Cosmogenic Production Research Articles

Cosmogenic isotope 7Be: A case study of depositional processes in Rio de Janeiro in 2008–2009

We present here an investigation of the depositional processes of 7Be-carrying aerosols in the troposphere through an analysis of the isotope concentration variability measured at Rio de Janeiro (Brazil) during 2008 and 2009, with weekly resolution. By adopting a simplified description of the equilibrium scenario in the troposphere and combining our isotopic data with regional meteorological parameters and numerical CRAC:Be7 model of cosmogenic production, it was possible to quantitatively reproduce the observed seasonal variability and estimate the typical 7Be-aerosols residence time in the lower troposphere ( t r ∼ 1 day) as well as the washout coefficient for each season (wet: Λ = 0.029; and dry: Λ = 0.023 h −1). These results allowed us to discuss the origin of the seasonal patterns of 7Be concentrations, indicating that the wet deposition modulation, caused by changes in the regional weather condition, is the most important forcing in both seasons. Even an anomaly in isotopic short-term measured variability can be explained when a detailed air-mass dynamic is considered. Our results indicate that anomalous events of tropospheric dynamic, such as occurrence of strong downward air flux, imprint information about air masses 3-D movement in the near-ground air 7Be data, making 7Be a useful tracer of its peculiar dynamics at local and synoptic scales in the troposphere. This study, limited to a single location and one year time interval, illustrates the potential of the method. A more detailed general study is planned for the future.

Fast-neutron activation of long-lived isotopes in enriched Ge

We measured the production of \nuc{57}{Co}, \nuc{54}{Mn}, \nuc{68}{Ge}, \nuc{65}{Zn}, and \nuc{60}{Co} in a sample of Ge enriched in isotope 76 due to high-energy neutron interactions. These isotopes, especially \nuc{68}{Ge}, are critical in understanding background in Ge detectors used for double-beta decay experiments. They are produced by cosmogenic-neutron interactions in the detectors while they reside on the Earth's surface. These production rates were measured at neutron energies of a few hundred MeV. We compared the measured production to that predicted by cross-section calculations based on CEM03.02. The cross section calculations over-predict our measurements by approximately a factor of three depending on isotope. We then use the measured cosmic-ray neutron flux, our measurements, and the CEM03.02 cross sections to predict the cosmogenic production rate of these isotopes. The uncertainty in extrapolating the cross section model to higher energies dominates the total uncertainty in the cosmogenic production rate.

Steady state reach‐scale theory for radioactive tracer concentration in a simple channel/floodplain system

A steady state analytical model is presented for reach‐scale variation in the concentration of a decaying radioactive tracer associated with sediment particles that regularly pass through an off‐channel floodplain. The floodplain is represented as a series of well‐mixed sediment reservoirs that continually exchange sediment with the channel. The model allows for tributary input and valley‐wide aggradation or degradation. Tracer concentration depends on the upstream boundary concentration, the tracer and sediment load, floodplain geometry, and the rates of in‐floodplain tracer production and/or decay. The theory predicts relatively modest down‐channel change in the concentration of long‐lived isotopes but implies that significant change may occur for (1) tracers with a short‐enough half‐life (such as 14C) or (2) floodplains with sediment residence times that are large enough for cosmogenic production or meteoric fallout to increase tracer concentration in the down‐valley direction. The profiles are shown to be strongly dependent on the grain size distributions of both the sediment load and the floodplain. The results imply that down‐channel 14C profiles have the potential to constrain Holocene bed material loads in systems with sufficient storage. The theory concisely describes the general importance of a floodplain for modifying in situ produced cosmogenic tracer concentration and can also characterize floodplain importance for fallout radioisotopes (i.e., 10Be, 210Pb, or 7Be) or organic 14C.

Studies on cosmogenic production as a background for rare physics processes

We present the cosmogenic production rates of several long-lived isotopes estimated by using updated cosmic-ray neutron flux measurements and excitation functions from TALYS code 1.0. We find that the cosmogenic isotopes produced inside different detector target materials can be potential sources of background in searching for rare physics processes such as the detection of dark matter and neutrinoless double-beta decay.

On the use of 14CO2 as a tracer for fossil fuel CO2: Quantifying uncertainties using an atmospheric transport model

Δ14CO2 observations are increasingly used to constrain recently added fossil fuel CO2 in the atmosphere. We use the LMDZ global atmospheric transport model to examine the pseudo‐Lagrangian framework commonly used to determine recently added fossil fuel CO2 (CO2ff). Our results confirm that Δ14CO2 spatial variability in the Northern Hemisphere troposphere is dominated by the effect of CO2ff, whereas in the Southern Hemisphere, ocean CO2 exchange is more important. The model indicates that the free troposphere, at 3–5 km altitude, is a good choice for “background,” relative to which the recently added fossil fuel CO2 can be calculated, although spatial variability in free tropospheric Δ14CO2 contributes additional uncertainty to the CO2ff calculation. Comparison of model and observations suggests that care must be taken in using high‐altitude mountain sites as a proxy for free tropospheric air, since these sites may be occasionally influenced by (polluted) boundary layer air, especially in summer. Other sources of CO2 which have Δ14C different than that of the atmosphere contribute a bias, which, over the Northern Hemisphere land, is mostly due to the terrestrial biosphere, whereas ocean CO2 exchange and nuclear industry and natural cosmogenic production of 14C contribute only weakly. The model indicates that neglecting this bias leads to a consistent underestimation of CO2ff, typically between 0.2 and 0.5ppm of CO2, with a maximum in summer. While our analysis focuses on fossil fuel CO2, our conclusions, particularly the choice of background site, can also be applied to other trace gases emitted at the surface.

Cosmogenic nuclides in stony meteorites revisited

Abstract— We present new model calculations for depth and size dependent cosmogenic production rates in ordinary and carbonaceous chondrites by galactic cosmic rays. This model, essentially that of Leya et al. (2000a), folds together particle spectra and cross sections for the relevant nuclear reactions, but has been significantly improved due to major improvements in the neutron cross section database and better Monte Carlo modeling of the primary and the secondary particle spectra. The data presented here replace (and extend) the results of our earlier model predictions. Here we give for ordinary and carbonaceous chondrites elemental production rates for the cosmogenic radionuclides 10Be, 14C, 26Al, 36Cl, 41Ca, 53Mn, 60Fe, and 129I as well as for the noble gas isotopes 3He, 4He, 20Ne, 21Ne, 22Ne, 36Ar, and 38Ar. Using the new data and expressing size and depth scales to the unit [g/cm2], we are able to demonstrate that the matrix effect for both chondrite types is negligible for all target product combinations, except for those which are dominated by thermal or very low energy neutron reactions. Based on the new model predictions, we present a variety of elemental and isotopic production rate ratios allowing for a reliable determination of preatmospheric sizes, shielding depths, cosmic‐ray exposure ages, and diffusive losses.

Relative timing of last glacial maximum and late-glacial events in the central tropical Andes

Whether or not tropical climate fluctuated in synchrony with global events during the Late Pleistocene is a key problem in climate research. However, the timing of past climate changes in the tropics remains controversial, with a number of recent studies reporting that tropical ice age climate is out of phase with global events. Here, we present geomorphic evidence and an in-situ cosmogenic 3He surface-exposure chronology from Nevado Coropuna, southern Peru, showing that glaciers underwent at least two significant advances during the Late Pleistocene prior to Holocene warming. Comparison of our glacial-geomorphic map at Nevado Coropuna to mid-latitude reconstructions yields a striking similarity between Last Glacial Maximum (LGM) and Late-Glacial sequences in tropical and temperate regions.Exposure ages constraining the maximum and end of the older advance at Nevado Coropuna range between 24.5 and 25.3ka, and between 16.7 and 21.1ka, respectively, depending on the cosmogenic production rate scaling model used. Similarly, the mean age of the younger event ranges from 10 to 13ka. This implies that (1) the LGM and the onset of deglaciation in southern Peru occurred no earlier than at higher latitudes and (2) that a significant Late-Glacial event occurred, most likely prior to the Holocene, coherent with the glacial record from mid and high latitudes. The time elapsed between the end of the LGM and the Late-Glacial event at Nevado Coropuna is independent of scaling model and matches the period between the LGM termination and Late-Glacial reversal in classic mid-latitude records, suggesting that these events in both tropical and temperate regions were in phase.

Cosmogenic production as a background in searching for rare physics processes

We revisit calculations of the cosmogenic production rates for several long-lived isotopes that are potential sources of background in searching for rare physics processes such as the detection of dark matter and neutrinoless double-beta decay. Using updated cosmic-ray neutron flux measurements, we use TALYS 1.0 to investigate the cosmogenic activation of stable isotopes of several detector targets and find that the cosmogenic isotopes produced inside the target materials and cryostat can result in large backgrounds for dark matter searches and neutrinoless double-beta decay. We use previously published low-background HPGe data to constrain the production of 3H on the surface and the upper limit is consistent with our calculation. We note that cosmogenic production of several isotopes in various targets can generate potential backgrounds for dark matter detection and neutrinoless double-beta decay with a massive detector, thus great care should be taken to limit and/or deal with the cosmogenic activation of the targets.

New model calculations for the production rates of cosmogenic nuclides in iron meteorites

Abstract— Here we present the first purely physical model for cosmogenic production rates in iron meteorites with radii from 5 cm to 120 cm and for the outermost 1.3 m of an object having a radius of 10 m. The calculations are based on our current best knowledge of the particle spectra and the cross sections for the relevant nuclear reactions. The model usually describes the production rates for cosmogenic radionuclides within their uncertainties; exceptions are 53Mn and 60Fe, possibly due to normalization problems. When an average S content of about 1 ± 0.5% is assumed for Grant and Carbo samples, which is consistent with our earlier study, the model predictions for 3He, 21Ne, and 38Ar are in agreement. For 4He the model has to be adjusted by 24%, possibly a result of our rather crude approximation for the primary galactic α particles. For reasons not yet understood the modeled 36Ar/38Ar ratio is about 30–40% higher than the ratio typically measured in iron meteorites. Currently, the only reasonable explanation for this discrepancy is the lack of experimentally determined neutron induced cross sections and therefore the uncertainties of the model itself. However, the new model predictions, though not yet perfect, enable determining the radius of the meteoroid, the exposure age, the sulphur content of the studied sample as well as the terrestrial residence time. The determination of exposure ages is of special interest because of the still open question whether the GCR was constant over long time scales. Therefore we will discuss in detail the differences between exposure ages determined with different cosmogenic nuclides. With the new model we can calculate exposure ages that are based on the production rates (cm3STP/(gMa)) of noble gases only. These exposure ages, referred to as noble gas exposure ages or simply 3,4He, 21Ne, or 36,38Ar ages, are calculated assuming the current GCR flux. Besides calculating noble gas ages we were also able to improve the 41K‐40K‐and the 36Cl‐36Ar dating methods with the new model. Note that we distinguish between 36Ar ages (calculated via 36Ar production rates only) and 36Cl‐36Ar ages. Exposure ages for Grant and Carbo, calculated with the revised 41K‐40K method, are 628 ± 30 Ma and 841 ± 19 Ma, respectively. For Grant this is equal to the ages obtained using 3He, 21Ne, and 38Ar but higher than the 36Ar‐ and 36Cl‐36Ar ages by ˜30%. For Carbo the 41K‐40K age is ˜40% lower than the ages obtained using 3He, 21Ne, and 38Ar but equal to the 36Ar age. These differences can either be explained by our still insufficient knowledge of the neutron‐induced cross sections or by a long‐term variation of the GCR.

Cosmogenic neutrino production from the propagation of ultra-high energy cosmic-ray nuclei

In this proceeding, we study the production of cosmogenic neutrinos from the propagation of ultra-high energy cosmic-ray (UHECR) nuclei. After discussing the main production channels for cosmic-ray nuclei, we investigate the dependence of the expected fluxes on astrophysical parameter such as the composition, the cosmological distribution of the sources, or the maximum energy of the accelerated cosmic-rays. We finally discuss the detectability of these cosmogenic neutrinos between 10 12 and 10 20 eV .

A late Holocene slip rate for the central North Anatolian fault, at Tahtaköprü, Turkey, from cosmogenic 10Be geochronology: Implications for fault loading and strain release rates

Measurement of a stream offset and cosmogenic dating (10Be) of the alluvial surface into which the stream incised yield a preferred late Holocene slip rate of 18.6 +3.5/−3.3 mm a−1 for the central part of the North Anatolian fault (NAF) at Tahtaköprü, Turkey; use of variable cosmogenic production rate (VPR) models yields a slightly slower rate of ∼16.4 +6.4/−4.5 mm a−1. The offset drainage (Karanlık Dere), which flows southward almost perpendicular to the east‐west trace of the NAF at the site, is displaced right laterally by 55 ± 10 m, with no vertical displacement. A 10Be age of ∼3 ka (∼3.5 ka VPR) from the top of a boulder on the best preserved part of the incised alluvial surface provides the most reliable maximum age for the onset of incision; 11 10Be ages from cobbles collected from the cultivated surface to the south yield younger ages, consistent with exhumation, erosion, and mechanical mixing during plowing. Our 18.6 +3.5/−3.3 mm a−1 rate is similar to other geologic slip rates measured along the NAF, all of which cluster between 15 and 20 mm a−1 over a wide range of (103–105) timescales. All of these geological rates, however, are slower than the ∼25 ± 2 mm a−1 short‐term rate of elastic strain accumulation measured geodetically. This disparity suggests the possibility that the NAF is experiencing a strain transient in which the lower crust beneath the fault is deforming faster than its long‐term rate.

Cosmogenic beryllium-10 and neon-21 dating of late Pleistocene glaciations in Nyalam, monsoonal Himalayas

We present cosmogenic 10Be and 21Ne chronologies from 21 erratic boulders on three moraine sequences in Nyalam county, monsoonal Himalayas, southern margin of the Tibetan Plateau. The surface exposure ages provide evidence for at least two distinct glacial advances during the late stage of the last glacial cycle and for one or more significantly older glaciations. The distribution of cosmogenic ages from the three ridges of the old moraine sequence is inconsistent with their stratigraphic order. Because exposure periods of the erratics prior to deposition on the moraine surface is shown to be small, the chronology–stratigraphy mismatch suggests that the cosmogenic ages do not date moraine deposition but most likely significant moraine ridge denudation and related boulder exhumation after initial deposition of the moraines during the penultimate glacial cycle or earlier. The surface exposure ages based on various currently accepted production rate scaling protocols yield age differences of up to 35% reflecting the poor knowledge of terrestrial cosmogenic production rates at low latitude/high altitude sites. Even within this conservative uncertainty range, our results do not yield evidence for late Pleistocene glaciations in monsoonal Tibet to be asynchronous to those in mid-latitudes on both hemispheres. There is an urgent need to improve the knowledge of terrestrial cosmogenic nuclide production rates and their scaling to low latitude regions to fully exploit the climate information archived in tropical moraine sequences.

Late formation and prolonged differentiation of the Moon inferred from W isotopes in lunar metals

The Moon is thought to have formed from debris ejected by a giant impact with the early 'proto'-Earth and, as a result of the high energies involved, the Moon would have melted to form a magma ocean. The timescales for formation and solidification of the Moon can be quantified by using 182Hf-182W and 146Sm-142Nd chronometry, but these methods have yielded contradicting results. In earlier studies, 182W anomalies in lunar rocks were attributed to decay of 182Hf within the lunar mantle and were used to infer that the Moon solidified within the first approximately 60 million years of the Solar System. However, the dominant 182W component in most lunar rocks reflects cosmogenic production mainly by neutron capture of 181Ta during cosmic-ray exposure of the lunar surface, compromising a reliable interpretation in terms of 182Hf-182W chronometry. Here we present tungsten isotope data for lunar metals that do not contain any measurable Ta-derived 182W. All metals have identical 182W/184W ratios, indicating that the lunar magma ocean did not crystallize within the first approximately 60 Myr of the Solar System, which is no longer inconsistent with Sm-Nd chronometry. Our new data reveal that the lunar and terrestrial mantles have identical 182W/184W. This, in conjunction with 147Sm-143Nd ages for the oldest lunar rocks, constrains the age of the Moon and Earth to Myr after formation of the Solar System. The identical 182W/184W ratios of the lunar and terrestrial mantles require either that the Moon is derived mainly from terrestrial material or that tungsten isotopes in the Moon and Earth's mantle equilibrated in the aftermath of the giant impact, as has been proposed to account for identical oxygen isotope compositions of the Earth and Moon.

Can the 4He clock be calibrated by 36Cl for groundwater dating?

The ratio of dissolved excess 4He concentration to the 4He accumulation rate is equivalent to the residence time of groundwater if 4He is accumulated at a constant rate. Groundwater contains 36Cl from cosmogenic and subsurface production sources. The 4He clock can be applied by using the correlation between cosmogenic 36Cl decay or the subsurface 36Cl production and the excess 4He increase. We calibrated the 4He clock in the Great Artesian Basin (GAB), Australia, considering dissolution of chloride from the rock matrix. Cosmogenic 36Cl is dominant over 36Cl produced in the subsurface in the Coonamble Embayment of the GAB, because the quartzose sandstone aquifers have a low density of thermal neutrons. The 4He accumulation rate was estimated to be 9.6×10-11ccSTP/gH2O·y-1 in the GAB. We then applied this method to estimation of the groundwater residence time in the Tokachi Basin, Japan, where both cosmogenic and subsurface 36Cl are present in the groundwater. The longest estimated residence time was 2.3 million years, based on a 4He accumulation rate of (1.2-2.1)×10−12ccSTP/cmH2O3·y-1, assuming that ion filtration occurred as pore water was squeezed by the deeply subsiding sedimentary strata in the basin.

Application of 129I / 127I to define the source of hydrocarbons of the Pol-Chuc, Abkatún and Taratunich–Batab oil reservoirs, Bay of Campeche, southern Mexico

Homogeneous 129I / 127I ratios from 6.51 ± 1.36 × 10 − 14 to 12.6 ± 1.49 × 10 − 14 were measured in formation brine at the Pol-Chuc, Abkatún, Taratunich–Batab off-shore oil reservoirs, Bay of Campeche in S-Mexico. Cosmogenic production could account for a homogeneous, Late Cretaceous/Paleocene time period (71.3 ± 5.3 to 56.3 ± 2.9 Ma) for the sedimentation and burial of organic material in the source formation. As the actual reservoir column is formed by Paleocene to Kimmeridgian sediments, the lower part of the lithological column must have received hydrocarbons that migrated downward from an initial source rock (Upper Cretaceous?) during a post-Paleocene event, probably during Miocene. Cosmogenic production from Tithonian shales can be excluded, as 129I would have been decayed. As an alternative or complementary process, the subsurface, radiogenic production of 129I / 127I by 238U-fission in Uranium-enriched sediments should also be considered to explain the present, low 129I / 127I ratios.

Cosmogenic helium and neon in 11 Myr old ultramafic xenoliths: Consequences for mantle signatures in old samples

The helium and neon isotopic compositions of olivines coming from a 11 Myr old xenolith sampled at Mt. Hampton (West Antarctica) were analyzed by crushing. The helium isotopic ratio varies between 1340 and 6300 (R/Ra between 115 and 539) with 4He content around 3–8 10−10 ccSTP/g, confirming that cosmogenic helium can be extracted by crushing. The neon also shows a clear cosmogenic origin (20Ne/22Ne down to 7.7 and 21Ne/22Ne > 0.32), indicating that the cosmogenic neon can also be extracted by crushing out of the olivines. Melting of the powder left after the crushing experiment gives a 4He/3He ratio as low as 42 ± 8 (R/Ra = 17,300) and 21Ne/22Ne as high as 0.78, close to the cosmogenic production end‐member. This study shows that up to ∼0.5% of cosmogenic helium and neon can be extracted by crushing. In this way, for samples that had been exposed to cosmic rays for a long time (e.g., a few Myr), a crushing procedure may not give the mantle ratios without ambiguity, and measurement of neon can help to discriminate between cosmogenic and mantle origin of the 3He.

Fossil cosmogenic 3He record from K–Ar dated basaltic flows of Mount Etna volcano (Sicily, 38°N): Evaluation of a new paleoaltimeter

This study investigates the reliability of a paleoaltimeter based on the elevation dependency of the cosmogenic nuclides production rate. The proposed method relies on “fossil” cosmogenic record. Indeed, measuring the cosmogenic nuclide concentration in an exposed and then buried lava flow combined with an independent estimate (by K–Ar or 40Ar / 39Ar dating) of the past exposure duration theoretically allows recording “fossil” cosmogenic production rates, which can thus be converted in paleoelevations. This approach was tested by measuring cosmogenic 3He ( 3He c) in olivines and clinopyroxenes of Quaternary K–Ar dated basaltic flows of Mount Etna volcano (Sicily, 38°N). The agreement within uncertainties (1 σ ≤ 500 m) between current and cosmogenic-derived elevations demonstrates the paleoaltimeter reliability. However, dating imprecision, Earth's paleomagnetic fluctuations and erosion contemporary to the flow exposure are parameters that may affect the accuracy and the precision of the method on older geological scales. Their respective influences were thus carefully evaluated and discussed to conclude that the paleoaltimeter can potentially reach resolutions better than ∼1000 m, even for Cenozoic records.

Optimal estimation of atmospheric 14C production over the Holocene: paleoclimate implications

A tree-ring Δ14C record and a simple box model of the global 14C cycle are combined using a method of optimal estimation theory (Rauch-Tung-Striebel smoother). The combination is used to infer information about the time evolution of 14C production in the atmosphere % MathType!Translator!2!1!AMS LaTeX.tdl!TeX -- AMS-LaTeX! % MathType!MTEF!2!1!+- % feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbiGabGEbbWUcca % GGOaWefv3ySLgznfgDOfdaryqr1ngBPrginfgDObYtUvgaiuaacqWF % pepucaGGPaaaaa!448D! $$(\mathcal{P})$$ for the period 9400 year BC to AD 1900 year. Unlike previous attempts to infer % MathType!Translator!2!1!AMS LaTeX.tdl!TeX -- AMS-LaTeX! % MathType!MTEF!2!1!+- % feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbiGabGEbbWUctu % uDJXwAK1uy0HwmaeHbfv3ySLgzG0uy0Hgip5wzaGqbaiab-9q8qbaa % !4334! $$\mathcal{P}$$ changes from the tree-ring record, the errors in both the Δ14C data and the model, which are assumed to be purely random (not systematic), are formally considered. The optimal time evolution of % MathType!Translator!2!1!AMS LaTeX.tdl!TeX -- AMS-LaTeX! % MathType!MTEF!2!1!+- % feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbiGabGEbbWUctu % uDJXwAK1uy0HwmaeHbfv3ySLgzG0uy0Hgip5wzaGqbaiab-9q8qbaa % !4334! $$\mathcal{P}$$ is compared to independent evidence of changes in cosmogenic nuclide production over the Holocene from a variety of records on their original chronology, e.g., a record of the virtual axial dipole moment (VADM) based on a compilation of archeomagnetic data, the record of 10Be concentration from the GISP2 ice core (Central Greenland), and the record of 10Be concentration from the PS1 ice core (South Pole). The rank correlations between % MathType!Translator!2!1!AMS LaTeX.tdl!TeX -- AMS-LaTeX! % MathType!MTEF!2!1!+- % feaafeart1ev1aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaWefv3ySLgznf % gDOfdaryqr1ngBPrginfgDObYtUvgaiuaacqWFpepucaqGTaGaaeOv % aiaabgeacaqGebGaaeytaiaacYcacaaMe8Uae83dXdLaaeylamaaCa % aaleqabaGaaGymaiaaicdaaaGccaaMb8UaaeOqaiaabwgacaGGOaGa % ae4raiaabMeacaqGtbGaaeiuaiaaikdacaGGPaGaaiilaaaa!54D9! $$ \mathcal{P}{\text{ - VADM}},\;\mathcal{P}{\text{ - }}^{{10}} {\text{Be}}({\text{GISP}}2), $$ and % MathType!Translator!2!1!AMS LaTeX.tdl!TeX -- AMS-LaTeX! % MathType!MTEF!2!1!+- % feaafeart1ev1aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaWefv3ySLgznf % gDOfdaryqr1ngBPrginfgDObYtUvgaiuaacqWFpepucaqGTaWaaWba % aSqabeaacaaIXaGaaGimaaaakiaaygW7caqGcbGaaeyzaiaacIcaca % qGqbGaae4uaiaaigdacaGGPaaaaa!4A9C! $$ \mathcal{P}{\text{ - }}^{{10}} {\text{Be}}({\text{PS}}1) $$ are highly significant (p < 0.01), indicating that geomagnetic field intensity and 10Be concentration in GISP2 and PS1 changed monotonically with 14C production. The linear correlation coefficients between % MathType!Translator!2!1!AMS LaTeX.tdl!TeX -- AMS-LaTeX! % MathType!MTEF!2!1!+- % feaafiart1ev1aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbiGabGEbbWUctu % uDJXwAK1uy0HwmaeHbfv3ySLgzG0uy0Hgip5wzaGqbaiab-9q8qjaa % b2cacaqGwbGaaeyqaiaabseacaqGnbGaaiilaiaaysW7cqWFpepuca % qGTaWaaWbaaSqabeaacaaIXaGaaGimaaaakiaaygW7caqGcbGaaeyz % aiaacIcacaqGhbGaaeysaiaabofacaqGqbGaaGOmaiaacMcacaGGSa % GaaGjbVlaabggacaqGUbGaaeizaiaaysW7cqWFpepucaqGTaWaaWba % aSqabeaacaaIXaGaaGimaaaakiaaygW7caqGcbGaaeyzaiaacIcaca % qGqbGaae4uaiaaigdacaGGPaaaaa!67BE! $$\mathcal{P}{\text{ - VADM}},\;\mathcal{P}{\text{ - }}^{10} {\text{Be}}({\text{GISP}}2),\;{\text{and}}\;\mathcal{P}{\text{ - }}^{10} {\text{Be}}({\text{PS}}1)$$ are also highly significant (p<0.01) but relatively small (−0.76, 0.48, and 0.60, respectively). Thus, an important fraction (42–77%) of the variance in the geomagnetic and 10Be data is not accounted for by linear regression on the 14C productions implied by the tree-ring record. The % MathType!Translator!2!1!AMS LaTeX.tdl!TeX -- AMS-LaTeX! % MathType!MTEF!2!1!+- % feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbiGabGEbbWUctu % uDJXwAK1uy0HwmaeHbfv3ySLgzG0uy0Hgip5wzaGqbaiab-9q8qbaa % !4334! $$\mathcal{P}$$ variance near the 1500 yr period, which previous authors interpreted as solar variability, represents a small fraction of the total variance in the % MathType!Translator!2!1!AMS LaTeX.tdl!TeX -- AMS-LaTeX! % MathType!MTEF!2!1!+- % feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbiGabGEbbWUctu % uDJXwAK1uy0HwmaeHbfv3ySLgzG0uy0Hgip5wzaGqbaiab-9q8qbaa % !4334! $$\mathcal{P}$$ time series (<15% for the band 1200–1800 yr) and does not correspond to a spectral peak. Hence, the hypothesis of a direct solar forcing mechanism for the postulated millennial climate variability during the Holocene is not supported.

Analysis of 36Cl in atmospheric samples from Seville (Spain) by AMS

In this work, the time evolution of 36Cl concentration and 36Cl/Cl isotopic ratio has been studied in rainwater samples from Seville, Southern Spain. 36Cl concentrations range between 105 – 107 atl−1 and 36Cl/Cl ratios range between 10−15–10−13, in good agreement with other values found in literature. The time evolution of these values suggests that 36Cl is more available in late spring due to the injection of stratospheric air into the troposphere. The arrival of stable chlorine coming from the Atlantic Ocean also seems to have an important influence on the 36Cl/Cl isotopic ratio. Finally, the values obtained for the 36Cl deposition are noticeably higher than the values predicted by cosmogenic production models. This fact has been found by other authors.

Noble gas studies in CAIs from CV3 chondrites: No evidence for primordial noble gases

Abstract— Calcium‐aluminum‐rich inclusions (CAIs) were among the first solids in the solar system and were, similar to chondrules, created at very high temperatures. While in chondrules, trapped noble gases have recently been detected, the presence of trapped gases in CAIs is unclear but could have important implications for CAI formation and for early solar system evolution in general. To reassess this question, He, Ne, and Ar isotopes were measured in small, carefully separated and, thus, uncontaminated samples of CAIs from the CV3 chondrites Allende, Axtell, and Efremovka.The 20Ne/22Ne ratios of all CAIs studied here are &lt;0.9, indicating the absence of trapped Ne as, e.g., Ne‐HL, Ne‐Q, or solar wind Ne. The 21Ne/22Ne ratios range from 0.86 to 0.72, with fine‐grained, more altered CAIs usually showing lower values than coarse‐grained, less altered CAIs. This is attributed to variable amounts of cosmogenic Ne produced from Na‐rich alteration phases rather than to the presence of Ne‐G or Ne‐R (essentially pure 22Ne) in the samples. Our interpretation is supported by model calculations of the isotopic composition of cosmogenic Ne in minerals common in CAIs. The 36Ar/38Ar ratios are between 0.7 and 4.8, with fine‐grained CAIs within one meteorite showing higher ratios than the coarse‐grained ones. This agrees with higher concentrations of cosmogenic 36Ar produced by neutron capture on 35Cl with subsequent β−‐decay in finer‐grained, more altered, and thus, more Cl‐rich CAIs than in coarser‐grained, less altered ones.Although our data do not strictly contradict the presence of small amounts of Ne‐G, Ne‐R, or trapped Ar in the CAIs, our noble gas signatures are most simply explained by cosmogenic production, mainly from Na‐, Ca‐, and Cl‐rich minerals.