Boron Isotope Ratios Research Articles

High-precision isotopic analysis of boron by positive thermal ionization mass spectrometry with sample preheating

We present a methodology for the precise and accurate analysis of boron isotope ratios (11B/10B) by positive thermal ionization mass spectrometry (P-TIMS) using Cs2BO2+ ions. Samples in the form of caesium borate were loaded onto Ta filaments together with graphite and mannitol. The addition of mannitol to the samples is essential to suppress boron volatilization during acid treatment of the samples but is known to lower the performance of P-TIMS. Therefore, the prepared filaments were preheated in an oven at 240 °C to eliminate the mannitol thus stabilizing the chemical species of boron on the filament and increasing the ionization efficiency of Cs2BO2+, which enabled high-precision isotopic analysis of boron with small sample sizes. Analyses of NIST SRM 951 standard showed external reproducibility (2RSD) better than ±0.1‰ for 50–100 ng B and ±0.2‰ for 10 ng B. Ultrafiltration followed by cation- and anion-exchange chromatography was used to chemically separate boron from natural samples. Analyses of coral standard GSJ JCp-1 and seawater standard IRMM BCR-403 gave average δ11B values of +24.25 ± 0.08‰ and +39.58 ± 0.11‰ (2SD), respectively. The P-TIMS method developed in this study is applicable to a wide field of boron isotopic research that requires high precision and accuracy, including paleo-pH studies using marine carbonate samples.

Accurate and High-Precision Determination of Boron Isotopic Ratios at Low Concentration by MC-ICP-MS (Neptune)

Accurate and High-Precision Determination of Boron Isotopic Ratios at Low Concentration by MC-ICP-MS (Neptune)

Development and validation of a single collector SF-ICPMS procedure for the determination of boron isotope ratios in water and food samples

Boron isotope studies on technical materials and geological and environmental samples are one hot topic in nowadays isotope research. Provenance studies of artefacts, food and other products might become another one, as several recent studies demonstrate. Typically boron isotope determinations have been carried out by TIMS. To open up this research field to a broader scientific community we developed two analytical procedures for boron isotope determinations based on single collector SF-ICPMS combined with a sample preparation procedure consisting of dry-ashing and a three step ion chromatographic boron-matrix separation. The developed procedures consist of one low resolution (LR) and one medium resolution (MR) procedure. The repeatability for the δ11B determination in three independently measured aliquots lies between 0.2 and 0.8‰ for the LR procedure and between 0.3 and 1.5‰ for the MR procedure. The expanded uncertainties with a coverage factor of k=2 range between 1.4 and 1.6‰ for the LR procedure and between 2.9 and 3.2‰ for the MR procedure. The accuracy, expressed as average deviation from the reference values, is 0.43‰ for the LR procedure and 0.33‰ for the MR procedure. To test the practicability of the procedures the matrix tolerance has been investigated as well and was found to be up to 2 mg kg−1 of alkaline and alkaline earth elements in the final measurement solution containing 100 µg kg−1boron. Thus a highly efficient matrix separation for SF-ICPMS boron isotope determinations is required, similar to TIMS.

Accurate and High-Precision Determination of Boron Isotopic Ratios at Low Concentration by MC-ICP-MS (Neptune)

We report an approach for the accurate and reproducible measurement of boron isotope ratios in natural waters using an MC-ICP-MS (Neptune) after wet chemistry sample purification. The sample matrix can induce a drastic shift in the isotopic ratio by changing the mass bias. It is shown that, if no purification is carried out, the direct measurement of a seawater diluted one hundred times will induce an offset of −7‰ in the isotopic ratio, and that, for the same concentration, the greater the atomic mass of the matrix element, the greater the bias induced. Whatever the sample, it is thus necessary to remove the matrix. We propose a method adapted to water samples allowing purification of 100 ng of boron with a direct recovery of boron in 2 ml of 3% v/v HNO3, which was our working solution. Boron from the International Atomic Energy Agency IAEA-B1 seawater reference material and from the two groundwater reference materials IAEA-B2 and IAEA-B3, was chemically purified, as well as boron from the certified reference material NIST SRM 951 as a test. The reproducibility of the whole procedure (wet chemistry and MC-ICP-MS measurement) was ± 0.4‰ (2s). Accuracy was verified by comparison with positive-TIMS values and with recommended values. Seawater, being homogeneous for boron isotope ratios, is presently the only natural water material that is commonly analysed for testing accuracy worldwide. We propose that the three IAEA natural waters could be used as reference samples for boron isotopes, allowing a better knowledge of their isotopic ratios, thus contributing to the certification of methods and improving the quality of the boron isotopic ratio measurements for all laboratories. Nous présentons ici une approche permettant la mesure juste et reproductible des rapports isotopiques du bore dans les eaux naturelles par l’utilisation d’un MC-ICP-MS (Neptune) après purification chimique de l’échantillon. Comme nous le démontrons, la matrice de l’échantillon peut induire un fractionnement important des rapports isotopiques. La mesure directe d’une eau de mer non purifiée, simplement diluée cent fois, entraine une différence de −7‰ sur le rapport isotopique. Il est également montré, qu’à teneur identique, plus l’élément est de masse atomique élevée, plus le biais sera important. Quel que soit l’échantillon, il s’avère nécessaire de le purifier. Nous proposons une méthode adaptée aux eaux naturelles permettant la purification de 100 ng de bore avec une récupération directe du bore dans 2 ml de 3% v/v HNO3 qui est la solution utilisée en routine pour la mesure sur notre MC-ICP-MS. La purification chimique du bore a été réalisée sur une eau de mer (IAEA-B1) et deux eaux souterraines (IAEA-B2 et IAEA-B3) ainsi que sur le matériau de référence NIST SRM 951. La reproductibilité de la procédure (purification chimique et analyse au NEPTUNE) est de ± 0.4‰ (2s). La justesse est vérifiée par comparaison avec des valeurs obtenues en P-TIMS ainsi qu’avec les valeurs recommandées. L’eau de mer étant homogène pour les rapports isotopiques du bore, elle est actuellement la seule eau naturelle analysée couramment pour tester la justesse des mesures au sein de différents laboratoires. Nous proposons que les trois eaux naturelles de l’IAEA soient utilisées en tant que solutions de référence pour les isotopes du bore, permettant ainsi une meilleure connaissance de leur rapport isotopique, et par conséquent aidant à la certification des méthodes et améliorant la qualité de la mesure des rapports isotopiques du bore dans les différents laboratoires.

MC‐ICP‐MS Isotope Measurements with Direct Injection Nebulisation (d‐DIHEN): Optimisation and Application to Boron in Seawater and Carbonate Samples

We report here an optimisation of the demountable direct injection high efficiency nebuliser (d‐DIHEN) for isotopic measurements with a Neptune (ThermoFisher Scientific, Bremen, Germany) multi‐collector inductively coupled plasma‐mass spectrometer (MC‐ICP‐MS) and describe a method for boron isotopic ratio determination. With direct injection nebulisation 100% of the analyte was introduced into the ICP‐MS plasma and wash times were drastically reduced for elements such as boron and thorium. Compared to the classical stable introduction system (SIS: double Scott/cyclonic spray chamber), sensitivity for boron was 2–5 times higher with d‐DIHEN and wash times up to ten times shorter. Repeatability of 11B/10B sample‐calibrator bracketing measurements reached 0.25‰ (2s) for seawater and coral samples. Method accuracy and reproducibility were tested on mixed reference solutions having δ11B values in the ranges −90 to +40‰ and −2 to +2.5‰, demonstrating our ability to distinguish δ11B values with differences of only 0.25‰. The international seawater reference material NRCC NASS‐5 (National Research Council, Ottawa, Canada), analysed in different sessions over a 10‐month period, yielded an average δ11B value of +39.89 ± 0.25‰, in the upper range of previously published seawater values. A comparison between δ11B determined by d‐DIHEN MC‐ICP‐MS and positive‐TIMS (P‐TIMS) for four modern corals showed an excellent agreement (with bias of less than 0.4‰).

In situ boron isotope measurements of natural geological materials by LA-MC-ICP-MS

There are two main methods to determine boron isotopic composition. One is the solution method, in which boron is purified after the samples are dissolved in solution and the boron isotope ratios are determined by thermal ionization mass spectrometry (P-TIMS and N-TIMS) or multicollector inductively coupled plasma mass spectrometry (MC-ICP-MS). The other is an in-situ analysis method, in which the in-situ boron isotopic ratios in minerals are analyzed directly using secondary ion mass spectrometry (SIMS) or laser ablation multicollector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS). In the in-situ analysis method for boron isotopes, the multifarious chemical purification and separation processes of the solution method are avoided, with increased work efficiency. In addition, the microzones and microbeddings of minerals can be analyzed in-situ to reveal the fine processes and conditions of mineral formation. In this study, using the standard-sample-bracketing (SSB) method, mass bias of the instrument and the fractionation of isotopes were calibrated, and the in-situ determination method of LA-MC-ICP-MS for boron isotopes was established. Through detailed analyses on a series of boron isotope standards and samples, a matrix effect was assessed but not detected, and the analysis results were in accordance with the formerly reported values or P-TIMS determined values, within the error range. The analytical results for IAEA B4 and IMR RB1 with relatively high boron contents were δ11B = −(8.36±0.58)‰ (2σ, n=50) and δ11B = −(12.96±0.97)‰ (2σ, n=57), respectively; the analytical result for IAEA B6 with relatively low boron content was δ11B = −(3.29±1.12)‰ (2σ, n=35). In-situ measurements for B isotopes were performed on geological samples such as tourmaline, ulexite, ludwigite, inyoite and ascharite, with the results consistent with those determined by P-TIMS, within the error range.

Boron isotope ratio determination in carbonates via LA-MC-ICP-MS using soda-lime glass standards as reference material

A new in situ method using LA-MC-ICP-MS (193 nm excimer laser) for the determination of stable boron isotope ratios (δ11B) in carbonates was developed. Data were acquired via a standard sample standard bracketing procedure typically providing a reproducibility of 0.5‰ (SD) for samples containing 35 ppm of boron. A single ablation interval consumed about 5 µg of sample corresponding to about 0.2 ng of boron. The major finding was the similar instrumental fractionation behaviour of carbonates, soda-lime glass and sea salt with respect to boron isotopes. As no matrix induced offset was detectable between these distinct materials we propose the use of NIST glasses as internal standards for boron isotope ratio measurements via LA-MC-ICP-MS. This finding overcomes the problem of a missing matrix matched carbonate standard for in situ boron isotope studies. As a first application a set of coral samples from a culturing experiment was analysed. δ11B values range from 19.5 to 25‰ depending on the pH of the water used in the particular treatment. This is in good agreement with the results of earlier studies.

Boron isotope ratio (δ11B) measurements in Water Framework Directive monitoring programs: comparison between double focusing sector field ICP and thermal ionization mass spectrometry

The aim of our research was to compare delta B-11 measurements performed with thermal ionization mass spectrometry (TIMS) and sector field-inductively coupled plasma-mass spectrometry (SF-ICP-MS) and evaluate the feasibility of implementing stable isotope methods in European water framework directive (WFD) monitoring programs. The comparison was based on delta B-11 measurements of 192 ground-and surface water samples and 15 leachates of nitrate pollution source materials (organic and mineral fertilisers). The precision of delta B-11 measurements attainable with SF-ICP-MS, 2 sigma= +/- 2.6 parts per thousand; (n = 192), is as expected lower than the precision achieved by TIMS, 2 sigma= +/- 0.3 parts per thousand (n=183). However the ease of use, rapidity and availability of SF-ICP-MS on one hand and the observed variability in delta B-11 in ground-and surface water on the other (from -3.4 to +37 parts per thousand), demonstrates that using SF-ICP-MS as an isotopic screening method would promote the use of isotopic methodology for WFD monitoring. Based on the results of the different case studies it is shown that retrieving precise information on the identification of pollution sources from delta B-11 values requires reaching the best analytical precision and accuracy possible. Hence, the superior precision of TIMS advantages tracing of nitrate pollution sources. However for some cases, e. g. trying to decipher contributions between sources with really distinct delta B-11 signatures (e.g. manure and sewage effluent), SF-ICP-MS results lead to the same conclusions and can therefore be used as a first approachable screening method for the determination of delta B-11 in WFD monitoring programs.

Interlaboratory Comparison for Boron Isotope Ratio Measurement with Inductively Coupled Plasma - Quadrupole Mass Spectrometer

Boron isotope ratios were analyzed in seven domestic analytical labs for boric acid solutions with various compositions of boron isotope abundances, using an Inductively Coupled Plasma–Quadrupole Mass Spectrometer (ICP-QMS). Five sample solutions with different isotope abundances of 10B were prepared in the range of 10 to 20% by mixing two boric acid solutions containing natural B and enriched 11B, respectively. Then, the 10B isotope abundances of each sample were certified by analyzing with thermal ionization mass spectrometry (TI-MS) according to ASTM-C791-04. Results obtained from each lab have indicated good coincidences with TI-MS results. Also, the relative standard deviations of results with ICP-QMS of seven analytical labs were 0.11 to 0.81%. The measurement precision for ICP-QMS would be sufficient in terms of practical use, while taking into consideration a valid requirement required for verifying a depletion of the 10B isotope abundance in the PWR coolant, while this is greater than a nominal analytical error (relative value : 0.22%) for TI-MS shown in ASTM-C791-04.

Intra-shell boron isotope ratios in the symbiont-bearing benthic foraminiferan Amphistegina lobifera: Implications for δ 11B vital effects and paleo-pH reconstructions

The boron isotope composition of marine carbonates is considered to be a seawater pH proxy. Nevertheless, the use of δ 11B has some limitations such as the knowledge of the fractionation factor ( α 4-3) between boric acid and the borate ion and the amplitude of “vital effects” on this proxy that are not well constrained. Using secondary ion mass spectrometry (SIMS) we have examined the internal variability of the boron isotope ratio in the shallow water, symbionts bearing foraminiferan Amphistegina lobifera. Specimens were cultured at constant temperature (24 ± 0.1 °C) in seawater with pH ranging between 7.90 and 8.45. Intra-shell boron isotopes showed large variability with an upper limit value of ≈30‰. Our results suggest that the fractionation factor α 4-3 of 0.97352 ( Klochko et al., 2006) is in better agreement with our experiments and with direct pH measurements in seawater vacuoles associated with the biomineralization process in these foraminifera. Despite the large variability of the skeletal pH values in each cultured specimen, it is possible to link the lowest calculated pH values to the experimental culture pH values while the upper pH limit is slightly below 9. This variability can be interpreted as follows: foraminifera variably increase the pH at the biomineralization site to about 9. This increase above ambient seawater pH leads to a range in δ 11B (Δ 11B) for each seawater pH. This Δ 11B is linearly correlated with the culture seawater pH with a slope of −13.1 per pH unit, and is independent of the fractionation factor α 4-3, or the δ 11B sw through time. It may also be independent of the p K B (the dissociation constant of boric acid) value. Therefore, Δ 11B in foraminifera can potentially reconstruct paleo-pH of seawater.

Boron isotope determinations in waters and other geological materials: Analytical techniques and inter-calibration of measurements†

The 11B/10B ratio exhibits wide variations in nature; thus, boron isotopes have found numerous applications in geochemistry, hydrology, and environmental studies. The main analytical techniques used are as follows: positive thermal ionisation mass spectrometry is the most precise (about 0.2‰ of the boron isotope ratio), but requires complex and laborious sample preparation; negative thermal ionisation mass spectrometry is less precise (about 0.5‰), but rapid and suitable for water samples, whereas total evaporation-NTIMS allows for identification of the precise boron isotope composition of marine carbonates. It is expected that multi-collection system inductively coupled plasma mass spectrometry (MC-ICPMS) will eventually combine high precision with simple analytical procedures. Secondary ion mass spectrometry and laser ablation (LA)-MC-ICPMS allow in situ determinations on solid samples, but require the availability of calibration materials which are chemically and mineralogically similar to samples. These features of boron isotope measurement techniques were confirmed by the results of the first inter-laboratory comparison of measurements, organised by the Istituto di Geoscienze e Georisorse in Pisa. Finally, two examples of boron isotope applications in groundwater investigations are reported. †Updated paper: originally presented on the IAEA International Symposium “Quality Assurance for Analytical Methods in Isotope Hydrology” (August 2004, Vienna).

B and Li isotopes as intrinsic tracers for injection tests in aquifer storage and recovery systems

Abstract Boron and Li isotopes have been tested as environmental tracers of treated sewage injected into a sandy aquifer (Shafdan reclamation project, Israel). During a 38 days injection test in a newly dug injection well, a conservative artificial tracer (Br−) was monitored together with δ11B and δ7Li in the injectate, in the unsaturated soil zone (porous cup) and an observation well in the aquifer. In spite of B and Li concentrations in the injectate close to background values, significant shifts of the isotope signatures could be observed over the duration of the injection test. Boron isotope ratios show a breakthrough curve delayed with respect to Br− breakthrough due to some reversible sorption on the aquifer material. No isotope fractionation was observed in the unsaturated or the saturated zone so that B isotopes can be considered as conservative in the investigated part of the aquifer system. Lithium isotopes are strongly fractionated, probably due to sorption processes. Lithium concentrations point to a Li sink in the system, δ7Li values vary strongly with a tendency of 7Li depletion in the liquid phase over the duration of the experiment. This is opposite to the expected preferential sorption of 6Li onto clay minerals. Boron isotopes reveals a valuable tracer of artificial recharge of freshwaters derived from treated sewage, both for short term tracer tests and for long-term monitoring of artificial recharge, even if in aquifers with higher clay contents, sorption-linked isotope fractionation cannot be excluded. More data are needed on Li isotope fractionation in natural groundwater systems to assess the potential of this tracer as monitoring tool.

Estimation of boron isotope ratios using high resolution continuum source atomic absorption spectrometry

In the production of 10B enriched steels, the production–recycling process needs to be closely monitored for inadvertent mix-up of materials with different B isotope levels. A quick and simple method for the estimation of boron isotope ratios in high alloyed steels using high resolution continuum source flame AAS (HR-CS-FAAS) was developed. On the 208.9 nm B line the wavelength of the peak absorption of 10B and 11B differs by 2.5 pm. The wavelength of the peak absorption of boron was determined by fitting a Gauss function through spectra simultaneously recorded by HR-CS-FAAS. It was shown that a linear correlation between the wavelength of the peak absorption and the isotope ratio exists and that this correlation is independent of the total boron concentration. Internal spectroscopic standards were used to compensate for monochromator drift and monochromator resolution changes. Accuracy and precision of the analyzed samples were thereby increased by a factor of up to 1.3. Three steel reference materials and one boric acid CRM, each certified for the boron isotope ratio were used to validate the procedure.

In situ boron isotope analysis in marine carbonates and its application for foraminifera and palaeo-pH

The boron isotope composition of marine carbonates such as foraminiferal tests and coral skeletons is increasingly being used to reconstruct seawater pH values and atmospheric pCO 2 concentrations spanning hundreds of thousands or even millions of years. However, inter specific and small scale (microns) intra specific isotopic variation, either due to life processes of an organism or patchy recrystallisation and dissolution in fossilised material, can limit the use of the boron isotope ratio as palaeo-pH recorder. One approach to address this problem is the combined use of in situ and high spatial resolution mass spectrometry and high precision bulk analytical techniques. While much effort has been invested to establish reference material for silicates little attention has been devoted towards characterizing and using carbonate material allowing direct isotopic comparisons between B isotope data produced on carbonates by different techniques and laboratories. Hence, here we present data on the boron isotope composition of carbonate material determined by multicollector inductively coupled plasma mass spectrometry (MC-ICP-MS), thermal ionization mass spectrometry (TIMS), and secondary ionization mass spectrometry (SIMS). The new reference material permits the B isotope analysis of single foraminiferal chambers using SIMS and to empirically relate between seawater pH, the B isotope composition of O. universa and the predicted foraminiferal vital effect.

Development of a reflectron time-of-flight mass spectrometer for non-destructive analysis of isotope ratios in irradiated B 4C pellets—Test measurements on an unirradiated control rod pellet

A laser mass spectrometric facility is developed using a home-built reflectron time-of-flight mass spectrometer (RTOFMS) to analyze the boron isotopic ratio 10B/ 11B in the irradiated B 4C pellets of the FBTR control rod. Compared to other mass spectrometry-based methods, the present method is practically non-destructive and makes it relatively easier to handle irradiated (radioactive) B 4C pellets through remote operation. The results with inactive samples indicate that the method yields 10B percentage values, accurate to within ±1%.

Composition‐Induced Variations in SIMS Instrumental Mass Fractionation during Boron Isotope Ratio Measurements of Silicate Glasses

An analytical artefact is reported here related to differences in instrumental mass fractionation between NIST SRM glasses and natural geological glasses during SIMS boron isotope determinations. The data presented demonstrated an average 3.4‰ difference between the NIST glasses and natural basaltic to rhyolitic glasses mainly in terms of their sputtering‐induced fractionation of boron isotopes. As no matrix effect was found among basaltic to rhyolitic glasses, instrumental mass fractionation of most natural glass samples can be corrected by using appropriate glass reference materials. In order to confirm the existence of the compositionally induced variations in boron SIMS instrumental mass bias, the observed offset in SIMS instrumental mass bias has been independently reproduced in two laboratories and the phenomenon has been found to be stable over a period of more than one year. This study highlights the need for a close match between the chemical composition of the reference material and the samples being investigated.

Hydrothermal gold mineralization at the Hira Buddini gold mine, India: constraints on fluid evolution and fluid sources from boron isotopic compositions of tourmaline

We determined the boron isotope and chemical compositions of tourmaline from the Hira Buddini gold deposit within the Archean Hutti-Maski greenstone belt in southern India to investigate the evolution of the hydrothermal system and to constrain its fluid sources. Tourmaline is a minor but widespread constituent in the inner and distal alteration zones of metabasaltic and metadacite host rocks associated with the hydrothermal gold mineralization. The Hira Buddini tourmaline belongs to the dravite–schorl series with variations in Al, Fe/(Fe+Mg), Ca, Ti, and Cr contents that can be related to their host lithology. The total range of δ11B values determined is extreme, from −13.3‰ to +9.0‰, but 95% of the values are between −4 and +9‰. The boron isotope compositions of metabasalt-hosted tourmaline show a bimodal distribution with peak δ11B values at about −2‰ and +6‰. The wide range and bimodal distribution of boron isotope ratios in tourmaline require an origin from at least two isotopically distinct fluid sources, which entered the hydrothermal system separately and were subsequently mixed. The estimated δ11B values of the hydrothermal fluids, based on the peak tourmaline compositions and a mineralization temperature of 550°C, are around +1 and +10‰. The isotopically lighter of the two fluids is consistent with boron released by metamorphic devolatilization reactions from the greenstone lithologies, whereas the 11B-rich fluid is attributed to degassing of I-type granitic magmas that intruded the greenstone sequence, providing heat and fluids to the hydrothermal system.

炭素循環から考える新生代のグローバル気候変動

The global carbon cycle controls the climate change in the Earth's environment on a geological timescale and is mainly associated with greenhouse effects produced by atmospheric carbon dioxide (CO2) and methane (CH4). This paper reviews the relationship between the global carbon cycle and presumed climate events during the Cenozoic. The global carbon cycle is primarily regulated by the balance between weathering and metamorphism-volcanism. Moreover, the organic carbon subcycle involving oxidative weathering and burial is of secondary importance. The balance of these geochemical processes results in variations of atmospheric CO2. The past climate on a geological time scale is reconstructed by several geochemical and paleontological methods or proxies. For example, sea-surface and deep-water temperature are deduced from oxygen isotope ratio and Mg/Ca ratio of foraminiferal tests. Terrestrial atmospheric temperature is estimated from leaf fossil and paleovegetation. Atmospheric CO2 level is calculated from carbon isotope ratios of phytoplankton and soil carbonate, stomatal density of leaf fossil, boron isotope ratio of foraminiferal test, Ce anomaly, and global carbon cycle modeling. It is important to consider their advantages and disadvantages in order to evaluate the paleoclimate adequately. Next, we discuss climate change based on these proxies. As a general trend, the Cenozoic climate change is characterized by a transition from ice-free to ice-covered conditions across the Eocene/Oligocene boundary. The Earth's surface environment was significantly warmed from the Paleocene to the Eocene by high levels of atmospheric CO2. Thereafter, it gradually cooled towards the present, which is possibly attributed to changes in ocean currents and other marine environments accompanying continental drift. This trend has been punctuated by several short-term climate events. The Paleocene-Eocene Thermal Maximum (PETM) was a remarkable warming event at the Paleocene/Eocene boundary, possibly attributed to the release of methane from hydrates into the atmosphere. Rapid cooling occurred at the Eocene/Oligocene boundary to form extensive continental ice sheets including the Antarctica, which seems to have been caused by atmospheric CO2 and change of oceanographic circulation and marine environment. After a moderate period from the late Oligocene to the early Miocene, there was a transient but significant warming in the middle Miocene. Since then, the Earth's environment has gradually cooled towards the present accompanied by the evolution of glaciations and marine environmental changes but a causal link between cooling and global carbon cycle has recently been pointed out. Although the carbon cycle including atmospheric CO2 and CH4 cannot explain all of the global climate changes in Cenozoic, it has undoubtedly played a dominant role on the Earth's climate.

Multi-isotopic tracing (δ 7Li, δ 11B, 87Sr/ 86Sr) and chemical geothermometry: evidence from hydro-geothermal systems in France

In the present work, we report the results of a multi-isotopic study (δ 7Li, δ 11B and 87Sr/ 86Sr) on waters collected from different hydro-and geothermal sites in France. The aim of this study was to characterize hydro-and geothermal reservoirs by coupling a multi-isotopic approach with in-depth temperature of the reservoir calculated using chemical geothermometers. A database constituted by 36 water samples (thermal, thermo-mineral and geothermal waters) was selected in order to cover a wide range of temperatures and to be representative of water/rock interactions with various types of lithologies. We clearly observed that the wide range of 87Sr/ 86Sr isotopic ratios in the waters (0.70755-0.72187) appear to be largely controlled by the dominant host lithologies with Sr isotopic signatures ranging from high values (resulting from interaction from granite and/or gneiss type > 0.714) to lower 87Sr/ 86Sr ratios (closer to Sr isotopic ratios observed in the sedimentary zones < 0.712). Boron isotopic ratios lay between - 8.3 and + 21.6‰, also reflecting a lithological control over δ 11B signatures. In addition, no simple or direct relationship was observed for either boron or strontium isotopic signatures with the temperature of the reservoir. In contrast, temperature plays an important role in controlling the lithium isotope composition of the hydro-and geothermal fluids. δ 7Li signatures are comprised between - 0.1 and + 10.0‰ for temperatures ranging from 60 to 230 °C. This result seems to prove that lithium isotopic systematics represents a useful tool suitable for the characterization of hydrothermal and geothermal waters and suggests that the δ 7Li composition of geothermal waters may be utilised as a geothermometer (δ 7Li = - 0.043 ± 0.003 T + 11.9 ± 0.5).

Evidence for lithium and boron from star‐forming regions implanted in presolar SiC grains

Abstract— We report the first measurements of lithium and boron isotope ratios and abundances measured in “gently separated” presolar SiC grains. Almost all analyses of presolar SiC grains since their first isolation in 1987 have been obtained from grains that were separated from their host meteorite by harsh acid dissolution. We recently reported a new method of “gently” separating the grains from meteorites by using freeze‐thaw disaggregation, size, and density separation to retain any nonrefractory coatings or alteration to the surfaces of the grains that have been acquired in interstellar space. Nonrefractory coats or amorphized surfaces will almost certainly be removed or altered by the traditional acid separation procedure. High Li/Si and B/Si ratios of up to ∼10−2 were found implanted in the outer 0.5 μm of the grains dropping to ∼10−5 in the core of the grains. 7Li/6Li and 11B/10B ratios indistinguishable from solar system average values were found. Analyses obtained from SiC grains from the acid dissolution technique showed isotope ratios that were the same as those of gently separated grains, but depth profiles that were different. These results are interpreted as evidence of implantation of high velocity (1200–1800 km s−1) Li and B ions into the grains by shock waves as the grains traveled through star‐forming regions some time after their condensation in the outflow of an AGB star that was their progenitor. The results are in line with spectroscopic measurements of Li and B isotope ratios in star‐forming regions and may be used to infer abundances and isotopic sources in these regions.