/16O) ratios of VSMOW (or VPDB-CO2), and the slope of the triple oxygen isotope line (λ). Here we investigate the influence that these isotopic parameters exert on measured Δ47 values, using real-world data corresponding to 7 months of measurements; simulations based on randomly generated data; precise comparisons between water-equilibrated CO2 samples and between carbonate standards believed to share quasi-identical Δ47 values; reprocessing of two carbonate calibration data sets with different slopes of Δ47 versus T. Using different sets of isotopic parameters generally produces systematic offsets as large as 0.04 ‰ in final Δ47 values. What's more, even using a single set of isotopic parameters can produce intra- and inter-laboratory discrepancies in final Δ47 values, if some of these parameters are inaccurate. Depending on the isotopic compositions of the standards used for conversion to "absolute" values, these errors should correlate strongly with either δ13C or δ18O, or more weakly with both. Based on measurements of samples expected to display identical Δ47 values, such as 25°C water-equilibrated CO2 with different carbon and oxygen isotope compositions, or high-temperature standards ETH-1 and ETH-2, we conclude that the isotopic parameters used so far in most clumped isotope studies produces large, systematic errors controlled by the relative bulk isotopic compositions of samples and standards, which should be one of the key factors responsible for current inter-laboratory discrepancies. By contrast, the isotopic parameters of Brand et al. [2010] appear to yield accurate Δ47 values regardless of bulk isotopic composition. References:Brand, Assonov and Coplen [2010] http://dx.doi.org/10.1351/PAC-REP-09-01-05

Mass dependent fractionation of stable chromium isotopes in mare basalts: Implications for the formation and the differentiation of the Moon

NASA Astrophysics Data System (ADS)

Bonnand, Pierre; Parkinson, Ian J.; Anand, Mahesh

2016-02-01

We present the first stable chromium isotopic data from mare basalts in order to investigate the similarity between the Moon and the Earth's mantle. A double spike technique coupled with MC-ICP-MS measurements was used to analyse 19 mare basalts, comprising high-Ti, low-Ti and KREEP-rich varieties. Chromium isotope ratios (δ53Cr) for mare basalts are positively correlated with indices of magmatic differentiation such as Mg# and Cr concentration which suggests that Cr isotopes were fractionated during magmatic differentiation. Modelling of the results provides evidence that spinel and pyroxene are the main phases controlling the Cr isotopic composition during fractional crystallisation. The most evolved samples have the lightest isotopic compositions, complemented by cumulates that are isotopically heavy. Two hypotheses are proposed to explain this fractionation: (i) equilibrium fractionation where heavy isotopes are preferentially incorporated into the spinel lattice and (ii) a difference in isotopic composition between Cr2+ and Cr3+ in the melt. However, both processes require magmatic temperatures below 1200 °C for appreciable Cr3+ to be present at the low oxygen fugacities found in the Moon (IW -1 to -2 log units). There is no isotopic difference between the most primitive high-Ti, low-Ti and KREEP basalts, which suggest that the sources of these basalts were homogeneous in terms of stable Cr isotopes. The least differentiated sample in our sample set is the low-Ti basalt 12016, characterised by a Cr isotopic composition of -0.222 ± 0.025‰, which is within error of the current BSE value (-0.124 ± 0.101‰). The similarity between the mantles of the Moon and Earth is consistent with a terrestrial origin for a major fraction of the lunar Cr. This similarity also suggests that Cr isotopes were not fractionated by core formation on the Moon.

An interlaboratory study to test instrument performance of hydrogen dual-inlet isotope-ratio mass spectrometers

USGS Publications Warehouse

Brand, Willi A.; Coplen, T.B.

2001-01-01

An interlaboratory comparison of forty isotope-ratio mass spectrometers of different ages from several vendors has been performed to test 2H/1H performance with hydrogen gases of three different isotopic compositions. The isotope-ratio results (unsufficiently corrected for H3+ contribution to the m/z = 3 collector, uncorrected for valve leakage in the change-over valves, etc.) expressed relative to one of these three gases covered a wide range of values: -630??? to -790??? for the second gas and -368??? to -462??? for the third gas. After normalizing the isotopic abundances of these test gases (linearly adjusting the ?? values so that the gases with the lowest and highest 2H content were identical for all laboratories), the standard deviation of the 40 measurements of the intermediate gas was a remarkably low 0.85???. It is concluded that the use of scaling factors is mandatory for providing accurate internationally comparable isotope-abundance values. Linear scaling for the isotope-ratio scales of gaseous hydrogen mass spectrometers is completely adequate. ?? Springer-Verlag 2001.

A Cerenkov-delta E-Cerenkov detector for high energy cosmic ray isotopes and an accelerator study of Ar-40 and Fe-56 fragmentation. Ph.D. Thesis

NASA Technical Reports Server (NTRS)

Lau, K. H.

1985-01-01

A high energy cosmic ray detector--the High Energy Isotope Spectrometer Telescope (HEIST) is described. It is a large area (0.25 m(swp 2) SR) balloon borne isotope spectrometer designed to make high resolution measurements of isotopes in the element range from neon to nickel (10 Z 28) at energies of about 2 GeV/nucleon. HEIST determines the mass of individual nuclei by measuring both the change in the Lorentz factor (delta gamma) that results from traversing the NaI stack, and the energy loss (delta E) in the stack. Since the total energy of an isotope is given by E = (gamma M), the mass M can be determined by M = delta E/delta, gamma. The instrument is designed to achieve a typical mass resolution of 0.2 amu. The isotopic composition of the fragments from the breakup of high energy An-40 and Fe-56 nuclei are measured experimentally. Isotope yields are compared with calculated yields based on semi-empirical cross-section formulae.

Utilizing Stable Isotopes and Isotopic Anomalies to Study Early Solar System Formation Processes

NASA Technical Reports Server (NTRS)

Simon, Justin

2017-01-01

Chondritic meteorites contain a diversity of particle components, i.e., chondrules and calcium-, aluminum-rich refractory inclusions (CAIs), that have survived since the formation of the Solar System. The chemical and isotopic compositions of these materials provide a record of the conditions present in the protoplanetary disk where they formed and can aid our understanding of the processes and reservoirs in which solids formed in the solar nebula, an important step leading to the accretion of planetesimals. Isotopic anomalies associated with nucleosynthetic processes are observed in these discrete materials, and can be compared to astronomical observations and astrophysical formation models of stars and more recently proplyds. The existence and size of these isotopic anomalies are typically thought to reflect a significant state of isotopic heterogeneity in the earliest Solar System, likely left over from molecular cloud heterogeneities on the grain scale, but some could also be due to late stellar injection. The homogenization of these isotopic anomalies towards planetary values can be used to track the efficiency and timescales of disk wide mixing,

Using semi-continuous, in-situ measurements of nitrous oxide isotopic composition at a suburban site to track emission processes

NASA Astrophysics Data System (ADS)

Harris, Eliza; Henne, Stephan; Christoph, Hüglin; Christoph, Zellweger; Béla, Tuzson; Erkan, Ibraim; Lukas, Emmenegger; Joachim, Mohn

2017-04-01

Nitrous oxide (N2O) is a potent greenhouse gas and the strongest ozone-destroying substance emitted this century. The atmospheric N2O mole fraction has been increasing at a rate of 0.2-0.3% per year over the past decades due to anthropogenic emissions; in addition, recent results suggest that the rate of increase is rising - therefore effective mitigation of N2O emissions is a critical point for environmental policy. However, N2O sources are poorly defined and disperse, complicating the development of targeted mitigation strategies. Online isotopic measurements using preconcentration and laser spectroscopy [1,2,3] have great potential to unravel spatial and temporal variations in sources, sinks and chemistry of trace gases such as N2O. Semi-continuous, real-time measurements of N2O isotopic composition (δ18O, site preference [SP = 14N15N16O - 15N14N16O] and δ15Nbulk) were performed at the suburban site of Dübendorf, Switzerland, for 19 months between July 2014 and February 2016. The data precision reached 0.1‰ in the final months, thus the results could clearly identify nocturnal build-up of N2O, with a corresponding decrease in δ18O, SP and δ15Nbulk due to isotopically depleted anthropogenic sources. Daily mean source isotopic composition was calculated by considering the measured and the background mole fraction and isotopic composition. Delta values of the mean emission source were highest in winter, with a seasonal cycle of 12, 8 and 5‰ for δ18O, SP and δ15Nbulk respectively. The chemical and meteorological parameters controlling source isotopic composition were considered using data from the Swiss National Air Pollution Monitoring Network (NABEL) as well as a transport regime cluster analysis. A clear spatial distribution for source isotopic composition was observed for δ18O, as well as a significant relationship with the level of urban pollution, indicating δ18O may be a strong indicator of combustion/industrial vs. agricultural N2O. In contrast, δ15Nbulk and particularly SP appear to vary too strongly in response to other factors affecting emission processes to provide a useful distinction between source categories on a regional scale - these isotopocules may however be useful to distinguish emission pathways on a local scale. For comparison, FLEXPART-COSMO transport simulations [4] were combined with emissions from the EDGAR inventory and estimates of source isotopic composition from literature, to simulate N2O isotopic composition at the sampling site. The model was able to capture variability in N2O mole fraction adequately (R2 = 0.34; p <<0.01). However, the measured variability in source isotopic composition was 1-2 orders of magnitude larger than simulated, illustrating that our knowledge of isotopic source signatures - in particular technical N2O sources - is still too limited to successfully model variations in ambient N2O isotopic composition. [1] Mohn et al. (2012) Atmospheric Measurement Techniques, doi:10.5194/amt-5-1601-2012 [2] Harris et al. (2014) Analytical Chemistry, doi: 10.1021/ac403606u. [3] Röckmann et al. (2016) Atmospheric Chemistry and Physics, doi:10.5194/acp-16-10469-2016. [4] Henne et al. (2016) Atmospheric Chemistry and Physics, doi:10.5194/acp-16-3683-2016.

Gradients in seasonality and seawater oxygen isotopic composition along the early Permian Gondwanan coast, SE Australia

NASA Astrophysics Data System (ADS)

Beard, J. Andrew; Ivany, Linda C.; Runnegar, Bruce

2015-09-01

Oxygen isotope compositions of marine carbonates are commonly employed for understanding ancient temperatures, but this approach is complicated in the very distant past due to uncertainties about the effects of diagenesis and the isotopic composition of seawater, both locally and globally. Microsampled accretionary calcite from two species of the fossil bivalve Eurydesma Sowerby and Morris 1845 collected from sediments of Cisuralian age in high latitude marine sediments along the SE coast of Australia records cyclic seasonal fluctuations in shell δ18O values during growth, demonstrating the primary nature of the isotope signal and thus allowing investigation of early Permian seawater isotopic composition and water temperature in the high southern latitudes. The mean and seasonal range of δ18Ocarb decreases poleward across about 10° of paleolatitude (∼67°S-77°S). The presence of co-occurring dropstones and stratigraphically associated glendonites constrains winter temperatures across the region to near-freezing, thus permitting calculation of realistic estimates of water composition and summer temperatures. Summer δ18Ocarb values indicate water temperatures between 5 °C and 12 °C, with warmer values at lower latitudes. The decrease in both mean sea surface temperature and seasonal amplitude with increasing latitude on the Gondwanan coast is much like that observed along high-latitude coastlines today. Calculated δ18Owater decreases toward the pole, likely associated with an increasing contribution of isotopically light fresh water derived from summer snow-melt. The gradient in δ18Owater is similar to that documented over a similar span of latitude on the modern SE Greenland coast. We infer the presence of a north-flowing coastal current of cold, O18-depleted water that entrains progressively greater amounts of more typical seawater as it moves away from the pole. δ18O values in SE Australia, however, are about 3‰ lower than those off Greenland, suggesting comparatively lower salinity water or more O18-depleted glacial ice/runoff in the Permian Gondwanan high latitudes, perhaps augmented by more depleted (negative) global average seawater. Conditions in southeastern Australia during the largest of the Permian deglaciations were warmer than present-day Antarctica at similar latitudes, but may approximate those of early-mid Miocene Antarctica, with frozen winters but summers closer to 10 °C.

The He isotope composition of the earliest picrites erupted by the Ethiopia plume, implications for mantle plume source

NASA Astrophysics Data System (ADS)

Stuart, Finlay; Rogers, Nick; Davies, Marc

2016-04-01

The earliest basalts erupted by mantle plumes are Mg-rich, and typically derived from mantle with higher potential temperature than those derived from the convecting upper mantle at mid-ocean ridges and ocean islands. The chemistry and isotopic composition of picrites from CFB provide constraints on the composition of deep Earth and thus the origin and differentiation history. We report new He-Sr-Nd-Pb isotopic composition of the picrites from the Ethiopian flood basalt province from the Dilb (Chinese Road) section. They are characterized by high Fe and Ti contents for MgO = 10-22 wt. % implying that the parent magma was derived from a high temperature low melt fraction, most probably from the Afar plume head. The picrite 3He/4He does not exceed 21 Ra, and there is a negative correlation with MgO, the highest 3He/4He corresponding to MgO = 15.4 wt. %. Age-corrected 87Sr/86Sr (0.70392-0.70408) and 143Nd/144Nd (0.512912-0.512987) display little variation and are distinct from MORB and OIB. Age-corrected Pb isotopes display a significant range (e.g. 206Pb/204Pb = 18.70-19.04) and plot above the NHRL. These values contrast with estimates of the modern Afar mantle plume which has lower 3He/4He and Sr, Nd and Pb isotope ratios that are more comparable with typical OIB. These results imply either interaction between melts derived from the Afar mantle plume and a lithospheric component, or that the original Afar mantle plume had a rather unique radiogenic isotope composition. Regardless of the details of the origins of this unusual signal, our observations place a minimum 3He/4He value of 21 Ra for the Afar mantle plume, significantly greater than the present day value of 16 Ra, implying a significant reduction over 30 Myr. In addition the Afar source was less degassed than convecting mantle but more degassed than mantle sampled by the proto-Iceland plume (3He/4He ~50 Ra). This suggests that the largest mantle plumes are not sourced in a single deep mantle domain with a common depletion history and that they do not mix with shallower mantle reservoirs to the same extent.

Evidence for a nonmagmatic component in potassic hydrothermal fluids of porphyry cu-Au-Mo systems, Yukon, Canada

NASA Astrophysics Data System (ADS)

Selby, David; Nesbitt, Bruce E.; Creaser, Robert A.; Reynolds, Peter H.; Muehlenbachs, Karlis

2001-02-01

Isotopic (H, Sr, Pb, Ar) and fluid inclusion data for hydrothermal fluids associated with potassic alteration from three Late Cretaceous porphyry Cu occurrences, west central Yukon, suggest a nonmagmatic fluid component was present in these hydrothermal fluids. Potassic stage quartz veins contain a dominant assemblage of saline and vapor-rich fluid inclusions that have δD values between -120 and -180‰. Phyllic stage quartz veins are dominated by vapor-rich fluid inclusions and have δD values that overlap with but are, on average, heavier (-117 to -132‰) than those in potassic stage quartz veins. These δD values are significantly lower than those from plutonic quartz phenocrysts (-91 to -113‰), and from values typically reported for primary fluids from porphyry-style mineralization (-40 to -100‰). The initial Sr ( 87Sr/ 86Sr i) isotopic values for the plutons are 0.7055 (Casino), 0.7048 (Mt. Nansen), and 0.7055 (Cash). The 87Sr/ 86Sr i compositions of hydrothermal K-feldspar ranges from magmatic Sr i values to more radiogenic compositions (Casino: 0.70551-0.70834, n = 8; Mt. Nansen: 0.7063-0.7070, n = 4; Cash: 0.7058, n = 1). The fluid inclusion waters from potassic quartz veins have 87Sr/ 86Sr i values that are similar to those of co-existing hydrothermal K-feldspar. The Pb isotopic compositions of hydrothermal K-feldspar show a weak positive correlation with Sr i for identical samples. Fluid inclusion waters of phyllic quartz veins also have Sr i compositions more radiogenic than the plutons. The Pb isotopic composition of pyrite and bornite from phyllic alteration veins are similar to, or more radiogenic than, hydrothermal K-feldspar Pb isotopic values. Hydrothermal K-feldspar samples yield 40Ar/ 39Ar ages (Casino = 71.9 ± 0.7 to 73.4 ± 0.8 Ma; Mt. Nansen = 68.2 ± 0.7 and 69.5 ± 0.6 Ma; Cash = 68.3 ± 0.8 Ma) similar to the U-Pb zircon, K-Ar biotite and Re-Os molybdenite ages of the Late Cretaceous plutons, with the age spectra indicating no excess 40Ar or disturbance. The 40Ar/ 36Ar values (285-292) of the K-feldspar samples are similar to the atmospheric compositions (295 ± 5) during Late Cretaceous time. The H, Sr, Pb, and Ar isotopic compositions of hydrothermal K-feldspar and quartz vein fluid inclusion waters that characterize the potassic hydrothermal fluids show evidence for an exotic component in addition to magmatic water (fluid). This component has a low δD, radiogenic Sr and Pb, and an atmospheric Ar composition. The inheritance of pre-existing isotope compositions from the host rocks, postpotassic alteration isotope exchange, or the replenishment of the magma chamber with magma of different isotopic composition cannot explain the isotope data. We suggest that to generate the observed H, Sr, Pb, and Ar isotope compositions, crustal fluids must be a component (15-94%) of potassic hydrothermal fluids in porphyry mineralization in the deposits studied.

Osmium uptake, distribution, and 187Os/188Os and 187Re/188Os compositions in Phaeophyceae macroalgae, Fucus vesiculosus: Implications for determining the 187Os/188Os composition of seawater

NASA Astrophysics Data System (ADS)

Racionero-Gómez, B.; Sproson, A. D.; Selby, D.; Gannoun, A.; Gröcke, D. R.; Greenwell, H. C.; Burton, K. W.

2017-02-01

The osmium isotopic composition (187Os/188Os) of seawater reflects the balance of input from mantle-, continental- and anthropogenic-derived sources. This study utilizes the Phaeophyceae, Fucus vesiculosus, to analyse its Os abundance and uptake, as well as to assess if macroalgae records the Os isotope composition of the seawater in which it lives. The data demonstrates that Os is not located in one specific biological structure within macroalgae, but is found throughout the organism. Osmium uptake was measured by culturing F. vesiculosus non-fertile tips with different concentrations of Os with a known 187Os/188Os composition (∼0.16), which is significantly different from the background isotopic composition of local seawater (∼0.94). The Os abundance of cultured non-fertile tips show a positive correlation to the concentration of the Os doped seawater. Moreover, the 187Os/188Os composition of the seaweed equalled that of the culture medium, strongly confirming the possible use of macroalgae as a biological proxy for the Os isotopic composition of the seawater.

Influence of magmatic volatiles on boron isotope compositions in vent fluids from the Eastern Manus Basin, Papua New Guinea

NASA Astrophysics Data System (ADS)

Wilckens, F. K.; Kasemann, S.; Bach, W.; Reeves, E. P.; Meixner, A.; Seewald, J.

2016-12-01

In this study we present boron (B), lithium (Li) and strontium (Sr) concentrations and isotopic composition of submarine hydrothermal fluids collected in 2006 and 2011 from PACMANUS, DESMOS and SuSu Knolls vent fields located in the Eastern Manus Basin [1,2]. Hydrothermal vent fluids within the Eastern Manus Basin range from high-temperature black smoker fluids to low-temperature diffuse fluids and acid-sulfate fluids. In general, the different fluid types show variable water-rock ratios during water-rock interaction and different inputs of magmatic volatiles. End-member black smoker fluids, which have in general high temperatures (mostly higher than 280°C) and pH values higher than 2 (measured at 25°C) are characterized by low δ7Li values (3.9 to 5.9‰) and 87Sr/86Sr ratios (0.704 to 0.705) similar to the values for island arc basalts. These results suggest low water-rock ratios during hydrothermal circulation. B concentrations and isotopic compositions in these fluids range from 1.0 to 2.6μM and 13 to 20‰, respectively. These data match with other vent fluids from island arc settings in the Western Pacific and plot in a B versus δ11B diagram on a two-component mixing line between seawater and island arc basalts [3]. Sr and Li isotopic composition of white smoker and acid-sulfate fluids overlap generally with the isotopic ratios for the black smoker fluids. However, in some fluids Sr isotope ratios are up to 0.709 near seawater composition suggesting higher water-rock ratios during water-rock interaction. B concentrations and isotope ratios in the white smoker and acid-sulfate fluids range from 0.6 to 2.2μM and 9 to 16‰, respectively which are lower compared with the values of black smoker fluids. In addition, these fluids do not fit on the mixing line between seawater and island arc basalt, and define another mixing trend in a B versus δ11B diagram. To explain this contradictory trend, a third mixing endmember is required that shifts B concentrations and δ11B to lower values. A possible mixing endmember is B volatized from magmatic gases. This endmember seems to be reasonable because it only influences B, whereas Li and Sr stay unaffected. [1] Reeves et al. (2011) GCA 75, 1088-1123 [2] Seewald et al. (2015) GCA 163, 178-199 [3] Yamaoka et al. (2015) CG 392, 9-18

Optimizing isotope substitution in graphene for thermal conductivity minimization by genetic algorithm driven molecular simulations

NASA Astrophysics Data System (ADS)

Davies, Michael; Ganapathysubramanian, Baskar; Balasubramanian, Ganesh

2017-03-01

We present results from a computational framework integrating genetic algorithm and molecular dynamics simulations to systematically design isotope engineered graphene structures for reduced thermal conductivity. In addition to the effect of mass disorder, our results reveal the importance of atomic distribution on thermal conductivity for the same isotopic concentration. Distinct groups of isotope-substituted graphene sheets are identified based on the atomic composition and distribution. Our results show that in structures with equiatomic compositions, the enhanced scattering by lattice vibrations results in lower thermal conductivities due to the absence of isotopic clusters.

Selective recharge and isotopic composition of shallow groundwater within temperate, epigenic carbonate aquifers

NASA Astrophysics Data System (ADS)

Florea, Lee J.

2013-05-01

This paper considers the variation of δ18O and δ2H (VSMOW) in precipitation and shallow groundwater from carbonate aquifers that lend insight into the source and timing of recharge within temperate, epigenic karst. The shallow groundwater collected during 2010 and 2011 at Stream Cave (SC) and Natural Bridge Caverns (NBC) represent one input to and the primary output from the Redmond Creek karst aquifer in the Cumberland Plateau of southeast Kentucky, respectively. These data are compared with the isotopic composition of concurrent samples of precipitation from the same watershed that covers some 1900 ha. Values of δ18O and δ2H at SC and NBC are statistically similar and cluster at the midpoint of the local meteoric water line. These values remain surprisingly constant despite seasonal changes in temperature regimens and discharge. Samples in 2012 from regional springs that include Redmond Creek are more depleted in the heavier isotope and similarly stable despite coming from aquifers of a range of sizes and physical characteristics. Applying a Priestly-Taylor model for daily values of potential evapotranspiration, only 43% of the 1.10 m of precipitation in the 2010-2011 dataset remains as potential recharge, primarily during cooler months with lower solar insolation. Weighting δ18O and δ2H values of precipitation by potential recharge creates a better match with the isotopic composition of shallow groundwater than by weighting by precipitation amount. The isotopic composition and deuterium excess of precipitation samples are directly and inversely proportional to temperature, respectively. Deuterium excess in this study and displays intra- and inter-annual variation that ranges from a minimum of +11.1‰ to a maximum of +29.5‰ that demonstrate the higher-than-average deuterium excess in greater Appalachia and the shifting latitude of moisture sources, including a significant winter component of re-evaporated, continental moisture.

Sedimentological and Stable Isotope Changes at the Messinian-Pliocene Boundary Along a West to East Mediterranean Transect.

NASA Astrophysics Data System (ADS)

Pierre, C.; Rouchy, J.; Blanc-Valleron, M.

2001-12-01

During Messinian times, the whole Mediterranean area was submitted to evaporitic conditions which ended by the "Lago-Mare" brackish episode before the reset of open marine conditions in the early Pliocene. These major paleoceanographic changes resulted from regional tectonic reorganizations and global climate changes at this critical time interval, both acting to modify drastically the physiography and the hydrological budget of the Mediterranean basins. There exist outcropping sections and a few deep-sea ODP cores which contain the complete and continuous sedimentary sequence of the Messinian-Pliocene boundary (MPB), making it possible to follow the paleoenvironmental changes at a high resolution scale. We compare here sedimentological and carbonate stable isotope records on three sections for which a high- resolution sampling was applied to the 2 meters thick interval including the MPB. In the Vera section from South Spain, there is no clear change in the carbonate content of the silty clay succession when crossing the MPB. The oxygen and carbon isotopic compositions of calcite both increase by 1 permil across a 40 cm-thick interval which corresponds to the Messinian-Pliocene transition. At ODP Site 968 from the eastern Levantine basin, there is an important sedimentary change between Messinian brown silty clays containing about 20 percent of carbonate and Pliocene gray nannofossil ooze which carbonate content averages 60 percent. Across this 10 cm-thick transitional interval, the oxygen and carbon isotopic compositions of bulk calcite both increase by 4.5 permil. In the Pissouri section from Cyprus, the uppermost Messinian reddish to brown marls with paleosoils are overlain by white Pliocene marls. The carbonate content increases from 20 percent to reach 60 percent across a 40 cm-thick transitional interval. Within this interval corresponding to the MPB, the oxygen and carbon isotopic compositions increase by 4 permil and 2 permil respectively. These results indicate that the MPB is recorded everywhere from W to E Mediterranean by significant and sharp increases in the oxygen and carbon isotopic compositions, which indicate that the early Pliocene marine flooding of the Mediterranean basins was a very abrupt event.

Revising Estimates of the Methane Production Pathway in Peatland Porewater Using Intramolecular Isotopic Analyses of Acetate

NASA Astrophysics Data System (ADS)

Thomas, B.; Arthur, M. A.; Freeman, K. H.

2007-12-01

Stable isotopic measurements of methane and carbon dioxide are routinely applied to environmental samples to assess the relative importance of methane production by either aceticlastic or hydrogenotrophic methanogenesis. Such estimates rely upon assumptions about isotopic fractionation during methane production and oxidation. Rigorous isotope-based pathway estimates require knowledge of the carbon isotopic composition of both carbon dioxide and acetate. In practice, technical barriers have limited measurements of the isotopic composition of whole acetate in natural samples. Yet, the estimate of whole acetate isotopic values, even when available, may not represent accurately the composition of the methyl carbon, which is, in fact, the precursor to methane. It is exceedingly rare to find carbon isotopic measurements of acetate-methyl in the literature, and, to our knowledge, the d13C of the acetate-methyl precursor to methane has never before been reported from peatland porewater samples. Extremely 13C-depleted methane, -70 permil VPDB, and 13C-enriched carbon dioxide from acidic northern peat bogs are typically interpreted as signatures of hydrogenotrophic methanogenesis. The hypothesized dominance of methane production from hydrogen in acidic bogs contrasts with the vast majority of freshwater wetlands in which aceticlastic methanogenesis dominates. Using a new technique for the online analysis of the intramolecular carbon isotopic composition of acetate in natural samples, we find the acetate-methyl in peat porewaters can be significantly depleted relative to bulk organic matter. In porewater profiles from both winter and summer, acetate is as much as 15 permil depleted relative to bulk carbon. We hypothesize that acetate- methyl isotopic depletion results from conditions that favor autotrophic acetogenesis and subsequent acetate consumption by aceticlastic methanogens. Porewater depth profiles during winter and summer illustrate depth- dependent increases in the fraction of methane derived from carbon dioxide, with deeper peat dominated by hydrogenotrophic methanogenesis, but shallow peat dominated by aceticlastic methanogens. Significant aceticlastic methane production from autotrophically produced acetate challenges the ability of hydrogen isotopic measurements of methane to represent the pathway of methanogenesis. Supplementing our field observations, intramolecular acetate measurements of incubation experiments confirm that an aceticlastic methanogen can facilitate significant acetate-carboxyl exchange with DIC. This novel technique confirms two caveats associated with whole acetate carbon isotopic data: 1, the carboxyl carbon isotopic composition may not accurately reflect the composition of the parent molecule, and 2, the acetate methyl may be derived from inorganic carbon or the fractionation effect of fermentation in acidic porewaters may be significant.

Methane clumped isotopes: Progress and potential for a new isotopic tracer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Douglas, Peter M. J.; Stolper, Daniel A.; Eiler, John M.

The isotopic composition of methane is of longstanding geochemical interest, with important implications for understanding hydrocarbon systems, atmospheric greenhouse gas concentrations, the global carbon cycle, and life in extreme environments. Recent analytical developments focusing on multiply substituted isotopologues (‘clumped isotopes’) are opening a potentially valuable new window into methane geochemistry. When methane forms in internal isotopic equilibrium, clumped isotopes can provide a direct record of formation temperature, making this property particularly valuable for identifying different methane origins. However, it has also become clear that in certain settings methane clumped isotope measurements record kinetic rather than equilibrium isotope effects. Here wemore » present a substantially expanded dataset of methane clumped isotope analyses, and provide a synthesis of the current interpretive framework for this parameter. We review different processes affecting methane clumped isotope compositions, describe the relationships between conventional isotope and clumped isotope data, and summarize the types of information that this measurement can provide in different Earth and planetary environments.« less

Technical note: An inverse method to relate organic carbon reactivity to isotope composition from serial oxidation

NASA Astrophysics Data System (ADS)

Hemingway, Jordon D.; Rothman, Daniel H.; Rosengard, Sarah Z.; Galy, Valier V.

2017-11-01

Serial oxidation coupled with stable carbon and radiocarbon analysis of sequentially evolved CO2 is a promising method to characterize the relationship between organic carbon (OC) chemical composition, source, and residence time in the environment. However, observed decay profiles depend on experimental conditions and oxidation pathway. It is therefore necessary to properly assess serial oxidation kinetics before utilizing decay profiles as a measure of OC reactivity. We present a regularized inverse method to estimate the distribution of OC activation energy (E), a proxy for bond strength, using serial oxidation. Here, we apply this method to ramped temperature pyrolysis or oxidation (RPO) analysis but note that this approach is broadly applicable to any serial oxidation technique. RPO analysis directly compares thermal reactivity to isotope composition by determining the E range for OC decaying within each temperature interval over which CO2 is collected. By analyzing a decarbonated test sample at multiple masses and oven ramp rates, we show that OC decay during RPO analysis follows a superposition of parallel first-order kinetics and that resulting E distributions are independent of experimental conditions. We therefore propose the E distribution as a novel proxy to describe OC thermal reactivity and suggest that E vs. isotope relationships can provide new insight into the compositional controls on OC source and residence time.

In search of the noble gas 3.52 Ga atmospheric signatures

NASA Astrophysics Data System (ADS)

Pujol, M.; Marty, B.; Philippot, P.

2008-12-01

The isotopic signatures of noble gases in the Present-day mantle and in the atmosphere permit exceptional insight into the evolution of these reservoirs through time ([1]). However, related exchange models are under- constrained and would require direct measurements of the atmospheric composition long ago, e.g., in the Archaean. Drilling in the the 3.52 Ga chert-barite ([2]) of the Dresser formation(Pilbara Drilling Project) , North Pole, Pilbara craton (Western Australia), led to recovery of exceptionally fresh samples preserving primary fluid inclusions unaffected by surface weathering. The whole formation is considered to be an already established basin when hydrothermal processes started. The chemical composition of primary fluid inclusions trapped in hydrothermal quartz from vacuolar komatiitic basalt from 110 m depth were determined by synchrotron X-ray microfluorescence (ESRF, Grenoble,France). Data show that fluids are relatively homogenous, consisting of a Ba-rich fluid and a Fe (+Ba)-rich fluid of hydrothermal origin as concluded by Foriel et al.([3]). The isotopic compositions of xenon and argon trapped in these fluids were measured by mass spectrometry following vacuum crushing. The three argon isotopes show a homogeneous signature quite different from present-day Earth atmosphere but we cannot exclude the possibility that secondary nuclear reactions produced these anomalies. Despite this, the Xe isotopic trends indicate a less radiogenic signature than the Present-day atmosphere, and probably represent a remnant of the Archaean atmosphere. If this xenon composition is primitive then it implies that there is no cosmogenic production through time. However, argon ratios could be explained by cosmogenic production which implies significant surface exposure times. Cosmogenic production will produce correlated argon and xenon isotope signatures. Therefore it is necessary to differentiate primary from secondary composition. To investigate the effects of these nuclear reactions on Xe isotope production, barite from 30m shallower depth in the same core were analyzed. Variable excesses can be linked to spallogenic and cosmogenic reactions ([4] [5] [6]) which allow the primitive Xe isotopic signature to be isolated from subsequent secondary production. Models of the archaean atmospheric noble gas signature can thereby be compared with different theories on primitive atmospheric composition. [1] Staudacher T. Allègre C.J. (1982) EPSL 60, p 389-406 [2] Van Kranendonk MJ., Hickman A.H., Williams I.R. and Nijman W. (2001) Rec.-Geol. Surv. West. Aust. 2001/9, 134 [3] Foriel J., Philippot P., Rey P., Somogyi A., Banks D. and Ménez B. (2004) EPSL, 228, 451-463 [4]Srinivasan B. (1976) EPSL, 31, 129-141 [5]Charalambus S. (1971) Nuclear Physics, A166, 145 [6]Meshik A. P., Hohenberg C. M., Pravdivtseva O. V. and Kapusta Y. (2001) Phys. Rev., C 64, 035205-1 035205-6

Oxygen-isotope, X-ray-diffraction and scanning-electron-microscope examinations of authigenic-layer-silicate minerals from Mississippian and Pennsylvanian sandstones in the Michigan Basin

USGS Publications Warehouse

Zacharias, K.F.; Sibley, D.F.; Westjohn, D.B.; Weaver, T. L.

1993-01-01

Oxygen-isotope compositions of authigenic-layer silicates (<2-micrometer fraction) extracted from Mississippian and Pennsylvanian sandstones in the Lower Peninsula of Michigan were determined. Petrographic and scanning-electron-microscope examinations, and X-ray diffractograms show that chlorite and kaolinite are the most common authigenic-layer silicates in Mississippian sandstones. The range of oxygen-isotope compositions of chlorite and kaolinite are +10.3 to +11.9 and +12.9 to +19.3 pars per thousand (per mil) (relative to Standard Mean Ocean Water), respectively. Kaolinite is the only authigenic-isotopic compositions of kaolinite range from +16.8 to +19.0 per mil.

Stalagmite geochemistry and the timing of the last interglacial-glacial transition in Central Europe (NE Hungary)

NASA Astrophysics Data System (ADS)

Siklosy, Z.; Demeny, A.; Pilet, S.; Leel-Ossy, Sz.; Lin, K.; Shen, C.-C.

2009-04-01

Speleothems can provide accurate chronologies for reconstructions of climate change by combination of U/Th dating and climate-related geochemical compositions. Geochemical studies of speleothems from Central Europe are mostly based on stable C and O isotope analyses, thus, complex geochemical studies combining isotope and trace element measurements are needed for more reliable climate models for this transitional area between oceanic and continental regions. We present stable H-C-O isotope and trace element records obtained on speleothems covering the Last Interglacial (MIS 5e) and the transition to MIS 5d. A stalagmite from Baradla Cave grew from 127.5 to 110 ka. Accelerated growth rates have been detected by U/Th age data in the 127 to 126 ka and 119 to 117 ka parts. Trace element compositions and 230Th/232Th ratios suggest changes in the hydrological regime, whereby early calcite precipitates formed in fissures during the dry and cold glacial period were dissolved by the starting flux of infiltrating meteoric water (producing elevated dissolved ion concentration but low detrital Th component), then the increasing amount of dripwater during the interglacial period resulted in trace element dilution. Temperature and precipitation amount variations are also reflected by the stable isotope compositions. Oxygen isotope composition shows a continuous increase from 127.5 ka until about 118 ka most probably related to temperature rise, whereas C isotope values are shifted in negative direction suggesting increasing humidity in accordance with trace element contents. The presumably warmest period at ca. 118 ka is associated with rather arid climate as indicated by peak d18O values coinciding with the highest dD values of fluid inclusion water. This is followed by a pronounced negative shift in both O and H isotope values, similarly to recent Alpine studies (Meyer et al., 2008), most probably related to cooling. Hydrogen isotope compositions of fluid inclusion water evaluated together with calculated oxygen isotope compositions of water indicate warming and increasing significance of summer precipitation at the latest period of the last interglacial, then increasing importance of winter precipitation and/or changes in oceanic source composition during the cooling phase. The good agreement with other (Alpine and marine) records indicate a synchronous climate change. However, after a negative shift in the wet/warm phase (increasing soil activity), C isotope values start to increase already at about 119 ky BP, warning to the use of the two isotope systems as event correlation tools. In conclusion, our combined isotope and trace element study indicate a complex pattern of temperature and humidity variations during and right after the Last Interglacial. Acknowledgements — This study was financially supported by the Hungarian Scientific Research Fund (OTKA T 049713). Measurements of U-Th isotopic compositions and and 230Th dates were supported by the National Science Council grants (94-2116-M002-012, 97-2752-M002-004-PAE & -005-PAE to C.C.S.). [Meyer, M.; Spötl, C.; Mangini, A. (2008): The demise of the Last Interglacial recorded in isotopically dated speleothems from the Alps. Quaternary Science Reviews, 27, 476-496.

Carbon isotope geochemistry and geobiology

NASA Technical Reports Server (NTRS)

Desmarais, D.

1985-01-01

Carbon isotope fractionation values were used to understand the history of the biosphere. For example, plankton analyses confirmed that marine extinctions at the end of the Cretaceous period were indeed severe (see Hsu's article in Sundquist and Broeker, 1984). Variations in the isotopic compositions of carbonates and evaporitic sulfates during the Paleozoic reflect the relative abundances of euxinic (anoxic) marine environments and organic deposits from terrestrial flora. The carbon isotopic composition of Precambrian sediments suggest that the enzyme ribulose bisphosphate carboxylase has existed for perhaps 3.5 billion years.

Seasonal Cyclicity in Trace Elements and Stable Isotopes of Modern Horse Enamel.

PubMed

de Winter, Niels J; Snoeck, Christophe; Claeys, Philippe

2016-01-01

The study of stable isotopes in fossil bioapatite has yielded useful results and has shown that bioapatites are able to faithfully record paleo-environmental and paleo-climatic parameters from archeological to geological timescales. In an effort to establish new proxies for the study of bioapatites, intra-tooth records of enamel carbonate stable isotope ratios from a modern horse are compared with trace element profiles measured using laboratory micro X-Ray Fluorescence scanning. Using known patterns of tooth eruption and the relationship between stable oxygen isotopes and local temperature seasonality, an age model is constructed that links records from six cheek upper right teeth from the second premolar to the third molar. When plotted on this age model, the trace element ratios from horse tooth enamel show a seasonal pattern with a small shift in phase compared to stable oxygen isotope ratios. While stable oxygen and carbon isotopes in tooth enamel are forced respectively by the state of the hydrological cycle and the animal's diet, we argue that the seasonal signal in trace elements reflects seasonal changes in dust intake and diet of the animal. The latter explanation is in agreement with seasonal changes observed in carbon isotopes of the same teeth. This external forcing of trace element composition in mammal tooth enamel implies that trace element ratios may be used as proxies for seasonal changes in paleo-environment and paleo-diet.

Seasonal Cyclicity in Trace Elements and Stable Isotopes of Modern Horse Enamel

PubMed Central

Snoeck, Christophe; Claeys, Philippe

2016-01-01

The study of stable isotopes in fossil bioapatite has yielded useful results and has shown that bioapatites are able to faithfully record paleo-environmental and paleo-climatic parameters from archeological to geological timescales. In an effort to establish new proxies for the study of bioapatites, intra-tooth records of enamel carbonate stable isotope ratios from a modern horse are compared with trace element profiles measured using laboratory micro X-Ray Fluorescence scanning. Using known patterns of tooth eruption and the relationship between stable oxygen isotopes and local temperature seasonality, an age model is constructed that links records from six cheek upper right teeth from the second premolar to the third molar. When plotted on this age model, the trace element ratios from horse tooth enamel show a seasonal pattern with a small shift in phase compared to stable oxygen isotope ratios. While stable oxygen and carbon isotopes in tooth enamel are forced respectively by the state of the hydrological cycle and the animal’s diet, we argue that the seasonal signal in trace elements reflects seasonal changes in dust intake and diet of the animal. The latter explanation is in agreement with seasonal changes observed in carbon isotopes of the same teeth. This external forcing of trace element composition in mammal tooth enamel implies that trace element ratios may be used as proxies for seasonal changes in paleo-environment and paleo-diet. PMID:27875538

Geology, geochronology, and geochemistry of basaltic flows of the Cat Hills, Cat Mesa, Wind Mesa, Cerro Verde, and Mesita Negra, central New Mexico

USGS Publications Warehouse

Maldonado, F.; Budahn, J.R.; Peters, L.; Unruh, D.M.

2006-01-01

The geochronology, geochemistry, and isotopic compositions of basaltic flows erupted from the Cat Hills, Cat Mesa, Wind Mesa, Cerro Verde, and Mesita Negra volcanic centres in central New Mexico indicate that each of these lavas had unique origins and that the predominant mantle involved in their production was an ocean-island basalt type. The basalts from Cat Hills (0.11 Ma) and Cat Mesa (3.0 Ma) are similar in major and trace element composition, but differences in MgO contents and Pb isotopic values are attributed to a small involvement of a lower crustal component in the genesis of the Cat Mesa rocks. The Cerro Verde rock is comparable in age (0.32 Ma) to the Cat Hills lavas, but it is more radiogenic in Sr and Nd, has higher MgO contents, and has a lower La/Yb ratio. This composition is explained by the melting of an enriched mantle source, but the involvement of another crustal component cannot be disregarded. The Wind Mesa rock is characterized by similar age (4.01 Ma) and MgO contents, but it has enriched rare-earth element contents compared with the Cat Mesa samples. These are attributed to a difference in the degree of partial melting of the Cat Mesa source. The Mesita Negra rock (8.11 Ma) has distinctive geochemical and isotopic compositions that suggest a different enriched mantle and that large amounts of a crustal component were involved in generating this magma. These data imply a temporal shift in magma source regions and crustal involvement, and have been previously proposed for Rio Grande rift lavas. ?? 2006 NRC Canada.

Calcium and Titanium Isotope Fractionation in CAIS: Tracers of Condensation and Inheritance in the Early Solar Protoplanetary Disk

NASA Technical Reports Server (NTRS)

Simon, J. I.; Jordan, M. K.; Tappa, M. J.; Kohl, I. E.; Young, E. D.

2016-01-01

The chemical and isotopic compositions of calcium-aluminum-rich inclusions (CAIs) can be used to understand the conditions present in the protoplantary disk where they formed. The isotopic compositions of these early-formed nebular materials are largely controlled by chemical volatility. The isotopic effects of evaporation/sublimation, which are well explained by both theory and experimental work, lead to enrichments of the heavy isotopes that are often exhibited by the moderately refractory elements Mg and Si. Less well understood are the isotopic effects of condensation, which limits our ability to determine whether a CAI is a primary condensate and/or retains any evidence of its primordial formation history.

Modeling the carbon isotope composition of bivalve shells (Invited)

NASA Astrophysics Data System (ADS)

Romanek, C.

2010-12-01

The stable carbon isotope composition of bivalve shells is a valuable archive of paleobiological and paleoenvironmental information. Previous work has shown that the carbon isotope composition of the shell is related to the carbon isotope composition of dissolved inorganic carbon (DIC) in the ambient water in which a bivalve lives, as well as metabolic carbon derived from bivalve respiration. The contribution of metabolic carbon varies among organisms, but it is generally thought to be relatively low (e.g., <10%) in shells from aquatic organism and high (>90%) in the shells from terrestrial organisms. Because metabolic carbon contains significantly more C-12 than DIC, negative excursions from the expected environmental (DIC) signal are interpreted to reflect an increased contribution of metabolic carbon in the shell. This observation contrasts sharply with modeled carbon isotope compositions for shell layers deposited from the inner extrapallial fluid (EPF). Previous studies have shown that growth lines within the inner shell layer of bivalves are produced during periods of anaerobiosis when acidic metabolic byproducts (e.g., succinic acid) are neutralized (or buffered) by shell dissolution. This requires the pH of EPF to decrease below ambient levels (~7.5) until a state of undersaturation is achieved that promotes shell dissolution. This condition may occur when aquatic bivalves are subjected to external stressors originating from ecological (predation) or environmental (exposure to atm; low dissolved oxygen; contaminant release) pressures; normal physiological processes will restore the pH of EPF when the pressure is removed. As a consequence of this process, a temporal window should also exist in EPF at relatively low pH where shell carbonate is deposited at a reduced saturation state and precipitation rate. For example, EPF chemistry should remain slightly supersaturated with respect to aragonite given a drop of one pH unit (6.5), but under closed conditions, equilibrium carbon isotope fractionation relations dictate that shell carbonate should be preferentially enriched in C-13 by 3 to 5 per mill (from 30° to 0°C) compared to EPF at a pH of 7.5. Anomalous positive excursions are rarely, if ever, observed in shell carbonate and they have yet to be associated with growth cessation markers in bivalves. The most likely explanation for the lack of anomalous positive values is that the percentage of metabolic carbon increases in EPF when bivalves experience stressful condition. This influx of metabolic carbon is balanced to a measureable extent by the enhanced fractionation of carbon isotopes during shell deposition from EPF at relatively low pH. These two processes may be combined in a quantitative model to extract a historical record of metabolic activity from the carbon isotope profiles of bivalve shells.

Spatial, seasonal, and source variability in the stable oxygen and hydrogen isotopic composition of tap waters throughout the USA

USGS Publications Warehouse

Landwehr, Jurate M.; Coplen, Tyler B.; Stewart, David W.

2013-01-01

To assess spatial, seasonal, and source variability in stable isotopic composition of human drinking waters throughout the entire USA, we have constructed a database of δ18O and δ2H of US tap waters. An additional purpose was to create a publicly available dataset useful for evaluating the forensic applicability of these isotopes for human tissue source geolocation. Samples were obtained at 349 sites, from diverse population centres, grouped by surface hydrologic units for regional comparisons. Samples were taken concurrently during two contrasting seasons, summer and winter. Source supply (surface, groundwater, mixed, and cistern) and system (public and private) types were noted. The isotopic composition of tap waters exhibits large spatial and regional variation within each season as well as significant at-site differences between seasons at many locations, consistent with patterns found in environmental (river and precipitation) waters deriving from hydrologic processes influenced by geographic factors. However, anthropogenic factors, such as the population of a tap’s surrounding community and local availability from diverse sources, also influence the isotopic composition of tap waters. Even within a locale as small as a single metropolitan area, tap waters with greatly differing isotopic compositions can be found, so that tap water within a region may not exhibit the spatial or temporal coherence predicted for environmental water. Such heterogeneities can be confounding factors when attempting forensic inference of source water location, and they underscore the necessity of measurements, not just predictions, with which to characterize the isotopic composition of regional tap waters. Published 2013. This article is a U.S. Government work and is in the public domain in the USA.

Multiple enrichment of the Carpathian-Pannonian mantle: Pb-Sr-Nd isotope and trace element constraints

NASA Astrophysics Data System (ADS)

Rosenbaum, Jeffrey M.; Wilson, Marjorie; Downes, Hilary

1997-07-01

Pb isotope compositions of acid-leached clinopyroxene and amphibole mineral separates from spinel peridotite mantle xenoliths entrained in Tertiary-Quaternary alkali basalts from the Carpathian-Pannonian Region of eastern Europe provide important constraints on the processes of metasomatic enrichment of the mantle lithosphere in an extensional tectonic setting associated with recent subduction. Principal component analysis of Pb-Sr-Nd isotope and rare earth element compositions of the pyroxenes is used to identify the geochemical characteristics of the original lithospheric mantle protolith and a spectrum of infiltrating metasomatic agents including subduction-related aqueous fluids and silicate melts derived from a subduction-modified mantle wedge which contains a St. Helena-type (HIMU) plume component. The mantle protolith is highly depleted relative to mid-ocean ridge basalt-source mantle with Pb-Nd-Sr isotope compositions consistent with an ancient depletion event. Silicate melt infiltration into the protolith accounts for the primary variance in the Pb-Sr-Nd isotope compositions of the xenoliths and has locally generated metasomatic amphibole. Infiltration of aqueous fluids has introduced radiogenic Pb and Sr without significantly perturbing the rare earth element signature of the protolith. The Pb isotope compositions of the fluid-modified xenoliths suggest that they reacted with aqueous fluids released from a subduction zone which had equilibrated with sediment derived from an ancient basement terrain. We propose a model for mantle lithosphere evolution consistent with available textural and geochemical data for the xenolith population. The Pb-Sr-Nd isotope compositions of both alkaline mafic magmas and rare, subduction-related, calc-alkaline basaltic andesites from the region provide important constraints for the nature of the asthenospheric mantle wedge and confirm the presence of a HIMU plume component. These silicate melts contribute to the metasomatism of the mantle lithosphere rather than being derived therefrom.

Crustal forensics in arc magmas

NASA Astrophysics Data System (ADS)

Davidson, Jon P.; Hora, John M.; Garrison, Jennifer M.; Dungan, Michael A.

2005-01-01

The geochemical characteristics of continental crust are present in nearly all arc magmas. These characteristics may reflect a specific source process, such as fluid fluxing, common to both arc magmas and the continental crust, and/or may reflect the incorporation of continental crust into arc magmas either at source via subducted sediment, or via contamination during differentiation. Resolving the relative mass contributions of juvenile, mantle-derived material, versus that derived from pre-existing crust of the upper plate, and providing these estimates on an element-by-element basis, is important because: (1) we want to constrain crustal growth rates; (2) we want to quantitatively track element cycling at convergent margins; and (3) we want to determine the origin of economically important elements and compounds. Traditional geochemical approaches for determining the contributions of various components to arc magmas are particularly successful when applied on a comparative basis. Studies of suites from multiple magmatic systems along arcs, for which differentiation effects can be individually constrained, can be used to extrapolate to potential source compositions. In the Lesser Antilles Arc, for example, differentiation trends from individual volcanoes are consistent with open-system evolution. However, such trends do not project back to a common primitive magma composition, suggesting that differentiation modifies magmas that were derived from distinct mantle sources. We propose that such approaches should now be complemented by petrographically constrained mineral-scale isotope and trace element analysis to unravel the contributing components to arc magmas. This innovative approach can: (1) better constrain true end-member compositions by returning wider ranges in geochemical compositions among constituent minerals than is found in whole rocks; (2) better determine magmatic evolution processes from core-rim isotopic or trace element profiles from the phases contained in magmas; and (3) constrain rates of differentiation by applying diffusion-controlled timescales to element profiles. An example from Nguaruhoe Volcano, New Zealand, underscores the importance of such a microsampling approach, showing that mineral isotopic compositions encompass wide ranges, that whole-rock isotopic compositions are consequently simply element-weighted averages of the heterogeneous crystal cargo, and that open-system evolution is proved by core-rim variations in Sr isotope ratios. Nguaruhoe is just one of many systems examined through microanalytical approaches. The overwhelming conclusion of these studies is that crystal cargoes are not truly phenocrystic, but are inherited from various sources. The implication of this realization is that the interpretation of whole-rock isotopic data, including the currently popular U-series, needs careful evaluation in the context of petrographic observations.