The effect of debris supply on glacier evolution: sensitivities and challenges

Debris on glacier surfaces has a strong effect on glacier melt and is currently expanding and thickening due to climate change. Several studies have applied coupled debris-ice dynamic modelling in order to simulate the evolution of debris-covered glaciers. However, many aspects within these dynamic systems remain poorly constrained, as data is scarce and processes are complex and interdependent. So far, most approaches focused on the simulation of the debris layer in the ablation area, but preceding processes of debris supply through gravitational processes and englacial debris transport are often represented based on simple assumptions or limited measurements and with unknown uncertainties. In this study, we address this issue by investigating how changes in the spatial distribution of debris supply affect down-glacier debris transport and debris cover.

For this, we apply a novel 3-dimensional coupled debris-ice dynamics model, implemented within the Instructed Glacier Model (IGM), that uses particle tracking to model englacial and supraglacial debris transport. In this approach, particles need to be seeded to initialize their entry into the glacier system. This involves the development of a framework to decide where and at what rate we seed these particles. We test several approaches and implement a scheme that automatically generates seeding locations based on local topography. In our experiments, we find that small differences in along-flow seeding location can have a strong impact on englacial transport paths, debris cover extent, and finally glacier extent. This reasserts the need to better constrain debris supply as an important part of the process chain if we want other aspects to be accurately represented in models.