In-situ and meteoric cosmogenic 10Be constraints on coupling chemical weathering and denudation in monolithologic catchments

Abstract

Deciphering Earth's surface denudation—encompassing both physical erosion and chemical weathering—is essential for understanding sediment flux and its impact on long-term carbon cycle. However, quantifying denudation and chemical weathering across different timescales remains challenging. Here, we combine the covariation of different fluxes derived from in-situ ¹⁰Be_in (quartz, 250–500 μm), the ratio of meteoric ¹⁰Be_met to mineral-weathered ⁹Be (fine grains, < 63 μm), and water chemistry in granitic catchments from the northeastern China to identify the contribution of chemical weathering to overall denudation. Millennial-scale chemical weathering fluxes (W_bulk) derived from the ¹⁰Be_met/⁹Be ratio in authigenic phase capture signals from both the dissolved phase and the reactive phase (adsorbed onto or precipitated in secondary weathering products), ranging from 7.7 to 12.2 mm/kyr. Modern water chemical weathering fluxes (W_water, 2.1–4.0 mm/kyr), which represent only the dissolved phase flux, are positively correlated with W_bulk (R² = 0.38) but are consistently lower. Assuming constant weathering fluxes over time, this correlation suggests that only one-third of the bulk weathering products are removed through water discharge. The weathering intensity, defined as the ratio of W_bulk to in-situ ¹⁰Be_in denudation flux (D_in), spans a wide range of 0.14–0.39, in contrast to the relatively narrow range of W_bulk. This highlights the dominant influence of physical erosion in these catchments, likely reflecting a “kinetic limitation” on regional silicate chemical weathering. By integrating previously published global data on D_in and W_bulk, we find that W_bulk scales linearly with D_in in log-log space over three orders of magnitude (10–10⁴ t/km²/yr). This relationship contrasts with the relationship between W_water and D_in, which shows highly limited weathering flux in uplands with high D_in. The faster decline of W_water compared to W_bulk as D_in increases suggests that W_water is sensitive not only to D_in but also to water discharge. To expand the application of ¹⁰Be_met/⁹Be to any fine-grain Earth surface sample, unlike the strong dependence of ¹⁰Be_in-derived denudation fluxes on the presence of quartz minerals, we also estimate potential weathering intensity proxies such as the mobilized ⁹Be fraction in dissolved and reactive phases ($f_{\text{reac}}^{{}_{}{}^9\mathrm{Be}}+f_{\text{diss}}^{{}_{}{}^9\mathrm{Be}}$) and the chemical depletion factor (CDF). We find that $f_{\text{reac}}^{{}_{}{}^9\mathrm{Be}}+f_{\text{diss}}^{{}_{}{}^9\mathrm{Be}}$ exhibits a much narrower range (0.22–0.32) compared to W_bulk/D_in. Its insensitivity to weathering intensity is likely due to its strong dependence on particle sorting. Although the CDF is also grain-size dependent and overall higher by 0.29 (< 63 μm) than W_bulk/D_in, we find that the CDF derived from grain sizes of 250–500 μm is roughly consistent with W_bulk/D_in. Therefore, the CDF shows promise as a potential weathering intensity proxy for quantifying catchment-wide denudation fluxes through ¹⁰Be_met/⁹Be-derived chemical weathering fluxes.