Summer speedup at Zachariæ Isstrøm, northeast Greenland

The dynamics of The North East Greenland Ice Stream (NEGIS) are influenced by various factors such as ice thickness, topography, basal conditions, and surface meltwater inputs. The presence of basal lubrication significantly affects NEGIS ice flow by reducing friction at the ice-bed interface. Consequently, alterations in subglacial hydrology and the prevalence of meltwater can result in significant variations in ice stream velocity and mass discharge. In this study, we utilize GPS data from six stations along the main trunk to identify the inland propagation of summer speed-ups, peaking between June and August. Complementing the GPS data, we incorporate ice speed information from mosaics based on ESA Sentinel-1 SAR offset tracking, covering the entire NEGIS. These velocity maps, derived from intensity-tracking of ESA Sentinel-1 data with a 12-day repeat and utilizing the operational interferometric post-processing chain IPP for analysis, reveal substantial acceleration in surface speed from June onwards, followed by a deceleration in August. To simulate the observed summer speed-up, we employ the Ice-sheet and Sea-level System Model (ISSM). Our model results indicate that hydrology is the primary driver of the summer speed-up, leading to changes in speed that extend deep into the interior, reaching over 150 km inland. Understanding the dynamics of NEGIS is essential for predicting its future behavior and potential contributions to sea level rise in a warmer climate with increased meltwater.