Geometric Controls on Tidewater Glacier Retreat in Central Western Greenland

Glacier terminus changes are one of the hallmarks of worldwide glacier change, and thus, there is significant focus on the controls and limits to retreat in the literature. Here we use the observational record of glacier terminus change from satellite remote sensing data to characterize glacier retreat in central West Greenland with a focus on the last 30 years. We compare terminus observations of retreat to glacier/fjord geometry from available bed and bathymetry data and find that glacier retreat accelerates through wide, overdeepened parts of the bed characterized by retrograde bed slopes. We find that the morphology of the overdeepening can be used as a predictive measure for the length of retreat and that short regions (less than twice the seasonal change in terminus position) of the bed with prograde bed slopes are not sufficient to stop a retreating terminus. Even narrow overdeepenings can control glacier retreat, likely because they focus subglacial runoff, which entrains warm water in the fjords when it emerges at the grounding line and melts the terminus, creating enhanced local retreat. Future retreat of these glaciers is assessed given upstream fjord geometry.