10Be Concentrations Research Articles

Unsteady topography in the eastern Tianshan due to imbalance between denudation and crustal thickening

The Tianshan mountains have complex and variable topography and documenting their growth is important for understanding both intracontinental mountain building and the evolution of the global climate. We investigate whether this topography is in equilibrium with crustal influx (thickening) and sediment outflux (denudation). Based on literature, we estimate that the eastern Tianshan has been subject to a total crustal shortening rate of ∼9.4 mm/a across the Kuitun–Kuche transect, implying ∼1.3 mm/a of crustal thickening and a total crustal influx of ∼9 × 107 m3/a. We measured in-situ cosmogenic 10Be concentrations in modern river sands of 34 catchments to constrain recent (0–6 ka) basin-averaged denudation rates within the range and on its two flanks. Denudation rates range from 0.020 ± 0.002 to 0.53 ± 0.07 mm/a, averaging 0.20 ± 0.04 and 0.11 ± 0.02 mm/a in the north and south, respectively; these rates correspond to respective total sediment outfluxes of (542 ± 69) × 104 and (164 ± 24) × 104 m3/a. To ensure that these values can be compared to Pleistocene tectonic rates, we reconstructed Pleistocene denudation rates in seven of the studied basins. For this, we determined inherited in-situ cosmogenic 10Be concentrations from 11 cosmogenic depth profiles of abandoned fluvial terraces deposited in the Tianshan piedmonts. These data indicate that denudation rates have been relatively steady since the Pleistocene and thus that recent and Pleistocene sediment fluxes can be compared. These results show that crustal thickening outpaced denudation and sediment outflux by a factor of ∼10. Therefore, the Tianshan topography is not in dynamic equilibrium and is growing, even if materials are being subducted into the mantle. Consequently, to sustain this disequilibrium, the range grew laterally. This lateral growth and the inheritance of structures and basins are likely responsible for the complex topography of the range.

Non‐Steady‐State 14C‐10Be and Transient Hillslope Dynamics in Steep High Mountain Catchments

AbstractPaired in situ cosmogenic nuclides 14C and 10Be present an opportunity to explore erosion rate disequilibria over Holocene to latest Pleistocene timescales and are a new avenue in surface processes research. 14C and 10Be concentrations in quartz from river sand collected at the outlets of five mountainous catchments in the Argentine Andes are compared in this study. River gauge and 10Be‐derived erosion rates are in good agreement; however, 14C concentrations are approximately 2.7–4 times lower than expected relative to 10Be under steady‐state erosion. Low 14C to 10Be ratios imply that sediment eroded from the high mountains was shielded for at least 7–15 ky. Neoglacial advances and storage in terraces may account for some of the reduced 14C concentrations but are insufficient alone. Transient storage in dynamic talus slopes in the steep topography of the High Andes provides the best explanation for the observed 14C concentrations.

Aspect-dependent bedrock weathering, cliff retreat, and cliff morphology in a hyperarid environment

Deciphering aspect-related hillslope asymmetry can enhance our understanding of the influence of climate on Earth’s surface morphology and the linkage between topographic morphology and erosion processes. Although hillslope asymmetry is documented worldwide, the role of microclimatic factors in the evolution of dryland cliffs has received little attention. Here, we address this gap by quantifying aspect-dependent bedrock weathering, slope-rill morphology, and sub-cliff clast transport rates in the hyperarid Negev desert, Israel, based on light detection and ranging (LiDAR)-derived topography, clast-size measurements, and cosmogenic 10Be concentrations. Cliff retreat rates were evaluated using extrapolated profiles from dated talus flatirons and 10Be measurements from the cliff face and sub-cliff sediments. We document systematic, aspect-dependent patterns of south-facing slopes being less steep and finer-grained relative to east- and north-facing aspects. In addition, cliff retreat and clast transport rates on slopes of the south-facing aspect are faster compared to the other aspects. Our data demonstrate that bedrock weathering of the cliff face and the corresponding grain size of cliff-derived clasts delivered to the slopes constitute a first-order control on cliff retreat and sediment transport rates. We demonstrate that the morphology of the cliff and the pattern of bedrock weathering co-vary with the solar radiation flux and hence that cliff evolution in hyperarid regions is modulated by aspect-dependent solar radiation. These results help to better understand interactions between climate and dryland surface processes.

Late Pleistocene slip rate and subsurface fault-plane geometry of the Latgan Fold (Bole Basin, North Tian Shan, NW China) derived from a deformed cosmogenically dated alluvial fan

Deformed alluvial fans can indicate the subsurface fault-plane geometry of thrusts. Numerous seismic profiles have illustrated the subsurface fault-plane geometry of thrusts in the Tian Shan piedmonts. However, due to a lack of seismic profiles, the subsurface fault-plane geometry in the Tian Shan is not well-known. This paper focuses on a thrust-related anticline in the eastern Kusongmuxiek Fault (KF), the Latgan Anticline (LA), located in the southern margin of the Bole Basin, northern Tian Shan. Five alluvial fan surfaces, A1-A5 from young to old, are determined along the Dilike River. We used the alluvial fan surfaces and fault attitude to determinate the subsurface fault-plane geometry of the Latgan Fault. The geometric model reveals that the Latgan Fault can be divided into three segments: an upper ramp with a dip of 55°S, a central listric fault, and a lower ramp with a dip of 31°S. The abandonment age of the A4 surface based on its cosmogenic 10Be concentrations and use of a kinematic model of a listric fault fold reveal that the fault dip-slip rate is c. 0.5 mm/a, and the horizontal crustal shortening rate is c. 0.4 mm/a during the Pleistocene. The vertical incision rates of the Dilike River are 0.5–0.6 mm/a in the uplifted area and 0.2 mm/a in the non-uplifted area. This difference may be the result of tectonic uplift. Our field and remote sensing observations and the geometric characteristics of the eastern Keguqin Mountains piedmont thrusts indicate fault propagation into the basin via thick-skinned tectonics. The LA crustal shortening rate and previous studies indicate that the crustal shortening rates of the Bole, Borohoro, and Turfan Units are ~1.7–2.0 mm/a, >4.0 mm/a, and 3.2–4.4 mm/a, respectively. The lower shortening rate of the Bole Unit and higher shortening rates of the Borohoro and Turfan Units indicate that the Bole Unit is the lowest crustal shortening rate unit in the northern Tian Shan.

Spatial variations of 10Be in surface snow along the inland traverse route of Japanese Antarctic Research Expeditions

To contribute further to understanding of the nature of 10Be deposition in Antarctica, we determined 10Be concentrations in surface snow samples obtained along the inland traverse route of the 59th and 60th Japanese Antarctic Research Expeditions (JAREs) in eastern Dronning Maud Land. The 10Be concentrations ranged between 3.7 × 103 and 8.6 × 104 atoms/g. When plotted against latitude, they showed a clear trend of increasing concentration southward with an upward inflection point at around 75°S (elevation 3.5 km) for the 59th JARE. Comparison with both snow accumulation rate and δ18O data suggests that the inflection point divides the dominant deposition regime into two different groups: wet deposition (north of 75°S) and dry deposition with slight enhancement of 10Be fallout further inland (south of 75°S). Additional factors associated with 10Be transport from the stratosphere are also proposed.

10Be ion detection: SiN foil stack method benchmarked against absorber cell technique

Increasing interest in applications where 10Be concentrations are low leads to a challenge in measurement and how to minimise the losses in accelerator mass spectrometry. Selecting a 2+ charge state for analysis instead of 3+ after the accelerator offers a potential gain by a factor of 2 in total measurement efficiency. Benchmarking the 10Be2+ SiN foil stack ion detection against well-established 10Be3+ absorber cell technique, using a set of samples with artificially elevated B concentrations, we demonstrate that there is no clear benefit in using 20.3 MeV 10Be3+ ions for 10Be measurement. Equal suppression against 10B derived interferences can be achieved with 10Be2+ and 10Be3+ ions.

Total Solar Irradiance during the Last Five Centuries

The total solar irradiance (TSI) varies on timescales of minutes to centuries. On short timescales it varies due to the superposition of intensity fluctuations produced by turbulent convection and acoustic oscillations. On longer timescales, it changes due to photospheric magnetic activity, mainly because of the facular brightenings and dimmings caused by sunspots. While modern TSI variations have been monitored from space since the 1970s, TSI variations over much longer periods can only be estimated either using historical observations of magnetic features, possibly supported by flux transport models, or from the measurements of the cosmogenic isotope (e.g., 14C or 10Be) concentrations in tree rings and ice cores. The reconstruction of the TSI in the last few centuries, particularly in the 17th/18th centuries during the Maunder minimum, is of primary importance for studying climatic effects. To separate the temporal components of the irradiance variations, specifically the magnetic cycle from secular variability, we decomposed the signals associated with historical observations of magnetic features and the solar modulation potential Φ by applying an empirical mode decomposition algorithm. Thus, the reconstruction is empirical and does not require any feature contrast or field transport model. The assessed difference between the mean value during the Maunder minimum and the present value is ≃2.5 W m−2. Moreover it shows, in the first half of the last century, a growth of ≃1.5 W m−2, which stops around the middle of the century to remain constant for the next 50 years, apart from the modulation due to the solar cycle.

PSCF and CWT methods as a tool to identify potential sources of 7Be and 210Pb aerosols in Granada, Spain

This research is focused on studying the preferred source regions and the pathways of the air masses with high particulate concentrations impacting on the activity concentrations of 7Be and 210Pb aerosols in Granada atmosphere. For this purpose, three different source-receptor methods have been used: Cluster Analysis, Potential Source Contribution Function (PSCF), and Concentration Weighted Trajectory (CWT). Air filter samples were weekly collected and analysed in Granada university (Spain 37.177N, 3.598 W, 687m a.s.l.) during 12 years (2006–2017) for the activity concentration of 7Be, and during 5 years (2010–2014) for the one of 210Pb. The time series of the collected data indicate that the concentration of both radiotracers present a cyclical and seasonal pattern, in association with their origins and atmospheric conditions. Clustering analysis showed that the air masses arriving to Granada can be classified as: (1) tropical continental air masses coming from the Mediterranean Sea, (2) tropical and warm polar maritime air masses produced over the Atlantic Ocean, and (3) continental air masses originated over Europe and Northern Africa. The PSCF and CWT methods confirmed that the main source areas of 7Be are located in the Atlantic coast of southern Morocco, and Northern Africa. On the other hand, southern France and the Algerian desert were found to be the main region sources of 210Pb. In addition, the Mediterranean Basin has been postulated as a strong source region for 7Be and 210Pb. Furthermore, the PSCF and CWT models show that the regions with larger 7Be/210Pb ratios are located in the Atlantic Ocean, due to frequent stratospheric intrusions specially during the winter months.

Quantifying geomorphological evolution from 10Be denudation rates: Insights from high‐resolution depth profiles, topsoils, and stream sediments (Strengbach CZO, France)

AbstractA rare dataset of in‐situ 10Be from high‐resolution depth profiles, soils, rock outcrops, and stream sediments is combined with geochemical analysis and modelling of regolith evolution to understand the variability of denudation rates in a mountain watershed (Strengbach critical zone observatory). High‐resolution depth profiles are key to detect the presence of mobile regolith and to highlight how it affects the critical zone evolution. The modelling of regolith evolution and 10Be concentrations along depth profiles allow us to estimate both the cosmic ray exposure age (19 kyr) and the mean denudation rate (22 mm kyr−1) of the regolith without any steady‐state assumption on 10Be concentrations. Comparison with maximum denudation rates inferred from topsoil samples collected from the surface of the depth profiles and calculated using the temporal steady‐state assumption of 10Be concentrations highlights an overestimation of denudation by a factor of two. Maximum spatially averaged denudation rates determined from stream sediment samples also likely overestimate denudation rates by a factor of two. These biases are significant for investigating the geomorphological evolution and we propose a method to correct denudation rates using the inherited 10Be concentrations and the cosmic ray exposure age deduced from the high‐resolution depth profiles. A key result is also that a steady state of 10Be concentrations and a steady state of regolith thickness are two different equilibrium states that do not necessarily coincide. The comparison between locally corrected and spatially averaged denudation rates indicates that the watershed geomorphology is not in a topographic steady state but is modulated by regressive fluvial erosion. Nonetheless, our study demonstrates that even in a watershed where the steady‐state assumption of 10Be concentrations is not verified, the spatial variations of in‐situ 10Be concentrations in sediments still carry qualitatively relevant information on the geomorphological evolution of landscapes.

SITE-SPECIFIC DRY AND WET DEPOSITION VELOCITIES USING 7BE AND MASS INTERCEPTION FACTOR FOR VARIOUS TYPES OF PLANT LEAVES AT NARORA SITE, INDIA.

Comprehensive studies were carried out during the period 2016-19 on the estimation of site-specific wet and dry deposition velocities and the mass interception factor for Narora site based on the concentrations of 7Be in air, air deposits, rain water and vegetation samples. Mean wet and dry deposition velocities for Narora site were found to be 1.64E-2 and 1.58E-3ms-1, respectively. Mass interception factors for vegetation found to be 0.34-2.51m2kg-1 dry weight with a mean of 0.97m2kg-1 dry weight. The obtained parameters shall be used for estimation of impact due to radionuclide related to Narora Atomic Power station.

Cosmogenic nuclide and solute flux data from central Cuban rivers emphasize the importance of both physical and chemical mass loss from tropical landscapes

Abstract. We use 25 new measurements of in situ produced cosmogenic 26Al and 10Be in river sand, paired with estimates of dissolved load flux in river water, to characterize the processes and pace of landscape change in central Cuba. Long-term erosion rates inferred from 10Be concentrations in quartz extracted from central Cuban river sand range from 3.4–189 Mg km−2 yr−1 (mean 59, median 45). Dissolved loads (10–176 Mg km−2 yr−1; mean 92, median 97), calculated from stream solute concentrations and modeled runoff, exceed measured cosmogenic-10Be-derived erosion rates in 18 of 23 basins. This disparity mandates that in this environment landscape-scale mass loss is not fully represented by the cosmogenic nuclide measurements. The 26Al / 10Be ratios are lower than expected for steady-state exposure or erosion in 16 of 24 samples. Depressed 26Al / 10Be ratios occur in many of the basins that have the greatest disparity between dissolved loads (high) and erosion rates inferred from cosmogenic nuclide concentrations (low). Depressed 26Al / 10Be ratios are consistent with the presence of a deep, mixed, regolith layer providing extended storage times on slopes and/or burial and extended storage during fluvial transport. River water chemical analyses indicate that many basins with lower 26Al / 10Be ratios and high 10Be concentrations are underlain at least in part by evaporitic rocks that rapidly dissolve. Our data show that when assessing mass loss in humid tropical landscapes, accounting for the contribution of rock dissolution at depth is particularly important. In such warm, wet climates, mineral dissolution can occur many meters below the surface, beyond the penetration depth of most cosmic rays and thus the production of most cosmogenic nuclides. Our data suggest the importance of estimating solute fluxes and measuring paired cosmogenic nuclides to better understand the processes and rates of mass transfer at a basin scale.

The impact of different atmospheric phenomena to cosmogenic 22Na/7Be ratio

The isotopic ratio of two cosmogenic isotopes, 22Na and 7Be, has been recognized as a possible tracer for atmospheric dynamics. We studied how different atmospheric phenomena affect the 22Na/7Be ratio that are known to affect the ground level 7Be concentrations. The 22Na/7Be ratio was studied in the following context: estimation of aerosol residence time, in the intrusions of stratospheric air after Sudden Stratospheric Warming (SSW) events, seasonal variations due to different atmospheric mixing conditions and finally the interannual variations caused by the large-scale atmospheric circulation such as North Atlantic Oscillation (NAO), Arctic Oscillation (AO), Scandinavian Pattern (SCAND) and Quasi-Biennial Oscillation (QBO). This study utilized airborne radioactivity monitoring data from three Finnish stations located in Rovaniemi (66.51 °N, 25.73 °E), Kajaani (64.08 °N, 27.71 °E) and Kotka (60.48 °N, 26.92 °E). The theoretical calculations were performed to see how the 22Na/7Be ratio changes as a function of altitude during when produced by the galactic cosmic rays. The calculations showed that the 22Na/7Be ratio is higher in the stratosphere and lower in the troposphere. At mid-stratosphere level the ratio was 0.001, at tropopause level approximately 0.0007 and at ground level approximately 0.00045. Due to the different half-lives of 22Na and 7Be the mean atmospheric residence time can be estimefrom the radioactive decay law by assuming an initial activity concentration ratio of 0.0007 and using the measured ground level 22Na/7Be ratios. This resulted in the median atmospheric residence time as 91–95 days. The atmospheric impact on 22Na/7Be ratio was studied at different time scales starting from short-term impact from SSW, the known seasonal cycle and variations at interannual timescale. SSW events caused rapid increases in the ground level 7Be and 22Na concentrations while the impact on 22Na/7Be ratio was relatively small. A clear seasonal cycle in the 22Na/7Be ratio was observed where the 22Na/7Be ratio was at low value during November–February, increased during March–May, stayed at stable high value during June–July and steadily decreased during August–October. The long-term average for 22Na/7Be ratio was established to be 1.1 × 10−4 by using the Kotka data from 1993 to 2020. During 1995–2009, the 22Na/7Be ratio was below the long-term average, and during 2010–2020, generally above. The interannual variations in the 22Na/7Be ratio were studied by using wavelet transform analysis of the Kotka data. The analysis showed 4-6-year and 11-year periodicities. The wavelet coherence analyses with AO, NAO, SCAND, QBO and Southern Oscillation (SO) indices showed that the shorter periodicity was caused by the NAO/AO effects the atmospheric circulation in Scandinavia and hence the transport of the isotopes from upper atmosphere to ground level. The observed coherence with the Southern Oscillation Index (SOI) starting from 2012 onwards appeared at an approximately 3–4year scale while the AO and NAO had a coherence at an approximately 6-year scale. The observed 11-year periodicity was caused by the Solar cycle which modulates the 7Be and 22Na production in the upper atmosphere.

Technical note: Accelerator mass spectrometry of <sup>10</sup>Be and <sup>26</sup>Al at low nuclide concentrations

Abstract. Accelerator mass spectrometry (AMS) is currently the standard technique to measure cosmogenic 10Be and 26Al concentrations, but the challenge with measuring low nuclide concentrations is to combine high AMS measurement efficiency with low backgrounds. The current standard measurement setup at ANSTO uses the 3+ charge state with Ar stripper gas at 6 MV for Be and 4 MV for Al, achieving ion transmission through the accelerator for 10Be3+ and 26Al3+ of around 35 % and 40 %, respectively. Traditionally, 26Al measurement uncertainties are larger than those for 10Be. Here, however, we show that 26Al can be measured to similar precision as 10Be even for samples with 26Al / 27Al ratios in the range of 10−15, provided that measurement times are sufficiently long. For example, we can achieve uncertainties of 5 % for 26Al / 27Al ratios around 1×10-14, typical for samples of late Holocene age or samples with long burial histories. We also provide empirical functions between the isotope ratio and achievable measurement precision, which allow predictive capabilities for future projects and serve as a benchmark for inter-laboratory comparisons. For the smallest signals, not only is understanding the source of 10Be or 26Al background events required to select the most appropriate blank correction method but also the impact of the data reduction algorithms on the obtained nuclide concentration becomes pronounced. Here we discuss approaches to background correction and recommend quality assurance practices that guide the most appropriate background correction method. Our sensitivity analysis demonstrates a 30 % difference between different background correction methods for samples with 26Al / 27Al ratios below 10−14. Finally, we show that when the measured signal is small and the number of rare isotope counts is also low, differing 26Al or 10Be concentrations may be obtained from the same data if alternate data reduction algorithms are used. Differences in the resulting isotope concentration can be 50 % or more if only very few (≲ 10) counts were recorded or about 30 % if single measurement is shorter than 10 min. Our study presents a comprehensive method for analysis of cosmogenic 10Be and 26Al samples down to isotope concentrations of a few thousand atoms per gram of sample, which opens the door to new and more varied applications of cosmogenic nuclide analysis.

Spatio-temporal variability and controlling factors for postglacial denudation rates in the Dora Baltea catchment (western Italian Alps)

Abstract. Disentangling the influence of lithology from the respective roles of climate, topography and tectonic forcing on catchment denudation is often challenging in mountainous landscapes due to the diversity of geomorphic processes in action and of spatial and temporal scales involved. The Dora Baltea catchment (western Italian Alps) is an ideal setting for such investigation, since its large drainage system, extending from the Mont Blanc Massif to the Po Plain, cuts across different major lithotectonic units of the western Alps, whereas this region has experienced relatively homogeneous climatic conditions and glacial history throughout the Quaternary. We acquired new 10Be-derived catchment-wide denudation rates from 18 river-sand samples collected both along the main Dora Baltea river and at the outlet of its main tributaries. The inferred denudation rates vary between 0.2 and 0.9 mm yr−1, consistent with previously published values across the European Alps. Spatial variability in denudation rates was statistically compared with topographic, environmental and geological metrics. 10Be-derived denudation rates do not correlate with modern precipitation and rock geodetic uplift. We find, rather, that catchment topography, in turn conditioned by bedrock structures and erodibility (lithotectonic origin) and glacial overprint, is the main driver of 10Be-derived denudation patterns. We calculated the highest denudation rate for the Mont Blanc Massif, whose granitoid rocks and long-term tectonic uplift support high elevations, steep slopes and high relief and thus favour intense glacial and periglacial processes and recurring rockfall events. Finally, our results, in agreement with modern sediment budgets, demonstrate that the high sediment input from the Mont Blanc catchment dominates the Dora Baltea sediment flux, explaining the constant low 10Be concentrations measured along the Dora Baltea course even downstream the multiple junctions with tributary catchments.

Variations of 7Be concentration in plants and its significance for 7Be in soil on the Loess Plateau, China: Based on three-year monitoring data

Variations of 7Be concentration in plants and its significance for 7Be in soil on the Loess Plateau, China: Based on three-year monitoring data

Temporal evolution of headwall erosion rates derived from cosmogenic nuclide concentrations in the medial moraines of Glacier d'Otemma, Switzerland

AbstractClimate change affects the stability and erosion of high‐alpine rock walls above glaciers (headwalls) that deliver debris to glacier surfaces. Since supraglacial debris in the ablation zone alters the melt behaviour of the underlying ice, the responses of debris‐covered glaciers and of headwalls to climate change may be coupled. In this study, we analyse the beryllium‐10 (10Be)‐cosmogenic nuclide concentration history of glacial headwalls delivering debris to the Glacier d'Otemma in Switzerland. By systematic downglacier‐profile‐sampling of two parallel medial moraines, we assess changes in headwall erosion through time for small, well‐defined debris source areas. We compute apparent headwall erosion rates from10Be concentrations ([10Be]), measured in 15 amalgamated medial moraine debris samples. To estimate both the additional10Be production during glacial debris transport and the age of our samples we combine our field‐based data with a simple model that simulates downglacier debris trajectories. Furthermore, we evaluate additional grain size fractions for eight samples to test for stochastic mass wasting effects on [10Be]. Our results indicate that [10Be] along the medial moraines vary systematically with time and consistently for different grain sizes. [10Be] are higher for older debris, closer to the glacier terminus, and lower for younger debris, closer to the glacier head. Computed apparent headwall erosion rates vary between ~0.6 and 10.8 mm yr−1, increasing over a maximum time span of ~200 years towards the present. As ice cover retreats, newly exposed headwall surfaces may become susceptible to enhanced weathering and erosion, expand to lower elevations, and contribute formerly shielded bedrock of likely different [10Be]. Hence, we suggest that recently lower [10Be] reflect the deglaciation of the debris source areas since the end of the Little Ice Age.

Beryllium isotope variations recorded in the Adélie Basin, East Antarctica reflect Holocene changes in ice dynamics, productivity, and scavenging efficiency

The Adélie Basin is a relatively small (∼1600 km2), semi-enclosed continental shelf bathymetric depression located adjacent to the Wilkes Subglacial Basin, a basin underlying a sector of the East Antarctic Ice Sheet that contains ∼3–4 m sea level equivalent of ice. Located within the Adélie Basin is a ∼184 m thick laminated sediment deposit, the Adélie Drift, ideal for examining regional changes in ice sheet and ocean dynamics. Here, we examine the ratio of reactive beryllium-10 to reactive beryllium-9 ((10Be/9Be)reac) in a marine sediment core obtained from the Adélie Drift to assess these changes during the Holocene epoch (11.7 ka BP to present). The (10Be/9Be)reac record provides insight into changes in freshwater input, primary productivity, and scavenging efficiency, while removing the influence of particle size on 10Be concentration. During the early Holocene, (10Be/9Be)reac ratios indicate increased meltwater discharge from ca. 11.7 to 10 ka BP, as grounded ice retreated from the Adélie Basin and adjacent bathymetric highs. After ∼10 ka BP, beryllium isotopes are influenced by scavenging efficiency and dilution controlled by ocean currents and accumulation rate, operating alongside meltwater input, suggesting there are additional factors to consider when using (10Be/9Be)reac as a proxy for ice shelf cover and glacial dynamics.

A Combined Cosmogenic Nuclides Approach for Determining the Temperature‐Dependence of Erosion

AbstractPhysical weathering in cold, steep bedrock hillslopes occurs at rates that are thought to depend on temperature, but our ability to quantify the temperature‐dependence of erosion remains limited when integrating over geomorphic timescales. Here, we present results from a 1D numerical model of in‐situ cosmogenic 10Be, 14C, and 3He concentrations that evolve as a function of erosion rate, erosion style, and ground surface temperature. We used the model to explore the suitability of these nuclides for quantifying erosion rates in areas undergoing non‐steady state erosion, as well as the relationship between bedrock temperature, erosion rate, and erosional stochasticity. Our results suggest that even in stochastically eroding settings, 10Be‐derived erosion rates of amalgamated samples can be used to estimate long‐term erosion rates, but infrequent large events can lead to bias. The ratio of 14C to 10Be can be used to evaluate erosional stochasticity, and to determine the offset between an apparent 10Be‐derived erosion rate and the long‐term rate. Finally, the concentration of 3He relative to that of 10Be, and the paleothermometric interpretations derived from it, are unaffected by erosional stochasticity. These findings, discussed in the context of bedrock hillslopes in mountainous regions, indicate that the 10Be‐14C‐3He system in quartz offers a method to evaluate the temperature‐sensitivity of bedrock erosion rates in cold, high‐alpine environments.

Low variability runoff inhibits coupling of climate, tectonics, and topography in the Greater Caucasus

Hypothesized feedbacks between climate and tectonics are mediated by the relationship between topography and long-term erosion rates. While many studies show monotonic relationships between channel steepness and erosion rates, the degree of nonlinearity in this relationship varies by landscape. Mechanistically explaining controls on this relationship in natural settings is critical because highly nonlinear relationships imply low sensitivity between climate and tectonics. To this end, we present a coordinated analysis of cosmogenic 10Be concentrations in river sands paired with topographic, hydroclimatic, and tectonic data for the Greater Caucasus Mountains where topography is invariant along-strike despite large gradients in modern precipitation and convergence rates. We show that spatial patterns in erosion rates largely reflect regional tectonics with little sensitivity to mean precipitation or runoff. The nonlinearity in the erosion rate – steepness relationship may arise from very low runoff variability, which we attribute to the large contribution from snowmelt. Transitioning from rainfall- to snowmelt-driven runoff as mean elevation increases is common to many mid-latitude mountain ranges. The associated decrease in runoff variability may represent important, unrecognized dynamics inhibiting the sensitivity of tectonics to climate more broadly.

Induced Radionuclides and Their Activity Concentration in Gel Dosimeters Irradiated by Carbon Ion Beam.

Radioactivity was measured in a micellar gel dosimeter, a polymer gel dosimeter, and water was irradiated by carbon ion beams at various beam energy conditions. Monte Carlo simulation was also performed to estimate the radioactivity. Short-lived positron-emitting nuclides were observed immediately after irradiation, but they decayed rapidly into the background. At 24 h post-irradiation, the dominant measured radioactivity was of 7Be. The simulation also showed minor activity of 24Na and 3H; however, they were not experimentally observed. The measured radioactivity was independent of the type of gel dosimeter under all irradiation conditions, suggesting that the radioactivity was induced by the interaction of carbon ions with water (the main component of the gel dosimeters). The ratio between the simulated and measured radioactivity was within 0.9–1.5. The activity concentration of 7Be was found to be less than 1/10 of the value derived using the exemption concept proposed by the International Atomic Energy Agency. This result should be applicable to irradiated gel dosimeters containing mainly water and 0–4 wt.% C and 0–1.7 wt.% N.