Boron Isotope Ratios Research Articles

Determination of Boron Isotopic Ratio by Using an Alpha Track Technique

The determination of the boron isotopic ratio in solutions was achieved by means of a solid state track detector by using an alpha track. The neutron flux was optimized by using a Cd-foil to find the optimum conditions for counting the number of alpha tracks on the selected solid detector caused by the (n, ) nuclear reaction of boron. The home-made multi-dot detector plate was utilized in this study to increase the reproducibility of the measurement by uniformly drying the boron solution within the marked circle area on the detector plate. The experimental results of this study verified that the isotopic ratio can be measured by observing the number of alpha tracks for different concentrated standard solutions with various isotopic compositions. This technique was applied to the determination of enrichment factor in a biological sample for a boron neutron capture therapy.

Resonant laser-SNMS of boron for analysis of paleoceanographic samples

Calcite shells of foraminifera, which are accumulated in the ocean sediment, are an important object of paleoceanographic studies to reconstruct environmental parameters of the past. Foraminifera are unicellular organisms living in almost all parts of the ocean during the entire paleoceanographic time scale. The isotope ratio of boron incorporated in the calcite shell delivers information about the pH-value of the ocean at the time the shell was formed. Since the boron fraction of such a shell is about 5 ppm, an extremely sensitive technique is necessary for an exact boron isotope ratio determination. Resonant laser secondary neutral mass spectrometry (r-laser-SNMS) was used to measure boron isotope ratios in calcite shells. Analysis was carried out with a time-of-flight mass spectrometer equipped with an electron impact gun for sputtering and a Ga + primary ion source. Resonant ionization of sputtered boron neutrals was performed via a three-step ionization scheme accomplished with two tunable dye lasers and the fundamental wavelength of a Nd:YAG laser. After optimizing the boron ionization and detection process, boron isotope ratios were directly measured on single foraminiferal shells after removing contaminants by Ar + ion beam sputtering.

Laser ablation multicollector ICPMS determination of δ11B in geological samples

A method for the in situ single spot δ 11B characterisation of geological materials with laser ablation multicollector ICP mass spectrometry (LA-MC-ICPMS) has been developed. The mass spectrometer was equipped with both Faradays and multiple ion counters. Four samples with different B contents (12–31,400 ppm) and isotopic compositions ( δ 11B are between −8.71 and +13.6‰) were analysed. Samples include the B4 tourmaline and 3 MPI-DING glasses (StHs6/80-G, GOR132-G and GOR128-G). All sources of B isotopic fractionation during the analysis (mass bias, laser-induced isotopic fractionation and detector efficiency drift) have been evaluated and quantified. Instrumental mass bias is the major source of fractionation, altering the original isotopic ratio up to 13%. Fractionation related to laser sampling and transport to the ICP was found to be very low (less than 0.0015% s −1). Fractionation effects due to drift in ion counter efficiencies were found to be significant. Nevertheless, the “standard-sample-standard” bracketing approach could be used to correct for the above fractionation effects using NIST SRM 610 as external standard. With spot sizes of 60–80 μm in diameter, geologically meaningful results can be achieved on samples containing at least 10 ppm B, i.e., results with precisions that can discriminate between the different reservoirs on Earth. Data obtained with Faraday detectors on NIST SRM 610 and B4 tourmaline show high precision (down to 0.04‰, 1 σ) and accuracy. Boron isotope ratios measured in the glass samples using multiple ion counting show significantly higher standard deviations (up to 2.5‰, 1 σ), but they are very close to the values that can be expected from counting statistics. No significant variations with spot size or B contents were observed. Most of the values are within 1 σ level of the reference values. The developed method was applied to a series of ashes from Mt. Etna erupted in 1995 having B contents between 14 and 20 ppm. The B isotope compositions of the ashes are between −4.8 and −10.7‰, with a weighted average value of −8.0 ± 1.9‰ (1 σ).

Boron isotopic geochemistry of karst groundwater in Guiyang City, China

Boron has two stable isotopes (l~ and liB) with relative abundances of about 20% and 80%, respectively. Boron isotopic ratios in natural materials show a huge range of variations, from -7096o to +60%0, when expressed with the classical 8laB notation. Most of these isotopic variations occur at the surface of the Earth. Hence, boron isotopic composition can be used as a sensitive tracer in geochemical study, for instance, to identify the different sources of contamination and factors controlling the salinity of groundwater. During the last decade, boron isotopes have been used to discriminate between the influences of seawater intrusion and anthropogenic discharge. But few of those researches can precisely identify the different sources of contamination. We measured the boron concentrations and boron isotopic ratios of groundwater samples collected in Guiyang City, as well as the major ions. The results indicate that the major ion composition of the groundwater in the investigated area is mainly controlled by the interactions between water and the dominant rock i.e. carbonates. All the water compositions are characterized by high concentrations of Ca 2+, Mg 2+, HCO3, SO42, and NOr, which are the dominant contaminants. Both dissolved boron concentrations and isotopic ratios show large variations among the ground waters, from 2 lag/L to 90 lag/L and from -6%o to +26%0, respectively. The boron concentrations and isotopic ratios indicate that the river across the studied city has been seriously contaminated by urban discharge. Boron concentrations of river water samples varied from 20 lag/L to 140 lag/L, with an average 811B value of +2.0%0. Using boron isotopic compositions and different geochemical indices allowed us to clearly identify and distinguish the two major sources of contamination, agricultural activity and urban wastewater. Both of the two sources are characterized by high boron concentrations but their boron isotopic compositions significantly differ. The 8nB values of urban effluents range from -6.0%0 to +5.0%o, clearly lower than the mean 8nB values of a typical fertilizer, about +15%o. For the studied city, some groundwater sites of the suburban area were contaminated by agricultural activities and most sites of the urban area were contaminated by sewerage waters. The two types of contamination present distinct evolution during a hydrologic cycle.

Determination of boron isotope ratios by Zeeman effect background correction-graphite furnace atomic absorption spectrometry

A new method for the determination of isotopic ratio of boron using Zeeman effect background correction-graphite furnace atomic absorption spectrometry with conventional atomizer and natural-boron hollow cathode source is described. The isotope-shift Zeeman effect at 208.9 nm is utilized for isotopic ratio determination. At a given concentration of total boron, the net absorbance decreases linearly with increasing 10B/ 11B ratio. The absorbances are recorded at the field strength of 1.0 T. The isotope ratios measured by the proposed method were in good agreement with the results obtained by inductively coupled plasma-quadruple mass spectrometry or thermal ionization mass spectrometry. The present method is fairly fast and less expensive compared to the above techniques and is quite suitable for plant environments.

Accurate and precise isotopic measurement of sub-nanogram sized samples of foraminiferal hosted boron by total evaporation NTIMS

We report a total evaporation negative ion thermal mass spectrometry (TE-NTIMS) technique that enables precise and accurate (± 0.7‰; 2 s.d.) measurements of boron isotope ratios. The fundamental advantage of TE-NTIMS is that the effect of instrumental mass fractionation is minimised and sample signal maximised by analysing samples to exhaustion. We can analyse as little as 300 pg of B, which enables repeat analyses of dissolutions of small numbers of foraminifera (as little as 0.1 mg or ∼10 individual foraminfera). This represents a several fold reduction in the number of tests required compared to previous NTIMS studies and brings the amount of sample into line with other commonly used paleo-proxies. Standard addition experiments indicate that the 11B / 10B ratio of the NIST SRM 951 standard is not biased by differing amounts of seawater or carbonate matrix and yield an 11B / 10B within error of the certified value. We also show that our sample preparation induces no additional variations (e.g. blank contribution) beyond our analytical uncertainty. We obtain 11B / 10B ratios for seawater within error of values obtained using plasma ionisation, positive and negative thermal ionisation mass-spectrometry. Our measurements of core-top G. sacculifer from three ocean basins yield δ 11B within analytical error (23.3–24.3‰) and fall within the range of published values. This study, however, further highlights significant interlaboratory biases in isotopic compositions of core-top foraminifera. Significantly, we show that our approach is not influenced by processing blank nor systematic differences in mass bias between measurements of sample and standard, which has yet to be documented for some other laboratories.

Determination of Isotopic Ratio of Boron in Boric Acid Using Laser Mass Spectrometry

A reflectron time-of-flight mass spectrometer (RTOFMS) with a laser ablation ion source was used to determine the isotopic ratio of 10B/11B present in boric acid solutions, using graphite as the matrix. The atom % 10B values obtained were within +/-1% of the actual ones. The determination of the boron isotopic ratio using this method is, in comparison to other methods, faster, less expensive and easier to perform. The results are compared with the values determined using thermal ionization mass spectrometry.

Classifying wine according to geographical origin via quadrupole-based ICP–mass spectrometry measurements of boron isotope ratios

The potential of quadrupole-based ICP-MS as a tool for B-isotopic analysis of wines and its usefulness in provenance determinations were assessed. A precision of 0.1-0.25% RSD (corresponding to a relative standard deviation of the mean of three replicate measurements of 0.06-0.12%) was sufficient to establish small differences in the B isotope ratios in wines from different geographical origins. Each sample measurement was bracketed by measurements of a standard and mass bias drift correction made by interpolation. Sample preparation was kept to a minimum to avoid possible fractionation. Dilution of the wine samples by a factor of 100 with 0.65% HNO3 was found to reduce matrix-induced mass discrimination substantially. Wines from three wine-producing regions, Stellenbosch, Robertson, and Swartland, in the Western Cape Province of South Africa, and wines from specific regions in France (Bergerac) and Italy (Valpolicella) were analyzed by ICP-QMS for their B-isotopic compositions. It was concluded that the 11B/10B ratios can be used to characterize wines from different geographical origins. Average 11B/10B ratios in red wines from South Africa (Stellenbosch), France (Bergerac), and Italy (Valpolicella) were found to differ by between 0.5 and 1.5%.

A Melt Inclusion Record of Volatiles, Trace Elements and Li–B Isotope Variations in a Single Magma System from the Plat Pays Volcanic Complex, Dominica, Lesser Antilles

Glass inclusions in plagioclase and orthopyroxene from dacitic pumice of the Cabrits Dome, Plat Pays Volcanic Complex in southern Dominica reveal a complexity of element behavior and Li–B isotope variations in a single volcanic center that would go unnoticed in a whole-rock study. Inclusions and matrix glasses are high-silica rhyolite with compositions consistent with about 50% fractional crystallization of the observed phenocrysts. Estimated crystallization conditions are 760–880 C, 200 MPa and oxygen fugacity of FMQ þ 1 to þ2 log units (where FMQ is the fayalite– magnetite–quartz buffer). Many inclusion glasses are volatile-rich (up to 6 wt % H2O and 2900 ppm Cl), but contents range down to 1 wt % H2O and 2000 ppm Cl as a result of shallow-level degassing. Sulfur contents are low throughout, with <350 ppm S. The trace element composition of inclusion glasses shows enrichment in light rare earth elements (LREE; (La/Sm)n 1⁄4 2 5–6 6) and elevated Ba, Th and K contents compared with whole rocks and similar or lower Nb and heavy REE (HREE; (Gd/Yb)n 1⁄4 0 5– 1 0). Lithium and boron concentrations and isotope ratios in melt inclusions are highly variable (20–60 ppm Li with dLi 1⁄4 þ4 to þ15 2‰; 60–100 ppm B with dB 1⁄4 þ6 to þ13 2‰) and imply trapping of isotopically heterogeneous, hybrid melts. Multiple sources and processes are required to explain these features. The mid-ocean ridge basalt (MORB)-like HREE, Nb and Y signature reflects the parental magma(s) derived from the mantle wedge. Positive Ba/Nb, B/Nb and Th/Nb correlations in inclusion glasses indicate coupled enrichment in strongly fluid-mobile (Ba, B) and less-mobile (Th, Nb) trace elements, which can be explained by fractional crystallization of plagioclase, orthopyroxene and Fe–Ti oxides. The dLi and dB values are at the high end of known ranges for other island arc magmas. We attribute the high values to a B and Li-enriched slab component derived from seafloor-altered oceanic crust and possibly further enriched in heavy isotopes by dehydration fractionation. The heterogeneity of isotope ratios in the evolved, trapped melts is attributed to shallow-level assimilation of older volcanic rocks of the Plat Pays Volcanic Complex.

Boron isotope geochemistry of Paleozoic brachiopod calcite: Implications for a secular change in the boron isotope geochemistry of seawater over the Phanerozoic

Boron isotope composition of marine carbonates has been proposed as a paleo-pH proxy and potential tool to reconstruct atmospheric pCO 2. The precise knowledge of the boron isotopic composition of ancient seawater represents the fundamental prerequisite for any paleo-pH reconstruction. This contribution presents boron isotope values for Silurian to Permian brachiopod calcite that might be used to reconstruct pH or boron isotope composition of past oceans. All brachiopod shells were screened for diagenetic recrystallization by means of cathodoluminescence microscopy, trace element geochemistry (B, Fe, Mn, Sr) as well as SEM. Only nonluminescent shells revealing well-preserved microstructures, high strontium and boron concentrations as well as low iron and manganese contents were accepted for boron isotope analysis. The boron isotope ratios of Silurian, Devonian, Pennsylvanian and Permian brachiopod calcite range from 6.8 to 11.0‰, 7.3 to 14.9‰, 12.4 to 15.8‰ and 10.1 to 11.7‰, respectively. These δ 11B values are significantly lower in comparison to δ 11B values of modern biogenic carbonates and indicate that the Paleozoic oceans were depleted in 11B by up to 10‰. Box modeling of the boron geochemical cycle suggests that the significant depletion of 11B in the oceanic reservoir may have been initiated by an enhanced continental boron discharge. Our data support the earlier made conclusion that boron isotopes may not be used in the geological past as reliable paleo-pH proxy unless the boron isotopic composition of ancient oceans can be constrained by further studies.

Stable boron isotope fractionation between dissolved B(OH) 3 and B(OH) 4−

The stable boron isotope ratio ( 11B/ 10B) in marine carbonates is used as a paleo-pH recorder and is one of the most promising paleo-carbonate chemistry proxies. Understanding the thermodynamic basis of the proxy is of fundamental importance, including knowledge on the equilibrium fractionation factor between dissolved boric acid, B(OH) 3, and borate ion, B(OH) 4 − ( α ( B ( OH ) 3 − B ( OH ) 4 − ) , hereafter α (B3–B4)). However, this factor has hitherto not been determined experimentally and a theoretically calculated value ( Kakihana and Kotaka, 1977, hereafter KK77) has therefore been widely used. I examine the calculations underlying this value. Using the same spectroscopic data and methods as KK77, I calculate the same α ( B 3 − B 4 ) = 1.0193 at 300 K. Unfortunately, it turns out that in general the result is sensitive to the experimentally determined vibrational frequencies and the theoretical methods used to calculate the molecular forces. Using analytical techniques and ab initio molecular orbital theory, the outcome for α (B3–B4) varies between ∼1.020 and ∼1.050 at 300 K. However, several arguments suggest that α (B3–B4) ≳ 1.030. Measured isotopic shifts in various 10B-, 2D-, and 18O-labeled isotopomers do not provide a constraint on stable boron isotope fractionation. I conclude that in order to anchor the fundamentals of the boron pH proxy, experimental work is required. The critics of the boron pH proxy should note, however, that uncertainties in α (B3–B4) do not bias pH reconstructions provided that organism-specific calibrations are used.

Effective elimination of isobaric ions interference and precise thermal ionization mass spectrometer analysis for boron isotope

An ionization depressor, 1% H 3PO 4 was used to eliminate the isobaric interference that has been of a great concern during the procedure of boron isotopic ratio analysis by thermal ionization mass spectrometer (TIMS). Our experiments have shown that it appears to be an effective method to completely restrain the formation of isobaric ions of CNO − and Cs 2CNO + in the ionization source of mass spectrometer. We have also discussed the optimum proportion of depressor to nitrite for precise analysis of boron isotopes in natural samples based on a conditional experiment. In this case, the pretreatment of boron extraction from natural samples is greatly simplified since it is not necessary to remove nitrite and organic matter completely. In virtue of the method, we determined boron isotope in different types of natural samples, and our results are consistent with previous reports.

Precise and accurate determination of boron isotope ratios by multiple collector ICP-MS: origin of boron in the Ngawha geothermal system, New Zealand

A new technique has been developed for the measurement of boron isotope ratios in fluids using a double focusing multiple collector inductively coupled plasma (ICP) mass spectrometer. Sample introduction using a direct injection nebuliser was found to eliminate memory problems that are common where spray chambers are involved. The 4–9% mass bias can be corrected for by bracketing sample measurements with standards. As matrices were found to affect the mass bias all samples must be purified and that sample and standard solutions must be similar. A new purification technique was developed that yields adequately purified samples. Using this technique, it is possible to make rapid measurements (4 min) from samples containing 250 ng B to a precision of ±0.2‰. This analytical technique has been applied to the Ngawha geothermal system in New Zealand in an attempt to determine the source of B in geothermal fluids where the B concentrations can exceed 100 mmol/l. The δ11B values range between −3.1‰ and −3.9‰ indicating that no seawater sources are involved and that the elevated B concentrations can only be accounted for by low water/rock ratios with the B being derived from basement greywacke/argillite. The similarity of B isotope ratios for hydrothermal fluids that have been diluted and cooled with groundwaters indicates that isotope fractionation due to adsorption is unlikely to occur in cool geothermal fluids (<40 °C).

Boron isotope dilution in cellular fractions of coffee leaves Evaluated by Inductively Coupled Plasma Mass Spectrometry with direct injection nebulization (DIN-ICP-MS)

Enriched 10B (94.14 atom %) was supplied to coffee plantlets for three months. Then boron isotope ratios were determined in the leaf cell compartments, cell wall, nuclei and chloroplast, after a sub-cellular fractionation procedure. The isotopic measurements were performed by Inductively Coupled Plasma Mass Spectrometry (ICP-MS) provided with a direct injection nebulizer (DIN), introducing a sample volume of 50 mL. Isotopic ratios from 1.002 to 1.326 were determined with precision characterized by RSD lower than 1.5% for the enriched cell fractions with B concentrations ranging from 3.3 to 10.8 mg g-1. The detection limit (3s) was 0.5 ng B mL-1. The average enrichments in 10B atom % found in the cell walls, nuclei and chloroplasts were 46.7, 44.5 and 48.8, respectively.

Investigation of planktonic foraminifera with ToF‐SIMS

AbstractVarious oceanic sediment properties deliver useful information for reconstructing environmental parameters of the past. Those properties that are closely related to environmental parameters are called ‘proxies’. They are measurable descriptors for desired (but unobservable) variables. Among others, promising advances were made in the field of boron isotopes in foraminiferal shells as a palaeo‐pH recorder. The isotope ratios are typically measured with thermal ionization mass spectrometry, which requires ∼200 shells to achieve high accuracy. We have investigated the possibility of using time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) for imaging single foraminiferal shells and determining their elemental and isotopic distribution. The data show that ToF‐SIMS is a useful technique for determining their elemental distribution and for measuring boron isotopic ratios with high precision in a single foraminiferal shell. The use of well‐characterized standards for calibration as well as appropriate surface cleaning procedures for foraminiferal shells should improve data accuracy. Furthermore, the data imply that the parallel detection of all masses would simplify the establishment of new proxies. Copyright © 2002 John Wiley &amp; Sons, Ltd.

Boron Isotope Ratio Measurements by Negative Thermal Ionization Mass Spectrometry Method Using Boron-free Seawater

We used boron-free seawater as an ionization promoter for negative thermal ionization mass spectrometry to obtain correct and precise boron isotope ratios. The time profiles were recorded for a whole exhaustion process with 1–10ng boron samples. From a maximum in the initial stable stage, the boron isotope ratios were obtained with 0.05% reproducibility from 1–10ng and 50–400ng boron samples. The observed boron isotope ratio (42/43) is 0.24841±0.0013 for NIST SRM 951, which was a little smaller than that obtained with Ca(NO3)2 as an ionization promoter (42/43=0.24900±0.00013). The negative mode results were normally larger than the positive mode results. The observed value (42/43) was corrected to an absolute value (10/11=0.2455, 02461) using the Rayleigh fractionation factor (1.011835). The standard 0.2473 for Na2BO+ 2 (86/87) was also corrected to an absolute value (10/11=0.2459) using the Rayleigh fractionation factor (1.005666). The positive and negative mode results agreed well within experimental error.

An optimized procedure for boron separation and mass spectrometry analysis for river samples

An optimized procedure for the separation of boron from natural river samples and an improved mass spectrometry determination of boron isotopic ratio are presented. The chemical procedure, based on the use of the boron-specific resin Amberlite IRA 743, is especially efficient in separating boron from natural organic matter-rich samples like river waters. The properties of Amberlite IRA 743 have been investigated. The two factors important in determining the boron affinity for the resin are: the pH value and the ionic strength of the solution from which B is to be extracted. A logarithmic relationship between B partition coefficients and pH values is found. High ionic strength significantly lowers the fixation of B onto the Amberlite resin. The knowledge of the factors controlling the affinity of the resin Amberlite IRA 743 for boron enables us to design a simple and miniaturized chemical separation procedure characterized by (i) three chromatographic steps using, respectively, 50, 10 and 3 μl of resin, (ii) no evaporation step between each column, and (iii) final separation of boron from residual organic matter by sublimation of boric acid at 75 °C. Boron isotopic ratios are measured using an improved cesium metaborate technique, with graphite and mannitol. Adequate loading conditions enable us to obtain typical signal intensities of 5×10 −12 A for 250 ng of boron. No in-run isotopic fractionation is observed, the external reproducibility for standards processed through the entire chemical procedure, as well as for samples, corresponds to 0.35‰ (±2 σ). According to this precision, a slight, but reproducible isotopic fractionation of 0.4‰ is observed for standards processed through the entire chemical procedure whose origin is discussed, but is still unclear.

Boron Isotope Ratio Measurement by Negative Thermal Ionization Mass Spectrometry Method Using Boron-free Seawater.

We used boron-free seawater as an ionization promoter for negative thermal ionization mass spectrometry to obtain correct and precise boron isotope ratios. The time profiles were recorded for a whole exhaustion process with 1–10ng boron samples. From a maximum in the initial stable stage, the boron isotope ratios were obtained with 0.05% reproducibility from 1–10ng and 50–400ng boron samples. The observed boron isotope ratio (42/43) is 0.24841±0.0013 for NIST SRM 951, which was a little smaller than that obtained with Ca(NO3)2 as an ionization promoter (42/43=0.24900±0.00013). The negative mode results were normally larger than the positive mode results. The observed value (42/43) was corrected to an absolute value (10/11=0.2455, 02461) using the Rayleigh fractionation factor (1.011835). The standard 0.2473 for Na2BO+ 2 (86/87) was also corrected to an absolute value (10/11=0.2459) using the Rayleigh fractionation factor (1.005666). The positive and negative mode results agreed well within experimental error.

Boron isotopic ratio by electrospray mass spectra of tetrafluoroborate Part 1. Instrumental conditions, data acquisition, memory effect, and ion stability

The use of electrospray mass spectrometry (ES-MS) of tetrafluoroborate solutions is proposed for the determination of the boron isotopic ratio (10B/11B). When a mixture of methanol and water is used as the solvent and a neutral to alkaline medium is kept, spectra obtained at mild electrospray conditions show free-of-interference peaks with base-line resolution in the region of m/z 86 and 87, which corresponds to 10BF4− and 11BF4−. The study was carried out on a quadrupolar mass spectrometer Platform II (Micromass, UK). To minimize the memory effect in the ion source, the original pepper pot counter electrode was substituted by a cross-flow counter electrode. This geometry reduces the memory effect, but a cleaning process based on mannitol injection assures a suitable background level. Occasional corona discharge corrupts the numerical results, thus median and median of absolute deviations were used as central tendency and dispersion estimators, respectively, because spikes and outliers do not affect them. The influences of the source and detector voltages and the gas flows over the isotopic ratio were investigated. No systematic effect was observed, but there are mass discrimination and drift that were corrected by successive injections of a solution of boric acid NIST 951 converted to sodium tetrafluoroborate. Common ions such as K+, Na+, Mg2+, Ca2+, SO42−, Br− and Cl− do not cause significant isobaric interference and isotopic fractionation. The isotopic ratio precision obtained for 5 min injection of 100 µmol L−1 boron solution at 10 µL min−1 was typically 0.4‰, which is comparable to those from inductively coupled plasma (ICP-MS) and thermal ionization mass spectrometry (TIMS).

Tracing the evolving flux from the subducting plate in the Tonga-Kermadec arc system using boron in volcanic glass

The influence of fluid flux on petrogenesis in the Tonga-Kermadec Arc was investigated using ion microprobe measurements of B/Be and boron isotope ratios (11B/10B) to document the source and relative volumes of the fluids released from the subducting oceanic plate. We analyzed young lavas from eight different islands along the Tonga-Kermadec Arc, as well as glass shards in volcanic sediments from Ocean Drilling Program (ODP) Site 840, which record the variations in the chemistry of Tonga magmatism since 7 Ma. B/Be is variable (5.8–122), in young Tonga-Kermadec Arc lavas. In contrast, glass shards from ∼3 to 4 Ma old volcanic sediments at Site 840 have the highest B/Be values yet reported for arc lavas (18–607). These values are too high to be related simply to a sediment influence on petrogenesis. Together with very high δ11B values (−11.6 to +37.5) for the same shards and lavas these data indicate that most of the B is derived from fluid escaped from the subducting altered Pacific oceanic crust, rather than from sediment. High δ11B values also reflect large degrees of isotopic fractionation in this cold fast subduction zone. Lower δ11B values noted in the Kermadec Arc (17 to −4.4) are related to the influence of sediment eroded from New Zealand and slower convergence. High fluid flux (B/Be) is synchronous in Tonga and the Marianas at 3 to 4 Ma and may be related to acceleration of the Pacific Plate just prior to this time.The timing of maximum B/Be at 3 to 4 Ma correlates with maximum light rare earth (LREE) and high field strength element depletion. This suggests maximum degrees of partial melting at this time. Although thinning of the arc lithosphere during rifting to form the Lau Basin is expected to influence the arc geochemistry, variable aqueous fluid flux from the subducting plate alone appears capable of explaining boron and other trace element systematics in the Tonga-Kermadec Arc with no indication of slab melting.