Ice velocity of Jakobshavn Isbr?, Petermann Glacier, Nioghalvfjerdsfjorden, and Zachari? Isstr?m, 2015–2017, from Sentinel 1-a/b SAR imagery

摘要

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 four key outlet glaciers in Greenland: Jakobshavn Isbr?, Petermann Glacier, Nioghalvfjerdsfjorden, and Zachari? Isstr?m. These data provide a new high temporal resolution record (6-day averaged solutions) of each glacier's evolution since 2014, and resolve recent seasonal speedup periods and inter-annual changes in Greenland outlet glacier speed with an estimated certainty of 10?%. We find that since 2012, Jakobshavn Isbr? has been decelerating, and now flows approximately 1250?m?yr sup?1/sup (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 sup?1/sup (14?%) at a distance of 12?km inland of the terminus. We also use our new dataset to estimate the duration of speedup periods (80–95?days) and to demonstrate a strong relationship between ice front position and ice flow at Jakobshavn Isbr?, with increases in speed of ～ 1800?m?yr sup?1/sup in response to 1?km of retreat. Elsewhere, we record significant seasonal changes in flow of up to 25?% (2015) and 18?% (2016) at Petermann Glacier and Zachari? Isstr?m, 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. Please read the corrigendum first before continuing.