Feedbacks and timescales in the modelled transient response of debris-covered glaciers

Glaciers worldwide are becoming increasingly debris-covered, yet many aspects within the coupled glacier-debris system are not well-understood. While the insulating effect of continuous debris layers is well-known, the transient feedbacks with glacier dynamics are poorly understood. The main aim of this study is to better understand the complex transient glacier response and debris-induced feedbacks through numerical flow modelling. We present an improved flowline model that couples ice flow, depth-resolved debris transport, and debris cover impact on mass balance. This approach allows for a detailed examination of the dynamics of debris-covered glaciers under transient forcing conditions of climate and debris input over extended timescales. Our results indicate that low-amplitude, decade-scale variability in debris or climate forcing does not substantially impact glacier evolution. However, large debris supply events can have a sustained impact. We find that debris-covered glacier response to warming climate forcing is non-monotonic, with distinct phases of thinning, retreat, and long-term re-advance. We attribute this to a separate, longer timescale process of englacial debris transport. Additionally, feedbacks in the englacial debris trajectory and complex bed topography further amplify the non-linear pattern of retreat in the transient glacier response to warming.