Helheim velocity controlled both by terminus effects and subglacial hydrology with distinct realms of influence

Two outstanding questions for future Greenland predictions are (1) how enhanced meltwater draining beneath the ice sheet will impact the behavior of large tidewater glaciers, and (2) to what extent tidewater glacier velocity is driven by changes at the terminus versus changes in sliding velocity due to meltwater input. We present a two-way coupled framework to simulate the nonlinear feedbacks of evolving subglacial hydrology and ice dynamics using the Subglacial Hydrology And Kinetic, Transient Interactions (SHAKTI) model within the Ice-sheet and Sea-level System Model (ISSM). Through coupled simulations of Helheim Glacier, we find that terminus effects dominate the seasonal velocity pattern up to 15 km from the terminus, while hydrology primarily drives the velocity response upstream. With increased melt, the hydrology influence yields seasonal acceleration of several hundred meters per year in the interior, suggesting that hydrologic forcing will play an important role in future mass balance of tidewater glaciers.