Precipitation Control on Weathering Intensity and Depositional Flux of Meteoric 10Be Revealed From Soil Profiles Along a Climate Gradient (Chile)

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 rates In regolith profiles, both the infiltration depth of 10Be and the fraction of 9Be released by weathering depends on p