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Abstract 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.

Abstract The evolution of Earth's climate over geological timescales is linked to surface erosion via weathering of silicate minerals and burial of organic carbon. However, methodological difficulties in reconstructing erosion rates through time and feedbacks among tectonics, climate, and erosion spurred an ongoing debate on mountain erosion sensitivity to tectonic and climate forcing. At the heart of this debate is the question of whether late Cenozoic climate cooling has increased global erosion rates or not. The Himalaya plays a prominent role in this debate as its erosion produces a large fraction of global sediments delivered to ocean basins. We report a 6‐Myr‐long record of Be10‐derived erosion rates from the north‐western Himalaya, which indicates that erosion rates in this region varied quasi‐cyclically with a period of ∼1 Myr and increased gradually toward the present. We hypothesize that the observed pattern of erosion rates occurred in response to the tectonic growth of the Himalaya by punctuated basal and frontal accretion of rocks from the underthrusting Indian plate and concomitant changes in topography. In this scenario, basal accretion episodically changes rock‐uplift patterns, which brings landscapes out of equilibrium and results in quasi‐cyclic variations in erosion rates. We used numerical landscape evolution simulations to demonstrate that this hypothesis is physically plausible. We attribute the long‐term increase in erosion rates to the erosional response of topography due to frequent basal accretion relative to frontal accretion. Because tectonic accretion processes are inherent to collisional orogenesis, they likely confound climatic interpretations of erosion rate histories.

New developments in Geochemistry during the last two decades have revolutionized our understanding of the processes that shape Earth's surface. Here, complex interactions occur between the tectonic forces acting from within the Earth and the exogenic forces like climate that are strongly modulated by biota and, increasingly today, by human activity. Within the Helmholtz Laboratory for the Geochemistry of the Earth Surface (HELGES) of the Helmholtz Centre Potsdam GFZ German Research Centre for Geosciences, it is our goal to quantify the rates and fluxes of these processes in detail and to develop new techniques to fingerprint them over various temporal and spatial scales. We use mass spectrometry facilities to analyze metal stable isotopes, element concentrations and cosmogenic nuclides to fingerprint and quantify geomorphological changes driven by erosion and weathering processes. We use these novel geochemical tools, to quantify, for example, the recycling of metals in plants after their release during weathering of rocks and soils, soil formation and its erosion rates, and mechanisms and speed of sediment transport through drainage basins. Our research is thus dedicated towards understanding material turnover rates at the Earth's surface by using geochemical fingerprints.

Abstract: Enormous volumes of sediment are produced in the Central Andes and are then delivered into the foreland basins of Amazon basin tributaries. While cosmogenic nuclides in sediment are a suitable tool to measure the denudation rates of sediment-producing areas, the requirement of steady state between nuclide production and nuclide removal by denudation appears to make this method less obvious in depositional foreland basins, where sediment storage may alter 10Be-based erosion signals from the sediment-providing areas. A published cosmogenic nuclide-based modeling approach however predicts that source-area cosmogenic nuclide concentrations are not modified by temporary sediment storage. We tested this approach in the large Beni foreland basin by measuring cosmogenic 10Be nuclide concentrations in detrital sediment along a 600 km long floodplain reach. The outcome of our study is that the 10Be-based denudation rate signal of the Bolivian Andes is preserved in the Beni floodplain even though this basin stores the sediment for thousands of years. For the floodplain part of the Beni basin, the cosmogenic nuclide-derived denudation rate is 0.45 ± 0.07 mm/yr, and the respective Andean source area erodes at a very similar rate of 0.37 ± 0.06 mm/yr. We thus suggest that any sample collected along a river traversing a floodplain will yield the denudation rate of the source area. This finding opens the unique possibility of constraining paleo-sediment budgets for these large basins using cosmogenic nuclides as the denudation rate signal of the sediment-producing area is preserved in sedimentary archives.