A cosmogenic 10Be anomaly during the late Miocene as independent time marker for marine archives

Cosmogenic nuclide dating relies on the constancy of production and incorporation of radionuclides in geological archives. Anomalous deviations from constancy during the Holocene or Pleistocene are frequently used as global benchmarks to harmonize different data sets. A similar dating anchor on the million year timescale was so far not presented. In this work, we report on a prolonged cosmogenic 10Be anomaly during the late Miocene recorded in several Central and Northern Pacific deep-ocean ferromanganese crusts in the time period 9-11.5 Myr ago peaking at 10.1 Myr. Potential origins of this anomaly are discussed in the light of geological, climatic, solar and astrophysical events. This anomaly has the potential to be an independent time marker for marine archives.

Revisiting the historical tritium levels in precipitation in Greece - Preliminary assessment of groundwater transit times

The radioactive isotope of hydrogen, known as tritium (3H), is very often used as a dating tool in hydrogeological studies, since it enters the water cycle as part of the water molecule through precipitation. However, the assessment of groundwater transit times and recharge often requires knowing the local historical records of tritium levels in precipitation during the previous seven decades, or the tritium in precipitation (TIP) time series. Here, we compiled all tritium records in precipitation in Greece, with the majority of stations showing sporadic measurements, with the aim of reconstructing a TIP for groundwater dating purposes. The monitoring station of Vienna proved to be more reliable for filling the gaps in the time series than the Ottawa station. Conventional methods to fill the TIP gaps, such as the correlation method (CM), were compared with more advanced machine learning tools, such as the Convolutional Neural Networks (CNN). The comparison showed that the artificial Intelligence Method (AIM) performed best, due to its ability to capture complex nonlinear trends that are usually inherent in real-world data. The preliminary qualitative assessment of groundwater tritium data from Greece, in comparison to the TIP, showed the occurrence of groundwaters of mean transit times ranging from a few years to decades. Better incorporation of groundwater transit times and recharge rates into the study of aquifer systems is essential for developing strategies for sustainable water management in Greece and worldwide.

Transport of dust across the Solar System: Constraints on the spatial origin of individual micrometeorites from cosmic-ray exposure

The origin of micrometeorites (MMs) from asteroids and comets is well-established, but the relative contribution from these two classes remains poorly resolved. Likewise, determining the precise origin of individual MMs is an open challenge. Here, cosmic-ray exposure ages are used to resolve the spatial origins of 12 MMs collected from urban areas and Antarctica. Their 26Al and 10Be concentration, produced during cosmic-ray irradiation in space, were measured by accelerator mass spectrometry. These data are compared to results from a model simulating the transport and irradiation of the MM precursors in space. This model, for the first time, considers a variety of orbits, precursor particle sizes, compositions and densities and incorporates non-isotropic solar and galactic cosmic-ray flux profiles, depth-dependent production rates, as well as spherical evaporation during atmospheric entry. While the origin for six MMs remains ambiguous, two MMs show a preferential tendency towards an origin in the Inner Solar System (Near Earth Objects to the Asteroid Belt) and four towards an origin in the Outer Solar System (Jupiter Family Comets to the Kuiper Belt). These findings challenge the notion that dust originating from the Outer Solar System is unlikely to survive long-term transport and delivery to the terrestrial planets. This article is part of the theme issue 'Dust in the Solar System and beyond'.

Assessment of Be-7, Pb-210 and Po-210 Activities in Airborne Particulate Matter Over Istanbul, Türkiye

Airborne particulate matter is one of the air pollutants which can have detrimental health effects in the human body. Radionuclides adsorb onto air particles and make their way to humans primarily through inhalation. Naturally-occurring radionuclides, 210Pb and 210Po, are of notable health concern due to their relatively elevated ingestion and inhalation doses. In the current study, activity concentrations of 7Be, 210Pb and 210Po were determined in air particulate matter (PM). PM2.5 was collected on the European side, while PM10 was collected on the Anatolian side of Istanbul. Be-7, 210Pb and 210Po activities were found to be 5.17 ± 2.35, 0.96 ± 0.42; 0.25 ± 0.14 mBq m- 3 in Anatolian side, respectively. Be-7, 210Pb and 210Po activities were found to be 3.81 ± 2.27, 0.62 ± 0.29, 0.29 ± 0.26, mBq m- 3 in European side, respectively. The ratio of 210Po/210Pb was found to be higher (0.47 ± 0.31 for PM2.5 and 0.34 ± 0.27 for PM10) than the global average of 0.1. This result can be explained by the fact that Po is more volatile than Pb and enhanced in the air by the combustion process. Inhalation dose rates of 210Pb and 210Po due to PM10 exposure were calculated to be 7.70 ± 3.30 and 4.05 ± 2.31 µSv year- 1, respectively. Pb-210 bioaccessibility was assessed by the extraction of the particles in simulated lung fluids. Approximately 24.8% of inhaled 210Pb was estimated to be bioaccessible. This study suggests that 210Po and 210Pb activities are partially enhanced in the air particles in Istanbul and should be regularly monitored.

Tritium contents in drinking and surface seawaters before the nuclear power plant planned in Sinop (Türkiye) and their radiological risks on human population

This study aims to determine the background levels of tritium radioisotope in drinking and seawater samples of Sinop province before the nuclear power plant was established in Sinop. In this context, a total of 174 water samples were collected, these are as follows: nine drinking water samples from the Sinop center and districts and 165 seawater samples from the seacoast from Samsun to Kastamonu. Tritium concentrations in the collected water samples were measured by the liquid scintillation counter. The minimum detectable activity for the method used was found to be 1.48 Bq/L. The tritium concentrations of the seawater and drinking water samples were found in the range of Collapse

Key Words Collapse

MESH Headings

• Adult
• Child
• Infant
• Humans
• Tritium
• Nuclear Power Plants
• Drinking Water
• Turkey

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Grants Collapse

Affiliation(s)

Serdar Dizman Department of Physics, Faculty of Arts and Sciences, Recep Tayyip Erdogan University, Rize 53100, Türkiye E-mail:
Feyza Zeynep Aşık Institute of Graduate Studies, Recep Tayyip Erdogan University, Rize 53100, Türkiye
Ali Erdem Özçelik Department of Landscape and Architecture (Geomatics Engineer), Faculty of Engineering and Architecture, Recep Tayyip Erdogan University, Rize 53100, Türkiye
Recep Keser Department of Basic Sciences, Faculty of Engineering, Samsun University, Samsun 55100, Türkiye
Filiz Korkmaz Görür Department of Physics, Faculty of Arts and Science, Bolu Abant İzzet Baysal University, Bolu 14100, Türkiye

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First quantitative constraints on chlorine 36 dry deposition velocities on grassland: Comparing measurements and modelling results

Once released into the atmosphere, radionuclide dry deposition represents a major transfer process. It can be accurately characterized by its deposition velocity. However, this parameter is poorly constrained for most radionuclides, including chlorine 36. Chlorine 36 is a radionuclide of cosmogenic and anthropogenic origin. It may be discharged into the environment as gases and/or particles during the decommissioning of nuclear plants and the recycling of nuclear fuels. In this study, chlorine 36 deposition velocities are, for the first time, experimentally determined on grass downwind from the Orano La-Hague plant. The atmospheric chlorine 36 measurements were on average 50 nBq.m-3 for the gaseous fraction and 19 nBq.m3 for the particulate fraction. To measure the chlorine 36 transferred from the atmosphere to the grass, a method was devised for extracting the chlorides contained in solid matrices. With this method, chlorides were extracted with a mean efficiency of 83%. Chlorine 36 concentrations in the grass were on average 4 μBq.g-1, suggesting fast uptake of atmospheric chlorine 36. The yielded 36Cl dry deposition velocities varied with the season and were between 1 × 10-3 and 6 × 10-3 m s-1. The chlorine 36 depositions were modelled by adapting the existing deposition models and based on meteorological and micro-meteorological data. The dry deposition velocities calculated by the model showed less than one order of magnitude of difference with those determined experimentally. The deposition fluxes calculated by the model showed that the atmospheric depositions were predominantly gaseous chlorine 36 (>97%). However, on remote sites, the particulate fraction could be larger and have a greater influence on dry deposition. As chlorine 36 is a highly soluble and bioavailable element, these results will enable a better study of its behaviour in the environment and a more accurate evaluation of its dosimetric impact.

High spatial resolution prediction of tritium (3H) in contemporary global precipitation

Tritium (³H) in Earth’s precipitation is vigilantly monitored since historical nuclear bomb tests because of radiological protection considerations and its invaluable role as a tracer of the global water cycle in quantifying surface, groundwater, and oceanic fluxes. For hydrological applications, accurate knowledge of ³H in contemporary local precipitation is prerequisite for dating of critical zone water and calibrating hydrogeologic transport and groundwater protection models. However, local tritium input in precipitation is hard to constrain due to few ³H observation sites. We present new high-spatial resolution global prediction maps of multi-year mean ³H in contemporary “post-bomb” (2008–2018) precipitation by using a robust regression model based on environmental and geospatial covariates. The model accurately predicted the mean annual ³H in precipitation, which allowed us to produce global ³H input maps for applications in hydrological and climate modelling. The spatial patterns revealed natural ³H in contemporary precipitation sufficient for practical hydrological applications (1–25 TU) but variable across continental regions and higher latitudes due to cumulative influences of cyclical neutron fluxes, stratospheric inputs, and distance from tropospheric moisture sources. The new ³H maps provide a foundational resource for improved calibration of groundwater flow models and critical zone vulnerability assessment and provides an operational baseline for quantifying the potential impact of future anthropogenic nuclear activities and hydroclimatic changes.

Correlation between the latitudinal profile of the 7Be air concentration and the Hadley cell extent in the Southern Hemisphere

The cosmogenic radionuclide ⁷Be is one of the best tracers for aerosol transport since its half-life of 53 days is in the time scale of many atmospheric circulation phenomena. In this work, we analyze a 12-years-long daily time-series for the airborne ⁷Be concentration for nine air filtering stations in the Southern Hemisphere or close to it. The observed latitudinal distribution of ⁷Be concentration, with its maximum at the southern subtropical high-pressure belt, is similar to the one in the Northern Hemisphere. A good time correlation was found between the 7°-shift of the ⁷Be concentration latitudinal distribution and the seasonal displacement of the extent of the Hadley cell. This is consistent with tropopause folding events, mostly occurring in spring, being the main contribution for the injection of stratospheric ⁷Be into the descending branch of the Hadley cell.

Tritium concentrations and consequent doses in bottled natural and mineral waters sold in Turkey and Azerbaijan

In this study, tritium levels in commercially sold bottled natural and mineral waters in Turkey and Azerbaijan were determined. Tritium measurements were performed using Liquid Scintillation Counter (PerkinElmer TriCarb 2910 TR). 16 natural and 11 mineral samples from Turkey and 7 natural and 8 mineral samples from Azerbaijan, for a total of 42 commercially sold water samples were analyzed. The Minimum Detectable Activity (MDA) value for the method used was found as 1.69 Bq L^-1. In total, 7 of the natural water samples and 8 of the mineral water samples were found to be below the MDA value. The average activity concentrations in natural and mineral water samples were found as 2.23 ± 0.90 Bq L^-1 and 2.51 ± 0.90 Bq L^-1 for Turkey and 2.69 ± 0.91 Bq L^-1 and 2.43 ± 0.89 Bq L^-1 for Azerbaijan, respectively. In addition, annual effective dose rates and lifetime cancer risk values for the water samples were calculated. These radiological parameters were compared with the values recommended by international organizations. The results demonstrated that consumption by humans of the studied waters would not constitute any health risks in terms of tritium.

Radioisotopes demonstrate changes in global atmospheric circulation possibly caused by global warming

In this paper, we present a new method to study global atmospheric processes and their changes during the last decade. A cosmogenic radionuclide measured at ground-level, beryllium-7, is utilized as a proxy to study atmospheric dynamics. Beryllium-7 has two advantages: First, this radionuclide, primarily created in the lower stratosphere, attaches to aerosols that are transported downwards to the troposphere and travel around the globe with the general atmospheric circulation. By monitoring these particles, we can provide a global, simple, and sustainable way to track processes such as multi-annual variation of the troposphere, tropopause heightening, position and speed of atmospheric interface zones, as well as the poleward movement and stalling patterns of jet streams. Second, beryllium-7 is a product of cosmic rays which are themselves directly linked to solar activity and the earth magnetic field. This study shows whether beryllium-7 observed concentration changes are correlated with such natural processes or independent of them. Our work confirms that major changes in the atmospheric circulation are currently ongoing, even though timeseries are too short to make climatological assessments. We provide solid evidence of significant and progressive changes of the global atmospheric circulation as well as modifications of tropopause heights over the past decade. As the last decade happened to be the warmest on record, this analysis also indicates that the observed changes are, at least to some extent, attributable to global warming.

Tritium in precipitation on 5 sites in North-West France during the 2017-2019 period

Between October 2017 and May 2019, measurements of tritium in rainwater were carried out at several sites in north-west France. Tritium is an important tracer for hydroclimatic studies and this work provided up-to-date data that we compared with Global Network for Isotopes in Precipitation (GNIP) measurements. Of the various sites studied, some could potentially be affected by atmospheric gaseous emissions from the nuclear industries in the region (reprocessing plant, nuclear power plant). On our reference site, the activities measured in rainwater are often below the decision threshold (<0.15 Bq.L^-1). Two other sites with little impact from nuclear industries have mean activities of less than 0.7 Bq.L^-1. At the two Cherbourg sites closer to the nuclear industries, the activities in rainwater are slightly higher on average, though still close to 1 Bq.L^-1, but the activities are more variable when the rainfall accompanies an air mass from the Orano La Hague nuclear site. Using existing GNIP data and a simple model to simulate predicted data up to 2019, it is shown that all our measured data are comparable with the predicted activities for GNIP stations with a marine influence, in the case of the reference site and the sites with little impact from nuclear industries, and for GNIP stations with a continental influence, in the case of the other sites. Seasonal variation in activities was detected, with greater activities in the spring-summer period corresponding to the well known 'spring leak' phenomenon. This study also reveals significant differences between the activities measured on the western side of France (influenced by the Atlantic Ocean) and those measured in a continental zone. The mean levels of tritium in rainwater in France, excluding any nuclear influence, can be estimated on average at less than 0.3 Bq.L^-1 in the western marine zone, and at around 1 Bq.L^-1 in the continental zones.

Seasonal and Spatial Distribution of Atmospheric Tritiated Water Vapor in Mainland China

To reveal the distribution of atmospheric tritium water (HTO) vapor and provide a baseline for tritium pollution control, a subnational survey was conducted in mainland China. As the largest study on HTO vapor in China that has ever been formally reported, this study provides a macroimpression of the atmospheric HTO specific activity from March 2017 to March 2018. A total of 102 passive samplers were deployed at 34 sites in 30 provinces to determine the seasonal and spatial distributions of HTO vapor. In general, the HTO specific activity in the atmosphere ranged from lower than the minimum detectable activity (0.18 Bq·L^-1) to 5.5 Bq·L^-1. Spatially, the specific activity of HTO was positively correlated to the latitude and the distance to proximal coastline. Seasonally, significantly higher HTO specific activities were observed in spring and relatively lower in summer. Based on correlation analysis, the atmospheric HTO distributions were considered to be the consequence of combined factors of the stratospheric-tropospheric net mass flux, the distance from the tropopause to the ground, the fraction of air mass that originated from ocean re-evaporation and long-distance transport from high-latitude continents.

Inventory and distribution of tritium in the oceans in 2016

Tritium concentrations in oceans were compiled from the literature, online databases and original measurements in order to determine the global distribution of tritium concentrations according to latitude and depth in all oceans. The total inventory of tritium decay corrected in 2016 has been estimated using evaluation of the natural and artificial contributions in 23 spatial subdivisions of the total ocean. It is determined equal to 26.8 ± 14 kg including 3.8 kg of cosmogenic tritium. That is in agreement with the total atmospheric input of tritium from nuclear bomb tests and the natural inventory at steady-state estimated from natural production rates in the literature (27.8-29.3 kg in the Earth). We confirm the global increase in tritium according to latitude observed in the Northern hemisphere since 1967 with a maximum in the Arctic Ocean. The minimum tritium concentrations observed in the Southern Ocean were close to steady-state with known natural tritium deposition. We focused on the temporal evolution of surface (0 to 500 m) tritium concentrations in a selected area of the North Atlantic Ocean (30°N-60°N) where we found the 2016 concentration to be 0.60 ± 0.10 TU (1σ). Results showed that in that area, between 1988 and 2013, tritium concentrations: i) decreased faster than the sole radioactive decay, due to a mixing with lower and lateral less concentrated waters, and ii) decreased towards an apparent steady state concentration. The half-time mixing rate of surface waters and the steady state concentration were respectively calculated to be 23 ± 5 years (1σ) and 0.38 ± 0.07 TU (1σ). This apparent steady-state concentration in the North Atlantic Ocean implies a mean tritium deposition of 1870 ± 345 Bq·m^-2 (1σ), five folds higher than the known inputs (natural, nuclear tests fallout and industrial releases, ~367 Bq·m^-2) in this area.

Dispersion and removal characteristics of tritium originated from nuclear power plants in the atmosphere

The activities of tritium in water-vapor (n = 649) and precipitation (n = 2404) samples were measured from 1998 to 2015 around the Wolsong nuclear power plant (NPP) site where four pressurized heavy water reactors and two pressurized water reactors operated. The activity concentrations of tritium in the water-vapor and precipitation samples were in the ranges of 2.2-2200 Bq/L and 0.3-1090 Bq/L, respectively. The concentrations of tritium in the water-vapor in spring were approximately 7 times higher than those in fall and winter, mainly owing to the wind directions at the power plant location. The annual geometric mean activities of tritium in the water-vapor and precipitation samples varied within 56% and 83% from the average, respectively, depending primarily on the annual discharge amount of tritium to the atmosphere. The activities of tritium in the water-vapor and precipitation samples rapidly decreased away from the power plant. Approximately 0.5-30% of tritium discharged from the NPP site was removed by precipitation to the ground within an area with a radius of 30 km from the NPP site, which linearly depended on the precipitation amount. Our results suggest that the wind direction and precipitation, in addition to the amount of discharge, are important factors that control the tritium concentrations in air near the NPP site.

18 years of continuous observation of tritium and atmospheric precipitations in Ramnicu Valcea (Romania): A time series analysis

To get more information on the origin of tritium and to evidence any possible presence of anthropogenic sources, between January 1999 and December 2016, the precipitation level and tritium concentration were monthly recorded and investigated by the Cryogenic Institute of Ramnicu Valcea, Romania. Compared with similar data covering a radius of about 1200 km westward, the measurements gave similar results concerning the time evolution of tritium content and precipitation level for the entire time interval excepting the period between 2009 and 2011 when the tritium concentrations showed a slight increase, most probable due to the activity of neighboring experimental pilot plant for tritium and deuterium separation. Regardless this fact, all data pointed towards a steady tendency of tritium concentrations to decrease with an annual rate of about 1.4 ± 0.05%. The experimental data on precipitation levels and tritium concentrations form two complete time series whose time series analysis showed, at p < 0.01, the presence of a single one-year periodicity whose coincident maximums which correspond to late spring - early summer months suggest the existence of the Spring Leak mechanism with a possible contribution of the soil moisture remobilization during the warm period.

Solar superstorm of AD 774 recorded subannually by Arctic tree rings

Recently, a rapid increase in radiocarbon (¹⁴C) was observed in Japanese tree rings at AD 774/775. Various explanations for the anomaly have been offered, such as a supernova, a γ-ray burst, a cometary impact, or an exceptionally large Solar Particle Event (SPE). However, evidence of the origin and exact timing of the event remains incomplete. In particular, a key issue of latitudinal dependence of the ¹⁴C intensity has not been addressed yet. Here, we show that the event was most likely caused by the Sun and occurred during the spring of AD 774. Particularly, the event intensities from various locations show a strong correlation with the latitude, demonstrating a particle-induced ¹⁴C poleward increase, in accord with the solar origin of the event. Furthermore, both annual ¹⁴C data and carbon cycle modelling, and separate earlywood and latewood ¹⁴C measurements, confine the photosynthetic carbon fixation to around the midsummer.

Tree rings retain information of sudden variations of ancient radiocarbon (¹⁴C) content, however the origin and exact timing of these events often remain uncertain. Here, the authors analyze a set of Arctic tree rings and link a rapid increase in ¹⁴C to a solar event that occurred during the spring of AD 774.

Assessment of 53Mn deposition on Earth via accelerator mass spectrometry

The ⁵³Mn flux onto Earth is a quantity relevant for different extraterrestrial and astrophysical questions. It is a proxy for related fluxes, such as supernova-produced material or interplanetary dust particles. In this work, we performed a first attempt to assess the ⁵³Mn flux by measuring the ⁵³Mn/¹⁰Be isotopic ratio in a 1400 L sample of molten Antarctic snow by AMS (Accelerator Mass Spectrometry). Using the ¹⁰Be production rate in the atmosphere, an upper limit of 5.5 × 10³ atoms cm^-2 yr^-1 was estimated for the deposition of extraterrestrial ⁵³Mn. This result is compatible with one of the two discrepant values existing in the literature.

Circulation of cosmogenic 22Na using the global monitoring network of the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO)

Using a recently published global data set of ²²Na and ⁷Be from the global monitoring network of the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO), atmospheric circulation and stratosphere-troposphere interactions are examined. Cosmogenic ²²Na has a half-life well-suited to environmental processes with durations from several months to a decade. Combined with corresponding ⁷Be observations, these two cosmogenic isotopes form a useful environmental tracer and new radiochronometer to study physical interactions of air masses in the stratosphere and troposphere.

Multi-centennial fluctuations of radionuclide production rates are modulated by the Earth's magnetic field

The production of cosmogenic isotopes offers a unique way to reconstruct solar activity during the Holocene. It is influenced by both the solar and Earth magnetic fields and thus their combined effect needs to be disentangled to infer past solar irradiance. Nowadays, it is assumed that the long-term variations of cosmogenic production are modulated by the geomagnetic field and that the solar field dominates over shorter wavelengths. In this process, the effects of the non-dipolar terms of the geomagnetic field are considered negligible. Here we analyse these assumptions and demonstrate that, for a constant solar modulation potential, the geomagnetic field exerts a strong modulation of multi-centennial to millennial wavelengths (periods of 800 and 2200 yr). Moreover, we demonstrate that the non-dipole terms derived from the harmonic degree 3 and above produce maximum differences of 7% in the global average radiocarbon production rate. The results are supported by the identification, for the first time, of a robust coherence between the production rates independently estimated from geomagnetic reconstructions and that inferred from natural archives. This implies the need to review past solar forcing reconstructions, with important implications both for the assessment of solar-climate relationships as well as for the present and future generation of paleoclimate models.

Analysis of air mass trajectories to explain observed variability of tritium in precipitation at the Southern Sierra Critical Zone Observatory, California, USA

Understanding the behavior of tritium, a radioactive isotope of hydrogen, in the environment is important to evaluate the exposure risk of anthropogenic releases, and for its application as a tracer in hydrology and oceanography. To understand and predict the variability of tritium in precipitation, HYSPLIT air mass trajectories were analyzed for 16 aggregate precipitation samples collected over a 2 year period at irregular intervals at a research site located at 2000 m elevation in the southern Sierra Nevada (California, USA). Attributing the variation in tritium to specific source areas confirms the hypothesis that higher latitude or inland sources bring higher tritium levels in precipitation than precipitation originating in the lower latitude Pacific Ocean. In this case, the source of precipitation accounts for 79% of the variation observed in tritium concentrations. Air mass trajectory analysis is a promising tool to improve the predictions of tritium in precipitation at unmonitored locations and thoroughly understand the processes controlling transport of tritium in the environment.

Authigenic 10Be/9Be ratio signatures of the cosmogenic nuclide production linked to geomagnetic dipole moment variation since the Brunhes/Matuyama boundary

Geomagnetic dipole moment variations associated with polarity reversals and excursions are expressed by large changes of the cosmogenic nuclide beryllium-10 (10Be) production rates. Authigenic 10Be/9Be ratios (proxy of atmospheric 10Be production) from oceanic cores therefore complete the classical information derived from relative paleointensity (RPI) records. This study presents new authigenic 10Be/9Be ratio results obtained from cores MD05-2920 and MD05-2930 collected in the west equatorial Pacific Ocean. Be ratios from cores MD05-2920, MD05-2930 and MD90-0961 have been stacked and averaged. Variations of the authigenic 10Be/9Be ratio are analyzed and compared with the geomagnetic dipole low series reported from global RPI stacks. The largest 10Be overproduction episodes are related to dipole field collapses (below a threshold of 2 × 1022 Am2) associated with the Brunhes/Matuyama reversal, the Laschamp (41 ka) excursion, and the Iceland Basin event (190 ka). Other significant 10Be production peaks are correlated to geomagnetic excursions reported in literature. The record was then calibrated by using absolute dipole moment values drawn from the Geomagia and Pint paleointensity value databases. The 10Be-derived geomagnetic dipole moment record, independent from sedimentary paleomagnetic data, covers the Brunhes-Matuyama transition and the whole Brunhes Chron. It provides new and complementary data on the amplitude and timing of millennial-scale geomagnetic dipole moment variations and particularly on dipole moment collapses triggering polarity instabilities.

Analytical Model for Estimating the Zenith Angle Dependence of Terrestrial Cosmic Ray Fluxes

A new model called "PHITS-based Analytical Radiation Model in the Atmosphere (PARMA) version 4.0" was developed to facilitate instantaneous estimation of not only omnidirectional but also angular differential energy spectra of cosmic ray fluxes anywhere in Earth's atmosphere at nearly any given time. It consists of its previous version, PARMA3.0, for calculating the omnidirectional fluxes and several mathematical functions proposed in this study for expressing their zenith-angle dependences. The numerical values of the parameters used in these functions were fitted to reproduce the results of the extensive air shower simulation performed by Particle and Heavy Ion Transport code System (PHITS). The angular distributions of ground-level muons at large zenith angles were specially determined by introducing an optional function developed on the basis of experimental data. The accuracy of PARMA4.0 was closely verified using multiple sets of experimental data obtained under various global conditions. This extension enlarges the model's applicability to more areas of research, including design of cosmic-ray detectors, muon radiography, soil moisture monitoring, and cosmic-ray shielding calculation. PARMA4.0 is available freely and is easy to use, as implemented in the open-access EXcel-based Program for Calculating Atmospheric Cosmic-ray Spectrum (EXPACS).

Analytical Model for Estimating Terrestrial Cosmic Ray Fluxes Nearly Anytime and Anywhere in the World: Extension of PARMA/EXPACS

By extending our previously established model, here we present a new model called "PHITS-based Analytical Radiation Model in the Atmosphere (PARMA) version 3.0," which can instantaneously estimate terrestrial cosmic ray fluxes of neutrons, protons, ions with charge up to 28 (Ni), muons, electrons, positrons, and photons nearly anytime and anywhere in the Earth's atmosphere. The model comprises numerous analytical functions with parameters whose numerical values were fitted to reproduce the results of the extensive air shower (EAS) simulation performed by Particle and Heavy Ion Transport code System (PHITS). The accuracy of the EAS simulation was well verified using various experimental data, while that of PARMA3.0 was confirmed by the high R2 values of the fit. The models to be used for estimating radiation doses due to cosmic ray exposure, cosmic ray induced ionization rates, and count rates of neutron monitors were validated by investigating their capability to reproduce those quantities measured under various conditions. PARMA3.0 is available freely and is easy to use, as implemented in an open-access software program EXcel-based Program for Calculating Atmospheric Cosmic ray Spectrum (EXPACS). Because of these features, the new version of PARMA/EXPACS can be an important tool in various research fields such as geosciences, cosmic ray physics, and radiation research.

Short-term variability of 7Be atmospheric deposition and watershed response in a Pacific coastal stream, Monterey Bay, California, USA

Beryllium-7 is a powerful and commonly used tracer for environmental processes such as watershed sediment provenance, soil erosion, fluvial and nearshore sediment cycling, and atmospheric fallout. However, few studies have quantified temporal or spatial variability of (7)Be accumulation from atmospheric fallout, and parameters that would better define the uses and limitations of this geochemical tracer. We investigated the abundance and variability of (7)Be in atmospheric deposition in both rain events and dry periods, and in stream surface-water samples collected over a ten-month interval at sites near northern Monterey Bay (37°N, 122°W) on the central California coast, a region characterized by a rainy winters, dry summers, and small mountainous streams with flashy hydrology. The range of (7)Be activity in rainwater samples from the main sampling site was 1.3-4.4 Bq L(-1), with a mean (±standard deviation) of 2.2 ± 0.9 Bq L(-1), and a volume-weighted average of 2.0 Bq L(-1). The range of wet atmospheric deposition was 18-188 Bq m(-2) per rain event, with a mean of 72 ± 53 Bq m(-2). Dry deposition fluxes of (7)Be ranged from less than 0.01 up to 0.45 Bq m(-2) d(-1), with an estimated dry season deposition of 7 Bq m(-2) month(-1). Annualized (7)Be atmospheric deposition was approximately 1900 Bq m(-2) yr(-1), with most deposition via rainwater (>95%) and little via dry deposition. Overall, these activities and deposition fluxes are similar to values found in other coastal locations with comparable latitude and Mediterranean-type climate. Particulate (7)Be values in the surface water of the San Lorenzo River in Santa Cruz, California, ranged from <0.01 Bq g(-1) to 0.6 Bq g(-1), with a median activity of 0.26 Bq g(-1). A large storm event in January 2010 characterized by prolonged flooding resulted in the entrainment of (7)Be-depleted sediment, presumably from substantial erosion in the watershed. There were too few particulate (7)Be data over the storm to accurately model a (7)Be load, but the results suggest enhanced watershed export of (7)Be from small, mountainous river systems compared to other watershed types.

A signature of cosmic-ray increase in AD 774-775 from tree rings in Japan

Increases in (14)C concentrations in tree rings could be attributed to cosmic-ray events, as have increases in (10)Be and nitrate in ice cores. The record of the past 3,000 years in the IntCal09 data set, which is a time series at 5-year intervals describing the (14)C content of trees over a period of approximately 10,000 years, shows three periods during which (14)C increased at a rate greater than 3‰ over 10 years. Two of these periods have been measured at high time resolution, but neither showed increases on a timescale of about 1 year (refs 11 and 12). Here we report (14)C measurements in annual rings of Japanese cedar trees from ad 750 to ad 820 (the remaining period), with 1- and 2-year resolution. We find a rapid increase of about 12‰ in the (14)C content from ad 774 to 775, which is about 20 times larger than the change attributed to ordinary solar modulation. When averaged over 10 years, the data are consistent with the decadal IntCal (14)C data from North American and European trees. We argue that neither a solar flare nor a local supernova is likely to have been responsible.

9,400 years of cosmic radiation and solar activity from ice cores and tree rings

Understanding the temporal variation of cosmic radiation and solar activity during the Holocene is essential for studies of the solar-terrestrial relationship. Cosmic-ray produced radionuclides, such as (10)Be and (14)C which are stored in polar ice cores and tree rings, offer the unique opportunity to reconstruct the history of cosmic radiation and solar activity over many millennia. Although records from different archives basically agree, they also show some deviations during certain periods. So far most reconstructions were based on only one single radionuclide record, which makes detection and correction of these deviations impossible. Here we combine different (10)Be ice core records from Greenland and Antarctica with the global (14)C tree ring record using principal component analysis. This approach is only possible due to a new high-resolution (10)Be record from Dronning Maud Land obtained within the European Project for Ice Coring in Antarctica in Antarctica. The new cosmic radiation record enables us to derive total solar irradiance, which is then used as a proxy of solar activity to identify the solar imprint in an Asian climate record. Though generally the agreement between solar forcing and Asian climate is good, there are also periods without any coherence, pointing to other forcings like volcanoes and greenhouse gases and their corresponding feedbacks. The newly derived records have the potential to improve our understanding of the solar dynamics and to quantify the solar influence on climate.

Measurement of the 36Cl deposition flux in central Japan: natural background levels and seasonal variability

Essential parameters for the applications of (36)Cl as a tracer in groundwater studies include the initial (36)Cl/Cl ratio, at the time of recharge, and/or the natural background deposition flux of (36)Cl in the recharge area. To facilitate the hydrological use of (36)Cl in central Japan, this study aimed to obtain a precise estimate of the long-term average local (36)Cl flux and to characterize its seasonal variability. The (36)Cl in precipitation was continuously monitored in Tsukuba, central Japan over a period of >5 years. The (36)Cl flux showed a clear seasonal variation with an annual peak during the spring, which was attributed to the seasonal variability of tropopause height. The long-term average (36)Cl flux (32±2atoms m(-2)s(-1)), estimated from the measured data, was consistent with the prediction from the (36)Cl latitudinal fallout model scaled using the global mean production rate of 20atoms m(-2)s(-1). The initial (36)Cl/Cl ratio was estimated to be (41±6)×10(-15), which is similar to that of pre-bomb groundwater in the Tsukuba Upland. An observation period covering an 11-year solar cycle would yield more accurate estimates of the values, given the increased (36)Cl flux during the solar minimum.