10Be Concentrations Research Articles

Denudation rates across the Pamir based on <sup>10</sup>Be concentrations in fluvial sediments: dominance of topographic over climatic factors

Abstract. A clear understanding of erosion processes is fundamental in order to comprehend the evolution of actively deforming mountain ranges. However, the relative contributions of tectonic and climatic factors and their feedbacks remain highly debated. In order to contribute to the debate, we quantify basin-wide denudation rates from cosmogenic 10Be concentrations in modern river sediments in the Pamir. This mountain range is a unique natural laboratory because the ongoing India–Eurasia collision sustains high deformation rates and, on account of its position at the transition between Westerlies and monsoon, a strong regional climatic variability arises. Sample acquisition and preparation for accelerator mass spectrometry measurements were challenging due to difficult field accessibility, low quartz and high feldspar concentrations and crystal coating. Six samples along the main draining river, the Panj, and five samples within the major, east–west elongated tributary basins allow us to quantify basin-wide denudation rates for the first time in this orogen. An average denudation rate of ~ 0.64 mm yr−1 reveals a rapid evolution of the entire Pamir. Denudation rates of tributary sub-basins highlight the strong contrast between the Pamir Plateau (0.05 to 0.16 mm yr−1) and its margins (0.54 to 1.45 mm yr−1). The intensity of denudation is primarily correlated with geometric properties of the surface, such as slope steepness (0.75 quartiles; R2 of 0.81), and to a lesser extent to climatic factors such as precipitation. We thus argue that either tectonic uplift or base-level lowering are the main contributors to denudation processes. Multiple linear regression analysis (best R2 of 0.93) suggests that precipitation may act as a limiting factor to denudation. The highest denudation rates coincide with areas of the northwestern Pamir margin that receive precipitation predominantly from the Westerlies during winter. There, the concentrated discharge during spring and early summer may sustain the pronounced denudation and allow the rapid sediment transport out of the basins. Low slope angles and dry conditions hamper the sediment flux on the plateau and, consequently, denudation. The magnitude of denudation in the Pamir is similar to rates determined in the southern Himalaya despite very different climatic and tectonic conditions. The discrepancy between rates of basin-wide denudation and the fluvial incision that is up to 10 times higher evidences a transient landscape in the Pamir. This underpins the hypothesis that river captures may have caused the strong base-level lowering that drives the enhanced incision of the Panj and its main tributaries.

A Lateglacial 10Be production rate from glacial lake shorelines in Scotland

ABSTRACTThe identification of tephra within varved deposits of a former ice‐dammed lake that existed in Scotland during the Younger Dryas provides an opportunity to calibrate 10Be production rates using previously published 10Be concentrations from the lake shoreline and independently derived ages for the tephras derived from the Greenland Ice Core records. The best‐estimate ages of the tephras yield indistinguishable 10Be production rate values for spallation with an average value of 4.26 ± 0.21 atoms g−1 a−1 using the ‘Lm’ scaling scheme. These values are in best agreement with the most proximal reference 10Be production rate from Norway.

Bedrock bedding, landsliding and erosional budgets in the Central European Alps

AbstractWe explore the controls of the litho‐tectonic architecture on the erosional flux in the 370‐km2 Glogn basin (European Alps). In this basin, the bedding and schistosity of the bedrock dip parallel to the topographic slope on the NW valley flank, leading to a non‐dip slope situation on the opposite SE valley side. While the dip slope condition has promoted the occurrence of landslides (e.g. the c. 30‐km2 deep‐seated Lumnezia landslide), the opposite non‐dip slope side of the valley hosts >100‐m‐deeply incised tributary streams. 10Be concentrations of stream sediments yield catchment‐averaged denudation rates that vary between 0.27 ± 0.03 and 2.19 ± 0.37 mm a−1, while the spatially averaged denudation rate of the entire basin is 1.99 ± 0.34 mm a−1. Our 10Be‐based approach reveals that the Lumnezia landslide front contributes c. 30–65% of the entire sediment budget, although it covers <5% of the Glogn basin. This suggests a primary control of the bedrock bedding on erosion rates and processes.

Study of 7Be and 210Pb as radiotracers of African intrusions in Malaga (Spain)

The relationship between the particulate matter in the atmosphere of Malaga and the origin of air masses with special attention to African intrusions was analyzed. The concentrations of PM10 and the activities of some radionuclides (7Be and 210Pb) as tracers of these intrusions are discussed. The origin of these radiotracers is completely different. 210Pb is a good tracer of air masses traveling close to the ground and come from inland areas. On the other hand, the production of 7Be is very low in the vicinity of the Earth's surface, and increases with altitude, making it a great tracer of stratospheric air masses in the troposphere.Studies of radionuclide activities in aerosol particles provide a means for evaluating the integrated effects of transport and meteorology on the atmospheric loadings of substances with different sources. Measurements of aerosol mass concentration and specific activities of 7Be and 210Pb in aerosols at Malaga (36° 43′ 40″ N; 4° 28′ 8″ W) for the period 2009–2011 were used to obtain the relationships between radionuclide activities and airflow patterns by comparing the data grouped by air mass trajectory. The average concentration values of 7Be and 210Pb over the 3-year period have been found to be 5.05 and 0.55 mBq m−3, respectively, with mean aerosol mass concentration of 53.6 μg m−3. Taking into account the outbreaks of the daily values limits of PM10 in the study period (2009–2011), the origin of air masses is studied to explain three different situations of both radionuclides 7Be and 210Pb: 1) high concentrations of 7Be and low concentrations of 210Pb; 2) high concentrations of 210Pb and low concentrations of 7Be and 3) high concentrations of 7Be and 210Pb.

In situ cosmogenic 10Be production rate in the High Tropical Andes

Continental climate change during the late glacial period has now been widely documented thanks to Cosmic-Ray Exposure (CRE) dating of glacial features. The accuracy of these CRE ages mainly relies on a priori knowledge of the production rate of the cosmogenic nuclide that has accumulated in a specific mineral. To produce unequivocal and accurate chronologies of glacier fluctuations during the late glacial period, it is crucial that the cosmogenic nuclide production rates are better constrained, particularly in the high tropics where existing spatial and temporal scaling models show significant discrepancies. Here we report a new production rate established at low latitude (19°S) and high elevation (3800 masl) on the Challapata fan-delta, at the edge of the Paleolake Tauca, on the flank of Cerro Azanaques (Bolivia). Sedimentological evidence for synchronicity with the Tauca Lake highstand along with U–Th and 14C measurements established that the fan-delta is 16.07 ± 0.64 kyr BP old. In situ-produced 10Be concentrations measured in 15 boulders lying on the fan-delta yield a mean 10Be concentration of 4.92 ± 0.05 × 105 at g−1. A local in situ 10Be production rate of 30.8 ± 1.3 at g−1 yr−1 is thus obtained at 3800 masl and 19°S. Application of the “Lal-modified” scaling scheme to this Azanaques production rate, using a standard atmosphere and the Muscheler et al. (2005) geomagnetic reconstruction, leads to a Sea Level High Latitude (SLHL) in situ 10Be production rate of 3.76 ± 0.15 at g−1 yr−1 (1σ uncertainty). In addition, we propose a reference in situ 10Be calibration dataset for the region that combines the production rates of this study with those of Blard et al. (2013b) and Kelly et al. (2015). This dataset of three calibration sites shows a good consistency and yields a regional in situ 10Be production rate of 3.74 ± 0.09 at g−1 yr−1 using the same scaling.

Defining rates of landscape evolution in a south Tibetan graben with in situ‐produced cosmogenic 10Be

AbstractThe Tangra Yum Co graben is one of the active structures that accommodate the east‐west extension of the southern Tibetan Plateau and hosts one of the largest Tibetan lakes, which experienced lake‐level changes of ~200 m during the Holocene. In this study, cosmogenic 10Be is employed to: (1) quantify catchment‐wide denudation rates in fault‐bounded mountain ranges adjacent to the Tangra Yum Co graben; (2) date palaeo‐shorelines related to the Holocene lake‐level decline; and (3) determine the age of glacial advances in this region. The fault‐bounded, non‐glaciated mountain range north of Tangra Yum Co – and presumably most other areas around the lake – erode at low rates of 10–70 mm/ka. Owing to the slow erosion of the landscape, the sediments delivered to Tangra Yum Co have high 10Be concentrations. As a consequence, accurate exposure dating of sediment‐covered terraces and beach ridges is difficult, because the pre‐depositional 10Be concentration may exceed the post‐depositional 10Be concentration from which exposure ages are calculated. This difficulty is illustrated by a rather inaccurate 10Be exposure age of 2.3 ± 1.4 ka (i.e. an error of 60%) for a terrace that is located 67 m above the lake. Nevertheless, the age is consistent with luminescence ages for a series of beach ridges and provides further evidence for the decline of the lake level in the late Holocene. At Tangra Yum Co exposure dating of beach ridges via 10Be depth profiles is not feasible, because the pre‐depositional 10Be component in these landforms varies with depth, which violates a basic assumption of this approach. 10Be ages for boulders from two moraines are much older than the early Holocene lake‐level highstand, indicating that melting of glaciers in the mountain ranges adjacent to Tangra Yum Co has not contributed significantly to the lake‐level highstand in the early Holocene. Copyright © 2015 John Wiley & Sons, Ltd.

Latitudinal distributions of activities in atmospheric aerosols, deposition fluxes, and soil inventories of 7Be in the East Asian monsoon zone

Activities of atmospheric aerosols, bulk deposition fluxes, and undisturbed soil inventories of 7Be were investigated in China's East Asian monsoon zone at various latitudes ranging from 23.8°N to 43.5°N. The annual latitudinal distributions of 7Be concentrations in aerosols follow a distribution pattern which looks similar to a normal distribution with the maxima occurring in the mid-latitude region. Simultaneous measurements of 7Be at various latitudes suggest that atmospheric circulation may play an important role in the latitudinal distributions of 7Be in surface air. Latitude and wet precipitation are the main factors controlling the bulk 7Be depositional fluxes. Significant seasonal variations in 7Be depositional fluxes in Beijing, a mid-latitude city, were observed with the highest flux in summer and the lowest in winter, whereas less seasonality were found in the high- and the low-latitude cities. The highest 7Be inventory in undisturbed soils in summer also occurred at a mid-latitudinal area in the East Asian monsoon zone. Precipitation is the main factor controlling the 7Be soil inventory in Qingdao with the highest values occurring in autumn followed by summer.

Spatial variability of 10Be-derived erosion rates across the southern Peninsular Indian escarpment: A key to landscape evolution across passive margins

The persistence of significant topography in ancient, tectonically inactive orogenic belts remains one of the outstanding questions in geomorphology. In southern Peninsular India, the impressive topographic relief of the Western Ghat Mountains in tectonic quiescence since at least ca. 65 Ma has raised important questions concerning the long-term mechanism of topographic evolution. Quantifying the distribution of erosion in space and time is critical to understanding landscape evolution. Although the long-term erosion rates are reasonably well known, the short-term erosion rates and the relative importance of factors controlling erosion in southern Peninsular India are less well constrained. We present a new suite of catchment-averaged and local erosion rates using in situ produced 10Be concentrations in river sediments and exposed bedrock samples in southern Peninsular India. Catchment-averaged erosion rates vary from 9.6±0.8 mMa−1 in the highlands to 114.3±13.8 mMa−1 on the escarpment side. Bedrock erosion rates range from 2.4±0.2 mMa−1 in the ridge-top to 143.4±25.4 mMa−1 in active channel beds of the highlands. Catchment-averaged erosion rates derived from the across-escarpment, westward-draining catchments are significantly higher than those derived from the eastward-draining, over highland catchments. The difference indicates that long-term down-wearing of the highland proceeds at lower rates than in the escarpment zones. Catchment-averaged erosion rates are moderately correlated with mean hillslope angles and local relief whereas they are strongly correlated with catchment-averaged channel steepness index. This suggests that topographic steepness is the major control on the spatial variability of erosion while strong rainfall gradient is of minor importance in this area. 10Be-derived average erosion rates in highlands are consistent with previous long-term erosion rate estimated from thermochronometry. These results collectively point to large-scale steady-state topography, only decaying slowly with time. Steady state likely reflects the balance between erosion and isostatically driven uplift of the southern Peninsular India.

A cluster analysis of back trajectories to study the behaviour of radioactive aerosols in the south-east of Spain

This research is focused on the study of the influence of the air masses together with the local meteorological fluctuations on the amount of radioactive elements in aerosols at surface air of the southeastern of Iberian Peninsula. The radioactivity in aerosols has been determined by measuring the concentration activity of Gross β and 7Be from January 4th, 2011 to December 31st, 2013. The activity concentration (Bq/m3) of gross beta was measured by α/β Low-Level counter, whereas the activity concentration of 7Be (Bq/m3) was detected by gamma spectrometry (Eγ = 477.6 KeV, Yield = 10.42%). The air mass origings have been set using k-means clustering analysis of daily 72-h kinematic 3D backward trajectories at 500 m, 1500 m and 3000 m of altitude. Finally, a multiple Regression Analysis (MRA) have been carried out in order to determine the influence of the origins and trajectories of the air masses and local meteorology variations on the evolution of Gross β and 7Be activity concentration. In conclusion, the results of the current research demonstrate that the re-suspended mineral dust from Northern Africa transported by Mediterranean air masses at low altitude (500 m) and African air masses at high altitude (3000 m) increases the radioactivity concentration in aerosols at the surface atmosphere. In addition, the opposite influence of the Saharan intrusions at 1500 m of altitude on the behaviour of 7Be aerosols deserves special attention.

Alluvial fan surfaces and an age-related stability for cultural resource preservation: Nevada Test and Training Range, Nellis Air Force Base, Nevada, USA

Surface geomorphology studies, measurements of cosmogenic 10Be concentrations, and satellite imagery analysis are employed to construct a surface stability model for the preservation of archeological features in Stonewall Flat, Nevada, USA. Primary fan processes of incised channel floods and sheet floods construct alluvial fans and secondary processes of sheetwash, eolian erosion and deposition, bioturbation, and soil development subsequently modify fan surfaces. Each process leaves distinctive surface features, but collectively darkens and smooth's the surface with age. Concentrations of cosmogenic 10Be in surface and subsurface samples for fans with recently active surfaces have effectively zero ages, whereas concentrations for fans with mature pavements have ages of 35 to 40thousandyears (ka). Surface age data from other Stonewall Flat studies indicate that fans in transition from primary process to secondary process domination are younger than 13ka, and that older fan surfaces are dominated by secondary processes. Image analysis demonstrates a correlation between fan surface darkening and age, and permits age estimations for undated surfaces. Results indicate that surfaces dominated by primary processes are younger than 3ka and unstable for the preservation of older sites; surfaces dominated by secondary processes are older than 10ka and stable for site preservation.

Detecting Be-7 in the orbits of the COSMOS series spacecraft during solar cycle 24

Experiments to detect the radionuclide Be-7 in the orbits of the COSMOS series satellites at altitudes of 200–400 km continued in the period 2007–2012. Measurements of Be-7 radioactivity during solar proton events and quiet periods of the Sun confirm the correlation found earlier between observed Be-7 concentrations and the magnitude of the flux of energetic solar protons near the Earth.

Signature of a sudden stratospheric warming in the near-ground 7Be flux

We present here an evidence that cosmogenic 7Be isotopes produced in the lower stratosphere were measured in near-ground air at Rio de Janeiro, Brazil, after the southern hemispheric Sudden Stratospheric Warming (SSW) of 2002. The analysis presented here is based on a comparison of 7Be data measured around Angra Nuclear Power Station (23°S 44°W) during the last three decades and a model estimate of the near-ground air 7Be concentration using the CRAC:7Be model of cosmogenic production together with a simplified model for atmospheric 7Be deposition that assimilates the regional precipitation data. Our results indicate that an anomalous stratosphere–troposphere coupling associated to the unique SSW of 2002 allowed stratospheric aerosols carrying 7Be to reach the ground level very quickly. This methodology points to an important use of 7Be as a quantitative tracer for stratospheric influence on near-ground air patterns.

10Be-derived denudation rates from the Burdekin catchment: The largest contributor of sediment to the Great Barrier Reef

Terrestrial cosmogenic nuclides (TCNs) such as Beryllium-10 (10Be) are now routinely used to reconstruct erosional rates over tens of thousands of years at increasingly large basin scales (>100,000km2). In Australia, however, the approach and its assumptions have not been systematically tested within a single, large drainage basin. This study measures 10Be concentrations in river sediments from the Burdekin catchment, one of Australia's largest coastal catchments, to determine long-term (>10,000years), time-integrated rates of sediment generation and denudation. A nested-sampling design was used to test for effects of increasing catchment scale on nuclide concentrations with upstream catchment areas ranging from 4 to 130,000km2. Beryllium-10 concentrations in sediment samples collected from the upstream headwater tributaries and mid-stream locations range from 1.8 to 2.89×105atomsg−1 and data confirm that nuclide concentrations are well and rapidly mixed downstream. Sediment from the same tributaries consistently yielded 10Be concentrations in the range of their upstream samples. Overall, no decrease in 10Be concentrations can be observed at the range of catchment scales measured here. The mean denudation rate for all river sediment samples throughout the Fanning subcatchment (1100km2) is 18.47mMa−1, which compares with the estimate at the end of the Burdekin catchment (130,000km2) of 16.22mMa−1. Nuclide concentrations in the lower gradient western and southern catchments show a higher degree of variability, and several complications emerged as a result of the contrasting geomorphic processes and settings. This study confirms the ability of TCNs to determine long-term denudation rates in Australia and highlights some important considerations in the model assumptions that may affect the accuracy of limited sampling in large, low-gradient catchments with long storage times.

Effects of a tectonically-triggered wave of incision on riverine exports and soil mineralogy in the Luquillo Mountains of Puerto Rico

We document the long-term response of a tropical mountain stream to tectonics and show how this response exerts a first-order spatial control on the delivery of weatherable minerals to forest soils in its catchment. These minerals, in turn, affect nutrient availability and biogeochemical cycles. The Luquillo Mountains is a rainforest-covered isolated massif on Puerto Rico Island. Instead of displaying typical concave-up long profiles of most mountain streams, the rivers draining the southern flank of these mountains display a systematic downstream increase in gradient. Using concentrations of in situ-produced cosmogenic 10Be in quartz from river sediments, we find that the downstream steepening is due to the propagation of an erosion wave along the rivers from the coastal plain upstream, toward the headwaters. Decreased 10Be concentration along the steepened reaches (knickpoint faces or knickzones) results from faster denudation of the valley sides around the steepened reaches. The upper portions of the steepened reaches (knickpoint lips) cluster in elevation around the altitude of a flat-lying, dissected surface traceable around the Luquillo Mountains. Inspection of similar platforms over other parts of Puerto Rico and in the surrounding seas suggests that the dissected surface is an uplifted shore platform formed in the Early Pliocene (∼4 My ago). Upstream of the knickpoints, rivers possess alluvial reaches still graded to this uplifted platform. They represent relict profiles of the rivers that once drained an island that was surrounded by the now-uplifted platform. We conclude that the knickpoints initiated when the platform started to rise above the Caribbean Sea. The knickpoints then started propagating upstream, defining the front of a slow-moving wave of erosion. 10Be-derived catchment-scale denudation rates measured above and below the knickpoints indicate a 30–210% increase in denudation associated to the passage of the knickpoints. Mineralogical analysis of the soils show that soils upstream of the knickpoints overlie deeply depleted saprolite and only contain recalcitrant minerals, whereas soils downstream of the knickpoints experience an input of fresh, weatherable minerals. This influx considerably increases nutrient availability (Porder et al., 2015) in a forest where atmospheric inputs are otherwise the main source of nutrients (McDowell et al., 1990; Zarin and Johnson, 1995; Pett-Ridge, 2009).

Influence of precipitation on 7Be concentrations in air as measured by CTBTO global monitoring system

Data collected by the International Monitoring System (IMS) during 2009–2012 were used to study influence of precipitation and relative humidity on changes in 7Be concentrations in atmosphere. The significant decrease in 7Be concentrations, corresponding to measurements collected by stations located within Intertropical Convergence Zone (ITCZ) is demonstrated. This effect can be attributed to the process of enhanced wet deposition within the ITCZ. To quantify this effect data collected by IMS stations within ITCZ were thoroughly analyzed. It was found that the atmospheric content of 7Be strongly decreases under the rain conditions. The rain mediated depletion of 7Be to half of its before rain value, needs about 62 h in case of light precipitation, while in the case of moderate precipitation about 38 h is needed. In addition the evaluated impact of humidity showed that increase in relative humidity by 20%, for example from 70% ± 5% to 90% ± 5% causes almost a double decrease in beryllium concentration in surface air.

Separation of Be and Al for AMS using single-step column chromatography

With the aim of simplifying AMS target preparation procedures for TCN measurements we tested a new extraction chromatography approach which couples an anion exchange resin (WBEC) to a chelating resin (Beryllium resin) to separate Be and Al from dissolved quartz samples. Results show that WBEC–Beryllium resin stacks can be used to provide high purity Be and Al separations using a combination of hydrochloric/oxalic and nitric acid elutions. 10Be and 26Al concentrations from quartz samples prepared using more standard procedures are compared with results from replicate samples prepared using the coupled WBEC–Beryllium resin approach and show good agreement. The new column procedure is performed in a single step, reducing sample preparation times relative to more traditional methods of TCN target production.

Beryllium-10 concentrations in the hyper-arid soils in the Atacama Desert, Chile: Implications for arid soil formation rates and El Niño driven changes in Pliocene precipitation

Meteoric 10Be concentrations in soil were measured to understand the mechanism, timescale, and climatic dependence of soil formation in the hyper-arid Atacama Desert. The observed systematic decline of soil 10Be concentrations with depth has been reproduced using a simple model that assumes soil matrix, including 10Be, builds up as layers over time while 10Be decays in situ. This suggests a mechanism of soil accumulation via atmospheric deposition, which is in agreement with stable isotopic evidence. The model estimates an age of ∼6.6±0.4Ma for the total soil profile. Small discrepancies between the model and observations are likely mainly due to changes in precipitation rates that can impact 10Be delivery rates and 10Be movement within the profile. Interpreted in this way, the 10Be data suggest drying in the Atacama after ∼4.7Ma, and returning to an insignificant wet period at ∼1Ma, which was possibly connected to El Niño- or La Niña-like climate change.

Mussels (Mytilus galloprovincialis) as a bio-indicator species in radioactivity monitoring of Eastern Adriatic coastal waters

Croatian Adriatic coastal waters are systematically monitored within the Mediterranean Mussel Watch Project using mussels (Mytilus galloprovincialis) as a bio-indicator species. The study includes determination of naturally occurring (7Be, 40K, 232Th, 226Ra and 238U), as well as anthropogenic 137Cs radionuclides. Activity concentrations in dry weight of mussels' soft tissue along the Croatian Adriatic coast are presented, with spatial and seasonal variations given and discussed. Samples were collected in spring and autumn for the period between 2009 and 2013. Radionuclides were determined by gamma-ray spectrometry. Activity concentrations of 7Be were the highest in spring periods, especially in the areas with significant fresh water discharges. Activity concentrations of 40K did not vary significantly with season or location. 137Cs activities were low, while 232Th, 226Ra and 238U activities were mostly below the detection limit of performed gamma-spectrometric measurement.

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.

Cosmic ray event of A.D. 774-775 shown in quasi-annual10Be data from the Antarctic Dome Fuji ice core

14C content in tree rings and 10Be concentration records in polar ice core provide information about past cosmic ray intensities. The A.D. 774–775 cosmic ray event has been identified by 14C measurement in several tree rings from all over the world. Although the quasi-decadal 10Be Dome Fuji data in the Antarctic ice core also shows a sharp peak around A.D. 775, annual 10Be variations in the Dome Fuji core or in other cores have not been revealed. We have measured quasi-annual 10Be concentrations from approximately A.D. 763–794 in the Dome Fuji ice core, and detected a clear increase (~80% above the baseline) in 10Be concentration around A.D. 775. However, an accurate height of this increase is not straightforwardly estimated due to the background variation in 10Be concentration. The 10Be increase can be due to the same cosmic ray event as shown in the 14C content in A.D. 774–775.