Abstract Predictions of the Greenland Ice Sheet's response to climate change are limited in
part by uncertainty in the coupling between meltwater lubrication of the ice-sheet bed and
ice flow,,. This uncertainty arises largely from a lack of direct measurements of water flow
characteristics at the bed of the ice sheet. Previous work has been restricted to indirect
observations based on seasonal and spatial variations in surface ice velocities,,, and on
meltwater flux. Here, we employ rhodamine and sulphur hexafluoride tracers, injected into …