Supraglacial forcing of subglacial drainage in the ablation zone of the Greenland ice sheet

We measure hydrological parameters in meltwater draining from an outlet glacier in west Greenland to investigate seasonal changes in the structure and behaviour of the hydrological system of a large catchment in the Greenland ice sheet (GrIS). Our data reveal seasonal upglacier expansion and increase in hydraulic efficiency of the subglacial drainage system, across a catchment >600 km(2), to distances >50 km from the ice-sheet margin. This expansion occurs episodically in response to the drainage of surface meltwaters into a hitherto inefficient subglacial drainage system as new input locations become active progressively further upglacier; this system is similar to Alpine glaciers. These observations provide the first synopsis of seasonal hydrological behaviour in the ablation zone of the GrIS.