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Soil mixing plays a significant role in contaminant transport, carbon sequestration, and landscape evolution, yet the rates and driving mechanisms are poorly constrained. Here we use depth profiles and advection-diffusion modeling of fallout nuclides to quantify differences in short-term (< 100 yr) physical soil mixing across contrasting landscapes. We constrain advection in soils using the distribution of cosmogenic 7 Be and weapons-derived isotopes, and quantify mixing with a steady-state model of vertical 210 Pb transport. On a forested landscape in the Bega Valley in southeastern Australia and on grasslands in Marin County, California, where bioturbation is documented as the dominant sediment transport mechanism, we calculate diffusion-like mixing coefficients of 1–2 cm 2 yr− 1. In montane forest soils of northern New England, we observe little field evidence of short-term mixing, and find that the traditional …