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Jérôme Gaillardet - One of the best experts on this subject based on the ideXlab platform.
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crystallographic control on the Boron Isotope paleo ph proxy
Earth and Planetary Science Letters, 2015Co-Authors: Johanna Noireaux, Jacques Schott, Jérôme Gaillardet, Pascale Louvat, Vasileios Mavromatis, V Montouillout, Claire Rollionbard, Daniel R NeuvilleAbstract:When using the Boron isotopic composition (δ11B) of marine carbonates as a seawater pH proxy, it is assumed that only the tetrahedral borate ion is incorporated into the growing carbonate crystals and that no Boron Isotope fractionation occurs during uptake. However, the δ11B of the calcium carbonate from most modern foraminifera shells or corals skeletons is not the same as the δ11B of seawater borate, which depends on pH, an observation commonly attributed to vital effects. In this study, we combined previously published high-field 11B MAS NMR and new δ11B measurements on the same synthetic calcite and aragonite samples precipitated inorganically under controlled environments to avoid vital effects. Our results indicate that the main controlling factors of δ11B are the solution pH and the mineralogy of the precipitated carbonate mineral, whereas the aqueous Boron concentration of the solution, CaCO3 precipitation rate and the presence or absence of growth seeds all appear to have negligible influence. In aragonite, the NMR data show that Boron coordination is tetrahedral (BO4), in addition, its δ11B is equal to that of aqueous borate, thus confirming the paleo-pH hypothesis. In contrast, both trigonal BO3 and tetrahedral BO4 are present in calcite, and its δ11B values are higher than that of aqueous borate and are less sensitive to solution pH variations compared to δ11B in aragonite. These observations are interpreted in calcite as a reflection of the incorporation of decreasing amounts of boric acid with increasing pH. Moreover, the fraction of BO3 measured by NMR in calcite is higher than that inferred from δ11B which indicates a coordination change from BO4 to BO3 upon Boron incorporation in the solid. Overall, this study shows that although the observed differences in δ11B between inorganic and biological aragonite are compatible with a pH increase at calcification sites, the B speciation and Isotope composition of biological calcites call for a more complex mechanism of Boron incorporation.
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a fully automated direct injection nebulizer d dihen for mc icp ms Isotope analysis application to Boron Isotope ratio measurements
Journal of Analytical Atomic Spectrometry, 2014Co-Authors: Pascale Louvat, Guillaume Paris, Julien Moureau, Julien Bouchez, Johanna Noireaux, Jérôme GaillardetAbstract:This work presents a fully automated setup for using direct injection nebulization as an introduction system for solution measurements by MC-ICP-MS, here applied to Boron Isotopes in pure boric acid solutions and natural samples. In this setup, a direct injection nebulizer (d-DIHEN) is plugged into the plasma torch without any spray chamber, and an automated 6-port valve interfaces the nebulizer and the autosampler. The advantages of a d-DIHEN for Boron Isotope ratio measurements are high sensitivity and short washout times, allowing for sample–standard bracketing (SSB) measurements at a higher rate than spray chambers. The measurement of Boron Isotopes by MC-ICP-MS at an unprecedented sub 0.1‰ repeatability level (2 standard deviation = 2SD) was achieved for pure boric acid solutions. The improved precision is allowed by a better stability of the introduction system with continuous operation of the peristaltic pump (which was manually switched off between samples before automation) and due to the possibility of multiple analyses of the same sample solution. However, such a good repeatability was not systematically obtained for Boron Isotopes SSB measurements of natural samples (in fine 2SD are between 0.02 and 0.5‰). Boron from natural samples has to be extracted before Isotope analysis, with one to four steps depending on the sample type. Repeated analyses of Boron independently separated up to ten times from the same sample lead to an external reproducibility no better than 0.2‰. Boron chemical separation from the samples prior to MC-ICP-MS analyses seems to remain the main limitation to precise measurements of Boron Isotope ratios.
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A fully automated direct injection nebulizer (d-DIHEN) for MC-ICP-MS Isotope analysis: application to Boron Isotope ratio measurements
Journal of Analytical Atomic Spectrometry, 2014Co-Authors: Pascale Louvat, Guillaume Paris, Julien Moureau, Julien Bouchez, Johanna Noireaux, Jérôme GaillardetAbstract:This work presents a fully automated setup for using direct injection nebulization as an introduction system for solution measurements by MC-ICP-MS, here applied to Boron Isotopes in pure boric acid solutions and natural samples. In this setup, a direct injection nebulizer (d-DIHEN) is plugged into the plasma torch without any spray chamber, and an automated 6-port valve interfaces the nebulizer and the autosampler. The advantages of a d-DIHEN for Boron Isotope ratio measurements are high sensitivity and short washout times, allowing for sample-standard bracketing (SSB) measurements at a higher rate than spray chambers. The measurement of Boron Isotopes by MC-ICP-MS at an unprecedented sub 0.1 parts per thousand, repeatability level (2 standard deviation = 2SD) was achieved for pure boric acid solutions. The improved precision is allowed by a better stability of the introduction system with continuous operation of the peristaltic pump (which was manually switched off between samples before automation) and due to the possibility of multiple analyses of the same sample solution. However, such a good repeatability was not systematically obtained for Boron Isotopes SSB measurements of natural samples (in fine 2SD are between 0.02 and 0.5 parts per thousand). Boron from natural samples has to be extracted before Isotope analysis, with one to four steps depending on the sample type. Repeated analyses of Boron independently separated up to ten times from the same sample lead to an external reproducibility no better than 0.2 parts per thousand. Boron chemical separation from the samples prior to MC-ICP-MS analyses seems to remain the main limitation to precise measurements of Boron Isotope ratios.
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Boron Isotope Fractionation in Soils at Shale Hills CZO
Procedia Earth and Planetary Science, 2014Co-Authors: Johanna Noireaux, Jérôme Gaillardet, Pamela L. Sullivan, Susan L. BrantleyAbstract:Isotope fractionation of many elements can fingerprint the biogeochemical, weathering and erosion processes that govern the evolution of the Critical Zone (CZ). This study investigates Boron Isotope fractionation in two soil profiles developed on the same shale bedrock at Shale Hills Critical Zone Observatory. The first soil profile, located at the valley floor, is isotopically similar to the bedrock and appears to have lost Boron mostly through the loss of fine particles matter (clays) with no isotopic fractionation. The second soil profile, located at the ridge top appears to be more depleted in Boron concentration and isotopically fractionated toward lower values, as expected from mineral dissolution followed by adsorption/co-precipitation processes.
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Boron behavior in the rivers of Réunion island, inferred from Boron Isotope ratios and concentrations of major and trace elements
Procedia Earth and Planetary Science, 2014Co-Authors: Pascale Louvat, E. Gayer, Jérôme GaillardetAbstract:A combined study of Boron concentrations and isotopic ratios and of major and trace elements measured in Réunion waters, sampled up to four times between 1995 and 2012, illustrates Boron behavior during water-rock interactions in tropical basaltic catchments. Boron Isotope ratios measured in Réunion rivers and springs show a large range of variation between 1 and 48‰, that reflect mixed B sources and water-rock interaction processes: rain (δ 11 B≈40‰), hydrothermalism (δ 11 B≈0‰), low temperature basalt weathering in steep sided basins (δ 11 B≈30‰), and cycling within soil and vegetation (δ 11 B>40‰). Réunion rivers have schematically two types of δ 11 B signatures for low-temperature water-rock interactions: ≈30‰ for rivers with high weathering rates, and ≈45‰ for small forested catchments with relatively smoother slopes and lower weathering rates. High temperature water-rock interaction produces B enriched waters with a B isotopic signature close to that of the rocks. B behavior in the soil and vegetation cycle is more difficult to characterize but seems to result in soil solutions enriched in 11 B, with δ 11 B≥45‰.
Gavin L. Foster - One of the best experts on this subject based on the ideXlab platform.
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mapping coral calcification strategies from in situ Boron Isotope and trace element measurements of the tropical coral siderastrea siderea
Scientific Reports, 2021Co-Authors: Thomas B Chalk, Christopher D Standish, Cecilia Dangelo, Karl D Castillo, J A Milton, Gavin L. FosterAbstract:Boron isotopic and elemental analysis of coral aragonite can give important insights into the calcification strategies employed in coral skeletal construction. Traditional methods of analysis have limited spatial (and thus temporal) resolution, hindering attempts to unravel skeletal heterogeneity. Laser ablation mass spectrometry allows a much more refined view, and here we employ these techniques to explore Boron Isotope and co-varying elemental ratios in the tropical coral Siderastrea siderea. We generate two-dimensional maps of the carbonate parameters within the calcification medium that deposited the skeleton, which reveal large heterogeneities in carbonate chemistry across the macro-structure of a coral polyp. These differences have the potential to bias proxy interpretations, and indicate that different processes facilitated precipitation of different parts of the coral skeleton: the low-density columella being precipitated from a fluid with a carbonate composition closer to seawater, compared to the high-density inter-polyp walls where aragonite saturation was ~ 5 times that of external seawater. Therefore, the skeleton does not precipitate from a spatially homogeneous fluid and its different parts may thus have varying sensitivity to environmental stress. This offers new insights into the mechanisms behind the response of the S. siderea skeletal phenotype to ocean acidification.
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Robust Constraints on Past CO2 Climate Forcing From the Boron Isotope Proxy
Paleoceanography and Paleoclimatology, 2018Co-Authors: Mathis P. Hain, Gavin L. Foster, T. ChalkAbstract:The atmospheric concentration of the greenhouse gas carbon dioxide, CO2, is intimately coupled to the carbon chemistry of seawater, such that the radiative climate forcing from CO2 can be changed by an array of physical, geochemical and biological ocean processes. For instance, biological carbon sequestration, seawater cooling and net CaCO3 dissolution are commonly invoked as the primary drivers of CO2 change that amplify the orbitally-paced ice age cycles of the late Pleistocene. Based on first-principle arguments with regard to ocean chemistry we demonstrate that seawater pH change (ΔpH) is the dominant control that effectively sets CO2 radiative forcing (ΔF) on orbital timescales, as is evident from independent late Pleistocene reconstructions of pH and CO2. In short, all processes relevant for CO2 on orbital timescales, including temperature change, cause pH to change to bring about fractional CO2 change so as to yield a linear relationship of ΔpH to CO2 climate forcing. Further, we show that ΔpH and CO2 climate forcing can be reconstructed using the Boron Isotope pH-proxy more accurately than absolute pH or CO2, even if seawater Boron Isotope composition is poorly constrained and without information on a second carbonate system parameter. Thus, our formalism relaxes otherwise necessary assumptions to allow the accurate determination of orbital timescale CO2 radiative forcing from Boron Isotope-pH reconstructions alone, thereby eliminating a major limitation of current methods to estimate our planet’s climate sensitivity from the geologic record.
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Boron Isotopes in the earth and planetary sciences a short history and introduction
2018Co-Authors: Horst R. Marschall, Gavin L. FosterAbstract:This volume on Boron Isotope geochemistry contains chapters reviewing the low- and high-temperature geochemistry, marine chemistry, and cosmochemistry of Boron Isotopes. It covers theoretical aspects of B Isotope fractionation, experiments and atomic modeling, as well as all aspects of Boron Isotope analyses in geologic materials by the full range of solution and in situ methods. The book provides guidance for researchers on the analytical and theoretical end, and introduces the various scientific applications and research fields in which Boron Isotopes play a growing role today. This chapter provides a brief history of Boron Isotope research and analytical development and provides an overview of the other chapters of the volume “Boron Isotopes—The Fifth Element” in the series Advancements in Isotope Geochemistry.
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Boron Isotopes in the Earth and Planetary Sciences—A Short History and Introduction
Boron Isotopes, 2017Co-Authors: Horst R. Marschall, Gavin L. FosterAbstract:This volume on Boron Isotope geochemistry contains chapters reviewing the low- and high-temperature geochemistry, marine chemistry, and cosmochemistry of Boron Isotopes. It covers theoretical aspects of B Isotope fractionation, experiments and atomic modeling, as well as all aspects of Boron Isotope analyses in geologic materials by the full range of solution and in situ methods. The book provides guidance for researchers on the analytical and theoretical end, and introduces the various scientific applications and research fields in which Boron Isotopes play a growing role today. This chapter provides a brief history of Boron Isotope research and analytical development and provides an overview of the other chapters of the volume “Boron Isotopes—The Fifth Element” in the series Advancements in Isotope Geochemistry.
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Boron Isotope Analysis of Geological Materials
Boron Isotopes, 2017Co-Authors: Gavin L. Foster, Horst R. Marschall, Martin R. PalmerAbstract:Over the last twenty years applications of the Boron Isotope system have expanded from the analysis of Boron-rich phases (e.g., tourmaline, borates) to include other materials with low B concentrations (e.g., carbonates, basaltic glass). The accurate and precise determination of the Boron isotopic composition of geological materials is however a difficult task, particularly for those where Boron is present in low-concentration. For solution methods, this difficulty arises principally from the near ubiquitous level of Boron contamination in most standard clean laboratories, the light mass of the element, the occurrence of only two stable Isotopes, and the large mass difference between them. For in situ approaches, such as secondary-ion mass spectrometry, additional difficulties arise from the restricted availability of well-characterized reference materials, from surface contamination, from limited precision in low-concentration samples, and limitations in reproducibility in high-concentration samples that may partly arise from small-scale heterogeneities in the analyzed materials. Nevertheless, a variety of novel techniques, strategies and methodologies have been developed over the past two decades to meet these challenges. We describe here some of these developments and focus on those that we feel are going to play a major role in the growing use of the Boron Isotope system in the earth and planetary sciences in decades to come.
Emmanuel Lemarchand - One of the best experts on this subject based on the ideXlab platform.
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how surface complexes impact Boron Isotope fractionation evidence from fe and mn oxides sorption experiments
Earth and Planetary Science Letters, 2007Co-Authors: Emmanuel Lemarchand, Jacques Schott, Jérôme GaillardetAbstract:Abstract Although the pH-dependence of Boron Isotope fractionation between solution and precipitating minerals has been widely used in Earth Sciences, especially for reconstructing ancient seawater pH, the mechanisms by which Boron adsorbs on solids or coprecipitates in minerals are still poorly known. Here we have investigated Boron isotopic fractionation during its adsorption on goethite (α-FeOOH) and birnessite (K0.1MnO2.2,0.9H2O) as a function of solution pH at T = 25 °C and I = 0.1 M. Maximum partition coefficients (Kd) between adsorbed and aqueous Boron, equal to 39 and 34 for goethite and birnessite, respectively, are observed at pH = 8–9. B adsorption at the surface of goethite induces its strong pH-dependent isotopic fractionation ranging from Δ = − 40‰ (10B enrichment on goethite) at pH 10. During adsorption on birnessite at acid and neutral pH, Boron isotopic fractionation is lower than during its sorption on goethite (Δ = − 15‰), decreases (α increases) with increasing pH above pH = 8, and reverses at pH > 9: 11B enrichment (+ 23‰ at pH = 10.8) is observed at birnessite surface. Based on combined infrared (DRIFT) spectroscopic analysis and modeling of B speciation at oxides–solution interfaces, the observed isotopic fractionations can be rationalized by the formation of trigonal and tetrahedral Boron inner-sphere complexes on goethite surface, and tetrahedral inner-sphere and trigonal outer-sphere and inner-sphere complexes on birnessite surface. B isotopic fractionation is strongly dependent on the structure of surface complexes formed: the high steric strain induced by the formation of trigonal Boron bidendate binuclear complexes at goethite surface leads to a much higher isotopic fractionation (isotopically lighter sorbed Boron) than that following the formation of tetrahedral bidendate binuclear complexes. Conversely, the formation at birnessite surface of trigonal complexes, having almost the same isotopic composition than aqueous boric acid, accounts for the heavier isotopic composition of birnessite than goethite Boron, both at acid and alkaline pH. These results show that, in nature, 11B enrichment is expected in waters in equilibrium with iron or manganese oxides and that this enrichment is a function of pH that changes Boron speciation in solution and at solid surfaces. This is typically the case for soil solution in Fe- and Mn-rich environments and in seawater. In addition, the markedly different isotopic fractionation factor, at the same pH, of Boron sorbed on goethite and birnessite (at pH = 8.2, α is equal to 0.967 and 0.986 for goethite and birnessite, respectively) may be used to determine past ocean pH values without requiring knowledge of past isotopic composition.
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How surface complexes impact Boron Isotope fractionation: Evidence from Fe and Mn oxides sorption experiments
Earth and Planetary Science Letters, 2007Co-Authors: Emmanuel Lemarchand, Jacques Schott, Jérôme GaillardetAbstract:Although the pH-dependence of Boron Isotope fractionation between solution and precipitating minerals has been widely used in Earth Sciences, especially for reconstructing ancient seawater pH, the mechanisms by which Boron adsorbs on solids or coprecipitates in minerals are still poorly known. Here we have investigated Boron isotopic fractionation during its adsorption on goethite (α-FeOOH) and birnessite (K0.1MnO2.2,0.9H2O) as a function of solution pH at T = 25 °C and I = 0.1 M. Maximum partition coefficients (Kd) between adsorbed and aqueous Boron, equal to 39 and 34 for goethite and birnessite, respectively, are observed at pH = 8–9. B adsorption at the surface of goethite induces its strong pH-dependent isotopic fractionation ranging from Δ = − 40‰ (10B enrichment on goethite) at pH < 8, to zero at pH > 10. During adsorption on birnessite at acid and neutral pH, Boron isotopic fractionation is lower than during its sorption on goethite (Δ = − 15‰), decreases (α increases) with increasing pH above pH = 8, and reverses at pH > 9: 11B enrichment (+ 23‰ at pH = 10.8) is observed at birnessite surface. Based on combined infrared (DRIFT) spectroscopic analysis and modeling of B speciation at oxides–solution interfaces, the observed isotopic fractionations can be rationalized by the formation of trigonal and tetrahedral Boron inner-sphere complexes on goethite surface, and tetrahedral inner-sphere and trigonal outer-sphere and inner-sphere complexes on birnessite surface. B isotopic fractionation is strongly dependent on the structure of surface complexes formed: the high steric strain induced by the formation of trigonal Boron bidendate binuclear complexes at goethite surface leads to a much higher isotopic fractionation (isotopically lighter sorbed Boron) than that following the formation of tetrahedral bidendate binuclear complexes. Conversely, the formation at birnessite surface of trigonal complexes, having almost the same isotopic composition than aqueous boric acid, accounts for the heavier isotopic composition of birnessite than goethite Boron, both at acid and alkaline pH. These results show that, in nature, 11B enrichment is expected in waters in equilibrium with iron or manganese oxides and that this enrichment is a function of pH that changes Boron speciation in solution and at solid surfaces. This is typically the case for soil solution in Fe- and Mn-rich environments and in seawater. In addition, the markedly different isotopic fractionation factor, at the same pH, of Boron sorbed on goethite and birnessite (at pH = 8.2, α is equal to 0.967 and 0.986 for goethite and birnessite, respectively) may be used to determine past ocean pH values without requiring knowledge of past isotopic composition.
Jacques Schott - One of the best experts on this subject based on the ideXlab platform.
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crystallographic control on the Boron Isotope paleo ph proxy
Earth and Planetary Science Letters, 2015Co-Authors: Johanna Noireaux, Jacques Schott, Jérôme Gaillardet, Pascale Louvat, Vasileios Mavromatis, V Montouillout, Claire Rollionbard, Daniel R NeuvilleAbstract:When using the Boron isotopic composition (δ11B) of marine carbonates as a seawater pH proxy, it is assumed that only the tetrahedral borate ion is incorporated into the growing carbonate crystals and that no Boron Isotope fractionation occurs during uptake. However, the δ11B of the calcium carbonate from most modern foraminifera shells or corals skeletons is not the same as the δ11B of seawater borate, which depends on pH, an observation commonly attributed to vital effects. In this study, we combined previously published high-field 11B MAS NMR and new δ11B measurements on the same synthetic calcite and aragonite samples precipitated inorganically under controlled environments to avoid vital effects. Our results indicate that the main controlling factors of δ11B are the solution pH and the mineralogy of the precipitated carbonate mineral, whereas the aqueous Boron concentration of the solution, CaCO3 precipitation rate and the presence or absence of growth seeds all appear to have negligible influence. In aragonite, the NMR data show that Boron coordination is tetrahedral (BO4), in addition, its δ11B is equal to that of aqueous borate, thus confirming the paleo-pH hypothesis. In contrast, both trigonal BO3 and tetrahedral BO4 are present in calcite, and its δ11B values are higher than that of aqueous borate and are less sensitive to solution pH variations compared to δ11B in aragonite. These observations are interpreted in calcite as a reflection of the incorporation of decreasing amounts of boric acid with increasing pH. Moreover, the fraction of BO3 measured by NMR in calcite is higher than that inferred from δ11B which indicates a coordination change from BO4 to BO3 upon Boron incorporation in the solid. Overall, this study shows that although the observed differences in δ11B between inorganic and biological aragonite are compatible with a pH increase at calcification sites, the B speciation and Isotope composition of biological calcites call for a more complex mechanism of Boron incorporation.
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how surface complexes impact Boron Isotope fractionation evidence from fe and mn oxides sorption experiments
Earth and Planetary Science Letters, 2007Co-Authors: Emmanuel Lemarchand, Jacques Schott, Jérôme GaillardetAbstract:Abstract Although the pH-dependence of Boron Isotope fractionation between solution and precipitating minerals has been widely used in Earth Sciences, especially for reconstructing ancient seawater pH, the mechanisms by which Boron adsorbs on solids or coprecipitates in minerals are still poorly known. Here we have investigated Boron isotopic fractionation during its adsorption on goethite (α-FeOOH) and birnessite (K0.1MnO2.2,0.9H2O) as a function of solution pH at T = 25 °C and I = 0.1 M. Maximum partition coefficients (Kd) between adsorbed and aqueous Boron, equal to 39 and 34 for goethite and birnessite, respectively, are observed at pH = 8–9. B adsorption at the surface of goethite induces its strong pH-dependent isotopic fractionation ranging from Δ = − 40‰ (10B enrichment on goethite) at pH 10. During adsorption on birnessite at acid and neutral pH, Boron isotopic fractionation is lower than during its sorption on goethite (Δ = − 15‰), decreases (α increases) with increasing pH above pH = 8, and reverses at pH > 9: 11B enrichment (+ 23‰ at pH = 10.8) is observed at birnessite surface. Based on combined infrared (DRIFT) spectroscopic analysis and modeling of B speciation at oxides–solution interfaces, the observed isotopic fractionations can be rationalized by the formation of trigonal and tetrahedral Boron inner-sphere complexes on goethite surface, and tetrahedral inner-sphere and trigonal outer-sphere and inner-sphere complexes on birnessite surface. B isotopic fractionation is strongly dependent on the structure of surface complexes formed: the high steric strain induced by the formation of trigonal Boron bidendate binuclear complexes at goethite surface leads to a much higher isotopic fractionation (isotopically lighter sorbed Boron) than that following the formation of tetrahedral bidendate binuclear complexes. Conversely, the formation at birnessite surface of trigonal complexes, having almost the same isotopic composition than aqueous boric acid, accounts for the heavier isotopic composition of birnessite than goethite Boron, both at acid and alkaline pH. These results show that, in nature, 11B enrichment is expected in waters in equilibrium with iron or manganese oxides and that this enrichment is a function of pH that changes Boron speciation in solution and at solid surfaces. This is typically the case for soil solution in Fe- and Mn-rich environments and in seawater. In addition, the markedly different isotopic fractionation factor, at the same pH, of Boron sorbed on goethite and birnessite (at pH = 8.2, α is equal to 0.967 and 0.986 for goethite and birnessite, respectively) may be used to determine past ocean pH values without requiring knowledge of past isotopic composition.
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How surface complexes impact Boron Isotope fractionation: Evidence from Fe and Mn oxides sorption experiments
Earth and Planetary Science Letters, 2007Co-Authors: Emmanuel Lemarchand, Jacques Schott, Jérôme GaillardetAbstract:Although the pH-dependence of Boron Isotope fractionation between solution and precipitating minerals has been widely used in Earth Sciences, especially for reconstructing ancient seawater pH, the mechanisms by which Boron adsorbs on solids or coprecipitates in minerals are still poorly known. Here we have investigated Boron isotopic fractionation during its adsorption on goethite (α-FeOOH) and birnessite (K0.1MnO2.2,0.9H2O) as a function of solution pH at T = 25 °C and I = 0.1 M. Maximum partition coefficients (Kd) between adsorbed and aqueous Boron, equal to 39 and 34 for goethite and birnessite, respectively, are observed at pH = 8–9. B adsorption at the surface of goethite induces its strong pH-dependent isotopic fractionation ranging from Δ = − 40‰ (10B enrichment on goethite) at pH < 8, to zero at pH > 10. During adsorption on birnessite at acid and neutral pH, Boron isotopic fractionation is lower than during its sorption on goethite (Δ = − 15‰), decreases (α increases) with increasing pH above pH = 8, and reverses at pH > 9: 11B enrichment (+ 23‰ at pH = 10.8) is observed at birnessite surface. Based on combined infrared (DRIFT) spectroscopic analysis and modeling of B speciation at oxides–solution interfaces, the observed isotopic fractionations can be rationalized by the formation of trigonal and tetrahedral Boron inner-sphere complexes on goethite surface, and tetrahedral inner-sphere and trigonal outer-sphere and inner-sphere complexes on birnessite surface. B isotopic fractionation is strongly dependent on the structure of surface complexes formed: the high steric strain induced by the formation of trigonal Boron bidendate binuclear complexes at goethite surface leads to a much higher isotopic fractionation (isotopically lighter sorbed Boron) than that following the formation of tetrahedral bidendate binuclear complexes. Conversely, the formation at birnessite surface of trigonal complexes, having almost the same isotopic composition than aqueous boric acid, accounts for the heavier isotopic composition of birnessite than goethite Boron, both at acid and alkaline pH. These results show that, in nature, 11B enrichment is expected in waters in equilibrium with iron or manganese oxides and that this enrichment is a function of pH that changes Boron speciation in solution and at solid surfaces. This is typically the case for soil solution in Fe- and Mn-rich environments and in seawater. In addition, the markedly different isotopic fractionation factor, at the same pH, of Boron sorbed on goethite and birnessite (at pH = 8.2, α is equal to 0.967 and 0.986 for goethite and birnessite, respectively) may be used to determine past ocean pH values without requiring knowledge of past isotopic composition.
Pascale Louvat - One of the best experts on this subject based on the ideXlab platform.
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Sub‐Permil Interlaboratory Consistency for Solution‐Based Boron Isotope Analyses on Marine Carbonates
Geostandards and Geoanalytical Research, 2020Co-Authors: Marcus Gutjahr, Pascale Louvat, Barbel Honisch, Louise Bordier, Éric Douville, Jesse Farmer, Gavin Foster, Ed Hathorne, Damien Lemarchand, Malcolm MccullochAbstract:Boron Isotopes in marine carbonates are increasingly used to reconstruct seawater pH and atmospheric pCO 2 through Earth's history. While Isotope ratio measurements from individual laboratories are often of high quality, it is important that records generated in different laboratories can equally be compared. Within this Boron Isotope Intercomparison Project (BIIP), we characterised the Boron isotopic composition (commonly expressed in δ 11 B) of two marine carbonates: Geological Survey of Japan carbonate reference materials JCp-1 (coral Porites) and JCt-1 (giant clam Tridacna gigas). Our study has three foci: (a) to assess the extent to which oxidative pre-treatment, aimed at removing organic material from carbonate, can influence the resulting δ 11 B; (b) to determine to what degree the chosen analytical approach may affect the resultant δ 11 B; and (c) to provide well-constrained consensus δ 11 B values for JCp-1 and JCt-1. The resultant robust mean and associated robust standard deviation (s*) for un-oxidised JCp-1 is 24.36 AE 0.45‰ (2s*), compared with 24.25 AE 0.22‰ (2s*) for the same oxidised material. For un-oxidised JCt-1, respective compositions are 16.39 AE 0.60‰ (2s*; un-oxidised) and 16.24 AE 0.38‰ (2s*; oxidised). The consistency between laboratories is generally better if carbonate powders were oxidatively cleaned prior to purification and measurement.
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crystallographic control on the Boron Isotope paleo ph proxy
Earth and Planetary Science Letters, 2015Co-Authors: Johanna Noireaux, Jacques Schott, Jérôme Gaillardet, Pascale Louvat, Vasileios Mavromatis, V Montouillout, Claire Rollionbard, Daniel R NeuvilleAbstract:When using the Boron isotopic composition (δ11B) of marine carbonates as a seawater pH proxy, it is assumed that only the tetrahedral borate ion is incorporated into the growing carbonate crystals and that no Boron Isotope fractionation occurs during uptake. However, the δ11B of the calcium carbonate from most modern foraminifera shells or corals skeletons is not the same as the δ11B of seawater borate, which depends on pH, an observation commonly attributed to vital effects. In this study, we combined previously published high-field 11B MAS NMR and new δ11B measurements on the same synthetic calcite and aragonite samples precipitated inorganically under controlled environments to avoid vital effects. Our results indicate that the main controlling factors of δ11B are the solution pH and the mineralogy of the precipitated carbonate mineral, whereas the aqueous Boron concentration of the solution, CaCO3 precipitation rate and the presence or absence of growth seeds all appear to have negligible influence. In aragonite, the NMR data show that Boron coordination is tetrahedral (BO4), in addition, its δ11B is equal to that of aqueous borate, thus confirming the paleo-pH hypothesis. In contrast, both trigonal BO3 and tetrahedral BO4 are present in calcite, and its δ11B values are higher than that of aqueous borate and are less sensitive to solution pH variations compared to δ11B in aragonite. These observations are interpreted in calcite as a reflection of the incorporation of decreasing amounts of boric acid with increasing pH. Moreover, the fraction of BO3 measured by NMR in calcite is higher than that inferred from δ11B which indicates a coordination change from BO4 to BO3 upon Boron incorporation in the solid. Overall, this study shows that although the observed differences in δ11B between inorganic and biological aragonite are compatible with a pH increase at calcification sites, the B speciation and Isotope composition of biological calcites call for a more complex mechanism of Boron incorporation.
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a fully automated direct injection nebulizer d dihen for mc icp ms Isotope analysis application to Boron Isotope ratio measurements
Journal of Analytical Atomic Spectrometry, 2014Co-Authors: Pascale Louvat, Guillaume Paris, Julien Moureau, Julien Bouchez, Johanna Noireaux, Jérôme GaillardetAbstract:This work presents a fully automated setup for using direct injection nebulization as an introduction system for solution measurements by MC-ICP-MS, here applied to Boron Isotopes in pure boric acid solutions and natural samples. In this setup, a direct injection nebulizer (d-DIHEN) is plugged into the plasma torch without any spray chamber, and an automated 6-port valve interfaces the nebulizer and the autosampler. The advantages of a d-DIHEN for Boron Isotope ratio measurements are high sensitivity and short washout times, allowing for sample–standard bracketing (SSB) measurements at a higher rate than spray chambers. The measurement of Boron Isotopes by MC-ICP-MS at an unprecedented sub 0.1‰ repeatability level (2 standard deviation = 2SD) was achieved for pure boric acid solutions. The improved precision is allowed by a better stability of the introduction system with continuous operation of the peristaltic pump (which was manually switched off between samples before automation) and due to the possibility of multiple analyses of the same sample solution. However, such a good repeatability was not systematically obtained for Boron Isotopes SSB measurements of natural samples (in fine 2SD are between 0.02 and 0.5‰). Boron from natural samples has to be extracted before Isotope analysis, with one to four steps depending on the sample type. Repeated analyses of Boron independently separated up to ten times from the same sample lead to an external reproducibility no better than 0.2‰. Boron chemical separation from the samples prior to MC-ICP-MS analyses seems to remain the main limitation to precise measurements of Boron Isotope ratios.
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A fully automated direct injection nebulizer (d-DIHEN) for MC-ICP-MS Isotope analysis: application to Boron Isotope ratio measurements
Journal of Analytical Atomic Spectrometry, 2014Co-Authors: Pascale Louvat, Guillaume Paris, Julien Moureau, Julien Bouchez, Johanna Noireaux, Jérôme GaillardetAbstract:This work presents a fully automated setup for using direct injection nebulization as an introduction system for solution measurements by MC-ICP-MS, here applied to Boron Isotopes in pure boric acid solutions and natural samples. In this setup, a direct injection nebulizer (d-DIHEN) is plugged into the plasma torch without any spray chamber, and an automated 6-port valve interfaces the nebulizer and the autosampler. The advantages of a d-DIHEN for Boron Isotope ratio measurements are high sensitivity and short washout times, allowing for sample-standard bracketing (SSB) measurements at a higher rate than spray chambers. The measurement of Boron Isotopes by MC-ICP-MS at an unprecedented sub 0.1 parts per thousand, repeatability level (2 standard deviation = 2SD) was achieved for pure boric acid solutions. The improved precision is allowed by a better stability of the introduction system with continuous operation of the peristaltic pump (which was manually switched off between samples before automation) and due to the possibility of multiple analyses of the same sample solution. However, such a good repeatability was not systematically obtained for Boron Isotopes SSB measurements of natural samples (in fine 2SD are between 0.02 and 0.5 parts per thousand). Boron from natural samples has to be extracted before Isotope analysis, with one to four steps depending on the sample type. Repeated analyses of Boron independently separated up to ten times from the same sample lead to an external reproducibility no better than 0.2 parts per thousand. Boron chemical separation from the samples prior to MC-ICP-MS analyses seems to remain the main limitation to precise measurements of Boron Isotope ratios.
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Boron behavior in the rivers of Réunion island, inferred from Boron Isotope ratios and concentrations of major and trace elements
Procedia Earth and Planetary Science, 2014Co-Authors: Pascale Louvat, E. Gayer, Jérôme GaillardetAbstract:A combined study of Boron concentrations and isotopic ratios and of major and trace elements measured in Réunion waters, sampled up to four times between 1995 and 2012, illustrates Boron behavior during water-rock interactions in tropical basaltic catchments. Boron Isotope ratios measured in Réunion rivers and springs show a large range of variation between 1 and 48‰, that reflect mixed B sources and water-rock interaction processes: rain (δ 11 B≈40‰), hydrothermalism (δ 11 B≈0‰), low temperature basalt weathering in steep sided basins (δ 11 B≈30‰), and cycling within soil and vegetation (δ 11 B>40‰). Réunion rivers have schematically two types of δ 11 B signatures for low-temperature water-rock interactions: ≈30‰ for rivers with high weathering rates, and ≈45‰ for small forested catchments with relatively smoother slopes and lower weathering rates. High temperature water-rock interaction produces B enriched waters with a B isotopic signature close to that of the rocks. B behavior in the soil and vegetation cycle is more difficult to characterize but seems to result in soil solutions enriched in 11 B, with δ 11 B≥45‰.