Greenlands' outlet glaciers are among the most dynamic elements of the Earth system, directly linking the cryosphere, hydrosphere, and oceans. Sermeq Kujalleq (Jakobshavn Isbræ), the fastest marine-terminating glacier worldwide, is a critical contributor to global sea-level rise. Understanding the interplay between its changing front position, meltwater input, ice thickness, and ocean forcing is therefore essential for improving projections of ice-sheet change and informing sustainable adaptation strategies.

Here, we combine high-frequency satellite observations with advanced numerical experiments to examine how seasonal and multi-annual changes in glacier geometry and basal conditions shape flow variability. Using sub-monthly calving-front positions from 2016–2022, we find that retreat of the glacier front explains more than 76% of observed velocity changes, with effects extending over 30 km inland. However, substantial seasonal accelerations occur in late summer and autumn when surface meltwater input enhances thinning, reduces effective pressure, and lowers basal resistance. This dynamic leads to a persistent mismatch between modeled and observed velocities. Incorporating thickness- and hydrology-dependent variations in basal shear stress reduces this mismatch by more than 90%, demonstrating the critical role of seasonal hydrological forcing and ice-thickness variability in modulating glacier dynamics. These results highlight the interconnected roles of terminus retreat, ice–ocean interactions, and subglacial hydrology in amplifying both short-term ice-flow variability and longer-term dynamic mass loss. By integrating these coupled cryosphere–hydrosphere–ocean processes into predictive frameworks, we can better constrain Greenland’s future contribution to sea-level rise and provide a stronger scientific basis for sustainable coastal resilience worldwide.
 

Greenland Ice Sheet change, mass loss, ice-flow dynamics, ice thickness variability, driving mechanisms