Using single-grain multiple elevated temperature luminescence to understand fluvial sediment transport at the system scale

Multiple elevated temperature infra-red stimulated luminescence (MET-IRSL) has great potential to provide detailed information on the movement of sediment grains through time and space. MET-IRSL stimulates grains using infra-red light at a series of elevated temperatures to access multiple charge populations with different bleaching behaviours. Length of past light exposure and duration of storage events can be determined by the relative difference between multiple signals, or ages, for a single grain. With more signals, we can see deeper into the history of an individual grain. Single-grain measurements paint a fine-resolution picture of how a system operates, often masked by multiple grain average measurements. The power of single-grain measurement is underpinned by three basic principles: 1) A single grain has a single transport-storage history (Rhodes and Leathard, 2022), 2) Populations of >200 grains per sample allows for quantitative estimation of the most likely, or ‘dominant’ history for a given sample, 3) It is possible to isolate different grain populations, with different histories or provenance within a single sample. Using samples collected from the active channel of the Allt Dubhaig in Scotland, we present results from a bleach recovery experiment to illustrate an optimal method for quantifying most likely length of past light exposure using single grains, and a gaussian mixture model approach to isolating different grain populations within a single sample. Combined with a numerical model of single-grain bleaching and burial, we apply these approaches to elucidate past and present fluvial sediment transport information for the Allt Dubhaig, Scotland, and the Santa Clara River, southern California.