10Be Measurements Research Articles

An approach for optimizing in situ cosmogenic 10Be sample preparation

Optimizing sample preparation for the isotopic measurement of 10Be extracted from quartz mineral separates has a direct positive effect on the accuracy and precision of isotopic analysis. Here, we demonstrate the value of tracing Be throughout the extraction process (both after dissolution and after processing), producing pure Be (by optimizing ion exchange chromatography methods and quantifying quartz mineral separate and final Be fraction purity), and minimizing backgrounds (through reducing both laboratory process blanks and 10B isobaric interference). These optimization strategies increase the amount of 10Be available for analysis during accelerator mass spectrometry (AMS), while simultaneously decreasing interference and contamination, and ensuring that sample performance matches standard performance during analysis. After optimization of our laboratory's extraction methodology, 9Be3+ ion beam currents measured during AMS analysis, a metric for sample purity and Be yield through the extraction process, matched the 9Be3+ beam currents of AMS standards analyzed at the same time considering nearly 800 samples. Optimization of laboratory procedures leads to purer samples that perform better, more consistently, and more similarly to standards during AMS analysis, allowing for improved precision and accuracy of measurements used for dating and quantification of Earth surface processes.

Reactions with a10Be beam to study the one-neutron halo nucleus11Be

Halo nuclei are excellent examples of few-body systems consisting of a core and weakly-bound halo nucleons. Where there is only one nucleon in the halo, as in 11Be, the many-body problem can be reduced to a two-body problem. The contribution of the 1s1/2 orbital to the ground state configuration in 11Be, characterized by the spectroscopic factor, S, has been extracted from direct reaction data by many groups over the past five decades with discrepant results. An experiment was performed at the Holifield Radioactive Ion Beam Facility using a 10Be primary beam at four different energies with the goal of resolving the discrepancy through a consistent analysis of elastic, inelastic, and transfer channels. Faddeev-type calculations, released after the publication of the experimental results, show that dynamic core excitation in the transfer process can lead to reduced differential cross sections at higher beam energies. This reduction would lead to the extraction of decreasing values of S with increasing beam energy. A 10Be(d,p) measurement at Ed greater than 25 MeV is necessary to investigate the effects of core excitation in the reaction.

The effect of sediment mixing on mercury dynamics in two intertidal mudflats at Great Bay Estuary, New Hampshire, USA

Estuarine sediments store particulate contaminants including mercury (Hg). We studied Hg sediment dynamics in two intertidal mudflats at Great Bay estuary, NH, over multiple years. Sediments at both mudflats were physically mixed down to ~10cm, as determined by 7Be measurements, albeit via different mechanisms. Portsmouth mudflat (PT) sediments were subject to bioturbation by infaunal organisms and Squamscott mudflat (SQ) sediments were subject to erosion and redeposition. The presence of higher concentrations of fresh Fe(III) hydroxide at PT suggested bioirrigation by the polychaetes (Nereis virens). At depths where infaunal bioirrigation was observed, pore-water inorganic Hg (Hgi) and methylmercury (MeHg) were lower potentially due to their interaction with Fe(III) hydroxide. Methylmercury concentrations increased immediately below this zone in some samples, suggesting that the observed increase in material flux in bioirrigated sediments may initiate from lower depths. Pore water in sediment at PT also had higher fractions of more protein-like and labile DOC than those at SQ that can lead to increased MeHg production in PT, especially at depths where Hgi is not removed from solution by Fe(III) hydroxide. Where sediment erosion and redeposition were observed at SQ, Hg species distribution was extended deeper into the sediment column. Moreover, methyl coenzyme M reductase (MCR) and mercury reductase (mer-A) genes were higher at SQ than PT suggesting differences in conditions for Hg cycling. Results showed that the near-surface region of high MeHg concentrations commonly observed in unmixed sediments does not exist in physically mixed sediments that are common in many estuarine environments.

Multiradionuclide evidence for the solar origin of the cosmic-ray events of ᴀᴅ 774/5 and 993/4.

The origin of two large peaks in the atmospheric radiocarbon (14C) concentration at AD 774/5 and 993/4 is still debated. There is consensus, however, that these features can only be explained by an increase in the atmospheric 14C production rate due to an extraterrestrial event. Here we provide evidence that these peaks were most likely produced by extreme solar events, based on several new annually resolved 10Be measurements from both Arctic and Antarctic ice cores. Using ice core 36Cl data in pair with 10Be, we further show that these solar events were characterized by a very hard energy spectrum with high fluxes of solar protons with energy above 100 MeV. These results imply that the larger of the two events (AD 774/5) was at least five times stronger than any instrumentally recorded solar event. Our findings highlight the importance of studying the possibility of severe solar energetic particle events.

Preparation of ASTER in-house 10Be/9Be standard solutions

Since its commissioning in 2006, the commercially available certificated National Institute of Standards and Technology standard reference material NIST SRM 4325 is used at the French national facility ASTER (CEREGE, Aix-en-Provence) to normalize 10Be measurements. This standard solution being no longer disposable, we thus decided to produce in-house standards. As a first attempt, a STD-12 standard (10Be/9Be=(4.939±0.053)×10−12) has been prepared from 2.5kg of marine sediments with an adapted chemical protocol. Then, a 10Be enriched solution of known concentration being available, a STD-11 standard (10Be/9Be=(1.191±0.013)×10−11) that will be used at ASTER in the near future to calibrate 10Be measurements and its dilution to the 10−14 level (STD-14 (10Be/9Be=(5.468±0.064)×10−14)) have been prepared from it.

Preliminary AMS measurements of 10Be at the CENTA facility

Very sensitive methods, presently mainly accelerator mass spectrometry (AMS) are necessary for analysis of cosmogenic 10Be in the environment. AMS is mainly limited by the stable isobar 10B, while the requirements for mass separation are the least stringent of all standard isotopes analyzed by AMS. We tested a possibility to measure 10Be using a small switching magnet as an analyzer of accelerated ions, and an ionization chamber with a silicon nitride foil stack used as a passive absorber. A detection limit of 10−12 for the 10Be/9Be isotopic ratio was obtained using this technique, which was mainly determined by scattering of 9Be+2 ions on residual gas inside the switching magnet.

Glaciation history of Queen Maud Land (Antarctica) – New exposure data from nunataks

Terrestrial cosmogenic nuclide exposure ages for the Wohlthat Massif (Antarctica), have previously been determined. This was done with 10Be and 26Al measurements by accelerator mass spectrometry (AMS) at the AMS facility at the ETH Zurich.In order to determine the extent to which the results from the Wohlthat Massif are of regional significance, additional samples were collected during the 2007 BGR-expedition “Queenmet”. Two of the Steingarden Nunataks (isolated mountain peaks) were chosen as sampling locations, approximately 100km south-east of the Wohlthat Massif/Queen Maud Land, at the edge of the Polar Plateau. Quartz rich samples were collected at different elevations on the nunataks to reconstruct an elevation-dependent exposure history. The in situ produced cosmogenic nuclides 10Be and 26Al in these samples were measured by AMS. During sample processing the quartz separates were prepared by two different methods (Kohl and Nishiizumi, 1992, Altmaier, 2000) and measurements were performed at two different facilities (CologneAMS und Zurich AMS) to confirm the reproducibility of the results.The new results of rock surface exposure ages reveal that the exposure of the lower nunatak to cosmic radiation started between 0.65 and 1.1Ma ago, while the more elevated regions of the second nunatak were apparently above the ice 3–4Ma ago.

A new AMS facility at Inter University Accelerator Centre, New Delhi

Inter University Accelerator Centre (IUAC), a national facility of government of India, is having a 15UD Pelletron accelerator for multidisciplinary ion beam based research programs. Recently, a new accelerator mass spectrometry (AMS) facility has been developed after incorporating many changes in the existing 15UD Pelletron accelerator. A clean chemistry laboratory for 10Be and 26Al with all the modern facilities has also been developed for the chemical processing of samples. 10Be measurements on sediment samples, inter laboratory comparison results and 26Al measurements on standard samples are presented in this paper. In addition to the 10Be and 26Al AMS facilities, a new 14C AMS facility based on a dedicated 500kV tandem ion accelerator with two cesium sputter ion sources, is also being setup at IUAC.

A preliminary study of direct 10Be2+ counting in AMS using the super-halogen anion BeF3−

The key to effective 10Be measurements by AMS is to efficiently suppress the interference of the isobar 10B and at the same time optimize 10Be transmission. In this work, a new approach of measuring 10Be by AMS has been studied. It uses the super-halogen anion of beryllium, BeF3−, which inherently suppresses 10B interference by nearly 5 orders of magnitude because the accompanying BF3− anion is rarely formed. The resulting 10B suppression factor is not as high as that achieved with energy degrader foils, but the 10B and 10Be separation in the final ionization detector was found to result in sufficient total 10B suppression for 10Be2+ to be counted directly at ∼6MeV energies. Although the stripping yield from 10BeF3− to 10Be2+ is not as large as that from 10BeO−, this inefficiency is compensated by avoiding the reduction in transmission due to charge fraction splitting and optical transmission losses after the degrader foil. This paper summarizes our first observation of the direct 10Be2+ counting approach using the 3MV multi-element system at the Xi’an AMS.

Decadal 10Be, 26Al and 36Cl QA measurements on the SUERC 5 MV accelerator mass spectrometer

We quantify the routine performance and uncertainties of cosmogenic 10Be, 26Al and 36Cl QA measurements made on the SUERC 5MV accelerator mass spectrometer since 2004. Our analysis compiles data from primary (NIST SRM4325 for 10Be, Purdue Z92-0222 for 26Al and Purdue Z93-0005 for 36Cl) and secondary (Nishiizumi’s series for 10Be, 26Al and 36Cl) reference samples with 10Be/9Be, 26Al/27Al and 36Cl/Cl ratios ranging between 10−11 and 10−13. Our decadal datasets indicate that the 10Be, 26Al and 36Cl secondary standard samples have average standard deviations 1.1%–2.4%, 1.1%–2.8% and 3.0%–3.1%, respectively. The average statistical uncertainties based on counting statistics are 1.0%–1.8%, 0.9%–2.8% and 2.5%–2.7% for 10Be, 26Al and 36Cl, respectively. These indicate additional uncertainties (0.6%–1.6% for 10Be, 0.5%–2.4% for 26Al and 1.4%–1.7% for 36Cl) above those calculated from counting statistics alone. The average differences between the measured and the nominal values are within ±1% in 13 of 14 secondary samples.

Further improvement for 10Be measurement on an upgraded compact AMS radiocarbon facility

The Peking University 500kV NEC compact AMS radiocarbon facility (PKU-CAMS) has been modified in order to have additionally the possibility to measure 10Be. In the preliminary experiment a silicon nitride foil was mounted in front of the electrostatic deflector as passive boron degrader, and the original Si detector for radiocarbon detection was replaced by an ETHZ-designed high-resolution ΔE−Eres gas ionization chamber (GIC) for 10Be identification. This simple arrangement has yielded an overall 10Be transmission of 2.2% and a 10Be/9Be background level of 3.5×10−14. To further reduce the background and increase the transmission by re-focusing the 10Be ions, an additional 90° bending magnet with 350mm radius was installed after the electrostatic deflector. The silicon detector was shifted slightly relative to its position of original NEC system setup in opposite direction of beam and can be lifted up manually without breaking vacuum when 10Be measurements are carried out. In this way the system can be easily and fast set up for 10Be without affecting any parameters for radiocarbon measurement. The gas detector for 10Be was mounted at the end of the beam line after the additional magnet. The lay-out of the upgraded spectrometer is very compact and does not require more space than the original instrument. Using this compact setup, the overall transmission for 10Be was doubled to 5–6% and the 10Be/9Be background level was reduced to radios as low as 2.4×10−15.

Climate-induced changes in sediment supply revealed by surface exposure dating of Sijiquan River terraces, northeastern Tibet

In this paper, we report cosmogenic isotope evidence for dramatic changes in sediment supply during glacial–interglacial climatic cycles in the Late Quaternary. Previous work on fluvio-glacial processes in cold environments has qualitatively revealed that significant increases in debris production occurred in glacial periods, due typically to accelerated glacial and periglacial processes on high-relief slopes, resulting in river aggradation (accumulation) in the drainage. In interglacial periods, rivers behave in the opposite way, forming incised valleys. However, little has been studied on climatically controlled production-and-reworking processes with radiometric evidence. The evidence presented here is from the northeastern margin of the Tibetan Plateau, where lateral growth of the plateau is now ongoing. Reconstructions of fluvial response to Quaternary glacial fluctuations are crucial also to better understand the active tectonic process in the region using geomorphological information. The Sijiquan River drainage basin on the north of the East Kunlun Mountains was investigated. Detailed geomorphological mapping of fluvio-glacial landforms indicates two phases of aggradation, each of which was followed by valley incision. 10Be and 26Al concentrations in fluvial terrace deposits suggest that these two aggradational phases correspond most likely to the penultimate and last glacial periods, assuming a low rate of surface erosion on the terraces and zero inherited concentration. On the other hand, present-day river gravel has higher concentrations in amalgamated samples of 10Be and 26Al than the terrace deposits. Surface-exposure and burial analyses based on grain-by-grain measurements of both 10Be and 26Al indicate that the present-day river gravel consists mostly of reworked grains from terrace deposits and underlying fluvio-lacustrine rocks in the drainage basin. It is concluded that significant changes in clastic sediment supply occur in cold environments in response to glacial–interglacial cycles; clastic sediments are transported from mountain slopes much more directly in glacial periods than in interglacial periods. This violates the common assumption for surface exposure dating that the inherited cosmogenic isotope concentration is constant through time.

Upwelling velocity and eddy diffusivity from 7Be measurements used to compare vertical nutrient flux to export POC flux in the Eastern Tropical South Pacific

Five 7Be profiles, measured in an area bounded by 10°S–20°S and 80°W–100°W, were used to determine upwelling velocity (wH) and vertical diffusivity (Kz). A positive correlation between wH and 14C primary production rate and a negative correlation between the inventories of 7Be and phosphate were observed. We interpret this as the influence of deeper, nutrient-rich, 7Be-poor water brought up by upwelling. Excluding two stations that appear to be influenced by non-steady state dynamics or horizontal transport, upwelling velocities were estimated to be 0 to 1.0md−1 and Kz values ranged from 0.4 to 2.6cm2s−1. From these parameters, NO3− fluxes into the euphotic zone were assessed and ranged from 0.15 to 2.9mmolm−2d−1. Using these values, we estimate 1.0 to 19mmolCm−2d−1 of new production in the ETSP. New production based on 7Be-derived transport parameters agree with carbon export estimates using a 234Th balance, sediment traps and O2/Ar supersaturation for stations along 20°S, but are higher than export estimates at 10°S, 100°W.

Quaternary landscape development, alluvial fan chronology and erosion of the Mecca Hills at the southern end of the San Andreas Fault zone

Quantitative geomorphic analysis combined with cosmogenic nuclide 10Be-based geochronology and denudation rates have been used to further the understanding of the Quaternary landscape development of the Mecca Hills, a zone of transpressional uplift along the southern end of the San Andreas Fault, in southern California. The similar timing of convergent uplifts along the San Andreas Fault with the initiation of the sub-parallel San Jacinto Fault suggest a possible link between the two tectonic events. The ages of alluvial fans and the rates of catchment-wide denudation have been integrated to assess the relative influence of climate and tectonic uplift on the development of catchments within the Mecca Hills. Ages for major geomorphic surfaces based on 10Be surface exposure dating of boulders and 10Be depth profiles define the timing of surface stabilization to 2.6 +5.6/–1.3 ka (Qyf1 surface), 67.2 ± 5.3 ka (Qvof2 surface), and 280 ± 24 ka (Qvof1 surface). Comparison of 10Be measurements from active channel deposits (Qac) and fluvial terraces (Qt) illustrate a complex history of erosion, sediment storage, and sediment transport in this environment. Beryllium-10 catchment-wide denudation rates range from 19.9 ± 3.2 to 149 ± 22.5 m/Ma and demonstrate strong correlations with mean catchment slope and with total active fault length normalized by catchment area. The lack of strong correlation with other geomorphic variables suggests that tectonic uplift and rock weakening have the greatest control. The currently measured topography and denudation rates across the Mecca Hills may be most consistent with a model of radial topographic growth in contrast to a model based on the rapid uplift and advection of crust.

Use of 7Be measurements to estimate rates of soil loss from cultivated land: Testing a new approach applicable to individual storm events occurring during an extended period

AbstractThe techniques available for documenting rates and patterns of soil redistribution in the landscape have many limitations and the value of those employing fallout radionuclides (FRNs), including caesium‐137 (137Cs) and excess lead‐210 (210Pbex) is being increasingly recognized. However, the use of 137Cs and 210Pbex measurements is best suited to investigations of longer‐term soil redistribution rates (i.e., ∼50–60 years for 137Cs and ∼100 years for 210Pbex). For many purposes, a much shorter timeframe is required. Beryllium‐7 (7Be), another FRN (half‐life 53 days), offers the potential to document soil redistribution associated with individual events or short periods of heavy rainfall. However, existing approaches for using 7Be possess important limitations related to both the timing of the study period and its length. This contribution reports the development of a new approach that permits estimation of the soil loss associated with all individual events or short periods of rainfall occurring during a study period extending over a year or more. The approach was validated using data collected from an erosion plot located in southern Italy. The close agreement of the measured and estimated values demonstrates the validity of the new approach which has the potential to greatly increase the scope for using 7Be measurements to document short‐term soil redistribution associated with individual storm events.

36Cl production rate from K‐spallation in the European Alps (Chironico landslide, Switzerland)

ABSTRACTThe abundant production of in situ cosmogenic 36Cl from potassium renders 36Cl measurements in K‐rich rocks or minerals, such as K‐feldspars, potentially useful for precisely dating rock surfaces, either in single‐nuclide or in multi‐nuclide studies, for example combined with 10Be measurements in quartz. However, significant discrepancies in experimentally calibrated 36Cl production rates from spallation of potassium (36PK‐sp), referenced to sea‐level/high‐latitude (SLHL), limit the accuracy of 36Cl dating from K‐rich lithologies. We present a new 36Cl calibration using K‐feldspars, in which K‐spallation is the most dominant 36Cl production pathway (>92% of total 36Cl), thus minimizing uncertainties from the complex multi‐pathway 36Cl production systematics. The samples are derived from boulders of an ∼13.4 ka‐old landslide in the Swiss Alps (∼820 m, 46.43°N, 8.85°E). We obtain a local 36PK‐sp of 306 ± 16 atoms 36Cl (g K)−1 a−1 and an SLHL 36PK‐sp of 145.5 ± 7.7 atoms 36Cl (g K)−1 a−1, when scaled with a standard scaling protocol (‘Lm’). Applying this SLHL 36PK‐sp to determine 36Cl exposure ages of K‐feldspars from 10Be‐dated moraine boulders yields excellent agreement, confirming the validity of the new SLHL 36PK‐sp for surface exposure studies, involving 36Cl in K‐feldspars, in the Alps.

Cosmogenic noble gas paleothermometry

We present a theoretical basis for reconstructing paleotemperatures from the open-system behavior of cosmogenic noble gases produced in minerals at Earth's surface. Experimentally-determined diffusion kinetics predicts diffusive loss of cosmogenic 3He and 21Ne from common minerals like quartz and feldspars at ambient temperatures; incomplete retention has also been observed empirically in field studies. We show that the theory of simultaneous production and diffusion that applies to radiogenic noble gases in minerals—the basis of thermochronology—can also be applied to cosmogenic noble gases to reconstruct past surface temperatures on Earth. We use published diffusion kinetics and production rates for 3He in quartz and 21Ne in orthoclase to demonstrate the resolving power of cosmogenic noble gas paleothermometry with respect to exposure duration, temperature, and diffusion domain size. Calculations indicate that, when paired with a quantitatively retained cosmogenic nuclide such as 21Ne or 10Be, observations of cosmogenic 3He in quartz can constrain temperatures during surface exposure in polar and high altitude environments. Likewise, 21Ne retention in feldspars is sensitive to temperatures at lower latitudes and elevations, expanding the potential geographic applicability of this technique to most latitudes. As an example, we present paired measurements of 3He and 10Be in quartz from a suite of Antarctic sandstone erratics to test whether the abundances of cosmogenic 3He agree with what is predicted from first principles and laboratory-determined diffusion kinetics. We find that the amounts of cosmogenic 3He present in these samples are consistent with the known mean annual temperature (MAT) for this region of Antarctica between −25 and −30 °C. These results demonstrate the method's ability to record paleotemperatures through geologic time.

The impacts of the great Mississippi/Atchafalaya River flood on the oceanography of the Atchafalaya Shelf

Rivers are the primary means by which water, sediment, and dissolved material are transported from the continents to the ocean. Despite previous advances, much remains to be learned about the dynamics of large shelf-discharging rivers, and their functional differences with deep water-discharging rivers, particularly with respect to the distribution of sediments in the coastal zone. The great Mississippi/Atchafalaya River flood of 2011 provided an excellent opportunity to examine the impacts of a large, shelf-discharging river on the coastal ocean, and the role that event pulses from such rivers play in the delivery of sediment to the inner continental shelf. Vessel-based surveys were conducted on the inner-continental shelf within the Atchafalaya and Mississippi River plume regions, providing in situ measurements of salinity, temperature, dissolved oxygen, turbidity, particle size, and current velocity profiles. MODIS satellite images and 7Be measurements were used to assist in data interpretation.We demonstrate that the Atchafalaya River plume produced intense vertical gradients in temperature, salinity, oxygen and turbidity. This occurred despite the shallow bathymetry of this system and the presence of winds, which alternated between onshore to offshore, and that might have otherwise mixed systems with less freshwater. Sedimentation rates along the inner-continental shelf were about 5–10 times greater than those measured previously during smaller “typical” floods. This large deposit is likely to be preserved, at least in the near term, because sedimentation occurred beyond normal depths of wave reworking and the intense stratification induced by this flood likely reduced mixing at the time of sedimentation. A sediment budget for this system reveals that sediment fluxes to the coastal zone during 2011 were similar to those observed in previous years, suggesting that this system is supply limited, rather than transport limited. As such, we postulate that the major impact of this flood was to change the location of the depocenter of Atchafalaya River sediments, rather than increase the annual flux of sediments to the coastal zone. These findings imply that extreme flood events may not be an ideal analog for coastal restoration along this deltaic coast.

Sediment resuspension in the Lake Erie nearshore

A decline in water quality in Lake Erie during the last decade, despite increased efforts to limit nutrient loading, may be better understood by examining internal processes in the lake. We employed 7Be, 210Pb and 137Cs measurements of suspended matter in tributaries, in the lake water column, in atmospheric precipitation, in sediment traps and in bottom sediments collected in June and August/September 2011 to estimate the fraction of the suspended matter that is resuspended from the bottom. Mass balances on 7Be and 210Pb using sediment trap material indicated that at the nearshore site ~83–94% of suspended matter in the water column was resuspended bottom sediment, while, offshore, resuspended sediment made up only ~62–75%. A mass balance using the 7Be/210Pb ratio for each sediment source indicated that resuspension of bottom sediment accounted for 52–97% of the suspended material in the nearshore and from 53 to 86% of the suspended matter in the offshore and was greater after the fall overturn. The amount of nutrients delivered to the water column by resuspension indicates that the resuspension loading of particle-bound P to the lake is about the same as the tributary loading, although the resuspended P is likely to be significantly less bioavailable.

10Be detection at the new AMS beam line at CEDAD: Performance tests and first results

A new AMS (Accelerator Mass Spectrometry) beam line has been recently installed at CEDAD (Centre for Dating and Diagnostics)-university of Salento, Lecce, Italy for the detection by AMS of rare isotopes such as 10Be, 26Al, 129I and actinides. In this paper the performances of the new line for the measurement of 10Be are presented. Different tests were carried out in order to determine proper operating parameters and experimental conditions such as acceleration voltage, selected charge states and silicon nitride degrader thickness. The obtained results allow to assess the good performances of the new spectrometer in terms of boron suppression and background levels.