Spatial and temporal variability of water-filled crevasse hydrologic states along the shear margins of Jakobshavn Isbrae, Greenland

Abstract. The impact of melt water injection into ice streams over the Greenland Ice Sheet is not well understood. Water-filled crevasses along the shear margins of Jakobshavn Isbræ are known to fill and drain, resulting in weakening of the shear margins due to reduced basal friction. Seasonal variability in the hydrologic dynamics of these features has not been quantified. In this work, we characterize the spatial and temporal variability in the hydrological state (filled or drained) of these water-filled crevasse systems. A fusion of multi-sensor optical satellite imagery was used to examine hydrologic states from 2000 to 2015. The monthly distribution of crevasse systems observed as water filled is unimodal with peak number of filled days during the month of July at 329 days, while May has the least at 15. Over the study period the occurrence of drainage within a given season increases. Inter-seasonal drain frequencies over these systems ranged from 0 to 5. The frequency of multi-drainage events are correlated with warmer seasons and large strain rates. Over the study period, summer temperatures averaged from −1 and 2 °C and tensile strain rates have increased to as high as ~ 1.2 s^-1. Intermittent melt water input during hydrofracture drainage responsible for transporting surface water to the bed is largely facilitated by high local tensile stresses. Drainage due to fracture propagation may be increasingly modulated by ocean-induced calving dynamics for the lower elevation ponds. Water-filled crevasses could expand in extent and volume as temperatures increase resulting in regional amplification of ice mass flux into the ice stream system.