Applications of fallout plutonium at the University of Cologne to resolve Anthropocene Earth (sub-)surface processes

Anthropogenic fallout radionuclides (FRNs), in particular 137Cs, are frequently measured to investigate Anthropocene sediment or soil particle redistribution patterns and rates. However, applications of 137Cs can be complicated due to contaminations from nuclear power plant accidents. In addition, decreasing global 137Cs activities mean that it will become increasingly difficult to measure in coming decades. Fallout 239+240Pu measured by Accelerator Mass Spectrometry (AMS) remains largely unaffected by these issues and allows more precise measurements on smaller sample sizes. There is thus much potential for 239+240Pu in modern Earth (sub-)surface processes investigations. The Institute of Geology and Mineralogy, together with the Division of Nuclear Chemistry, and the Centre for Accelerator Mass Spectrometry (CologneAMS), University of Cologne, have developed 239+240Pu capabilities, calibrated against published and externally referenced in-house standards. Measurement uncertainties regularly achieved are < 5%. Based on these preconditions, we now aim to comprehensively exploit the wealth of possible 239+240Pu applications to decipher modern Earth (sub-)surface processes. We present a selection of ongoing projects, in which we assess deflation processes (South Africa, northern Chile), aspect-induced differential soil erosion (central Chile), seismic-induced boulder slip rates (northern Chile), and sediment transport through natural pipes associated with sapping processes (Germany). Furthermore, we test the application of 239+240Pu as proxy for rainfall in the Atacama Desert (northern Chile). Our approaches contribute to a better understanding of Earth (sub-)surface processes in the Anthropocene, and, where applicable, we seek to compare these data to longer-term background rates of topography formation.