First Alps-wide reconstruction of LGM glacial sediment transport enabled by GPU-accelerated particle tracking

Abstract. Reconstructing the transport histories and provenances of glacial sediments and ice-contact deposits (e.g. tills, moraines) in formerly glaciated regions remains a major challenge, particularly at icefield- to ice-sheet scales and over multi-millennial timescales. Yet such reconstructions are central to key questions in Quaternary science, including estimates of past glacial erosion rates and sediment fluxes, the role of subglacial sediment storage in erosion reduction, or the reconstruction of past ice-flow dynamics, ice divides, and transfluences. While numerical modelling can enable one to reproduce past glacial sediment transport via coupling glacier models with particle tracking, this becomes computationally unfeasible over large spatial domains and paleo timescales using traditional computing. As a result, no study to date has simulated glacial sediment transport using large particle numbers (tens of millions) across continental-scale icefields such as the one occupying the European Alps during the Last Glacial Maximum (LGM). Here, we overcome this limitation using the Instructed Glacier Model (IGM), which allows the coupling of 3D Lagrangian particle tracking with high-resolution glacier simulations, both accelerated on Graphics Processing Units (GPU). This unlocks the modelling of ice advection of millions of particles at minimal additional computational cost, allowing simulations of glacial sediment transport across the European Alps over multi-millennial timescales (40–18 ka) and at the unprecedented spatial resolution of 300 m. We achieve ∼ 50× faster computation tracking 20 million particles across the Alps using a single GPU instead of 60 CPU threads. In doing so, we produce the first Alps-wide modelling reconstruction of glacial sediment transport during the LGM, using process-based particle seeding schemes to represent both subglacial (e.g. abrasion, plucking) and supraglacial (e.g. rockfall, landslides) sediment sourcing. Results are analysed through complementary “sink-to-source” (deposit provenance) and “source-to-sink” (potential depositional pathways) analyses, enabling us to reconstruct the LGM glacial transport of numerous ice-contact deposits and surface lithologies across the Alps. We find that supraglacially sourced glacial sediments are typically eroded earlier, experience longer glacier residence times, and undergo greater cumulative ice-free exposure than those of subglacial origin, with implications for the interpretation of cosmogenic nuclide inheritance in glacial deposits. Our new coupled glacier-particle modelling framework opens avenues for quantitative model-data comparisons using glacial geomorphology and provides a powerful tool for reconstructing paleo ice dynamics, sediment provenance, and Quaternary glacial landscape evolution.