Soil Particle Transport and Mixing Near a Hillslope Crest: 2. Cosmogenic Nuclide and Optically Stimulated Luminescence Tracers. Issue 5 (22nd May 2018)

• Record Type: Journal Article
• Authors: Furbish, David Jon; Roering, Joshua J.; Keen‐Zebert, Amanda; Almond, Peter; Doane, Tyler H.; Schumer, Rina
• Is Part Of: Journal of geophysical research. Volume 123:Issue 5(2018)
• Page Start: 1078
• Page End: 1093
• Publication Date: 2018-05-22
• Subjects: soil transport -- cosmogenic nuclide -- optically stimulated luminescence; Geomorphology -- Periodicals; 551.3
• DOI: 10.1029/2017JF004316
• Languages: English
• ISSNs: 2169-9003

Abstract

Abstract : We examine probabilistic elements of how cosmogenic nuclide (e.g., 10 Be) concentrations and optically stimulated luminescence (OSL) particle ages are distributed within a soil mantle near a hillslope crest as a consequence of disturbance‐driven transport and particle mixing. We use an Eulerian‐Lagrangian algorithm in which fluctuating particle motions, representing depth‐dependent mixing, are superimposed on a two‐dimensional mean motion. The intensity of mixing is characterized by a Péclet number involving the vertical speed of particles entering the soil mantle at the soil‐bedrock interface, the mechanically active soil thickness, and a particle diffusivity at the soil surface. With weak mixing, the vertical profile of 10 Be concentration reflects the strong influence of the mean motion in which particles spend much of their lives in the higher part of the soil column with higher 10 Be production rates. With increasing mixing intensity, the profile becomes linear, then uniform, and the vertically averaged concentration is larger than that expected with one‐dimensional motion. With weak mixing, particles possessing a finite OSL age tend to remain near the soil surface; with increasing mixing they become more uniformly distributed with depth. Depth‐interval‐averaged OSL ages increase linearly with depth and then become uniform with strong mixing. With moderate to strong mixing, the probability distribution of OSL ages is approximately exponential with an average much less than the mean residence time of particles. The formulation is consistent with profiles of 10 Be concentrations and interval‐averaged OSL particle ages compiled from published data, suggesting moderate to strong mixing in the cases examined. Key Points: We examine the structure of 10 Be concentrations and OSL ages in response to transport and depth‐dependent mixing Profiles show a systematic variation in going from weak to strong mixing, characterized by a Peclet number The analysis is consistent with published profiles, suggesting moderate to strong mixing