Constraining sediment dynamics in proglacial rivers: novel insights from a combined luminescence-modelling approach

High mountain and polar regions are among the most impacted by present-day climate change, with cryosphere degradation altering geomorphic processes and sediment dynamics. These changes affect ecosystem functioning, hydrogeomorphological hazards, and sediment fluxes from glaciated catchments to the ocean. Understanding sediment transport mechanisms in proglacial rivers is thus crucial for predicting how sediment dynamics in these regions will evolve under continued climate warming.Here, we advance understanding of sediment dynamics in ice sheet-fed proglacial rivers by applying a coupled luminescence–modelling approach to the Qunnguata Kuussua river (Watson river) in south-western Kalaallit Nunaat (south-western Greenland). We build on the work of recent studies which have shown that luminescence signals in modern alluvial sediments can serve as sediment tracers and, when combined with numerical models, provide constraints on transport distances, velocities and storage times (Gray et al., 2018; Guyez et al., 2023).We collected a large dataset (~600 samples) of portable-reader luminescence measurements on bulk sandy sediment samples along the ~30 km-long Watson River during three summer melt seasons (2021–2023). The luminescence signal intensities of different samples are highly variable near the river source (Russell and Leverett glacier termini) and at junctions with tributaries, while the inter-sample signal variability reduces following progressive signal bleaching (i.e. resetting) with increasing downstream transport distance. To interpret and quantify this pattern, we develop a probabilistic luminescence-based sediment transport model that simulates suspended particle transport and luminescence bleaching in a proglacial river. The model successfully reproduces the observed downstream evolution of luminescence signal distributions observed along the Watson River, enabling estimation of sediment transport parameters from combined luminescence and hydrological data.ReferencesGray et al., 2018, Geophysical Research Letters 45.Guyez et al., 2023, Journal of Geophysical Research: Earth Surface 128.