Ice velocity of Jakobshavn Isbræ, Petermann Glacier, Nioghalvfjerdsfjorden, and Zachariæ Isstrøm, 2015–2017, from Sentinel 1-a/b SAR imagery

Systematically monitoring Greenland’s outlet glaciers is central to understanding the timescales over which their flow and sea level contributions evolve. In this study we use data from the new Sentinel-1a/b satellite constellation to generate 187 velocity maps, covering 4 key outlet glaciers in Greenland; Jakobshavn Isbrae, Petermann Glacier, Nioghalvfjerdsfjorden and Zachariae Isstrom. These data provide a new high temporal resolution record of each glacier’s evolution since 2014, and resolve recent seasonal and inter-annual changes in Greenland outlet glacier speed with an estimated certainty of 10 %. We find that since 2012, Jakobshavn Isbrae has been decelerating, and now flows approximately 1250 m yr −1 (10 %) slower than 5 years previously, thus reversing an increasing trend in ice velocity that has persisted during the last decade. Despite this, we show that seasonal variability in ice velocity remains significant; up to 750 m yr −1 (14 %) at a distance of 12 km inland of the terminus. We also use our new dataset to demonstrate a strong relationship between ice front position and ice flow at Jakobshavn Isbrae, with increases in speed of ~ 1800 m yr −1 in response to 1 km of retreat. Elsewhere, we record significant seasonal changes in flow of up to 25 % and 18 % at Petermann Glacier and Zachariae Isstrom, respectively. This study provides a first demonstration of the capacity of a new era of operational radar satellites to provide frequent, and timely, monitoring of ice sheet flow, and to better resolve the timescales over which glacier dynamics evolve.