Boron Isotope Research Articles

Reconstruction of Cenozoic δ11Bsw Using a Gaussian Process

AbstractThe boron isotope ratio of seawater (δ11Bsw) is a parameter which must be known to reconstruct palaeo pH and CO2 from boron isotope measurements of marine carbonates. Beyond a few million years ago, δ11Bsw is likely to have been different to modern. Palaeo δ11Bsw can be estimated by simultaneously constraining the vertical gradients in foraminiferal δ11B (Δδ11B) and pH (ΔpH). A number of subtly different techniques have been used to estimate ΔpH in the past, all broadly based on assumptions about vertical gradients in oxygen, and/or carbon, or other carbonate system constraints. In this work we pull together existing data from previous studies, alongside a constraint on the rate of change of δ11Bsw from modeling. We combine this information in an overarching statistical framework called a Gaussian Process. The Gaussian Process technique allows us to bring together data and constraints on the rate of change in δ11Bsw to generate random plausible evolutions of δ11Bsw. We reconstruct δ11Bsw, and by extension palaeo pH, across the last 65Myr using this novel methodology. Reconstructed δ11Bsw is compared to other seawater isotope ratios, namely , , and δ7Li, which we also reconstruct with Gaussian Processes. Our method provides a template for incorporation of future δ11Bsw constraints, and a mechanism for propagation of uncertainty in δ11Bsw into future studies.

Sea surface acidification events in the Andaman Sea associated with the last Toba volcanic activity

To date, little is known about the impact of super-eruptions on ocean biogeochemistry. Using boron isotopes ratios measured on planktonic foraminifera in the marine sediment core BAR94–25, we provide a high-resolution pH record in the Andaman Sea (North of Sumatra), spanning Marine Isotopic Stage 5 to 3. This transition encompasses the super-eruption of the Toba volcano, 74,000 years ago, making it possible to decipher the potential impact of the super-eruption emissions on the ocean pH for the first time. Our results show that inferred foraminiferal pH values generally follow those predicted by glacial-interglacial CO2 variations. However, several abrupt pH drops coincide with Toba ash deposition. This suggests the occurrence of acidification events possibly related to Toba volcanic sulphur emission episodes. These pH drops are followed by anomalous pH increases, possibly relating to localised increases in seawater alkalinity following the alteration of large ash deposits on land.

The source of lithium in Lakkor Co Salt Lake on Qinghai-Tibet Plateau, China: evidence from hydrochemical characteristics and boron isotope

The source of lithium in Lakkor Co Salt Lake on Qinghai-Tibet Plateau, China: evidence from hydrochemical characteristics and boron isotope

Boron in wildfires: New insights into boron isotope fractionation during volatilisation, leaching and adsorption after combustion

Wildfires are hazards of increasing significance in recent decades. Our ability to forecast the evolution of fire regimes is inhibited by the lack of records of key fire parameters such as fire severity. Boron isotopes in the soil clay fraction have been shown to vary with fire severity, where increased δ11B coincides with higher fire severity. To elucidate the relationship between the B isotope composition of soil clays and fire events, we performed adsorption experiments by reacting rainwater with combusted leaves to analyse how B isotopes are fractionated during processes leading to the imparting of boron from plants to clay minerals in soil during and following combustion. We find that < 5% of B is volatilised during combustion of leaves and barks, where 11B is preferentially volatilised. No isotopic fractionation was detected during the leaching of leaves ash with rainwater, possibly due to the large water:clay ratio in our experiments. Adsorption of B from leaching solutions onto clay minerals shows isotopic fractionation, and hysteresis of the adsorbed B fraction. For experiments at pH between 7 and 9, the isotope fractionation between adsorbed and dissolved B (Δ11Badsorbed-dissolved) ranges from −8.8 to −14.5‰, indicating preferential adsorption of 10B onto clays compared to 11B. For experiments at pH > 10, the Δ11Badsorbed-dissolved values range from +11.2 to +19.4‰, indicating a preferential adsorption of 11B over 10B. Irregardless of pH, clay fractions in all experiments show increases in δ11B, as the leaching solutions have high δ11B relative to the soil clay minerals prior to their interaction. Ash of leaves combusted at 550 °C (highest temperature in our experiments) induce the greatest increase in solution pH and δ11B in clays. Our experiments suggests that the higher B isotope composition of clays following a high severity fire is likely imparted by solutions that leach isotopically heavy B from the combusted canopy.

Source and Formation of Boron Deposits in Mahai Basin on the Northern Qinghai-Tibet Plateau: Clues from Hydrochemistry and Boron Isotopes

Source and Formation of Boron Deposits in Mahai Basin on the Northern Qinghai-Tibet Plateau: Clues from Hydrochemistry and Boron Isotopes

Synthesis of 2D-Material(G,GO,rGO,h-BN)-Magnetic(Fe,Fe3O4)Nanocomposites

For the purpose of synthesizing 2D-Material–Magnetic nanocomposites, several new modifications of existing 2D-materials synthesis methods by exfoliation and chemical synthesis from liquid charge are developed. Using them, graphene (G), graphene oxide (GO), reduced graphene oxide (rGO) and hexagonal boron nitride (h-BN) matrix magnetic nanocomposites for the first time are obtained by coating or intercalation their nanoparticles with ferromagnetic iron (Fe) or ferrimagnetic iron oxide – magnetite (Fe3O4). These materials are prospective for variety of high tech applications. In particular, h-BN–Fe3O4 composite nanoparticles can serve for neutron-capturing boron isotope 10B effective delivery agents in BNCT (Boron Neutron Capture Therapy) of cancer as they allow the controlling by an external magnetic field targeting to tumor tissue.

Geochemical characteristic and B isotopic compositions of tourmaline from the Chaqiabeishan Li-rich pegmatite in the Quanji Massif, NW China

The Chaqiabeishan Li-rich pegmatite deposit is located in Tianjun County, Qinghai Province. Due to the complex magmatic evolution, there are still numerous controversies surrounding the diagenetic and metallogenic mechanisms of pegmatites. In this study, we investigated tourmalines from pegmatites in Chaqiabeishan by means of analyzing the in situ major element compositions, trace element contents, and boron isotopes. The collected samples can be classified into two types: pegmatitic tourmaline (Tur 1) and fine tourmaline (Tur 2). Based on the observation of geological characteristics, specimens, and microphotographs, the tourmalines have a basically paragenetic relationship with the predominant lithium-bearing mineral (spodumene), tourmalines and spodumenes would crystallize at a late magmatic stage of the pegmatitic sequence. Both tourmalines have similar geochemical characteristics, and Tur 1 crystallized earlier than Tur 2. The major elements show that both tourmalines belong to the alkali group, schorl series, and Li-poor pegmatite. Additionally, they have ∑(Mg + Fe) values less than 3 apfu, and redundant Al (0.04–0.89 apfu, average of 0.61) in the Y-site occupancy. The trace elements show that both tourmalines are characterized by enrichment in LREE relative to the MREE, with a slight negative Eu anomaly, indicating that they are of magmatic origin. The high Li/Sr ratios ranging from 38.56 to 6292.28 (average of 701.01 ppm) further support the magmatic origin. The δ11B values of all tourmalines range from −13.86 to −12.46 ‰, with an average of −13.14 ‰, indicating that the boron in the pegmatites was derived from S-type granitic magma or Dakendaban Group mica schist basement. The δ11B values of Tur 1 (average of −13.13 ‰), the rim of Tur 1 (average of −12.95 ‰), the core of Tur 1 (average of −13.25 ‰), and Tur 2 (average of −13.19 ‰) show a slight variation, indicating that the tourmalines have a consistent boron source and basically no foreign B-rich fluids involved. In conclusion, the petrological and geochemical characteristics suggest that the pegmatites in Caqiabeishan are likely the direct products of anatexis, and the tourmalines and spodumenes were formed in secondary faults at the late magmatic stage.

The history of serpentinisation at mid-ocean ridges: Insights from in situ trace elements coupled with oxygen and boron isotopes

Oceanic serpentinisation is the principal process of water incorporation into the oceanic lithosphere, thus playing a significant role in the elements cycle. The conditions of serpentinisation vary in temperature, water-rock ratio, and fluid composition, but the investigation of the interplay of these factors, rather than their individual variation, is rarely attempted. This study examines mid-ocean ridge (MOR) serpentinite samples from Mid-Atlantic Ridge 15°20′N Fracture Zone (Leg 209, Sites 1272 and 1274) and from Hess Deep (Leg 147, Site 895D and 895E) to gain insight into the combined effects of these variables. Various in situ geochemical tools are used to evaluate the mutual influence of the different factors in the successive stages of serpentinisation. The Cl/B content of serpentine is employed as a proxy for fluid salinity, enabling a more precise temperature calculation when the constant Cl/B correlates with varying δ18O. The combined in situ temperature-dependent oxygen and boron isotope compositions reveal instances of localised fluctuations in fluid pH that impact the boron isotope composition of serpentine. The δ18O compositions of serpentine vary between 0.8 and 7.8 ‰, implying temperature variations within the range of ∼115 °C to 290 °C. Where the δ11B compositions of serpentine exceed the expected temperature-related variations of circa 9–13 ‰, we propose that pH variations during progressive serpentinisation are the cause (δ11B up to 22 ‰ variability observed between serpentine textures from a single sample). Moreover, this study emphasises the divergence in serpentinisation conditions between MOR and passive margin settings. Serpentinisation can occur at higher temperatures (up to 290 °C) with a more saline fluid (Cl/B > 25) under variable pH conditions in MOR settings, while the serpentinisation in PaMa settings takes place at lower temperatures (< 200 °C) with a less saline fluid (Cl/B < 25) and probably more alkaline conditions.

Tourmaline chemical composition and boron isotopic composition at the Longmenshan pegmatite in Dahongliutan area, West Kunlun: Implication for rare-metal Li-Be mineralization

Tourmaline is a common mineral in rocks. It can record geological information during its formation and is a geochemical tracer. Its in-situ element and boron isotope tests provide a broader application perspective. Therefore, the chemical and boron isotope characteristics of tourmaline can be used to trace the mineralization of pegmatite-type rare metals. West Kunlun is an important Li-Be metallogenic belt, and many important Li-Be deposits have been developed. Longmenshan is one of the recently discovered pegmatite-type Li-Be deposits in the Dahongliutan area. There are barren and spodumene-bearing pegmatites that all contain tourmaline in Longmenshan. According to their occurrence, crystal form, and chemical composition, the tourmalines in Longmenshan are divided into two types: Tur-I tourmaline in the barren pegmatite close to the granite and Tur-II tourmaline from the spodumene-bearing pegmatite. Compositionally belongs to the alkali group and schorl-dravite solid solution series, with Tur-I being mainly schorl and Tur-II being schorl-dravite. Tur-I tourmalines are rich in Li, Sn, V, Cr, Zn, and Mn, while Tur-II tourmalines are rich in Be, Sr, and Sc. The δ11B of the Tur-I tourmalines hosted in the barren pegmatite and Tur-II from the spodumene-bearing pegmatite ranges from −8.38‰ to −6.81‰ and from −10.00‰ to −6.41‰, respectively. These characteristics indicate that the formation fluid of tourmaline in Longmenshan is mainly derived from magma, and other fluids are rarely involved. The large range of B isotope variation indicates that the Tur-II tourmalines are more obviously affected by fluid activity.

Designing Gold Nanoparticles for Precise Glioma Treatment: Challenges and Alternatives.

Glioblastoma multiforme (GBM) is a glioma and the most aggressive type of brain tumor with a dismal average survival time, despite the standard of care. One promising alternative therapy is boron neutron capture therapy (BNCT), which is a noninvasive therapy for treating locally invasive malignant tumors, such as glioma. BNCT involves boron-10 isotope capturing neutrons to form boron-11, which then releases radiation directly into tumor cells with minimal damage to healthy tissues. This therapy lacks clinically approved targeted blood-brain-barrier-permeating delivery vehicles for the central nervous system (CNS) entry of therapeutic boron-10. Gold nanoparticles (GNPs) are selective and effective drug-delivery vehicles because of their desirable properties, facile synthesis, and biocompatibility. This review discusses biomedical/therapeutic applications of GNPs as a drug delivery vehicle, with an emphasis on their potential for carrying therapeutic drugs, imaging agents, and GBM-targeting antibodies/peptides for treating glioma. The constraints of GNP therapeutic efficacy and biosafety are discussed.

A Simple, Low‐Blank Batch Purification Method for High‐Precision Boron Isotope Analysis

AbstractBoron (B) isotopes are widely used in the Earth sciences to trace processes ranging from slab recycling in the mantle to changes in ocean pH and atmospheric CO2. Boron isotope analysis is increasingly achieved by multi‐collector inductively coupled plasma mass spectrometry, which requires separation of B from the sample matrix. Traditional column chromatography methods for this separation have a well‐established track record but are time consuming and prone to contamination from airborne blank. Here, we present an extensive array of tests that establish a novel method for B purification using a batch method. We discuss the key controls and limitations on sample loading, matrix removal and B elution including sample volume, ionic strength, buffer to acid ratio and elution volume, all of which may also help optimize column‐based methods. We find consistent, low procedural blanks of 10 ± 16 pg and excellent reproducibility: 10 ng NIST RM 8301 foram [8301f] yields 14.58 ± 0.11‰ 2SD n = 15; 2.5 ng 8301f yields 14.60 ± 0.19‰ 2SD, n = 31; and overall long term 2SD on n = 218 samples pooling different sample sizes yields 14.62 ± 0.21‰ 2SD. This method also offers significant advantages in throughput, allowing the processing of 24 samples in ∼5 hr. This boron batch method thus provides a fast, reproducible, low‐blank method for purification of boron for high precision isotopic analyses.

Water-driven evolution of hydrous boron-bearing silicate melts at high pressures up to 8 GPa: Implications for dynamic properties and boron isotope content in hydrous mantle melts

A prominent seismic weakening has suggested the potential presence of H2O-bearing complex silicate melts in the Earth’s interiors. As boron is typically accompanied by the hydrous fluids and melts and may be transported into deep mantle, boron isotopic evolution enables us to trace the deep-water cycle. The impact of H2O on the structures of boron-bearing magmas is essential to grasp the melting processes and the seismic weakening in Earth’s mantle. In this study, we report experimental results on the structural changes in volatile-bearing, partially-depolymerized aluminoborosilicate glasses (NaAl0.5B0.5Si3O8) - an analog for boron-rich rhyolitic melts - with varying H2O content and at pressure conditions from 6 to 8 GPa (∼180–240 km depth in the mantle) via multi-nuclear (1H, 17O, 27Al, 11B, 29Si, and 23Na) magnetic resonance (NMR) spectroscopy. At isobaric conditions both at 6 GPa and 8 GPa, compared to the coordination environments of anhydrous quenched melts, adding water up to 4 wt% generally promotes the formation of [4]B and systematically suppresses the [5,6]Al fractions; however, in the glasses with 8 wt% water (at 8 GPa), a dramatic increase in both [6]Al and [4]B is observed, while Si coordination number remains unchanged. In contrast, at a constant H2O content of 4 wt%, an increase in the pressure from 6 to 8 GPa results in an increase in the [5,6]Al fractions and a decrease in the [4]B fraction. The results highlight complex water-pressure dependences on the cation coordination transformation. Upon adding water content at isobaric condition, boron is more prone to be highly-coordinated over aluminum. In contrast, with increasing pressure at a constant water content, aluminum prefers to be highly-coordinated over boron. These NMR results allow us to refine water dissolution schemes, highlighted by selective network depolymerization of B and Al-bearing bridging oxygens and subsequent annihilation of oxygen triclusters consisting primarily of Al, consistent with a water-driven evolution of B-Al coordination numbers in response to pressurization. These changes induce non-linear decrease in melt viscosity and seismic weakening in the mantle at depths of ∼180–240 km. Observed boron coordination evolutions indicate that deep mantle melts could exhibit complex pressure-water-driven changes in the tendency to enrich 10B. In particular, the effect of 8 wt% water contributes to ∼41 % of the overall reduction of δ11B in deep melts. Finally, as the deep magmatic melts could also be more mafic than those studied here, the water-driven structural changes in more mafic melts with much less boron contents under compression remain to be explored. While the details may vary with melt composition, the current probing of the structures of boron-bearing compressed melts with varying degree of hydration enables better prediction of the deep boron and water cycles.

Multi-isotopic composition (Li and B isotopes) and hydrochemistry characterization of the Lakko Co Li-rich salt lake in Tibet, China: Origin and hydrological processes

A comprehensive comprehension of the origin and ore-forming process of lithium brine deposits is imperative prior to engaging in lithium resource exploration, development and utilization. Nevertheless, the provenance of lithium in salt lakes has always been controversial. The lithium and boron (Li and B) isotopes, which serve as discerning geochemical tracers, can facilitate the monitoring of geological processes and sources. In this study, we investigated the hydrochemistry, Li and B isotope characteristics of surface brine and recharge river samples collected from the Lakko Co on the Qinghai-Tibet Plateau in China. The dissolved Li concentrations range from 0.11 to 590.8 mg/L, δ7Li and δ11B values exhibit a range of 0.75∼8.11 ‰ and -18.29∼-4.01 ‰, respectively. Concentrations of elements such as Rb, and Cu are relatively high and exhibit a strong correlation with Li. Ions composition and content ratios indicate the deep origin of Li and B. The analysis of δ7Li and δ11B suggests that, apart from hot spring, weathering of surrounding rocks also contributes to the presence of Li and B. Besides, variations in δ11B values within the lake brine analysis may be attributed to the deposition of water Magnesite at the lake bottom. The findings suggest that the recharge water system and hot springs serve as the primary source of Li and B in Lakko Co. Additionally, the interaction between water and rock in the deep crust as well as chemical weathering in the shallow environment, significantly contribute to formation of Li-rich fluids. The transportation process is characterized by the precipitation of secondary mineral, resulting in an increase of δ7Li and δ11B. Furthermore, the presence of water Magnesite in the lake brine leads to fluctuations in δ11B. This investigation of the lake contributes to a more comprehensive understanding of the origins and mechanisms involved in the transportation and storage of lithium in lithium-rich salt lakes.

Resetting of Shallow-Water Carbonate Boron Isotope Values During Marine Burial Diagenesis

The boron isotopic composition (δ11B) of bulk carbonates may provide an archive to reconstruct changes in ocean pH. Reconstructions from ancient carbonates typically assume that no significant resetting of δ11B occurred during marine burial diagenesis. However, our understanding of B isotopic behavior associated with this process remains limited. Here we provide measurements of B/Ca and B isotopic composition (δ11B) from a modern peri-platform carbonate sequence near the Great Bahama Bank that has undergone marine burial diagenesis. Our results reveal significant decreases in both δ11B (~13 ‰) and B/Ca (~80 %) of bulk carbonates with depth. We attribute this pattern to the release of isotopically light B (δ11B ~20 ‰) to porewater during aragonite dissolution, with uptake of substantially isotopically lighter borate ions (δ11B ~-1 ‰) from porewater by newly forming low-Mg calcite. A quantitative model adds further support for this interpretation and provides an estimate of average neomorphism rate ( k0) in the range of 1×10-6 to 5×10-6 yr-1, which is comparable to previous rate estimates for neomorphism and/or recrystallization during meteoric diagenesis. Our results demonstrate the strong potential for resetting δ11B signatures in bulk carbonates during recrystallization, which must be considered in future attempts to reconstruct pH and pCO2 from these records and may require reinterpretation of existing records. Our results also suggest the potential of B isotopes as a proxy for carbonate recrystallization/neomorphism and original carbonate mineralogy.

Atmospheric CO2 Estimates for the Late Oligocene and Early Miocene Using Multi‐Species Cross‐Calibrations of Boron Isotopes

AbstractThe boron isotope (δ11B) proxy for seawater pH is a tried and tested means to reconstruct atmospheric CO2 in the geologic past, but uncertainty remains over how to treat species‐specific calibrations that link foraminiferal δ11B to pH estimates prior to 22 My. In addition, no δ11B‐based reconstructions of atmospheric CO2 exist for wide swaths of the Oligocene (33–23 Ma), and large variability in CO2 reconstructions during this epoch based on other proxy evidence leaves climate evolution during this period relatively unconstrained. To add to our understanding of Oligocene and early Miocene climate, we generated new atmospheric CO2 estimates from new δ11B data from fossil shells of surface‐dwelling planktic foraminifera from the mid‐Oligocene to early Miocene (∼28–18 Ma). We estimate atmospheric CO2 of ∼680 ppm for the mid‐Oligocene, which then evolves to fluctuate between ∼500–570 ppm during the late Oligocene and between ∼420–700 ppm in the early Miocene. These estimates tend to trend higher than Oligo‐Miocene CO2 estimates from other proxies, although we observe good proxy agreement in the late Oligocene. Reconstructions of CO2 fall lower than estimates from paleoclimate model simulations in the early Miocene and mid Oligocene, which indicates that more proxy and/or model refinement is needed for these periods. Our species cross‐calibrations, assessing δ11B, Mg/Ca, δ18O, and δ13C, are able to pinpoint and evaluate small differences in the geochemistry of surface‐dwelling planktic foraminifera, lending confidence to paleoceanographers applying this approach even further back in time.

Determining the sources of (sub)permil-level inaccuracy during laser ablation-MC-ICPMS boron isotope measurements of carbonates

New empirical evidence for the different sources of inaccuracy during boron isotope measurement of carbonates using (LA-)MC-ICPMS.

Determination of boron isotopic compositions in five fractions of soil boron: traces of the environmental behavior of boron in soil

A stepwise extraction method established for boron isotope measurement of five fractions in soil boron showed their feathered isotopic signals.

Purification of boron using a combination of cationic and boron-specific resins and determination of boron isotopic composition in sediments by MC-ICP-MS

Boron is a lithophilic and biophilic element. Boron isotopes in sediments provide insight in the Earth's history. Boron is purified by a combination of cationic and boron-specific resins, and the isotopic composition of boron in sediments can be determined with high accuracy by MC-ICP-MS.

Fractionation of stable boron isotopes in alfisols: Application of a novel tool for tracing boron behavior in two soil profiles

Available boron (AB) and total boron (TB) in soil have distinct isotopic values, which are mainly influenced by the pH, organic matter and clay minerals, and can be used to explore the chemical behaviors of boron (B) in adsorption, weathering and eluviation processes. The B isotopic compositions of AB and TB in brown soil (slightly acidic) and cinnamon soil (neutral to slightly alkaline) profiles were investigated by multicollector inductively coupled plasma mass spectrometry. Variations in pH value and organic matter in the two soils directly affected the adsorption of B isotopes (dissolved 11B(OH)3 or 10B(OH)4-) in the aqueous solution, as shown by AB having an average negative δ11B value of −1‰ and a great range of −10.83‰ to +8.32‰ in the cinnamon soil. Furthermore, the long-term effects of adsorption and transportation processes were evidenced by the large range of δ11BTB values (-24.22‰ to +21.07‰) in the two soils. The topsoil layers with more organic matter and higher δ11B values indicated that B isotope fractionation occurred as a result of the input of rainfall, recycling of plant litter and the adsorption of organic matter and clay minerals. The lower δ11B values, the higher B contents and the element ratios in the underlying layers resulted from the weathering of different minerals and the adsorption of AB in the leaching process. This finding is supported by the relationship between AB and the clay/silt ratio, with more negative δ11B values being associated with finer clay particles via the adsorption of 10B(OH)4- in a weakly alkaline soil solution. The δ11B values in soils may be a useful tool for distinguishing geochemical cycling and processes and characterizing long-term processes that are difficult to assess.

On Demand Degradable h-BN–Fe3O4 Nanocomposite Powders for BNCT Delivery Agents (Focused Mini-Review)

This mini-review is focused on the nanopowder composite material h-BN–Fe3O4 (hexagonal boron nitride–magnetite) developed by the author’s research group in recent years. Effective methods of their synthesis, structural and morphological characteristics, and physical properties are briefly described. They show that h-BN–Fe3O4 composite nanoparticles can serve as boron isotope 10B delivery agents in BNCT (Boron-Neutron-Capture-Therapy) having high medical efficacy with controlled delivery, low toxicity and on-demand degradability.