Recurrent surge dynamics and ongoing acceleration at Devon Ice Cap's Southeast basin, Canadian Arctic

This study analyses the dynamics of Southeast-1 and Southeast-2 glaciers on Devon Ice Cap for 1959-2024 using multiple remote sensing datasets.Sharing a common tidewater terminus, the glaciers experienced two dynamic instabilities: an 8-9-year surge in the 1970s-80s advancing the terminus by up to ~5 km and reaching velocities of >3000 m a -1 , and a multiannual acceleration of Southeast-2 beginning in the mid-2000s, suggesting the start of a new surge within that basin.This instability progressed through stepwise increments each summer and propagated up-glacier, reaching velocities over an order of magnitude above quiescent levels.In 2020-23, Southeast-2 showed dynamic thickening of ~1-5 m a -1 within the lower ~7.5 km and thinning in the upper trunk (~7.5-17 km from the terminus) of <-1 m a -1 , indicating down-glacier mass transfer.Long-term terminus thinning and retreat increased surface slopes and driving stress, preconditioning the glacier for instability.Seasonal velocity patterns, crevasse expansion, strain rate evolution, and modelled runoff support a hydro-thermodynamic feedback, where meltwater increasingly accesses the bed and enhances basal motion.Southeast-1 remains quiescent but may destabilise similarly to the previous surge.The short surge cycle of Southeast-2 allows the first determination of a complete quiescent phase (~36-37 years) in this region.