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Along a climate gradient in the Chilean coastal mountains, we investigated denudation rates using the meteoric cosmogenic nuclide 10Be and its ratio to stable 9Be, and chemical depletion fractions (CDFs) in bulk soil samples. We find that the fraction of 9Be released from bedrock is a sensitive indicator of weathering, similar to CDF. Meteoric 10Be decreases exponentially with depth, reflecting the reactive nature of this tracer. We also measured denudation rates by the well‐understood in situ cosmogenic 10Be system on quartz. Assuming that both systems record the same denudation rate we calculated the depositional flux of meteoric 10Be for each study site. The flux agrees to that derived from atmospheric models in the mediterranean and humid areas. In contrast, in the arid and semi‐arid areas, the calculated flux agrees with a precipitation‐derived flux, indicating delivery of 10Be to be affected by small‐scale climatic variations not reflected by current atmospheric models. Plain Language Summary: To identify how geologic and climatic conditions control how fast soil is removed from the Earth's surface (denudation), we need to measure these rates over long periods, like thousands of years. A common method makes use of a rare radioactive nuclide, cosmogenic 10Be, formed by cosmic rays in quartz. However, if rocks do not contain quartz, an alternative system is provided by meteoric cosmogenic 10Be precipitated from the atmosphere and stable 9Be that is released during rock weathering. From the ratio 10Be to 9Be we can estimate denudation rates if we know the fraction of 9Be released by weathering and how much meteoric 10Be is deposited from the atmosphere per unit time and area. In a comparison with the quartz‐based method we explored these two unknowns on soil samples from four locations in Chile with different climates, all from granitic rock. We discovered two key points: (a) The amount of stable 9Be indicates soil alteration, which depends on water infiltration. (b) In arid climate, the deposition of meteoric 10Be is limited by rainfall, whereas in areas of sufficient yearly rainfall the 10Be deposition reflects large‐scale atmospheric distribution and is predicted by combined global cosmogenic nuclide production and climate models. Key Points: The ratio of meteoric cosmogenic 10Be to stable 9Be was used to determine soil denudation ratesIn regolith profiles, both the infiltration depth of 10Be and the fraction of 9Be released by weathering depends on precipitationAtmospheric models reflect the flux of meteoric 10Be well in humid areas; in arid areas the flux strongly depends on local precipitation [ABSTRACT FROM AUTHOR]

The denudation of rocks in mountain belts exposes a range of fresh minerals to the surface of the Earth that are chemically weathered by acidic and oxygenated fluids. The impact of the resulting coupling between denudation and weathering rates fundamentally depends on the types of minerals that are weathering. Whereas silicate weathering sequesters CO2 , the combination of sulfide oxidation and carbonate dissolution emits CO2 to the atmosphere. Here, we combine the concentrations of dissolved major elements in stream waters with 10Be basin-wide denudation rates from 35 small catchments in eastern Tibet to elucidate the importance of lithology in modulating the relationships between denudation rate, chemical weathering pathways, and CO2 consumption or release. Our catchments span 3 orders of magnitude in denudation rate in low-grade flysch, high-grade metapelites, and granitoid rocks. For each stream, we estimate the concentrations of solutes sourced from silicate weathering, carbonate dissolution, and sulfide oxidation using a mixing model. We find that for all lithologies, cation concentrations from silicate weathering are largely independent of denudation rate, but solute concentrations from carbonates and, where present, sulfides increase with increasing denudation rate. With increasing denudation rates, weathering may therefore shift from consuming to releasing CO2 in both (meta)sedimentary and granitoid lithologies. For a given denudation rate, we report dissolved solid concentrations and inferred weathering fluxes in catchments underlain by (meta)sedimentary rock that are 2–10 times higher compared to catchments containing granitoid lithologies, even though climatic and topographic parameters do not vary systematically between these catchments. Thus, varying proportions of exposed (meta)sedimentary and igneous rocks during orogenesis could lead to changes in the sequestration and release of CO2 that are independent of denudation rate. [ABSTRACT FROM AUTHOR]

The ratio of the meteoric cosmogenic nuclide 10 Be, precipitated from the atmosphere, to the stable nuclide 9 Be, released by silicate weathering, was measured in suspended sediment of the Ganga River basin to determine denudation rates, degrees of weathering, and sediment storage in the floodplain. The 10 Be precipitated and the 9 Be released are carried to ca. 90% by amorphous and to 10% by crystalline Fe-hydroxides, as revealed by chemical extractions, whereas the dissolved Be transport is negligible due to the river pH of 8. Resulting 10 Be/ 9 Be ratios increase from 0.75 × 10 − 9 for the northern and Himalaya-draining rivers to 1.7 × 10 − 9 in the downstream basin. The increase in 10 Be/ 9 Be ratios results from two compounding effects: with 1) average denudation rates decrease from 0.5 mm yr −1 in the Himalayas to 0.17 mm yr −1 for the Ganga main stem in the lowlands, 2) the southern tributaries draining the low-relief craton contribute sediment with a ratio of 2.0 × 10 − 9 , corresponding to a denudation rate of 0.03 mm yr −1 . We find that at the spatial scale of the entire basin, the atmospheric delivery flux of 10 Be equals its sedimentary export flux. Hence fluxes can be considered to be at steady state and radioactive decay of 10 Be during sediment storage is not discernible. The lack of a resolvable increase in 10 Be concentration during sediment transfer along the floodplain stretch furthermore suggests that the sediment transfer time is indeed short. We also cannot resolve any additional release of silicate-bound 9 Be there, testifying to the lower degree of weathering there. When multiplied with the basin area the 10 Be/ 9 Be-derived denudation rate of 0.14 mm yr −1 corresponds to a sediment flux of 350 Mt yr −1 which is in good agreement with gauging-derived sediment fluxes (ca. 400 Mt yr −1 ). Because they integrate over the entire basin, denudation rates from 10 Be/ 9 Be are lower than floodplain-corrected denudation rates from in situ cosmogenic 10 Be that reflect the rates of the sediment-producing mountain areas. [ABSTRACT FROM AUTHOR]

About 75% of the terrestrial land surface of our planet is covered by sedimentary rocks, butabout 80% of this area is composed of fine-grained shale or carbonate lithologies. When alsoincluding mafic rocks, a large global terrestrial area is inaccessible to the in situ 10Becosmogenic nuclide method, as it requires the presence of sand-sized quartz minerals. Hence,in order to quantitatively constrain the erosion and weathering rates of these areas andto derive globally meaningful solid and solute fluxes, new methods are required.A recently developed tracer to study Earth surface erosion and weathering is themeteoric 10Be/9Be ratio1, from which meteoric denudation rates (Dmet) can becalculated. Meteoric cosmogenic 10Be is deposited from the atmosphere onto Earthsurface, where it is adsorbed to any fine-grained solid material or, depending on pH,is present in the dissolved form, whereas stable 9Be is a trace metal released byweathering. We show the broad versatility of this new approach by its application to twogeomorphically contrasting settings. In the transport-limited setting of the middle Europeanuplands of the Slavkov Forest, Czech Republic, small (<1 km2) neighboring catchments ofsimilar size, climate, slope, and vegetation are underlain by mafic (amphibolite), ultramafic(serpentinite), and felsic (granitic) rocks. Quartz is present in all these catchments in thebedrock or in quartz veins, making a comparison with in situ cosmogenic-deriveddenudation rates (Dinsitu)possible. Due to acid rain deposition in the 20th century,pH values of stream waters vary from acidic to alkaline, depending on the acidbuffering capability of individual lithologies. By balancing the depositional 10Be fluxwith the exported dissolved and particulate 10Be flux, we show that steady stateattained before industrial soil acidification in all three catchments, suggesting anegligible loss of dissolved Be due to acidic conditions. This is supported by the overallagreement of Dmet with Dinsituin the studied catchments that range from 0.04 to 0.08mm/yr2. In the supply-limited setting of the high and steep mountainous island of Taiwan, amongthe World´s highest denudation rates prevail due to high uplift rates and frequent typhoonattacks. We studied Taiwan´s longest river, the Zhuoshui River (3000 km2), whereheadwaters are dominated by slate with Dmet ranging from 4-8 mm/yr, agreeing withpublished long-term exhumation rates. In the mid-lower sandstone-dominated reaches, lowerDmet agree with published Dinsitu, being in the order of 1-2 mm/yr. We suggest that agradual dilution of the sediment contribution from the rapidly-eroding slate in the headwaterswith sediment from slowly-eroding sandstone reaches is responsible for the downstreamdecrease in Dmet. In both these settings representing geomorphic end members, denudation rates calculatedfrom the 10Be/9Be ratio of the particle-bound Be are very similar to independent denudationrate estimates and prevailing lithological and geomorphological conditions. This agreementevidences the versatile potential of the meteoric 10Be/9Be proxy to quantify Earth surfaceprocesses in a wide range of landscapes, lithologies, hydrological conditions and sedimenttransport processes. 1 von Blanckenburg, F., et al. EPSL, 2012. 2 Dannhaus, N. et al., GCA, 2018. [ABSTRACT FROM AUTHOR]